HomeMy WebLinkAboutAPA2623TURBIDITY IN FRESHWATER HABITATS OF ALASKA
A Review ·of Published and Unpublished
Literature Relevant to the Use .of Turbidity
as a Water Quality Standard
by
Denby S. Lloyd
Report No. 85-1
Alaska Department of Fish & Game
Division of Habitat
TURBIDITY IN FRESHWATER HABITATS OF ALASKA
A Review of Published and Unpublished
Literature Relevant to the Use of Turbidity
as a Water Qua1 ity Standard
by
Denby S. Lloyd
Report No. 85-1
Don W. Coll insworth
Comissioner
John A. Clark
Di rector
Alaska Department of Fish and Game
Habitat Division
P.O. Box 3-2000
Juneau, A1 as ka 99802
January 1985
EXECUTIVE SUMMARY
Turbidity is an optical property of water, wherein suspended sediments
and other material in the water scatter and absorb light. Turbidity
measurements can be used to estimate both the penetration of 1 ight into
a body of water and the concentration of suspended material in water.
The value of water quality standards based upon specific turbidity
criteria has been questioned, and the Alaska State Water Quality
Standards (18 AAC 70) are currently being reevaluated. This paper
attempts to outline relationships between turbidity and a suite of
parameters that are most relevant to sustained increases of turbidity
in clear-water systems. Speci f ical ly, examples from recent studies
performed in Alaska, and el sewhere, provide ample illustration that
turbidity criteria can be used as reasonable and effective water
quality standards which, if implemented, can prevent or ameliorate the
following adverse effects caused by suspended sediments in water:
I. Extinction of light in lakes and streams
2. Reduction or loss of primary (plant) production in lakes and
st reams
3. Reduction or loss of secondary (zooplankton and aquatic
insect) production in lakes and streams
4. Reduction or loss of fish production in lakes and streams
5. Reduction in recreational fishing use of streams
6. Reduction in efficiency of fishery management techniques
Furthermore, because turbidity can be directly related to the
concentration of suspended sediments in water, with adequate data
predictive relationships between turbidity and suspended sediment
concentration can be developed. This type of relationship can allow
for the use of turbidity standards to address and regulate the direct
physical effects of suspended material on aquatic life, which have also
been described in available literature.
Productivity in takes
Studies conducted by the Alaska Department of Fish and Game (Koenings
1984) on the production of sockeye salmon in lakes provide the
following information on clear and naturally turbid (glacial' lakes,
i .e. lakes ranging in turbidity from approximately 0 nephelometric
turbidity units fNTU1 to an average of approximately 52 NTU:
Increases in turbidity from 0-1 NTU to approximately 10 FITU
cause a dramatic reduction in the depth to which one percent
of available surface light penetrates into water. Such
compensation depths for cl ear-water 1 akes were measured at
approximately 16-17 meters, while compensation depths for
lakes with turbidity of between 2-10 NTU were measured at
only 2-6 meters. The compensation depth for a lake averaging
52 NTU occurred at less than 1 meter. A 5 NTU increase of
turbidity can reduce the productive volume of a clear-water
lake by approximately 75 percent.
2. Abundance of zooplankton in naturally turbid lakes was
observed to be lower than that in clear-water lakes.
Moreover, abundance of preferred food i tems (Cl adocera) for
juveni 1 e sockeye salmon was observed to be dramati cal ly
reduced in turbid lakes.
3. Production of juvenile sockeye salmon and returns of adult
sockeye salmon were observed to be lower in turbid lake
systems than in clear-water lake systems.
A study conducted by R&M Consultants (1982b) also compares the
extinction of light and turbidity in a glacial lake. The results
describe a similar dramatic reduction in light penetration with small
increases of turbidity above 0-1 NTU.
Productivity in Streams
Studies conducted by the University of A1 aska-Fai rbanks (LaPerriere et
al. 1983, Van Nieuwenhuyse 1983, LaPerriere 1984, Simmons 1984, Wagener
1984) describe the following set of adverse effects associated with
human-induced turbidity and sedimentation in clear-water streams:
1. Light penetration is reduced by turbidity, and light
extinction is directly related to turbidity.
Primary production in streams is reduced or eliminated by
turbidity. Calculations derived in this report using
equations relating turbidity, 1 ight availability, and primary
productivity indicate that a turbidity of 5 NTU may reduce
primary production in a normally clear-water stream 0.5
meters (1.5 feet) deep by approximately 13 percent; a 25 NTU
increase in turbidity over normally clear-water conditions
may reduce plant production by 50 percent. These effects may
be even more pronounced in deeper streams.
3. Abundance of macroinvertebrates in turbid and sedimented
streams is much lower than that in clear-water streams.
4. Abundance of fish (arctic grayl ing) in turbid and sedimented
streams is reduced or eliminated. Also, physiological stress
is exhibited by grayl ing in highly turbid streams.
Observations by the Alaska Department of Fish and Game (Townsend 1983,
Ott 1984b) indicate that recreational use of streams for sportf ishing
is reduced in normally clear-water stream when turbidity increases
above 8 NTU, and that aerial survey techniques employed in the
management of commercial fisheries are hampered at turbidities of 4-8
NTU and above.
Suspended Sediment Concentration
Turbidity can be directly related to suspended sediment concentration.
Therefore turbidity standards can be used to control the direct
physical effects of sediment on aquatic life. Using data retrieved
from statewide sampl i ng conducted by the U. S. Geological Survey (USGS
1984), we have cal culated a general re1 ationshi p between turbidity and
suspended sediment concentration. This relationship indicates that 25
mg per liter is associated with turbidity on the order of 5 NTU and
that 100 mg per liter is associated with turbidity on the order of 25
NTU. A regression equation derived by Peratrovich et al. (1982)
illustrates a similar relationship for the Susitna River. From recent
data compiled from selected streams- in interior Alaska (Post 1984,
To1 and 1984) we have calculated a more specific re1 ationship indicating
a one-to-one correspondence between turbidity in NTU and suspended
sediment concentration in mg per liter.
Turbidi tv Standards
Based upon the information summarized in this report, derived from
studies conducted in Alaska and elsewhere, the current State Water
Quality Standard for turbidity to protect the propagation of fish and
wildlife (25 NTU above natural conditions in streams, 5 NTU above
natural conditions in lakes) may be sufficient to provide a moderate
level of protection for clear-water aquatic habitats. A 25 NTU
increase in turbidity in shallow clear-water systems may potentially
reduce stream primary productivity by 13 to 50 percent or more,
depending on stream depth and ambient water quality, and be associated
with an increase in suspended sediment concentration of approximately
25 to 100 mg per liter.
A higher level of protection will require the application of a stricter
turbidity standard. The standard presently appl ied to drinking water
is 5 NTU above natural conditions in streams and lakes. A 5 NTU
increase in turbidity in clear-water systems may reduce the primary
productive volume of lakes by approximately 75 percent, reduce stream
productivity by 3 to 13 percent or more, depending on stream depth and
ambient water quality, and be associated with an increase in suspended
sediment concentration of approximately 5 to 25 mg per liter. The
current Interagency Placer Mining Guide1 ines (State of Alaska 1984) use
turbidity of 3 NTU or less as a criterion to specify high priority
streams. Application of a 5 NTU above ambient standard would bring
total turbidities in these streams to 8 NTU, the level at which
recreational fishing may decline and at or above the level at which
efficiency of aerial surveys for fishery management are affected.
TABLE OF CONTENTS
.......................................... Executive Sumry....
Productivity in Lakes
Productivity in Streams
Suspended Sediment Concentration
Turbidity Standards ................................................ List of Figures
List of Tables ................................................. .................................................. Preface......
Acknowledgements ...............................................
Introduction. ..................................................
Purpose
Scope
Limitations ................................................ Brief History.. ................. Turbidity, Light Penetration, and Productivity
Naturally Turbid, Glacial Lake Systems in Alaska
Artificially Turbid Stream Systems in Alaska ............................... Turbidity and Suspended Sediment
Turbidity and Suspended Sediment in Alaska Streams
Turbidity, Suspended Sediment, and Land Use in Alaska .......... Relevance of Turbidity and Suspended Sediment to Fish ............ Standards and Conclusions Regarding Water Qua1 i ty..
Light Penetration and Productivity
Suspended Sediment
Concl usi on ..... Limitations, Further Study, and Alternative Standards.....
Limitations to Existing Information
Topics for Further Study
Suggestions for Possible Alternative Standards
Glossary ....................................................... ............................................... Literature Cited
Page
1
LIST OF FIGURES
Page
Figure 1. Theoretical curve of light intensity versus depth
in a body of water................................. 15
Figure 2. Empirical relationship of compensation depth versus
turbidity for lakes in southcentral Alaska ......... 17
Figure 3. Conformance of lakes in Alaska to a general
re1 ati on of phytoplankton production versus
phosphorus availability in north temperate lakes. .. 2 1
Figure 4. Zooplankton density and compensation depth for
clear-water and glacial ly-turbid lakes in ................................ southcentral Alaska 2 3
Figure 5. Relationship of annual production of adult sockeye
salmon versus euphotic volume for lakes in
southcentral Alaska.. .............................. 24
Figure 6. Annual production of juvenile sockeye salmon per
unit of surface area for clear-water and turbid
1 akes in southcentral A1 aska.. ..................... 26
Figure 7. Annual production of adult sockeye salmon per unit
of surface area for clear-water and turbid lakes in
southcentral Alaska. ............................... 27
Figure 8. Potential effect of increased turbidity on plant
production for shallow streams in interior Alaska.. 3 4
Figure 9. Empirical relationship of naturally occurring
turbidity versus suspended sediment concentration
for rivers and streams in Alaska................... 43
Figure 10. Empirical re1 ationship of turbidity versus
suspended sediment concentration for placer-mined
and neighboring unmined streams in interior Alaska. 45
Figure 11. Turbidity and suspended sediment concentrations for
certain placer-mined streams in Alaska.. ........... 48
Figure 12. Grain size analysis of sediment from placer mines
compared to natural suspended sediment in Alaska
streams. ........................................... 4 9
LIST OF TABLES
Table 1. Effect of turbidity on light extinction and ............... compensation depth in an Alaska lake..
Table 2. Size and juvenile sockeye production of selected lake ..................... systems in southcentral Alaska..
Table 3. Size and adult sockeye production of selected lake ..................... systems in southcentral Alaska..
Table 4. Sumnary of impacts resulting from increased turbidity
and sedimentation due to placer mining in interior
Alaska streams.......................................
Table 5. Potential effect of increased turbidity on light
penetration at depth and plant production in shallow ....................... interior Alaska streams.......
Table 6. Prediction of turbidity caused by suspended sediment
concentrations in streams throughout Alaska, the
Susitna River, and interior Alaska streams...........
Table 7. Recently documented effects and relationships of
turbidity and suspended sediment in freshwater .................................. habitats of Alaska.
Table 8. Some reported effects of turbidity and suspended
sediment on salmonid fish outside of Alaska.. ........
Table 9. Numerical turbidity standards for protection of fish
and wildlife in Alaska and other western and northern
states...............................................
Tab1 e 10. Recommended 1 eve1 s of suspended sediment
concentration for the protection of fish habitat and ...................... translation to turbidity values
Page
19
28
2 9
PREFACE
This paper has been prepared by the Alaska Department of Fish and Game
(ADF&G) to present a comprehensive examination of the most recent
information available from studies conducted in Alaska and el sewhere
addressing the effects of turbidity on freshwater aquatic habitats.
Although few systematic studies have been performed directly
quantifying the effects of turbidity on aquatic habitats, there is a
large body of information that examines individual aspects of these
effects. This paper is a synthesis and interpretation of the
information currently available. The reader interested only in a
summary of this information and possible conclusions regarding the use
of turbidity as a water quality standard may choose to refer directly
to the EXECUTIVE SUMMARY and the section on STANDARDS AND CONCLUSIONS
REGARDING WATER QUALITY.
ACKNOWLEDGEMENTS
The Habitat Division of the Alaska Department of Fish and Game (ADF&G)
wishes to grateful ly acknowledge:
Dr. J. Koenings, Mr. G. Kyle and Ms. T. Tobias, F.R.E.D. Division,
ADF&G, for sharing their unpublished information on the
productivity of glacially-influenced and clear-water lakes.
Dr. J. LaPerriere and Mr. E. Van Nieuwenhuyse, A1 aska Cooperative
Fishery Research Unit, University of Alaska, for personally
sharing their information regarding the effects of placer
mining on the productivity of streams.
Mr. R. Madison, U.S. Geological Survey, Alaska District, for
providing records of water analyses from Alaska streams.
Mr. R. Post and Dr. P. Weber, Habitat Division, ADF&G, for
providing their unpublished data on water quality in
placer-mined and neighboring unmined streams.
Mr. D. Bishop and Mr. L. Peterson, independent consultants, for
providing critical review of earlier drafts of this paper.
TURBIDITY IN FRESHWATER HABITATS OF ALASKA
A Review of Published and Unpublished Literature
Relevant to the Use of Turbidity as a Water Quality Standard
Few water quality characteristics are as easy to observe and as
difficult to define as turbidity (Koeppen 1974). Simply put, however,
turbid waters are those that are muddy or cloudy as a result of having
sediment added or stirred up (Guralnik 1980). More precisely,
turbidity is considered a measure of water clarity, an expression of
the optical property of water that causes light to be scattered and
absorbed rather than transmitted in straight lines, and is caused by
the presence of suspended material such as clay, silt, finely divided
organic and inorganic matter, plankton and other microscopic organisms
(APHA 1980). The definition illustrates two important uses of
turbidity as a water quality criterion: first as a measure of water
clarity and 1 ight penetration and second as a measure of the amount of
suspended material, particularly sediment, in a body of water.
There currently exists some disagreement about the value of turbidity
as a water qual ity criterion and standard (Pickering 1976, Wilber
1983). However, to date there has not been a detailed interpretation
of available information regarding the specific effects associated with
turbidity in aquatic systems. The purpose of this paper is to review
and interpret recent information on turbidity as it relates to
freshwater aquatic habitats in Alaska, and to provide guidance for
establ i shing reasonable water qual i ty standards to protect aquatic
habitats from potentially adverse effects of human-induced turbidity.
Largely at issue is whether or not turbidity should be retained as a
simple and effective indicator of light penetration and suspended
sediment concentration, to be used as a statewide water quality
standard in regulating the discharge of wastewater to freshwater
aquatic habitats.
This paper includes information developed in A1 aska and relevant
information developed elsewhere that addresses turbidity and its
effects on freshwater aquatic habitats. This paper specifically
addresses turbidity as it affects light penetration, primary
production, secondary production, fish production, and the human use of
freshwater habitats. Also, relationships between turbidity and the
concentration of suspended sediment in water are discussed and related
to information on the direct effects of these suspended sediments.
Even though it is often difficult to distinguish between sediments
suspended within a body of water and those deposited on lake bottoms or
stream beds, this paper does not intend to discuss deposited materials
or bedload (settleable sol ids).
Limitations
There are many physical and chemical parameters that affect or control
the productivity of aquatic habitats, such as solar radiation, water
depth, temperature, flow regime, bed stabil ity, and nutrient
concentration. This paper is not intended to portray turbidity as the
only parameter responsible for different levels of productivity but to
illustrate how, and to what extent, increased levels of turbidity can
affect aquatic habitats.
BRIEF HISTORY
Turbidity, as a measure, was originally derived to provide a quick
estimation of the amount of suspended sediment within a water sample.
The original Jackson Candle Turbidimeter, developed in the late
nineteenth century, was used to determine that length of a path of
light passed through a suspension of sediment and water at which an
observer just fails to detect the flame of a beeswax/spermaceti candle
(APHA 1980). The light path in centimeters was standardized against
known concentrations of diatomaceous earth in water, in parts per
mi 11 ion, to yield Jackson Candle Units (JCU) (Pickering 1976);
measurements were also expressed as parts per mil 1 ion (ppm) of Si02.
It was real ized, however, that sediment particle size fractionation in
addition to total concentration of suspended particles and other
factors, affected the scattering and absorption of 1 i ght. Therefore,
formazin polymer subsequently became an accepted standard because of
its more uniform particle size and ease of preparation; Formazin
Turbidity Units (FTu) were derived. Other materials have also been
used to standardize measurements, such as titanium dioxide and
polystyrene latex microspheres, and many units have been derived,
including Jackson Turbidity Units (JTU) , He1 1 ige units, severity, and
Nephelometric Turbidity Units (NTU) (Freeman 1974, Pickering 1976,
Stern and Stickle 1978, LaPerriere 1983, Wi 1 ber 1983).
This last unit, NTU, has recently replaced all of the others (EPA 1979,
APHA 19801, and is based upon the use of a nephelometer, an instrument
that measures the amount of light scattered by a water sample at 90" to
the path of the incident light. This measurement is calibrated against
the scattering of light in a standard suspension of formazin polymer
and is reported in Nephel ometri c Turbidity Units (NTU) .
TURBIDITY, LIGHT PENETRATION, AND PRODUCTIVITY
As an optical measurement, turbidity most directly represents the
extent to which light can penetrate into a body of water. However,
turbidity has not often been used to measure light penetration.
Perhaps the most rigorous and comprehensive study investigating the
relationship of turbidity and light penetration was performed as long
ago as the 1930's (Ellis 1936). However, most recent studies have
stressed the use of turbidity measurements only to estimate suspended
sediment concentrations.
Using presently archaic terms, Ellis (1936) sumnarized that the depth
at which turbidity screened out 99.9999 percent of the light entering
at the water surface, or the "millionth intensity depth" (m.i.d.),
decreased from 15 to 34 meters in clear inland streams to 0.3 to 1.0
meters or less in streams such as the Mississippi, which carry a high
erosional silt load. Ellis (1936) also looked at particle settling and
light penetration over time. His study showed that even after 96 hours
of undisturbed settling, which would not occur under natural rivet=
conditions, the m. i .d. of Mississippi River water increased only from
0.157 to 1.5 meters, as compared to a calculated m.i.d. of 15 meters
for the same water with its silt load artificially removed by
filtering.
Light is needed in aquatic systems to provide energy for photosynthesis
by plants. Photosynthesis is the beginning of energy transfer within
food webs in lakes and streams; other energy may be provided by
terrestrial material. Photosynthesis is often a crucial determinant of
the ultimate production of fish or other higher life forms in aquatic
environments . A1 though contributions of detritus from terrestrial
sources, such as leaf litter and other organic debris, may supply a
large amount of energy to lake and stream ecosystems, the importance of
this terrestrial energy source is often overstated (Minshall 1978),
particularly in waters with 1 i ttle or no terrestrial vegetation along
the banks (Vannote et al. 1980). Recent studies have confirmed the
importance of aquatic primary production over terrestrial input in many
aquatic systems. High turnover rates of aquatic plant production
(McIntire 1973, McIntire and Colby 1978, Lamberti and Resh 1983) and
high food quality of aquatic plants (McCullough et al. 1979, Benke and
Wallace 1980, Hornick et al. 1981) are cited as reasons to believe that
many aquatic food chains are largely supported by aquatic plants. A
recent study conducted by the University of A1 aska-Fai rbanks (Anderson
1984) concludes that aquatic plant production is likely very important
to maintenance of stream ecosystems and that changes to this production
may have many effects on other biological components in stream systems.
Chapman and Knudsen (1980) and Murphy et al. (1981) state that
increased light availability to streams in the Pacific northwest
trans1 ates through aquatic food webs to higher abundance of salmoni d
fishes.
Another recent study conducted by the University of Alaska - Fairbanks
has shown that contributions of detritus from terrestrial sources into
subarctic Alaska streams is relatively low compared to that in
temperate streams (Cowan and Oswood 1983), and that seasonal pulses of
energy associated with seasonal variations in aquatic primary
production may be critical to the maintenance of invertebrate and fish
populations (Oswood, pers. corn.). The value of seasonal pulses of
aquatic primary production to stream food webs is corroborated by
studies conducted in Appalachian mountain streams (Hornick et al. 1981)
and in Oregon coastal streams (Chapman and Demory 1963).
In lakes and reservoirs the majority of aquatic plant production is
generally derived from phytoplankton, which are microscopic or other
small plants suspended in the water column. In contrast, in rivers and
streams much of the primary production is available as periphyton or
macrophytes, which are algae and larger plants attached to rocks and
other components of the substrate. However, regardless of the type of
water body or the predominant mode of plant production, the depth to
which light penetrates into the water, or the amount of light which
penetrates to any specific depth, will have a direct influence on the
amount of biological production occurring within that body of water.
The rate at which light is naturally scattered or absorbed in a body of
water is theoretically constant with depth. Therefore, the intensity
of light penetrating to depth decreases exponentially. This
relationship (Reid and Wood 1976) is described by the equation:
where
Id = 1 ight intensity at a particular depth, d
I, = light intensity at the water surface
e = base of the natural logarithm
k = extinction coefficient, which is dependent on
the clarity of the water
d = depth of interest
Figure 1 presents theoretical curves of light intensity at depth for
two degrees of water clarity (Reid and Wood 1976). It is apparent from
these curves that light is extinguished fairly rapidly with depth and
much more rapidly in turbid water.
ZC TURBID
Zc CLEAR
SURFACE LIGHT (Ole)
I 25 50 75 100
- Clear water
-0- Turbid water
Zc = ~om~ensati'on depth (one
percent light level)
Figure I. Theoretical curves of light intensity versus depth in a body of water, showing
compensation depth (adapted from Reid and Wood, 1976).
The depth to which only one percent of the light available at the
surface of a lake penetrates is generally considered the compensation
depth. This compensation depth is the depth at which light intensity
is just sufficient to promote photosynthesis equal to the respiratory
requirements of most phytoplankton. Above the compensation depth light
intensity promotes net primary production; below the compensation depth
there is little or no net production of plant material. The
compensation depth, then, as influenced by surface light intensity and
water clarity or turbidity, determines the volume of water available in
an aquatic system for the production of plant material, upon which the
rest of the food web depends. Disregarding the contributory effects of
inorganic nutrient concentrations, the shallower that the compensation
depth occurs in a lake the less productive the system will be.
The concept of a compensation depth, per se, is more meaningful when
applied to lakes, where water depth commonly exceeds the compensation
depth. In streams, water depth is usual ly considerably shallower than
the compensation depth. However, the decrease in light intensity with
water depth and turbidity can still be used to indicate expected plant
production in the water or on the bottom of streams, since plant
production is related to the intensity of light as well as depth of
penetration.
Naturally Turbid, Glacial Lake Systems in Alaska
Freshwater systems in Alaska exhibit a range of turbidi ties, from
extremely low (less than 1 NTU) in clear-water drainages, through
intermediate levels (near 50 NTU) in glacial ly-influenced lakes, to
naturally high levels (50-4000 NTU) in several major rivers. A1 though
no systematic study of the relationship between turbidity and
productivity in freshwater lakes in Alaska has been completed to date,
the Fisheries Rehabi 1 i tation Enhancement and Development [FRED)
Division of the ADF&G has compiled information on several
salmon-producing lake systems in the state (Koenings 1984). Figures 2 - 7 illustrate their findings, showing that increased levels of
turbidity are responsible for dramatic decreases in 1 ight penetration
and correspond with decreases in primary production, decreases in the
production of fish food organisms, and ultimately decreases in
production of juvenile sockeye salmon in and return of adult sockeye
salmon to lake systems.
Figure 2 depicts the depth within several lake systems in the Cook
Inlet region to which one percent of the surface light intensity
penetrates. The compensation depth, which is the depth to which one
percent of available surface 1 ight penetrations, shows a strong inverse
0 0.5 1.0 I. 2.0
LOG TURBIDITY
Figure 2. Empirical relationship of compensation depth ( 1% light level ) versus turbidity for lakes
in southcentral Alaska (from Koeninga, 1984 ).
18
16
A
I4
W
C
W
1 12
Y
x 10
C a
z8-
Z
EKLUTNA
5 25
0 10 20 30 40 50 60
-
4
-
-
-
COOPER
LEISURE
relationship (r2 = 0.85, for log/log transform) with recorded turbidity
levels in NTU. Therefore, turbidity is a good indicator of light
penetration and intensity at depth. Tustumena Lake, which is a turbid,
glacial ly-infl uenced water body, has a compensation depth of less than
1 meter (approximately 3.3 feet) at mean natural turbidities of 52 NTU.
By contrast, the clear-water Cooper and Leisure lakes have compensation
depths greater than 16 meters (approximately 52.5 feet) at natural
turbidities of less than 2 NTU. The relationship between compensation
depth and turbidity is reflected in a sharp decrease in compensation
depth, and potential lake productivity, between turbidities of 2 and 10
NTU (Figure 2). Apparently, only very small increases in turbidity are
required to dramatical ly reduce the penetration of 1 ight energy into
aquatic systems and thereby reduce their potential productivity.
According to Figure 2, a 5 NTU increase in turbidity may reduce the
productive volume of a clear-water lake by approximately 75 percent.
These observations of reduced light penetration with increasing
turbidity are. corroborated by other studies in Alaska (R&M Consultants
1982b), where a strong relationship (r2 = 0.96) was found between light
extinction coefficients and turbidity in Eklutna Lake:
where
Nt = extinction coefficient (meters-')
T = turbidity (NTU)
By using Equation 2 to calcuqate light extinction coefficients
corresponding to specific turbidity level s and then plugging these
extinction coefficients into Equation 1, we can calculate the depth to
which one percent of available surface light penetrates. Table 1
presents the values of compensation depth derived in this way for
turbidities in Eklutna Lake. The resulting relationship of
compensation depths and turbidity (Table 1) is very similar to the
empirical data plotted in Figure 2: there is a dramatic decrease in
compensation depth at turbidities just above 5 NTU and a more gradual
decline after turbidities of 25 NTU. Values in Table 1 also agree with
studies by Barsdate and Alexander (1971) on Tangle Lakes in the Alaska
Range. Similar findings in Lake Superior (Swenson 1978) indicate that
the depth of one percent light level was reduced from approximately
16.5 meters in clear water to an average of 2.5 meters at turbidities
of 10 to 12 FTU. Studies in North Carolina showed that each unit (NTU\
increase in turbidity caused a 0.06 unit (meter-') increase in light
extinction coefficient (Reed et al. 1983), very similar to results
presented in Table 1.
Table 1. EFFECT OF TURBIDITY ON LIGHT EXTINCTION AND COMPENSATION
DEPTH IN AN ALASKA LAKE (derived in this report from data
provided by RLM Consultants, 1982b)
TURB l D l TY
( NTU
*
EXTINCT ION
COEFFICIFNT
(meter-
COMPENSATION*
DEPTH
(meters)
*
Calculated from Equation 2:
N = 0.064 (T) - 0.093
where t
-1 N = total extf nctfon coeff. (meter )
T~ = turbidity (NTU)
**
Derfved from Equation 1:
using:
Id - = 0.01 = Compensation point of 18 1 ight level lo -1 k = N = total extf nction coeff. (meter 1
t d = depth (meters)
+
Equation 2 does not apply to turbidity less than 15 - 2 NTU, but RLM Consultants -7
(1982b) also present an extfnction coefficient of 0.26 m for turbidity of 5.5 NTU
based upon 1 ight transrnissivity information at low turbidities in Eklutna Lake.
Figure 3 plots various clear-water lake and glacial lake systems in
Alaska onto a generalized graph of north temperate clear-water lake
systems developed by Vollenweider (1976), where primary production, or
more precisely standing crop, expressed as chlorophyll a concentration
is compared to phosphorus loading. Phosphorus is typically the
1 imi ting nutrient in north temperate freshwater 1 akes (Di 11 on and
Rigler 1974, Oglesby 1977a, Shindler 1977), so if 1 ight penetration
levels are similar, as they are in clear-water systems, it has been
demonstrated that phosphorus concentrations usually control plant
production. Cl ear-water systems in Alaska conform to this
relationship; all of those investigated fall within the 99% confidence
limits found on Figure 3. The glacially-turbid systems, however, do
not conform. Rather, for a given level of phosphorus loading each of
the glacial systems shows significantly reduced levels of primary
production as expressed by chlorophyll a concentrations. It is 1 i kely
that reduced light availability caused-by high turbidities 1 imits the
production of phytoplankton even when sufficient nutrients are
avai 1 abl e (Koenings 1984).
Similar effects on primary production caused by turbidity in lakes have
been described by studies of Lake Erie (Meyer and Heritage 1941,
Chandler 1942) of ponds in Oklahoma (Claffey 1955) and of a pond in
North Carolina (Reed et al. 1983). A recent study performed in a large
reservoir in Oklahoma (Hunter and Wilhm 1984) suggests that even low
levels of turbidity, between 4 and 15 NTU, can disrupt expected
relationships between compensation depth, phosphorus and chlorophyll a
exhi bi ted i n cl ear-water systems. As stated by Ogl esby ( 1977a) ,
pub1 ished 1 i terature amply indicates that turbidity 1 imi ts primary
production be1 ow otherwise expected levels (Gulati 1972, Marzol f and
Osborne 1972, Cheng and Tyler 1976). Brylinsky and Mann (1973) credit
variables related to solar energy input, and turbidity, rather than
nutrient concentration with the major control over primary production
in lakes and reservoirs worldwide. Disregarding the influence of
different nutrient concentrations, Goldman (1960) observed significant
decreases in compensation depth and primary productivity with increased
turbidity in large salmon producing lakes in southwest Alaska.
Although in some instances the photosynthetic efficiency of plants may
compensate for low light conditions, compensatory mechanisms are
limited and will not maintain plant production under conditions of high
turbidity. Recent work in northern Canada (Hecky 1984, Hecky and
Guildford 1984) indicates that aquatic plants wi 11 not overcome
extinction coefficients of approximately 2 meters'l. As shown earlier
in Table 1, an extinction coefficient of 2 meters-' corresponds
to turbidity on the order of 30 NTU; therefore, we cannot expect
PREDICTED AVERAGE CHLOROPHYLL 2
CONCENTRATION ( mp/m3
compensatory mechanisms to overcome turbidities above approximately 30
NTU.
Figure 4 illustrates a translation of energy to higher trophic levels
in Alaska lakes of different turbidities. Zooplankton densities within
the glacially-turbid lakes are as little as one-twentieth of those
densities within clear-water lakes. Furthermore, Figure 4 shows that
. decreasing zooplankton density with increasing turbidity corresponds
with decreasing compensation depth. Reduced zooplankton abundance in
turbid waters has been corroborated by other studies, particularly in
Oklahoma (Matthews 1984).
Recent studies by the ADF&G (Koenings 1984) indicate that densities of
zooplankton fa1 1 with increased turbidity in lakes. In addition, these
studies indicate that particular species of zooplankton which are
preferred by juvenile sockeye salmon as a food source are partially or
completely el iminated. In the eight glacial 1y-turbid lakes inspected
none had populations of Cladocera, a group of highly favored food
organisms for juvenile fish (Foerster 1968, Hoag 1972, Carlson 1974,
Craddock et a1 . 1976, Jaenicke and Kirchhofer 1976, Manzer 19762, while
a1 1 five cl ear-water 1 akes investigated supported these zooplankters.
McCabe and O'Brien (1983) observed that a turbidity level of 10 NTU
resulted in significant declines in the feeding rate and food
assimilation capability of a comnon Cladoceran in Kansas. Furthermore,
their calculations indicate that even low levels of turbidity, caused
by low suspended sediment concentrations, reduced the reproductive
potential of that Cladoceran species from that exhibited in clear
water. Mills and Schiavone (1982) noted reduced abundance of
Cl adocerans in 1 akes of 1 ower primary productivity in upstate New York.
Recent work in northern Canada documents reduced abundances of
Cladocerans after impoundment of a large reservoir, due to decreased
water transparencies as we1 1 as reduced chlorophyll concentrations and
1 ower temperatures (Patal as and Sal ki 1984).
Given that turbid lakes in Alaska have a reduced volume in which
photosynthesis can occur, as determined by the compensation depth, and
that they exhibit lower level s of primary production and zoopl ankton
density because of their turbid characteristics, it is reasonable to
conclude that fish production in turbid lakes is correspondingly
reduced as a consequence of turbid conditions. Results of analyses
which are depicted in Figures 5, 6, and 7 support this conclusion.
Figure 5 plots mean annual return of adult sockeye salmon in certain
Alaska lakes against the euphotic volume of those lakes. The euphotic
volume is simply the surface area of the lake multiplied by the
Bear Ptarmigan Crescent Tus t umena
TURBIDITY -c
(NTU )
Figure 4. Zooplankton density and compensation depth for clear-water and glacially-
turbid labs in southcentral Alaska ( from Koenings, 1984 ) . Turbidity
measurements for each lake are not available; clear lakes are assumed to have
tur bidities near 0 NTU, Tustumena Lake has been measured at 52 NTU .
2,004000 -
a y t-62,828 + 2547 x
r2 = 0.98
1,500,000 -
I,000,000 -
500,000 -
TUSTUMENA ( 1968-1982)
0 1
0 200 400 600 800
EUPHOTIC VOLUME ( x 10 METERS )
FIgure 5. Relatkmship of armol production of odult wckqe salmon to euphotic volume
(surface area multlplld by compensation depth) for lakes in southcentral Alaska
(from Koonings , 1984).
compensation depth; it is the volume of biologically productive water
in any particular lake. Turbidity reduces the euphotic volume of any
lake by decreasing the compensation depth. So, for any two lakes with
the same surface area the more turbid lake will have less euphotic
volume. A regression of salmon production against euphotic volume in
different sired lakes results in an extremely good relationship (r2 =
0.98). Mean annual adult sockeye production decreases with decreasing
euphotic volume. The effect of turbidity and light penetration can be
seen by noting turbid Tustumena Lake, which is almost six times as
large as clear Karluk Lake in surface area, averages a return of only
one-fifth as many adult sockeye salmon (see Table 3).
The relationship between fish production and turbidity in lakes is more
easily understood by examining Figures 6 and 7 (see also Tables 2 and
3). Although turbidity measurements are not available for all of the
lakes discussed, Tustumena Lake has been observed to have a mean
turbidity of 52 NTU; the clear lakes have turbidities close to 0 NTU
and semi-glacial lakes have turbidities in between (see Figure 2).
Trends for production of juvenile (smo] t) sockeye salmon and returns of
adult sockeye salmon per unit area of lake surface decline appreciably
with increased turbidity, In other words, turbid lakes (ranging to
approximately 50 NTU) are observed to produce far fewer fish than
clear-water lakes per unit surface area.
These results of reduced fish production in turbid water are confirmed
by other investigations, particularly Buck (1956), who detected reduced
individual growth rates, reduced reproduction rates, and l ower
population sizes of fish in turbid versus clear-water ponds in
Oklahoma. A positive relationship between primary production and
warm-water fish production has been observed by Mills and Schiavone
(1982) , and they propose that assessment of zooplankton populations and
measures of primary production can be used to develop fish management
strategies. Moreover, they concl ude that 1 ake productivity i s di rectly
related to a1 gae, or phytoplankton, abundance and inversely
proportional to water clarity. Several other studies on lakes
throughout the world confirm positive and predictive relationships
between primary production and abundance or yield of fish (Melack 1976,
McConnel 1 et a1 . 1977, Ogl esby 1977b).
Nelson f1958) reported a close relationship between increased rates of
photosynthesis in Bare Lake, Kodiak Island and increased growth of
juvenile sockeye salmon. Burgner et al. (1969) suggest that lakes in
southwestern Alaska with high primary productivity rates may produce
more salmon per unit area than lakes with lower plant production.
MEAN ANNUAL SOCKEYE SMOLT PRODUCTION
PER UNIT SURFACE AREA (SMOLT / lo6 m2
TABLE 2. SIZE AND JUVENILE SOCKEYE PRODUCTION OF
SELECTED LAKE SYSTEMS IN SOUTHCENTRAL ALASKA
(from Koenings, 1984)
DATES OF EUPHOT l C
PRODUCTION RELAT l VE SURFACE AREA VOLUME
LAKE EST I MATES TURBIDITY (x 1 06m2 ) (xl~6m3)
Tustumena 1980 - 1982 Glacial 225.0 225.0
Crescent 1981 - 1982 Semi -glacial 16.2 105.0
Packers 1981 - 1982 Stained 2.1 8.4
Upper Russian 1978 '- 1979 Clear 4.6 51 .O
Lei sure 1983 Clear 1.1 16.3
TOTAL
ANNUAL SOCKEYE
SMOLT PRODUCTION
(number of smolt)
ANNUAL ANNUAL SOCKEYE
SOCKEYE SHOLT WILT PER UNIT
PER UNl T AREA EWT IC VOLUME
(smolt/106m2) ($In01 t/l 06m3 )
TABLE 3. SIZE AND ADULT SOCKEYE PRODUCTION OF
SELECTED LAKE SYSTEMS IN SOUTHCENTRAL ALASKA
(from Koeni ngs, 1984)
TOTAL ANNUAL ANNUAL ADULT
DATES OF EUPHOT I C ANNUAL AWLT AWLT SOCKEYE SOCKEYE PER UNIT
PRODUCTION RELAT l VE SURFACE AREA VOLUME RETURN SOCKEYE PER UNIT AREA EUPHOTIC VOLUME
LAKE EST l MATES TURBIDITY (xl0 m ) (number of fish) (no./lO m ) (no. /lo6m3) 6 2 (x10 m ) 6 3 6 2
Tustumena 1968 - 1982 Glacial 225.0 225.0 400,000 1 ,800 1,800
+ Kenai System 1968 - 1982 Glacial
Crescent 1979 - 1982 Semi -glacial 16.2 105.0 180,000 11,100 1,700
Packers Stained
Upper Russian 1963 - 1981 Clear 4.6 51 .O 150,000 32,600 2,900
Karl uk 1921 - 1936 Clear 39.0 780.0 . 2,000,000 51,000 2,500
+ Kenai System includes Kenai, Skilak and Upper Trail lakes.
Artificially Turbid Stream Systems in Alaska
The foregoing analysis of naturally-turbid and clear-water lake systems
described differences in the productivity of turbid and clear-water
aquatic habitats in A1 aska. There are apparently no pub1 ished results
of studies on the primary productivity of natural ly turbid and
clear-water streams in Alaska, beyond observations made by Mil ner
(1983). in streams near Glacier Bay and Anderson (1984) in streams near
Fairbanks. Milner (1983) observed mats of filamentous algae in
glacially-turbid streams with turbidity up to 160 NTU, but few benthic
invertebrates and no fish. Unfortunately, Milner provided little data
on physical parameters, such as depth, with which to evaluate the
effects of turbidity alone on aquatic plant production. Anderson
(1984) measured productivity of periphyton in interior Alaska
clear-water streams, but made no comparisons to production in turbid
st reams.
As a water quality criterion turbidity is used as a measure of the
environmental impact resulting from various 1 and use activities, such
as placer mining, timber harvest and road or pipe1 ine construction, and
is most often of concern with respect to impacts to streams. The most
complete suite of information on the effects of human-i nduced
turbidity, siltation, and sedimentation in waters of Alaska is
presented in preliminary reports and theses from the University of
Alaska-Fairbanks for studies conducted in streams of interior Alaska in
1982-1983. These studies show - for streams similar negative
relationships between turbidity and 1 ight penetration as shown earlier
for lakes. That is, increasing turbidity results in decreasing light
penetration and light intensity at depth which causes reductions in
primary production, and is associated with reduced production of fish
food organisms and ultimately the reduced abundance of fish (LaPerriere
et al. 1983, Van Nieuwenhuyse 1983, LaPerriere 1984, Simnons 1984,
Wagener 1984) (see Table 4).
In stream systems, as opposed to lake systems, most primary production
is derived from benthic algae or larger plants attached to the stream
bottom, a1 though energy may a1 so be contributed from terrestrial
sources of detritus. Primary production by benthic algae or
macrophytes can occur only if light penetrates all the way to the
bottom of the stream. A reduction in the amount, or intensity, of
light reaching the bottom of a stream, other factors remaining the
same, will cause corresponding reductions in primary production.
The discharge of placer-mining wastewater often increases the turbidity
of receiving waters by hundreds or thousands of NTU (R&M 1982a, Sexton
CHARACTERISTIC
TABLE 4. SUMMARY OF IMPACTS RESULTING FROM INCREASED TURBIDITY AND
SEDIMENTATION DUE TO PLACER MINING IN INTERIOR ALASKA STREAMS
(adapted from LaPerriere et a1 ., 1983)
INTERIOR ALASKA STREAMS
NATURAL M l NED
Turbidity Low (0.4 - 1.1 NTU) High (721 - 2250+ NTU)
Suspended Sediment ~oncentrati ont
Settleable Solids
Light Penetration
Primary, Plant, Productivity
LOW (400 - 152 mg/l iter
LOW (not detectable)
Hf gh
Higher
Density of Macroinvertebrates Higher (460 - 693 /mL)
High (462 - 1388 mg/l i ter)
High (trace - 3.5 ml/liter)
Low
Low (0.1 - 0.39 g-02/m2/day)
Low (8 - 206 /m2)
Abundance of Gray 1 ing High None - Low
+ Suspended sediment concentrations reported in LaPerriere et al. (1983) were actually total residues. The difference is that total residue
includes both dissolved sol ids (f i 1 trable residue) and suspended sol ids (nonfi ltrable resf due)i dissolved sol ids can comprf se a substantial
proportion of the total residues reported under these natural conditions.
feed. This may be a result of observed reductions in the abundance of
macroinvertebrates in mined streams on which grayling feed or a
reduction in the capability of these fish to feed. Simnons (1984)
observed an absence of internal fat reserves and parr-mark development
in grayling caged in turbid waters and attributed these effects to
dietary deficiencies.
Another recent Alaska study, performed on arctic grayling at Toolik
Lake in the Brooks Range, has shown that the reactive distance, which
is the distance between a fish and its prey within which a positive
feeding response occurs, of grayl ing decreases with decreasing levels
of available light (Schmidt and O'Brien 1982). This implies that
reductions in light penetration caused by turbidity in waters
containing grayling may hamper their ability to capture food. Studies
in the Yukon Territory indicate that grayling appear to avoid turbid
waters except when driven by migrational impulses (Knapp 1975) and that
numbers of grayling below sources of suspended sediment have been
observed to be consistently lower than clear-water areas upstream of
these turbid-discharges (Bi rtwell et a1 . 1984).
Preliminary studies conducted by ADF&G show that juvenile coho salmon
prefer clear-water habitats over turbid waters in the Susitna River
drainage (ADF&G 1983a) and in the Stikine River drainage (Shaul et al.
1984), and that juvenile chinook salmon exhibit faster growth in
clear-water tributaries than in the mainstem of the glacially-turbid
Taku River (Kissner 1983). Other Alaska studies have il lustrated that
arctic grayl ing prefer clear-water tributaries and migrate to deeper
mainstem rivers primarily to overwinter when sediment and turbidity
levels are significantly reduced (Tack 1980, ADF&G 1983b1, and that
grayl ing avoid streams carrying silt produced by mining (Wojci k 1955,
Warner 1957, Durtsche and Webb 1977, Meyer and Kavanaugh 1982). The
most recent studies conducted in the Susi tna River drainage (Suchanek
et al. 1984a, 1984b) indicate that adult rainbow trout and arctic
grayling avoid turbid water above 30 NTU and that juvenile chinook
salmon use turbid waters but only in the absence of other object-type
cover. An older study, conducted on the Taku River (Meehan and Siniff
1962), suggests that turbidity acts to mask differences in light
between night and day and thus alters the daily pattern of downstream
migration for salmon smol ts.
The avoidance of turbid water by some salmonid fishes is corroborated
by field studies in California (Sumner and Smith 1940!, and by
laboratory studies conducted by Weyerhaeuser Company in Washington
(Bisson and Bi 1 by 1982) where juvenile coho salmon exhi bi ted
significant avoidance of water with turbidities of 70 NTU and above.
P = 0.01491 (PAR)
where
P = gross productivity (g - ~~m-~d-l)
PAR = incident photosynthetically active
2 -1 radiation (E m' d )
This relationship was derived only from unmined streams where there was
very 1 i ttle 1 ight extinction, because most mined streams investigated
were highly turbid and essential ly no productivity could be detected.
Unfortunately, Van Nieuwenhuyse (1983) did not relate primary
production to light available at depth, and thus did not account
directly for natural light extinction or that caused by turbidity.
However, subsequent to release of his thesis, the University of Alaska
has developed an equation (r2 = 0.80) relating primary production to
light at depth (LaPerriere 1984):
where
P = gross productivity (kcal moZ d-l)
PARz = photosynthetically active radiation
available at mean depth z (kcal m-' d-l)
2 = mean depth (meters)
This equation allows a comparison of primary production occurring at a
particular depth between 0 and 0.5 meters for waters of varying
turbidi ties by util izing Equations 3. and 4. Since gross productivity
is described as directly proportional to light available at depth, any
reduction in light penetration caused by turbidity above clear-water
conditions would be expected to cause a corresponding decrease in plant
production. Therefore, we have used Equations 3 and 4 to calculate the
effect of various turbidity levels on light available at depth and
consequently on production of plant material. This information is
presented in Table 5 and plotted in Figure 8. Calculations from these
relationships indicate that a turbidity level of only 5 NTU can
decrease the primary productivity of shal low clear-water streams by
approximately 3 to 13 percent. An increase of 25 NTU may decrease
primary production in shallow streams by 13 to 50 percent. Production
in streams of depth greater than 0.5 meters (1.5 feet) would be reduced
even further.
This conclusion is corroborated by studies in Great Britain (Swale
1964, Westlake 1966, Lack and Berrie 1976, Lund 1969) which reported
turbidity and 1 ight intensity, as opposed to nutrient concentrations,
as the most commonly limiting factors to primary production in streams.
= Stream depth of 0. I meter
0 = Stream depth of 0.3rneter
a = Stream depth of 0.5 meter
-= Stream deeper than 0.5 meter ( 1.5 feet)
TURBIDITY (NT U )
Figure 8. Potential effect of increased turbidity on plant production for shallow streams in
interior Alaska (derived in this report from data presented by Van Nieuwenhuyse, 1983;
La Perriare, 1984. )
TABLE 5. POTENTIAL EFFECT OF INCREASED TURBIDITY ON LICHT PENETRATION AT DEPTH
AND PLANT PRODUCTION IN SHALLOW INTERIOR ALASKA STREAMS (derived in this
report from data presented by Van Nieuwenhuyse, 1983; LaPerrfere, 1984)
* PERCENT REDUCTION
PERCENT OF SURFACE PERCENT OF CLEAR-WATER** FROM CLEAR-WATER
DEPTH TURBIDITY LIGHT AT DEPTH PLANT PRODUCT l ON PLANT PRODUCTION
(meters) (NTU) (%I (%) (%)
- - - - - - - - - - - *
Calculated from Equations 3 and 4:
N = 1.00 + 0.024(T)
where t
-1 N = total extinction coeff. (meter 1
Tt = turbidity (NTU)
C*
Calculated from Equation 6:
P = 0.0021 (PAR ) -
where z -2 -1
P = gross productivity (kcal m d 1
where
I = percent of inct dent PAR z at depth Z
Z = depth (meters)
Note: PAR = I - z z
PAR = incident photosynthetically active - -2 -1
z radiation (kcal m d ) at mean depth z
Stross and Stottlemeyer (1965) reported lower primary production per
unit surface area in the Patuxent River, Maryland due to elevated
turbidity; Hancock (1973) reported lower production and a1 tered plant
species composition caused by turbidity in South Africa. A1 though
conducted in a shallow pond rather than a stream, studies in North
Carolina (Reed et al. 1983) have shown that a reduction in turbidity
from only 12 NTU to 6 NTU resulted in a significant increase in growth
of plants attached to the pond bottom. Van Nieuwenhuyse (1983)
concluded in his thesis on interior Alaska streams that the
demonstrated importance of light in controlling a stream's productivity
argues that increased turbidity is the single most important disruption
to that productivity.
The University of Alaska a1 so investigated the abundance of
macroinvertebrates in mined and unmined streams of interior A1 aska
(LaPerriere et a1 . 1983, Wagener 1984). These macroinvertebrates
comprise the basic food supply of stream-dwelling salmonid fishes.
LaPerriere et al. (1983) sumnarized their studies by reporting that .
unmined streams supported significantly higher densities of benthic
invertebrates than did mined streams and that with a high degree of
mining most taxa became very rare or were completely eliminated.
Wagener (1984) also reported that biomass was substantially reduced in
mined streams. A1 though reduced invertebrate densities were
hypothesized to have resulted from habitat alteration caused by
settleable sol ids (LaPerriere et a1 . 1983), Wagener ( 1984) concluded
that turbi di ty compri sed the strongest descri ptor of reduced density
and biomass of macroinvertebrates in those mined streams. Simi 1 ar
reductions in the abundance of macroinvertebrates due to sediment input
have been observed in the Yukon and Northwest Territories, Canada
(Rosenberg and Snow 1975, Mathers et al. 1981, Soroka and
McKenzie-Grieve 1983, Birtwe11 et al. 1984). The direct effects of
those sediments will be more fully discussed in the next section of
this paper.
Finally, the University of Alaska studies considered the effects of
mining on fish (LaPerriere et al. 1983, Simmons 1984). Throughout
their sampl ing , investigators caught many gray1 ing within unmined
streams and none in the mined streams, except during the presumed
autumn migration of some fish through streams influenced by mining.
The direct physical effects of sediment on fish will be discussed in
the following section, but one hypothesized effect of turbidity is to
reduce the feeding capability of grayling since these fish feed by
sight (Simmons 1984). The researchers examined stomachs of caged
grayling in mined and unmined streams and found that grayling in the
turbid waters were not capable of locating aquatic insects on which to
feed. This may be a result of observed reductions in the abundance of
macroinvertebrates in mined streams on which grayling feed or a
reduction in the capability of these fish to feed. Simnons (1984)
observed an absence of internal fat reserves and parr-mark development
in grayling caged in turbid waters and attributed these effects to
dietary deficiencies.
Another recent Alaska study, performed on arctic grayling at Toolik
Lake in the Brooks Range, has shown that the reactive distance, which
is the distance between a fish and its prey within which a positive
feeding response occurs, of grayling decreases with decreasing levels
of available light (Schmidt and O'Brien 1982). This implies that
reductions in light penetration caused by turbidity in waters
containing grayling may hamper their ability to capture food. Studies
in the Yukon Territory indicate that grayling appear to avoid turbid
waters except when driven by migrational impulses (Knapp 1975) and that
numbers of grayl ing below sources of suspended sediment have been
observed to be consistently lower than clear-water areas upstream of
these turbiddischarges (Bi rtwell et a1 . 1984).
Prel imi nary studies conducted by ADF&G show that juvenile coho salmon
prefer clear-water habitats over turbid waters in the Susitna River
drainage (ADF&G 1983a) and in the Stikine River drainage (Shaul et al.
1984), and that juvenile chinook salmon exhibit faster growth in
clear-water tributaries than in the mainstem of the glacial ly-turbid
Taku River (Kissner 1983). Other Alaska studies have illustrated that
arctic grayl ing prefer cl ear-water tributaries and migrate to deeper
mainstem rivers primarily to overwinter when sediment and turbidity
levels are significantly reduced (Tack 1980, ADF&G 1983b), and that
grayl ing avoid streams carrying silt produced by mining (Wojci k 1955,
Warner 1957, Durtsche and Webb 1977, Meyer and Kavanaugh 1982). The
most recent studies conducted in the Susi tna River drainage (Suchanek
et al. 1984a, 1984b) indicate that adult rainbow trout and arctic
grayling avoid turbid water above 30 NTU and that juvenile chinook
salmon use turbid waters but only in the absence of other object-type
cover. An older study, conducted on the Taku River (Meehan and Siniff
1962), suggests that turbidity acts to mask differences in light
between night and day and thus alters the daily pattern of downstream
migration for salmon smolts.
The avoidance of turbid water by some salmonid fishes is corroborated
by field studies in California (Sumner and Smith 1940!, and by
laboratory studies conducted by Weyerhaeuser Company in Washington
(Bisson and Bilby 1982) where juvenile coho salmon exhibited
significant avoidance of water with turbidities of 70 NTU and above.
This avoidance of turbid water has been commonly attributed to the
sight-feeding requirements of salmonids (Bachmann 1958, Sykora et a1.
1972, Langer 1980, Berg 1982). A recent study by Crecco and Savoy
(1984) suggests that turbidity may reduce feeding success of larval
shad in the Connecticut River. Brett and Groot (1963) state that
turbidity may directly affect the migration of salmon through
interference with visual cues.
Turbidity also has an effect on the human use of aquatic systems. It
is generally acknowledged that turbid water is less acceptable than
clear water for consumption, contact recreation, and perhaps aesthetic
enjoyment. In many cases turbidity reduces the range of opportunities
available for the use of a water body (NAs 1973, EPA 1976). An
analysis of angl er-effort on the Chatani ka River in interior Alaska,
performed by ADF&G (Townsend 1983), indicates that turbidity ranging
from 8 to 50 NTU, 25 miles downstream from mine discharges, coincided
with and may have contributed to a 55 percent decline in sportfishing.
In 1977 and 1978, the Chatanika River was the second most popular water
body for sportfishing in interior Alaska; but in 1979, when increased
mining activity caused muddy-water conditions, the Chatani ka fell to
seventh in popularity. A study in Denali National Park and Preserve
(Mi 1 ler 1981) a1 so reports reduced sportfi shing in streams made turbid
by mining activities. Avoidance of turbid waters by sport fishermen
and reduced angler success in turbid waters have been described outside
Alaska as well (Buck 1956, Tebo 1956, Bartsch 1960, Oschwald 1972,
Ritter and Ott 1974, Langer 1980).
Furthermore, the efficient management of fisheries can be directly
affected by turbidity (Tait et al. 1962, Cousens et al. 1982).
Biologists from the Comnercial Fisheries and Sport Fisheries Divisions
of ADF&G in western, southcentral, and interior Alaska have reported
specific instances where wastewater di scharges from placer mines have
obstructed aerial escapement surveys for adult salmon (Schneiderhan
1982, Barton 1983a, Barton 1983b, Hepler 1983). An informal consensus
from ADF&G biologists indicates that an absolute turbidity of 4-8 NTU
is sufficient to interfere with these aerial surveys (Ott 1984b).
TURBIDITY AND SUSPENDED SEDIMENT
Sediment in water is generally considered in two broad classes: 1)
suspended sediment, which remains in the water column due to water
turbulence, particle shape, and/or the low specific gravity of
individual particles, and 2) settleable sol ids, which rapidly settle to
the lake or stream bottom and move only if rolled along the bottom or
resuspended by currents. A large number of original investigations and
literature reviews have identified the effects of an increase in
suspended sediment or settleable solids on primary production, on the
production of fish-food organisms, and ultimately on various aspects of
the production of fish in aquatic habitats (Shaw and Maga 1943, Bartsch
1960, Cordone and Kelley 1961, Herbert et al. 1961, King and Ball 1964,
Cooper 1965, EIFAC 1965, Saunders and Smith 1965, Peters 1967, Angino
and O'Brien 1968, Chutter 1969, Hall and Lantz 1969, Gamnon 1970,
McDonald and Thomas 1970, Koski 1972, Oschwald 1972, Ritchie 1972,
Gibbons and Salo 1973, Hynes 1973, Clarke 1974, Williams and Harcup
1974, Phillips et al. 1975, Rosenberg and Snow 1975, Horkel and Pearson
1976, Swenson and Matson 1976, Zemansky et a1. 1976, Bjornn et a1.
1977, Iwamoto et al. 1978, Noggle 1978, Walmsley 1978, Redding and
Schreck 1980, Cederholm et al. 1981, Crouse et al. 1981, Mathers et al.
1981, Singleton et al. 1981, Berg 1982, Hesse and Newcomb 1982, Hall
and McKay 1983, McLeay et a1 . 1983, Reed et a1 . 1983, Bi rtwel 1 et a1.
1984, McLeay et al. 1984).
Several studies and reviews have also described the importance of
sediments in transporting other pol lutants (Gri ssinger and McDowell
1970, Morris and Johnson 1971, Alabaster 1972, Feltz and Culbertson
1972, NAS 1973, Lehmann 1977, Metsker 1982, Soroka and MacKenzie-Grieve
1983, West 1983).
Although it is beyond the scope of this paper to fully describe these
impacts, the following briefly out1 ines the various effects attributed
to or coincident with increases of suspended and settleable solids in
aquatic habitats. Increased sediments in water may:
Reduce the penetration of light and intensity of light in water
Alter the spectral composition of light penetrating in water
Increase water temperatures by absorption of radiation or decrease
water temperatures by back-radi ation, depending on amount of
insolation and thermal stratification
Alter pH, alkalinity, and conductivity
Decrease oxygen avai 1 abi 1 i ty through increased chemical oxygen
demand, increased water temperature, and/or reduced exchange
between surface flow and groundwater in the streambed
Alter nutrient availability through absorption or complexation
Transport heavy metals and other potential toxicants
Reduce primary production through decreased 1 i ght penetration
and/or preferential extinction of specific spectra of 1 ight
required by plants
A1 ter plant species composi tion and abundance through changes in
light levels, smothering, scouring, and other physical
effects
Reduce zooplankton production and abundance
A1 ter zooplankton species composition
Reduce benthic invertebrate production and abundance
A1 ter benthic invertebrate species composition
Cause "drift" of benthic invertebrates .
Embed and cement spawning gravels
Coat and suffocate incubating eggs
Decrease survival of newly hatched fish
Promote premature emergence of fry from stream gravels
Reduce successful emergence of fry from stream gravels
Reduce feeding efficiency of fish
Decrease growth rate and production of fish
Physically abrade and clog fish tissues, such as gill filaments
Promote contact of absorbed pollutants with sensitive tissues,
such as gill filaments
Promote other physiological stress in fish
Reduce amount of suitable rearing, feeding habitat of juvenile
sal moni ds
Interfere with migrational movements of salmon
Reduce the aesthetic qua1 i ty and recreational use of previously
productive recreational fishing waters
Reduce the efficiency of fi shery management efforts to determine
salmon escapements
Studies performed in Alaska have substantiated many of these effects
(McNeil et al. 1962; McNeil 1964; McNeil and Ahnell 1964; Shapley and
Bishop 1965; Schallock 1966; Vaux 1968; Phillips 1971; Tyler and
Gibbons 1973; Meehan 1974; Meehan and Swanston 1977; R&M Consultants
1982a; Schmidt and OIBrien 1982; Van Nieuwenhuyse 1983; Simnons 1984;
Wagener 1984; West and Deschu 1984; Bjerklie and LaPerriere, unpubl.
ms. ; LaPerriere et a1 . , unpubl . ms. ).
While there is a temporal relationship between suspended sediment and
settleable solids, as well as an overlap in particle size, we are
concerned in this paper with only the measurement of and impacts
associated with those sediments suspended in the water column. If
turbidity can be used to estimate the concentrat ion of suspended
sediment in water, then we can relate impacts associated with suspended
sediment concentration to turbidity measurements.
Turbidity actually measures the scattering of light within a sample of
water, but the turbidity measure was developed primarily to be used as
an index of the concentration of suspended material in water
(Hardenbergh 1938, in McCl uney 1975). However, some investigators have
criticized the use of turbidity as a measure of suspended sediment
concentration on the grounds that precise estimation of natural
suspended sediment concentrations by light scattering is not possible
because of the variable particle size, angularity or shape, refractive
index, and other properties of sediments that affect the amount of
light scattered or absorbed by any particular amount of material, as
well as the variability of different units of turbidity measurement and
the variability in sediment particle sizes carried at different flow
regimes in streams (Duchrow and Everhart 1971, McCluney 1975, Pickering
1976, Beschta 1980).
Detailed criticism (Beschta 1980) has acknowledged that good predictive
re1 ationships between suspended sediment concentration and turbidity
can be developed on a drainage-by-drainage basis, however, since any
particular drainage will erode similar sediment material over a period
of time, but that between-drainage comparisons are not as useful since
different drainages are comprised of different sediment material.
One problem with using turbidity as a measure of the concentration of
suspended sediment, as i 11 ustrated by Duchrow and Everhart (1971), is
that turbidity is a result of the total amount of sediment suspended in
the water at any particular time. At any point in time, the suspended
load includes large particles that may soon settle out (settleable
solids) and smaller particles that may remain in suspension for
considerable lengths of time (suspended sediment), depending on
specific gravity, particle shape, and water turbulence. As long as
there is sediment suspended in the water column turbidity, and thus
reduced 1 i ght penetration, wi 11 continue downstream from the source of
sediment input, even as the settleable solids fall onto the lake or
stream bottom, producing effects associated with sedimentation (Hal 1
and McKay 1983). It should be noted, however, that suspended sediment
can also be deposited in stream gravels by being filtered out during
intragravel flow (Cooper 1965, Einstein 1968, Vaux 1968).
The use of mixing zones in monitoring and enforcement of sediment and
turbidity standards, however, seeks to accommodate the temporal
suspension of larger size fractions. Most of the larger solids will
fall out of the water column within the mixing zone, so that turbidity
measured at the perimeter of a mixing zone should be produced by
suspended sediments that will continue to contribute to turbidity for
considerable distances downstream.
The usefulness of turbidity measurement has been supported by a
consensus of environmental scientists at a workshop on sediment and
water quality conducted by the U.S. Environmental Protection Agency
(Iwamoto et al. 1978). Turbidity has been used to estimate sediment
loads in streams by the Pennsylvania Department of Transportation
(~ruhlar 1976) and has been recommended for use in monitoring suspended
solids in wastewater treatment processes (Liskowitz 1974). A detailed
analysis of suspended sediment concentration versus turbidity ,
conducted by Kunkle and Comer (1971) in. Vermont, showed extremely good
correspondence between drainages. They concl uded that using turbidity
measurements to estimate suspended sediment concentration can be a very
useful technique.
It is apparent, then, that while a single relationship between
turbidity measurements and suspended sediment concentration (SSC) may
not be extremely accurate for a wide spectrum of streams, the impacts
caused by specific levels of SSC can be associated with a range of
turbidity levels. Conversely, turbidity standards based upon impacts
such as reduced 1 ight penetration and aquatic productivity can be
further justified by direct effects caused by levels of SSC associated
with those'turbidity standards.
Turbidity and Suspended Sediment in Alaska Streams
Many natural waters in Alaska have been sampled for turbidity and
suspended sediment concentration, and the U.S. Geological Survey (USGS)
maintains a computer database (WATSTORE) on these water analyses. A
regression analysis of information from WATSTORE for the period 1976 to
1983 (May - October), involving 229 samples from 37 stations on 34
rivers, yields a relatively good relationship (r2 = 0.83, for logllog
transform) between turbidity and suspended sediment concentration
(Figure 9):
log T = -0.357 + 0.858 log SSC (7)
where
T = turbidity (NTU)
SSC = suspended sediment concentration
(mgll i ter)
SUSPENDED SEDIMENT CONCENTRATION
( mq / liter )
Figure 9. Empirical relationship of naturally occurring turbidity versus suspended sediment
concentration for rivers and streams in Alaska, sampled during May-October , 1976 -
1983 (derived in this report from data provided by USGS, 1984).
This log/log equation can be transformed back to:
Although this relationship is driven by a high proportion of samples
from larger silt-laden rivers, a diversity of stream types and
locations are represented in the data. For this sample set, the
regression shows that turbidity and SSC are related. The relationship
shown in Equation 8 can be used to illustrate, for example, that a
suspended sediment concentration of 25 mg per liter may be associated
with turbidities around 7 NTU and that a SSC of 100 mg per liter
corresponds to a turbidity of approximately 23 NTU.
A similar relationship between turbidity and SSC was developed by
Peratrovich et al. (1982) using data from the Susitna River. Their
relationship is given in Equation 9.
(r2 = 0.92, for log/log transform)
Using this equation for Susitna River sediments, 25 rng per liter SSC
corresponds to turbidities of only 4.6 NTU, and a SSC of 100 mg per
1 iter yields a turbidity level of 18.3 NTU.
Using data gathered from pl acer-mi ned and neighboring unmi ned streams
in interior Alaska we derive the relationship given in Equation 10
(Figure 10) :
log T = 0.0425 + 0.9679 log SSC (10)
This log/log equation can be transformed back to:
This equation was derived from data for the following drainages near
Fairbanks: Chatani ka River, Upper Birch Creek, Crooked Creek,
Goldstream Creek, Tolovana River, and Chena River, gathered by Post
(1984) and Toland (1984). Table 6 outlines values of turbidity
estimated for various concentrations of suspended sediment in Alaska
streams from the equations listed above.
T = I. 103 (SSC ) 0.968
r2= 0.92
SUSPENDED SEDIMENT CONCENTRATION
( mg / liter )
Figure 10. Empirical relationship of turbidity versus suspended sediment concentration for placer-
mined and neighboring unmined streams in interior Alaska, sampled during summer,
1983- 1984 (derived in this report from data provided by Post, 1984 ; Toland, 1984).
TABLE 6. PREDICTION OF TURBIDITY CAUSED BY SUSPENDED SEDIMENT
CONCENTRATIONS IN STREAMS THROUGHOUT ALASKA,
SUSITNA RIVER, AND INTERIOR ALASKA STREAMS
* *X m
ESTIMATED EST I MATED EST I MATED
TURBIDITY (NTU) TURB l D l TY (NTU) TURBIDITY (NTU)
FROM FROM FROM
SUSPENDED SEDIMENT STATE-WIDE SUSITNA RIVER I NTER I OR ALASKA
CONCENTRATION (mq/liter) EQUAT I ON EQUAT l ON EQUAT l ON
*
Equation derived in this report from USCS WAJ:Jg%E water records for Alaska, May - October
1976 - 1983 (see Equation 8): T = 0.44(SSC)
*.*
Equat i on fromJgatrovich et al., (1982) for Susitna River (see Equation 9):
T = 0.185(SSC)
m
Equation derived in this report from data provided by Post (1984) and Toland (1984) for
placer-mined and neighboringO;ggtfned streams in interior A1 aska, sumner 1983-1 984 (sw
Equation 11 ): T = 1.103(SSC)
Turbidity, Suspended Sediment, and Land Use in Alaska
Land use activities such as timber harvest, agriculture, mining, and
road and pipeline construction can contribute to elevated sediment
loads in streams (Stern and Stickle 1978, Farnworth et al. 1979). In
Alaska, studies associated with wastewater discharges from placer mines
provide the most comprehensive data base on the production of turbidity
and suspended sediment by land use activities.
R&M Consultants (1982a) performed a study on wastewater discharge from
sixteen placer mines in interior Alaska. These mines, like most others
in Alaska, are located on naturally clear-water streams. From data
presented in their report it is possible to calculate mean mine-induced
increases of turbidity and SSC of 2500 NTU and 3600 mg per liter,
respectively. A plot of natural upstream levels and downstream
effluent levels of turbidity and SSC measured at these mines is
presented in Figure 11. Examination of this plot and that presented
for natural streams in Alaska (Figure 9) illustrates that placer mining
can increase turbidity and SSC well above natural clear-water levels
and above levels found in naturally turbid rivers such as the Copper,
Susitna, Kuskokwim, and Yukon. It should be noted that the wide range
in values for placer mining effluents reflects the different degrees of
wastewater treatment employed at various mines and possibly differences
in sediment characteristics evident at those mines.
A study performed by the A1 aska Department of Environmental
Conservation (Sexton 1983) in the Kantishna Hllls area found that mean
mine-induced increases of turbidity and SSC were approximately 3600 NTU
and 6500 mg per liter, respectively. Other reports on studies
conducted in Alaska have illustrated or discussed various similar
effects of placer mining on water quality (FWPCA 1969, Frey et al.
1970, Morrow 1971, Dames & Moore 1976, EPA 1977, ADEC 1979, Rainbridge
1979, Chang 1979, Cook 1979, Yang 1979, Blanchet 1981, Madison 1981,
Wol ff and Thomas 1982, KRE 1984, Peterson et a1 . 1984, To1 and 1984).
The R&M Consultants study (1982a) a1 so developed a relationship
(r2 = 0.89) between turbidity and SSC from settling column tests
performed with the sluice box discharge of selected placer mines in
interior Alaska:
log T = 1.13 + 0.68 log SSC (12)
This log/log equation can be transformed back to:
x = Downstream of mine
= Upstream of mine
SUSPENDED SEDIMENT CONCENTRATION
( mq/ liter 1
Figure 11. Plot of turbidity and suspended sediment concentration for certain placer-mined streams
in Alaska (plotted in this repat from data presented in R BM Consultants, 19820 ).
Equation 13 predicts a substantially higher level of turbidity for any
given level of SSC in the settling columns than do the equations
presented earl ier for natural waters statewide (8), the Susi tna River
!9), and streams in interior Alaska (11). Since the particle size
fractionation of measured s1 uice box discharges is reasonably
comparable to that described for information available from some
natural waters in Alaska (Figure 12), the higher levels of turbidity
associated with any particular level of SSC may be due to the
undisturbed settling of sluice box effluent for up to three days in the
settling column tests. Under natural conditions of stream turbulence,
or within settling ponds with less than a three-day quiescent residence
time, larger particles, which intuitively are be1 ieved to produce less
turbidity per unit SSC, would remain in suspension. The result, under
conditions other than within artificial settling columns, may be a
relationship between NTU and SSC in mine effluents more closely
resembling Equations 8, 9 or 11, with lower levels of turbidity per
unit SSC. Therefore, re1 ationships developed from settl ing column
testing 1 ikely do not represent conditions in streams.
The establishment of relationships between turbidity and SSC allows us
to associate impacts caused by suspended sediment to specific levels,
or ranges, of turbidity measurements. In this way turbidity standards
can be used not only to control adverse effects to light penetration
and aquatic productivity, but also to some extent the direct impacts
associated with suspended sediment.
RELEVANCE OF TURBIDITY AND SUSPENDED SEDIMENT TO FISH
The recent studies summarized in this report illustrate the effects
that turbidity has on freshwater aquatic habitats in Alaska. As
out1 ined in Table 7, increasing levels of turbidity dramatical ly reduce
light penetration and are associated with decreased production of plant
material (primary production), decreased abundance of fish food
organi sms (secondary production), and ul timately with decreased
production and abundance of fish. Turbidity resulting from suspended
sediment introduced to naturally clear-water streams also adversely
affects the human use of these streams, for recreational fishing and
management of f i sh resources. Moreover, there are useabl e
relationships between turbidity and the suspended sediment
concentration of Alaska waters, wherein turbidity can be used as a
reasonable estimator of suspended sediment concentration. Elevated
suspended sediment concentrations have been directly related to adverse
impacts on aquatic systems in studies performed outside of Alaska. The
numerous effects of sediment that settles out of suspension are not
discussed here; for a description of these effects the reader is
referred to Hall and McKay (1983).
The fact that turbid waters produce fewer fish may on first impression
appear contradictory to the common know1 edge that l arge, muddy rivers
in Alaska, such as the Copper, Susitna, Kuskokwim, and Yukon rivers,
contain massive salmon runs. To explain this apparent contradiction we
need only look at the way these fish utilize their aquatic environment.
Pacific salmon and other anadromous fish migrate from the ocean to
fresh water to spawn, and although millions of these fish ascend large
muddy rivers they almost invariably seek out the clear-water
tributaries, sloughs, or areas of groundwater upwell ing to deposit
their eggs. Juvenile fish that hatch from these eggs generally remain
in clear-water habitats for periods ranging from days to years and then
descend through the turbid rivers to reach the ocean. The larger
turbid rivers, then, serve primarily as migration corridors to and from
the headwaters and tributaries of these systems.
It is sometimes held that land use activities contribute sediment loads
to clear-water streams and account for turbidity levels that are
comparable to those of our naturally silt-laden and turbid rivers. An
analysis of available data, however, indicates that placer mining
without proper wastewater treatment can elevate suspended sediment
loads and turbidity levels of naturally clear-water streams up to an
order of magnitude (ten times) above those of our large muddy rivers
and perhaps three orders of magnitude (one thousand times) above
natural clear-water conditions (see Figures 9 and 11).
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At what levels of suspended sediment concentration or turbidity are
aquatic habitats adversely affected? In addition to the studies
conducted in Alaska, which are sumnarized earlier in this report and
indicate that reductions in aquatic productivity can trans1 ate to
reduced abundance of fish, there is a large albeit disjointed body of
literature regarding the effects of turbidity and suspended sediments.
Hollis et al. (1964), Sherk 1971, Sorensen et al. (1977), Stern and
Stickle (1978), Farnworth et al. (1979), Muncy et al. (1979), and
Wilber (1983) provide recent reviews of this literature, including a
description of studies performed by Wall en (1951).
Wallen (1951) reported that lethal levels of turbidity, measured in
parts per million (ppm, roughly equivalent to mg per liter), range in
the tens of thousands of ppm. These high levels of turbidity, which
are actually proxies for SSC, required to kill fish led Wallen (1951)
to conclude that natural turbidity levels do not represent a lethal
threat to fish. Wal len 's information, however, is generated primarily
from tests of acute effects on warm-water non-salmonid fishes,
including ca'rp, bass, and bull heads, and 1i kely is not applicable to
col d-water salmonid fishes which are prevalent in Alaska. Moreover,
other more recent studies on bass and sunfish (Heimstra et al. 1969)
indicate that lower levels of turbidity, of 4-16 JTU, alter fish
behavior, including decreased levels of activity. Studies on
cold-water salmonids indicate that low levels of turbidity or SSC may
stress, alter behavior patterns, or kill these fish.
The fol lowing citations , and Tab1 e 8, briefly summarize relevant
literature from studies conducted outside of Alaska on the effects of
turbidity or sediments measured as suspended material on cold-water
salmonid fishes.
Herbert and Merkens (1961), in a study on the effect of mineral solids
on rainbow trout in Great Britain, concluded that concentrations of
kaolin and diatomaceous earth at 270 ppm negatively affect ability to
survive and that concentrations of 90 ppm appear to have some adverse
effect. Herbert et al. f1961) found reduced densities of brown trout
at SSC of 1000 and 6000 ppm. Herbert and Richards (1963) found that 50
ppm of wood fiber or coal washery waste caused reduced growth in
juvenile rainbow trout, and that concentrations of 100 and 200 ppm wood
fiber promoted fin-rot in these fish.
In a study on juvenile coho salmon, Noggle ' 1978) noted that changes
from clear-water conditions resulted in a decrease in feeding, and that
a complete cessation of feeding occurred at SSC above 300 mg per liter.
He also estimated an acute lethal concentration causing 50 percent
TABLE 8. SOME REPORTED EFFECTS OF TURBIDITY AND SUSPENDED
SEDIMENT ON SALMONID FISH OUTSIDE OF AUSKA
EFFECT SPEC l ES LOCAT I ON
Mortality
(96 hour LC ) 50
Reduced survival
(marked )
Reduced survi val
(marked)
Reduced survival
(marked)
Reduced survival
(marked)
Reduced survival
(slight)
Reduced survival
(marked)
Reduced abundance
(marked)
Reduced growth
(marked)
Reduced growth
(slight)
Reduced growth
(slight)
Coho salmon Washington
(juvenile)
Chum salmon Canada
(eggs)
Rainbow trout Great Britain
(eggs 1
Rainbow trout Great Bri tai n
(juveni le)
Rainbow trout Great Britain
(juvenile)
Rainbow trout Great Britain
(juvenile)
Coho salmon Pennsy 1 vani a
(juvenile)
Brown trout Great Bri tat n
Brook trout Pennsylvania
(juveni 1 e )
Brook trout Pennsylvania
(juvenile)
Rai nbow trout Great Britain
(juveni le)
REPORTED
TURBIDITY OR
SUSPENDED SEDIMENT
CONCENTRATION
1200 mg/l I ter
97 mg/l i ter
270 ppm
6, 12 sg Fe/liter
15-27 JTU
1000, 6000 ppm
50 mg Fe/li ter
86 JTU
12 mg Fe/l i ter
32 JTU
50 Pprn
ClTAT ION
Noggle 1978
Langer 1980
Scullion and Edwards 1980
Herbert and Merkens 1961
Herbert and Richards 1963
Herbert and Herkens 1961
Smith and Sykora 1976
Herbert et 81. 1961
Sykora et al. 1972
Sykora et al. 1972
Herbert and Richards 1963
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mortality (LC 50) for coho salmon at 1200 mg per liter during summer.
He concluded that human-induced sediment in waters during summer poses
a greater possibility of harm to juvenile salmonids than generation of
sediment in phase with natural hydro1 ogi c cycles (Noggl e 1978).
Langer (1980) reports from Canada that SSC of 97 mg per liter caused by
a release of sediment in the Coquitlam River resulted in only a 23
percent survival of chum salmon eggs, whereas SSC of 10 mg per liter in
a tributary stream allowed almost 94 percent survival. In a recent
study on the effects of placer mining effluents on arctic grayling in
the Yukon Territory, McLeay et al. (1983) found that a SSC level of as
low as 50 mg per liter may cause identifiable stress. Redding and
Schreck (1980) observed several stress responses to suspended sediment
and turbidity by juvenile coho salmon and steelhead trout at SSC of 500
and 2000-3000 mg per liter, and suggested that effects of chronic
exposure to sediment are more severe than effects of acute exposure.
Sykora et al. (1972) demonstrated marked reductions in growth of
juvenile brook trout in Pennsylvania at concentrations of 50 mg Fe per
liter neutralized iron hydroxide and slight reductions in growth at
concentrations as low as 12 mg Fe per liter. Smith and Sykora (1976)
also found reduced survival of juvenile coho salmon at 6 and 12 mg Fe
per 1 i ter concentrations of neutral i zed iron hydroxide, with associated
turbidity of 15 to 27 JTU, as well as respiratory distress and
listlessness. These authors (Sykora et al. 1972, Sykora and Smith
1976) attribute these effects to the reduced visibility and other
impacts caused by the suspended iron hydroxide rather than to any toxic
qua1 i ties of the material.
Bachmann (1958) found that cutthroat trout in Idaho sought cover and
stopped feeding at turbidities measured at 35 ppm. Scullion and
Edwards (1980) found that rainbow trout in Great Britain exhibited
increased egg mortal i ty, a1 tered diets, lower condition factors, and
downstream displacement caused by human-induced SSC averaging 110 mg
per 1 i ter.
Based upon an extensive review of available 1 i terature commissioned by
the Food and Agriculture Organization of the United Nations, the
European In1 and Fisheries Advisory Commission concluded that waters
containing 0 to 25 ppm of chemically inert sol ids should not adversely
affect freshwater fisheries but that SSC of 25 to 80 ppm may lower the
production of fish and that waters containing SSC exceeding 80 pprn are
unl i kely to support good fisheries (EIFAC 1964!. Moreover, they
emphasize that "the spawning grounds of salmon and trout require
special consideration and should be kept as free as possible from
finely divided sediments" (EIFAC 1964). Gammon (1970) stated in a
report to the U. S. Envi ronmental Protection Agency on studies conducted
in Indiana, for warm-water systems, that the suspended sol ids criteria
proposed by EIFAC (see Table 10) may be too liberal for fish
populations in the United States.
As noted earlier, studies in California show that adult chinook salmon
may generally avoid entering turbid waters (Sumner and Smith 1940), and
turbidity.may interfere with migrational movements of salmon (Brett and
Groot 1963). Lake trout have also been observed to avoid turbid water
in Lake Superior, and associated laboratory studies indicate that lake
trout are sensitive to turbidities as low as 6 FTU (Swenson 1978).
A1 though brook trout exhibited no avoidance in 1 aboratory experiments
of turbidities up to an average of 61 FTU (Gradall and Swenson 1982)
these studies did note behavioral changes caused by turbidity of 7 FTU.
Laboratory studies conducted with juvenile coho salmon illustrate
avoidance of water with turbidities of 70 NTU and above (Bisson and
Bilby 1982). Studies conducted at a hatchery in Arizona indicate that
the feeding .activity of rainbow trout drops off sharply at 70 JTU
(Olson et al. 1973); moreover, they documented a much lower food energy
conversion ratio for fish in turbid water compared to those in clear
water.
Most recently, laboratory studies conducted in Idaho on the chronic, as
opposed to short-term, effects of turbidity i 11 ustrate that juveni 1 e
steelhead trout and coho salmon tend to avoid turbid waters of between
22 and 265 NTU, that these fish are displaced downstream at turbidity
levels between 40 and 50 NTU, and that steelhead and coho salmon
remaining in these turbid waters exhibit slower growth than similar
fish in clear water (Sigler 1981, Sigler et al. 1984). Moreover, they
conclude that turbidities of 25 NTU caused a reduction in fish growth,
presumably due to reduced ability to feed (Sigler et al. 1984). A
reduction in the sight-feeding ability of salmonid fishes due to
reduced 1 i ght intensity or increased turbidity is discussed in several
previously referenced reports (Bachmann 1958, Sykora et al. 1972,
Langer 1980, Schmidt and O'Brien 1982). Langer (1980) specifically
notes 25 JTU as a turbidity at which trout may cease to feed; Bell
(1973) states that fish food production declines and visual references
are lost at turbidities of 25 to 30 JTU. Berg (1982) determined that
turbidity of 60 NTU had a marked effect on the visual ability of
juvenile coho salmon, and that turbidities between 10 and 60 NTU caused
reduced feeding, reduced territorial i ty , and 1 oss of aggressive
interactions among juvenile coho salmon.
For comparative purposes, the reactive distance of bluegills, a warm
water fish, has been observed to decrease with increases of turbidity
from 1 to 30 JTU (Vinyard and O'Brien 1976), and the feeding rate of
bluegills has been observed to drop 20 percent at turbidities of 60 NTU
(Gardner 1981).
As stated earlier, research in Kansas on a comnon Cladoceran, which is
a preferred food item of juvenile fishes including salmon, has shown
that a turbidity level of 10 NTU can cause significant declines in
feeding rate, food assimilation, and reproductive potential (McCabe and
O'Brien 1983). Robertson (1957) found reduced reproduction in
Cladocera at clay and charcoal concentrations between 82 and 392 ppm.
Arruda et al. (1983) observed that suspended sediment concentrations of
50 to 100 mg per liter reduced the algal carbon ingested by Cladocerans
to potential starvation levels.
Perhaps the most comprehensive study completed recently on the direct
effects of suspended sediment, and resulting turbidity, on salmonid
fish was conducted on arctic grayling and placer mine sediments from
the Yukon Territory (McLeay et al. 1984). They conducted controlled
experiments in laboratory streams maintained at nominal suspended
sediment concentrations of 0, 100, 300 and 1000 mg per liter; actual
mean values were 4, 86-93, 273-286 and 955-988 mg per 1 i ter
respectively. Although overall survival of fish during the tests was
not affected by these levels of SSC several other sublethal effects
were observed. Fish growth was depressed by 6 to 10 percent in SSC of
100 and 300 mg per liter and by 33 percent in SSC of 1000 mg per liter.
Distribution of the grayling was unaffected by SSC of 100 mg per liter,
but fish were displaced downstream at SSC of 300 and 1000 mg per liter.
Feeding responses of grayling were slower at SSC of 100, 300 and 1000
mg per liter, particularly responses to food available at the water
surface. Coloration of fish was paler at SSC of 300 and 1000 mg per
1 i ter. Tolerance of fish to a reference toxicant was reduced at SSC of
300 and 1000 mg per liter, and oxygen uptake rates were increased.
McLeay et a1 . (1984) conclude that SSC of 100 mg per 1 i ter can affect
fish growth and feeding responses, and that SSC of 300 mg per 1 iter or
higher. can increase metabolic rate, lower tolerance to toxicants and
cause displacement of fi sh downstream from the source of sediment
discharge. They (McLeay et al. 1984) continued to emphasize that
sustained SSC of 100 mg per liter may prove harmful to the long-term
well-being of grayling in natural streams and that short-term pulses of
SSC of 100 mg per liter, or turbidity on the order of 40 to 50 NTU
(Sigler 1981), may cause downstream migration of otherwise resident
fish.
It is apparent from this information, derived from outside of Alaska,
as well as information obtained in Alaska described earlier, that
introductions of even small amounts of sediment and turbidity in
freshwater habitats can adversely affect fish and other aquatic life
and that effects short of fish mortality may be a factor in reducing
the productive potential of fish resources.
STANDARDS AND CONCLUSIONS REGARDING WATER QUALITY
The use of turbidity as a water quality criterion and standard has been
criticized, principal ly because of a 1 ack of readily avai 1 able
information on the impacts associated with elevated turbidities in
natural waters. A more provincial argument against the use of
turbidity is that there have been no studies conducted in Alaska to
demonstrate effects. This report, however, contains A1 aska
i 1 lustrations of the effects of turbidity on clear freshwater habitats,
and the relationship between turbidity and suspended sediment
concentration. We a1 so report effects of turbidity and suspended
sediment documented from studies conducted outside of Alaska.
The State Water Qua1 ity Standards for Alaska (18 AAC 70) impose 1 imits
to a1 lowable human-induced a1 terations of natural waters. These 1 imits
are specified for various water quality parameters with respect to the
designated use or classification of a particular body of water. Most
of Alaska's freshwaters have been classified as suitable for drinking
and other consumptive uses. The turbidity standard for drinking water
is:
Shall not exceed 5 NTU above natural conditions when the natural
turbidity is 50 NTU or less, and not have more than 10% increase
in turbidity when the natural condition is more than 50 NTU, not
to exceed a maximum increase of 25 NTU. [18 AAC
70.02o(b)(l)(A)(i>(4)1
Although there are few, if any, waters in Alaska designated only for
use by fish and wildlife, because of their already more restrictive
classification for human consumption, the State Water Quality Standards
do contain a separate standard for waters classified for the growth and
propagation of fish, shellfish, other aquatic life, and wildlife
including waterfowl and furbearers:
Shall not exceed 25 NTU above natural condition level. For all
lake waters, shall not exceed 5 NTU over natural conditions.
r18 AAC 70.020(b)f l)(c)(4)]
For simp1 ici ty in considering a1 lowable increases of turbidity in
clear-water systems, we can restate the above standards:
Drinking water: no more than 5 NTU above natural
Fish and wild1 ife: no more than 25 NTU above natural - streams
no more than 5 NTU above natural - lakes
Alaska does not have a numerical standard for suspended sediment
concentration or for settleable solids in drinking waters, but the
state does have a generic narrative standard for sediment. The
sediment standard for drinking water is:
No measurable increase in concentrations of sediment above natural
levels. [la AAC 70.020(b) (l)(A)(i)(7)]
The sediment standard for the propagation of fish and wildlife .is much
more complex. That part of the standard dealing with settleable solids
is difficult to enforce, and that part addressing suspended sediment is
difficult to define:
The percent accumulation of fine sediment in the range of 0.1 mn
to 4.0 mn in the gravel bed of waters utilized by anadromous or
resident fish for spawning may not be increased more than 5% by
weight over natural condition (as shown from grain size
accumulation graph). In no case may the 0.1 mn to 4.0 mm fine
sediment range in the gravel bed of waters utilized by anadromous
or resident fish for spawning exceed a maximum of 30% by weight
(as shown from grain size accumulation graph). (See note 3 and
4). In a1 1 other surface waters no sediment loads (suspended or
deposited) which can cause adverse effects on aquatic animal or
plant 1 ife, their reproduction or habitat.
r18 AAC 70.020(b) (1) (c) (7)]
How could this sediment standard be improved? By definition, turbidity
and suspended sediment concentration are closely intertwined. While
there have not been extensive investigations of the lethal and
sublethal effects of suspended sediments on fish in Alaska to determine
acceptable levels of SSC, or the development of precise regression
equations of SSC versus turbidity for each drainage of concern,
information summarized in this report indicates that a statewide
turbidity standard can be used to address the effects of turbidity as
an optical property of water and also as an indicator of suspended
sediment concentration. The effects of sedimentation onto lake and
stream bottoms could then be addressed by a separate, enforceable
settleable sol ids standard.
Whether or not such changes are made to the sediment standard, there is
still a need to establish or reaffirm those levels of turbidity, and
consequently SSC, which are appropriate as standards for regulating
human activity. What, then, are acceptable level s of human-induced
turbidity in freshwater aquatic habitats that support fish and
wi 1 dl i fe?
Light Penetration and Productivity
To protect aquatic habitats, an acceptable turbidity standard must:
1) prevent a loss of aquatic productivity and 2) cause no lethal or
chronic, sublethal effects to fish and wildlife. The studies
summarized in this report indicate that even small increases in
turbidity may dramatical ly reduce primary plant production in lakes and
streams, which apparently translates to a reduced production and
abundance of fish. With reference to the current standard for the
propogation of fish and wildlife, a 5 NTU increase of turbidity in a
clear-water lake can reduce the productive volume of that lake by
approximately 75 percent; a 25 NTU increase in a clear-water stream
only 1.5 ,feet deep may reduce primary plant production by approximately
50 percent. Alaska's standard for protection of fish and wildlife is
above the 10 JTU criteria previously recomnended by the Federal Water
Pol lution Control Administration (FWPCA 1968). A comparison of
turbidity standards used in Alaska and other western and northern
states (Table 9) indicates that Alaska currently a1 lows liberal
increases over natural conditions.
The current drinking water standard of 5 NTU over ambient levels in
shallow clear-water lakes and streams may also induce a reduction of
primary plant production, however not to the extent the 25 NTU over
ambient standard would induce in streams. For comparison, a 5 NTU
increase of turbidity in a clear-water stream may reduce primary
production by 3 to 13 percent or more, depending on stream depth.
Additional arguments can be applied to a 5 NTU standard: that absolute
turbidities of 4-8 NTU and above preclude the efficient management of
fisheries in Alaska because aerial observers cannot see into the
streams and estimate returns of adult salmon, and that absolute
turbidities of 8 NTU and greater have been shown to reduce sportfishing
activity in fish-beari ng waters in A1 aska. The current Interagency
Placer Mining Guidelines (State of Alaska 1984) use turbidity of 3 NTU
or less as a criterion for establishing "high priority" streams.
Application of a 5 NTU above ambient standard would bring total
turbidities in these streams to 8 NTU, the level at which recreational
fishing may decline and at or above the level at which efficiency of
aerial surveys is affected.
So, in light of the information produced by recent studies in Alaska
and elsewhere, it appears that the turbidity standard for the
propagation of fish and wildlife should be more restrictive, perhaps at
the level currently used for drinking water, if aquatic productivity is
to be maintained.
TABLE 9. NUMERICAL TURBIDITY STANDARDS FOR PROTECTION OF
FISH AND WILDLIFE IN AMKA AND OTHER WESTERN
AND NORMERN STATES (ADEC, 1978; API , 1980)
*
TURB l D l TY
STATE (NTU or JTU)
A1 aska
California
25 above natural in streams
5 above natural in lakes
20% above natural,
not to exceed 10
above natural
l daho 5 above natural
Minnesota 10
Montana
Oregon
+
10 (5 above natural)
10% above natural
Vermont 10 (col d-water )
Washington
Wymi ng
25 above natural ++
(5 6 10 above natural
10 above natural
*
NTU and JTU are roughly equivalent.
+
Montana places the more stringent limit on waters containing salmonid
f i shes.
++
API (1980) reports different values in Washington, for excellent and good
classes of water.
Suspended Sediment
Regarding appropriate limitations to suspended sediment concentrations,
there is evidence (non-Alaskan) that high concentrations prove lethal
to fish, and additional information that lower levels of SSC and
turbidity cause chronic, sublethal effects such as loss of
sight-feeding capabilities, reduced growth, increased stress,
interference with environmental cues necessary for orientation in fish
migrations, transport of heavy metals and other pol lutants, and other
potentially adverse effects to the quality of aquatic habitats.
Several organizations have made recomnendations for appropriate
suspended sediment concentrations in fish-bearing waters. Using our
statewide equation (Equation 8) relating turbidity to suspended
sediment concentration, we can trans1 ate these recommendations into
approximate turbidity criteria (Tab1 e 10).
Recomnendations for a "moderate" level of protection (up to 100 mg per
liter) translate into turbidity values up to 2.3 NTU. This is very
close to the current Alaska standard of 25 NTU above natural conditions
for protection of fish and wildlife.
Recomnendations for a "high" level of protection (0-25 mg per liter)
translate into turbidity values ranging from 0 to 7 NTU, closely
approximating Alaska's drinking water standard of 5 NTU above natural
conditions. Application of the present drinking water standard, 5 NTU
above natural conditions, to waters statewide would conform to a
consensus view of a "high" level of protection 'from suspended
sediments.
Using our equation for interior Alaska streams (Equation ll),
"moderate" and "high" levels of protection from suspended sediment
translate into higher turbidities (95 and 25 NTU, respectively) (see
Table lo), but these turbidities would not offer protection from light
extinction and reduced production of plants, fish food, and fish as
discussed earl ier.
Concl us ion
The conclusion of this report is that turbidity is a reasonable water
quality standard for use on a statewide basis. Although turbidity is
not a direct measure of either light penetration (Phinney 1959, Austin
1974) or of suspended sediment concentration (Pickering 19761, it is
shown to be a very useful indicator of these characteristics (Gibbs
1974, Ritter and Ott 1974). Use of a turbidity standard in the
regulation of water quality is justified much in the same way that
TABLE 10. RECOMMENDED LEVELS OF SUSPENDED SEDIMENT
CONCENTRATION FOR THE PROTECTION OF FISH
HABITAT AND TRANSLATION TO TURBIDITY VALUES
f*
* TRANSLATED
CITED CITED TRANSLATED MAX l MUM
LEVEL OF RECOMMENDED MAX I NH TURB l D l TY
PROTECTION SUSPENDED TURB l D l TY LEVEL
FROM SEDIMENT LEVEL l NTER l OR
SUSPENDED CONCENTRATION (mg/l) STATE-WIDE ALASKA
CITATION SED I MENT LIMITATION (NN) (NfU)
EIFAC, 1964; High 0 - 25
A1 abaster, 1972 Moderate 26 - 80
High 0 - 25
Moderate 26 - 80
Alabaster and High 0 - 25
Lloyd, 1980 Moderate 26 - 80
Newport and
Moyer, 1974
Hf gh 0 - 25 7
Moderate 26 - 100 23
Wilber, 1969; 1983 High 0 - 30
Moderate 30 - 85
Hill, 1974 High 0 - 10 3 10
DFO, 1983 High 0
Moderate 1 - 100
*
Derived from a state-wide equatfon for Alaska streams developed in this report from
U.S. Geological Survey water analyses May - October, 1976 - 1983 (see Equation 8):
T = 0.44(SSC) 0.858
where
T = Turbidity (NTU)
SSC = Suspended sediment concentration (rng/liter)
f*
Derived from an equation for interior Alaska streams developed in this report from data
compf led by Post (1984) and Toland (19841, for sumner 1983-1984 (see Equation 11 ):
Equatfon 13, from RLM Consultants (1982a), was not used due to concerns outlined in the
text, and because the equation describes a set of data which includes only four values
of SSC equal to or less than 100 mg per liter and none less than 25 rng per liter.
fecal coliform bacteria are widely used as a water quality standard
indicating the presence and concentration of other harmful bacteria
! LaPerriere 1983).
Increased turbidity accounts for demonstrable decreases in aquatic
productivity, in the presence and abundance of fish, in the human use
of fish-bearing waters, and in the efficiency of certain fishery
management techniques. Turbidity is also directly related to
concentrations of suspended sediments, which can cause demonstrable
lethal and sublethal impacts to fish. Based upon current information,
continued appl ication of the present State Water Qua1 i ty Standard for
the propagation of fish and wildlife (25 NTU above natural conditions
in streams, 5 NTU in 1 akes) can be expected to provide a moderate level
of protection to clear-water aquatic habitats. A higher level of
protection would require a more restrictive standard, similar to the
one currently applied to drinking water (5 NTU above natural conditions
in streams and lakes).
LIMITATIONS, FURTHER STUDY, AND ALTERNATIVE STANDARDS
The information presented in this report justifies a general statewide
water qua1 ity standard based on turbidity. Such a statewide turbidity
standard can be established from consistent physical relationships,
derived from studies on lakes and streams in Alaska and elsewhere,
between turbidity and light penetration, and resulting effects on
aquatic primary productivity. Furthermore, a statewide turbidity
standard can be established based upon observed effects of turbidity
on, or associations with, secondary production, distribution and
abundance of fish, recreational use of streams, and fishery management
practices. Also, a statewide turbidity standard can be used to provide
protection from direct effects of suspended sediment on aquatic life
including fish.
However, it may be desirable at some point, if sufficient data allow,
to further justify or modify statewide turbidity standards. In order
to take a more detailed look at the effect of turbidity on freshwater
habitats in Alaska we need to identify the limitations of existing
information and develop plans for further study. On another tack, it
may be desirable in the future to create alternative standards to
turbidity, perhaps based more directly on measures of 1 ight extinction
and sediment loading.
Limitations to Existing Information
It is apparent that even though current information from Alaska and
elsewhere supports the need for regulating land use with fairly strict
turbidity standards, there is detailed information for only a small
sample of aquatic habitats in the state. With regard to primary
production, assumptions made about the importance of primary production
in interior Alaska streams may not be completely applicable to heavily
forested watersheds in southeast Alaska, which likely rely more upon
organic material derived from terrestrial sources (see Chapman and
Demory 1963, Chapman 1966). In addition, there has been little work
performed to identify the capacity of compensatory mechanisms to
increase photosynthetic efficiency under low-light or turbid conditions
(see ,Van Nieuwenhuyse 1983, Anderson 1984\, the effect of organic
staining of water on turbidity and suspended sediment concentration, or
the influence of increased or depressed nutrient concentrations caused
by the same sediments that decrease light availability (see Tilzer et
a1 . 1976, Jackson and Hecky 1980).
Regarding any relationship between turbidity and sediment loading, the
current information is understandably tentative. First, it is we1 1
recognized that the amount of turbidity produced per unit of suspended
sediment concentration depends upon sediment particle size, shape or
angularity, and refractive index, and that re1 ationships wi 11 change,
based upon hydrologic or hydraul ic conditions such as increasing flows
versus decreasing flows (rising limb versus falling limb of the
hydrograph), spring versus fall seasonal flows, and interactions with
sediment reservoirs in the streambed, as well as the geologic
composition of the sediment source (see Duchrow and Everhart 1971,
Beschta 1980, Mi 1 hous 1982).
Second, as i 1 lustrated in a recent study on placer-mined streams by the
A1 as ka Department of Envi ronmental Conservation (To1 and 1984) , the
relationship between turbidity and SSC can change along a downstream
gradient from a sediment (discharge) source. Specifically , To1 and
(1984) found that within the first fifteen miles downstream from placer
mine discharges on the Chatanika River each mg per liter of SSC
produced less than one NTU of turbidity but that below fifteen miles
each mg per liter of SSC produced more than one NTU of turbidity
(within the range of 10-150 units for each of MTU and mg/l iter). This
fo1 lows the intuitive notion that larger particles, which generally
produce less turbidity per unit concentration than smaller particles,
will gradually settle out, thus shifting the turbidity versus SSC
relationship to a higher NTU per unit SSC at distances downstream.
Third, an instantaneous, or even continuous, measurement of turbidity
may contain suspended sediment and some settleable solids, depending on
the amount of settling that takes place before the sample is taken (see
Duchrow and Everhart 1971). Moreover, it is often difficult to
distinguish adverse impacts to aquatic habitats caused by suspended as
opposed to settleable material. This confusion is illustrated by our
citation of Langer (1980) who reported reduced survival of chum salmon
eggs, presumably caused by sediment material deposited onto the eggs,
with increased concentrations of suspended sediment measured in mg per
liter. However, as we mentioned earlier, Cooper f1965) describes a
mechanism whereby suspended sediment may be incorporated into the
streambed, not only through settl ing but through filtration during
intragravel flow.
Fourth, depending on geomorphic, hydrologic, and hydraulic factors,
different streams are able to accommodate different levels of sediment
input and may natural ly support different biotic communities. A1 so,
different species and even different life stages within species are
susceptible to adverse effects from varying levels of sediment and to
sediments of different sizes. In this paper we have reported that
cold-water salmonids are generally more susceptible to acute and
chronic effects of sediment than many species of warm-water
non-salmonid fishes. However, even among salmonids some species may be
more sensitive than others, and the eggs and juvenile stages of these
species are apparently much more sensitive than adults.
Topics for Further Study
To address the limitations outlined above, topics warranting study
include the relationships of specific levels of turbidity and sediment
loading with the following factors in the various types of aquatic
habitats in Alaska:
Light Penetration
Primary Productivity
Compensatory Mechanisms in Photosynthetic Efficiency
Aquatic Plant Species Composition
Abundance and Species Composition of Benthic
Invertebrates
Abundance and Species Composition of Fish
Other topics for study may include the dependence of particular aquatic
habitats on aquatic versus terrestrial sources of production, the
threshold level of adverse effects of turbidity and sediment on benthic
invertebrates, similar thresholds for fish in their various life
stages, as well as the association of toxic concentrations of trace
metals with levels of turbidity.
Regarding the use of turbidity to estimate suspended sediment
concentration, it may be necessary to establish detailed relationships
for specific drainage types, account for variability caused by temporal
factors such as fluctuating flows and erosion rates, and consider the
change in those relationships downstream from a point source of
sediment. Recently, data have been collected in selected drainages
near Fairbanks that may a1 low the development of these detailed types
of relationships (see EPA 1984, KRE 1984, Post 1984, Toland 1984). A
particular gap in data available from Alaska and elsewhere is the
extent downstream from a source of sediment, such as a placer mine,
that the various impacts exist, what mechanisms act to modify these
effects, and how long it takes a system to recover.
In view of the potential to develop alternative standards, an important
topic for consideration and study should be possible tiering or grading
of turbidity standards dependent upon ambient water qua1 i ty conditions
and the level of protection desired for a particular body of water. A
grading approach could allow a certain percentage increase in turbidity
above ambient levels rather than an absolute increase; a tiered
approach could a1 low different increases for different ranges of
ambient turbidity. These approaches must recognize, however, the
effects of turbidity on 1 ight penetration particularly at low ambient
levels of turbidity and the direct effects of suspended sediment
concentration at higher ambient levels of turbidity.
Suggestions for Possible Alternative Standards
Several authors have suggested the need for standards other than simple
turbidity levels to control pol lution from sediments. Wilson f 1957)
proposed that turbidity standards be based on a percentage increase
above normal 1 ow-fl ow conditions. Tarzwe11 (1957) recomnended that
turbidity standards be altered to state that some percentage of
incident light at the surface be allowed to reach a specified depth,
standardized to a time between 11:OO a.m. and 1:00 p.m. The National
Academy of Sciences (NAS 1973) recomnended that the depth of light
penetration not be decreased by more than 10 percent, and that
suspended sediment concentrations be limited to specific values, as
outlined for the NAS in Table 10.
Cairns (1968) recognized the value of more flexible approaches but
suggested that truly responsive regulations should be developed on a
drainage-by-drainage basis and should change with streamflow and other
temporal characteristics. A significant problem with this approach,
however, is that implementation and enforcement of such standards would
require an enormous base1 ine study and almost continuous surveil lance
and monitoring. There is a question as to whether such an approach is
feasible in Alaska.
The U.S. Environmental Protection Agency (EPA 1976) recommended a joint
standard for turbidity and solids:
Freshwater fish and other aquatic 1 ife: Settleable and suspended
solids should not reduce the depth of the compensation point for
photosynthetic activity by more than 10 percent from the
seasonal ly establ i shed norm for aquatic 1 ife.
This standard suffers from several deficiencies. First, the standard
does not address any impacts associated with sediment deposited on the
bottom, even though it mentions settleable solids. Second, in relation
to the water column, the standard does not address specific levels of
suspended sediment concentration and places a severe burden on
regulatory agencies to define a "seasonally established norm" for the
compensation point. Final ly, as emphasized by the American Fisheries
Society (AFS)(Thurston et al. 1979), compensation point is of little
value in streams, particularly where the water is so clear and shallow
that light naturally penetrates all the way to the bottom. The AFS
[Thurston et a1 . 1979) recommends that separate sol ids standards
(mg/l i ter) and turbidity standards (NTU) be developed, designed to
facilitate ease of measurement.
Any alternative standards to turbidity should account for both major
aspects of turbidity :. 1 ight extinction and suspended sediment
concentration. Di rect measurement of both of these parameters is
possible and may be conducted in a feasible manner, however it should
be recognized that the measure of turbidity was developed to make such
measurements easier. Light penetration can be measured with portable
photometers and extinction coefficients calculated with simple graphs
or equations; sediment concentration can be sampled in the field and
measured gravimetrically in a laboratory.
The development of any a1 ternative standards will require considerable
research and justification. It is premature to judge in this paper
whether such alternatives will or will not provide more effective
regulatory tools than the current turbidity standards can offer us
today, particularly if we consider that turbidity standards can be
tiered or graded, if necessary, to ambient water quality conditions and
the level of protection desired for a body of water.
GLOSSARY
Chlorophyll - green pigment that facil i tates photosynthesis in
plants. Measurement of chl orophyll concentration is used as an
indication of abundance and production of plant material in water.
Compensation depth - the depth within a body of water at which light
intensity is just sufficient to promote photosynthesis equal to
respiratory , or metabol ic, requirements of phytoplankton
populations. Usually considered the depth to which one percent of
available surface light penetrates into a body of water. Net
production of plant material occurs above this depth.
Euphotic volume - the volume of water above the compensation depth.
Equal s surface area mu1 ti pl ied by compensation depth.
FTU - formazin turbidity unit. Roughly equivalent to NTU. -
JTU - Jackson turbidity unit. Roughly equivalent to NTU. -
LCSO - the concentration of a material that proves lethal to fifty - percent of a sample of organisms being tested. Usually modified
by a specified length of time, such as a 96-hour LCSO.
Macroinvertebrates - those invertebrate animals (without backbones)
that are not microscopic. In streams, usually consist of aquatic
insects on the stream bottom.
Macrophytes - large plants, often rooted in sediment, that grow from
the bottom of a body of water.
Mixing zone - a zone of mixing or dilution within a body of water,
adjacent to a wastewater discharge, within which receiving water
may exceed water quality standards.
mg per liter - milligrams per 1 iter. Used to describe a
weight-to-volume concentration of a solid material in a fluid.
Nephelometer - an instrument that transmits a beam of light through a
sample of water and records the amount of that light scattered by
that sample to an anale of approximately 90" from the original
light path.
NTU - nephelometric turbidity unit. A unit of light scattering in a -
sample of water measured by a nephelometer, standardized against
the scattering of light caused by a suspension of formazin in
water.
Periphyton - small, often single-celled, plants that are attached to
rocks and other substrates on the bottom of a body of water.
Phytoplankton - small, often single-celled, plants that are suspended
in a body of water.
ppm - parts per million. Used to describe a weight-to-weight
concentration of one material in another. Roughly equivalent to
mg per 1 iter when considering concentration of a so1 id in water.
Primary production - the amount of tissue or energy assimilated
through photosynthesis by plants.
Reactive distance - the distance between a fish and its prey within
which a positive feeding response occurs.
Secondary production - the amount of tissue or energy assimilated by
consumers of plants. Usage in this paper generally refers to
production of zooplankton (small floating animals) and
macroi nvertebrates (aquatic insects).
Settleable solids - solid material in water that settles to the
bottom. Usually standardized to the volume of solid material
within a one-1 iter sample of water that settles to the bottom of
an Imhoff Cone within one hour.
SSC - abbreviation for suspended sediment concentration. Usually -
expressed in units of milligrams of sediment per liter of water
(mg per 1 iter, mg/l iter), sometimes expressed as parts per mil 1 ion
( PP~>
Stained - refers to color imparted to water, usually by natural
organic (dissolved) material.
Suspended sediment - solid material in water that remains suspended,
does not settle, often times due to low specific gravity and/or
water turbulence. Usually measured as total nonfi 1 crab1 e residue,
meaning material that will not pass through a standard-sized
filter. Generally does not include dissolved material.
Turbidity - an optical property of water wherein light is scattered
or absorbed rather than transmitted in a straight line. Caused by
suspended material such as clay, silt, finely divided organic and
inorganic matter, plankton , and other microscopic organisms. In
comnon usage, refers to a muddy condition of water. Historically
expressed as ppm, but more recently reported in FTU, JTU or NTU.
Zooplankton - small animals, such as copepods and Cladocerans, that
are suspended in a body of water.
LITERATURE CITED
ADEC. 1978. Nationwide 1 isting of parameters: turbidity, total
dissolved sol ids, settleable sol ids, and suspended sol ids for
water suitable for fishing, wild1 ife and recreation. List
compiled by Alaska Department of Environmental Conservation,
provided by A. Viteri (ADEC) to D. Lloyd (ADF&G) on Jan. 30, 1984.
. 1979. Placer mining and water quality. Alaska Department
of Environmental Conservation, A1 aska Water Qual i ty Management
Planning Program, Non-point Source Study Series, Juneau, 100 pp. +
appendices.
ADF&G. 1983a. Susitna Hydro Aquatic Studies Phase I1 report:
synopsis of the 1982 aquatic studies and analysis of fish and
habitat relationships. Alaska Department of Fish and Game,
Susitna Hydro Aquatic Studies, Anchorage, 152 pp. + appendices.
. 1983b. Susitna Hydro Aquatic Studies Phase 11 basic data
report, Volume 5: upper Susi tna River impoundment studies 1982.
Alaska Department of Fish and Game, Susitna Hydro Aquatic Studies,
Anchorage, 150 pp. + appendices.
Alabaster, J.S. 1972. Suspended solids and fisheries. Proc. Royal
Soc., London, Series B , 180: 395-406.
Alabaster, J.S. and R. Lloyd. 1980. Finely divided solids. In:
Water Qual ity Criteria for Freshwater Fish. Butterworths (for
FAO, U.N. ) , London, p. 1-20.
Anderson, P.R. 1984. Seasonal changes of attached algae in two
Alaskan subarctic streams. M.S. thesis, Univ. of Alaska,
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