EPA-600/3-77-097
August 1977
Ecological Research Series
IMPACT OF NEARSTREAM VEGETATION AND
STREAM MORPHOLOGY ON WATER
QUALITY AND STREAM BIOTA
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30805
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-77-097
August 1977
IMPACT OF NEARSTREAM VEGETATION AND STREAM
MORPHOLOGY ON WATER QUALITY AND STREAM BIOTA
by
James R. Karr and Isaac J. Schlosser
Department of Ecology, Ethology and Evolution
University of Illinois
Champaign, Illinois 61820
Contract No. 68-01-3584
Project Officer
George W. Bailey
Associate Director for Rural Lands Research
Environmental Research Laboratory
Athens, Georgia 30605
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30605
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory,
EPA, Athens, Georgia, and approved for publication. Approval does not
signify that the contents necessarily reflect the views and policies of the
Environmental Protection Agency, nor does mention of trade names or commer-
cial products constitute endorsement or recommendation for use.
ii
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FOREWORD
As environmental controls become more costly to implement and the penal-
ties of judgment errors become more severe, environmental quality management
requires more efficient analytical tools based on greater knowledge of the
environmental phenomena to be managed. The development of management or
engineering tools to help pollution control officials achieve water quality
goals through watershed management is an integral part of this Laboratory's
research on the occurrence, movement, transformation, impact, and control of
environmental contaminants.
Water quality in streams receiving pollution from nonpoint sources is of
great concern to EPA. Through the literature review presented in this report,
gaps in scientific knowledge of the ways in which nearstream vegetation and
stream morphology affect water quality and of the manner in which NPS pollu-
tion affects stream biota are identified. Particular stress is given to the
beneficial use of greenbelts, but important questions are raised concerning
their effectiveness in controlling NPS pollution from agricultural lands.
In addition, the review suggests research to be accomplished prior to the
adoption of rational management strategies to effectively control water pollu-
tion in streams receiving NPS pollutants, which should be of particular inter-
est to persons in a wide variety of disciplines.
David W. Duttweiler
Director
Environmental Research Laboratory
Athens, Georgia
111
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PREFACE
We have attempted a synthesis of research from several fields to evalu-
ate the effects of nearstream vegetation and channel morphology on water
quality and stream biota in agricultural watersheds. An inevitable result of
such a synthesis is inadequate coverage of the literature from each field. We
acknowledge this deficiency and solicit comments on weaknesses in our cover-
age. However, we are less concerned about further references supporting our
suggestions than about references which add new perspectives or disagree with
our conclusions. Since our goals are wise use of biological, soil, and water:
resources, we hope readers will bring relevant studies to our attention. (A
glossary is included (p. 85-90) for readers unfamiliar with the terminology
of all fields discussed in this report.)
From our perspective a major problem in the effort to control non-point
sediment pollution is the common philosophy that it is an agricultural pro-
blem. This is an error on two counts. First, not all sediment pollution
derives from agricultural, activities and second, fields other than agricul-
ture, including agricultural engineering, have expertise which should be
brought to bear on sediment pollution problems. The two problems are only
indirectly related. The long-term objective of improved water quality can
best be served with multi-disciplinary efforts which transcend the classical
disciplines, such as agriculture, engineering, and ecology. We are particu-
larly concerned that more thought be given early in the planning phase of pro-
jects to the long-term ecological consequences of management alternatives.
Water quality degradation can be reversed if the past emphasis on control of
soil erosion is supplemented with a broader approach to water quality pro-
blems.
An early draft of this paper was read by a number of scientists from
many backgrounds. The most intriguing comments came from a biologist and
from an agriculturist. One suggested that we attempted to generalize too
broadly; that is, since most of our examples come from midwestern situations
we should, perhaps, explicitly state that our conclusions might apply only to
that region. Another individual commented that the general principles might
apply to some regions but they probably could not be used in the high inten-
sity agriculture of central Illinois. These comments illustrate the problems
which result from differing perspectives. In addition, they are related to
the problems involved in defining areas of applicability. For example, do
our discussions pertain to highly modified agricultural drains, to natural
stream channels, to drains and channels of specific sizes, or to all of
these? We feel they apply primarily to headwater streams in most watersheds,
but as we hope to demonstrate in this review, definitive answers to these
questions are not available. That is an alarming statement after decades of
research effort. Rigorous scientific investigations addressing the problems
posed in this report are long overdue.
iv
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ABSTRACT
Like all functional parts of landscape units, streams have dynamic
equilibria in nutrient and sediment loads and biota. As man modifies water-
sheds by removal of natural vegetation and stream channelization, disequili-
bria in both the terrestrial and aquatic environments result. These dis-
equilibria are the major problem in controlling sediments and nutrients from
non-point sources and improving the quality of the stream biota. Unfortu-
nately, most attempts to control non-point pollutants in agricultural water-
sheds emphasize reestablishing the terrestrial equilibrium via tillage prac-
tices such as minimum tillage, winter crop cover, and terraces. These
efforts, which depend on erosion control as measured by the Universal Soil
Loss Equation, utilize technologies for preserving soil productivity. This
approach must be replaced by one in which improvement in water quality and
quality of the stream biota is a primary objective. This requires erosion
control on the general landscape plus an increased understanding of the link
between terrestrial and aquatic systems and the effect of stream morphology
on the dynamics of sediment transport and quality of the stream biota.
In this report we review the literature dealing with (1) the possible
use of near stream vegetation to reduce the transport of sediment and nutri-
ents from the terrestrial to the aquatic environment and decrease stream
temperature fluctuations, (2) the effect of stream morphology on sediment
transport, and (3) how near stream vegetation and stream morphology affect
the biota of streams. The results of this review suggest proper management
of near-stream vegetation and channel morphology can lead to significant
improvements in both the water and biological quality of many streams. How-
ever, critical research outlined in this report is still necessary if we are
to properly use this management alternative to attain the objectives of the
Federal Water Pollution Control Act of 1972 (Public Law 92-500).
This report was submitted in fulfillment of Contract No. 68-01-3584 by
the University of Illinois, Champaign, IL, under the sponsorship of the U.S.
Environmental Protection Agency. This report covers a period from January
1976 to July 1977, and work was completed as of July 1977.
v
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CONTENTS
Foreword ........... . ................. ±±±
Preface . . ...... , ............ „ ..... „ . iv
Abstract ....... . ........... „ ......... v
Figures ........................ ..... viii
Tables ......................... . , . . x
Acknowledgments .......... . ........... ... xi
1. Introduction ...................... 1
2. Conclusions ...................... 3
3. Recommendations .................... 7
Specific research problems ... ......... 7
Large scale research ............... 10
What type of research approach is best? ...... 11
4. Vegetation As a Nutrient Filter . . .......... 12
5. Vegetation As a Sediment Filter ....... ..... 16
Overland flow . . ................. 17
Channel flow ................... 20
6. Effect of Channel Morphology On Water Quality ..... 30
7. Determinants of Sediment Loads in Flowing Waters .... 40
8. Effect of Streamside Vegetation on Water Temperature . . 44
9. Impact of Nearstream Vegetation and Channel
Morphology on Stream Biota ............... 49
Effects of sediment ................ 49
Fish ...................... 49
Invertebrates ................. 50
Stream Productivity .............. 52
Summary .................... 53
Effects of temperature .............. 54
Effects on stream energetics ........... 56
Effects of stream channelization ......... 57
Conclusions .................... 63
10. Recreational Benefits of Greenbelts .......... 65
11. Other Advantages of Greenbelts .......... ... 66
12. Discussion and Conclusions ............... 67
References ............................ 73
Glossary ............................. 85
Vll
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FIGURES
Number Page
1 Relationship between slope of a vegetative (sediment) filter
and effective filter width . 18
2 Effect of land use on discharge rates on two watersheds .... 20
3 Silt volume as percent of basin capacity for Lake McMillan
near Carlsbad, New Mexico 21
4 Water velocity through vegetation as a function of depth .... 22
5 Relationship between depth of flow and amount of retardance
with bermudagrass 22
6 Hypothesized relationship between filter width and percent
of sediment remaining for several vegetation types 25
7 Hypothesized relationship between distance solution is
filtered and percent of sediment remaining for several slopes . 26
8 Relationship between water surface slope and total sediment
discharge ..... 31
9 Relationship between velocity and total.sediment discharge ... 32
10 Relation between effective unit stream power and measured
suspended sediment concentration 33
11 Bed and water surface profiles for several flow conditions in
the Middle Fork of the Vermillion River 37
12 Changing suspended solids loads in agricultural and forested
sections of a headwater stream 38
13 Variation in suspended sediment load for a given unit stream
power 43
14 Seasonal changes in stream temperatures in streams from
forested and farm watersheds 45
Vlll
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Number Page
15 Hypothetical relationship between angular canopy density
and thermal input to a stream 46
16 Relationship between stream size and effectiveness of buffer
strip in reducing thermal inputs to a stream 46
17 Effect of temperature on the release of phosphorus from
sediments during a 12-week period 48
18 Regression of fish species diversity on substrate diversity . . 51
19 Species diversity vs. substrate diversity for molluscs
collected at 650 sampling stations in New York 52
20 Flow chart illustrating the basic pathways of energy flow
in organisms - 54
21 Theoretical effect of temperature change on food consumption
and energy budget of two hypothetical fish species 55
22 Percent of species lost versus temperature in warm and cold
water streams 57
23 Major components of a headwater stream foodweb 58
24 Factor train analysis of the effects of channelization on
the physical environment and biota of streams 59
25 Estimated total standing crop of fish in channelized and
unchannelized sections of the Chariton River, Missouri ... 61
26 Estimated standing crop of catchable-size fish in channelized 61
and unchannelized sections of the Chariton River, Missouri. .
27 Regressions between sinuosity index and several physical and
biological properties of streams 62
28 Eegression of fish species diversity on habitat diversity ... 63
29 Range on three environmental gradients under which
hypothesized generalist (a) and specialist (b) could exist. . 64
30 General model of the primary factors governing the quality and
quantity of outflow water from an ecosystem 68
IX
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TABLES
Number Page
1 Percent of nitrogen and phosphorus attached to sediment in
surface runoff ............ ... 15
2 Effect of a bluegrass sod strip on sediment concentration
in runoff 19
3 Percent removal of sediment after varying lengths of
filtration through bermudagrass ......... 24
4 Percent of sand, silt, and clay in sediment deposited after
filtration through coastal Bermudagrass 25
5 Land uses immediately adjacent to modified streams and drainage
ditches in the Black Creek watershed .... ..... 28
6 Roughness coefficients (n) for various stream conditions • 35
7 Unit stream power for three flow conditions 36
8 Relationship between temperature and maximum dissolved oxygen
concentration in water 47
9 Effects of particle size of substrate on egg survival in
sockeye salmon 51
10 Energy budgets for Red Cedar River before and during periods
of heavy siltation, summer, 1961 53
11 Effect of varying "management practices" on equilibria of
equivalent watersheds . 70
12 Costs and benefits of more effective management of nearstream
vegetation and channel morphology 72
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ACKNOWLEDGMENTS
Any attempt to integrate information from a variety of fields depends on
cooperation and help from many individuals. Many persons and agencies (too
many to list individually) have responded to our inquiries and provided us
with valuable reference material.
The Institute for Environmental Studies and Water Resources Center at
the University of Illinois at Urbana-Champaign have provided support in a
number of ways. The following persons have read and commented on earlier
drafts of this report: W. D. Seitz, Institute for Environmental Studies;
G. C. Sanderson, R. W. Larimore, P. W. Smith, Illinois Natural History Survey;
R. W. Bachman, Iowa State University; R. R. Schneider, University of
Wisconsin; N. G. Benson, National Stream Alteration Team; D. R. Dudley,
Allen County, Indiana, Soil and Water Conservation District; H. Kuder, Soil
Conservation Service; D. Toetz, USEPA; and 0. Gorman, Purdue University.
Errors remaining in the present draft are our responsibility. Stephanie
Heard, Barbara Jauhola, and Margaret LeGrande have provided valuable steno-
graphic services, and Marcia Clark assisted in finding many obscure refer-
ences. Preparation of this report was initiated as a subproject under con-
tract No. 68-01-3584 to Dr. W. D. Seitz, Associate Director, Institute for
Environmental Studies at the University of Illinois.
XI
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SECTION 1
INTRODUCTION
Sediments are largely non-point sources of pollution. Because of this
diffuse nature, erosion and sediment control methods are inherently more com-
plex than those used to control point sources of pollution and will probably
involve several control strategies acting synergistically. The Environmental
Protection Agency and the United States Department of Agriculture have sug-
gested several feasible methods of control which should be investigated
(Agricultural Research Service 1975, 1976, Becker and Mills 1972). These
methods can generally be divided into two broad classes: (1) those which
attempt to prevent erosion from occurring, i.e. minimum tillage, winter crop
cover, terraces and other soil conservation practices and (2) those which
attempt to prevent the sediment from entering streams once erosion has
occurred.
Early conservation efforts emphasized soil erosion prevention (1 above)
with little emphasis on maintenance of water quality. Incorporation of water
quality as another objective of conservation practices represents a major
shift in conservation policy. To meet the water quality standards set for
1983 by the federal government an even broader perspective will have to be
established, including more detailed understanding of (1) the link between
terrestrial ecosystems and water quality and (2) the dynamics of sediment and
nutrient transport within streams. This increasing breadth of perspective
requires a more demanding synthesis of several bodies of knowledge, including
hydraulic engineering, geology, the study of stream morphology and dynamics,
and terrestrial and aquatic ecology.
We do not suggest that past management efforts have been in vain. Rather
our main point is that continued efforts to stabilize the terrestrial environ-
ment (minimum tillage, rotational practices, etc.) must be supplemented
with improved management of in and near channel areas before significant
improvements in water quality and quality of the stream biota will occur.
Furthermore, there is a serious deficiency in our knowledge of the dynamics
of in and near channel characteristics. Hopefully, this report will stimu-
late research addressed to the solution of land-water resource problems.
In this report we evaluate (1) existing data regarding the ability of
vegetation to act as a nutrient and sediment filter, (2) the effects of
stream morphology on water quality, (3) the effects of streamside vegetation
on water temperature, and (4) the potential impact of greenbelts (a combina-
tion of nearstream vegetation and stream morphology) on stream biota and
their possible uses for other recreational activities. We then use this
information to judge the feasibility of using greenbelts for improving
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water quality and quality of the stream biota. Finally, we propose several
major questions which must be addressed before the social and economic bene-
fits of greenbelts can be fully evaluated.
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SECTION 2
CONCLUSIONS
1. Vegetation as a Nutrient Filter.
a. Past efforts to use vegetation to filter nutrients in solution from
surface runoff have yielded conflicting results. The reasons for
this variability are largely unknown due to poorly controlled experi-
ments. Important variables include type of vegetation, detention
time, volume of water treated, and soil type.
b. Conflicting data exists regarding the importance of subsurface in-
puts of phosphorus into streams. The magnitude of subsurface inputs
appears to be primarily related to the quality of the tile line and
the presence of surface intakes.
c. Nearly all of the phosphorus (greater than 85%) and most of the nitro-
gen (greater than 70%) in surface runoff is attached to sediment.
d. Nutrients are usually absorbed to the smaller-sized particles,
especially the clay fraction. Hence, removal of nutrients from sur-
face runoff by vegetation will be achieved primarily by removing the
sediments to which the nutrients are attached.
2. Vegetation as a.Sediment Filter.
a. Recent data from Black Creek watershed in Indiana indicates the major
fraction of sediment loss in an agricultural watershed is via surface
flow. Therefore, sediment inputs into streams can be controlled by
adequate treatment of surface runoff.
b. Data from field and laboratory studies in forestry and agriculture
indicate vegetation can effectively filter sediment from both sheet
and shallow channel flow. Sediment reduction is less likely during
channel flow exceeding the height of herbaceous vegetation. Several
variables appear to act in an interrelated manner to determine the
effectiveness of vegetation filters. These include filter length,
slope of the filter, vegetation characteristics, size distribution
of the incoming sediments, degree of submergence of the filter,
application rate of the water to be filtered, and initial concentra-
tion of the sediment.
c. The placement of a vegetative filter and the width or length of the
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filter required to remove a given fraction of the incoming sediment
and the duration of its effectiveness is dependent on the inter-
action of physical factors, biological factors, and the specifica-
tions of water quality, all of which are yet to be thoroughly evalu-
ated under normal agricultural conditions and quantitatively related
to each other in any predictive manner.
3. Effect of Channel Morphology on Water Quality.
a. The ability of a stream to transport sediment appears to be directly
related to its Unit Stream Power (USP) —the rate of energy expendi-
ture by a stream as it flows from a higher to a lower point. Math-
ematically USP is a function of water velocity and surface slope of
the water.
b. Unit stream power is useful in predicting sediment loads only when
available material equals or exceeds the amount that can be carried
in a channel.
c. A stream naturally decreases its USP and sediment transporting capa-
bility by making lateral (meandering) and vertical (pools and
riffles) adjustments.
d. USP is reduced by pools and riffles only at low and intermediate
flows. The effect of meanders on USP in conjunction with pools and
riffles at various flow rates does not appear to have been quantified.
e. Channelization destroys nearly all characteristics of "natural"
stream morphology, i.e. pools and riffles and meanders. As a result,
the USP of these streams is increased and their ability to transport
sediment and erode stream banks is enhanced.
f. Allowing streams to maintain their natural morphology or reinitiate
meandering may be a feasible management alternative for improving
water quality, especially during periods of low and intermediate
flows.
4. Effect of Nearstream Vegetation on Water Temperature and Water Quality.
a. Removal of vegetation from along headwater streams in agricultural
watersheds can result in water temperature increases of 6-9°C.
b. As water temperature increases, its capacity to hold oxygen decreases,
which exaggerates the impact of each additional unit of organic waste
added to the system.
c. Laboratory studies have demonstrated an exponential increase in the
rate at which nutrients attached to sediment are converted to readily
available forms as temperature increases. Slight increases in tem-
perature above 15°C produced substantial increases in the amount of
phosphorus released.
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d. Removal of nearstream vegetation along streams in agricultural water-
sheds results in blooms of nuisance algae and periphyton due to ele-
vated temperatures, rate of nutrient release from sediment, and light
availability.
e. An examination of temperatures in various streams with different
types of vegetation indicates that angular canopy density (a measure
of the shading capability of the vegetation) is the only character-
istic of the vegetation correlated with temperature control. Width
of the vegetation strip is not important.
f. Small streams in agricultural watersheds have the greatest temperature
problem but they are also the easiest to control with nearstream
vegetation, due to the inverse relationship between temperature
change and stream discharge for a given input of thermal radiation.
5. Effect of Nearstream Vegetation and Stream Morphology on Stream Biota.
a. Sediments reduce the structural complexity and productivity of
aquatic plant, invertebrate and vertebrate communities. Their detri-
mental effect results when they settle out of suspension, cover the
periphyton and essential spawning grounds of fish and decrease
bottom (substrate) diversity.
b. When vegetation is removed along streambanks and water temperature
' increases from 6-9°C, it may become energetically impossible for
species with lower temperature optimums to continue living in an area,
regardless of changes in sediment load, habitat structure or other
environmental conditions. A shift in community structure may occur
with resident species being replaced by less desirable species which
are more tolerant of the increased temperatures.
c. Headwater streams (stream orders 1, 2, and 3) are dependent on near-
stream vegetation as a major source of energy and are extremely
important as spawning and nursery grounds for many commercial and
sport species which spend their adult lives in rivers or large lakes.
Removal of nearstream vegetation in these areas results in signifi-
cant reductions in invertebrate and fish production because of the
loss of allochthonous (terrestrial) energy inputs.
d. Channelization results in a significant reduction in invertebrate
and vertebrate production due to the destruction of habitat complex-
ity. Recent research relating stream morphometry to habitat charac-
teristics of aquatic organisms indicates that maintaining stream
sinuosity and a diversity of depths, water velocities, and substrate
types will lead to substantial improvements in the quality of stream
biota in agricultural watersheds.
e. Because organisms are simultaneously adapted to a number of different
environmental gradients, any attempt to improve the quality of the
stream biota must utilize a broad-based, multi-purpose approach.
Future stream management practices must optimize for a number of
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environmental variables, including flow characteristics, water
temperature, oxygen concentration, habitat diversity, food avail-
ability and water quality, all of which interact to determine the
quality of the stream biota. Data in the literature suggest a
more realistic management of nearstream vegetation and stream
morphology can provide the basis for such an interactive approach
and lead to a more productive, diverse, and stable biotic community.
6. Feasibility of Greenbelts.
a. The conclusions listed above suggest that proper management of near-
stream vegetation and stream morphology may produce substantial
improvements in water quality and the stream biota of agricultural
watersheds. Vegetation may reduce sediment and attached nutrient
inputs to streams and temperature fluctuations. A more natural
stream morphology can reduce sediment loads and provide suitable
habitat for both fish and invertebrates.
Therefore, before major improvements in water quality and stream
biota can be realized, the present emphasis on erosion control on
the land surface must be combined with the management of nearstream
vegetation and stream morphology. This approach will require a sub-
stantial new research effort on a number of questions outlined in
the recommendations section of this report. These problems must be
dealt with at individual drainage and watershed levels before the
environmental and economic feasibility of this management strategy
can be fully evaluated.
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SECTION 3
RECOMMENDATIONS
We have divided our recommendations for future studies into two broad
categories: (1) research aimed at providing answers to specific questions
dealing with the possible use of nearstream vegetation and/or stream morphol-
ogy for improving water quality and the stream biota and (2) large-scale
research projects to be initiated at the single drainage or watershed level
to clarify the economic costs and benefits of the greenbelt management alter-
native. We also briefly comment on the benefits and costs of these two
research approaches with respect to solving water quality problems in the
non-point source area.
SPECIFIC RESEARCH PROBLEMS
1. Vegetation as a Nutrient Filter
a. Substantially more research needs to be done elucidating variables
important in determining the levels of nutrients in subsurface flows.
Emphasis should be placed on the effects of soil type, slope, drain-
age characteristics, and type and quality of tile line.
b. Four factors should be more rigidly controlled in attempts to deter-
mine the efficiency of vegetation for filtering nutrients from
surface runoff:
(1) Detention time: should be accurately quantified so that
filtering success can be more precisely related to this
variable.
(2) Vegetation effects: controls should be maintained to clarify
the relationship between type of vegetation and nutrient removal
with specific emphasis on the effects of (a) structure and phys-
iological capabilities of the plants and (b) single plant
species versus more complex plant communities.
(3) Volume of water treated: the relationship of volume of water
treated to efficiency of nutrient removal should be studied in
more detail.
(4) Soil type: soil type affects filter efficiency, with sandy loam
soils being more efficient than clay loam soils. More attention
should be directed to this variable, especially with respect to
its effect on shallow percolation into the soil versus rapid
overland flow of the solution.
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2. Vegetation as a Sediment Filter
Before nearstream vegetation can be efficiently utilized as a land manage-
ment alternative for improving water quality, the following problems must be
addressed:
a. The importance of runoff over streambanks as a sediment source ver-
sus runoff entering streams from intermittent tributaries and water-
ways needs to be established. How does the contribution from the two
sources change with stream size (stream order)?
b. The relationship between efficiency of sediment filtration and volume
of runoff, initial sediment concentration, size distribution of the
incoming sediment, filtration length, slope of the filter, character-
istics of the vegetation, and degree of filter submergence should be
established for runoff conditions encountered in typical agricultural
watersheds.
c. The quantitative relationship between the retardance of flow, vegeta-
tion type, and filtering efficiency should be established and its
implications for an economic cost and benefit model be evaluated.
d. For different vegetation types the shape of the curve relating dis-
tance the water has passed through the filter to percent of sediment
remaining should be established and an evaluation of why vegetation
types differ should be performed.
e. The duration of effectiveness of vegetative filters should be
established along with how arrangement of the strip(s) of vegetation
affect its efficiency and/or duration of effectiveness.
f. Harvestable crops should be evaluated to determine their value as a
vegetative filter and their potential as an economic incentive for
filter use.
g. The effect of surface litter on filter efficiency and the longevity
of effectiveness of the filter should be evaluated.
h. The effect tillage practices have on filter efficiency by reducing
peak rates of runoff should be established.
i. The effect of filters along streambanks in reducing erosion from
flood waters should be examined along with their effect on sediment
deposition by flood waters.
j. The effect of nearstream vegetation on drainage rates in agricul-
tural watersheds should be systematically established and evaluated
w.-th respect to the economic costs and benefits of this decreased
drainage rate.
k. The amount of land to be taken out of production to minimize nutrient
and sediment loads must be determined.
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3. Effect of Channel Morphology on Water Quality
a. The relationship between stream morphology, Unit Stream Power (USP),
and suspended sediment concentration should be rigorously evaluated
in agricultural watersheds to establish the effect of present stream
management practices on USP, suspended sediment load and total sedi-
ment load leaving a watershed.
b. A systematic evaluation of the effect of stream morphology on
drainage rates in headwater streams should be performed to establish
what options are available, depending on the balance desired between
the goals of agriculture (rapid drainage) and those of water quality
(slower drainage, lower USP's, reduced suspended sediment loads, and
reduced downstream flood and silt damage).
4. Predicting Sediment Loads in Flowing Waters
a. A realistic model for predicting sediment losses from agricultural
watersheds is critically needed. Among other things, the model
must consider the magnitude of erosion from the watershed, how and
where eroded material is removed before the runoff reaches waterways,
the addition of sediment from underground (drain) tile systems and
the energy the stream has available to transport the sediment
entering it. Future research should emphasize combining the Univer-
sal Soil Loss Equation, information concerning the nature of the
erosion-deposition equilibrium between the terrestrial and aquatic
environment, and the Unit Stream Power model.
5. Stream Biota
a. Systematic experiments should be performed on headwater streams,
evaluating the effect of removal of nearstream vegetation on the
distribution and abundance of organisms in these areas.
b. A multivariate analysis should be performed relating invertebrate and
vertebrate abundance and diversity to several relevant environmental
variables. This would provide significant insights into what com-
bination of water quality and stream morphometric variables are of
prime importance in determining the quality and quantity of stream
biota. This data could then be utilized to make significant improve-
ments in future engineering designs for alteration of the nearstream
vegetation and channel morphology.
c. A rigorous economic re-evaluation of all aspects of channelization
should be performed.
6. Floodplain Ecology
Ecosystems which have evolved in the regular flooding regimes of
small stream or river floodplains require periodic flooding for
normal growth and reproduction. Modifications of stream channels
by channelization and by construction of dams modifies the
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periodicities of flood and result in shifts in species composition of
floodplain floras. Such problems may preclude management for natural
vegetation along streams and the benefits deriving from their pre-
sence. Any efforts to assess the value of greenbelts should consider
both "artificial" and "natural" assemblages of species. Intuitively,
it seems likely that more natural assemblages will optimize a wider
range of societal objectives.
LARGE SCALE RESEARCH
Before the use of nearstream vegetation and channel morphology can be
fully evaluated as a management alternative, its costs and benefits must be
assessed at the level of a single drainage and at the watershed level. The
design of this research must explicitly recognize the functional interrela-
tionships of the terrestrial and aquatic components of watersheds. For
example, research examining the effects of tillage practices alone compared
with other research on the effects of greenbelts and/or more natural channel
morphology is inadequate. Significant benefits may derive from combinations
of several practices that do not accrue from either practice used alone.
1. Changes in nearstream vegetation could be instituted in a watershed
by preventing plowing along one or several of the drainages and
letting vegetation recolonize the area or by planting some selected
species. The effects of nearstream vegetation on water quality, rate
of stream discharge, and total sediment discharge could be evaluated.
Unless this type of land treatment could be performed on a number of
different drainages with different stream morphologies, substantial
insights' into the interaction between nearstream vegetation and
s.tream morphology will not be forthcoming. However, it could pro-
vide a sound data base for the economic evaluation of the costs and
water quality benefits from alternate management strategies of the
nearstream vegetation.
2. To evaluate the combined effect of nearstream vegetation and channel
morphology on water quality and quality of the stream biota, a
number of streams differing in distance to nearest cropland and in
the length of time since removal of nearstream vegetation and chan-
nelization should be intensively studied. Depending on the length of
time since alteration, the streams would differ in type of vegeta-
tion along their streambanks and the degree to which new meanders
and pool-riffle sequences have developed. An intensive examination
of water quality, sediment transport, and the structure of biotic
communities in these streams would provide a substantial data base
and significant insights into how the terrestrial-aquatic interface
and stream morphology can be more efficiently managed to maximize the
quality of the water and biota in agricultural watersheds and mini-
mize the costs.
10
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WHAT TYPE OF RESEARCH IS BEST?
In this section we have outlined a number of both specific and broad
research problems which could be undertaken to more fully evaluate the feasi-
bility of the greenbelt management alternative. Although it would be best
to extensively investigate each of these problems, time and resource limita-
tions demand that those problems with the highest benefit-cost ratio be
investigated first. As we have documented in this report, the quality of
water leaving a watershed and the quality of the stream biota are based upon
complex interactions on the land surface, in the stream, and between the
land and stream. The classical reductionist approach of controlling as many
variables as possible and examining the effect of one or a series of treat-
ments will be difficult (if not impossible) and expensive to do at the water-
shed level and will probably have limited success in identifying feasible,
comprehensive management strategies for controlling non-point pollution; the
interactions between the variables are too important and the variables are
too numerous. Rather, we emphasize the need for a more holistic approach
towards the solution of non-point pollution problems in which emphasis is
placed on identifying groups of interacting variables which, if properly
managed, can lead to significant improvements in a broad range of water
quality problems. We believe the nearstream vegetation and stream morphology
are two such variables. Future research should document the magnitude of the
benefits and costs produced through the interaction of these variables along
with their feasibility of implementation.
11
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SECTION 4
VEGETATION AS A NUTRIENT FILTER
Previous studies investigating the use of vegetation to remove nutrients
from solution are largely associated with the renovation of secondary efflu-
ent by spray irrigation techniques. These methods rely on rapid infiltration
of the solution with both the vegetation and soil acting as a filter medium.
Nutrients are removed through uptake by plant roots and microorganisms and
by chemical adsorption of the ions onto the surface of soil particles.
Studies of the use of combined soil and vegetative filters suggests consider-
able effectiveness at phosphorus removal (98-99%), with lower efficiencies
for removal of nitrogen (10-60%) and other nutrients (Lehman and Wilson 1971,
Kardos et al. 1974, Sopper and Kardos 1973, Younge et al. 1976, Inst, Water
Research, Michigan State University 1976). The effectiveness of vegetative-
soil filters appears to be related to soil and vegetation type and quantity
of effluent applied to the system. Unfortunately, long term effects on soil
nutrient loads are still not clear.
We will not consider "infiltration filters" in further detail in this
report, since we are primarily interested in the feasability of using vege-
tation to remove nutrients from shallow overland flow and not percolation of
solution into the soil. (We were not able to find experimental studies on
the use of vegetation to remove nutrients from channel flow.) An excellent
example of the use of grass filters to remove nutrients from overland flow
was conducted by the Campbell Soup Company in Paris, Texas (Mather 1969,
Law et al. 1970). Wastewater was sprayed on the top of grass plots 60 to
90 m long with a slope of one to 12 percent. Because of the impermeability
of the soil, an average of 61% of the water applied left the area as surface
runoff. Chemical analyses of the runoff showed that BOD and nitrogen removal
varied from 85-99% and 76-90%, respectively. However, the efficiency of
phosphorus removal was dependent on application frequency, with the percent
removed increasing from 50 to 80% by a change in the spray schedule from
once a day to three times a week. Detention time was a key factor control-
ling both nutrient and BOD removal but quantitative information relating
detention time to percent reduction was not given.
Other studies using grass filters to remove nutrients from municipal
effluents were not as successful. In one study, effluent from an oxidation
pond was applied to grass plots 300 m long (Wilson and Lehman 1966 in Butler
et al. 1974). Apparently only one trial was performed and nitrogen and
phosphorus concentrations were reduced 4 and 6%, respectively. Information
regarding application rate and slope were not available and detention times
were not given.
12
-------
A similar study (Butler et al. 1974) applied secondary effluent to reed
canarygrass plots 150 feet long with a 6% slope. Reductions in phosphate
and nitrate concentrations were only 0-20%. Insufficient contact time, due
to high flow rates and a short flow distance, was suggested as the reason
for the inefficiency of the system.
Popkin (1973) performed a series of tests using a grass covered soil
filter for renovating urban runoff in Tucson. The filter was 60 m long,
1.2 m wide and 1.5 m deep. The volume of water treated per acre of grass
per day varied from 3.8 to 25.1 acre feet. For the grass filter, the fol-
lowing percent reductions compared to untreated runoff occurred: COD-62%,
suspended solids-35%, turbidity-97%, total coliforms-84%, and fecal
coliforms-87%. The efficiency of the filter for removing nutrients was
not reported.
The treatment of feedlot wastes by grass filters is a rapidly expanding
area. The systems used usually consist of a lagoon for settling of solid
wastes followed by a grass waterway through which the lagoon effluent is
allowed to filter. Much of the research in this area has just been initi-
ated and extensive sets of data are not yet available (D. H. Vanderholm,
Associate Professor of Agricultural Engineering, University of Illinois,
personal communication, 1976). The grass waterways used are usually long,
i.e. 260-800 meters (Sievers et al. 1975, Swanson et al. 1975) but even
extremely long waterways, up to 3600 meters, have not been successful at
reducing nutrient concentrations (Kreis et al. 1972). Furthermore, when
systems are successful (Edwards et al. 1971, Swanson et al. 1975) it is
difficult to determine if the reduction in nutrients is due to some action
of the vegetation or is merely a result of dilution by water entering the
waterway from the cropland area.
From this brief literature review it is clear that the use of vegetation
for removing nutrients in solution from surface runoff is not always success-
ful. The reasons for success, or lack of success are not always clear. We
suggest four factors should be more rigidly controlled and evaluated in
future research:
1. Detention time: it should be accurately quantified so that filtering
success can be related to detention time and slope of the filter.
2. Vegetation effects: when possible, controls should be maintained to
more fully elucidate the relationship between type of vegetation
and nutrient removal with special emphasis on the effects of (a)
structure and physiological capabilities of the plants and (b)
single plant species versus more complex plant communities.
3. Volume of water treated: the relationship of volume of water
treated to efficiency of nutrient removal should be studied in more
detail.
13
-------
4. Soil type: soil type affects filter efficiency, with sandy loam
soils being more efficient than clay loam soils (Mather, 1969). More
attention should be directed to this variable, especially with res-
pect to its effect on shallow percolation into the soil versus rapid
overland flow of the solution.
Even if these variables are properly evaluated, certain problems must be
clarified before final recommendations for use of vegetation to control
nutrient inputs from agricultural runoff can be made. First, a common
assumption is that nutrients like phosphorus are entering streams via sur-
face runoff rather than subsurface or groundwater runoff. This is probably
true under most circumstances. Some studies (Jones et al. 1975, Hanway and
Laflen 1974) have found very small quantities of phosphorus in tile flows
and they have been much less than concentrations in surface flows. However,
when tile lines have surface intakes, including along road ditches, they may
carry significant amounts of nutrients and sediments (R. Bachman, Iowa State
University, pers. comm.).
Other recent reports (Ryden et al. 1973, Sommers et al. 1975a,b) also
suggest substantial inputs of phosphorus from subsurface flows. In some
cases concentrations of N and P were comparable to or greater than those in
surface runoff in the Black Creek watershed (Sommers et al. 1975a). Based
on average concentrations, tile effluents and surface runoff were equally
important sources of nutrients entering surface waters. Variability in the
importance of subsurface inputs among watersheds is due to differences in
soil, slope, drainage characteristics, and quality of tile lines. Observa-
tions at Black Creek suggest that very efficient surface filters, if acting
alone, may have limited potential for controlling eutrophication when
inefficient tile systems are present. This is especially true in streams
where small concentrations of nutrients from subsurface flows could have
substantial effects when moderate flow velocities are involved (Phaup and
Gannon 1961). The conflicting results outlined above suggest the need for
more research on the variables important in determining the levels of nutri-
ents in subsurface flows.
Second, the distribution of nutrients between the solid and aqueous
phases of runoff must be examined. Again data from Black Creek are rela-
vant to this question. Sommers et al. (1975a) and Nelson et al. (1976)
found that a large proportion of nitrogen and phosphorus in surface runoff
is attached to sediment (Table 1). With fertilizer additions, a slightly
larger proportion of the nutrients are in the solution phase of the runoff
but even then nearly all of the phosphorus (greater than 85%) and most of
the nitrogen (greater than 70%) is attached to sediment. (Although nutrients
adsorbed to sediment particles are not directly available to plants, removal
of nutrients in solution by plants will result in movement of some of the
adsorbed nutrients from sediment particles to solution. In solution they
are directly available to biological systems.)
Soil types differed only slightly, with clay loams typically having ,
a smaller fraction of the nutrients in solution. Nutrients are usually
adsorbed to the smaller sized particles, especially clay (Sommers et al.
14
-------
1975a,b, Scarseth and Chandler, 1938, Monke et al. 1975b) and this is also
the soil fraction that is selectively lost during the erosion process
(Stotlenberg and White 1935, J. V. Mannering, personal communication,
Professor of Agronomy, Purdue University, 1976).
TABLE I. PERCENT OF NITROGEN (N) AND PHOSPHORUS (P) ATTACHED TO SEDIMENT IN
SURFACE RUNOFF FROM FOUR SOIL TYPES UNDER FERTILIZED AND UNFERTIL-
IZED CONDITIONS (Adapted from Sommers et al. 1975a)
Soil Treatment % N as Sediment N % P as Sediment P
Fertilized
Unfertilized
Average
75
88
Range
49-91
69-98
Average
92
96
Range
85-98
91-100
These observations suggest four main conclusions regarding the use of
vegetation as a nutrient filter:
1. There has been variable success in the use of vegetation to filter
nutrients in solution from surface runoff. The reasons for this
variability are largely unknown due to poorly controlled experiments.
2. Even at high efficiencies of nutrient removal, in some agricultural
areas surface filters acting alone may not control eutrophication
because of the inputs of nutrients into streams via subsurface path-
ways. This does not imply that surface filters should not be used.
Rather, we emphasize that no single factor is likely to solve the
problem.
*
3. Conflicting data exists regarding the importance of subsurface inputs
of phosphorus into streams. More research is needed to clarify the
effects of soil type, slope, drainage characteristics and type and
quality of tile lines on this variable.
4. Substantial amounts of nutrients can be removed from surface runoff
by removing sediments, especially the clay fraction, to which the
nutrients are attached.
15
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SECTION 5
VEGETATION AS A SEDIMENT FILTER
Three potential sources of sediments exist: (1) streambank erosion,
(2) subsurface inputs (i.e. tile), and (3) surface inputs. The value of
vegetation as a sediment filter depends on the relative amounts of sediment
from these three sources. Data from Black Creek suggest that streambank
erosion is a minor source of sediment inputs (Wheaton 1975, Mildner, 1976)
especially if treatment is applied to the few sites where most bank erosion
occurs. Studies of surface versus subsurface inputs at Black Creek yielded
conflicting results. Some tile effluents contained low sediment concentra-
tions while concentrations in others were large enough to suggest tiles may
contribute a significant amount to the sediment yield from watersheds
(Monke et al. 1975a). There are probably two reasons for the variability of
the data obtained. The samples were random "grab samples." As a result
they varied depending on when they were taken relative to the last storm
event. Furthermore,, the concentration of sediment in tile outflows is signi-
ficantly influenced by the quality of the tile line (Karr, personal observ.).
This latter point, along with more recent data from Black Creek indicating
that surface runoff accounts for 50% of the water and 99% of the suspended
solids loss in the watershed (Nelson et al. 1976), suggests maintenance of
tile lines will insure that surface runoff will be the main source of sedi-
ment inputs into agricultural drainages. Sediment inputs into streams can
therefore be controlled by adequate treatment of surface runoff.
Wischmeier (1962) examined the effect of storm intensity on erosion and
demonstrated that about three-fourths of the total soil loss from agricul-
tural land occurs during an average of four storms each year. A more recent
study suggests caution in such conclusions (Piest 1963). He found that the
sediment contributions of large storms (with a return period greater than
2 yrs.) varied from 3-45% of total suspended-sediment yield; the yield from
moderate storms (1-2 yr. return period) ranged from 3-22% of total yields
and storms with a return period of less than 1 yr. carried 34-92% of total
suspended sediments. Since small storms carried more than one-half of the
soil losses in most watersheds, small scale conservation practices with low
cost can result in significant reductions in downstream sedimentation
(Piest 1963). Piest also concluded that the soil losses resulting from
large storms were higher in the semi-arid Great Plains than in the humid
Southeast. Furthermore, relative sediment contributions for a given large
storm decrease with increasing watershed size.
Therefore, in most watersheds, filters can contribute significantly to
the reduction of sediments if they are efficient during low storm intensi-
16
-------
ties. If they can also be demonstrated to be efficient at high storm
intensities an even greater contribution to the reduction of sediments will
re -;ult.
This section of the report examines (1) the ability of vegetation to
filter sediment from water which spreads as a shallow layer more or less uni-
formly over the surface of the land (overland or sheet flow) and (2) the
ability of vegetation to filter sediment from shallow channel flow entering
streams as intermittently flowing tributaries or waterways (channelized flow).
OVERLAND FLOW
Unfortunately only a minimal amount of data has been found regarding
this topic. Much of the work in this area is descriptive, relating to the
effectiveness of filter strips between logging roads and mountain streams.
In Idaho, Haupt and Kidd (1965) observed that sediment flows off logging
roads during major storm events reached streams if the undisturbed filter
strip was only 2.5m wide but did not if they were 9 m wide. In Montana, silt
flows off skid and logging roads fanned out and deposited sediment soon
(6-9 m) after reaching an undisturbed mat of pine needles and other forest
litter (Johnson 1953).
The relationship between the slope of a vegetative filter and minimum
effective greenbelt width for treatment of surface runoff is direct (Fig.l;
Trimble and Sartz 1957). Generally minimum width of filter strips increases
with slope of land and varies with water quality objectives. Where mainte-
nance of the highest possible water quality is important, such as in munici-
pal watersheds, recommended filter widths are higher (Trimble and Sartz
1957). However, the scatter of their original data suggests that other
variables are also determining the efficiency of the filter. Apparently,
increased flow velocity results from increased slope and enhances the ability
of the surface flow to transport sediment. Although some recommendations
for greenbelt width are in the literature, little or no data are given.
Recommendations, then, must be viewed as tentative. Significantly, in fil-
ters observed for long periods of time (i.e., 15 months), sediments did not
clog the loose surface litter nor decrease the efficiency of the filter.
Trimble and Sartz suggested that leaves fall each year and form a fresh sur-
face for deposition of new sediment. This indicates that sediment filters
may be effective for long periods of time without sediment buildup along
streambanks due to natural variability in the plant community from year to
year (Gosz et al. 1972). However, the length of the effective period must
be examined by more detailed, long-term research.
More elaborate equations were later developed for predicting the sedi-
ment flow distances using multiple regression techniques (Haupt 1959, cited
in Broderson 1973). Sediment flow distance is primarily a function of (1)
slope of the filter and the density of obstructions within the filter, i.e.
grass, brush, tree stumps, depressions, etc. and (2) the slope and length of
the embankment which the runoff passes down before it enters the filter.
More recently, Ohlander (1976) developed an equation to predict the size of
17
-------
buffer required to trap sediment exitting a logging road drainage. His pre-
diction was based on soil erodibility (K—see page 40), slope of the filter,
and the infiltration rate of water into the filter.
_C
-*->
T3
75
60
45
30
£_
(D
Li. 15
Recommended
widths for:
^Weighted means
for observed
data
1
I
I
1
I
10 20 30 40 50
Filter Slope
60
Figure 1. Relationship between slope of a vegetative (sediment) filter and
effective filter width. Note that the recommended widths are
"evaluated guesses" rather than empirically defined widths. As
noted in the text the scatter of data is broad suggesting that a
number of factors may be important in determining optimal filter
width. (Modified from Trimble and Sartz 1957).
Although much work evaluating the use of natural vegetation for filter-
ing sediments from overland flow has been conducted by foresters, relatively
little has been done in agricultural watersheds. One study relevant to this
problem (Mannering and Johnson 1974) passed sediment-laden water through a
'15 m strip of bluegrass sod (Table 2) . They found in a single trial that 54%
of the sediment was removed from the water.
Studies of surface runoff through heavy cornstalk residue on the lower
3 m of a 11 m erosion plot carried only 3-5% of the sediment expected from a
bare surface (G. R. Foster, pers. comm.). The study was done with simulated
rainfall (6.2 cm per hour). Foster, an hydraulic engineer with USDA-ARS in
West Lafayette, Indiana, felt that well-designed and maintained grass strips
18
-------
would be more effective at sediment removal than is reflected in the P values
of the Universal Soil Loss Equation (USLE) (Wischmeier and Smith 1965).
TABLE 2. EFFECT OF A BLUEGRASS SOD STRIP ON SEDIMENT CONCENTRATION IN RUNOFF
(Modified from Manner ing and Johnson 1974)
Distance into Slope between Sediment concentration
sod strip sample points expressed as percent of
(M) (%) original
0
3
8
15
4
20
4
100
78
66
46
The effect of grass and presumably other vegetation types on sediment
load is really a two-fold phenomenon. The studies already mentioned docu-
ment the value of vegetation or surface litter for reducing the amount of
sediment in a given volume of water. A second benefit is the reduction in
volume of runoff from vegetated areas.* USDA studies on demonstration plots
in Wisconsin (0.04 hectares-400 sq. meters) have shown that runoff from grass
is one-fifth of that from continuous row crop plots (Glymph and Holtan 1969).
Rotations with grain or hay had intermediate delivery rates. They concluded
that runoff is inversely related to the density of vegetation and frequency
of cultivation. When forested watersheds are compared to areas under intense
cultivation,differences in runoff may be as great as 40X (Hornbeck et al.
1970). Hewlett and Nutter (1970) have shown that in natural watersheds over-
land flow is a rare phenomenon. The retardance of the flow by the vegetation
allows the soil to absorb much of the water, which then goes on yielding it
to the stream for extended periods of time (Fig. 2). The results of this are
(1) the water is passed through a soil filter before entering the stream and
(2) there is a more controlled release of water from the watershed, resulting
in a more stable water supply and aquatic environment (Curry 1975). On land
with reduced vegetation cover, the probability of flooding increases and
seasonal shortages of water are more common. This suggests that incorpora-
tion of greenbelts along streams might not only reduce sediment loads but
also produce small reductions in runoff. Vegetation, with associated litter
and soil characteristics, might serve as a sponge to hold water for a slow
release amd more stable aquatic environment. Incidentally, the same object-
ives (slow release and reduced sediment loads) may be accomplished with
some construction practices such as parallel tile outlet terraces.
*Actually a third factor is also important. Rainfall impact on soil struc-
ture is reduced when it strikes vegetation before reaching the soil surface.
These factors are dealt with implicitly in the C and P terms of the USLE. A
clearer definition of their relative importance is required.
19
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£ 60
L-
(D
Q.
if)
0
Q)
£_
CO
I
Q
40
-Farmed
/''jX^Forested
Figure 2.
40 80 120
Time (min.)
Effect of land use on discharge rates on two watersheds (Modified
from Borman et al. 1969).
In summary, limited data indicates that vegetation and surface litter
can effectively remove sediment, and perhaps reduce runoff, from surface flow
before water reaches channels. However, the size and type of vegetative strip
needed to remove a given fraction of the overland sediment load or its
effect on rate of water release cannot be established at this time.
CHANNEL FLOW
Early observations documenting the ability of vegetation to act as a sed-
iment filter in channels are primarily descriptive. When tamarisk invaded an
area along a stream above a reservoir in Carlsbad, New Mexico, the stream
spread across a broader flood plain, decreased its velocity, and deposited
sediment around the tamarisk (Tamarix gallica) rather than in the reservoir
(Brown 1943). This resulted in a decrease in the rate of silt deposition in
the reservoir (Fig. 3). Similar observations were made by others (Taylor
1930) but quantitative measurements of the effect of vegetation on flow
velocity and efficiency of sediment removal were not performed.
Other more quantitative field experiments examined the effect of vegeta-
tion on the flow of water in open channels (Cook and Campbell 1939, Palmer
20
-------
1946, Ree and Palmer 1949, Ree 1949). Although designed to evaluate scouring
problems, they provide quantitative documentation of how vegetation affects
the velocity of water.
'u 80
05
§"60
O
40
20
or
i Tamarisk
'_/ colonizes
Water
ediment
1895 1905
1915
Year
1925 1935
Figure 3. Silt volume as percent of basin capacity for Lake McMillan near
Carlsbad, New Mexico. Flattening of the curve after 1915 is
attributed to the effect of tamarisk in the valley above the
head of the reservoir (Modified from Brown 1943)
When water depth is less than the grass height, velocities tend to be
low (Fig. 4). From the channel bottom to the top of the grass the veloci-
ties do not exceed two feet per second. At the upper surface of the vegeta-
tion the velocity increases rapidly. These results suggest (1) a substan-
tial reduction in the flow velocity due to the retarding action of the
vegetation, (2) deposition of a fraction of the sediment the runoff is
carrying, (3) the effectiveness of the vegetation at retarding the runoff
and allowing deposition of sediments depends on the relationship between
the depth of runoff and the height of the vegetation and (4) reduced water
velocities retard drainage. When water velocities are slowed enough to
retard drainage the potential for crop damage exists. Vegetative filters
should be designed so that water is not detained long enough to damage corn
or soybeans, i.e. 4-6 days (Hamilton 1969), but sufficiently long to provide
a more regulated release of water from the land surface and allow sediment
deposition to occur. This may also be significant at reducing downstream
flooding and erosion due to flooding outside the streambank. This latter
point has recently been documented below the washed-out Teton Dam where iso-
lated tree stands prevented excess erosion (N.G. Benson, National Stream
Alteration Team, pers. comm., 1976).
The importance of depth of runoff is further illustrated in Figure 5.
Maximum flow retardance is obtained during low flows since vegetation is
still upright (neither bent nor submerged). The gradual increase in retarda-
tion in this range is probably due to the greater surface area of vegetation
21
-------
Figure 4.
Water surface^
60 120 180
Velocity (cm/sec)
Water velocity as a function of depth. Note that velocity
increases rapidly near the top of the grass and even faster for
channel flows exceeding grass height (Modifled from Ree 1949).
5 1.0
(J
CD
O
u
(D
u
c
03 0.1
-Q
L.
03
.01
Low Flows
Intermediate
Submer'g
begins
Depth (ft)
Figure 5.
Relationship between depth of flow and amount of retardance with
bermudagrass (Modified from Ree 1949) .
22
-------
encountered with increasing depth. As the depth is further increased, the
plants start to bend and retardance of the flow is decreased. Finally the
vegetation is shingled or flattened and offers little or no resistance to
the flow of water. This indicates that flexible vegetation may be ineffi-
cient at filtering sediment from channel runoff of large depths, i.e., 0.1 m
or larger. The exact depth will of course depend on both the height and
flexibility of the vegetation. This effect of depth on filtering efficiency
has been partially substantiated by Wilson (1967) and the importance of it
will be discussed later in this report. (Note that when water depths are
low relative to grass height the channel characteristics are similar to those
of overland flow filters discussed above.)
More recently, a mathematical model of the sediment filtering capability
of simulated vegetation in shallow channel flows suggested that the impor-
tance of depth of flow and the effect of vegetation on flow velocity are only
two of several factors determining the efficiency of vegetative filters
(Trollner et al. 1973, 1975, 1976; Barfield et al. 1975). Using nails to
simulate vegetation and glass beads of varying sizes to simulate sediment,
the percent of "sediment" trapped in the channel was correlated with the inde-
pendent variables: (1) slope of the nails, (2) spacing of the nails, (3)
particle size, (4) velocity of flow, (5) filter length, and (6) input sedi*-
ment concentration. Evaluation of the effect of the independent variables
was achieved by "optimizing" a linear regression so that the standard error
for predicting the percent of sediment trapped from the independent variables
was minimized and the correlation coefficient was maximized. The final model
revealed that (1) a large percent of the input sediment in a shallow channel
is filtered by the "vegetation" and (2) the most important independent vari-
ables determining the fraction of sediment trapped are, in order of importance,
flow velocity, depth of flow, spacing of "grass" blades, sediment size, and
filter length.
In a similar experiment stiff, medium, and high flexibility strips of
plastic proved to be efficient sediment traps (Kayo et al. 1975). At high
velocities filter efficiency decreased due to bending of the flexible strips.
This suggests that the relationship between depth of flow and retardance
illustrated in Figure 5 is also a function of flow velocity.
These simulations and models cannot be used to predict the efficiency of
real vegetation as a sediment filter. They are restricted to an artificial
set of independent variables thought to be important and are evaluated in a
non-random and artificial sequence. As a result they ignore other variables
which may be more important in the real world, i.e. the effect of duration
of input into the filter, and they fail to evaluate the frequently random
and synergistic nature of these independent variables, i.e. a large storm
event while the vegetation is still dormant. Therefore their usefulness is
limited. Their importance is their clarification of relationships which re-
quire more research under natural conditions.
Unfortunately only a minimal amount of data exists to evaluate the
efficiency of real vegetative filters in open channels. However, the data
are encouraging. Wilson (1967) attempted to develop economical methods for
23
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sediment removal from flood waters to allow use of the water for artificial
recharge. He allowed turbid flood water to filter through various types of
vegetation and analyzed their efficiency at sediment removal. The major
findings of his study are discussed and illustrated in the next several pages,.
1. Filter efficiency varies with vegetation type. The most efficient
species studied to date, coastal and common bermuda grass (Cynodon
dactylon), usually removed 99% of the initial sediment concentration
(5000 ppm) in 300 m of filtering (Table 3). The percent removed
increased with distance. Sediment removal seems to be a decreasing
exponential function, differing with vegetation type. This is
schematically illustrated by the set of curves in Figure 6. Varia-
tion in the efficiency of sediment removal among grasses is corre-
lated with retardance of flow by the vegetation. This finding has
two important implications:
a. Intensive studies are needed to document variation among plants.
Limited data already available (Ree 1949, Ree and Palmer 1949)
may provide first approximations to suggest which vegetation
types should be examined for use as sediment filters.
b. There will be a trade-off between rapid drainage of the land and
amount of sediment removed from the runoff. Clarification of
patterns of variation within and between vegetation types must
be a major objective of research in this area.
TABLE 3. PERCENT REMOVAL OF SEDIMENT AFTER VARYING LENGTHS OF FILTRATION
THROUGH BERMUDA GRASS* (Modified from Wilson 1967)
„ c . Distance (M)
Grass Species — *-^-
90 215 300
Common Bermuda
Coastal Bermuda
0
0
50.0
55.5
90.4
97.5
97.0
98.5
*Initial concentration - 5000 ppm.
2. Filter efficiency varies not only with vegetation type but also with
distribution of particle sizes in the suspended material (Table 4).
There is an inverse relationship between the filtration length re-
quired to remove a given percent of a particle size and that particle
size. This inverse relationship will have two important implications
for sizing vegetative filters:
a. The size distribution of particles in the runoff will have a
definite effect on how wide the strips of vegetation must be to
filter a given percent of the total load and
24
-------
b. Emphasis of water quality regulations will have a definite
effect on their required width; that is, it may be desirable to
remove various volumes of sediment or a given particle size.
The preferred alternative will depend on water quality objectives
and the local situation.
oilOO
c
c
'ni
E
(L)
80
(D
E
T5
(D
O
-*->
C
u
(L)
Q_
60
40
20
Distanced filtered
Figure 6. Hypothesized relationship between filter width and percent of
sediment remaining for several vegetation types. The four curves
are hypothetical. We expect differences among vegetation types
but data are not available to show how sediment loads and filter
distance will vary among vegetation types.
TABLE 4. PERCENT OF SAND, SILT, AND CLAY IN SEDIMENT DEPOSITED AFTER FIL-
TRATION THROUGH COASTAL BERMUDA GRASS (From Wilson 1967)
Distance from head
of filter (M)
Sand
Silt
Clay
3
8
15
30
60
90
120
51.6
43.2
3.6
3.4
20.2
31.2
21.6
40.0
46.6
77.0
69.4
47.0
37.6
39.6
8.4
10.2
19.4
27.2
32.8
31.2
38.8
25
-------
The rate of sediment deposition is constant over a range of slopes.
After a critical (threshold) slope is reached, the efficiency of
the vegetative filter declines (Table 2). These data indicate the
section of the filter with the largest slope (jsection 2) had the
smallest proportion of sediment deposited within it, even though its
length was longer than that of section 1 and only slightly shorter
than that of section 3. This suggests that not only will vegetation
types differ in their relationship between distance runoff is fil-
tered and percent of sediment remaining (Figure 6) but also, for a
given type of vegetation, the shape of the curve will differ depend-
ing on the slope of the filter. This hypothesized relationship is
illustrated by the theoretical curves of Figure 7. More extensive
data are needed to substantiate this relationship. The critical
slope depends on several factors, including application rate of the
water to be filtered, grass characteristics, (surface area, height,
etc.) and the particle size distribution of the incoming sediments
(Wilson 1967). If the relationship in Figure 7 is supported by field
data, the width of the filter required will depend on the slope of
the land. Like most environmental technologies this will produce
varying effects among farmers depending on the slopes of their land.
Under some topographic, soil, or other conditions, filter width may
be impossibly large for effective implementation.
en 100
80
C
E
o
c
(b
u
Q_
Figure 7.
60
40
20
below
critical
slope Sc
Distance filtered
Hypothesized relationship between distance solution is filtered
and percent of sediment remaining for several slopes. These ar
hypothisized curves and assume vegetation type is constant.
are
26
-------
4. When grasses are clipped and flow rates are high enough to submerge
the grass, filtering efficiency declines to zero. This correlates
well with retardance coefficients being lower for shorter grasses
than for taller ones and retardance decreasing with increased sub-
mergence as shown in Figure 5. It further emphasizes the importance
of examining the filter efficiency of vegetation under normal storm
runoff conditions. It also suggests that mowing of grass waterways
and streamside vegetation should be discouraged, especially during
periods when storms are likely.
5. Grasses used for filters should have the following characteristics:
a. deep root systems to resist scouring in swift currents;
b. dense, well-branched top growth;
c. resistance to flooding;
d. ability to recover growth subsequent to inundation by sediment;
e. if possible, it should yield an economic return.
It is apparent that several variables are important in determining how
effective real vegetation will be at filtering sediments from shallow channel
flow. These variables appear to act in an interrelated manner and include
filtration length, slope of the filter, grass characteristics, size distribu-
tion of the incoming sediments, degree of submergence of the filter, applica-
tion rate of the water to be filtered and initial concentration of the sedi-
ments. Fortunately, many of these same variables were judged to be important
by the laboratory studies previously discussed (Trollner et al. 1973, 1975,
1976) and the minimal amount of data regarding filtering from overland flows.
Unfortunately there is no quantitative information available on how these
variables are interrelated when real vegetation is used as a filter under
runoff conditions normally encountered in agricultural watersheds.
An important problem yet to be discussed concerns the placement of
these vegetative filters. It is unlikely that a significant amount of sur-
face runoff (and sediment) enters directly into the main channel of a river.
Rather it most likely comes in through smaller, often intermittent tribu-
taries, gullies, and drainage ditches which dissect the landscape. There-
fore, any use of vegetative filters must concentrate on these areas,
especially areas where tributaries enter larger channels. More precise
statements on the placement of these filters will require more detailed
understanding and quantification of the dynamics of sediment movement at the
land-water interface. Only then can a full evaluation of the economic costs
and benefits of filters be completed.
The data obtained by this literature review suggests that vegetation
can serve as an effective sediment filter. However, the placement of the
filter and the width or length of the filter required to remove a given
fraction of the incoming sediment, and the duration of its effectiveness is
dependent on the interaction of physical factors, biological factors, and
27
-------
the specifications of water quality standards, all of which are yet to be
thoroughly evaluated under normal agricultural conditions and quantitatively
related to each other in any predictive manner. Present land use practices
immediately adjacent to streams (Table 5) indicates these relationships
should be investigated. The following questions must be answered before
informed nearstream vegetation management programs can be implemented.
TABLE 5 LAND USES IMMEDIATELY ADJACENT TO MODIFIED STREAMS AND DRAINAGE
DITCHES IN THE BLACK CREEK WATERSHED (Data from Mildner 1976)
Land Use Type Modified Stream Drainage Ditch
Crops
Pasture
Forest
Urban
69.9%
4.7%
17.7%
3.6%
74.2%
0.0%
0.0%
0.0%
Other (Farmsteads, roads,
etc.) 4=1% 25.8%
1. How important is runoff over streambanks as a sediment source com-
pared with runoff entering from intermittent tributaries? How do
the contributions from these two sources change among land uses and
with stream volume?
2. What general relationship exists under normal runoff conditions
between efficiency of sediment filtration and volume of runoff,
initial concentration of sediment, size distribution of incoming
sediment, filtration length, slope of filter, characteristics of
the vegetation, and degree of filter submergence?
3. Is there a quantitative relationship between the retardance of flow,
vegetation, and filtering efficiency? If so, what are the implica-
tions for an economic cost and benefit model?
4. For different vegetation types what is the shape of the curve
relating distance the water has passed through the filter to percent
of sediment remaining? Why do vegetation types differ in the shape
of this curve?
5. What is the duration of effectiveness of the vegetative filter?
Does arrangement of the strip(s) of vegetation effect their effi-
ciency and/or duration of effectiveness?
6. Could a sediment filter be harvested and still be effective? If so,
this will provide another economic incentive for filters.
7. How much phosphorus can be removed by filtering the sediments?
28
-------
8. What is the effect of surface litter on filter efficiency and the
longevity of effectiveness of the filter?
9. What effect will tillage practices (i.e. contouring vs. straight row)
have on filter efficiency by reducing the peak rates of runoff
(Glymph and Holtan 1969)?
10. How much will filters along streambanks reduce erosion from flood-
waters which overflow stream banks? Will they result in sediment
deposition by the floodwaters (Parsons 1963)?
11. How much will greenbelts reduce drainage rates of agricultural land?
Will it be economically detrimental?
12. How much land will be taken out of production to minimize sediment
and nutrient loads?
We believe the last two questions regarding the economic impact of managing
for improved water quality by the use of vegetative filters can only be
addressed when more comprehensive information regarding the first ten ques-
tions is available.
29
-------
SECTION 6
EFFECT OF CHANNEL MORPHOLOGY ON WATER QUALITY
Studies of sediment movement and deposition in aquatic environments have
largely been from either a geological or hydraulic engineering perspective.
Geologists have been primarily interested in sediment deposition (Leopold
et al. 1964,,Friedkin 1945, Bridge 1975, Jackson 1975) and have directed
little attention towards the dynamics of suspended solids. Hydraulic engi-
neers have emphasized the governing processes in the sediment environment,
with most emphasis on the shearing flow of fluids, turbulences, and vortices
(Chow 1959, Graf 1971).
The relationship between environmental factors like stream morphology
and sediment discharge appears to have only recently been examined in any
detail in the natural environment (Stall and Yang 1972, Yang 1972). The
data found regarding this, relationship will be presented here, along with
the hydraulic theory relevant to the feasibility of maintaining a more
"natural" stream morphology to improve water quality.
There are a number of hydraulic parameters determining the amount of
sediment transported within a stream, including intensity of turbulences,
velocity of water flow, slope of the water surface, bed roughness, shear
stress and many others (Morisawa 1968, Blench 1972). Because these variables
are not independent, the precise relationship between them as a group and
the sediment load of a stream is difficult if not impossible to establish.
As a result, hydraulic engineers have determined the relationship between
single variables and sediment transport. Interrelationships between total
sediment load and velocity, slope, shear stress or water discharge have been
examined (Yang 1972). In many cases predictions of sediment transported by
a given flow are possible but conflicting results are also common. For
example, for a given water surface slope two different discharges can be
observed (Fig. 8) and for nearly identical flow velocities large differences
in sediment discharges can occur (Fig. 9). It is apparent that more indepen-
dent variables and a more process oriented approach needs to be utilized to
provide a better predictive capability.
Because of these inconsistencies the concept of unit stream power was
proposed to predict total suspended sediment concentrations (Yang 1972,
Stall and Yang 1972, Yang and Stall 1974). The concept is an expansion of
previous equations and employs two variables, velocity and slope, to predict
sediment loads. Basically, they suggest that the rate of sediment transfer
is related to unit stream power (USP)—the rate of energy expenditure by a
stream as it flows from a higher to a lower point. It is defined as the time
30
-------
rate of potential energy expenditure per unit weight of water in an alluvial
channel and can be expressed mathematically in terms of average water velo-
city (V) and, under steady uniform flow conditions, the surface slope of the
water (S) (Yang 1972, Stall and Yang 1972).
UNIT STREAM POWER = — = — — = VS
dt dt dX
where t = time
Y = elevation above a given datum and is equivalent
to the potential energy per unit weight of water
X = longitudinal distance
More complex considerations of lift force, critical velocity, drag force, and
particle diameter were added to this basic concept to more precisely estab-
u
1 0
1/1
-Q
(L)
cn
-^ irf 1
u 1 U
1/1
~° m
CD IU
"m
o
'2
10
-3
-2
10
-3
10
Water surface slope(feet/foot)
Figure. 8. Relationship between water surface slope and total sediment dis-
charge for one set of experimental conditions (Adapted from Yang
1972).
31
-------
1.0
u
in
CO
-Q
CD
CD
03
_C
U
TJ
10
-1
52 10
r2
0)
E
TJ
03
-f->
O
h-
Figure 9.
1<53
id4
1
2 46
Velocity (ft/sec)
. , I
8 10
Relationship between velocity and total sediment discharge for
one set of experimental conditions (Adapted from Yang 1972).
blish the relationship between USP and sediment transport (Yang 1972, Yang
and Stall 1974). For a detailed discussion of these considerations those
publications should be examined. The suspended sediment concentration in a
stream or agricultural drainage is to a large degree determined by the
stream's USP (Fig. 10)-
Before we discuss the concept of Unit Stream Power in more detail, it
is important to discuss a very important point. The Unit Stream Power con-
cept was developed to predict the amount of energy available to transport
sediment. A stream will only carry that amount of sediment which can be
transported by the available energy. However, the stream may carry less than
32
-------
that amount if no source of sediment is available. In watersheds with little
or no surface erosion and stable banks, sediment loads may be well below the
level predicted from consideration of USP- The energy available to transport
sediment is only useful in predicting actual sediment loads if other things
(sediment availability and other factors discussed below) are held constant.
104F
E
Q.
Q.
00
C
I
TJ
CO
"O
(D
C
(U
Q.
LO
ZJ
CO
10
10
1 n
0.01 0.1
Effective unit stream
power (ft-lbs/1 b/sec)
Figure 10. Relationship between effective unit stream power and measured sus-
pended sediment concentration for four streams. (Modified from
Yang and Stall 1974).
Although these cautions should always be kept in mind, the concept of
unit stream power provides a tremendously useful tool as a first step to
understanding a variety of characteristics of stream channels. These in-
clude bed roughness, bedform, width adjustments, pool-riffle frequency,
meandering characteristics, stream bed profile, and sediment load. (See
Blench 1972 for a good, brief introduction into this field.) Basically, a
flowing stream has an energy potential which must be dissipated. Man must
learn to recognize the extent to which he can minimize the effects of that
energy dissipation on water quality and, therefore, on human society.
33
-------
Two questions will be examined in this section of the report:
1. What characteristics of natural streams or channels control
flow velocity, slope, unit stream power, and the potential of the
stream to transport sediment?
2. What are the effects of present stream management practices on sedi-
ment dynamics in watersheds?
Only the most relevant and "manageable" variables will be discussed hera
A more detailed account of other variables which control velocity and slope
can be found in Graf (1971) or Chow (1959) .
1. Area of Flow: This parameter is critical in determining the velocity
of flow for a stream at a given discharge and slope. Its effect is illus-
trated by the continuity equation from hydraulic engineering;
Q = VA
where Q = discharge Ccfs)
V = velocity (jfps)
2
A = area (ft )
or from our perspective a more meaningful form
Under constant discharge conditions (Qi = Q2 = Qn) differences in velocities
(V^, V2, Vn) are a function of differences in area of flow. Therefore, for
a given discharge under steady and uniform flow conditions, a drainage with
a restricted area of flow, such as by confinement in a ditched channel, will
have a higher flow velocity than a drainage which spreads its discharge over
a larger area. This implies that by channelizing small drainages and con-
centrating the flow in a minimal area with a maximal velocity, one increases
the USP and enhances the capability of the water to erode the stream banks
and transport sediment.
2. Roughness Factor (n) : The n value for a stream or channel is depen-
dent on factors which affect the roughness of the drainage area, including
size and shape of grains on the bed surface, sinuosity of the channel, and
obstructions in the channel such as vegetation, logs and sandbars. As rough-
ness increases, n increases and the flow velocity and USP decrease. Values
for n have been empirically determined for a number of channel conditions
(Chow 1959). Some effects of soil type, channel morphology and vegetation
on the magnitude of n are illustrated in Table 6. These data have two irapor^
tant implications :
a. Clean straight channels normally found in agricultural drainages have
very low n values. They will have high flow velocities, slopes, and
a high capability of carrying large loads of suspended sediment (high
USP) .
34
-------
Options in stream management practices are extensive in that a
broad range of n values, flow velocities, and USP magnitudes can be
obtained. For example, preservation of natural stream morphology
(meanders, pool and riffle topography) can increase n and decrease
flow velocities, slopes, and USP. Therefore numerous options are-
available depending on the balance desired between the goals of
agriculture (rapid drainage) and those of water quality (lower USP's
and reduced suspended sediment concentrations).
TABLE 6. ROUGHNESS COEFFICIENTS (n) FOR VARIOUS STREAM CONDITIONS
(From Chow 1959)
Description of Stream Average n
Clean straight channel, full
stage, no riffles or pools 0.030
Same as above, but with more
stones and weeds 0.035
Clean winding channel, some
pools and shoals 0.040
Sluggish reaches, weedy,
deep pools 0.070
Natural channel, variation in
depth, some logs and dead
fallen trees 0.125
Natural meandering river,
many roots, trees, brush
and other drift on bottom 0.150
It should be emphasized that no data has been found directly relating the
effect of altering the roughness of a natural stream on its USP and sus-
pended sediment concentration. From a stream management perspective, further
research should be done to more precisely establish the relationship between
the two variables.
3. slope or Gradient of Stream Channel: The main way in which a stream
can adjust its~~slope is via meandering. By doing so, a channel decreases not
only its slope but also its USP and potential for transporting sediments
(Wertz 1963). Unfortunately, present stream management practices emphasize
35
-------
maintenance of straight channels which will have larger flow velocities,
slopes, USP's and increased potential for transport of sediment and erosion
of stream banks (Emerson 1971, Hansen 1971).
The magnitude of the effect of several of these variables on USP was
demonstrated by a study of the Middle Fork of the Vermillion River (Stall and
Yang 1972). Measurements of area of flow, roughness coefficients, width,
depth, velocity, and slope were made on a 3360 feet test reach containing
three riffles and two pools. Measurements were made at low, medium, and high
discharges and USP was calculated for the natural stream and an "equivalent"
channel without pools and riffles (Table 7). USP was reduced by 23-26% in
a pool and riffle stream during medium and low flow conditions when compared
to an equivalent uniform channel of the type normally formed by present chan-
nelization practices. Pools and riffles served as an effective means for the
channel to reduce USP and its erosive energy and sediment transporting capa-
bility during low and medium flows. At high flows the pools and riffles were
obscured and had no effect on stream gradient or USP (Figure 11). Unfortu-
nately, suspended sediment concentrations were not measured and similar types
of data were not collected for an area of pools and riffles in conjunction
with meandering.
TABLE 7. UNIT STREAM POWER FOR THREE FLOW CONDITIONS, MIDDLE FORK VERMILLION
RIVER NEAR OAKWOOD (Modified from Stall and Yang 1972)
Amount
Q
(cfs)
18.9
43.6
681
Flow
Frequency
F
(% of days)
0.80
0.60
0.15
Unit
(foot-pounds
Pools
and
Riffles
0.000282
0.000452
0.002526
Stream Power
per pound
Uniform
equivalent
channel
0.000382
0.000589
0.002522
per second)
reduction
%
26.2
23.3
0
However, data collected at Black Creek (Karr and Gorman 1975) relating
suspended sediment concentrations to stream morphology correlates well with
the results of Stall and Yang (1972)- Karr and Gorman measured suspended
solid concentrations in a channelized section above a forest, a meandering
pool-riffle section within forest and a channelized section below forest.
The meandering pool-riffle section acted as a sediment trap during low and
medium flow conditions, resulting in a decrease of 28% in suspended solids
by the time the flow reached the lower end of the forest (Fig. 12). This
reduction is similar to the reduction in USP caused by pools and riffles
shown in Table 7. As the flow left the forest, suspended solid concentra-
tions attained the same level as the channel above the forest. The roughness
36
-------
(n) is the likely factor responsible for the decreased sediment loads -since
the slopes (S) are lower (.25) above and below the woodlot than in the
woodlot (.40).
We conclude that sediment reduction in the Karr and Gorman study
results from the effect of channel morphology instead of the impact of the
near stream biota, at least under normal flow regimes. However, during per-
iods of high runoff, the forest or other vegetation along the stream might
act in conjunction with the stream morphology to improve water quality. To
separate the effect of these two variables, one would have to compare streams
with and without vegetative filters along a major portion of their drainage
length, rather than a mere patch of natural vegetation as observed by Karr
and Gorman. Such a comparison should be made for a wide variety of flow
regimes.
At very high flow rates (100 yr. storm) no reduction in suspended sedi-
ment concentrations occurred at Black Creek, probably because pools and rif-
fles were obscured and no reduction in USP occurred. This result, which is
similar to the result of Stall and Yang (1972), suggests that knowing the
flow (Q) at which no reduction in USP occurs and its frequency (F), one
could predict what fraction of the year pools would act as sediment traps.
110
= Riffle
P=Pool
105
05
UJ
100
R
P
R
P
R
Water surface profiles
High flow
Medium f I ow
_L
J_
Streambed
_L
800
2400
stream
3000
(ft)
Figure 11.
1600
Distance along
Bed and water surface profiles for several flow conditions in
the Vermillion River. Note that the pool and riffle character of
the stream is obscured as flow volume increases. (Modified from
Stall and Yang 1972)
37
-------
—
g^oo
(f)
."5 90
O
(f)
-o 80
(D
c
g. 70
(/)
D
i/> <*
-
• i
-
'• — .<
-
—
—
7 i
Fo
i^^
*^<
^e
ct
1
i
i
i
i
i
i
\
\
t
\
i
t
i
\
\
*
1
I
>\)
1
0—0
/
A
1
^
I
/
/
/
Direction of
flo\
A/ tl
/V F
1 1
1
12 11 10 9 87 6543
Station number
2 1
Figure 12.
Changing suspended solids loads in agricultural and forested
sections of a headwater stream. Dashed lines indicate margin
of forest. High sediment loads at station 5 are due to an ero-
sion problem at the outlet of a field tile. Data from July 1974
to October 1975. Sample size varies from 12 to 16 at each sta-
tion. (Modified from Karr and Gorman 1975)
From this brief review of the literature and data relevant to the rela-
tionship between the "manageable" parameters of stream morphology and their
effects on water quality, four critical points have been established:
1. A stream naturally decreases its USP and sediment transporting capa-
bility by increasing its bed roughness and by making lateral (mean-
dering) (Hussey and Zimmerman 1953) and vertical (pools and riffles)
adjustments (Yang 1971a,b, Stall and Yang 1972).
2. USP is reduced by pools and riffles only at intermediate and low
flows.
3. The effect of meanders on USP in conjunction with pools and riffles
at various flow rates does not appear to have been quantified.
4. Channelization in agricultural areas destroys nearly all characteris-
tics of "natural" stream morphology. As a result USP is increased
38
-------
and the ability of the stream to transport sediment and erode its
banks is enhanced.
These four points, along with the data of Karr and Gorman (1975), indicate
that allowing streams to maintain their natural morphology or allowing them
to reinitiate meandering to reduce USP and suspended sediment concentrations
is a feasible management alternative for improving water quality, especially
during periods of low and intermediate flows. During these periods pools
act as sediment traps to reduce suspended sediment concentrations and in-
crease the suitability of the water for human uses. The overall effect on
aquatic organisms needs more detailed investigation.
This raises the question: Are materials deposited in low flow periods
flushed downstream during later storm events? The quantity of material
reaching the final sediment trap such as a lake or reservoir would not be
affected (unless of course stream bank erosion is a major sediment input)
but the sequence of input would be altered. Instead of a continual input
into the lake or reservoir, trapped sediment inputs would be restricted to
high flow periods when pools are flushed (Lane and Borland 1954, Straub
1942). The effect of flushing versus a continual input of attached nutrients
may have significant implications for nutrient dynamics in the receiving
body of water, especially during low flow periods in mid and late summer when
nutrient concentrations are frequently reaching limiting levels for algal
uptake. Furthermore, the nutrients attached to the sediments trapped during
these periods may have their eventual avilability altered by aquatic inverte-
brates (Davis 1974) before being flushed into the lake or reservoir. Also,
flushing of the sediment versus a continual input may have a significant
effect on the fraction of sediment trapped by the lake or reservoir via
decreasing its detention time (Rausch and Heinemann 1975) . All of these
possibilities should be examined by more detailed research on (1) the quanti-
ty of sediment trapped by the stream, (2) the size fraction of sediment
trapped by the stream, (3) timing of sediment transport, and (4) the biologi-
cal and physical interactions involved both on the stream bottom and in the
lake.
However we feel the main benefit, with respect to water quality, from
a more natural stream morphology would be a substantial reduction in the sus-
pended sediment concentration in a stream during low and intermediate flow
periods, resulting in monetarily important improvements in water quality.
The costs of such a management practice would include (1) taking some land
out of production to maintain a natural meandering channel and (2) the eco-
nomic effect of decreasing the rate of land drainage. Rough estimates for
(1) could be obtained by using one of the empirically determined relation-
ships between meander amplitude and channel width (Leopold and Wolman 1960,
Leopold et al. 1964). One should expect a large error in this type of esti-
mate (see Leopold et al. 1964). Determining the possible effect of decreas-
ing 'the rate of land drainage (#2 above) may also be difficult. However, if
natural stream morphology was used in conjunction with a vegetative filter
along the streambank and high quality tile lines were maintained.any detri-
mental effects would probably be minimal, especially in light of the length
of time (4-6 days) corn and soybeans can withstand flooding (Hamilton 1969).
39
-------
SECTION 7
DETERMINANTS OF SEDIMENT LOADS IN FLOWING WATERS
As noted in the introduction to this review early efforts in the soil
conservation field emphasized the control of erosion to insure the mainte-
nance of the productive capacities of soils. Recently, conservationists have
recognized that meeting this objective does not necessarily result in mainte-
nance of water quality. For example, in many situations soil losses of 5
tons/acre are tolerable as the soil replaces itself at that rate. Although
that loss from the soil may be tolerable, the addition of 5 tons/acre into
flowing waters has serious consequences for water resources. As a result of
this problem, conservationists are attempting to develop a set of water
quality criteria.
The theoretical foundation for calculation of soil loss is the Universal
Soil Loss Equation (USLE). The present form of the equation is a result of
more than 20 years of research by many scientists (Wischmeier and Smith 1965).
It has remained relatively unchanged for the past decade.
The equation is used by agriculturists to predict the average soil loss
in tons per acre per year. This is compared to the "soil-loss tolerance",
the maximum rate of erosion that will result in sustained production indefi-
nitely. This model is presented in the form of an equation:
A=RKLSCP-
Each of the terms of the equation are defined and discussed briefly
below. For more detailed discussion of the model and its use, the reader
is referred to Agriculture Handbook No. 282 (Wischmeier and Smith 1965).
Computed Soil Loss (A). The average soil loss in tons per acre per year
as computed from the six factors of the Universal Soil Loss equation.
The Rainfall Factor (R). This is the number of erosion-index units in
the average year of rain. An erosion-index unit is a measure of the
erosive force of specific rainfall reflecting the combined effect of
rainfall impact to dislodge soil particles and runoff to transport
dislodged particles.
The Soil-Erodibility Factor (K). This component of the equation measures
the susceptibility of the soil to erosion. Since erodibility varies with
s.1 ope, cover, management, and other factors it is essential that erodi-
bility be measured under controlled conditions. Generally, it is
expressed as a relative value for a specific soil in cultivated continu-
40
-------
ous fallow on a 9% slope 72.6 feet long. Soil characteristics which
affect the K-factor include, among others, infiltration rate, permeabil-
ity and total water-holding capacity.
The Slope-Length Factor (L). This is the value obtained by computing the
ratio of soil loss from a field of any length to that of a standard field
with a length of 72.6 feet. Soil type and gradient are assumed to be
constant.
The Slope-Gradient Factor (S). This is the ratio of soil loss from the
field to that from a 9% slope, other factors held constant.
The Cropping Management Factor (C). The factor C in the soil-loss equa-
tion is the ratio of soil loss from land cropped under specified condi-
tions to the corresponding loss from tilled, continuous fallow. This
factor attempts to evaluate the combined effect of cover, crop sequence,
and management practices. Crop residues may be left on the surface,
removed, chopped, or plowed under. Crops may be grown continuously or
rotated in various combinations. These and other variations in land
management which change erosion rates are incorporated into factor C.
The Erosion-Control Practice Factor (P). The factor P is the soil loss
with various practices relative to soil loss with straight-row farming,
up-and-down slope, contour tillage, stripcropping on the contour, ter-
race systems, and stabilized waterways are the most important practices
involved in the P factor of the USLE. A number of practices such as
improved tillage regimes, sod-based rotations, and fertility treatments
contribute to erosion control, but these are considered conservation
cropping and management practices. They are, therefore, incorporated in
the factor C discussed above.
Recently, a number of studies (Stall 1964, Karr and Gorman 1975, Great
Lakes Basin Commission 1976) have shown that the USLE may not be useful in
predicting the sediment transported by a stream or river. A regional analy-
sis of lakes and watersheds in central Illinois showed a predicted soil loss
of 3.2 tons/acre, while deposition in lakes averaged only about 1 ton per
acre per year (Stall 1964). The proportion of the eroded soil that reached
the lake bed varied among lakes from 10 to 50%. In the Maumee River Basin
only about 11% of total erosion is yielded annually as suspended sediments
to Maumee Bay (Great Lakes Basin Commission 1976). Clearly, much of the
material eroded from the land surface, using the assumptions of the USLE,
does not reach lakes or reservoirs.
This raises the question of where the sediments are deposited. Perhaps
they are deposited in the channels of the streams and rivers that flow into
the lakes. Perhaps the soil is deposited on the land surface before it
reaches the stream or on the banks of the stream. Or if it is in fact
reaching the lake, it may be carried out by the discharge water.
Alternatively, the techniques for measuring and calculating amounts of
sediment deposited in the lake or reservoir may not be accurate. In the
following discussion we shall comment on the problems associated with each of
these possibilities.
41
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1. Errors in calculating volumes of lake sediment. There certainly is
some error associated with this factor but it is probably minor when compared
to the range of variation observed among lakes.
2. Sediment removed from lakes by discharge water. The potential for
error here is larger. No doubt some small particles move downstream by this
route. Variables that might be considered here include the size, turnover
time, and cross-sectional area of the lake (Rausch and Heinemann 1975). Long,
narrow lakes or small lakes might have rapid flowthrough rates which result in
considerable fine particle material being carried out of the lake before it
is deposited. However, as Stall (1964) reported, a large share (39%) of the
sediment in lakes is clay, suggesting that much of the fine material is de-
posited in the lake bed. In summary, there is reason to believe that this
factor may be of some significance in the variation among lakes but more
careful study is needed.
3. Soil deposited on land surface at varying distances from the channel.
This problem is certainly dealt with in the USLE in the form of erosion con-
trol practices (P). However, a larger problem is the difficulty involved in
scaling differences between models and the real world. For example, erosion
determined from study of a small plot can only approximately be expanded to
very large areas. The problem is even more complex when the larger area
has a diversity of slopes, for example, and includes some pockets from which
there is no outlet except percolation down through the soil. Furthermore,
even small discontinuities such as fence rows, field borders, concave vs.
convex slopes as the floodplain is approached (Young and Mutchier 1969) are
commonly not incorporated into USLE determinations. This general factor—
sediment deposition before runoff reaches the stream—needs more investiga-
tion and is the larger class in which greenbelts should be included.
4. Deposition in the stream channel. Recognition of this possibility
stimulated the excellent research of Stall and Yang that resulted in the idea
of Unit Stream Power to predict suspended sediment concentrations. As dis-
cussed above (Section 6), this theory suggests that sediment concentration
is an increasing function of unit stream power (Figs. 10 and 13), and the
variation in suspended sediment loads for a given stream power should be low
(Fig. 13, stippled area). As is often the case, the real world is only a
rough approximation to the theory. For any USP there is commonly consider-
able variation in sediment loads (Fig. 13, cross-hatched area). That is,
sediment concentration is an increasing function of energy in the stream,
%which is an incresing function of USP. This is true as long as a myriad of
other factors are held constant: stability of bank, erodibility of soils,
bedload availability, variation in land use, and many others. A different
line could be necessary in Fig. 13 for each such factor, therefore accounting
for the variation in sediment load with USP which is frequently observed.
Clearly, the unit stream power concept is useful but some variation in
sediment loads is unaccounted for when this model is used. An example will
illustrate the weaknesses of the single factor approach of USP to account for
variation in sediment loads. Two identical forested watersheds are con-
42
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trasted in the following way: one is cleared of forest and planted with a
row crop such as corn, while the second is left as a forested control. The
streams in these two watersheds would carry markedly different sediment loads
despite identical unit stream powers. Clearly, velocity will vary due to
differing runoff rates but the general point here is that with the same
slopes and at similar flow rates sediment loads will not be the same in the
two streams.
What is needed then is a model, analogous to the universal soil loss
equation, which will predict sediment loads for a flowing stream. This
model, dare we call it the Universal Sediment Load Model (Equation), must
consider a complex of factors. It is too early to specify all the parameters
of this model. However, the previous discussion and comments in following
sections show that the situation is more complex than the Universal Soil
Loss Equation might lead us to believe. Among other things a realistic sedi-
ment model must consider the magnitude of erosion from a watershed, how and
where eroded material is removed before runoff reaches waterways, and the
addition of sediment from underground (drain) tile systems. Finally, as
discussed in a later section, the nature of the erosion-deposition equili-
brium between the terrestrial and aquatic environments must be clearly
understood.
ID
03
O
c
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SECTION 8
EFFECT OF STREAMSIDE VEGETATION ON WATER TEMPERATURE
This report has emphasized the feasibility of using vegetation along
streams to reduce sediment and nutrient inputs into agricultural drainages.
Another potential use of this vegetation is to control water temperature.
Past evaluations of the effect of streamside vegetation on water temperature
will be reviewed here, along with an examination of the significant effects
of temperature on dissolved oxygen levels and nutrient dynamics, especially
the release of nutrients from sediments and their uptake by nuisance algae
and periphyton. The importance of water temperature in maintaining a "fish-
able" water quality will be discussed in a later section of this report.
Because of the importance of temperature in regulating the physical and
biotic characteristics of streams, a number of studies have documented the
effect of streamside vegetation on water temperature. Green (1950), in a
study at the Cowetta Hydrologic Laboratory, documented the effect of land use
on water temperature. For a period of one year he compared the temperature
of a stream on a farm which had originally supported a hardwood forest but
for eight years had been under cultivation and pasturage and that of a
stream in mature hardwood forest (Fig. 14). The weekly maximum temperatures
of the farm stream ranged from 5.0 to 12.8°C above the forest stream (average
6.4°C). Both streams were coldest during the month of February but the
temperature of the forest stream frequently ranged as high as 3.9°C above
the farm stream. Similar effects of vegetation on temperature extremes were
found in studies of a stream before and after vegetation was removed from the
streambank (Gray and Eddington 1969). In another study, stream temperatures
inside a small woodlot (19°C) were much lower than in unshaded areas (28°C)
nearby (Karr and Gorman 1975). These data indicate vegetation serves as an
effective buffer against temperature extremes; shaded streams are cooler in
the summer and warmer during winter.
A more detailed analysis of the result of several types of land treat-
ment on stream temperature was performed in the Appalachian Mountains
(Swift and Messer 1971). Clear-cut streams averaged (5.5-6.5°C) warmer than
forested streams. During periods of highest temperatures, temperature mini-
mums were also increased. This indicates that the streams did not have a
"normal" cooling-off period during the night and that periods of elevated
temperatures may be prolonged. Long-term elevations in temperatures can
have significant effects on the energetic "balance sheet" of aquatic eco-
systems, resulting in major alterations in their biotic components. From a
management perspective, one other important observation was made by Swift and
Messer. If streamside vegetation was left to shade the channel, while the
44
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u_
GL
£
80
60
40
i i i i
JFMAMJJASON D
Month
Figure 14. Seasonal changes in water temperatures of streams from forested
and farm watersheds (From Greene 1950).
rest of the woods was clearcut, only minor changes in stream temperature
were observed. This latter point suggests that if a minimal vegetative
"buffer strip" is left along agricultural drainages, significant decreases
in stream temperature and improvements in water quality could be expected.
More recently, a detailed analysis of the use of "buffer strips" to
control temperature has been made in the field of forestry (Brown and Brazier
1972). Previous mathematical analyses by Brown (1969) and Brown and Krygier
(1970) demonstrated that net thermal radiation in relation to stream dis-
charge was the primary determinant of stream temperature. When strips of
brush or trees were left along the stream, no increase in temperature
occurred. From an economic and management perspective it is therefore desir-
able to know whether controlling the temperature of the stream is a function
of the volume of vegetation in the buffer strip, the strip width, or the
density of the canopy of the strip which is perpendicular to the suns rays.
An extensive examination of temperature in various streams with different
types of buffers indicated that angular canopy density (ACD - a measure of
the shading ability of the vegetation) is the only buffer strip parameter
correlated with temperature. The generalized relationship between ACD and
heat input into a stream is illustrated in Figure 15. Buffer strip width
was not important. A buffer strip 5-10 feet wide was as effective at temper-
ature control as a strip 50 feet wide, as long as its ACD was high. Brown
and Brazier (1972) also observed that buffer effectiveness decreased with
increasing stream size (Figure 16). Small streams have the greatest tempera-
ture problem but they are also the easiest to control, due to the inverse
relationship between temperature change and stream discharge for a given
input of thermal radiation. These results indicate that little or no land
would need to be taken out of production for temperature control on small
streams. Further, natural processes will provide sufficient ACD levels on
small streams through succession as cottonwoods, willows, or other types of
vegetation invade the stream banks. Finally, if temperature control is
accomplished in the upper reaches of drainages, a reduction in temperature
associated problems will result in upstream areas as well as in downstream
areas, including small lakes and reservoirs.
45
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Q.
C
03
E
Figure 15.
Angular canopy density
Hypothetical relationship between angular canopy density and
thermal input to streams (Modified from Brown and Brazier 1972)
10
to
C
u
0)
M—
H—
-------
The importance of temperature in determining various water quality para-
meters and regulating biotic communities cannot be overemphasized. As tem-
perature increases, the capacity of the water to hold oxygen decreases
(Table 8). Since oxygen is utilized during the decomposition of organic mat-
ter, at elevated temperatures the ability of the stream to assimilate organic
wastes without oxygen depletion is reduced. This exaggerates the impact of
each additional unit of waste added to the system.
TABLE 8. RELATIONSHIP BETWEEN TEMPERATURE AND MAXIMUM DISSOLVED OXYGEN
CONCENTRATION IN WATER
Temperature C Maximum oxygen concentration (jpm)
0 14.6
10 11.3
20 10.7
30 7.6
Even more important with respect to water quality and eutrophication is
the effect of temperature on the release of .nutrients from sediments.
Sommers et al. (1975b) studied the effect of incubation temperature on solu-
ble nutrient concentrations. They found significant effects of temperature
on the rate at which insoluble (attached nutrients) were converted to soluble
and readily available forms. Figure 17 illustrates the relationship between
temperature and amount of phosphorus released from the sediments in a 12-week
period. This plot indicates an exponential increase in phosphorus released
with an increase in temperature. Slight increases in temperature above 15°C
produce substantial increases in the amount of phosphorus released.
These data, along with those previously discussed, indicate that by re-
moving vegetation which shades agricultural drainages, several detrimental
patterns will develop: (1) Increases in temperature will occur during sum-
mer periods (5.5-9.0°C), resulting in increasing rates of phosphorus dis-
association from sediments. (2) Increases in phosphorus concentrations in
the drainages result in higher nutrient concentrations in receiving bodies
such as lakes and reservoirs. (3) Increasingly large blooms of nuisance
algae and periphyton will appear because of elevated nutrient concentrations,
temperatures, and light availability. The effect of all these will be to
decrease water quality and the quality of biotic communities.
The importance of streamside vegetation clearly goes beyond its use in
filtering sediments and nutrients from surface runoff. Its potential for
temperature control, enhancement of the oxygen carrying capacity of the
stream, and reducing nutrient availability and utilization is evident. Its
significant economic impact on fishery resources will be discussed in a
later section of this report. These benefits appear to outweigh the negli-
gible cost of this management practice. Little.or no land would have to be
taken out of production and natural processes would provide the vegetation
47
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for shading the streams by processes of natural succession. To fully evalu-
ate this management alternative, more detailed analyses of its benefits to
water quality and the stream biota in relation to the cost of decreased rate
of drainage must be performed.
to
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Q.
CO
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Figure 17-
10 20 30
Temperature (C)
Effect of temperature on the release of phosphorus from sedi-
ments over a 12-week period (Data from Sommers et al. 1975b).
48
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SECTION 9
IMPACT OF NEAR STREAM VEGETATION AND CHANNEL MORPHOLOGY ON STREAM BIOTA
Streams may be narrowly viewed as a means for transporting water axvay
from the land, as collecting points for a water supply, or as outlets to
carry away the refuse of modern society. This combination of uses relates to
the needs for water quality and is therefore relevant to the subject of
greenbelts—especially when increasing demands are being placed on resource
managers to improve the biological aspects of environments and to provide
areas suitable for use by an increasingly recreation oriented public. This
trend is demonstrated by the federal government's call for "fishable and
swimmable" water by 1983. Therefore, alternatives proposed for controlling
non-point pollution from agricultural areas must also be evaluated in light
of their effects on the biota of streams and on recreational opportunities.
A surprising fact to most non-biologists is that small headwater drain-
ages in agricultural watersheds are extremely important in maintaining fish-
able populations (sport and commercial) in larger streams, rivers, or lakes.
They are important as breeding grounds for many valuable species which mi-
grate into these areas from lakes or large rivers to spawn (Hall 1972, Smith
1972, Karr and Gorman 1975). Also, they serve as breeding grounds and/or
permanent habitats for the smaller fish used for food by these species. If
these environments are disrupted or destroyed, a major source of food for
the commercially valued species will be destroyed and many of the valued
species will be prevented from reproducing. This happened in the Lake Erie
basin and was one of the major causes of the destruction of a multi-million
dollar fishery in that region (Regier and Hartman 1973, Smith 1972, Ryder
and Johnson 1972).
In this section we briefly examine the effects on the biota in headwater
streams of (1) elevated sediment loads, (2) increased water temperature due
to removal of vegetation along stream banks, (3) disruption of the aquatic
food chain by removal of allochthonous (terrestrial) inputs of energy, and
(4) decreased habitat diversity due to stream channelization. With this
information we then evaluate the potential of greenbelts for improving the
biological quality of streams. In Section 10 we briefly outline some of the
possible recreational benefits of greenbelts.
EFFECTS OF SEDIMENT
Fish
Most research on the effects of sediment on fish emphasizes commercially
49
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important species such as the salmonids. For adult fish only very high con-
centrations of sediment (>20,000 ppm) cause mortality, primarily by clog-
ging the opercular cavity and the gill filaments (Wallen 1951). This pre-
vents normal water circulation and aeration of the blood. Such high sedi-
ment levels are rarely encountered in streams.
However, indirect effects on adults may occur at much lower sediment
concentrations. In areas with slightly increased suspended solids loads
(35 ppm) adult cutthroat trout showed no increase in distress or mortality,
but the fish did cease feeding and move to cover (Bachman 1958 cited in
Cordone and Kelly 1961). Similar subtle changes in behavior were noted in
smallmouth bass and green sunfish when turbidities were elevated (14-16 JTU)
for 30 days (Heimstra et al. 1969). Furthermore, the normal social hier-
archy was disturbed with elevated turbidities. When in search of spawning
areas, adult salmon swim through areas of high turbidity in search of clear
areas for spawning (Cooper 1956) . These results suggest that adult fish
tend to be physiologically resistant to the direct effects of elevated
sediment levels but that their behavior can readily be altered by only slight
increases in turbidity levels (Swenson et al. 1976).
The major effect of sediment on fish populations is the disruption of
normal reproduction (Cordone and Kelly 1961). When sediments settle out of
suspension they frequently cover essential spawning grounds of fish, cover
eggs, or prevent emergence of recently hatched fry. One of the earliest
experiments to document the effects of sediment on egg survival was that of
Harrison (1923, Table 9). As the particle sizes in the bottom decrease, the
survival rate of eggs declines. A number of other studies have documented
similar effects of sediment on egg survival and fry emergence (Shapavalov
1937, Shapavalov and Berrian 1940, Shapavalov and Taft 1954). The cause of
the reduced survival is a decrease in circulation of water around the devel-
oping eggs, resulting in the inhibition of oxygen uptake and carbon dioxide
release. This results in reduced metabolic rates which are lethal if inhi-
bition is prolonged (Snyder 1959). Thus, the effect of sediment on spawning
success has been one of the major causes for the decrease in the quality of
fisheries throughout the United States and has prompted some (Langlois 1941)
to suggest that changes in bottom type are of utmost importance in modifying
the breeding grounds and determining fish diversity. As bottom type is sim-
plified by the deposition of sediment, species diversity decreases. Recent
research (Gorman and Karr 1977) suggests a direct relationship between
species diversity and bottom diversity (Fig. 18). However, the low correla-
tion coefficient suggests that other factors are also important in determining
species distributions. As will be pointed out below, the effect of sediment
on bottom type is only one of several physical factors which interact to
determine the structure of fish communities in streams. Thus, the single
problem-single solution approach frequently used in the past (.e.g. reduction
in sediment inputs to improve fisheries) will have limited usefulness for
improving the quality of the stream biota.
Invertebrates
Many aquatic invertebrates spend a large proportion of their life on
or in the bottom substrate. Sediment deposition, resulting in decreased
50
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TABLE 9. THE EFFECTS OF PARTICLE SIZE OF SUBSTRATE ON EGG SURVIVAL IN SOCK-
EYE SALMON (Oncorhynchus nerka) (From Harrison 1923).
Number of
eggs planted
Description of Nest
Number of
eggs hatched
500
500
500
500
500
Large gravel, very little sand, no clay
or top covering of silt
Small gravel, some clean sand
Small gravel, top coating of silt
1/2 inch deep
Very fine gravel, sand, and small amount
of clay in sand
Very fine gravel and much clay or mud
in sand
420
350
325
200
170
>>
£2*5
CD
"^2.0
-------
substrate types, will inevitably cause changes in the species diversity and
numerical abundances of benthic organisms (Ellis 1931, Tebo 1955, Wilson
1957). Commonly these changes can be related to changes in substrate diver-
sity (Smith and Moyle 1944, Barman 1972, Fig. 19). There is a general rela-
tionship between substrate diversity and species diversity of molluscs but
the scatter, as in the fish data discussed above, suggests other environ-
mental variables are also important. Other studies have shown the importance
of depth diversity and water velocity (Zimmer and Bachman 1976), temperature
(Sprules 1947) and organic inputs from terrestrial environments (Ross 1963,
Woodall and Wallace 1972, Cummins 1975) in determining the distribution and
abundance of aquatic invertebrates. Clearly, reduction in sediment inputs
must be accompanied by improvements in other water quality characteristics
for maximal benefits to invertebrate populations.
15
(S)
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ecosystems will often decline. A comprehensive study of the energetics of
Red Cedar River in Michigan showed that stream productivity declined signifi-
cantly following siltation (King and Ball 1967). When turbidity levels
shifted from 20-30 JTU to 380 JTU, Aufwuchs production declined by 68% and
heterotrophic energy consumption declined by 58% (Table 10) . Sediment increases
resulted in reduced ecosystem productivities across all trophic levels.
TABLE 10. ENERGY BUDGETS FOR THE RED CEDAR RIVER BEFORE AND DURING PERIODS
OF HEAVY SILTATION, SUMMER, 1961. Units are cal uT2 day'1 (King
and Ball 1967)
Trophic level Energy fixed
Before siltation During siltation
Auto trophic Aufwuchs
Macrophytes
Total primary producers
1,140
127
1,267
368
127
495
Heterotrophic Aufwuchs 360 170
Insects:
Herbivores (net yield) 43 -9
Carnivores (net yield) 13 6
Tubificid worms 65 -39
Energy Required
Heterotrophic Aufwuchs 4,000 1,889
Total insects 283 4
Tubificid worms 200 -115*
Total energy required 4,483 1,893
*Negative values are not included in the total energy required.
Summary
Clearly, the impacts of sediments on the stream biota include alteration
of the structure and productivities of plant, invertebrate, and vertebrate
communities. Reductions in sediment loadings will improve the biota of
streams but, as we will demonstrate below, more comprehensive management
53
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programs will be necessary to improve stream biotas; that is, efforts to re-
duce sediment loads must be accompanied by more informed management of other
stream characteristics.
EFFECTS OF TEMPERATURE
Temperature has a significant effect on oxygen concentrations and nu-
trient dynamics within streams (.see pp. 44). Elevated temperature, due to
the removal of vegetation along stream banks, increases the susceptibility
of biological systems to inputs of nutrients and other pollutants. Tempera-
ture changes, regardless of other physico-chemical changes, may also cause
shifts in the entire structure of aquatic communities.
A clear understanding of this problem depends on knowledge of the ener-
getic processes of organisms. The use of energy by an organism can be repre-
sented by a flow chart (Figure 20). Energy is ingested but only a fraction
of what is ingested is actually available to the organism as net energy for
utilization. This net energy must then be divided among standard metabolism
(maintenance of body functions), active metabolism (providing energy for
swimming, feeding, etc.), growth, and reproduction. The ability of an organ-
ism to survive and reproduce is dependent on the organism being in an envi-
ronment where some fraction of energy input is available for growth and
reproduction.
Food Energy
J-
Feces
[Assimilated Energy!
I
NH
[Net Energy
Standard
Metabolism
Active
Metabolism
[Growth I [Reproduction!
Figure 20. Flow chart illustrating the basic pathways of energy flow in
organisms.
Because fish are cold-blooded organisms (poikilotherms), temperature
is extremely important in determining their standard metabolic rate (Brett
1972). As temperature increases, standard metabolism increases but other
factors, such as feeding rates (energy intake), also increase. As a result,
each species has an optimal temperature for feeding, general activity,
54
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growth, and reproduction. This can be illustrated by comparing two hypothe-
tical fish species (Figure 21). For both species, activity, food consump-
tion, and in turn growth, decrease at temperatures below the optimum. At
temperatures above the optimum, food consumption starts to decrease but more
importantly, increasing standard metabolism demands more and more of the
energy value of the food with less being available for growth and reproduc-
tion. This is of course a very simplified explanation of the effect of
temperature on the growth of fish. Numerous other factors such as food
availability, age of the fish, and oxygen concentration will affect the
exact form of the relationship. A more detailed discussion of these vari-
ables can be found in Warren (1971) or Brett (1964, 1970). Hypothetical
species 1 (Fig. 21) has a temperature optimum of 20°C. At this temperature
it has the maximum amount of energy available for growth and reproduction,
while species 2 has only a minimal amount of energy available for these acti-
vities because of decreased food consumption. If the temperature of the
water is increased to 25°C, species 2 would then have maximum energy avail-
able for growth and reproduction while species 1 would have little energy
available because of its increasing standard metabolic requirements.
03
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To
u
_*:
en
t_
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Food consumption
\
Active metabol.
Standard metabol.;
,/^C. jsy TL /^^ >^y~v 7^/^A. /^/ >- /%/ f^y -ic**
spec ies 1
species 2
15 20 25
20 25 30
Temperature (C)
Figure 21. Theoretical effect of temperature change on food consumption and
energy budget of two hypothetical fish species (Adapted from
Warren 1971).
55
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This illustrates an important point. When vegetation is removed from
along streambanks and water temperatures increase from 6-9°C (Gray and
Eddington 1969, Karr and Gorman 1975), it may become energetically impossible
for species with lower temperature optimums to continue living in the area,
regardless of changes in sediment loads, habitat structure or other environ-
mental conditions. A shift in community structure may occur with resident
species being replaced by the frequently less desirable species which are
more tolerant of increased temperatures.
A common misconception is that shifts in species composition will not
occur unless temperature increases are substantial, especially in warmwater
streams. It is believed that since warmwater species have higher tempera-
ture optimums than species living in coldwater streams, they have a greater
"assimilative capacity" for temperature increases. To test if this was true,
predictions of changes in fish communities of a coldwater (Columbia) and
warmwater (Tennessee) river were made based on the preferred (optimal) and
lethal temperatures of their respective species CBush et al. 1974). The per-
cent of species lost versus temperature is shown in Figure 22. In both
streams, significant individual losses start to occur after temperature
changes of 5-6°C. However, as a community, the preferred temperature is
closer to the lethal limit as one moves from cold to warmwater streams.
Warmwater species do not have a greater assimilative capacity for tempera-
ture increases. These observations, along with a
recent extensive field and laboratory study demonstrating that temperature is
an extremely important factor determining the distribution of fish species
(Stauffer et al. 1976), indicate that removal of vegetation along small
streams will result in substantial changes in fish community composition by
causing temperature changes which exceed the preferred and lethal limits for
species with lower temperature optimums and favor those with higher optima
and lethal limits. Similar arguments could be made for the effects of tem-
perature on invertebrate distributions. If a major goal of present research
on non-point pollution in agricultural watersheds is an improvement in the
biota of streams and their "fishability," substantially more effort must be
directed towards the effect of near stream vegetation on water temperature
and the distribution of organisms.
EFFECTS ON STREAM ENERGETICS
Up to now, this report has emphasized the indirect impact of near stream
vegetation on stream biota via its effect on sediment and nutrient inputs and
temperature fluctuations. An important direct effect of the removal of this
vegetation is disruption of the aquatic food web, especially in those areas
where terrestrial inputs are a major source of energy for the stream.
Headwater streams (stream orders 1, 2, and 3) make up about 85% of the
3.25 million miles of running waters in the continental United States
(Cummins 1975). These areas represent the maximum interface between the
terrestrial and aquatic environments. It is here that most sediment enters
streams and here that extensive channelization and removal of near stream
vegetation is occurring. These are the areas which are most dependent on
near stream vegetation for an energy source and are also extremely important
as spawning and nursery grounds for many commercial and sport species which
spend their adult life in lakes or large rivers (Smith 1972, Karr and Gorman
56
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1975, Hall 1972, Hynes 1970). In these areas most of the energy utilized by
the aquatic invertebrates and fish is terrestrial in origin (Cummins 1975,
Lotrich 1973, Chapman and Demory 1963, Hynes 1963, Minshall 1967 - Figure
23). Once the coarse particulate organic matter (CPOM) like leaves, twigs,
etc. is in the stream, either the dissolved organics leached from it are
utilized or the CPOM is directly ingested by shredders which have powerful
jaws to shred the organic matter and then digest the microflora growing on
it. The shredders then egest a fine particulate organic matter (FPOM) which
is utilized by a group of invertebrates called collectors. At the top of
this food web are the fish predators.
GO
O
£100
s.80
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Cold water
stream
Warmwater
stream
(30°)
Figure 22.
18 24 30 36 42
Temperature (C)
Percent of fish species lost versus temperature in warm and cold
water streams (Data from Bush et al. 1974).
The implication of this web is that in these upstream areas removal of
nearstream vegetation will result in significant reductions in invertebrate
production and, in turn, fish production because of the loss of allocthonous
energy inputs. Studies have indicated low diversity and numbers of inverte-
brates in streams flowing through areas lacking deciduous vegetation
(Minshall 1968). Therefore, if we are to maintain productive fisheries in
streams, we must not only maintain suitable instream habitat for the fish
and their invertebrate food source but we must also maintain a major source
of energy on which both invertebrates and vertebrates depend: the nearstream
vegetation.
EFFECTS OF STREAM CHANNELIZATION
Channelization is one of the most detrimental factors affecting the use
of streams for recreation (including fishing). The primary goals of channel-
ization are to prevent flooding of crops and increase the amount of tillable
agricultural land by allowing rapid drainage. These are desirable goals but
the substantial number of detrimental effects on water quality, fisheries
57
-------
Inputs to Headwater Stream
Coarse participate Dissolved organic
organic matter matter
(CPOM) (DOM)
. . , ,
Ll9ht
I
Producers
Macro Micro
Microbes
/
Flocculation
Scrapers
Shredders
-*Fme participate
organic matter
(FPOM)
Collectors
\
Predators
i
Functional Groups of Headwater Stream
Figure 23. Major components of a headwater stream foodweb. Note the
systems dependence on inputs of organic matter from the
terrestrial environment and processing of that organic matter
by stream animals (Modified from Cummins 1975).
resources, and the recreational potential of streams suggest caution in the
application of technology involving channel modifications. From a number of
esthetic, biological, and water quality perspectives the costs and benefits
of channelization should receive a rigorous economic reevaluation. Included
among its effects are (Fig. 24):
1. Increased stream temperatures and their associated problems due to
removal of vegetation along stream banks (Hansen 1971);
2. Increased bank erosion (Emerson 1971) and turbidities (Hansen 1971)
due to higher slopes and flow velocities, resulting in higher unit
stream-power;
58
-------
U3
STREAM
CHANNELIZATION
Destruction of
pools £ riffles
Cutting off of
meanders &
shortening of
stream length
Deepening of
channel
Removal of
near stream
vegetation
//
Increase in Increase
> stream > flow
gradient velocity
Lowering of
» floodplain
water table
Increased
temperature
\
in Increased Increased Increased
f unit stream * channel s * sediment
power bank erosion loads \
\ N \
\iMore rapid Widening of \
drainage of the channel \
the land \
^il Increased downstream
flood hazard
Loss of habitat
* diversity
V
\
\
\v
^ Loss of potential
aquatic habitat
\
\
V
Decrease in
water quality
BIOLOGICAL
EFFECTS
Figure 24. Factor train analysis of the effects of channelization of the physical
environment and biota of streams (Modified from Darnell, 1976).
-------
3. Increased flooding downstream (Campbell et al. 1972);
4. A reduction in habitat complexity, i.e. riffles and pools are des-
troyed, meanders are removed, the substrate is made uniform, and
cover in the stream channel is eliminated.
One result of the synergistic action of all these effects on the physi-
cal environment is a drastic reduction in both fish and invertebrate popula-
tions. A number of studies have documented this. Congdon (1971) examined
the effect of channelization on fish populations in the Chariton River in
Missouri. He observed an 83% reduction in total standing crop per acre
(Figure 25) and an 86% reduction in standing crop of catchable size fish per
acre (Figure 26) after channelization. Bayless and Smith (1967) reported a
90% reduction 'in catchable size fish (over 6 inches) per acre in 23 channel-
ized streams compared to 36 more natural streams. A 98% reduction in fish
standing crop in the Tippah River in Mississippi was observed immediately
after channelization (Wharton 1970 cited in Congdon 1971). Similar observa-
tions of reductions in fish populations in smaller agricultural drainages
after channelization have also been documented (Karr and Gorman 1975). Other
studies have demonstrated reductions in invertebrate populations due to
channelization (Morris et al. 1968, Moyle 1976). For more references con-
cerning the effects of channelization on the physical environment and fishery
resources, the review by Henegar and Harmon (1971) should be consulted.
Although these studies have provided us with substantial information
concerning the effects of channelization on the biota, there have been very
few attempts to identify and quantify those environmental variables altered
by channelization which affect the distribution and abundance of organisms.
Because the main effect of channelization is the alteration of stream mor-
phology, any relationship which can be established between morphometric
variables and the habitat characteristics of aquatic organisms or morpho-
metric variables and biological parameters should be useful in predicting the
impact of channelization upon aquatic communites and should provide valuable
information for improving engineering designs to minimize the biological
impact of channelization (Zimmer and Bachman 1976, Menzel and Fierstine 1976,
Gorman and Karr 1977).
Zimmer and Bachman (1976) examined the relationship between channel
morphology, habitat diversity, and drift density of invertebrates in 11
natural and channelized streams in Iowa. They found a significant positive
correlation between channel sinuosity and variability of stream depth
(Figure 27a) and stream velocity (Figure 27b). The more the stream meandered,
the more diverse the available habitats were with respect to water depth and
velocity. In conjunction with this, they observed that as sinuosity
increased (i.e. habitat diversity increased) the biomass (Figure 27c) and
number of organisms (Figure 27d) in the invertebrate drift increased. These
data indicate that by designing channels with more sinuosity or leaving
streams with natural meanders, significant improvements in the quality of the
invertebrate biota ar\d availability of food for fish would result.
60
-------
Figure 25.
Figure 26.
CD
L_
U
0)150
.0
§"100
U
O)
150
ro
Unchanneled
Channeled
CA CS
CC B D
Species
RH FC Oth.
Estimated standing crop for fish* of unchannelized (total 304
Ibs./acre) and channelized (total 53 Ibs. /acre) sections of the
Chariton River, Missouri (Adapted from Congdon 1971).
_Q
150
100
QL
O
L.
U
cn 50
c
ID
C
CO
Unchanneled
Channeled
CA CC D CR FC LMB
v /
Species
Estimated standing crop of catchable size fish* in unchannelized
(187 Ibs./acre) and channelized (total 27 Ibs./acre) sections of
the Chariton River, Missouri (Adapted from Congdon 1971).
*Codes for fish abbreviations:
CA - Carp (Cyprinus carpio) RH - Redhorse (Moxostoma)
CS - Carpsucker (Carpiodes) FC - Flathead Catfish (Pylodictis
CC - Channel Catfish (Ictalurus punctatus) olivaris)
B - Buffalo (Ictiobus) CR - Crappie (Pomoxis)
D - Drum (Aplodinotus grunniens) LMB - Large-mouth Bass (Micropterus
salmoides)
61
-------
A similar type of study (Gorman and Karr 1977) established a direct
relationship between habitat diversity and the quality of fish communities.
Streams were examined in three different areas and included both recently
channelized and natural streams. For each sample station, fish species
diversity and diversity of bottom type, depth of water, and velocity of flow
were determined. The relationship between habitat diversity and fish species
diversity (Figure 28) indicates fish are habitat specialists; as the diver-
sity of bottom types, water depths, and velocity increases (or any combina-
tion of them), fish diversity increases.
500
d
0)
TJ
O
U
C 100
05
> 50
1.1
= .62
1.5
u
O
o
CD
(J
C
03
'(b)
r= 78
1.1
1.5
CO
£
D)
O)
CD
Figure 27.
0.7
0.5
0.3
tc)
0.9
1.3
1.7
LO
£
120
C
03
O)
s_
O 80
O
(L>
-Q 40
£
D
r^.72
0.9
1.3
1.7
Sinuosity index
Regressions between sinuosity index and (A) variance of depth
between cross sections (expressed as a percentage of mean depth),
(B) variance of current velocity (expressed as percentage of the
mean), (C) mean drift sample weight, and (D) mean number of
organisms per drift sample. (From Zimmer and Bachman 1976).
62
-------
In the broader perspective of the control of non-point pollution, the
studies by.Ziflmer and Bachman (1976) and Gorman and Karr (1977) have extremely
important implications. Millions of dollars spent on preventing sediments
from entering streams will have minimal return value in improving the quality
of biota if present channelization practices continue to destroy the habitat
of stream organisms. High water quality is necessary for fishable streams
but insufficient in itself if suitable habitat is not maintained.
Figure 28.
1.0 2.0 3.0 4.0
Habitat diversity
Regression of fish species diversity on habitat diversity.
Habitat diversity is calculated from a combination of substrate,
depth, and current characteristics (From Gorman and Karr 1977).
CONCLUSIONS
It should be evident from this brief review of selected aspects of the
effects of land use on stream biota, that any attempt to improve the quality
of those resources must involve a broad based, multi-purpose program. The
reasons for this can be best understood by examining a graphical representa-
tion of how species-are adapted to the physical environment (Figure 29a,b).
An organism's physical environment can be represented by a number of differ-
ent environmental gradients. These gradients might represent factors such
as water temperature, water Velocity, oxygen concentration, size of substrate,
food type, depth of flow and others. For ease of representation only three
environmental gradients are plotted. Each organism can survive under a
limited range on each gradient, e.g. from 15°C to 25°C on the temperature
gradient. With all of these gradients defined for a species, a hypervolume
of conditions under which the organism can survive will be defined. For an
organism that is a generalist, the range of conditions will be large and in
turn the niche volume is larger (Figure 29b). For a specialist, the
range of conditions is reduced and hence the volume is smaller. In either
case a number of environmental conditions must be met before the organism
will be able to survive. If only one of the environmental variables is suf-
ficiently altered, the organism will not be able to tolerate the change and
63
-------
will be displaced, regardless of other environmental conditions. On an
average, the magnitude of the change must be larger to displace a generalist
than a specialist.
Therefore, eliminating only one of the factors detrimental to fish popu-
lations or other stream biota will result in very little improvement in these
resources. For example, if sediments are prevented from entering streams in
agricultural watersheds but vegetation is removed from streambanks, elevated
temperatures will probably prevent any substantial increase in the quality of
the fish community. Or if sediments and nutrients are prevented from enter-
ing streams but channelization is still performed, the lack of suitable habi-
tat will prevent any improvement in fisheries resources. Before substantial
improvements in the biota of streams can be obtained, realistic management
of nearstream vegetation and stream morphology must be used in conjunction
with improved tillage practices. Data presented here suggest that nearstream
vegetation may reduce sediment and attached nutrient inputs and temperature
fluctuations. Further, a more natural stream morphology may reduce sediment
loads and provide suitable habitat for both fish and invertebrates. Data
collected in forested watersheds (Hall and Lantz 1969) and in agricultural
areas (Karr and Gorman 1975), indicates that these factors acting in concert
result in a more productive, diverse, and stable stream biota.
(a)
(b)
x
X
Y|
Y
Figure 29. Range on three environmental gradients (X, Y, and Z) under which
hypothetical generalist (a) and specialist (b) could exist. Note
that the range of conditions under which a generalist can survive
is broader than that of a specialist.
64
-------
SECTION 10
RECREATIONAL BENEFITS OF GREENBELTS
Although space does not permit an extensive evaluation of all possible
benefits to recreation from greenbelts, a few of these should at least be
mentioned. Maintaining a strip of "natural" vegetation along the upper
reaches of streams in agricultural watersheds will provide a substantial
amount of habitat suitable for a number of terrestrial game species. The
improved cover and forage would result in significant increases in pheasants,
dove, quail, rabbits, and many non-game species in these areas (Ferguson
et al. 1975). The magnitude of increase could probably be estimated from
existing data or a minimal field survey. On larger streams, greenbelts
could have a number of significant uses if their development was planned
properly, including fishing, hunting, sightseeing, picnicking, camping,
nature study and canoeing. A study done by Fleener (1971) found that 96,500
trips and over 384,000 hours were spent in these activities in one year on
a greenbelt 30 m wide and 57 miles long on each side of the Platte River in
Missouri. Furthermore he found 67% of the people travelled 25 miles or less
and 31% travelled only 26-50 miles to get there. These data indicate the
potential of greenbelts for not only improving water quality and the stream
biota, but also for providing multiple-use recreational areas on larger
streams within close proximity to the majority of the people. The latter
point is particularly relevant in the present time of rapidly increasing
energy costs.
65
-------
SECTION 11
OTHER ADVANTAGES OF GREENBELTS
This report has addressed several major advantages which might accrue
from the use of greenbelts along streams. A number of other potential advan-
tages have not been specifically addressed. Some are mentioned briefly in
the following comments.
1. Suspended sediments can cause considerable damage including wear
and tear on metal parts wherever machinery contacts flowing water.
Reduction in sediment loads with greenbelts can reduce the magni-
tude of this problem.
2. Changes in water temperature and sediment and nutrient loads can
precipitate major shifts in algal communities. These shifts can
affect the taste and appearance of water.
3. High water quality and the associated rich biotic communities can
reduce the problem of pathogens surviving in water supplies.
4. Frequency and cost of removing sediment from drainage ditches or
streams could be decreased by filtering sediments from surface runoff
before it reaches the stream bed.
5. Cost for removing the excess turbidity from water used for human
consumption is reduced.
6. Flood damage, i.e., the cost of cleaning up the sediment deposited,
is reduced.
7. Probability of flooding is reduced due to less clogging of the
channel by sediments and because of the more controlled release of
runoff.
8. Costs for storage space destroyed by silting in of reservoirs is
diminished.
66
-------
SECTION 12
DISCUSSION AND CONCLUSIONS
Any attempts to understand the dynamics of sediment transport and the
biological communities of streams must recognize the interrelationships
between water bodies and the land and atmosphere which surrounds them.
Rivers are functional parts of much larger landscape units, and they receive
most of their individual characteristics from the landscapes of their drain-
age basin (Fig. 30; Sioli 1975). The channel bottom and suspended solids
loads are derived from the landscape and the form of the bed is at least
partially determined by the geological history of the surrounding area. The
biota of a watershed also determines many of the characteristics of a stream,,
including the amount of organic matter and the molecular characteristics of
that organic matter (Janzen 1974). The complex interplay of biological,
geological, chemical, and physical phenomena in both the terrestrial and
aquatic environments are of major importance in determining stream character-
istics (Hynes 1975, Likens and Bormann 1974).
In an undisturbed watershed both the terrestrial and aquatic environments
are in an equilibrium, albeit a dynamic equilibrium. In natural watersheds,
drastic fluctuations in water levels are uncommon (unless extremes in rainfall
occur). Under most circumstances rainfall is absorbed by the land surface
and subsequently released from the soil to the stream over a long period
(Hewlett and Nutter 1970). Furthermore, there is little surface runoff from
natural watersheds during periods of normal rainfall. Nutrient cycles are
"tight" in natural watersheds with very few nutrients being lost to the
drainage waters (Likens and Bormann 1974). Under most circumstances the
small amounts of nutrients lost from the terrestrial environment are readily
assimilated by the biotic communities of the stream. Erosion in this equili-
brium state is minimal (Hobble and Likens 1973).
When man arrives in the area the natural vegetation is removed and
instabilities in the terrestrial environment are an inevitable result,
especially if conservation practices are not employed. These instabilities
have repercussions which affect the aquatic environment and disturb the equil-
ibrium in that section of the biogeocoenoses, to use the European terminology
(Sukachev and Dylis 1964) or ecosystem, in the American literature (Tansley
1935). Often, the response is to modify the stream channel to (1) improve
drainage of the land surface, and (2) reduce natural bank erosion and other
bank instabilities stimulated by the modification of the land surface with
the advent of agriculture and urban development. These channelization activ-
ities create more instabilities in the aquatic environment. The combined
effects of modifications on the land and restructuring of channels result in
67
-------
Climate
Atmosphere
Sun
TERRESTRIAL ENVIRONMENT
/Parent
Material
Topography
Natural
Biological *-"
rCommunities.
Human
Influences
.Nutrients,
Sedimentf___ \
Energy
Sources
RUNOFF _WAJE_R_
Quality
Quantity
Tinning
AQUATIC
WATER
^Quantity*
[ Physico -chemical*
I Conditions
BOTTOM TYPE
'GRADIENT
ENVIRONMENT
BIOTA
•Producers
/ Herbivores
I Carnivores
Decomposers
Figure 30.
QUALITY
and
QUANTITY
of
OUTFLOW
WATER
General model of the primary factors governing the quality and
quantity of outflow water from -an ecosystem (From Karr and
Gorman 1975).
68
-------
disequilibria in both the aquatic and terrestrial areas. Readily observed
signs of this disequilibrium include:
1. Rapid runoff resulting in drastic fluctuations in the water levels of
streams. These include floods during heavy rains and nearly stagnant
conditions during dry periods.
2. Large volumes of nutrients and sediments are lost from terrestrial
ecosystems to aquatic ecosystems, often over short time periods
(Hobble and Likens 1973, Likens and Bormann 1974).
3. Increased fluctuations in stream temperature (Likens 1970).
4. Increased streambank erosion as the stream attempts to re-establish
its equilibrium by forming pools and riffles and meanders (Yang
1971a,b).
5. Decreased diversity and stability in the biotic component of the
aquatic ecoeystem due to the less stable environment produced by a
complex of sediment, nutrient, temperature and stream morphology
effects (Margalef 1968, Odum 1969, Karr and Gorman 1975, Gorman and
Karr 1977).
If we compare two hypothetical, identical forested watersheds, these
patterns can be illustrated in a study of disequilibrium in sediment loads
and biotic communities (Table 8). Clearing of the land without conservation
activities and channel modifications produces considerable instabilities. If
equilibrium is attained in the terrestrial component of the watershed but the
streams are channelized, increased sediment loads and major disequilibria in
the biotic and abiotic components of the aquatic ecosystem will result.
The natural tendency is for the ecosystem (terrestrial and aquatic) to
return to equilibrium by natural successional processes (Margalef 1968, Odum
1969). However, the activities of man—agriculture and construction in the
terrestrial area, and channel "maintenance" in the stream—tend to maintain
a disequilibrium. Regrettably, this is the situation throughout much of the
U. S., especially in the heavy agricultural areas of the Midwest.
Stabilization of the terrestrial environment within the requirements of
maintaining an intensive agricultural system is an essential component of
achieving water quality. With careful management in fields (i.e., minimum
tillage, rotational practices, etc.) and along streams (i.e., greenbelts)
effects of the terrestrial disequilibrium can be minimized.
However, major efforts in this area will yield only partial success in
achieving water quality goals as long as the present approach to stream
management prevails. That is, before major improvements in water quality and
stream biota can be realized, the present philosophy of erosion control on
the land surface must be combined with a more reasoned approach on the
management of stream channels (Table 11)- A coordinated management program
should, first, reduce sediment input and, second, manage the stream channel
to reduce USP. The stream channel will be filled with sediment transported
from the land surface if USP control is emphasized first.
69
-------
TABLE 11. EFFECT OF VARYING "MANAGEMENT PRACTICES" ON EQUILIBRIA OF EQUIVALENT WATERSHEDS. These
are best estimates of relative effects for a variety of watershed conditions, including
sources and amounts of sediment.
EFFECT ON EQUILIBRIUM
TERRESTRIAL
AQUATIC
ABIOTIC
TRANSPORT EROSION
BIOTIC
SUSPENDED
SOLIDS
LOAD
SOURCE
OF
SEDIMENT
Natural Watershed
Clear Land for Row
None
None
None
None
Moderate-
Low
Crop Agriculture
Channelize Stream
Clear Land and
Channelize Stream
Best Land Surface
Management with
Channelization
Best Land Surface
and "Natural" Channel
Major
None
Major
Low
Low
Major
Major
Major
Major
Low
Minor*
Major
Major
Major
Low
Major
Major
Major
Major
Low
Medium
High
Very
High
Medium
High
Low-
Medium
Land Surface
Channel Banks
Equilibrium Between
Land Surface and
Channel Banks
Channel Banks
Equilibrium Between
Land and Channel
*Will increase if hydrograph peaks (floods) more severe.
-------
In summary, before the admirable objectives of the Federal Water Pollu-
tion Control Act of 1972 (Public Law 92-500)—fishable and swimmable water
by 1983—can be attained, it is essential that an equilibrium concept be
implemented in the control of non-point source pollution. Furthermore, this
philosophy must involve equilibria in both terrestrial and aquatic ecosystems.
We believe this report has demonstrated the value of a perspective
which emphasizes the link between terrestrial and aquatic environments and
the dynamics of stream behavior. The suggestion that near-stream vegetation
along with soil conservation practices and "natural" stream morphology can
produce substantial improvements in water quality is supported for areas of
intensive agriculture. Furthermore, this management alternative should
enhance the quality of fishery resources and provide a variety of recreation-
al benefits. The magnitude of these benefits must, of course, be weighed
against the costs (Table 12). Perhaps the techniques of decision theory
recently used in studying buffer strips along streams in the field of for-
estry (Sadler 1970, Gillick and Scott 1975) should be applied. This approach
will require substantial new research efforts on a number of questions
raised in this paper. These problems must be dealt with at the individual
drainage and watershed levels before the environmental and economic value
of these management strategies can be fully evaluated.
71
-------
TABLE 12. COSTS AND BENEFITS OF MORE EFFECTIVE MANAGEMENT OF NEARSTREAM VEGETATION AND CHANNEL MORPHOLOGY.
This is not meant to be a comprehensive list. Furthermore, the magnitude of the suggested costs
and benefits have not been adequately evaluted.
Costs
Benefits
1. Land taken out of production to maintain
a vegetative filter.
2. Land taken out of production to allow
meandering.
3. Reduced drainage rates.
4. Maintenance of greenbelts.
5. Reservoir areas for various pests.
6. Need for management of recreational
areas.
1. Reduced sediment, nutrient, and pesticide inputs
into streams.
2. Increased shading resulting in decreased water
temperature; this will alleviate problems
associated with release of nutrients from sedi-
ments, oxygen carrying capacity, temperature and
nutrients in downstream reservoirs, and fewer
algal blooms.
3. Improved habitat for fisheries and terrestrial
wildlife.
4. Increased recreational opportunities.
5. Decreased cost of channel construction and
maintenance activities since nature will pro-
vide the vegetation along streambanks via natu-
ral succession and the stream itself will
initiate meandering and pool-riffle formation.
6. Reduced downstream flooding.
7. May allow more intensive agriculture with
reduced effects on the aquatic ecosystem when
best land management practices (i.e. minimum
tillage) are not feasible.
-------
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GLOSSARY
Active metabolism—metabolic requirements of an organism undergoing normal
activity, such as swimming, feeding, etc.
Allochthonous—Material, generally an energy source such as leaves or insects,
which falls into the water from the nearby terrestrial environment.
Angular canopy density—a measure of the ability of vegetation along a chan-
nel to shade the water in that stream.
Attached nutrients—elemental materials required by organisms (N, P, K, etc.)
that are adsorbed to the surface of sediments.
Autochthonous-material., generally an energy source such as algae or insects,
which are produced in the stream.
Autotroph—organisms which obtain their nourishment by oxidizing simple
chemical elements such as iron, sulfur, or via photosynthesis.
Benthos—bottom-dwelling organisms in stream, lake, and marine environments.
Biological oxygen demand—the oxygen required to reduce the organic material
(e.g. in a water sample). Measure of amount of organic pollution.
Biota—the plant and animal life of a region or period of time.
Buffer strip—a strip of vegetation along a streambank which serves to iso-
late the channel itself from the primary land use in the region. May be
a field border of grass or a strip of forest along the stream channel fol-
lowing clear cutting of forest.
Channel—an open conduit (natural or man-made) in which water flows from a
higher to lower point.
Channel gradient (slope)—the incline of a channel which may be expressed as
the number of feet of fall per 100 feet of horizontal distance.
Channelization—the process of straightening and deepening a stream along
with removal of nearstream vegetation in order to increase the rate of
drainage from the land.
Channel morphology—the structural characteristics of a channel including
such things as bank slopes, depth, sinuosity, etc. Important in determin-
ing runoff rates, channel capacity, sediment carrying ability, biotic
diversity, etc.
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Chemical oxygen demand—similar to biological oxygen demand defined above
but referring to the volume of oxygen-demanding chemical wastes in water.
Coarse particulate organic matter—organic matter in a stream, such as fallen
leaves, which is present in large size units; that is, before decomposi-
tion or invertebrates have fragmented the material.
Community—An association of interacting populations, commonly defined by
their co-occurrence in space.
Community structure—a complex of parameters (species diversity, trophic
structure, etc.) which can be used to identify the organizational charac-
teristics of a community.
Cold blooded—an organism whose temperature conforms with the temperature
of its environment - "poikilothermic".
Continuity equation—Hydraulic equation resulting from the principle of con-
servation of mass. For steady flow, the mass of fluid passing all sec-
tions in a stream of fluid per unit of time is the same, so that as area
of flow decreases, velocity of flow increases.
Critical slope—slope threshold above or below which efficiency of vegetation
to remove sediment from flowing water declines rapidly.
Delivery ratio—ratio used to describe the proportion of material eroded from
the land surface which actually reaches stream channels, lake beds, or
other locations.
Detention time—the time during which water is stored or held by, for example,
a PTO terrace before it is released slowly to a nearby channel.
Ecosystem—the totality involved in the plants and animals (biota) plus the
physical environment of an area and their interactions.
Environmental gradient—A physical or biological factor varies in its effect
over space; e.g., temperature changes as one climbs up a mountain.
Erosion—wearing away of land surface by detachment and transport of soil and
rock materials. May occur through action of wind, water, or other agents.
Eutrophication—the accumulation of nutrients in a body of water more
rapidly than natural biological processes can accommodate them.
Filter (vegetative)—the use of living vegetation or surface litter to reduce
sediment content of flowing water. Results from changing velocity, turbu-
lence, and other characteristics of flowing water.
Flow rate—The volume of water moving past a location per unit time.
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Flow retardance—situation when debris or other material in a channel
or other area of moving water inhibits the flow of that water.
Food chain—sequence of organisms which depend on each other as sources of
food; more or less linear sequence, (see food web)
Food web—complex of organisms with many pathways (food chains) interdigi-
tating from plants to top carnivore.
Fry—recently hatched young of fish.
Greenbelt—Narrow band of vegetation along the channel of a stream. May be
either natural assemblage of plant species or a selected species or group
of species.
Habitat—the natural environment of an organism.
Habitat diversity—as the number of habitats (pools, riffles; bottom types,
etc.) in a reach of stream increases, the habitat diversity of the stream
increases. It is important in determining the species diversity of the
resident biotic community.
Headwater—the upstream end of a drainage complex; usually considered to be
stream orders 1-3.
Heterotroph—organisms which obtain their nourishment from organic matter.
Holistic—the philosophy that for complete description of a system the
behavior of the individual components must be combined with knowledge of
the components joined as units; very simply, the whole is equal to more
than the sum of its parts.
Infiltration filter—area of vegetation where nutrients and/or sediment are
removed as water infiltrates down through the soil profile; there is no
surface runoff out of such an area.
Invertebrate drift—aquatic invertebrates which release their hold or are
torn loose from a substrate and move downstream with the moving water.
Jackson Turbidity Unit (JTU)—see turbidity.
Meander—the winding of a stream channel
Metabolism—the totality of chemical activity in a plant or animal which
results in the provision of energy and nutrients to the organism.
Microflora—microscopic organisms such as bacteria, fungi, and other groups
in a biotic community. Frequently used to refer to those organisms
colonizing decomposing organic matter.
Nursery area—the region where immature fish initiate growth and development.
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Nutrient—a substance required by an organism for normal growth and mainte-
nance.
Organic matter—materials which are produced by living organisms which con-
tain carbon and are not in a completely oxidized condition.
Opercular cavity—the region under the gill cover (or opercle) of a fish
where the gills and gill arches are located.
Overland flow—water flowing on the surface of the land; in contrast with
channel flow or underground movement of water.
Parallel tile outlet terrace (PTO terrace)—a system of low terraces con-
structed to impede the runoff of water from the land surface while pro-
viding for a slow release of water through a tile system; results in
improved water quality by reducing sediments carried to stream channels.
Periphyton—The plants and animals attached or clinging to stems and leaves
of rooted plants or other surfaces projecting above the bottom of a body
of water.
Productivity—rate at which energy or nutrients are assimilated by an indi-
vidual, population or community (amount per unit time). Important to
distinguish between net production which is the rate of accumulation in
a system and gross production which involves both accumulation and the
amount metabolized in the maintenance of the organisms. Primary produc-
tivity is productivity of plants, while secondary productivity is pro-
ductivity of animals.
Reductionist—the philosophy which suggests that a complex system can be
fully described by decomposing it into successively smaller components
and describing their behavior.
Roughness factor (n)—Measure of the irregularity in a drainage channel which
will reduce velocity of flow of water in the channel.
Salmonids—fishes in the family Salmonidae, including trout and salmon.
Sediment—fragmentary material that is transported by water or air or is
accumulated in beds by natural processes.
Sediment deposition—the placement of sediment in a location after its move-
ment by wind, water or other geological agents.
Sediment load—all particulate matter carried or transported by water.
Sediment trap—a specifically constructed area to reduce flow velocity of
water thereby reducing its sediment carrying capacity.
Shallow channel flow—water flowing in a channel when the depth of the water
does not exceed the herbaceous vegetation in the channel.
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Sinuosity—the ratio of channel length to down-valley distance. That is,
an index to the amount of meandering by a stream.
Social hierarchy—a social organization among animals in which dominance
position within the group determines use of available resources.
Spawning—the act of laying and fertilization of eggs in fishes and shell-
fishes, especially.
Spawning grounds—area or location where fish reproduce (lay eggs). Typi-
cally characterized by specific bottom type, current, etc. for each
species.
Species diversity—a measure of the complexity of a community, which may be
simply the number of species (species richness) or a more complex index
utilizing information on number of species and their relative abundances.
Standard metabolism—metabolic requirements of an organism for maintaining
normal physiological functions (e.g. heartbeat, muscle tone, respiration,
etc.) .
Streambank—the sides of a channel which are exposed during most normal flow
periods.
Stream order—A method for numbering streams as part of a drainage network.
The smallest stream channel is first order. A second order stream is
reached when two first order channels join, etc.
Subsurface runoff—underground movement of water either through natural
drainage pathways or through tile systems. Subsurface runoff may or may
not reach an open channel.
Succession—the process of replacement of one biotic community by another.
Each successive community changes the physical and biotic environment by
its presence.
Surface litter—plant debris deposited on the soil surface which helps to
protect that surface from disturbance by raindrop impact or overland flow.
Surface runoff—movement of water overland until it reaches a channel.
Suspended sediment—fine particulate material which remains in suspension and
without contact with the channel bottom.
Tile line—an underground conduit installed by man to facilitate drainage of
water from an area and thereby lower the water table.
Transfer coefficient—amount of material moved from a system component to
another component relative to the amount in the donor compartment usually
expressed as a ratio.
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Turbidity—condition of water resulting from the presence of suspended
material. Typically expressed in Jackson Turbidity Units, a measure of
interference with light transmission.
Unit stream power (USP)—the energy available in flowing water; a function
of the slope and velocity of the channel in which the water is flowing.
Universal soil loss equation (USLE)—equation developed by agricultural
scientists to predict the amount of soil eroded from a land area.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-Q97
3. RECIPIENT'S ACCESSI ON-NO.
4. TITLE AMD SUBTITLE
Impact of Nearstream Vegetation and Stream Morphology
on Water Quality and Stream Biota
5. REPORT DATE
August 1977 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
James R. Karr and Isaac J. Schlosser
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Ecology, Ethology and Evolution
University of Illinois
Champaign, IL 61820
10. PROGRAM ELEMENT NO.
1HB617
11. CONTRACT/GRANT NO.
68-01-3584
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency - Athens, GA,
Environmental Research Laboratory
College Station Road
Athens. GA. 30605
13. TYPE OF RE PORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/01
15. SUPPLEMENTARY NOTES
16. ABSTRACT
As man modifies watersheds by removal of natural vegetation and stream channeliza-
tion, disequilibria in both the terrestrial and aquatic environments result. These
disequilibria are the major problem in controlling sediments and nutrients from non-
point sources and improving the quality of the stream biota.
In this report we review the literature dealing with (1) the possible use of
near stream vegetation to reduce the transport of sediment and nutrients from the
terrestrial to the aquatic environment and decrease stream temperature fluctuations,
(2) the effect of stream morphology on sediment transport, and (3) how near stream
vegetation and stream morphology affect the biota of streams. The results of this
review suggest proper management of near-stream vegetation and channel morphology
can lead to significant improvements in both the water and biological quality of
many streams. However, critical research outlined in this report is still necessary
if we are to properly use this management alternative to attain the objectives of the
Federal Water Pollution Control Act of 1972 (Public Law 92-500).
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
Watersheds
Pollution
Water pollution
Agriculture
Nonpoint sources
06F
13B
08H
08M
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport!
UNCLASSIFIED
21. NO. OF PAGES
103
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
91
* U.S. GOVERNMENT PRINTING OFFICE 1977 0-241-037/76
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