U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigation Report 2008–5024

Prepared in cooperation with 

The Nature Conservancy, 

New York City Department of Environmental Protection, 

and the Towns of Thompson and Mamakating

Effects of Habitat Characteristics and Water Quality on 

Macroinvertebrate Communities along the Neversink River 

in Southeastern New York, 1991–2001
Cover. Photo of Neversink River near Godeffroy.
Effects of Habitat Characteristics and 

Water Quality on Macroinvertebrate 

Communities along the Neversink River 

in Southeastern New York, 1991–2001

By Anne G. Ernst, Barry P. Baldigo, George E. Schuler, Colin D. Apse, 

James L. Carter, and Gary T. Lester

Prepared in cooperation with The Nature Conservancy, 

New York City Department of Environmental Protection, 

and the Towns of Thompson and Mamakating

Scientific Investigations Report 2008–5024

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Ernst, A.G., Baldigo, B.P., Schuler, G.E., Apse, C.D., Carter, J.L., and Lester, G.T., 2008, Effects of habitat characteristics 

and water quality on macroinvertebrate communities along the Neversink River in southeastern New York, 

1991–2001: U.S. Geological Survey Scientific Investigations Report 2008–5024, 15 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................3

Study Area..............................................................................................................................................3

Methods..................................................................................................................................................3

Effects of Habitat Characteristics and Water Quality on Macroinvertebrate Communities.............4

Macroinvertebrate Communities .......................................................................................................4

Macroinvertebrate Taxa ............................................................................................................6

Functional Feeding Groups ........................................................................................................7

Statistical Correlations between Macroinvertebrate Communities and Stream Habitat 

and Water Quality....................................................................................................................8

Macroinvertebrate Discontinuum......................................................................................................8

Headwater Reaches..................................................................................................................10

Main-Stem Reaches Below the Reservoir............................................................................10

Comparing Headwater Reaches to Reaches Below the Reservoir .................................11

Potential Applications of this Study.................................................................................................11

Summary and Conclusions.........................................................................................................................11

Acknowledgments ......................................................................................................................................13

References Cited..........................................................................................................................................13

Glossary.........................................................................................................................................................15

Figures

1. Map showing locations of the 30 reaches investigated in the Neversink River 

basin in southeastern New York, 1991–2001 ............................................................................2

2–5. Graphs showing: 

2. Mean concentrations of selected constituents at 30 reaches in the 

Neversink River basin in southeastern New York, 1991–2001: (A) pH, 

total dissolved aluminum, and inorganic monomeric aluminum, and (B) Acidneutralizing capacity, calcium, and dissolved organic carbon ...................................5

3. Total macroinvertebrate-taxa richness, EPT (Ephemeroptera-PlecopteraTrichoptera) richness, and HBI (Hilsenhoff’s Biotic Index) values for 30 

reaches in the Neversink River basin, New York, 1991–97, with New York 

State thresholds for “slight impairment” shown with dashed lines ...........................6

4. Ephemeroptera, Plecoptera, Trichoptera, Chironomidae, and Oligochaeta, 

as a percentage of total macroinvertebrate community, at 30 reaches in the 

Neversink River basin, New York, 1991–97......................................................................7

5. Percentage of total macroinvertebrate population represented by 

selected functional feeding groups at 30 reaches in the Neversink River 

basin, New York, 1991–97 ..................................................................................................8

6. Map showing stream-water pH and composition of macroinvertebrate 

communities at eight reaches from the headwaters of the Neversink River to the 

lower basin, selected to show the range in macroinvertebrate-community 

composition with varying pH ....................................................................................................12
iv

Conversion Factors, Datum, and Acronyms

Multiply By To obtain

Length

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 247.1 acre

square kilometer (km2) 0.3861 square mile (mi2)

Volume

liter (L) 0.2642 gallon (gal)

cubic meter (m3) 264.2 gallon (gal)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88). 

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

ACRONYMS USED IN REPORT

ANC Acid-neutralizing capacity

DOC Dissolved organic carbon

EPT Ephemeroptera, Plecoptera, Trichoptera

HBI Hilsenhoff’s biotic index

TNC The Nature Conservancy

USGS U.S. Geological Survey

Tables

1. Significant correlations (p<0.05) for physical-habitat and water-quality factors 

with taxa and functional feeding groups ..................................................................................9
Effects of Habitat Characteristics and Water Quality on 

Macroinvertebrate Communities along the Neversink 

River in Southeastern New York, 1991–2001

By Anne G. Ernst, Barry P. Baldigo, George E. Schuler1, Colin D. Apse2, James L. Carter, and Gary T. Lester3

downstream continuum of macroinvertebrate communities 

that would normally be observed from the headwaters to the 

mouth. The information presented herein provides a basis 

for further evaluation of the Neversink and similar river 

systems, and for assessment of the effectiveness of future 

conservation efforts. 

Introduction

The Neversink River, in the Catskill Mountains of 

southeastern New York State (fig. 1), is impounded midway 

through its course by the Neversink Reservoir, which diverts 

about 85 percent of the river’s flow to New York City and 

provides some of the purest water in the city’s supply network. 

Changes in the physical and chemical conditions in some parts 

of the river since the construction of the reservoir in 1953, 

however, and the acidification of several streams in the upper 

parts of the basin through acidic deposition (“acid rain”), 

have altered ecosystem functions and some stream biota. 

The Neversink Reservoir (fig. 1) alters water quality and 

diminishes sediment transport for more than 8 km below the 

dam, affecting fish and macroinvertebrate populations, and 

the acidification of several headwater reaches has adversely 

affected macroinvertebrate and fish communities, including 

brook trout, locally within the upper basin (Baldigo and 

Murdoch, 1997; Baldigo and Lawrence, 2001). 

The structure and function of macroinvertebrate 

communities in streams with forested headwater reaches such 

as those of the Neversink River generally follow a predictable 

progression, from the small, cold headwaters to the large, 

warm, more productive reaches near the mouth, called the 

River Continuum Concept (Vannote and others, 1980). 

Small, shady headwater reaches tend to support invertebrates 

that consume fallen-leaf material (termed shredders and 

gatherers), whereas the larger downstream reaches, which 

receive more sunlight and less fallen-leaf material, support 

invertebrates that consume algae (known as scrapers) or that 

consume decomposed leaf matter transported from upstream 

(known as filterers). The acidification of some headwater 

Abstract

The Neversink River, in the Catskill Mountains of 

southeastern New York State, feeds the Neversink Reservoir, 

which diverts 85 percent of the river’s flow to New York 

City. Acidification of several headwater reaches has affected 

macroinvertebrate assemblages throughout the river system 

above the reservoir, and the alteration of flow conditions 

below the reservoir dam has affected macroinvertebrate 

assemblages for at least 10 kilometers downstream from the 

reservoir. In 1999, the U.S. Geological Survey, in cooperation 

with The Nature Conservancy, compiled data from 30 stream 

reaches to quantify the effects of acidification and of the 

reservoir on the structure and function of macroinvertebrate 

assemblages throughout the Neversink River.

 Acidic headwater reaches supported greater numbers 

of acid-tolerant chironomid taxa and fewer numbers of 

acid-sensitive Ephemeroptera and Trichoptera than neutral 

reaches, and fewer scraper individuals and more shredder 

individuals. The 14 reaches below the reservoir, with sharply 

decreased flows and altered flow patterns compared to reaches 

above the reservoir, supported more Chironomidae and fewer 

Ephemeroptera and Trichoptera than the upper reaches; 

they also had greater numbers of shredder individuals and 

fewer scraper and filterer individuals than reaches above the 

reservoir. Water-quality variables such as pH and aluminum 

concentration appear to have affected macroinvertebrate 

assemblages more strongly in the headwaters than below the 

reservoir, whereas physical-habitat variables such as mean 

channel width and water temperature have affected these 

assemblages more strongly downstream from the reservoir 

than in the headwaters. The water-quality changes due to 

acidification, combined with the decreased flows and lowered 

water temperatures below the reservoir, have disrupted the 

1

 The Nature Conservancy, Neversink Preserve, P.O. Box 617, 

Cuddebackville, NY 12729

2

 The Nature Conservancy, 108 Main St, New Paltz, NY 12561

3

 EcoAnalysts, 105 E. Second St, Ste. 1, Moscow, ID 83843
2 Effects of Habitat Characteristics & Water Quality on Macroinvertebrate Communities along the Neversink River, 1991–2001

Figure 1. Locations of the 30 reaches investigated in the Neversink River basin in 

southeastern New York, 1991–2001.

Base from U.S. Geological Survey digital data, 1:100,000, 1983

Universal Transverse Mercator Projection, Zone 18

eb01

nv02

nv03

nv04

nv05

nv06

nv07

nv08

nv09

nv10

nv11

nv12

nv13

nv14

nv15

nv16

nv01

Neversink River

Neversink River

Neversink Reservoir

WestBranch Neversink River

East Branch Neversink River

eb04

eb06

wb02 wb01

wb03 wb04

eb03

eb02

eb05

wb07

wb08

wb05

wb06

NEW

YORK

Vermont

Massachusetts

Connecticut New

Jersey

Pennsylvania

Neversink Basin

Catskill State Park

Port Jervis

0 2 4 6 8 10 MILES

0 2 4 6 8 10 KILOMETERS

41 ̊30'

41 ̊52'30"

74 ̊45' 74 ̊22'30"

former Cuddebackville

Dam location

eb East Branch Neversink River

and tributaries

West Branch Neversink River

and tributaries

Main-stem Neversink River

wb

nv

EXPLANATION

 

Study reaches
Abstract 3

reaches of the Neversink River, and the presence of the 

reservoir since 1953, appear to have disturbed the normal 

headwater-to-mouth progression of macroinvertebratecommunity composition, but these disturbances have not been 

thoroughly documented.

Since the 1980s, the U.S. Geological Survey (USGS), 

in cooperation with the New York City Department of 

Environmental Protection, The Nature Conservancy (TNC), 

and the towns of Thompson and Mamakating, has collected 

data on habitat, fish communities, flow patterns, channel 

geomorphology, basin physiography, and soil and water 

chemistry from many reaches throughout the 1,126 km2 

Neversink River basin. Multidisciplinary studies have 

inventoried macroinvertebrate communities at 30 of these 

reaches (fig. 1) to identify the effects of stream acidification 

and of various logging practices on macroinvertebrate 

assemblages (Baldigo and others, 2003; Murdoch and others, 

2007), and to define the spatial relations among environmental 

conditions, macroinvertebrate assemblages, and several rare 

mussel species (Baldigo and others, 2002; Baldigo and others, 

2004). In 2002, the USGS, in cooperation with TNC, began 

a 2-year study to compile macroinvertebrate data from the 

above studies to identify the effects that stream acidification 

and the reservoir have had on macroinvertebrate assemblages 

throughout the Neversink River and its tributaries. 

Purpose and Scope

The main objectives of this study were to document 

the following:

•	 the composition of macroinvertebrate communities at 

each of the 30 study reaches, 

•	 alterations in the expected downstream progression of 

macroinvertebrate-community structure, and

•	 the habitat and water-quality factors that have 

affected species distribution and macroinvertebratecommunity structure.

This report summarizes the macroinvertebrate data from 

four prior investigations (Baldigo and others, 2002; Baldigo 

and others, 2003; Baldigo and others, 2004; Murdoch and 

others, 2007). It (1) describes the study area, (2) discusses 

the habitat characteristics and water-quality changes that 

have affected macroinvertebrate communities, (3) describes 

and depicts through graphs the effects that these changes 

have had on macroinvertebrate communities and functional 

feeding groups throughout the river system, and (4) describes 

the utility of these results as a basis for assessment of future 

conservation efforts in the Neversink and similar river systems. 

A glossary of technical terms that may be unfamiliar to the 

reader is included at the back of the report.

Study Area

The Neversink River arises in the Catskill Mountains 

and flows to the Delaware River at Port Jervis, PA (fig. 1). 

The 1,126-km2 Neversink River basin is largely forested and 

consists of three physiographically distinct subbasins (fig. 1). 

The 238-km2 upper basin is mountainous and terminates at 

the Neversink Reservoir Dam, which was built in 1953 to 

supplement New York City’s water supply. Stream channels 

in the upper basin are generally carved in bedrock. The 

606-km2 middle basin lies between the reservoir dam and the 

decommissioned Cuddebackville Dam (fig. 1). Here the river 

begins along a broad flood plain, then passes through a narrow 

gorge for most of its length. The river in the 282-km2 lower 

basin is broad, with a relatively narrow flood plain. 

Water of the main-stem Neversink is generally clear 

and fairly soft, with calcium concentrations of less than 

200 μmol/L. Many of the headwaters of the East and West 

Branches (in the upper basin, fig. 1) are chronically or 

episodically acidified (Lawrence and others, 1999; Baldigo 

and Lawrence, 2001). This acidification has been shown 

to have had detrimental effects on the survival rates and 

community composition of several fish species, including 

brook trout (Baker and others, 1996; Van Sickle and 

others, 1996; Baldigo and Murdoch, 1997; Baldigo and 

Lawrence, 2000).

The predominant physical feature of the Neversink River 

basin is the Neversink Reservoir (fig. 1), which has a surface 

area of 6.1-km2 and impounds 132,500,000 m3 of water at 

maximum capacity. The impoundment itself, and the diversion 

of 85 percent of the river’s flow to New York City (Butch 

and others, 1998; Krejmas and others, 1998), have decreased 

the river’s potential for flooding in the middle and lower 

parts of the basin but also have decreased the river’s total 

annual discharge, lowered the duration of high-flow pulses, 

and increased the duration of low flows. The reservoir also 

acts as a settling basin that decreases the release of sediment 

downstream, which can interrupt the food supply for some 

macroinvertebrates. In addition, the dam is a bottom-release 

type that releases cold water. 

Methods

Data on habitat characteristics, stream-water quality, and 

macroinvertebrate assemblages were collected from as many 

as 30 reaches during 1991–2001 for use in three USGS studies 

of freshwater mussels (Baldigo and others, 2002) and forest 

harvest effects on macroinvertebrates (Baldigo and others, 

2003; Murdoch and others, 2007). The data were compiled 

and standardized for use in the data analyses for this report. 

The methods of sampling and measurement for each category 

are as follows: 

Habitat characteristics: More than 40 habitat conditions 

were characterized at 29 of the 30 reaches from 1991 
4 Effects of Habitat Characteristics & Water Quality on Macroinvertebrate Communities along the Neversink River, 1991–2001

through 2001. Among the factors that were quantified at every 

reach were the following: drainage area, elevation, gradient, 

pool-to-riffle ratio, amount of open canopy, bank stability, 

channel width and depth, substrate particle-size classes, and 

water temperature. 

Stream-water quality: From 2 to 155 water samples 

were collected at each of the 30 reaches during 1991–2001 

and analyzed for pH and concentrations of 17 constituents, 

including acid-neutralizing capacity (ANC), calcium, 

dissolved organic carbon (DOC), total dissolved aluminum 

(Al), inorganic monomeric Al, orthophosphate, and nitrate. 

Macroinvertebrates: Macroinvertebrates were collected 

from riffles and runs through a variety of collection methods 

from all 30 reaches during 1991–97. Macroinvertebrate data 

from the post-logging period of the forest harvest studies were 

omitted to avoid the effects of tree removal on stream-water 

quality. Sampling methods differed from year to year, as 

summarized below: 

•	 In 1991 and 1992, total counts (all specimens) were 

collected from three replicate Surber samples (0.093 m2) at 

each of 12 reaches surveyed in the East and West Branches 

and upper section of the main stem. 

•	 In 1995 and 1996, subsamples of 200 invertebrates were 

taken from three replicate Surber samples (0.093 m2) 

collected in both years from four of the eight headwater 

reaches in the West Branch Neversink. 

•	 In 1997, subsamples of 200 invertebrates were sorted 

from single traveling-kick samples applied for 5 minutes 

over a 5-m stretch of stream (Bode and others, 1996) from 

14 main-stem reaches. 

•	 Standardization of metrics among reaches entailed 

pooling data from all samples collected from each reach 

and each year (when sampled in more than 1 year). 

Macroinvertebrate-community metric values were estimated 

from the average of 100 random computer-generated 

200-count subsamples of the pooled data. The metrics used 

for each reach are defined as follows:

1. Total macroinvertebrate taxa richness—a measure of 

the number of taxa found at each reach.

2. EPT richness—a measure of the number of mayfly 

(Ephemeroptera), stonefly (Plecoptera), and caddisfly 

(Trichoptera) taxa found at each reach. These taxa are 

frequently used because they are common and tend to 

be sensitive to water quality.

3. Hilsenhoff’s Biotic Index (HBI)—an indicator of 

average tolerance to organic contamination. Sensitive 

taxa have low tolerance values, and tolerant taxa have 

high tolerance values. 

4. Feeding group percentage—the number of individuals 

in selected functional feeding groups, expressed as a 

percentage of the total macroinvertebrate count.

A reach in good condition will have high total richness and 

EPT richness, but a low HBI score.

Standardized macroinvertebrate-community metrics 

were evaluated through regression, correlation, and 

graphical analyses to assess the effects of the reservoir, and 

of water-quality and physical-habitat characteristics, on 

macroinvertebrate communities. Variables that were logtransformed to normalize their distributions included drainage 

area; pool-to-riffle ratio; mean particle size; temperature; 

concentrations of acid-neutralizing capacity (ANC), 

calcium, total dissolved aluminum, organic monomeric 

aluminum, orthophosphate, and nitrate; percent Plecoptera 

and Trichoptera individuals; and percent shredder, gatherer, 

filterer, and predator individuals.

Effects of Habitat Characteristics and 

Water Quality on Macroinvertebrate 

Communities

Most of the habitat characteristics that were analyzed 

reflected the typical differences between high-elevation 

reaches (small drainage area, steep slope, and low water 

temperatures) and low-elevation reaches (large drainage area, 

low slope, and high water temperatures). The stream-water 

pH data indicated acidification at several headwater reaches, 

mainly in the East Branch of the Neversink River (fig. 2A). 

Concentrations of other constituents generally followed 

expected patterns from headwaters to downstream reaches; for 

example, a reach-to-reach decrease in pH (increase in acidity) 

was accompanied by increased concentrations of inorganic 

monomeric aluminum (Al) and decreased concentrations of 

ANC, DOC, and calcium (fig. 2A, 2B). Inorganic monomeric 

Al concentration and pH reached acutely toxic levels in four 

acidified headwater reaches (sites wb04, eb03, eb04, and eb05, 

fig. 2A), three of which are along the East Branch, which is 

chronically acidified throughout most of its length (Baldigo 

and Murdoch, 1997). As expected, concentrations of ANC, 

DOC, and calcium generally increased from the headwaters 

downstream, whereas both total and inorganic monomeric 

aluminum concentrations decreased (fig. 2B). Water quality 

in nearly all reaches downstream from the reservoir (sites 

nv14–nv01) was generally not “impaired” as defined by the 

New York State Department of Environmental Conservation 

(Bode and others, 2002).

Macroinvertebrate Communities

The effects of stream acidification and the reservoir on 

macroinvertebrate communities were evaluated through two 

perspectives—predominance of given taxa, and predominance 

of given functional feeding groups—at each reach in 

downstream order. Results of both evaluations were then 

compared with the downstream progression that would be 

expected in an undisturbed system to reveal anomalies that 
Effects of Habitat Characteristics and Water Quality on Macroinvertebrate Communities 5

Figure 2. Mean concentrations of selected constituents at 30 reaches in the Neversink River basin in southeastern New York, 

1991–2001: (A) pH, total dissolved aluminum, and inorganic monomeric aluminum, and (B) Acid-neutralizing capacity, calcium, and 

dissolved organic carbon. (Locations of reaches are shown in fig. 1.)

-50

0

50

100

150

200

250

300

350

400

wb08

eb06

wb07wb06wb05wb04wb03

eb05

wb02

eb04

wb01

eb03eb02eb01

nv16nv15nv14nv13nv12nv11nv10nv09nv08nv07nv06nv05nv04nv03nv02nv01

CONCENTRATION (ANC, IN MICROEQUIVALENTS

PER LITER; CALCIUM AND DISSOLVED OXYGEN

CONCENTRATIONS, IN MICROMOLES PER LITER) 

Acid-neutralizing capacity (ANC)

Calcium

Dissolved organic carbon

0

2

4

6

8

10

12

14

16

18

20

wb08

eb06

wb07wb06wb05wb04wb03

eb05

wb02

eb04

wb01

eb03eb02eb01

nv16nv15nv14nv13nv12nv11nv10nv09nv08nv07nv06nv05nv04nv03nv02nv01

pH, IN STANDARD UNITS, AND ALUMINUM

CONCENTRATION, IN MICROMOLES PER LITER 

pH

Total dissolved aluminum

Inorganic monomeric aluminum

Neversink

Reservoir Dam 

STUDY REACH, BY INCREASING DRAINAGE AREA

Neversink

Reservoir Dam 

A

B
6 Effects of Habitat Characteristics & Water Quality on Macroinvertebrate Communities along the Neversink River, 1991–2001

may be attributed to acidification and habitat changes due to 

the impoundment and diversion of flow at the reservoir.

Macroinvertebrate Taxa 

Macroinvertebrate samples at all 30 reaches 

consisted predominantly of seven main invertebrate 

taxa-Chironomidae, other Diptera, Trichoptera, Plecoptera, 

Ephemeroptera, Oligochaeta, and Coleoptera. Sixteen other 

broad taxa (generally class or order) made up less than 

5 percent of the samples at any reach.

Comparison of values obtained for three metrics (total 

community richness, EPT richness, and HBI scores) with 

impairment thresholds defined by the New York State 

Department of Environmental Conservation (Bode and others, 

1996; Bode and others, 2002) indicated potential impairment 

at several reaches (fig. 3). All three of these metrics indicate 

that macroinvertebrate communities were impaired in three 

of the four strongly acidified reaches in the upper basin 

(eb03, eb04, and eb05), in two slightly acidified reaches 

in the upper basin (eb02 and eb06), and in the two reaches 

immediately downstream from the Neversink Reservoir 

(nv13, nv14). Two of the three metrics indicate impairment in 

three of the acidified reaches (eb01, wb03, and wb04) and in 

a circumneutral reach just above the reservoir (nv15). Most of 

the 14 headwater reaches with circumneutral pH generally had 

high total and EPT richness and low HBI values (for example, 

wb02, wb05, and wb07). This uneven geographic distribution 

of acidified reaches is attributed to the distribution of calciumrich bedrock or soils in the Catskill region.

Most acidified reaches had fewer EPT taxa and fewer 

EPT individuals than the other reaches. The acid-tolerant 

midge larvae (Chironomidae) dominated most tributaries and 

main-stem reaches in the upper basin (fig. 4) and constituted 

at least 50 percent of the macroinvertebrate communities in 

all reaches along the acidified East Branch of the Neversink 

STUDY REACH, BY INCREASING DRAINAGE AREA

0

5

10

15

20

25

30

35

40

45

50

wb08

eb06

wb07wb06wb05wb04wb03

eb05

wb02

eb04

wb01

eb03eb02eb01

nv16nv15nv14nv13nv12nv11nv10nv09nv08nv07nv06nv05nv04nv03nv02nv01

Total richness

EPT richness

HBI

TAXA RICHNESS, NUMBER OF EPT TAXA, AND HBI VALUE

Figure 3. Total macroinvertebrate-taxa richness, EPT (Ephemeroptera-Plecoptera-Trichoptera) richness, and HBI 

(Hilsenhoff’s Biotic Index) values for 30 reaches in the Neversink River basin, New York, 1991–97, with New York State 

thresholds for “slight impairment” shown with dashed lines. (Locations of reaches are shown in fig. 1.)
Effects of Habitat Characteristics and Water Quality on Macroinvertebrate Communities 7

River. Less tolerant EPT taxa dominated the macroinvertebrate 

communities in most reaches of the West Branch and in 

most main-stem reaches in the middle and lower basin. In 

general, the percentage of the macroinvertebrate community 

represented by EPT increased downstream, although 

Plecoptera typically decreased in relation to Ephemeroptera 

and Trichoptera. The two reaches immediately downstream 

from the reservoir showed relatively few EPT taxa, and 

increased numbers of chironomids and oligochaetes.

Functional Feeding Groups

Macroinvertebrates can be grouped into functional 

feeding groups according to their feeding mechanisms and 

behavior (Vannote and others, 1980; Merritt and Cummins, 

1996), which tend to vary with river size and productivity 

from headwaters to the mouth in most river systems. The 

distribution of functional feeding groups in the Neversink 

River basin generally followed expected patterns outlined by 

the River Continuum Concept (Vannote and others, 1980); 

that is, the percentages of total macroinvertebrate community 

that were represented by shredders and gatherers decreased 

downstream as fallen-leaf material decreased, whereas the 

percentages represented by scrapers and filterers increased 

downstream (fig. 5) with increased algae production and 

increased decomposed material from upstream. This pattern 

in biological communities is known as a continuum and 

is typical of undisturbed stream systems with forested 

headwaters (Vannote and others, 1980; Ward and Stanford, 

1983). Exceptions were found in several severely acidified 

headwater reaches; wb04 and eb04 contained more shredders 

and fewer gatherers than less acidified reaches nearby, and 

eb03 and eb04 had few or no scrapers. Other exceptions were 

found at the two reaches just below the Neversink Reservoir 

Dam (nv14 and nv13), which had fewer scrapers and filterers 

than nearby reaches, and more shredders (fig. 5). Generalist

feeders were uncommon at most reaches and represented less 

than 10 percent of the invertebrate population at all but four 

reaches (nv01, nv07, nv08, and nv09, all below the reservoir), 

where they represented 12–47 percent (fig. 5).

Figure 4. Ephemeroptera, Plecoptera, Trichoptera, Chironomidae, and Oligochaeta, as a percentage 

of total macroinvertebrate community, at 30 reaches in the Neversink River basin, New York, 1991–97. 

(Locations of reaches are shown in fig. 1.)

0

20

40

60

80

100

wb08

eb06

wb07wb06wb05wb04wb03

eb05

wb02

eb04

wb01

eb03eb02eb01

nv16nv15nv14nv13nv12nv11nv10nv09nv08nv07nv06nv05nv04nv03nv02nv01

STUDY REACH, BY INCREASING DRAINAGE AREA

Ephemeroptera

Plecoptera

Trichoptera

Chironomidae

Oligochaeta

PERCENTAGE OF TOTAL MACROINVERTEBRATE

POPULATION 

EXPLANATION
8 Effects of Habitat Characteristics & Water Quality on Macroinvertebrate Communities along the Neversink River, 1991–2001

Statistical Correlations between 

Macroinvertebrate Communities and Stream 

Habitat and Water Quality

The statistical relations between the macroinvertebrate 

metrics and the physical-habitat and water-quality factors 

(table 1) indicate that water-quality factors generally explained 

more of the variation in total richness and distribution of 

Ephemeroptera, Trichoptera, and Chironomidae individuals 

than the physical-habitat factors. Most of the water-quality 

factors that were positively correlated with Ephemeroptera, 

Trichoptera, and total richness were negatively correlated with 

Chironomidae (table 1). Physical-habitat factors generally 

explained more variation in the distribution of Plecoptera 

and filterers than did water-quality factors. A combination of 

physical-habitat and water-quality factors equally explained 

the other macroinvertebrate metrics and the percentages for 

functional feeding groups other than filterers.

Macroinvertebrate Discontinuum

Unusual water-quality and physical-habitat 

conditions can cause a discontinuum in the transition of 

macroinvertebrate communities from small headwater reaches 

to large downstream reaches. For example, the predominance 

of certain taxa and functional feeding groups, and the values 

of several metrics, indicated impairment of water quality 

in several acidified headwater reaches and of habitat in the 

two reaches immediately downstream from the Neversink 

Reservoir. This is consistent with the documented adverse 

effects of acidification (for example, Simpson and others, 

1985; Kimmel and others, 1996; Dangles and Guerold, 2000), 

and of reservoirs (for example, Ward and Stanford, 1983; 

Pringle and others, 2000) on macroinvertebrate assemblages 

in other streams. The following sections briefly describe the 

disruptions in the macroinvertebrate continuum found in 

this study.

Figure 5. Percentage of total macroinvertebrate population represented by selected functional feeding groups 

at 30 reaches in the Neversink River basin, New York, 1991–97. 

0

20

40

60

80

100

wb08

eb06

wb07wb06wb05wb04wb03

eb05

wb02

eb04

wb01

eb03eb02eb01

nv16nv15nv14nv13nv12nv11nv10nv09nv08nv07nv06nv05nv04nv03nv02nv01

STUDY REACH, BY INCREASING DRAINAGE AREA

Shredders

Gatherers

Predators

Scrapers

Filterers

Generalists

PERCENTAGE OF TOTAL MACROINVERTEBRATE

POPULATION 

EXPLANATION
Effects of Habitat Characteristics and Water Quality on Macroinvertebrate Communities 9

Table 1. Significant correlations (p<0.05) for physical-habitat and water-quality factors with taxa and functional feeding groups.[All values based on percentage of total macroinvertebrate population represented by taxon or feeding group]

Factor

Macroinvertebrate taxa Functional feeding groups

Total 

taxa 

richness

Ephemeroptera Plecop- tera Trichop- tera EPT individuals Chiro- nomidae Shredders Scrapers Gatherers Filterers Predators

Physical habitatDrainage area 0.58 -0.59 -0.51 -0.50 0.66 -0.47 0.70 -0.68Elevation -0.39 -.69 .53 -0.48 -0.45 .66 .58 -.78 .53 -.67 .61Gradient -.41 .62 .44 -.45 -.64 .67Pool-to-riffle ratio .41 .45 .44 -.53 -.12 .50 -.64 .38Open canopy -.61 -.41 .15 .43 -.59Bank stability .44 .41 .40 .45Mean channel width .65 -.55 .44 .48 -.64 -.55 .79 -.58 .70 -.64Mean channel depth .37 -.39 .52 -.37 .52 -.43Mean substrate particle size .49 -.47Water temperature .57 .56 .70 .68 -.72 -.52 .66 -.61 .47 -.36Water qualitypH .52 .66 -.41 .62 .51 -.65 -.49 .64 -.43 .58 -.53ANC .61 -.46 .51 .45 -.62 -.38 .70 -.67 .64 -.56Calcium .58 .72 -.40 .57 .57 -.72 -.59 .78 -.54 .66 -.55DOC .54 .56 .68 .69 -.75 .59 -.69Total dissolved Al -.45 -.59 -.40 .59 .57 -.76 .48 -.62 .45Al, organic monomeric -.36 -.59 .43 -.73 -.49 .68 -.76 .57 -.60 .50Orthophosphate .46 .80 .70 .77 -.85 -.55 .76 -.70 .54 -.61Nitrate .45 -.45 .53 .45 -.42 -.47 .40 .47 -.70
10 Effects of Habitat Characteristics & Water Quality on Macroinvertebrate Communities along the Neversink River, 1991–2001

Headwater Reaches

Macroinvertebrate taxa: Acidic conditions in headwaters 

of the East and West Branches of the Neversink River 

appear to have affected the structure of macroinvertebrate 

communities by strongly favoring certain acid-tolerant 

chironomid taxa over acid-sensitive Ephemeroptera and 

Trichoptera taxa. Acidified reaches showed much lower 

total richness and EPT richness than nearby, less acidified 

headwater reaches, which is a pattern seen in other acidic 

streams (Kimmel and others, 1996; Ventura and Harper, 

1996). Plecoptera were common in acidified reaches, despite 

lower overall EPT richness; their dominance of invertebrate 

communities, coupled with low numbers of mayflies, has 

been documented in other acidified streams of the Northeast 

(Simpson and others, 1985; Ventura and Harper, 1996), though 

some species of Plecoptera are acid-sensitive (Bradley and 

Ormerod, 2002; Lepori and others, 2003). Several acidified 

headwater reaches (for example, sites eb03 and eb05) 

contained five times as many Plecoptera as Ephemeroptera 

(five times the percentage of total macroinvertebrates). 

This apparent anomaly was especially striking at site wb04, 

which had the lowest median pH (4.72) of any site; here 

the Plecoptera represented more than 43 percent of the total 

macroinvertebrates, and the Ephemeroptera only 1 percent. 

This finding is not surprising, however, in that Plecoptera 

were found to be affected more by physical-habitat factors 

than by water-quality factors, whereas the Ephemoptera were 

affected more by water-quality factors than by physical-habitat 

factors. Most species of Ephemeroptera are rarely found in 

acidified stream reaches (Simpson and others, 1985), whereas 

Plecoptera can thrive in headwater reaches with high acidity 

and elevated aluminum concentrations.

Functional feeding groups: Acidic conditions in some 

headwater reaches of the Neversink River have affected the 

function of macroinvertebrate communities as well as their 

structure by altering the feeding-group distributions. The 

low numbers of scrapers in highly acidic reaches, especially 

those in the East Branch, have been observed in acidic 

streams in Europe as well (Dangles and Guerold, 2000; 

Ledger and Hildrew, 2001). Stream acidification can cause 

a decrease in the quality or quantity of biofilms (Ledger 

and Hildrew, 2001), which in turn may limit the numbers of 

macroinvertebrate scrapers for which biofilms are a primary 

food source (Merritt and Cummins, 1996). Acidic streams 

also tend to have a higher standing stock of coarse particulate 

matter than neutral streams because this material decomposes 

more slowly under acidic conditions (Dangles and Guerold, 

2000, Pretty and others, 2005). This can result in increased 

accumulations of leaf material that may support shredders 

and thereby account for the greater percentages of individual 

shredders in acidified reaches than elsewhere. The River 

Continuum Concept (Vannote and others, 1980) predicts 

fewer scrapers in headwater streams because of more shading, 

and more shredders in headwater streams because of greater 

inputs of leaf material. The key difference in the Neversink 

River headwaters, however, is that acidified reaches here had 

fewer scrapers and more shredders compared to less-acidified 

reaches, suggesting a change in community composition 

associated with pH. Certain streams may be unaffected by 

shifts in feeding groups; for example, a study of stoneflies 

in an acidic stream in England found that generalist feeders 

can graze in streams where specialist scrapers are absent, 

such that stream function may remain unchanged despite a 

shift in the functional feeding groups (Ledger and Hildrew, 

2000). Generalists are uncommon in the Neversink River 

and its tributaries, however, especially in the East and West 

Branches; therefore, the altered conditions there may alter the 

downstream distribution of feeding groups.

Main-Stem Reaches Below the Reservoir

Macroinvertebrate taxa: Physical-habitat conditions 

below the Neversink Reservoir appeared to affect the 

structure of macroinvertebrate communities by favoring taxa 

that tolerate the uniform flows and low water temperatures 

caused by the dam. Biodiversity in reaches below dams tends 

to be lower than in other reaches because the more stable 

habitat conditions below a dam favor assemblages with a few 

dominant taxa (Pringle and others, 2000; Vinson, 2001). This 

is consistent with observations below the Neversink Reservoir, 

where species richness at reaches immediately below the dam 

was far lower than at the reaches above the reservoir or farther 

downstream. The habitat immediately downstream from dams 

can be unfavorable for EPT taxa (Vinson, 2001; Bednarek and 

Hart, 2005; Tiemann and others, 2005), but macroinvertebrate 

communities generally recovered within the first 10 km 

below the dam, as has been reported in other impounded river 

systems (Bednarek and Hart, 2005).

Functional feeding groups: The structure of 

macroinvertebrate communities in terms of functional feeding 

groups below the reservoir also shifted. As in acidic reaches, 

shredders were more abundant just below the dam than in 

reaches farther downstream, and scrapers were slightly less 

abundant. This finding is inconsistent with that predicted 

by the Serial Discontinuity Concept (Ward and Stanford, 

1983), which states that the decreased ratio of coarse- to 

fine-particulate organic matter in reaches below upper- to 

middle-reach dams will decrease the number of shredders. 

This prediction is supported by studies in Spain and Portugal, 

which found decreases in the relative abundance of shredders 

below bottom-release dams (Camargo and others, 2005; 

Cortes and others, 2002). It is also supported by a study of 

dams worldwide that found that the decreased variability of 

streamflow generally leads to an abundance of periphyton 

and plant growth, which should in turn lead to an increase 

in the numbers of scrapers (Stanford and Ward, 1979). The 

greater relative abundance of shredders found just below 

the Neversink Reservoir, and the lesser relative abundance 

of scrapers, were surprising, but may simply be a result 

of sampling techniques. Invertebrate samples were taken 

only from riffles or runs. The extensive, dense, perennial 
Summary and Conclusions 11

macrophyte beds that are common in channels downstream 

from the reservoir provide a good substrate for periphyton 

and, therefore, scrapers, but these macrophyte beds were 

not sampled. 

Another effect of the dam on functional feeding groups 

was that fewer filterers than expected were found in reaches 

immediately downstream from the reservoir. Filter feeders 

are commonly abundant below dams that release water over 

a spillway (Allan, 1997), but the bottom-release Neversink 

Reservoir Dam probably causes a decrease in the amount of 

particulate organic matter downstream. This is consistent with 

conclusions of a study of macroinvertebrate communities 

below surface-release and bottom-release dams, which found 

that filterers were common only below the surface-release dam 

(Ward and Short, 1977). Dissolved oxygen levels may also be 

lower below the Neversink Reservoir Dam, which could lead 

to reduced numbers of filterers, but dissolved oxygen levels 

were not measured.

Recovery from the effects of the reservoir (stabilized 

flow, cold water, decreased sediment and nutrient content) 

occurred within a relatively short distance downstream, 

however; scrapers and filterers rebounded to high percentages 

of the invertebrate community within 10 km below the dam, 

and shredders returned to low percentages within 18 km. 

Comparing Headwater Reaches to Reaches 

Below the Reservoir 

Stream conditions both above and below the reservoir 

dam led to similar invertebrate communities, although 

the influences were different. The water-quality variables 

(chiefly pH and aluminum) found to shape macroinvertebrate 

communities in the upper basin resulted in macroinvertebrate 

communities with fewer EPT taxa at reaches in the chronically 

acidified East Branch than the neutral West Branch, even 

though the two branches are similar in physical-habitat 

characteristics. The physical-habitat characteristics (chiefly 

low temperatures and low flow rates) at the two reaches 

immediately downstream from the reservoir also resulted in 

communities that favored chironomids over EPT taxa (fig. 6).

 The reach-to reach differences in water quality and 

physical-habitat conditions found in this study, and the 

macroinvertebrate-metric results that were obtained, indicate 

that several reaches have been slightly to moderately affected 

and the distributions of functional feeding groups have been 

altered. For instance, the number of shredders in two acidified 

headwater reaches increased in response to the large amount 

of leaf matter that may be due to decreased decomposition 

rates; this number also decreased in two reaches below the 

reservoir, where low, stable flows and low water temperatures 

similarly decreased the decomposition rates of organic matter 

and permitted leaf accumulation. The number of scrapers 

both above and below the reservoir decreased, possibly in 

response to decreased food availability, either because acidic 

water above the reservoir affected the quality or quantity 

of biofilms, or because the variable physical and chemical 

conditions below the reservoir restricted periphyton growth. 

In summary, macroinvertebrate communities at two of the 

reaches downstream from the reservoir were similar to those 

in acidified reaches far upstream from the reservoir—an 

indication that impaired stream conditions, related either 

to physical habitat or water quality, can disrupt the normal 

downstream progression of stream-invertebrate communities.

Potential Applications of this Study

The data and findings from this study serve as indicators 

of the degree to which two significant environmental 

stresses—stream acidification and flow alteration by the 

dam—affected the macroinvertebrate community in the 

Neversink River Basin. These data and findings can be used 

to evaluate changes to the macroinvertebrate communities 

in other streams that are acidified or that have large 

impoundments. Such information also is useful in studies 

of the relative importance of given environmental stresses, 

a critical step toward the protection and conservation of 

aquatic systems from threats such as point- and nonpointsource pollution, dams, acidic atmospheric deposition, and 

invasive species. 

The findings of this study, some of which are in contrast 

to the accepted theory of linear progression of stream 

macroinvertebrate communities (the Serial Discontinuity 

Concept, Ward and Stanford, 1983), may serve to stimulate 

further studies in similar river systems with acidified streams 

and large impoundments. Such studies could be designed for 

use in evaluating the effectiveness of conservation actions 

and could lead to improved resource management in this and 

similar river systems in the future.

Summary and Conclusions

The Neversink River provides New York City with 

some of the purest water in its supply network and minimizes 

downstream flooding, but physical and chemical conditions 

in parts of the basin threaten some stream biota. Data were 

collected during 1991–2001 from 30 reaches of the Neversink 

River and its tributaries above and below the Neversink 

Reservoir Dam to identify the effects of stream acidification, 

selected habitat characteristics, and the reservoir on the 

health and composition of macroinvertebrate assemblages. 

Macroinvertebrate assemblages generally showed a predictable 

pattern of change from upstream headwaters to downstream 

reaches, with some exceptions. Water-quality data indicated 

that several headwater reaches, mainly in the East Branch 

of the Neversink River, had low pH, low acid-neutralizing 

capacity, low concentrations of dissolved organic carbon and 

calcium, and toxic concentrations of inorganic monomeric 

aluminum and, thus, that the structure and function of 

macroinvertebrate communities in these reaches were 
12 Effects of Habitat Characteristics & Water Quality on Macroinvertebrate Communities along the Neversink River, 1991–2001

Base from U.S. Geological Survey digital data, 1:100,000, 1983

Universal Transverse Mercator Projection, Zone 18

Study reach

Chironomidae taxa

Ephemeroptera, Plecoptera, and

Trichoptera (EPT) taxa

Other taxa

Neversink River

Neversink River

Neversink Reservoir West Branch Neversink River

East Branch Neversink River

EXPLANATION

 

NEW

YORK

Vermont

Massachusetts

Connecticut New

Jersey

Pennsylvania

Neversink Basin

Catskill State Park

Port Jervis

0 2 4 6 8 10 MILES

0 2 4 6 8 10 KILOMETERS

41 ̊30'

41 ̊52'30"

74 ̊45' 74 ̊22'30"

wb06, pH = 5.51 wb04, pH = 4.72

eb05, pH = 5.01

eb03, pH = 4.94

nv13, pH = 7.05

nv14, pH = 6.95

nv10, pH = 6.85

nv06, pH = 7.15

Figure 6. Stream-water pH and composition of macroinvertebrate communities at eight reaches 

from the headwaters of the Neversink River to the lower basin, selected to show the range in 

macroinvertebrate-community composition with varying pH.
References Cited 13

impaired. The physical-habitat data indicated that the low 

water temperature and low flows at two reaches downstream 

from the Neversink Reservoir created conditions that 

interrupted the expected progression of stream-invertebrate 

communities below the reservoir. The macroinvertebrate 

communities in acidified reaches and in two reaches below 

the reservoir supported fewer Ephemeroptera and Trichoptera, 

and fewer scraper and filterer macroinvertebrates, than 

reaches unaffected by acidification or the reservoir, and more 

Chironomidae and shredders. Acidification and flow alteration 

have disrupted the expected continuum of macroinvertebrate 

communities from headwaters to downstream reaches. The 

information provided in this report may serve to stimulate 

further studies in similar river systems with acidified streams 

and large impoundments.

Acknowledgments 

The authors thank Mari-Beth DeLucia, Tracy MacGregor, 

Rebecca Pratt Miller, and Michelle Brown of The Nature 

Conservancy for field assistance, and Frost Valley YMCA, the 

towns of Thompson and Mamakating, and many landowners 

within the Neversink River basin for access to field sites. 

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Glossary 15

Glossary

C

Chironomidae Midge larvae, a group of macroinvertebrates that tends to be tolerant of 

organic pollution.

E

EPT Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies), 

the invertebrate taxa that tend to be most sensitive to water quality. Streams with good 

water quality tend to have many EPT taxa, whereas streams with poor water quality tend to 

have fewer.

F

Filterer A macroinvertebrate that consumes particulate matter in transport. Filterers form a 

functional feeding group.

Functional feeding group A group of macroinvertebrates classified by their means of 

acquiring and consuming food, such as “scraper” or “filterer”.

G

Gatherer A macroinvertebrate that consumes the accumulated particles of leaves and algae 

from the surfaces of rocks or other hard substrata. Gatherers form a functional feeding group.

Generalist A macroinvertebrate that acquires and consumes a variety of food, and, therefore, 

is not able to be assigned to a single functional feeding group.

H

HBI Hilsenhoff’s Biotic Index, a measure of the average tolerance of an assemblage to 

contamination by organic compounds. Sensitive taxa within the assemblage have low tolerance 

values, whereas tolerant taxa have high values.

M

Macroinvertebrate An invertebrate that is visible to the naked eye, such as an insect larva.

Metric A measure of a characteristic that summarizes data and facilitates comparisons 

among sites, such as richness or HBI value.

R

Richness The number of taxa present in an area.

S

Scraper A macroinvertebrate that consumes algae, generally by scraping it off of rocks and 

other surfaces where it grows. Scrapers form a functional feeding group.

Shredder A macroinvertebrate that consumes fallen-leaf material. Shredders form a 

functional feeding group.

T

Taxon A group of similar organisms, such as a genus or species. (Taxa, plural)

For additional information write to: 

New York Water Science Center

U.S. Geological Survey

425 Jordan Road 

Troy, NY 12180

Information requests:

(518) 285-5602

or visit our Web site at:

http://ny.water.usgs.gov
Ernst and Others—Effects of Habitat Characteristics and Water Quality on Macroinvertebrate Communities

 along the Neversink River in Southeastern New York, 1991-2001

—Scientific Investigation Report 2008–5024