Long Term Resource Monitoring Program

 Technical Report 

2004-T005

December 2004

Multiyear Synthesis of the Macroinvertebrate Component 

from 1992 to 2002

for the Long Term Resource Monitoring Program 
Long Term Resource Monitoring Program Technical Reports

provide Long Term Resource Monitoring Program 

partners with scientific and technical support.

All reports in this series receive anonymous peer review.

Cover graphic by Mi Ae Lipe-Butterbrodt

Mention of trade names or commercial products does not constitute endorsement

or recommendation for use by the U.S. Department of the Interior, U.S. Geological Survey.
Multiyear Synthesis of the Macroinvertebrate Component

from 1992 to 2002

for the Long Term Resource Monitoring Program

by

Jennifer Sauer

Final Report submitted to

U.S. Army Corps of Engineer District, Rock Island

Clock Tower Building

PO Box 2004

Rock Island, Illinois 61204-2004

December 2004

U.S. Geological Survey

Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road

La Crosse, Wisconsin 54603
Suggested citation:

Sauer, J. 2004. Multiyear synthesis of the macroinvertebrate component from 1992 to 2002 for the Long Term Resource

Monitoring Program. 2004. Final report submitted to U.S. Army Corps of Engineers from the U.S. Geological Survey, 

Upper Midwest Environment Sciences Center, La Crosse, Wisconsin, December 2004. Technical Report LTRMP 2004-T005. 

31 pp. + Appendixes A–C.

Additional copies of this report may be obtained from the National Technical Information Service, 5285 Port Royal Road, 

Springfield, VA 22161 (1-800-553-6847 or 703-487-4650). Also available to registered users from the Defense Technical 

Information Center, Attn: Help Desk, 8725 Kingman Road, Suite 0944, Fort Belvoir, VA 22060-6218 (1-800-225-3842 or 

703-767-9050).
iii

Contents

Preface ......................................................................................................... v

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

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

Results: Stratified Random Sampling ..................................................................... 6

Target Macroinvertebrates ........................................................................... 6

Mayflies .......................................................................................... 6

Fingernail Clams ................................................................................. 9

Midges ............................................................................................. 9

Asiatic Clams and Zebra Mussels ............................................................ 11

Results: Historical (Fixed) Sites ........................................................................... 11

Pool 4 ................................................................................................... 11

Pool 8 ................................................................................................... 12

Pool 13 ................................................................................................... 14

Pool 26 ................................................................................................... 14

Open River Reach .................................................................................... 15

La Grange Pool ....................................................................................... 17

Discussion ................................................................................................... 17

Summary ...................................................................................................... 23

Acknowledgments .......................................................................................... 24

References ................................................................................................... 25

Appendix A. Life Histories of Target Taxa ............................................................ A-1

Appendix B. Macroinvertebrate Sampling Methods Used by Various Researchers at

Historical (Fixed) Sites in the Upper Mississippi River System ........................... B-1

Appendix C. Historical (Fixed) Sample Sites Resampled by the Long Term Resource

Monitoring Program ........................................................................... C-1

Tables

1. Annual numbers of random and fixed sample sites for macroinvertebrates, by study area and 

stratum from 1993 to 2002, and area (hectares) of strata available for macroinvertebrate 

sampling .......................................................................................... 4

2. Percentage of total annual variance associated with the true annual variance (real change in the 

means) in backwater, contiguous aquatic areas for mayflies (Ephemeroptera), fingernail 

clams (Pisidiidae), and midges (Chironomidae) by study area .............................. 9

3. Statistical significance of year, study area, and interaction terms for mean abundances of

mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and midges (Chironomidae) 9

4. Estimated mean densities of mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and

midges (Chironomidae), Asiatic clams (Corbicula spp.), and zebra mussels (Dreissena 

polymorpha) by year and study area, weighted by areas of strata. N = sample ......... 10

5. Modeling efforts on the Long Term Resource Monitoring Program macroinvertebrate data

undertaken by the U.S. Geological Survey, Upper Midwest Environmental Sciences

Center, La Crosse, Wisconsin .................................................................. 24

Number

Page
iv

Figures

1. Study areas for macroinvertebrate sampling in the Long Term Resource Monitoring

Program ............................................................................................. 2

2. Winch-mounted standard Ponar grab sampler ...................................................... 4

3. Field crew from the Long Term Resource Monitoring Program sorting macroinvertebrates

from a Ponar sample .............................................................................. 4

4. Frequency of presence of number of target macroinvertebrates per sample from the Long

Term Resource Monitoring Program ......................................................... 5

5. Mean percentage of presence of taxa sampled by the Long Term Resource Monitoring

Program ............................................................................................. 7

6. Percent composition of mayflies (Ephemeroptera), fingernail clams (Pisidiidae), Asiatic clams 

(Corbicula spp.), midges (Chironomidae), and zebra mussels (Dreissena polymorpha)

in samples by study area ........................................................................ 8

7. Estimated density of mayflies (Ephemeroptera; number per square meter, ±1 standard error)

by study area, weighted by area of strata ...................................................... 12

8. Mean density of mayflies (Ephemeroptera; number per square meter) by study reach and

aquatic strata ....................................................................................... 13

9. Estimated mean density of mayflies (Ephemeroptera; number per square meter) by

predominant substrate type, weighted by areas of strata .................................... 14

10. Estimated density of fingernail clams (Pisidiidae; number per square meter, ±1 standard

error) by study area, weighted by area of strata ............................................. 15

11. Mean density of fingernail clams (Pisidiidae; number per square meter) by study reach and

aquatic strata ....................................................................................... 16

12. Estimated mean density of fingernail clams (Pisidiidae; number per square meter) by

predominan substrate type, weighted by areas of strata .................................... 17

13. Estimated density of midges (Chironomidae; number per square meter, ±1 standard error)

by study area, weighted by area of strata ...................................................... 18

14. Mean density of midges (Chironomidae; number per square meter) by study reach and

aquatic strata ....................................................................................... 19

15. Estimated mean density of midges (Chironomidae; number per square meter) by

predominant substrate type, weighted by areas of strata .................................... 20

16. Estimated density of zebra mussels (Dreissena polymorpha; number per square meter,

±1 standard error) by study area, weighted by area of strata .............................. 21

17. Mean densities of mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and diving

ducks from areas of Pool 8 closed to waterfowl hunting, 1996–2002 ..................... 23

Number Page
v

Preface

The Long Term Resource Monitoring Program (LTRMP) was authorized under the Water Resources 

Development Act of 1986 (Public Law 99-662) as an element of the U.S. Army Corps of Engineers’ 

Environmental Management Program. The LTRMP is being implemented by the Upper Midwest 

Environmental Sciences Center, a U.S. Geological Survey science center, in cooperation with 

the five Upper Mississippi River System (UMRS) States of Illinois, Iowa, Minnesota, Missouri, 

and Wisconsin. The U.S. Army Corps of Engineers provides guidance and has overall Program 

responsibility. The mode of operation and respective roles of the agencies are outlined in a 1988 

Memorandum of Agreement.

The UMRS encompasses the commercially navigable reaches of the Upper Mississippi River, as 

well as the Illinois River and navigable portions of the Kaskaskia, Black, St. Croix, and Minnesota 

Rivers. Congress has declared the UMRS to be both a nationally significant ecosystem and a 

nationally significant commercial navigation system. The mission of the LTRMP is to provide 

decision makers with information for maintaining the UMRS as a sustainable large river ecosystem 

given its multiuse character. The long-term goals of the Program are to understand the system, 

determine resource trends and effects, develop management alternatives, manage information, and 

develop useful products.

This multiyear report supports Task 2.2.7 as specified in Goal 2, Monitor Resource Change, of 

the LTRMP Operating Plan (U.S. Fish and Wildlife Service 1993). This report was developed with 

funding provided by the LTRMP.
Multiyear Synthesis of the Macroinvertebrate Component 

from 1992 to 2002

for the Long Term Resource Monitoring Program

by

Jennifer Sauer

U.S. Geological Survey

Upper Midwest Environmental Sciences Center 

2360 Fanta Reed Road 

La Crosse, Wisconsin 54603

Abstract: In 1992, macroinvertebrate sampling was begun in Pools 4, 8, 13, and 26; the Open River Reach 

of the Mississippi River; and La Grange Pool of the Illinois River as part of the Long Term Resource 

Monitoring Program. Long-term monitoring is needed to detect population trends and local changes in 

aquatic ecosystems. We selected mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and the exotic 

Corbicula species for monitoring. Midges (Chironomidae) were added to the sampling design in 1993 and 

zebra mussels (Dreissena polymorpha) were added in 1995. Sampling was based on a stratified random 

design and conducted at approximately 125 sites per study area. Mean densities of taxa were weighted by 

strata for extrapolation. The poolwide estimated mean densities of mayflies, fingernail clams, and midges 

were all within the range of variation observed historically. Over the last 11 years of sampling, the northern 

study areas supported the highest densities of the target organisms. 

Key words: Benthic aquatic macroinvertebrates, Corbicula, fingernail clams (Pisidiidae), Illinois River,

Long Term Resource Monitoring Program, mayflies (Ephemeroptera), midges (Chironomidae), Mississippi 

River, zebra mussels (Dreissena polymorpha)

Introduction

The Upper Mississippi River System (UMRS) 

is one of this Nation’s unique natural resources. It 

encompasses the commercially navigable reaches 

of the Upper Mississippi River (UMR), as well 

as the Illinois River and navigable portions of the 

Kaskaskia, Black, St. Croix, and Minnesota Rivers. 

The ecosystem provides habitat to a wide array 

of fish and wildlife species distributed among a 

complex assortment of flowing channels, floodplain 

lakes, backwaters, wetlands, and floodplain forests 

(Patrick 1998). With an ecosystem as diverse and 

complex as the UMRS, many of its processes and 

their interrelationships are not well known. One 

way to help understand this multifaceted system is 

through environmental monitoring. 

Macroinvertebrate monitoring by the Long 

Term Resource Monitoring Program (LTRMP) 

is intended to provide a better understanding 

of the conditions needed to support viable 

macroinvertebrate populations at levels adequate 

for sustaining native fish and migrating waterfowl. 

Scientific nomenclature and common names are 

based on the Integrated Taxonomic Information 

System (http://www.itis.usda.gov). Mayflies 

(Ephemeridae), fingernail clams (Pisidiidae), and 

midges (Chironomidae)—part of the soft-sediment 

substrate fauna—were chosen as target organisms 

for the LTRMP because of their important 

ecological role in the UMRS, especially as a source 

of food for waterfowl and fish (Appendix A). 

Thompson (1973) found that in fall lesser scaup 

(Aythya affinis) gizzards contained 76% fingernail 

clams and about 13% mayflies. Thompson also 

found the target organisms to be important to 

canvasbacks (A. valisneria), ring-necked ducks (A. 

collaris), and American coots (Fulica americana) 

feeding in open water. The Waterfowl Management 

Handbook also discusses the importance of 

invertebrates to waterfowl (Eldridge 1988). 

Shorebirds and wading birds also consume large 
2

numbers of invertebrates (Kushlan 1978). A 

number of fish, including commercial and sport 

fish such as crappies (Pomoxis spp.), shovelnose 

sturgeon (Scaphirhynchus platorynchus), 

walleye (Stizostedion vitreum), bluegill (Lepomis

macrochirus), freshwater drum (Aplodinotus 

grunniens), and yellow perch (Perca flavescens) 

feed on the target organisms (Hoopes 1960; Jude 

1968; Ranthum 1969; Tyson and Knight 2001).

The Asiatic clam (Corbicula spp.) and zebra 

mussel (Dreissena polymorpha; Appendix A), 

both non-native freshwater bivalves, were chosen 

for monitoring because of possible detrimental 

effects they may have on the economy and 

biology of the UMRS (Tucker 1995a,b; Effler 

et al. 1996; Haynes et al. 1999; Pimentel et 

al. 2000) and their status is of concern to river 

managers.

Researchers have traditionally used 

macroinvertebrates as biological indicators 

of river water quality (Fremling 1964, 1973, 

1989; Myslinski and Ginsburg 1977; 

Rosenberg and Resh 1993; Steingraber 

and Weiner 1995). An indicator species 

can be defined as a species that has 

particular requirements with regard to 

a known set of physical or chemical 

parameters. Macroinvertebrates also 

perform an important ecological 

function by digesting organic material 

and recycling nutrients (Reice and 

Wohlenberg 1992). 

Long-term monitoring of biological 

resources is at the core of understanding 

the dynamics of ecological patterns 

and processes and trying to separate 

variation due to natural and 

anthropogenic influences (http://

www.pwrc.usgs.gov/research/sis98/

hammer8s.htm). Few long-term studies 

on the distribution and abundance 

of macroinvertebrates in large rivers 

have been published (LaRoe et al. 

1995). Several areas of the UMRS 

have been sampled sporadically for 

benthic macroinvertebrates by various 

researchers (Fremling 1964; Carlander 

et al. 1967; Gale 1969; Hubert et al. 

1983; Eckblad and Lehtinen 1991; 

Brewer 1992; Hornbach et al. 1993). 

Although these studies contain valuable 

information, in many circumstances comparative 

data for long-term resource trends do not exist 

because of changes in methods or discontinued 

sampling. The LTRMP macroinvertebrate 

monitoring framework will provide a better 

understanding of the long-term changes in the 

UMRS natural resources.

Methods

Macroinvertebrate sampling was conducted 

in 1992–2002 in six study areas on the UMRS 

(Figure 1). The six LTRMP study areas represent 

the variety of aquatic areas within the UMRS. 

They range in size (calculated from geographic 

information system coverage; Lowenberg 1993) 

from 19,000 (Pool 8) to 107,000 ha (Open 

River Reach). Program study areas are referred 

to herein by the navigation pool designations 

according to the U.S. Army Corps of Engineers 

Figure 1. Study areas for macroinvertebrate sampling in the Long Term 

Resource Monitoring Program.
3

lock and dam system and include: Pools 4 (river 

miles 752 to 797), 8 (river miles 679 to 703), 

13 (river miles 523 to 557), and 26 (river miles 

202 to 242); the Open River Reach (river miles 

29 to 80) of the Upper Mississippi River; and

La Grange Pool (river miles 80 to 158) of the 

Illinois River (Figure 1).

The Open River Reach was dropped from 

the monitoring design in 2001 because of 

extremely low densities of burrowing mayflies 

(Hexagenia spp.) and fingernail clams and 

unfavorable habitat for these taxa (McDonald and 

Strickland 2001; Sauer 2003). Although Pool 26 

and La Grange Pool also have low densities 

of the target organisms, these areas were kept 

in the monitoring design because they contain 

favorable habitat (i.e., soft substrates) for the 

target organisms. Monitoring should detect any 

changes (rebound) in the populations of the target 

organisms in these areas because of natural or 

anthropogenic changes in the system. 

Initially, burrowing mayflies, fingernail clams, 

and the non-native Asiatic clam were selected for 

monitoring. Midges were added to the sampling 

design in 1993 and the non-native zebra mussel 

in 1995.

In addition to collecting abundance data on 

the target taxa, in 1998 we began recording the 

presence or absence of Amphipoda (scuds), 

Decapoda (freshwater shrimp and crayfish), 

Diptera (aquatic flies excluding Chironomids), 

Dreissenidae (zebra mussels), Gastropoda 

(snails), Odonata (dragonflies and damselflies), 

Oligochaeta (aquatic worms and leeches), 

Plecoptera (stoneflies), and Trichoptera 

(caddisflies). The first year of macroinvertebrate 

sampling was used to refine the sampling design, 

and changes have been documented in the 

LTRMP Procedures Manual (Thiel and Sauer 

1999). Therefore, only 1993–2002 data will be 

used in statistical analysis of long-term trends. 

The LTRMP staff developed a spatial database 

of aquatic areas (Owens and Ruhser 1996) on 

the basis of aerial photographs taken in 1989. 

This database was used to select sites for 

stratified random sampling and the quantification 

of sampling strata distribution and size. For 

LTRMP macroinvertebrate monitoring, random 

sample sites were selected from grids whose 

cells are 50 m2. Sample sites also included some 

historical (fixed) sites where benthic samples 

were previously collected by researchers 

(Appendix B).

Sampling was conducted annually at about 

125 sites per study area in spring (April to 

mid-June) before the emergence of burrowing 

mayflies and substantial aquatic vegetation 

growth. Sample allocation was based on a 

stratified random design where strata were 

aquatic areas (Table 1). The LTRMP strata are 

groupings of aquatic area types at different levels 

within Wilcox’s (1993) hierarchy: 

• backwaters, contiguous (BWC)—non-channel areas lateral to the channel or within 

islands having apparent surface-water 

connection with channel habitats; 

• main channel borders (MCB)—the area 

between the designated channel and the 

riverbank (not including revetments and 

channel-training structures); 

• impounded areas (IMP)—the large, mostly 

open water areas in the downstream portion 

of the navigational pools; 

• side channels (SC)—channels that carry less 

flow than the navigational channel; and

• tributary delta lake (TDL)—a natural lake 

formed by a river delta, which in Pool 4 is 

Lake Pepin, a natural lake formed by the 

Chippewa River delta.

In 1992, we used nine strata to distribute 

the macroinvertebrate monitoring sites. Some 

of these strata included aquatic vegetation, a 

seasonal attribute, as part of their definition. This 

classification scheme was reduced to five strata 

in 1993 when vegetation status was dropped from 

the strata designation. 

Benthic samples were collected with a winchmounted 0.052-m2

 standard Ponar grab sampler 

(Ponar Grab Dredge, Wildlife Supply Company, 

Saginaw, Michigan; Figure 2). Mayflies, 

fingernail clams, midges, Asiatic clams, and 

zebra mussels were picked and counted in the 

field (Figure 3). The wash frame sieve size was 

changed from a U.S. Standard Sieve no. 30 

(595 μm), used in 1992, to a U.S. Standard Sieve 

no. 16 (1.18-mm) in 1993 to increase sorting 

efficiency for large-sized target organisms in the 
4

field. Thu_s, inferences on macroinvertebrate 

numbers from these data (1993–present) are 

restricted to larger individuals (see Dukerschein 

et al. 1996 for size measurements). In certain 

years, after the picking process was complete, 

leaving only detritus and organisms other 

than the target organisms, it was determined 

by random draw whether the sample would 

be brought back to the laboratory for quality 

assurance (Norris and Georges 1992). A 

total of 10% of the sites sampled within each 

stratum each year were brought back to the 

laboratory to evaluate field-picking efficiency. 

Macroinvertebrates found in the laboratory 

sorting process were not included in analyses.

At each site, substrate composition was 

determined by subjective characterization. Six 

categories of substrate composition were used: 

Figure 2. Winch-mounted standard 

Ponar grab sampler.

Figure 3. Field crew from the Long Term Resource Monitoring 

Program sorting macroinvertebrates from a Ponar sample.

Table 1. Annual numbers of random and fixed sample sites for macroinvertebrates, by study area and stratum from 1993 to 2002a, and area (hectares) of strata availableb for macroinvertebrate sampling.Study area

Backwater contiguous Impounded Side channel Main channel border

Number 

of sites

random Fixed Area (ha)

Number 

of sites

random Fixed

Area

(ha)

Number 

of sites

random Fixed

Area

(ha)

Number 

of sites

random Fixed

Area

(ha)

Pool 4 57 3 2,301 44 1 9,368c 10 — 722 10 — 563Pool 8 31 3 1,762 49 11 3,505 19 2 1,377 10 — 632Pool 13 43 2 2,779 46 1 3,672 14 4 985 15 — 1,145Pool 26 40 — 412 27 — 190 34 3 1,496 17 4 3,312Open River Reach — — — — — — 64 16 437 43 2 3,384La Grange Pool 24 18 1,136 — — — 35 7 179 40 1 2,444aSample size varies over years because of sampling difficulties (Sauer 2003).bNot all of the aquatic area in the study area is accessible for macroinvertebrate sampling.cImpounded area for Pool 4 is Lake Pepin, a Tributary Delta Lake.
5

hard clay, silt clay, silt clay with sand, sand with 

silt clay, sand, and gravel rock. The percentage of 

surface area coverage of submersed and floatingleaf aquatic vegetation was estimated in the 

column of water through which the Ponar dredge 

fell. The type and abundance of vegetation and 

open water in a 15-m radius from the boat were 

qualitatively characterized. Water depth also was 

measured at each site.

The number of each target taxa collected 

was recorded from individual Ponar samples. 

Whenever target taxa were not caught in a 

sample, the catch for those taxa in that sample 

was recorded as zero. Macroinvertebrate 

sampling procedures are described in detail in 

the LTRMP Procedures Manual (Thiel and Sauer 

1999). 

Frequency distributions varied among years; 

in 1992 low densities (<20 organisms per 

sample) were common, and higher densities 

(≥20) were present in about 6% of the samples 

(Figure 4). In 1992, stratified random sampling 

sites were distributed equally among the 

strata. After analysis of the 1992 data—where 

57% of the samples did not contain any target 

organisms—we decided to sample more suitable 

habitat of the target organisms (i.e., soft-sediment 

substrate; Table 1) with more frequency. The 

U.S. Environmental Protection Agency (2003) 

monitoring program states that more sampling 

effort in one area will not bias the data. 

Analyses of densities (DS) for temporal trends 

among mayflies, fingernail clams, and midges 

were based on estimates of mean densities (��) 

obtained by pooling data over all strata within a 

study area. 

The presence of differences between LTRMP 

study areas and trends was tested. All models 

were fitted using SAS® mixed modeling 

procedure (PROC MIXED®; SAS 2000). 

Imposing some simplifying assumptions, we 

tested for simple linear trends (straight-line 

increases or decreases) over the 10-year period 

and also comparisons of these trends among 

the LTRMP study areas. It was not feasible to 

perform more detailed time series and trend 

analyses because the data series were too short 

(i.e., in essence N = 10 per study area). Historical 

(fixed) sites were removed for this analysis. Data 

from the Open River Reach study area were 

Figure 4. Frequency of presence of number of target macroinvertebrates per sample from the Long Term 

Resource Monitoring Program. After 1992, sampling was modified by shifting more effort to soft substrates, 

which are more suitable for the target taxa.
6

Percent composition of target organisms 

varied among years within study areas (Figure 

6). Between 1993 and 1998, Pool 8 consistently 

had higher percentages of mayflies than any 

of the other four target organisms. However, 

from 1999 to 2001, zebra mussels became more 

prevalent than the other taxa. Pool 13 had high 

percentages of fingernail clams in 1993–1996, 

whereas zebra mussels dominated in 1997, 1999, 

2001, and 2002 when compared with other target 

organisms. Pool 26 had high percentages of 

midges for most of the years except 1998 when 

zebra mussels were most prevalent. Midges 

dominated samples in La Grange Pool from 1993 

to 2002.

The variance component estimates indicate 

that, on average, the majority of the variance 

seen among mayfly, fingernail clam, and midge 

annual means is derived from real changes in 

those means (Table 2). A minority of the year-toyear variance was attributed to sampling or error 

variance. The error variance refers to unexplained 

variation. The Open River Reach was not 

included in this analysis.

Target Macroinvertebrates

Variation associated with log-transformed 

means of mayfly, fingernail clam, and midge 

abundance data appeared primarily associated 

with study area only (Table 3). This reflects the 

large differences in abundances seen among the 

study areas (Table 4). Monotonic trends between 

1993 and 2002 in mean densities of mayflies and 

midges were not visually apparent or statistically 

significant. The marginally significant trendstudy area interaction term for fingernail clams 

was associated with a substantial increase in 

abundance in Pool 8 only.

Asiatic clams and zebra mussels were not 

included in the trend analyses because of low 

numbers (Table 4). 

Mayflies

Estimated poolwide mean densities (��) of 

mayflies ranged from a low of 3 m-2 in La Grange 

Pool in 2001 and in the Open River Reach in 

1999 to a high of 262 m-2 in Pool 8 in 2000 

not included for analysis, but were included in 

general description of the data. Data used in 

this report can be downloaded from http://www.

umesc.usgs.gov/data_library/

macroinvertebrate/invert1_query.html.

Differences between field stations and the 

presence of temporal trends were investigated 

using log-transformed poolwide means. Means 

were estimated from data deriving from our 

stratified random survey design using standard 

design-based assumptions (Cochrane 1977). 

Because of the short time series, linear trends 

(on the log scale) were assumed (note that linear 

trends on the log scale correspond to exponential 

trends on the untransformed scale). We made 

an assumption of independence across years; 

an assumption that has generally appeared 

reasonable for the LTRMP macroinvertebrate 

data (Brian Gray, U.S. Geological Survey, 

La Crosse, Wisconsin, personal communication) 

and corresponds to the observation that life 

cycles of the primary taxa groups are 1 year or 

less.

Variance components were estimated using 

a method-of-moments approach (Lenter and 

Bishop 1986) on transformed data. To avoid 

estimating across different strata, annual and 

error variances were estimated from backwater 

contiguous sample sites only.

Results: Stratified Random Sampling

More than 6,090 Ponar collections (stratified 

random sampling sites) were made from the six 

study areas in spring 1993 to 2002. Water depths 

at sampling sites ranged from 0.10 to 18.5 m. 

Visual classification of sediments indicated 

that sample sites in Pools 4, 8, 13, and 26 and 

La Grange Pool were dominated by silt clay. In 

the Open River Reach, main channel border and 

side channel strata were dominated by sand.

Mayflies and fingernail clams were most 

prevalent in the upper three LTRMP pools (Pools 

4, 8, and 13; Figure 5). Midges and aquatic 

worms and leeches (Oligochaete) were present 

in relatively high frequency of samples in all 

study areas except the Open River Reach. Not all 

taxa found inhabit soft substrates so they are not 

expected in great numbers in a Ponar sample.
7

(Table 4; Figure 7). The lowest �� of mayflies 

throughout the 10 years of sampling were from 

Pool 26, the Open River Reach, and La Grange 

Pool. Pool 13 had the most consistent densities 

over the years until 2001 when �� reached a 

low of 77 m-2; however, numbers rebounded in 

2002. No estimated mean densities of mayflies 

were calculated for Pool 26 in 1995 because 

Figure 5. Mean percentage of presence of taxa sampled by the Long Term Resource Monitoring Program. All years combined 

(1993–2002). Taxa include Ephemeridae (mayflies), Pisidiidae (fingernail clams), Chironomidae (midges), Corbicula spp. 

(Asiatic clams), Dreissenidae (zebra mussels), Odonata (dragonflies and damselflies), Plecoptera (stoneflies), Trichoptera 

(caddisflies), Diptera (aquatic flies excluding Chironomids), Unionidae (freshwater mussels), Oligochaeta (aquatic worms and 

leeches), Decapoda (freshwater shrimp and crayfish), Amphipoda (scuds), and Gastropoda (snails).
8

field crews were not able to sample certain sites 

because of high water. Pool 8 had the largest 

range in �� (223.6 m-2). 

Although mean densities of mayflies varied 

over the years among strata, the IMP, TDL, and 

BWC strata supported the highest mean number 

of mayflies in Pools 4, 13, and 26 (Figure 8). 

Highest mean mayfly densities in Pool 8 were 

present in side channel and impounded strata. 

Side channel areas had the highest mayfly 

Figure 6. Percent composition of mayflies (Ephemeroptera), fingernail clams (Pisidiidae), Asiatic clams (Corbicula spp.), 

midges (Chironomidae), and zebra mussels (Dreissena polymorpha) in samples by study area. Open River Reach not sampled 

in 1993 or 1997 because of high water. Sampling discontinued in the Open River Reach in 2001.
9

densities in La Grange Pool in 1993–2002. 

Overall, MCB areas supported the lowest 

densities of mayflies in all study areas.

The silt clay substrate tended to support the 

highest mean numbers of mayflies in all study 

areas (Figure 9). The large-particle substrates 

(i.e., sand with silt, sand, and gravel rock) had the 

lowest numbers of mayflies. 

Fingernail Clams

Estimated poolwide densities of fingernail 

clams ranged from zero in Pool 26 (1996, 2000, 

and 2002) and Open River Reach (1995–1996, 

1998–2000) to more than 2,500 m-2 in Pool 13 

in 1993 (Table 4; Figure 10). The density seen in 

Pool 13 in 1993 was 35 times that found in other 

study areas for the same year. In 1993–1998, 

relatively low numbers of fingernail clams in 

Pools 4 and 8 were reported; however, 

densities increased in 1999. Pool 13 

had the largest range in mean density 

(2,489.7 m-2) for the study period. 

Over all years, in Pool 8, IMP and SC 

strata supported the highest densities 

of fingernail clams, whereas in Pools 

4, 13, and 26 IMP strata, including 

the naturally impounded Lake Pepin, 

supported the highest densities of 

fingernail clams (Figure 11). Side 

channel areas had the highest fingernail 

clam densities in La Grange Pool, which 

has no impounded stratum. The IMP 

stratum seems to have more favorable 

habitat for fingernail clams.

The silt clay and silt clay with sand 

substrates tended to support the highest 

number of fingernail clams (Figure 12). 

The large-particle substrates (sand with 

silt, sand, and gravel rock) supported 

the lowest densities of fingernail clams.

Midges

Poolwide estimates of midges ranged 

from a high of 570 m-2 in Pool 13 in 

2000 to a low of 4 m-2 in the Open River 

Reach in 1998 (Table 4; Figure 13). Although no 

significant linear trends were detected, Pools 4, 

8, and 13 experienced apparent declines in midge 

densities from 1993 to1996; but then began an 

increase in densities in 1997. Pools 4 and 13 

and La Grange Pool contained the highest ��

of midges (Table 4). The lowest �� of midges 

was from the Open River Reach. Pool 13 had the 

largest range in �� (552.7 m-2) over the study 

period compared with other study areas. 

Midge densities varied widely among strata 

over years and study areas. The BWC strata had 

the highest densities of midges in Pools 8, 13, 

and 26 and La Grange Pool. In Pool 4, midge 

densities were highest in Lake Pepin (Figure 14).

The small-particle substrates (silt clay and silt 

clay with sand) tended to support the highest 

mean number of midges over all years in all 

study areas (Figure 15). 

Table 2. Percentage of total annual variance associated 

with the true annual variance (real change in the means) 

in backwater, contiguous aquatic areas for mayflies 

(Ephemeroptera), fingernail clams (Pisidiidae), and midges 

(Chironomidae) by study area. 

Study area

Mayflies

(%)

Fingernail clams

(%)

Midges

(%)

Pool 4 73 67 89

Pool 8 49 86 86

Pool 13 84 67 91

Pool 26 93 64 79

La Grange Pool 71 50 77

Table 3. Statistical significance of year, study area, and interaction 

terms for mean abundances of mayflies (Ephemeroptera), fingernail 

clams (Pisidiidae), and midges (Chironomidae).

Degrees of freedom F

Numerator Denominator Value Pr > F

Mayfliesa

 Year 1 31.8 0.04 0.8471

 Study area 4 16.5 75.33 <0.0001 

 Interaction 4 16.5 1.65 0.2102

Fingernail clamsa

 Year 1 26.4 1.08 0.3083

 Study Area 4 15.4 37.60 <0.0001

 Interaction 4 15.4 3.23 0.0417

Midgesa

 Year 1 25.5 1.04 0.3170

 Study area 4 16.9 11.16 0.0001

 Interaction 4 16.9 1.15 0.3675 a

Open River Reach removed for analysis.
10

Study area

and yeara

(N)

Mayflies (m-2)

(±1 SE)

Fingernail

clams (m-2)

(±1 SE)

Midges (m-2)

b

(±1 SE)

Asiatic

clams (m-2)

(±1 SE)

Zebra musselsc

(m-2)

(±1 SE)

Pool 4

 1992 (122) 59 (18) 47 (19) —d 0 (0) —

 1993 (121) 123 (35) 71 (10) 306 (38) 0 (0) —

 1994 (125) 196 (49) 84 (12) 182 (32) 0 (0) —

 1995 (121) 171 (34) 59 (13) 78 (13) 0 (0) 26 (26)

 1996 (121) 132 (34) 39 (7) 38 (12) 0 (0) 116 (113)

 1997 (120) 69 (18) 76 (9) 152 (35) 0 (0) 31 (27)

 1998 (121) 209 (44) 73 (10) 253 (40) 0 (0) 107 (98)

 1999 (120) 69 (18) 138 (21) 199 (33) 0 (0) 37 (33)

 2000 (120) 223 (39) 118 (14) 65 (15) 0 (0) 31 (29)

 2001 (119) 104 (19) 103 (14) 71 (13) 0 (0) 232 (218)

 2002 (121) 93 (31) 79 (10) 68 (16) 0 (0) 8 (6)

Pool 8

 1992 (109) 51 (25) 15 (11) — 0 (0) —

 1993 (109) 117 (40) 22 (11) 50 (9) 0 (0) —

 1994 (112) 91 (31) 11 (5) 26 (16) 0 (0) —

 1995 (109) 56 (14) 6 (3) 11 (4) 0 (0) 0 (0)

 1996 (109) 38 (11) 2 (1) 15 (4) 0 (0) 1 (0)

 1997 (112) 71 (16) 9 (4) 26 (6) 0 (0) 25 (11)

 1998 (109) 120 (36) 26 (8) 82 (18) 0 (0) 26 (17)

 1999 (107) 212 (57) 507 (155) 45 (15) 0 (0) 825 (581)

 2000 (107) 262 (70) 270 (55) 38 (12) 0 (0) 609 (349)

 2001 (108) 104 (30) 170 (39) 38 (10) 0 (0) 882 (563)

 2002 (109) 75 (25) 236 (39) 62 (17) 0 (0) 196 (113)

Pool 13

 1992 (118) 120 (31) 84 (28) — 0 (0) —

 1993 (119) 150 (38) 2,571 (489) 496 (93) 0 (0) —

 1994 (125) 189 (35) 606 (160) 73 (34) 0 (0) —

 1995 (118) 182 (52) 265 (83) 38 (9) 0 (0) 10 (7)

 1996 (118) 148 (38) 231 (58) 21 (7) 0 (0) 14 (8)

 1997 (118) 165 (43) 87 (23) 78 (36) 0 (0) 559 (446)

 1998 (118) 167 (45) 150 (33) 79 (27) 0 (0) 120 (93)

 1999 (118) 186 (46) 145 (33) 232 (74) 0 (0) 527 (320)

 2000 (118) 158 (51) 126 (37) 570 (87) 0 (0) 172 (131)

 2001 (117) 77 (19) 332 (121) 28 (14) 0 (0) 427 (168)

 2002 (118) 220 (54) 365 (86) 190 (47) 0 (0) 448 (201)

Pool 26

 1992 (117) 21 (10) 15 (9) — 2 (1) —

 1993 (66) 7 (2) 1 (1) 11 (2) 0 (0) —

 1994 (124) 22 (7) 5 (3) 14 (8) 1 (1) —

 1995 (67)e — — — — —

 1996 (112) 13 (10) 0 (0) 18 (9) 0 (0) 0 (0)

 1997 (87) 16 (8) 1 (1) 13 (6) 0 (0) 1 (1)

 1998 (72) 25 (16) 4 (4) 5 (2) 4 (3) 30 (25)

 1999 (117) 28 (15) 1 (1) 9 (4) 1 (1) 2 (2)

 2000 (118) 27 (11) 0 (0) 27 (8) 2 (2) 109 (105)

 2001 (115) 7 (3) 2 (1) 30 (8) 0 (0) 7 (6)

 2002 (104) 44 (22) 0 (0) 53 (14) 0 (0) 0 (0)

Table 4. Estimated mean densities of mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and midges (Chironomidae), 

Asiatic clams (Corbicula spp.), and zebra mussels (Dreissena polymorpha) by year and study area, weighted by areas of 

strata. N = sample size, SE = standard error.
11

Asiatic Clams and Zebra Mussels

Because of the low number of Asiatic clams 

and zebra mussels (Table 4), no statistical 

analyses were undertaken; however descriptive 

statistics follow. Low numbers of Asiatic clams 

were found in all study areas. Fewer than 15% 

of the samples contained Asiatic clams and 

zebra mussels. No study areas had estimated 

densities of more than 115 m-2 Asiatic clams (six 

individuals in a sample). Zebra mussel densities 

were extremely low in La Grange Pool in all 

years of monitoring (Figure 16). Densities of 

zebra mussels are most likely underrepresented 

because we sampled mainly soft substrates rather 

than the hard substrates that zebra mussels prefer. 

Zebra mussel densities were highest in MCB 

and IMP strata. The highest mean densities of 

zebra mussels in all study areas were found in 

the gravel rock substrate, which is preferred by 

zebra mussels for attachment by their byssal 

threads.

Results: Historical (Fixed) Sites

More than 730 samples were collected from 

historical sites (fixed sites; Appendix B) in 

the six study areas from 1993 to 2002. Only 

mayflies and fingernail clam densities were 

examined since they were the most consistent 

taxa reported historically. 

Pool 4 

In Pool 4, four historical sites sampled by 

North Star Research Institute (1973) were 

resampled by the LTRMP from 1993 to 2002 

(Appendix B). The highest number of mayflies 

and fingernail clams reported by North Star 

Research Institute (1973) were at historical sites 

502 and 503, where they reported concentrations 

of mayflies at 105.8 m-2 and of fingernail clams 

at 86.5 m-2 (Appendix C). In LTRMP data from 

1993 to 2002, the highest densities of mayflies 

Study area

and yeara

(N)

Mayflies (m-2)

(±1 SE)

Fingernail

clams (m-2)

(±1 SE)

Midges (m-2)

b

(±1 SE)

Asiatic

clams (m-2)

(±1 SE)

Zebra musselsc

(m-2)

(±1 SE)

Open Riverf,g

 1992 (92) 22 (12) 5 (3) — 1 (1) —

 1993 — — — — —

 1994 (84) 19 (9) 1 (1) 8 (4) 2 (1) —

 1995 (113) 12 (6) 0 (0) 14 (5) 2 (1) 2 (2)

 1996 (107) 11 (6) 0 (0) 5 (2) 1 (1) 0 (0)

 1997 — — — — —

 1998 (108) 12 (9) 0 (0) 4 (2) 1 (1) 20 (17)

 1999 (108) 3 (2) 0 (0) 6 (3) 1 (1) 100 (74)

 2000 (97) 9 (5) 0 (0) 22 (7) 0 (0) 71 (64)

La Grange Pool

 1992 (102) 13 (6) 4 (2) — 0 (0) —

 1993 (98) 10 (4) 18 (10) 47 (13) 0 (0) —

 1994 (124) 24 (8) 53 (13) 57 (10) 12 (3) —

 1995 (97) 6 (4) 17 (9) 29 (11) 2 (1) 11 (11)

 1996 (98) 4 (1) 5 (3) 150 (50) 1 (1) 0 (0)

 1997 (99) 8 (3) 9 (5) 101 (33) 0 (0) 0 (0)

 1998 (99) 9 (6) 21 (12) 91 (25) 1 (1) 3 (1)

 1999 (98) 9 (5) 13 (5) 46 (16) 0 (0) 0 (0)

 2000 (99) 7 (5) 10 (8) 67 (22) 0 (0) 1 (1)

 2001 (98) 3 (1) 9 (4) 51 (13) 0 (0) 0 (0)

 2002 (99) 4 (2) 33 (14) 98 (20) 0 (0) 0 (0) a

In 1992, a mesh size of 595 μm was used. In all other years, a mesh size of 1.18 mm was used. bSampling began in 

1993. cSampling began in 1995. dA dash (—) indicates no data. eSampling not completed in 1995 because of high 

water. fSampling not done in 1993 or 1997 because of high water. gSampling discontinued in 2001.

Table 4. Continued
12

were 576.9 m-2 (site 504; BWC) and of fingernail 

clams were 403.8 m-2 (site 501; TDL). Over 

the years, abundance of mayflies was highest at 

sample site 504—BWC strata. Fingernail clam 

densities were highest in the TDL stratum. Sites 

501 and 504 were the most productive sites over 

all years of the present study. 

Pool 8 

For LTRMP macroinvertebrate sampling, 

16 sites were resampled (Appendix B). Two 

researchers sampled historical sites in Pool 8 

(Elstad 1977; Brewer 1992). The highest number 

of mayflies and fingernail clams reported by 

Figure 7. Estimated density of mayflies (Ephemeroptera; number per square meter, ±1 standard error) by study area, weighted 

by area of strata. Horizontal line indicates grand mean.
13

Elstad (1977) at sample sites in Pool 8 were 

1,353.5 (site 504) and 5,184.9 m-2 (site 503), 

respectively (Appendix C). Brewer (1992) noted 

significant declines in total macroinvertebrate 

abundance in open water habitats and no 

significant changes in marsh, channel, and 

dredge areas when compared to Elstad’s (1977) 

findings. The highest density of mayflies found 

by Brewer (1992) was 241.3 m-2, and the highest 

density of fingernail clams was 243.5 m-2. In 

LTRMP data from 1993 to 2002, the highest 

densities of mayflies and fingernail clams were 

Figure 8. Mean density of mayflies (Ephemeroptera; number per square meter) by study reach and aquatic strata. Impounded 

area for Pool 4 is Lake Pepin, a Tributary Delta Lake.
14

at site 515; IMP strata (3,500.0 and 12,134.6 

m-2, respectively; Appendix C). Over the years, 

mayfly densities were highest at sample sites 

502, 504–506, 510, and 514—BWC and IMP 

areas. Fingernail clam distribution was highest in 

the IMP strata.

Pool 13

Seven sites sampled by Hubert et al. (1983) 

in February and March 1983 were chosen to be 

resampled for the LTRMP (Appendix B). The 

highest number reported by Hubert et al. (1983) 

at historical sites for mayflies was 1,017.4 m-2

(site 502; SC) and for fingernail clams was 

1,544.6 m-2 (site 507; IMP; Appendix C). 

Between 1993 and 2002, the highest densities of 

mayflies and fingernail clams were 1,615.4 and 

4,096.2 m-2 (site 503; SC), respectively. For these 

same years, mayfly densities were consistently 

high at sample sites 502–506 (SC strata). 

Fingernail clam densities were greatest at sites 

503 and 504. 

In 1983, Hubert et al. observed that lake 

habitats (N = 18) supported a mean of 66 m-2

Hexagenia mayflies and 295 m_2 Sphaerium

fingernail clams. In three of the lake sites 

resampled for the LTRMP (sites 505, BWC; 506, 

BWC; and 507, IMP), mean densities of mayflies 

were from 0.0 to 1,557.7 m-2 and mean densities 

of fingernail clams were from 0 to 1,134.6 m-2. 

Site 507 has never reached the densities found in 

Hubert’s (1983) study (Appendix C).

Pool 26 

A total of seven historical sites in Pool 26 

were chosen to be resampled for the LTRMP 

(Appendix B). The highest number of mayflies 

and fingernail clams observed by Colbert et al. 

(1975) in July 1974 at historical sites in Pool 

26 (Appendix C) was 172.0 (site 503; SC) and 

25.0 m-2 (site 501; MCB), respectively. Between 

1993 and 2002, the highest densities of mayflies 

and fingernail clams were 1,038.5 and 57.7 m-2

(site 507; SC), respectively. In fact, site 507 

Figure 9. Estimated mean density of mayflies (Ephemeroptera; number per square meter) by predominant substrate type, 

weighted by areas of strata. Because of small sample sizes, substrates defined as clay were combined with the silt clay 

category and gravel rock with the sand category. All years combined (1993–2002).
15

was the only site in which fingernail clams 

were present for all 10 years of monitoring. The 

highest densities of mayflies were measured at 

sample site 503, a SC strata. Seagle et al. (1982) 

reported a Hexagenia density as high as 454 m-2

(N = 9; 5 replicates at each site).

Open River Reach

Eighteen sites sampled by Emge et al. (1974) 

in summers 1972 and 1973 were chosen to be 

resampled for the LTRMP (Appendix B). The 

highest number of mayflies reported by Emge 

Figure 10. Estimated density of fingernail clams (Pisidiidae; number per square meter, ±1 standard error) by study area, 

weighted by area of strata. Horizontal line indicates grand mean.
16

et al. (1974) at sample sites in the Open River 

Reach (Appendix C) was 675.0 m-2 (site 518; 

MCB). Between 1993 and 2000, the highest 

densities of mayflies were 384.6 m-2 (site 

515; SC). Over the years, the highest density 

of mayflies was at sample site 515; SC area. 

Fingernail clams were not found at any of the 

sites. This was consistent with Emge at al. (1974) 

findings.

Figure 11. Mean density of fingernail clams (Pisidiidae; number per square meter) by study reach and aquatic strata. 

Impounded area for Pool 4 is Lake Pepin, a Tributary Delta Lake..
17

La Grange Pool 

Twenty-six sites sampled by Paloumpis and 

Starrett (1960) in 1952–1954 and Anderson 

(1977) in September 1975 were chosen to be 

resampled for the LTRMP (Appendix B). The 

highest concentration reported by Anderson 

(1977) for mayflies was 34.4 m-2 (site 523; SC) 

and for fingernail clams was 34.4 m-2 (site 524; 

SC; Appendix C). In Appendix C, the LTRMP 

sites 501–509 were combined to represent Lake 

Matanzas and sites 510–522 were combined to 

represent Quiver Lake. The highest densities of 

mayflies were in Quiver Lake. Fingernail clam 

distribution was also highest in the Quiver Lake 

area with a mean maximum of 17,201.9 m-2 in 

1952, reported by Paloumpis and Starrett (1960). 

Fingernail clams were virtually nonexistent in 

Lake Matanzas from 1993 to 2002 (Appendix C).

Discussion

A number of studies have shown the target 

taxa, especially mayflies, fingernail clams, 

and midges, to be ecologically important as 

fish and waterfowl food, biological indicators, 

and converters of phytoplankton and bacteria 

to higher energy pathways (Hoopes 1960; 

Fremling 1964, 1989; Jude 1968; Ranthum 1969; 

Thompson 1973; Anderson et al. 1978; Sandusky 

and Sparks 1979; Reice and Wohlenberg 1992; 

Rosenberg and Resh 1993; Winter et al. 1996; 

Diggins and Stewart 1998; Schloesser and 

Nalepa 2001; Tyson and Knight 2001). For these 

reasons, there is much interest in tracking the 

abundance of these taxa. 

In the 1950s, much concern arose when mayfly 

densities crashed in the Upper Mississippi River 

System and Lake Erie (Fremling 1964; Mills 

et al. 1966; Kreiger et al. 1996). The last large 

emergence of mayflies near Havana, Illinois, 

was in 1949 (Mills et al. 1966). In 1976 in Lake 

Pepin, Pool 4, Trapp (1979) collected only 

28 mayfly (Hexagenia) nymphs from 50 stations. 

By 1986, follow up investigations of Trapp’s 

work yielded 369 mayfly nymphs (Fremling 

and Johnson 1990). Fremling (1989) detected 

the rebound of mayflies in Pool 2 and Lake 

Figure 12. Estimated mean density of fingernail clams (Pisidiidae; number per square meter) by predominant substrate type, 

weighted by areas of strata. Because of small sample sizes, substrates defined as clay were combined with the silt clay 

category and gravel rock with the sand category. All years combined (1993–2002).
18

Pepin in Pool 4 during the 1980s. Subsequently, 

the population declined in 1988 following a 

drought period. In 1926, the Mississippi River 

from St. Paul to Lock and Dam 3 had dissolved 

oxygen levels less than 1 mg/L. By 1987, 

dissolved oxygen levels had rebounded to 7 mg/L 

or greater (Johnson and Aasen 1989).

Carlander et al. (1967) showed how dynamic 

year-to-year mayfly populations were in Pool 19. 

They estimated pool populations of 3.6 billion 

Figure 13. Estimated density of midges (Chironomidae; number per square meter, ±1 standard error) by study area, weighted 

by area of strata. Horizontal line indicates grand mean.
19

in 1959 to 23.6 billion in 1962. Carlander et al. 

(1967) found larval mayfly densities ranging 

from 0 to 1,292 m-2 in June.

Fingernail clams have also experienced boomand-bust cycles in abundance. Gale (1969) 

reported fingernail clam population densities 

for Pool 19 of more than 5,000 m-2. Fingernail 

clam populations in several backwater lakes in 

Pool 9 varied from 631.8 m-2 in 1976 to 11.3 m-2

in 1989. Consequently increasing to 78.0 m-2

in 1990 (Eckblad and Lehtinen 1991). Pool 9 

densities reached more than 1,000 m-2 in the fall 

Figure 14. Mean density of midges (Chironomidae; number per square meter) by study reach and aquatic strata. Impounded 

area for Pool 4 is Lake Pepin, a Tributary Delta Lake.
20

of the year (Eric Nelson, U.S. Fish and Wildlife 

Service, personal communication). From 1992 

to 1998, there were extremely low densities 

of fingernail clams in Pool 8; in 1999 they 

rebounded to densities well above the 10-year 

mean (Figure 10). Especially high densities 

of fingernail clams (2,596 m-2) were found in 

Pool 13 in 1993 and then collapsed to 87 m-2

in 1997. Wilson et al. (1995) reported that in 

1985 fingernail clam densities averaged 30,000 

m-2 in Pool 19. By 1990, no fingernail clams 

were found. In recent years, peak densities have 

rebounded to about 50,000 m-2 in Pool 19 (Rick 

Anderson, Western Illinois University, personal 

communication).

Fingernail clam populations were abundant 

in the Illinois River before the 1950s (Mills et 

al. 1966). Paloumpis and Starrett (1960) found 

fingernail clams extremely abundant in Lake 

Matanzas (La Grange Pool; 212 m-2) in 1952. 

By 1953, they had disappeared from the lake. 

Similar declines were seen in Lake Chautauqua 

and Quiver Lake. The densities have never 

rebounded to those reported for the early 1950s. 

Richardson (1921) took benthic samples at Lake 

Matanzas in 1915 and found no Hexagenia

mayfly nymphs and 225.7 m-2 fingernail clams 

in samples with depths between 2 and 2.6 m 

with no vegetation, and 5.5 m-2 Hexagenia and 

52.9 m-2 fingernail clams in samples with depths 

of 0.6 to 1.8 m and some vegetation at all sites. 

Richardson (1921) also took samples in middle 

Quiver Lake and found Hexagenia densities less 

than 0.5 m-2 in 1914 and 1915 and fingernail 

clam densities of 42.0 m-2 in 1914 and 0.8 m-2

in 1915. On the basis of the LTRMP data, the 

10-year mean density of mayflies and fingernail 

clams in Quiver Lake (N = 30) was 19 and 16 

m-2; respectively. Lake Matanzas (N = 89) had 

10-year mean densities of 4 m-2 mayflies and 1 

m-2 fingernail clams.

Midges can constitute a large portion of the 

benthic community (Eckblad 1986). However, 

few studies have examined the abundance and 

distribution of midges on the UMRS. Hornbach 

et al. (1993) found midge densities ranged from 

4 to 5,000 m-2 in a backwater lake in Pool 2. 

Midge densities in Pool 4 in 1928 were 2,508 

Figure 15. Estimated mean density of midges (Chironomidae; number per square meter) by predominant substrate type, 

weighted by areas of strata. Because of small sample sizes, substrates defined as clay were combined with the silt clay 

category and gravel rock with the sand category. All years combined (1993–2002).
21

m-2 (Johnson 1929). Carlson (1968) reported 

densities of 0 to 3,052 m-2 midges in Pool 19 in 

1960–1961.

The densities of mayflies, fingernail clams, 

and midges reported since the establishment of 

the LTRMP are well within the ranges reported 

by past studies. The fluctuations indicate that 

these taxa are able to rebound if conditions are 

right. Data show macroinvertebrate populations 

are dynamic in the UMRS. The question remains 

whether various fluctuations seen over the 

years are entirely natural or are influenced by 

Figure 16. Estimated density of zebra mussels (Dreissena polymorpha; number per square meter, ±1 standard error) by study 

area, weighted by area of strata. Horizontal line indicates grand mean.
22

anthropogenic factors. Long-term monitoring 

can develop hypotheses about causal relations; 

but focused research is also needed to understand 

these fluctuations fully.

The reason for differences in abundances 

and percent composition between study areas, 

particularly Pools 4, 8, and 13 compared with 

Pool 26, Open River Reach, and La Grange 

Pool is not known at this time. Possibilities 

range from differences in substrate, chlorophyll 

levels, dissolved oxygen levels, discharge 

levels, or temperatures. Continued monitoring 

and continued analyses (i.e., integration of 

macroinvertebrate data with water quality data) 

are needed to address these differences. 

Although LTRMP data yield adequate mean 

estimates for the study areas, few similar 

comprehensive inventories were made in the 

past; therefore, direct comparisons to other 

studies are difficult. Some studies suggest that 

mayfly and fingernail clam densities have been 

declining (Eckblad 1991; Wilson et al. 1995). 

The results from the stratified random sampling 

of the LTRMP over the past 10 years suggest that 

relatively low densities throughout the UMRS 

could be the rule rather than the exception. The 

apparent conflict of findings is probably due in 

part to differing purposes and spatial scopes of 

the studies. Focused studies are often designed to 

quantify change—often already under way—in 

a localized area known for its value as a source 

for macroinvertebrates and considered at risk 

because of some destructive event or activity. 

Declines in macroinvertebrate densities 

indicated in the localized studies are a cause 

for concern because of the value of the UMRS 

macroinvertebrate community as a source of food 

for fish and waterfowl. Tyson and Knight (2001) 

found that benthic invertebrate production played 

a role for increases in growth and recruitment of 

yellow perch. Pumpkinseed (Lepomis gibbosus) 

and golden shiner (Notemigonus crysoleucas) 

relative weight has also been correlated with 

macroinvertebrate biomass (Liao et al. 1995). 

Mills et al. (1966) reported a decline in the 

number of fingernail clams that coincided with 

a similar decline in the number of diving ducks 

using the Illinois River. Fingernail clam densities 

in Mississippi River, lower Pool 8, have been 

relatively low from 1992 to 1997 (0–211.5 m-2). 

However, fingernail clam densities began to 

increase in fall 1998 (U.S. Fish and Wildlife 

Service/U.S. Geological Survey, unpublished 

data) corresponding with an increase in divingduck use (Figure 17).

We did not detect any obvious linear trends 

among mayflies and midges across study areas. 

However, a positive trend in fingernail clams 

was observed in Pool 8 (Table 3). Gray et al. (in 

press) reported mean fingernail clam counts were 

negatively associated with inorganic suspended 

solid levels in Pool 8. This association seems 

to reflect substantial decreases in inorganic 

suspended solid levels (beginning 1998) and 

increases in mean fingernail clam densities 

(beginning the following year, 1999).

Differences in mayfly, fingernail clam, and 

midge abundances among study areas were 

detectable (Table 3). Canfield et al. (1998) 

also found there was an order of magnitude in 

differences of macroinvertebrate abundance 

values between Pools 1 and 26. While this in 

itself is important information, a more focused 

consideration is “Why are the study area taxa 

abundances different?” We have begun to address 

this issue through modeling.

Modeling efforts under the LTRMP 

macroinvertebrate component began in 2002. 

The reasons for modeling the macroinvertebrate 

data include quantifying differences by 

pools or aquatic areas (“status”), estimating 

temporal trends within pools or aquatic areas 

(“trends”), and exploring associations between 

macroinvertebrate densities and environmental 

factors. These modeling efforts brought many 

insights into macroinvertebrate dynamics on the 

river that will be published elsewhere but are 

summarized in Table 5. 

The modeling work stems from the 

management focus of the LTRMP. Resource 

managers are concerned with the abundance 

of mayflies and fingernail clams as they 

relate to migratory waterfowl and a number 

of game and sport fish including shovelnose 

sturgeon, walleye, and bluegills. Managers are 

interested in whether long-term changes in the 

UMRS—whether natural or anthropogenic in 

origin—might lead to changes in mayfly and 

fingernail clam abundances in the UMRS. Once 

macroinvertebrate abundance and distribution 
23

patterns are better understood, management 

actions can be undertaken. Of major interest 

to river managers is the negative correlation 

of inorganic suspended solids with fingernail 

clam density. This relation suggests that 

management actions taken to reduce inorganic 

suspended solid levels could increase fingernail 

clam density. This finding is also an example 

of a productive integration of information 

across LTRMP components (water quality and 

macroinvertebrates). 

Similar to macroinvertebrate densities on the 

UMRS, many biotic components in diverse 

aquatic ecosystems exhibit high temporal 

variability (Gido et al. 1997; Bunn and Davies 

2000; Dunham et al. 2002; Quist et al. 2003). 

Much of the year-to-year variability seen 

in the target taxa collected by the LTRMP 

is actual change and not error variance. 

Macroinvertebrates with annual or semiannual 

life cycles can exhibit substantial change 

when measured annually. Macroinvertebrate 

productivity, like many biotic variables, is 

strongly contingent upon a number of biotic and 

abiotic factors; therefore, large annual variations 

are expected. However, even with this variability, 

the LTRMP macroinvertebrate sampling yields 

adequate power to detect long-term trends 

(http://www.umesc.usgs.gov/ltrmp/power_plots.

html). Variable data such as the LTRMP data 

are well suited for long-term monitoring to help 

understand processes and patterns (Strayer et 

al. 1986; Franklin 1988; McEachern 2000). 

Information on the population status and trends 

of macroinvertebrates is needed to properly 

manage and understand the wildlife and fisheries 

of the UMRS that depend on macroinvertebrates 

for food.

Summary

This report documents 11 years of 

macroinvertebrate monitoring (1992–2002) 

on the UMRS. Abundances of the target taxa 

were highly variable over the study years; 

however, they do fall within the range of 

Figure 17. Mean densities of mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and diving ducks from areas of Pool 

8 closed to waterfowl hunting, 1996–2002. Duck numbers were estimated in fall by the U.S. Fish and Wildlife Service. 

Macroinvertebrate numbers were estimated in spring and represent the availability of macroinvertebrates as food for ducks 

during the previous fall.
24

abundances recorded in past studies. Variation 

in abundances is greater spatially (among 

study areas) than temporally (among years). 

The northern most study areas (Pools 4, 8, and 

13) have greater abundances of the target taxa 

than the more southern study areas (Pool 26, 

Open River Reach, and La Grange Pool). The 

macroinvertebrate component was reviewed to 

evaluate the usefulness of these data to managers 

and to suggest future work under this component. 

Results will be published separately (Sauer, in 

press).

Acknowledgments

The LTRMP is a cooperative effort involving 

the U.S. Geological Survey, the U.S. Army 

Corps of Engineers, and the States of Illinois, 

Iowa, Minnesota, Missouri, and Wisconsin 

represented by the Illinois Department of Natural 

Resources, the Illinois Natural History Survey, 

the Iowa Department of Natural Resources, the 

Minnesota Department of Natural Resources, 

the Missouri Department of Conservation, and 

the Wisconsin Department of Natural Resources. 

Table 5. Modeling efforts on the Long Term Resource Monitoring Program macroinvertebrate data undertaken by the U.S. 

Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin.

Modeling project Model objectives Model predictors Major findings

Mayflies 

(Ephemeridae)—

Pool 13 

1. Evaluate 

distributional 

assumptions suitable 

for modeling aquatic 

macroinvertebrates

2. Evaluate habitat 

predictors of mayfly 

counts

• Water depth (summer and 

winter

• Water velocity

• Fetch

• Minimum discharge, August 

and September previous year

• Maximum spring discharge 

before sampling

• Maximum fall discharge, 

previous year

• Annual peak discharge 

(expected to reoccur at a 10-

year interval), previous year

• Substrate

• Submersed vegetation

1. Mayfly counts best fit 

by the negative binomial 

distributional assumptions.

2. Best habitat predictor of 

mayflies in Pool 13 is 

substrate; associations with 

vegetation vary substantially 

from year-to-year (probably 

because of variations in 

temperature and river stage).

Mayflies—Pool 8 Model unsuitable 

habitat using zeroinflated modeling 

techniques

• Strata

• Substrate categories

Unsuitable habitat strongly 

associated with combinations 

of high current and sandier 

substrates. This confirms 

previous assumptions and 

provides quantitative evidence 

for resource managers and for 

sampling designs.

Fingernail clams 

(Pisidiidae)—

Pools 4, 8, and 13 

in backwaters and 

impounded strata

Model fingernail clam 

counts at sampling 

and aquatic area 

scales

• Discharge, spring maximum 

• Discharge, minimum 

• Temperature 

• Substrate (local and strata) 

• Chlorophyll a

• Volatile and inorganic 

suspended solids

Fingernail clam density 

associated with substrate 

categories and, at strata scale, 

with inorganic suspended 

solids. For Pool 8, inorganic 

suspended solids association 

reflects substantial changes 

in inorganic suspended solids 

levels (beginning 1998) 

and in mean clam densities 

(beginning 1999). Weak 

association also observed 

across backwater regions for 

spring maximum discharge.
25

The participating state resource management and 

research agencies conduct monitoring and also 

reviewed the present report. The author thanks 

these agencies and the participating field station 

staff. Thanks also to Dr. Brian Gray for statistical 

assistance.

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Wilcox, D. B. 1993. An aquatic habitat 

classification system for the Upper Mississippi 

River System. U.S. Fish and Wildlife Service, 

Environmental Management Technical Center, 

Onalaska, Wisconsin, May 1993. EMTC 

93-T003. 9 pp. + Appendix A (NTIS # PB93-

208981)

Wilson, D. M., T. J. Naimo, J. G. Wiener, R. 

V. Anderson, M. B. Sandheinrich, and R. E. 

Sparks. 1995. Declining populations of the 

fingernail clam Musculium transversum in 

the Upper Mississippi River. Hydrobiologia 

304:209–220.

Winter, A., J. J. H. Ciborowski, and T. B. 

Reynoldson. 1996. Influence of chronic 

hypoxia and reduced temperature on survival 

and growth of burrowing mayflies, Hexagenia 

limbata (Ephemeroptera: Ephemeridae). 

Canadian Journal of Fisheries and Aquatic 

Sciences 53:1565–1571.

Wright, L. L., and J. S. Mattice. 1981. Substrate 

selection as a factor in Hexagenia distribution. 

Aquatic Insects 3(1):13–24.
A-1

Appendix A. Life Histories of Target Taxa

Life histories of the target organisms chosen 

for Long Term Resource Monitoring Program 

(LTRMP) macroinvertebrate sampling have been 

well documented (Hunt 1953; Fremling 1960; 

Pennak 1978; Thorp and Covich 1991). Factors 

affecting the various life-history stages can affect 

abundance and distribution. Following are a few 

main points regarding the life history of the target 

taxa. 

Mayflies: Class, Insecta; Order, 

Ephemeroptera; Family, Ephemeridae, 

Hexagenia spp.

Mayflies are unique insects in that they have 

two adult stages (subimago and imago) along 

with an aquatic nymph and egg stage. This 

life-history strategy emphasizes the importance 

of mayflies to the aquatic (e.g., fish, predacious 

insects, and waterfowl) and terrestrial (e.g., bats, 

swallows, adult dragonflies) food web because 

they are accessible to a variety of predators 

throughout their life cycle. 

Typically, adult female mayflies (Figure A-1) 

lay two egg sacs containing on the average of 

4,000 eggs. The egg sacs burst when they enter 

the water and the individual eggs immediately 

disburse. Eggs are laid throughout the summer, 

but more intensively 1–2 days following a major 

hatch. Mayfly eggs hatch in 14–20 days (Hunt 

1953). Several factors including adult fecundity, 

water temperature, water flow, and predation can 

affect the distribution and abundance of eggs 

that hatch into aquatic nymphs. Growth is rapid 

during this stage until the water temperature 

falls to about 8.8°C. Studies have shown that 

growth essentially ceases overwinter (Hunt 1953; 

Brittain 1990).

Nymphs of Hexagenia spp. construct a Ushaped burrow in the sediment (Figure A-2). 

They consume algae and plant debris, deriving 

nutrients from organic material in the sediment 

along with digesting some bacteria (Hunt 1953). 

The character of the bottom sediment is the most 

essential factor in describing the abundance and 

distribution of mayfly nymphs (Lyman 1943; 

Hunt 1953; Ericksen 1968; Wright and Mattice 

1981). However, many other factors come 

into play including dissolved oxygen levels, 

predation, sedimentation, water temperature, 

sediment contamination, and flow (Hunt 1953; 

Mauck and Olson 1977; Clements and Kawatski 

1984; Rasmussen 1988; Koel and Stevenson 

2002).

As the nymph approaches emergence, it 

leaves the burrow and swims to the surface. 

Nymphs hatch into subimagoes when the water 

temperature reaches 14 to 18°C (Fremling 1973) 

taking 10–95 sec to emerge (Hunt 1953). The 

nymphs are susceptible to predation as they enter 

the water column. Adult stages are winged, shortlived, and do not feed. The mature adult (imago) 

emerges when the subimago moults. The role of 

the imago is mating and egg-laying (Fremling 

1973). Whereas the large synchronous hatches Figure A-1. Adult mayfly (Hexagenia spp.)

Figure A-2. Nymph of Hexagenia spp. in a U-shaped 

burrow. Permission to reprint photograph by 

courtesy of Dr. Calvin Fremling.
A-2

of mayflies can cause short-lived problems for 

humans, their return is a sign of good water 

quality and is important to the wildlife food 

chain. Because of its size, Hexagenia spp. may 

be the most important invertebrate to fish and 

waterfowl in the Upper Mississippi River System 

(Gale 1969). Mayflies are consumed by 9 of 

13 fish of management interest to the LTRMP 

partners (Hunt 1953; Hoopes 1960; Ranthum 

1969).

Fingernail Clams: Class, Bivalvia;

Order, Veneroida; Family, Pisidiidae, 

Sphaerium spp., Musculium spp.,

Pisidum spp.

One important aspect of fingernail clam

(Figure-3) life history is they are hermaphroditic. 

That is, they have both male and female 

reproductive organs with internal fertilization and 

the development of young exists in brood sacs 

(Gale 1973; Heard 1977; Anderson et al. 1978). 

Heard (1977) reported fingernail clams can 

have up to two broods a year. Fingernail clams 

have been reported to complete their life cycle 

in as little as 33 days. They are nonselective 

filter feeders consuming phytoplankton with gut 

contents having more green algae than diatoms. 

Ingestion stops at 2–4°C. Fingernail clams can 

remain buried in the sediment for up to a month 

and newborn clams are able to survive up to 

2 weeks in anaerobic conditions (Gale 1976). 

Factors affecting the abundance and distribution 

of fingernail clams include dissolved oxygen 

levels, unionized ammonia, predation, water 

temperature, sediment contamination, and flow 

(Anderson et al. 1978; Sandusky and Sparks 

1979; Sparks 1980).

Fingernail clams are important to the nutrient 

dynamics of an ecosystem through excretion 

and biodeposition of feces and pseudofeces 

(Vaughn and Hakenkamp 2001). A number of 

fish and wildlife include fingernail clams in their 

diet. At certain times of the year in Pool 19, 

fingernail clams made up 100% of the diet (by 

volume) of common carp (Cyprinus carpio) 

and smallmouth buffalo (Ictiobus bubalus) 

and 10–70% of black bullhead (Ameiurus 

melas), gizzard shad (Dorosoma cepedianum), 

pumpkinseed (Lepomis gibbosus), bigmouth 

buffalo (Ictiobus cyprinellus), freshwater drum 

(Ictiobus cyprinellus), and bluegill (Lepomis 

macrochirus; Jude 1968, 1973; Ranthum 1969). 

Fingernail clams are consumed by 4 of 13 fish 

of management interest to LTRMP partners 

(Hunt 1953; Hoopes 1960; Ranthum 1969). In 

spring, fingernail clams can make up to 85–95% 

of the diet (by volume) of lesser scaup (Aythya 

affinis), ring-necks (A. collaris), canvasbacks (A. 

valisineria), goldeneyes (Bucephala clangula), 

and ruddies (Oxyura jamaicensis; Thompson 

1973).

Midges: Class, Insecta; Order, Diptera; 

Family, Chironomidae

Midges are sometimes referred to as blood 

worms (Figure A-4). The red coloration is 

Figure A-3. Fingernail clam (Psidiidae) Figure A-4. Larval midge (Chironomidae)
A-3

because of the presence of hemoglobin that 

stores oxygen. This allows them to live in areas 

with limited oxygen conditions or areas of 

high organic pollution. Like other dipterans, 

chironomids have four life stages: egg, larva, 

pupa, and adult. Female midges deposit a 

gelatinous mass of eggs on the water surface or 

attach it to submersed vegetation. After hatching 

the larvae pass through four instars before 

pupating. The duration of the larval stage may be 

from 2 weeks to several years; depending mostly 

on temperature. Larvae feed primarily on algae 

and other organic debris. The pupal stage lasts no 

more than a few days (Mandaville 1999).

Adult chironomids are minute with generally 

reduced mouthparts. Adults often emerge, 

simultaneously, in huge numbers, and proceed 

to form vast mating clouds (Mandaville 1999). 

Similar to mayflies, the large synchronous 

hatches of midges can cause short-lived problems 

for humans; however, they are an important 

component of the river food web. 

A number of fish use midges in their diets 

including common carp, redhorse (Moxostoma

spp.), and channel catfish (Ictalurus punctatus). 

Gadwall (Anas strepera), red-heads (Aythya 

americana), and wood ducks (Aix sponsa) all 

use midges in their diets (Ringelman 1990; 

Drugger and Fredrickson 1992; Custer 1993). 

Factors affecting the abundance and distribution 

of midges include predation, water temperature, 

competition, and food availability (Pinder 1986).

Zebra Mussels: Class, Bivalvia; Order, 

Veneroida; Family, Dreissenidae, 

Dreissena polymorpha

The zebra mussel (Figure A-5) is a freshwater 

bivalve that invaded the Great Lakes about 1986. 

Zebra mussels first appeared in Lake St. Clair 

between Lakes Erie and Michigan, possibly 

from ship’s ballast water from the Black Sea 

region (Nalepa and Schloesser 1992). Aided by 

current, they rapidly spread downstream and, by 

human mediation, throughout many other basins. 

Zebra mussels are considered a nuisance species 

because they can foul water-treatment and power 

plants by attaching in large numbers to water 

intakes using their byssal threads plus they 

compete for food and space with native mussels.

Broadcast spawning disperses zebra mussel 

eggs and sperm and spawning can continue over 

a period of several weeks. As water temperatures 

rise above 12°C, external fertilization occurs 

when adult mussels release eggs and sperm into 

the water column. After fertilization, developing 

embryos (planktonic veligers) remain in the 

water column and drift for some distance. The 

time required to develop from egg to juvenile 

mussel varies according to water temperature, 

but averages about 2 weeks. They are able 

to spread so quickly because of their highly 

prolific reproduction—a mussel can lay more 

than 40,000 eggs in a reproductive cycle and 

up to 1 million in a spawning season—and the 

ease with which they, during their planktonic 

larval stages, can be transported to new areas, 

as well as their ability to attach to boat hulls. 

They may be found at high densities and filter 

large volumes of water, removing suspended 

particulate matter. Zebra mussels are tolerant of a 

wide range of environmental conditions. (Nalepa 

and Schloesser 1992; D’Itri 1997). Studies have 

shown that zebra mussels can be eaten by fish 

with pharnygeal teeth, such as the freshwater 

drum (Aplodinotus grunniens; French and Bur 

1992), and diving ducks, such as scaup (Custer 

and Custer 1996; Petrie and Knapton 1999).

Figure A-5. Zebra mussels (Dreissena polymorpha)
A-4

Asiatic Clam: Class, Bivalvia; Order, 

Veneroida; Family, Corbiculidae,

Corbicula spp.

The Asiatic clam (Figure A-6) is a freshwater 

bivalve that invaded the northwest United 

States in the late 1800s. The accidental spread 

of Asiatic clams by boat bilge water, aquarium 

hobbyists, and fishing bait along with migrating 

waterfowl are possible pathways of introduction 

to other areas of the United States. Similar to 

zebra mussels, Asiatic clams are considered a 

nuisance species because they can foul watertreatment and power plants by attaching in large 

numbers to water intakes using their byssal 

threads plus they compete for food and space 

with native mussels (McMahon 1983).

The clams are highly prolific with larval 

releases reaching 400 larvae/clam/day. Unlike 

zebra mussels, the larvae are not typically 

free-swimming veligers, but are adapted more 

for swimming and crawling. Sexes are normally 

separate; but can be hermaphroditic. On average, 

Asiatic clams have a life span of 1 to 4 years 

(Thorp and Covich 1991).

Figure A-6. Asiatic clam (Corbicula fluminea)

Asiatic clams may be present at high 

densities and filter large volumes of water, 

removing suspended particulate matter. They 

are tolerant of a wide range of environmental 

temperatures. (Mattice and Dye 1976). However, 

their northward expansion is probably limited 

by low temperatures in winter to where they 

are associated with warmwater discharges 

(McMahon 1983). Some fish and diving ducks 

have been recorded eating Asiatic clams 

(McMahon 1983; Hoope et al. 1986; Hendricks 

1998).
B-1

Appendix B. Macroinvertebrate Sampling Methods Used by Various Researchers

 at Historical (Fixed) Sites in the Upper Mississippi River System 

The following studies were used for the 

selection of historical sites that were resampled 

by the Long Term Resource Monitoring Program:

Pool 4—North Star Research Institute (1973)

• 2 Ponar grabs collected and contents pooled 

• No. 40 soil sieve size (425 μm)

• Sampling period spring and summer 1973

• 4 sites resampled for the Long Term Resource 

Monitoring Program (LTRMP)

Pool 8—Elstad (1977)

• 1 dredge haul (0.023 m2)

• No. 30 sieve size (595 μm)

• 41 sampling areas chosen, 2 main channel areas, and 

39 adjacent waters; transects run east–west

• Sampling period June 15 to July 15, 1975

• 16 sites resampled for the LTRMP

Pool 8—Brewer (1992)

• 2 Petite Ponar dredge hauls combined (0.046 m2)

• No. 30 sieve size (595 μm)

• Resampled Elstad’s sites

• Sampling period June 21 to July 13, 1990

• 16 sites resampled for the LTRMP

Pool 13—Hubert et al. (1983)

• 1 Peterson dredge (0.092 m2); 3 replicates at each site 

pooled

• Sieve (0.5 mm)

• 6 habitat types chosen for sampling (main channel, 

main channel border, tailwater, side channel, lakes, and 

sloughs) 

• Sampling period February 26 to March 6, 1983

• 7 sites resampled for the LTRMP

Pool 26—Seagle and Zumwalt (1981)

• 1 Ponar grab (0.052 m2)

• No. 30 sieve size (595 μm)

• Above wing dam

• Sampling period April 1981

• 1 site resampled for the LTRMP

Pool 26 - Colbert et al. (1975)

• 2 Peterson or Ponar grabs 

• No. 30 sieve size (595 μm)

• 4 habitat types sampled (main channel, side channel, 

main channel border, main channel border influenced by 

dikes); transects run

• Sampling period July 2–12, 1974

• 6 sites resampled for the LTRMP

Open River Reach—Emge et al. (1974)

• 2 Peterson dredge hauls collected and contents pooled 

(0.16 m2)

• No. 30 sieve size (595 μm)

• Side channels and main channel border sampled

• Sampling period late June 1972 or July 1973

• 18 sites resampled for the LTRMP

La Grange Pool—Paloumpis and Starrett (1960)

• Ekman dredge 6 × 6 inches

• No. 30 sieve size (595 μm)

• Lake Matanzas and Quiver Lake; 1952–1954

• 22 sites resampled for the LTRMP

La Grange Pool - Anderson (1977)

• Ekman dredge 6 × 6 inches

• No. 30 sieve size (595 μm)

• August through September 1975

• 4 sites resampled for the LTRMP
B-2

Location of historical (fixed) sites sampled by various researchers and resampled by the Long Term 

Resource Monitoring Program (Figures B-1 to B-6).

Figure B-1. Location of historical (fixed) sites 501–504 in Pool 4, Upper Mississippi River.
B-3

Figure B-2. Location of historical (fixed) sites 501–516 in Pool 8, Upper Mississippi River.
B-4

Figure B-3. Location of historical (fixed) sites 501–507 in Pool 13, Upper Mississippi River.
B-5

Figure B-4. Location of historical (fixed) sites 501–507 in Pool 26, Upper Mississippi River.
B-6

Figure B-5. Location of historical (fixed) sites 501–518 in Open River Reach, Upper Mississippi River.
B-7

Figure B-6. Location of historical (fixed) sites 523-526 including Quiver Lake and Lake Matanzas in La Grange Pool, 

Illinois River.
C-1

Appendix C. Historical (Fixed) Sample Sites Resampled

by the Long Term Resource Monitoring Program 

Figure C-1. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at sites 501–504 in Pool 4 of the 

Upper Mississippi River System (BWC = Backwaters, contiguous; TDL = tributary delta lake). The 1973 data are from North 

Star Research Institute (1973). The 1993–2002 data are from the Long Term Resource Monitoring Program.

These are sites where benthic samples were previously collected by researchers (Figures C-1 to 

C-7; see Appendix B).
C-2

Figure C-2. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at sites 501–516 in Pool 8 of the 

Upper Mississippi River System (BWC = Backwaters, contiguous; IMP = impounded areas; SC = side channels). The 1975 

data are from Elstad (1977) and the 1990 data are from Brewer (1992). The 1993–2002 data are from the Long Term Resource 

Monitoring Program.
C-3

Figure C-3. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at sites 501–507 in Pool 13 of 

the Upper Mississippi River System (BWC = Backwaters, contiguous; IMP = impounded areas; SC = side channels). The 1983 

data are from Hubert et al. (1983). The 1993–2002 data are from the Long Term Resource Monitoring Program.
C-4

Figure C-4. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at sites 501–507 in Pool 26 of 

the Upper Mississippi River System (MCB = main channel borders; SC = side channels). The 1974 data (sites 501–503 and 

505–507) are from Colbert et al. (1975) and site 504 was sampled in 1981 by Seagle et al. (1982). The 1993–2002 data are from 

the Long Term Resource Monitoring Program.
C-5

Figure C-5. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at sites 501–518 in Open River 

Reach of the Upper Mississippi River System (MCB = main channel borders, SC = side channels). The 1973 data are from 

Emge et al. (1974). The 1994–2000 data are from the Long Term Resource Monitoring Program.
C-6

Figure C-6. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at sites 523–526 in La Grange 

Pool of the Upper Mississippi River System (MCB = main channel borders, SC = side channels). The 1975 data are from 

Anderson (1977). The 1993–2002 data are from the Long Term Resource Monitoring Program.
C-7

Figure C-7. Abundance of (A) mayflies (Ephemeroptera) and (B) fingernail clams (Pisidiidae) at Quiver Lake and Lake 

Matanzas of the Upper Mississippi River System. The 1952 and 1953 data are from Paloumpis and Starrett (1960). The 

1993–2002 data are from the Long Term Resource Monitoring Program.
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Standard Form 298 (rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

NSN 7540-01-280-5500

In 1992, macroinvertebrate sampling was begun in Pools 4, 8, 13, and 26; the Open River Reach of the Mississippi River; and La Grange 

Pool of the Illinois River as part of the Long Term Resource Monitoring Program. Long-term monitoring is needed to detect population 

trends and local changes in aquatic ecosystems. We selected mayflies (Ephemeroptera), fingernail clams (Pisidiidae), and the exotic 

Corbicula species for monitoring. Midges (Chironomidae) were added to the sampling design in 1993 and zebra mussels (Dreissena 

polymorpha) were added in 1995. Sampling was based on a stratified random design and conducted at approximately 125 sites per study 

area. Mean densities of taxa were weighted by strata for extrapolation. The poolwide estimated mean densities of mayflies, fingernail 

clams, and midges were all within the range of variation observed historically. Over the last 11 years of sampling, the northern study 

areas supported the highest densities of the target organisms. 

Benthic aquatic macroinvertebrates, Corbicula, fingernail clams (Pisidiidae), Illinois River, Long Term 

Resource Monitoring Program, mayflies (Ephemeroptera), midges (Chironomidae), Mississippi River, 

zebra mussels (Dreissena polymorpha)

Release unlimited. Available from National Technical Information Service, 5285 Port Royal Road, 

Springfield, VA 22161 (1-800-553-6847 or 703-487-4650. Available to registered users from the 

Defense Technical Information Center, Attn: Help Desk, 8725 Kingman Road, Suite 0944, Fort 

Belvoir, VA 22060-6218 (1-800-225-3842 or 703-767-9050).

Unclassified Unclassified Unclassified

Jennifer Sauer

U.S. Geological Survey

Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road

La Crosse, Wisconsin 54603

U.S. Geological Survey

Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road

La Crosse, Wisconsin 54603

31 pp. + Appendixes A–C

2004-T005

Multiyear synthesis of the macroinvertebrate component from 1992 to 2002 

for the Long Term Resource Monitoring Program

 December 2004
The Long Term Resource Monitoring Program (LTRMP) for the Upper Mississippi

River System was authorized under the Water Resources Development Act of 1986 as 

an element of the Environmental Management Program. The mission of the LTRMP

is to provide river managers with information for maintaining the Upper Mississippi 

River System as a sustainable large river ecosystem given its multiple-use character.

The LTRMP is a cooperative effort by the U.S. Geological Survey, the U.S. Army Corps

of Engineers, and the States of Illinois, Iowa, Minnesota, Missouri, and Wisconsin.