Influence of Local Riparian Cover and 

Watershed Runoff Potential on Invertebrate 

Communities in Agricultural Streams in the 

Minnesota River Basin

By J.R. ZumBerge1, J.A. Perry2, and K.E. Lee3

Water-Resources Investigations Report 03-4068

Contribution from the National Water-Quality Assessment Program

1 Wyoming Department of Environmental Quality, Sheridan, Wyoming

2 Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, St. Paul, Minnesota

3 U.S. Geological Survey, Mounds View, Minnesota
U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Use of brand names in this report is for identification purposes only and does not 

constitute endorsement by the U.S. Geological Survey.

Mound View, Minnesota, 2003

For additional information write to:

U.S. Geological Survey

District Chief

2280 Woodale Drive

Mounds View, MN 55112

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286, MS 517

Federal Center

Denver, CO 80225

Information regarding the National Water-Quality Assessment (NAWQA) Program is available on the Internet via the World Wide Web. 

You may connect to the NAWQA Home Page using the Universal Resource Locator (URL) at:

URL: http://wwwrvares.er.usgs.gov/nawqa/nawqa_home.html

Information about the Upper Mississippi River Basin Project of the NAWQA Program is available at:

URL: http://mn.water.usgs.gov/umis/index.html

Water-Resources Investigations Report 03-4068
FOREWORD

The U.S. Geological Survey (USGS) is committed to serve the 

Nation with accurate and timely scientific information that helps 

enhance and protect the overall quality of life, and facilitates 

effective management of water, biological, energy, and mineral 

resources. (http://www.usgs.gov/). Information on the quality of 

the Nation’s water resources is of critical interest to the USGS 

because it is so integrally linked to the long-term availability of 

water that is clean and safe for drinking and recreation and that is 

suitable for industry, irrigation, and habitat for fish and wildlife. 

Escalating population growth and increasing demands for the 

multiple water uses make water availability, now measured in 

terms of quantity and quality, even more critical to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality 

Assessment (NAWQA) Program to support national, regional, 

and local information needs and decisions related to waterquality management and policy. (http://water.usgs.gov/nawqa/). 

Shaped by and coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is designed to 

answer: What is the condition of our Nation’s streams and 

ground water? How are the conditions changing over time? How 

do natural features and human activities affect the quality of 

streams and ground water, and where are those effects most 

pronounced? By combining information on water chemistry, 

physical characteristics, stream habitat, and aquatic life, the 

NAWQA Program aims to provide science-based insights for 

current and emerging water issues and priorities. NAWQA 

results can contribute to informed decisions that result in 

practical and effective water-resource management and strategies 

that protect and restore water quality.

Since 1991, the NAWQA Program has implemented 

interdisciplinary assessments in more than 50 of the Nation’s 

most important river basins and aquifers, referred to as Study 

Units. (http://water.usgs.gov/nawqa/nawqamap.html). 

Collectively, these Study Units account for more than 60 percent 

of the overall water use and population served by public water 

supply, and are representative of the Nation’s major hydrologic 

landscapes, priority ecological resources, and agricultural, urban, 

and natural sources of contamination. 

Each assessment is guided by a nationally consistent study 

design and methods of sampling and analysis. The assessments 

thereby build local knowledge about water-quality issues and 

trends in a particular stream or aquifer while providing an 

understanding of how and why water quality varies regionally 

and nationally. The consistent, multi-scale approach helps to 

determine if certain types of water-quality issues are isolated or 

pervasive, and allows direct comparisons of how human 

activities and natural processes affect water quality and 

ecological health in the Nation’s diverse geographic and 

environmental settings. Comprehensive assessments on 

pesticides, nutrients, volatile organic compounds, trace metals, 

and aquatic ecology are developed at the national scale through 

comparative analysis of the Study-Unit findings. 

(http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the communication and 

dissemination of credible, timely, and relevant science so that the 

most recent and available knowledge about water resources can 

be applied in management and policy decisions. We hope this 

NAWQA publication will provide you the needed insights and 

information to meet your needs, and thereby foster increased 

awareness and involvement in the protection and restoration of 

our Nation’s waters. 

The NAWQA Program recognizes that a national assessment 

by a single program cannot address all water-resource issues of 

interest. External coordination at all levels is critical for a fully 

integrated understanding of watersheds and for cost-effective 

management, regulation, and conservation of our Nation’s water 

resources. The Program, therefore, depends extensively on the 

advice, cooperation, and information from other Federal, State, 

interstate, Tribal, and local agencies, non-government 

organizations, industry, academia, and other stakeholder groups. 

The assistance and suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water

v

CONTENTS

Abstract.................................................................................................................................................................................1

Introduction...........................................................................................................................................................................1

Purpose and scope ..........................................................................................................................................................2

Description of study area................................................................................................................................................2

Acknowledgments..........................................................................................................................................................2

Methods .........................................................................................................................................................................2

Analysis of collected data.....................................................................................................................................................4

Influence of local riparian cover and basin runoff potential on invertebrate communities..................................................6

Summary.............................................................................................................................................................................11

References ..........................................................................................................................................................................12

ILLUSTRATIONS

Figure 1. Map showing location of sampling sites and watersheds.......................................................................................3

Figure 2. Graphs showing mean values of invertebrate variables for combinations of local riparian cover and 

watershed runoff potential.....................................................................................................................................7

TABLES

1. Site characteristics and corresponding classification........................................................................................................4

2. Instream physical variables and riparian characteristics that were measured or estimated at each site...........................5

3. Classification variables used to characterize the invertebrate communities.....................................................................6

4. Results of the analysis of variance....................................................................................................................................8

5. Results from the analysis of covariance using percent forested as a covariate ................................................................9

6. Results from the analysis of covariance using percent wetland as a covariate.................................................................9

7. Comparison of physical and chemical variables among the four study design classes..................................................10

CONVERSION FACTORS

Multiply By To obtain

centimeter (cm) 0.3937 inch

meter (m) 3.281 foot

kilometer (km) 0.6214 mile

square meter (m2) 10.76 square foot

square kilometer (km2) 0.3861 square mile
vi
1

Influence of Local Riparian Cover and 

Watershed Runoff Potential on Invertebrate 

Communities in Agricultural Streams in the 

Minnesota River Basin

by Jeremy R. ZumBerge1, James A. Perry2, and Kathy E. Lee3

ABSTRACT

During the summer of 1997, 23 streams in the highly agricultural Minnesota River Basin were studied to determine the influence 

of local riparian cover conditions (wooded or open) and watershed runoff potential (high or low) on invertebrate community composition. A two by two-factorial analysis of variance was used to determine dfferences in invertebrate community measures among the 

design classes

While it is difficult to determine the relative influence of watershed runoff potential and local riparian cover, invertebrate communities may be more strongly influenced by local wooded riparian cover than by watershed runoff potential. Invertebrate community 

measures indicate greater degradation at the open riparian cover, high runoff potential sites and less degradation at the wooded riparian 

cover, low runoff potential sites. In addition, differences between streams with wooded riparian cover and sites with open riparian 

cover were greater in watersheds with high runoff potential. The variance explained by riparian cover and runoff potential is relatively 

independent of other land-use effects. Wooded riparian cover influences invertebrate community composition by its relation to the 

other physical environmental variables. This study indicates that wooded riparian cover may be effective in maintaining stream biotic 

integrity in watersheds dominated by agricultural land use.

INTRODUCTION

Streams are influenced by complex interactions that operate 

across a range of spatial scales including watershed-wide scales 

(thousands of square kilometers), segment scales (square kilometers), and local scales, (hundreds of square meters or less). 

Examination of streams using a landscape perspective (Allan and 

others, 1997; Allan and Johnson, 1997; Richards and others, 

1996) has led to questions regarding the spatial scales at which 

these interactions are most appropriately viewed (Allan and 

Johnson, 1997). 

 Many recent studies have addressed the influence of both 

local and watershed-wide factors on stream biotic communities 

(Naiman and others, 1995; Richards and others, 1997). However, 

the importance of local factors in comparison to watershed-wide 

factors remains poorly understood (Allan and others,1997). To 

understand the interactions among factors operating at different 

spatial scales, it is necessary to consider streams as physical systems operating within nested spatial hierarchies (Frissell and 

others, 1986). Within these hierarchies, watershed-wide factors 

such as climate, geology, and soils may dominate segment-scale 

factors such as hydrology, riparian characteristics, and geomorphology (Richards and others, 1996). Segment-scale factors 

influence local-scale factors such as instream habitat, the availability and distribution of food resources, and primary production. 

Watershed-wide land use also may affect local physical and 

chemical stream conditions. Allan and others (1997) found that 

the amount of agricultural land within a watershed was the best 

single predictor of local chemical and physical conditions in 

streams. Watersheds dominated by row-crop agriculture were 

found to have greater alkalinities, total dissolved solids, and 

nitrite-plus-nitrate concentrations than watersheds dominated by 

other land uses (Troelstrup and Perry, 1989; Johnson and others, 

1997). Similarly, Richards and others (1993) found that riparian 

habitat was the most degraded at sites with intensive agricultural 

land use. 

Two important factors that influence physical, chemical and 

biological characteristics in streams are local riparian cover and 

watershed-wide soil properties. Riparian cover and soil properties influence the movement of precipitation, soil, and associated 

contaminants into streams (Osborne and Kovacic, 1993; Barling 

and Moore, 1994). Although extensive research has been done to 

determine the influence of local riparian characteristics on 

stream ecosystems and on invertebrate community composition, 

the relative magnitude of the influence compared to watershedwide factors such as soil properties and land use is not understood (Johnson and others, 1997). To address this need for 

improved understanding, the U.S. Geological Survey, through 

the National Water-Quality Assessment Program (NAWQA), 

designed a study to evaluate influences of local riparian cover 

and watershed runoff potential on invertebrate communities in 

agricultural streams in the Minnesota River Basin.

1 Wyoming Department of Environmental Quality, Sheridan, Wyoming 2 Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota, St. Paul, Minnesota 3 U.S. Geological Survey, Mounds View, Minnesota
2

Riparian zones are the interface 

between streams and the surrounding 

watershed. Wooded riparian vegetation 

can impede surface runoff and stabilize 

stream banks thereby reducing the delivery of sediment into streams (Schlosser 

and Karr, 1981). Reduced volumes of 

sediment delivered to streams may have 

beneficial effects on aquatic resources by 

reducing the amount of siltation on fish 

and invertebrate habitat areas. Reduced 

sediment in streams increases the visibility for animals that are site predators and 

increases light penetration that enhances 

the growth of algae. Reductions in suspended sediment may improve oxygen 

uptake in fish (Rabeni and Smale, 1995) 

and invertebrates by keeping gill tissues 

from being clogged by sediment (Merritt 

and Cummins, 1996). 

Wooded riparian vegetation absorbs 

and reflects solar radiation, resulting in 

greater thermal stability and decreased 

light availability for primary production 

(Gregory and others, 1991). It is also a 

direct source of allocthonous organic 

matter for invertebrate communities 

(Fisher and Likens, 1973). Wooded riparian vegetation increases habitat complexity by supplying woody debris, which 

contributes to greater variation in channel 

form (Montgomery, 1997) and provides 

habitat for invertebrates, especially in 

low-gradient streams (Benke and Wallace, 1990). Coarse particulate organic 

matter retained on woody debris (Maser 

and Sedell, 1994) provides food and refugia for invertebrates, which are an important food source for insectivorous fishes 

(Benke and others, 1985).

Watersheds with poorly drained soils 

have greater potential for surface runoff 

(high runoff potential) during precipitation events because precipitation does not 

rapidly infiltrate the soil. In these watersheds, which are typical for the Minnesota River Basin, tile drainage systems 

are frequently used to drain soil to 

increase agricultural production. Tile 

drainage systems rapidly move water 

from the soil surface to streams. The 

combination of high runoff potential and 

tile drains results in rapid fluctuations in 

streamflow during precipitation events. 

Soil and associated contaminants from 

the surrounding watershed may be carried to streams during precipitation 

events by runoff from the surface and 

through tile drains. 

Watersheds with well-drained soils 

have less potential for surface runoff 

(low-runoff potential) because precipitation can more rapidly infiltrate the soil, 

and eventually enters streams through 

ground-water discharge. Streams draining these watersheds generally have stable streamflow conditions (Richards and 

others, 1997) and receive low amounts of 

sediment and phosphorus input from the 

surrounding landscape (Lenat, 1984). 

Dissolved contaminants such as nitrate 

may be delivered to streams in low-runoff 

potential watersheds through groundwater discharge.

PURPOSE AND SCOPE

 This report presents the results of a 

study comparing the influences of a localscale factor (riparian cover) and a watershed-wide-scale factor (runoff potential) 

on invertebrate community composition 

in selected agricultural streams in the 

Minnesota River Basin. The objectives of 

the study were to determine if local riparian cover and watershed runoff potential 

influence invertebrate community composition in streams within an agricultural 

setting and to determine which factor has 

more influence on invertebrate community composition. 

DESCRIPTION OF STUDY 

AREA

The study area included 23 streams in 

the Minnesota River Basin, a highly agricultural watershed draining approximately 45,000 km2 in Minnesota, Iowa, 

and South Dakota (fig. 1) within the 

Western Cornbelt Plains and Northern 

Glaciated Plains ecoregion (Omernik, 

1987). All sampling sites were in Minnesota. The selected streams typically had 

low gradients, drainage areas ranging 

from 155-821 km2

, and land use that was 

at least 87 percent agriculture (table 1). 

Corn and soybeans are dominant in the 

eastern part of the watershed while wheat 

is concentrated in the western part. Most 

of the soils in the Minnesota River Basin 

are developed on calcareous glacial till 

deposits, but the soils adjacent to the 

streams tend to be developed on calcareous glacial outwash deposits, coarsegrained glacial-lake sediment, or coarseand fine-grained alluvium (Stark and others, 1996). 

ACKNOWLEDGEMENTS

We thank the staff of the Upper Mississippi River Basin NAWQA Study Unit 

for their assistance. We also thank Robert 

Goldstein, U.S. Geological Survey; 

Bruce Vondracek, U.S. Geological Survey; and Carl Richards, Natural 

Resources Research Institute, Duluth, 

Minnesota, for suggestions and comments that improved this report.

METHODS OF STUDY

The study design entailed a two-bytwo factorial analysis of variance. The 

classification factors were local riparian 

cover and watershed-wide runoff potential. The study design classes included the 

four combinations of the two classification factors; riparian cover (open or 

wooded), and watershed-wide runoff 

potential (high or low) (fig. 1; table 1). 

Determination of watershed-wide 

runoff potential was based on geographic 

information system (GIS) analysis of soil 

characteristics (State Soil Geographic 

Data Base (STATSGO), U.S. Department of Agriculture, 1994), supplemented with modified soil 

characterization data (Wolock, 1997). 

Within the STATSGO data base, soils are 

classified into hydrologic soil groups that 

are used to estimate surface runoff potential (United States Department of Agriculture, 2001). Soils are placed into 

hydrologic groups based on infiltration 

(rate at which water enters the soil) and 

transmission (rate at which water moves 

within the soil) (United States Department of Agriculture, 1986). Soils in 

group A are classified as low runoff 

potential soils because they consist of 

well-drained sand or gravel, have the 

greatest infiltration capacity, and a high 

rate of transmission (0.76 cm/hr (centimeters per hour)). Within low-runoffpotential watersheds delivery of runoff to 

a stream is expected to be primarily from 

ground-water discharge. Conversely, 

soils in group D are classified as high runoff potential because they consist of shallow clay or a bedrock layer with a high 

water table, have low infiltration rates 

and a low rate of water transmission (0-

0.13 cm/hr). Type B and C soils are inter
3

D D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D D

D D

D

Location of sampling sites and watersheds.

6

13

12

18

14

17

15

23

21

20 8 1

2

9

10

19

22

5

3

4

7

11

16

Sampling site. Number corresponds

to site number in table 1.

Low

WATERSHED

RUNOFF

POTENTIAL

Classification of sampling site: (Number in parentheses

indicated number of watersheds the classification, see

table 1)

EXPLANATION

Open Wooded

RIPARIAN

COVER

High

(6) (6)

8

(6) (5)

D

0

0

10

10

20

20

30

30

Miles

Kilometers

45°

46°

44°

95°

96°

97°

94°

MINNESOTA

Wisconsin

Minnesota

River basin

Twin Cities

metropolitan area

Iowa

South

Dakota

North

Dakota

Minnesota

River

Figure 1.

Base modified from U.S. Geological Survey

digital data 1:100,000, 1990,

Albers Equal-Area conic Projection.

Standard parallels: 29°30' and 45°30',

Central Meridian -93°00'.

riparian classification were the Cobb 

River (site 16) and the Watonwan River 

(site 22), which were classified as open 

although the percent wooded riparian 

cover was calculated to be 20 and 24 percent, respectively. In both cases, the 

wooded riparian cover for the segment 

was located at the very upstream portion 

of the segment and was not directly adjacent to the stream. The majority of the 

segment was open and sampling was conducted in an open section.

Physical and chemical variables are 

referred to in the report as environmental 

variables. Instream physical variables and 

riparian characteristics were measured at 

each site at the reach scale (Sorenson and 

others, 1999) (table 2). Each reach was set 

at 22 times the average wetted channel 

width and represented the overall segment 

riparian condition. When possible, each 

reach contained at least two of the following geomorphic channel units: pools, riffles, or runs (Meador and others, 1993). 

Three transects were established in the 

downstream end of each reach, spaced at 

an average of two wetted channel widths. 

Geomorphic-channel-unit data, as well as 

data from an additional nine transects, 

were available for 18 of the 23 streams 

from a concurrent study (Stauffer and others, 2000) and were used in this analysis. 

Chemical variables included measurements of specific conductance, pH, water 

temperature, and dissolved oxygen 

recorded at 15-minute intervals at each 

site during a 48-hour period using submersible data recorders with probes positioned in the euphotic zone. Additionally, 

a concurrent study provided data on algal 

species composition, chlorophyll a, and 

ash-free dry mass (S.D. Porter, U.S. Geological Survey, written commun. 1999).

Invertebrates were collected from 

woody debris at five points within each 

stream reach (Sorenson and others, 1999). 

Woody debris was sampled because it 

often presents the richest invertebrate habitat within streams with sandy or otherwise unstable substrates (Cuffney and 

others, 1993). Woody debris also was the 

most universal substrate found at all the 

sites. Woody debris meeting the following 

criteria was sampled: (1) diameter 

between 2.5 and 7.5 cm; (2) free of leaves; 

(3) submerged in flowing water for an

mediate classifications. Soils in group B 

are moderately well drained with intermediate transmission rates (0.38-0.76 

cm/hr). Soils in group C are fine textured 

and have low transmission rates (0.13-

0.38 cm/hr). For this report, watersheds 

containing greater than 50 percent Type A 

and B soils were classified as having low 

runoff potential. Watersheds containing 

50 percent or less Type A and B soils 

were classified as having high runoff 

potential.

Riparian cover within a stream segment was based on digital raster graphic 

data at the 1:24,000 scale (U.S. Geological Survey, 1996), updated using 1991 

aerial photographs provided by the 

National Aerial Photography Program of 

the U.S. Geological Survey (U.S. Geological Survey, 1980). Segment width was 

defined at 100 m from each stream bank. 

Segment length ranged from 2.2 to 2.9 km 

and was defined as the log10 of the watershed drainage area to normalize segment 

length for watershed size. Sites classified 

as open had wooded vegetation in 10 percent or less of the total riparian area 

within the segment (except for two sites 

discussed below). Open sites had primarily grass, pasture, or row-crop riparian 

vegetation. Sites classified as wooded had 

wooded cover in 28 percent or more of the 

total riparian area within the segment. 

Percentages were selected to provide the 

greatest degree of separation between 

design classes. The two exceptions to the 
4

apparently extended period of time; and 

(4) located at depths of less than 1 m. 

Branches were cut underwater and 

allowed to drift into a modified 425-μm 

mesh Surber sampler (Cuffney and others, 1993) placed directly downstream. 

Each branch sampled was removed from 

the net and placed in a bucket where 

organisms were hand picked or brushed 

from branch surfaces and cavities. All 

specimens were preserved in 10 percent 

buffered formalin. Surface areas of 

branches were calculated to determine 

invertebrate densities. 

The U.S.Geological Survey National 

Water-Quality Laboratory, Denver, Colorado, identified all invertebrate samples 

to the lowest practical taxonomic level. In 

some cases, the presence of small larval 

instars or damaged specimens made identification to genus or species impossible. 

ANALYSIS OF COLLECTED 

DATA

Taxonomic classifications such as 

taxa richness, percent Ephemeroptera, 

Plecoptera, and Trichoptera (EPT), and 

percent Chironomini provide a depiction 

of invertebrate community composition. 

The presence of EPT taxa is indicative of 

relatively undisturbed conditions (Merritt 

and Cummins, 1996), while the presence 

of Chironomini in streams may be indicative of degraded conditions (Storey and 

Cowley, 1997). Taxonomic classifications, although useful, do not provide a 

complete understanding of the mechanisms controlling the composition of 

invertebrate communities. The best perspective is gained by using a combination 

of methods (table 3). Through this 

approach, the relation of invertebrate 

communities to their environment can be 

best understood. Classifications based on 

feeding ecology (scrapers, shredders, collectors, and predators) provide insight 

into available food resources that influence the structure and function of invertebrate communities. Classifications based 

on habitat preference (erosional, depositional) and mode of movement (clingers, 

burrowers) provide information on the 

physical habitat and hydrologic conditions at a site (Merritt and Cummins, 

1996). 

Table 1. Site characteristics and corresponding classification

 [km2; square kilometers; A/B, STATSGO type A or B hydrologic soil group (U.S. Department of Agriculture, 2001)]

Classification factors

Site number (figure 

1)

Site name

Percent 

wooded 

cover

(segment)

Riparian 

cover

Watershed 

runoff 

potential

Percent 

type A/B 

soils

 (basin)

Drainage area 

(km2)

Percent 

agriculture

1 Coon Creek at Hwy 169 near Blue Earth, Minn. 43 wooded high 18 256 99

2 South Fork Watonwan River near St. James, 

Minn.

28 wooded high 31 497 97

3 Little Cobb River near Beauford, Minn. 52 wooded high 2 337 95

4 Maple River near Sterling Center, Minn. 45 wooded high 17 821 95

5 Rush River near New Rome, Minn. 65 wooded high 1 492 97

6 Dry Weather Creek near Watson, Minn. 55 wooded low 96 272 98

7 Little Cottonwood River near Searles, Minn. 67 wooded low 53 420 98

8 East Branch Blue Earth River below Bricelyn, 

Minn.

47 wooded low 82 482 95

9 Elm Creek near Northrup, Minn. 48 wooded low 60 601 96

10 Perch Creek below Vernon Center, Minn. 36 wooded low 51 389 97

11 Le Sueur River near Wilton, Minn. 60 wooded low 94 469 96

12 Shakopee Creek near Louriston, Minn. 0 open high 18 386 87

13 Spring Creek near Spring Creek, Minn. 10 open high 0 290 99

14 Chetomba Creek near Renville, Minn. 2 open high 7 311 99

15 Sleepy Eye Creek near Springfield, Minn. 0 open high 2 645 99

16 Cobb River near Mapleton, Minn. 20 open high 29 290 93

17 High Island Creek near Arlington, Minn. 1 open high 9 422 95

18 Hawk Creek near Maynard, Minn. 10 open low 66 821 94

19 West Branch Blue Earth River above Elmore, 

Minn.

4

open low 77 389 98

20 South Creek near Huntley, Minn. 1 open low 91 269 94

21 Center Creek at Huntley, Minn. 4 open low 81 290 88

22 Watonwan River near St. James, Minn. 24 open low 51 259 97

23 St James Creek near La Salle, Minn. 1 open low 57 155 93
5

Multimetric indices are integrative, 

semi-quantitative assessments of local 

biological integrity (Karr, 1981; Ohio 

Environmental Protection Agency, 

1987), and are popular tools for assessing 

stream ecosystem condition. The Hilsenhoff Improved Biotic Index (HBI), developed in Wisconsin, is an index based on 

both the abundance and tolerances of 

stream invertebrates to organic and nutrient enrichment (Hilsenhoff, 1987). HBI 

scores are expected to increase as environmental degradation increases. The 

Invertebrate Community Index (ICI) 

(Ohio Environmental Protection Agency, 

1987) is a multimetric index developed to 

evaluate overall invertebrate community 

condition in Ohio streams. Scoring criteria for individual ICI metrics are tailored 

to reference conditions in Ohio. ICI 

scores are expected to decrease as environmental degradation increases. 

Taxonomic ambiguities were 

addressed in two ways. First, each unique 

taxon (no further taxonomic subdivisions 

identified) was counted for the summation of taxa richness. Second, only taxa 

identified to an adequate level for assignment of feeding ecology or behavioral 

group were included in those analyses.

Prior to statistical analysis, each 

invertebrate dependent variable (table 3) 

was examined for normality using normal 

probability plots. If variables did not 

meet the assumption of univariate normality, log10 (Helsel and Hirsch, 1992) or 

square root of the arcsine transformations 

were applied. Each invertebrate variable 

was then used as a response variable in an 

analysis of variance (ANOVA) with a 

two-by-two factorial design, which 

included two levels of local riparian 

cover (wooded and open) and watershedrunoff potential (high and low) as independent variables. A significance level of 

p<0.05 was used for analysis of variance 

statistical procedures. Percent sum of 

squares was used to express the amount 

of variance explained by each factor.

Although the Minnesota River Basin 

is highly agricultural, small proportions 

of other types of land use and land cover 

(primarily forest and wetland) were 

present in the drainage areas of the studied streams and may have influenced the 

observed responses of the invertebrate 

community to riparian cover and runoff 

potential. To test the influence that the 

percentage of forest and wetland in each 

watershed may have had on the invertebrate communities, each was used in an 

analysis of covariance (ANCOVA). If the

Table 2. Instream physical variables and riparian characteristics that were measured or estimated at each site1, 2

 [Measurements or visual estimations were made at either the transect, reach, or segment scale; m2, square meters]

1

Twelve transects were established at each site except Maple River near Sterling Center, Minn., East Branch Blue Earth River near Bricelyn, Minn., Shakopee Creek near 

Louriston, Minn., and St. James Creek near La Salle, Minn.

2

Protocols of Sorenson and others (1999)

Method Scale

One measurement 

Wetted channel width (meters) measured transect

Canopy shading (percent) (measured by a densiometer) measured transect

Riffles, pools, and runs, in percent measured reach

Sinuosity measured segment

Temperature, dissolved oxygen, pH, conductance (at 15-minute intervals over 48 hours) measured reach

Chlorophyll a (phytoplankton and periphyton), ash-free dry mass (AFDM) on wood measured reach

Two measurements (each bank)

Frequency of bank erosion estimated transect

Bank Stability Index (BSI) (Simon and Downs, 1995)

BSI=sum of four scores based on:

bank angle in degrees: 0-30=1, 31-60=2, >60=3 estimated transect

bank cover (vegetative) in percent: >75=1, 51-75=2, 26-50=3, 0-25=4 estimated transect

bank height in meters: 0-1=1, 1.1-2=2, 2.1-3=3, 3.1-4=4, >4=5 estimated transect

bank material: bedrock/riprap=1, boulder/cobble=2, clay=3, silt=5, sand=8 estimated transect

Riparian tree density: based on 20-m2 plots or point quarter method with diameter at breast height (DBH)>3 

centimeters (Brower and others, 1990)

measured transect

Riparian tree basal area (m2) measured transect

Riparian ground cover in percent: trees, shrubs, annuals and perennials, and bare ground estimated transect

Three measurements (equally spaced across each transect)

Velocity measured transect

Depth measured transect

Substrate type in percent (boulder, cobble, gravel, sand, silt) estimated transect

Woody debris in percent estimated transect
6

variability explained by riparian cover or 

runoff potential decreased upon adjustment of a dependent variable for forest or 

wetland land cover, the observed 

response could not be solely attributed to 

riparian cover or runoff potential. Conversely, if the variability explained by 

riparian cover or runoff potential did not 

significantly decrease, then the observed 

response was attributed primarily to 

riparian cover and runoff potential. 

Differences in the environmental 

variables between the classification factors were identified using a conservative, 

nonparametric Wilcoxon signed-rank 

test. Geomorphic channel unit and additional transect data provided by Stauffer 

and others (2000) were only available for 

18 sites. Thus, to maintain consistent data 

between sites, only those sites were used 

in this analysis. Environmental variables 

found to be significantly different 

between the two classifications of riparian cover or runoff potential could 

explain how these factors affect invertebrate communities. A more conservative 

significance level of p<0.01 was used for 

multiple comparisons of environmental 

variables. A Bonferroni derived significance level with approximately 50 comparisons of environmental variables 

would have been p<0.001, which seemed 

too conservative for identifying biological significance with a non-parametric 

procedure (Moore and McCabe, 1993).

INFLUENCE OF LOCAL 

RIPARIAN COVER AND 

RUNOFF POTENTIAL ON 

INVERTEBRATE 

COMMUNITIES

Insects dominated the collections at 

all sites. Thirty six families in 10 orders 

were collected. In addition to insects, 

other major invertebrate taxa collected 

included Acari, Tubellaria, Amphipoda, 

Decapoda, Gastropoda, Oligochaeta, and 

Hirudinea. Across all the design classes, 

the mayfly genera Baetis, Stenomena, 

and Tricorythodes; the caddisfly genera 

Ceratopsyche and Cheumatopsyche, and 

the midge genera Polypedilum and Thienemanniella were most commonly found. 

Total abundance of invertebrates collected ranged from 130 per sample at an 

open riparian cover, high runoff potential 

site to 2,014 at a wooded riparian cover, 

low runoff potential site. 

In general, invertebrate measures 

described in this report indicate greater 

degradation at the open riparian cover, 

high runoff potential sites and less degradation at the wooded riparian cover, low 

runoff potential sites. The invertebrate 

measures at sites represented by the other 

two combinations of factors were intermediate and similar. Streams with 

Table 3. Classification variables used to characterize the invertebrate communities1

1

Unless otherwise noted, Merritt and Cummins (1996) was used to designate categories.

Invertebrate 

variable Description by category

Taxonomic 

Taxa richness Total number of invertebrate taxa

EPT Proportion of the total number of individuals that are Ephemeroptera, Plecoptera, and Trichoptera

Chironomini Proportion of the total number of individuals that are in Tribe Chironomini

Feeding ecology 

Scrapers (grazers) Proportion of the total number of individuals that are scrapers (scrape algae from hard substrates)

Shredders Proportion of the total number of individuals that are shredders (large organic particle feeders)

Collectors Proportion of the total number of individuals that are collectors (small organic particle feeders)

Predators Proportion of the total number of individuals that are predators

Habit preference

Erosional taxa Number of taxa that are found exclusively in erosional habitats

Depositional taxa Number of taxa that are found exclusively in depositional habitats

Mode of movement

Clinger taxa Number of taxa that are clingers (attach to hard substrates)

Burrower taxa Number of taxa that are burrowers (burrow into substrate)

Multimetric Indices

HBI Hilsenhoff’s Improved Biotic Index (Hilsenhoff,1987); a measure of tolerance to organic pollution

ICI Invertebrate Community Index (Ohio Environmental Protection Agency, 1987); a multimetric assessment of biotic integrity
7

40

20

60

80

0

100

PERCENT COLLECTORS

0

10

20

30

40

50

PERCENT SHREDDERS

Wooded and Low

Runoff Potential

Wooded and Low

Runoff Potential

Wooded and High

Runoff Potential

Wooded and High

Runoff Potential

Open and Low

Runoff Potential

Open and Low

Runoff Potential

Open and High

Runoff Potential

Open and High

Runoff Potential

Mean values of invertebrate variables for combinations of local riparian

cover and watershed runoff potential.

+1 Standard Error

Mean

-1 Standard Error

EXPLANATION

0

10

20

30

40

50

ICI SCORE

G

0

1

2

3

4

5

6

7

NUMBER OF DEPOSITIONAL TAXA

E

0

20

40

60

80

100

PERCENT EPT

A

D

10

20

30

40

PERCENT CHIRONOMINI

0

B

C

3

2

1

0

4

5

6

7

HBI SCORE

F

Figure 2.

wooded riparian cover and low runoff 

potential had the highest ICI scores and 

percentages of collectors, the smallest 

percentages of Chironomini and shredders, and the lowest HBI scores. Conversely, streams with open riparian cover 

and high runoff potential had the lowest 

ICI scores and percentages of EPT and 

collectors, the greatest percentages of 

Chironomini and shredders, and the 

highest HBI scores (fig. 2). In addition, 

differences between streams with 

wooded riparian cover and sites with 

open riparian cover were greater in 

watersheds with high runoff potential 

(fig. 2). 

Clear patterns in invertebrate community structure were evident between 

the classification factors. However, 

riparian cover and runoff potential have 

different influences on invertebrate communities in these agricultural streams. 

Significant differences in percent 

Chironomini, percent shredders, the 

number of depositional taxa, and ICI 

scores were evident between sites with 

wooded and open riparian cover (table 

4). Riparian cover explained about 20-25 

percent of the variance in these variables 

(table 4). Percent Chironomini and 

shredders were greater at sites with open 

riparian cover than at sites with wooded 

riparian cover (fig. 2e and 2f). Lower ICI 

scores and fewer depositional taxa were 

evident at sites with open riparian cover 

than at sites with wooded riparian cover 

(fig. 2a). The greater percentages of Chironomini and shredders, depositional 

taxa, and low ICI scores in streams with 

open riparian cover may be indicative of 

locally degraded or enriched conditions.

Chironomoni are miners or chewers 

of macrophyte and algal tissue (Merritt 

and Cummins, 1996). The greater abundance of shredders and in particular the 

most abundant shredder, Polypedilum 

sp. (Tribe Chironomini), at the open 

riparian cover sites indicates degraded 

conditions. Streams with wooded and 

open riparian cover had similar amounts 

of periphyton ash-free dry mass and periphyton chlorophyll a indicating that differences in Chironomini between 

streams with wooded and open riparian 

cover were not due to the presence of 

suitable periphyton sources. Storey and
8

Cowley (1997) suggest that the presence 

of Chironomini in streams is indicative of 

enriched or degraded conditions. They 

found a decrease in abundance of Chironomini in streams soon after they flowed 

into native forest remnants in New 

Zealand, a response coincident with 

decreasing streambed sediment and 

increasing dissolved oxygen concentrations. 

Significant differences in percent 

EPT taxa, percent collectors, and HBI 

were evident between the two types of 

runoff potential (table 4). Runoff potential explained about 17-27 percent of the 

variance in percent EPT taxa, percent collectors (primarily filter feeding hydropsychids), and HBI scores (table 4). Percent 

EPT taxa and percent collectors were 

more abundant in streams with low runoff 

potential (fig. 2). The low relative abundance of EPT taxa and collectors in high 

runoff potential watersheds indicates that 

their filter-feeding behavior may make 

them vulnerable to the rapid flow variations and the movement of fine substrate. 

In previous studies, filter-feeding invertebrates were found to be more abundant at 

the sites with the more stable hydrologic 

regime (Hemphill and Cooper, 1983; 

Scarsbrook and Townsend, 1993). HBI 

scores were greatest (high scores indicate 

lower resource quality) at sites in high 

runoff potential watersheds (fig. 2). The 

lower relative abundance of EPT taxa, 

high HBI scores, and low ICI scores indicate lower resource quality in streams 

draining watersheds with high runoff 

potential. Watershed soil characteristics 

may influence invertebrate communities 

through changes in stream hydrology.

While it is difficult to determine the 

relative influence of local riparian cover 

and watershed runoff potential on invertebrate community measures, invertebrate communities may be more strongly 

influenced by local wooded riparian 

cover than by watershed runoff potential. 

Local wooded riparian cover appears to 

mitigate the influence watershed runoff 

potential exerts on invertebrate communities (fig. 2). There were few differences 

in the invertebrate community variables 

between streams with wooded and open 

riparian cover within low runoff potential 

watersheds. However, in high runoff 

potential watersheds there were greater 

differences in invertebrate measures 

between wooded and open sites. For 

example, ICI scores were greater at 

wooded than open sites in high runoff 

potential watersheds. Stauffer and others 

(2000) studied fish communities in these 

same Minnesota River Basin streams and 

also found greater Index of Biotic Integrity (IBI) (Karr, 1981) scores at wooded 

than at open sites. The concurrence of IBI 

and ICI scores indicates that local 

wooded riparian cover has more influence on stream biotic integrity than 

watershed runoff potential.

The variance explained by riparian 

cover and runoff potential is relatively 

independent of other land-use effects. For 

most variables, p-values did not rise 

above the significance level of p<0.05 

when percentages of forest and wetland 

were included in analyses of covariance. 

However, percentage forest influenced 

scrapers independently of riparian cover 

and runoff potential (tables 4-6). Past 

studies support watershed land use as a 

dominant factor affecting stream biota 

(Richards and others, 1996; Roth and others, 1996; Allan and others, 1997; Wang 

and others, 1997). However, these previ

Table 4. Results of the analysis of variance. 

 [SS; sum of squares; interaction term indicates the interaction between local riparian cover and watershed runoff potential; bold type indicates a variable that is 

significantly different]

Dependent variable

Local riparian 

cover

p-value

Local riparian 

cover SS (percent)

Watershed runoff 

potential

p-value

Watershed runoff 

potential SS (percent)

Interaction

p-value

Interaction SS 

(percent)

Taxonomic

Taxa richness p=0.09 6.9 p=0.55 2.5 p=0.57 2.5

EPT p=0.29 4.4 p=0.04 17.9 p=0.22 6.3

Chironomini p=0.02 24.9 p=0.19 6.5 p=0.58 1.2

Density p=0.49 2.0 p=0.09 12.4 p=0.13 10.2

Feeding ecology

Scrapers p=0.23 6.3 p=0.11 11.7 p=0.30 4.5

Shredders p=0.02 22.2 p=0.29 4.4 p=0.38 3.0

Collectors p=0.27 4.7 p=0.01 27.1 p=0.84 0.0

Predators p=0.39 4.1 p=0.82 0.0 p=0.57 1.6

Habitat preference

Erosional taxa p=0.09 14.5 p=0.87 0.4 p=0.58 0.0

Depositional taxa p=0.05 24.0 p=0.57 8.6 p=0.53 0.3

Mode of movement

Clinger taxa p=0.18 19.1 p=0.17 2.0 p=0.74 1.4

Burrower taxa p=0.82 0.5 p=0.78 3.1 p=0.98 7.8

Multimetric indices

HBI p=0.20 6.6 p=0.05 16.6 p=0.22 6.0

ICI score p=0.03 19.7 p=0.07 12.8 p=0.41 2.3
9

Table 5. Results from the analysis of covariance using percent forested as a covariate

 [Values in bold indicate variables significantly different in the analysis of variance (table 4); italicized values indicate a significant influence of the covariate, 

independent of the classification factors

Dependent variable Local Riparian Cover Watershed Runoff 

Potential Interaction Percent Forested

p-value p-value p-value p-value

Taxonomic

Taxa richness p=0.09 p=0.63 p=0.65 p=0.75

EPT p=0.32 p=0.05 p=0.21 p=0.74

Chironomini p=0.02 p=0.23 p=0.64 p=0.85

Density p=0.50 p=0.11 p=0.15 p=0.95

Feeding ecology

Scrapers p=0.23 p=0.21 p=0.09 p=0.03

Shredders p=0.03 p=0.39 p=0.51 p=0.50

Collectors p=0.25 p=0.02 p=0.91 p=0.38

Predators p=0.41 p=0.78 p=0.55 p=0.80

Habitat preference

Erosional taxa p=0.10 p=0.95 p=0.68 p=0.69

Depositional taxa p=0.08 p=0.66 p=0.64 p=0.63

Mode of movement

Clinger taxa p=0.19 p=0.21 p=0.79 p=0.88

Burrower taxa p=0.80 p=0.90 p=0.86 p=0.56

Multimetric indicies

HBI p=0.22 p=0.04 p=0.17 p=0.43

ICI Score p=0.03 p=0.10 p=0.53 p=0.62

Table 6. Results from the analysis of covariance using percent wetland as a covariate. [Values in bold indicate variables significantly different in the ANOVA (table 4]

Dependent variableLocal riparian 

cover

Watershed runoff potential Interaction Percent wetlands

p-value p-value p-value p-value

Taxonomic

Taxa richness p=0.10 p=0.56 p=0.58 p=0.85

EPT p=0.37 p=0.05 p=0.23 p=0.49

Chironomini p=0.01 p=0.16 p=0.55 p=0.22

Density p=0.48 p=0.10 p=0.13 p=0.76

Feeding ecology

Scrapers p=0.31 p=0.09 p=0.32 p=0.33

Shredders p=0.02 p=0.26 p=0.36 p=0.31

Collectors p=0.23 p=0.01 p=0.83 p=0.51

Predators p=0.49 p=0.87 p=0.59 p=0.43

Habitat preference

Erosional taxa p=0.06 p=0.79 p=0.55 p=0.20

Depositional taxa p=0.08 p=0.57 p=0.53 p=0.85

Clinger taxa p=0.18 p=0.18 p=0.74 p=0.68

Burrower taxa p=0.85 p=0.80 p=0.98 p=0.90

Multimetric indicies

HBI p=0.27 p=0.05 p=0.23 p=0.41

ICI score p=0.03 p=0.07 p=0.42 p=0.72
10

ous studies considered a wider range of 

land uses in contrast to the study 

described in this report with all watersheds dominated by agricultural land use. 

The physical and chemical environment of streams strongly influences 

invertebrate communities (Richards and 

others, 1997). Identifying physical and 

chemical variables aligned with the classification factors may provide insight into 

how wooded riparian cover and runoff 

potential affect invertebrate communities 

(Stauffer and others, 2000). Significant 

differences in many of the physical and 

chemical environmental variables were 

identified between streams with wooded 

and open riparian cover (table 7). As 

expected, riparian variables (canopy 

shading, tree density, and mean tree basal 

area) significantly differed between the 

two conditions. The percentage of runs 

and pools, sinuosity, velocity, and percentage of woody debris also differed 

between wooded and open streams. 

These factors influence physical processes operating at the microhabitat-scale 

and may be the ultimate determinants of 

invertebrate community structure and 

function (Frissell and others, 1986; Minshall, 1988). Results from the study 

described in this report indicate that 

wooded riparian cover influenced invertebrate community composition by its’ 

relation to the other physical and chemical environmental variables. Similarly, 

Storey and Cowley (1997) found that 

existing remnants of riparian forests 

influenced invertebrate community composition through alteration of stream habitat characteristics.

Wooded riparian vegetation may be 

effective in maintaining stream biotic

Table 7. Comparison of physical and chemical variables among the four study design classes.

 [Differences in physical variables between riparian cover and watershed runoff potential were tested for significance using a Wilcoxon signed-rank test (n=18). Bold 

type indicates a variable that is significantly different between wooded and open riparian cover or high and low watershed runoff potential. HROP, high runoff potential; 

LROP, low runoff potential; m/s, meter per second; m, meter; m2

, square meter; mg/L, milligram per liter; DO, dissolved oxygen; μS/cm; microseimens per centimeter 

at 25°; °C, degree Celsius]

Study design class Wooded/HROP Wooded/LROP Open/HROP Open/LROP Local riparian 

cover

Watershed runoff potential

Variable mean SE mean SE mean SE mean SE p-value p-value

Substrate and instream habitat

Percent silt substrate 33.1 9.0 24.2 8.7 54.1 52.5 27.1 5.2 p<0.77 p<0.26

Percent sand substrate 33.9 9.5 29.5 11.1 23.9 27.6 37.0 9.2 p<0.68 p<0.59

Percent gravel substrate 22.8 7.3 33.4 11.4 19.8 24.4 25.2 7.2 p<0.59 p<0.44

Percent cobble substrate 6.7 3.1 7.7 2.6 1.3 2.4 7.3 3.0 p<0.59 p<0.21

Percent boulder substrate 3.3 1.7 5.3 3.1 0.9 1.3 2.8 1.5 p<0.26 p<0.26

Percent woody debris 14.7 3.4 11.1 5.8 1.5 2.5 2.6 1.1 p<0.01 p<0.44

Geomorphology

Sinuosity 2.2 0.2 1.9 0.0 1.5 0.3 1.6 0.1 p<0.01 p<0.13

Channel width (m) 11.7 0.6 11.2 1.4 10.8 1.4 10.7 1.1 p<0.44 p<0.37

Percent run 54.5 8.8 56.0 5.7 98.8 2.7 67.2 7.0 p<0.03 p<0.21

Percent riffle 12.5 3.5 13.8 4.8 0.0 0.0 15.0 7.4 p<0.26 p<0.16

Percent pool 31.0 5.4 30.0 1.7 0.0 0.0 17.8 1.2 p<0.01 p<0.21

Number of changes in geomorphic channel 

units

14.8 3.5 17.8 3.8 1.0 0.0 13.4 1.5 p<0.08 p<0.04

Hydrology

Maximum velocity (m/s) 0.6 0.4 0.6 0.4 0.4 1.0 0.4 0.2 p<0.06 p<0.68

Range of velocity (m/s) 0.6 0.5 0.5 0.3 0.2 0.8 0.3 0.1 p<0.01 p<0.68

Riparian Zone Characteristics

Canopy shading (percent) 59.9 12.6 37.4 3.2 4.4 2.5 5.7 1.5 p<0.01 p<0.11

Tree density (trees/m2) 1.7 1.2 0.3 0.2 0.0 0.0 0.0 0.0 p<0.01 p<0.40

Mean tree basal area (m2) 0.21 0.04 0.20 0.04 0.05 0.09 0.08 0.02 p<0.02 p<0.21

Percent annual grasses 66.1 6.6 74.4 5.2 96.5 5.1 76.9 8.2 p<0.09 p<0.68

Percent shrubs 10.5 5.1 12.6 5.2 0.5 0.9 5.7 3.1 p<0.11 p<0.37

Bank Characteristics

Bank Stability Index 12.5 0.3 12.3 0.3 11.8 1.8 12.6 0.4 p<0.82 p<0.68

Frequency of bank erosion 0.7 0.1 0.6 0.1 0.7 0.2 0.9 0.1 p<0.12 p<0.48

Water chemistry

Minimum DO concentration (mg/L) 6.48 0.56 7.10 0.71 6.38 1.42 5.81 0.54 p<0.26 p<0.59

Maximum DO concentration (mg/L) 9.64 0.68 9.70 0.32 11.72 3.00 11.94 1.46 p<0.09 p<0.59

Range of DO concentration (mg/l) 3.16 1.01 2.60 0.97 5.34 3.78 6.13 1.69 p<0.11 p<0.95

Median DO concentration (mg/l) 7.60 0.20 7.89 0.42 8.08 1.44 7.54 0.42 p<0.95 p<0.86

Maximum percent DO saturation (mg/L) 115.8 11.0 113.8 7.2 136.9 47.0 150.0 19.9 p<0.17 p<0.16

Median pH 8.1 0.1 7.6 0.2 7.9 0.4 8.0 0.2 p<0.78 p<0.31

Median specific conductance (μS/cm) 687.4 29.6 932.3 192.4 1175 396.2 749.8 70.7 p<0.11 p<0.95

Minimum water temperature (°C) 19.0 0.7 18.2 1.0 17.4 0.4 19.8 0.5 p<0.86 p<0.31

Maximum water temperature (°C) 23.9 1.1 21.8 1.4 23.2 1.8 26.0 0.7 p=0.17 p=0.77

Range of water temperature (°C) 4.9 1.3 3.6 0.8 5.8 1.9 6.2 0.5 p=0.26 p=0.44
11

integrity in watersheds dominated by 

agricultural land use. Other studies have 

indicated that grass riparian zones may 

also be effective. Trimble (1997) proposed that grass riparian zones are more 

effective than wooded riparian zones in 

stabilizing stream banks. Grass buffers 

encourage sediment deposition and bank 

encroachment, resulting in narrower 

stream widths and less bank erosion 

(Trimble, 1997). The results from the 

study described in this report do not support or discount grass riparian zones as an 

alternative to wooded riparian zones in 

maintaining stream biotic integrity. This 

study was not designed to evaluate the 

soil characteristics smaller than basin 

scale, which could confound the analyses 

of the effects of local wooded riparian 

cover.

 SUMMARY

Streams biota are influenced by complex interactions that 

operate across a range of spatial scales. Two important factors 

that influence physical, chemical and biological characteristics 

are local riparian cover, and watershed-wide soil properties. The 

importance of local factors in comparison to watershed-wide 

factors is poorly understood. Watersheds with poorly drained 

soils have increased runoff with associated contaminants from 

the surrounding watershed that are delivered to streams during 

precipitation. Watersheds with well-drained soils have less 

potential for surface runoff because precipitation infiltrates into 

the soil. Streams draining these watersheds generally have stable 

streamflow conditions and low sediment and phosphorus inputs. 

Riparian zones are the interface between streams and the surrounding watershed. Wooded riparian vegetation impedes surface runoff and stabilizes stream banks, thereby reducing the 

delivery of sediment into streams. Reduced volumes of sediment 

delivered to streams has beneficial effects on aquatic resources. 

Wooded riparian vegetation also absorbs and reflects solar radiation and serves as a source of food for invertebrate communities.

 This report presents the results of a study comparing the 

influences of a local scale factor (riparian cover) and a watershed-wide scale factor (runoff potential) on invertebrate community composition in selected agricultural streams in the 

Minnesota River Basin. The study included 23 streams in the 

Minnesota River Basin, a highly agricultural watershed draining 

approximately 45,000 km2

 in Minnesota, Iowa, and South 

Dakota. The selected streams typically had low gradients, drainage areas ranging from 155-821 square kilometers, and greater 

than 87 percent agricultural land use. The study entailed a twoby-two factorial analysis of variance of watershed-wide runoff 

potential and local riparian cover that included four combinations of the two factors. Instream physical variables and riparian 

characteristics were measured at the reach scale. Invertebrates 

were collected from woody debris at five points within each 

stream reach. 

 Invertebrate measures indicate greater degradation at the 

open riparian cover, high runoff potential sites and less degradation at the wooded riparian cover, low runoff potential sites. 

Streams with wooded riparian cover and low runoff potential 

watersheds had the highest ICI scores and percentages of collectors, the smallest percentages of Chironomini and shredders, and 

the lowest HBI scores. Conversely, streams with open riparian 

cover and high runoff potential watersheds had the lowest ICI 

scores, and percentages of EPT and collectors, the greatest percentages of Chironomini and shredders, and the highest HBI 

scores. In addition, differences between streams with wooded 

riparian cover and streams with open riparian cover were greater 

in watersheds with high runoff potential. 

Riparian cover and runoff potential have different influences 

on invertebrate communities in these agricultural streams. 

Riparian cover explained about 20-25 percent of the variance in 

Chironomoni, shredders, depositional taxa, and ICI. There were 

lower ICI scores and fewer depositional taxa at sites with open 

riparian cover than at sites with wooded riparian cover. Percent 

Chironomini and shredders were greater at sites with open riparian cover than at sites with wooded riparian cover. The greater 

percentages of shredders in streams with open riparian cover 

may be indicative of locally degraded or enriched conditions 

rather than food resources. Streams with wooded and open riparian cover had similar amounts of periphyton ash-free dry mass 

and periphyton chlorophyll a indicating that differences in Chironomini between streams with wooded and open riparian cover 

were not due to the presence of suitable periphyton sources. Runoff potential explained about 17-27 percent of the variance in 

percent EPT taxa, percent collectors, and HBI scores. There 

were significant differences in percent EPT taxa, percent collectors, and HBI between the two types of runoff potential. EPT 

taxa and collectors were more abundant at sites with low runoff 

potential watersheds. HBI scores were greatest at sites with 

high runoff potential watersheds. 

While it is difficult to determine the relative influence of 

watershed runoff potential and local riparian cover on invertebrate community measures, invertebrate communities may be 

more strongly influenced by local wooded riparian cover than by 

watershed runoff potential. Wooded riparian cover may influence invertebrate community composition by its relation to the 

other physical environmental variables. Wooded riparian vegetation may be effective in maintaining stream biotic integrity in 

watersheds dominated by agricultural land use. The study 

described in this report was not designed to evaluate the influence of local scale runoff processes which could confound the 

analyses of the effects of local woody riparian cover.
12

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