U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2011–1294

Prepared in cooperation with the U.S. Department of the Interior Bureau of Land Management; 

Montana Department of Environmental Quality; Wyoming Department of Environmental Quality; 

and Wyoming Game and Fish Department 

Assessment of Potential Effects of Water Produced from 

Coalbed Natural Gas Development on Macroinvertebrate and 

Algal Communities in the Powder River and Tongue River, 

Wyoming and Montana, 2010

Assessment of Potential Effects of Water 

Produced from Coalbed Natural Gas 

Development on Macroinvertebrate and 

Algal Communities in the Powder River and 

Tongue River, Wyoming and Montana, 2010

By David A. Peterson, Eric G. Hargett, and David L. Feldman

Prepared in cooperation with the U.S. Department of the Interior Bureau of Land 

Management; Montana Department of Environmental Quality; Wyoming Department of Environmental Quality; and Wyoming Game and Fish Department 

Open-File Report 2011–1294

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Peterson, D.A., Hargett, E.G., and Feldman, D.L., 2011, Assessment of potential effects of water produced from 

coalbed natural gas development on macroinvertebrate and algal communities in the Powder River and Tongue River, 

Wyoming and Montana, 2010: U.S. Geological Survey Open-File Report 2011–1294, 34 p.
iii

Contents

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

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

Purpose and Scope .............................................................................................................................2

Location of Sampling Sites..................................................................................................................2

Sample Collection and Laboratory Analysis ....................................................................................2

Methods of Data Analysis ...................................................................................................................5

Quality Assurance.................................................................................................................................6

Streamflow, Water Quality, and Habitat.....................................................................................................6

Powder River.........................................................................................................................................6

Tongue River........................................................................................................................................11

Macroinvertebrate Communities ..............................................................................................................11

Powder River.......................................................................................................................................11

Community Metrics ...................................................................................................................11

Observed/Expected Model.......................................................................................................19

Tongue River........................................................................................................................................23

Community Metrics ...................................................................................................................23

Observed/Expected Model.......................................................................................................23

Algal Communities.......................................................................................................................................24

Powder River.......................................................................................................................................24

Tongue River........................................................................................................................................25

Potential Effects of Water Produced from Coalbed Natural Gas Development on 

Biological Communities.................................................................................................................29

Powder River.......................................................................................................................................29

Tongue River........................................................................................................................................30

Further Study Needs...........................................................................................................................30

Summary........................................................................................................................................................32

Acknowledgments.......................................................................................................................................32

References....................................................................................................................................................32

Figures

1. Map showing location of aquatic ecological sampling sites and selected 

streamgages on the Powder River and Tongue River, Wyoming and 

Montana, 2010 ...............................................................................................................................3

2. Hydrographs for the Powder River at Arvada, July 15–31, 2010, and the 

Tongue River at the Montana-Wyoming State Line, September 1–17, 2010 .......................7

3. Graphs showing instantaneous streamflow, water-quality, and habitat 

measurements from ecological sampling sites on the Powder River, 

July 2010, and the Tongue River, September 2010, Wyoming and 

Montana .......................................................................................................................................10
iv

4. Boxplots of selected macroinvertebrate community metrics from 

ecological sampling sites, Powder River and Tongue River, Wyoming 

and Montana, 2010 .....................................................................................................................18

5. Boxplots of macroinvertebrate observed/expected model scores from 

ecological sampling sites, Powder River and Tongue River, Wyoming 

and Montana, 2010 .....................................................................................................................22

6. Graphs showing algal community metrics for ecological sampling sites 

on the Powder River and Tongue River, Wyoming and Montana, 2010 .............................28

7. Graphs showing comparison of mean macroinvertebrate metric scores 

from 2005–08 to mean scores from 2010, Powder River, Wyoming....................................31

Tables

1. Ecological sampling sites on the Powder River and Tongue River, Wyoming 

and Montana, 2010 .......................................................................................................................4

2. Environmental variables associated with biological samples, Powder River 

and Tongue River, Wyoming and Montana, 2010.....................................................................8

3. Macroinvertebrate community metrics, Powder River and Tongue River, 

Wyoming and Montana, 2010 ...................................................................................................12

4. Analysis of variance for macroinvertebrate community metrics, Powder 

River and Tongue River, Wyoming and Montana, 2010 ........................................................16

5. Observed/expected scores and analysis of variance among mean scores 

for macroinvertebrate communities, Powder River and Tongue River, 

Wyoming and Montana, 2010 ...................................................................................................20

6. Algal community metrics for the Powder River and Tongue River, Wyoming 

and Montana, 2010 .....................................................................................................................26

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

centimeter 0.3937 inch (in.)

cubic foot per second (ft3

/s) 0.3048 cubic meter per second (m3/s)

micrometer (μm) 0.00003937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

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

°F=(1.8×°C)+32
v

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Elevation, as used in this report, refers to distance above the vertical datum.

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) 

or micrograms per liter (μg/L). Concentrations of algal constituents are given in milligrams per 

square meter (mg/m2), grams per square meters (g/m2), billion cells per square meter, or cubic 

centimeters per square meter (cm3/m2).

The water year begins October 1 and ends September 30, and is designated by the year in which 

it ends. For example, water year 2005 begins October 1, 2004, and ends September 30, 2005.

Abbreviations, Acronyms, Initialisms, and Symbols

< less than

≤ less than or equal to

> greater than

≥ greater than or equal to

ANOVA analysis of variance

ATG Aquatic Task Group

BC Bray-Curtis 

BLM U.S. Department of the Interior Bureau of Land Management

CBNG coalbed natural gas

D84 diameter of the 84th percentile of particles

GPS global positioning system

IWG Interagency Working Group

MFWP Montana Fish, Wildlife, and Parks

MDEQ Montana Department of Environmental Quality

NTRU nephelometric turbidity ratio units

p probability level

O/E observed/expected 

QC quality control

RPD Relative percent difference

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WDEQ Wyoming Department of Environmental Quality

WGFD Wyoming Game and Fish Department

Assessment of Potential Effects of Water Produced from 

Coalbed Natural Gas Development on Macroinvertebrate 

and Algal Communities in the Powder River and Tongue 

River, Wyoming and Montana, 2010

By David A. Peterson1, Eric G. Hargett2, and David L. Feldman3

1

U.S. Geological Survey.

2

Wyoming Department of Environmental Quality.

3

Montana Department of Environmental Quality. 

Abstract

Ongoing development of coalbed natural gas in the 

Powder River structural basin in Wyoming and Montana led 

to formation of an interagency aquatic task group to address 

concerns about the effects of the resulting production water 

on biological communities in streams of the area. Ecological 

assessments, made from 2005–08 under the direction of the 

task group, indicated biological condition of the macroinvertebrate and algal communities in the middle reaches of the 

Powder was lower than in the upper or lower reaches. On the 

basis of the 2005–08 results, sampling of the macroinvertebrate and algae communities was conducted at 18 sites on the 

mainstem Powder River and 6 sites on the mainstem Tongue 

River in 2010. Sampling-site locations were selected on a 

paired approach, with sites located upstream and downstream 

of discharge points and tributaries associated with coalbed 

natural gas development. Differences in biological condition 

among site pairs were evaluated graphically and statistically 

using multiple lines of evidence that included macroinvertebrate and algal community metrics (such as taxa richness, 

relative abundance, functional feeding groups, and tolerance) 

and output from observed/expected (O/E) macroinvertebrate 

models from Wyoming and Montana.

Multiple lines of evidence indicated a decline in biological condition in the middle reaches of the Powder River, 

potentially indicating cumulative effects from coalbed natural 

gas discharges within one or more reaches between Flying E 

Creek and Wild Horse Creek in Wyoming. The maximum 

concentrations of alkalinity in the Powder River also occurred 

in the middle reaches. Biological condition in the upper and 

lower reaches of the Powder River was variable, with declines 

between some site pairs, such as upstream and downstream of 

Dry Fork and Willow Creek, and increases at others, such as 

upstream and downstream of Beaver Creek.

Biological condition at site pairs on the Tongue River 

showed an increase in one case, near the Wyoming-Montana 

border, and a decrease in another case, upstream of Tongue 

River Reservoir. Few significant differences were noted from 

upstream to downstream of Prairie Dog Creek, a major tributary to the Tongue River. Further study would be needed to 

confirm the observed patterns and choose areas to examine in 

greater detail. 

Introduction

Development of energy and mineral resources in the 

Powder River structural basin in northeastern Wyoming and 

southeastern Montana (fig. 1) includes coalbed natural gas, 

conventional oil and gas, and coal mining. A common byproduct of coalbed natural gas (CBNG) development is discharge of groundwater that commonly is saline or unsuitable 

for irrigation of crops and has unknown effects on the aquatic 

communities inhabiting streams that receive the water (Bureau 

of Land Management, 2009).

To address concerns about the potential effects of 

CBNG development on cultural and natural resources, the 

U.S. Department of the Interior Bureau of Land Management (BLM) formed an Interagency Working Group (IWG) 

of Federal, State, and tribal agencies. The charter of the IWG 

states that it “...was established as the forum for government 

agencies to address, discuss, and find solutions to issues of 

common concern to all parties involved in permitting and 

monitoring of CBNG development” (Powder River Natural 

Gas Interagency Working Group, 2004). The IWG charter 

also provides for establishment of working groups to address 

technical issues as envisioned by the April 2003 Record of 

Decision (Bureau of Land Management, 2003). One working group, the Aquatic Task Group (ATG), was tasked with 

assessing potential effects of CBNG produced water on 
2 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

aquatic ecological resources. Agencies involved in the ATG 

include the BLM, the Wyoming Department of Environmental 

Quality (WDEQ), Montana Department of Environmental 

Quality (MDEQ), the Wyoming Game and Fish Department (WGFD), the Montana Department of Fish, Wildlife, 

and Parks (MFWP), and the U.S. Environmental Protection 

Agency (USEPA). 

The ATG developed a monitoring plan to meet two 

main objectives: (1) establish current ecological conditions 

for aquatic biota and their habitat, and (2) determine existing and potential effects of CBNG-produced water on aquatic 

life (Bureau of Land Management, 2009). The assessment of 

current ecological conditions as of 2005–08 was performed 

by the U.S. Geological Survey (USGS) under the direction of 

the ATG (Peterson and others, 2009; 2010). The determination 

of effects from CBNG-produced water is addressed in part by 

this study, as well as by studies of potential effects of CBNG 

water on fish communities in the study area (Davis, 2008; 

Skaar and others, 2006) and a literature review of the effects 

of CBNG activities on fish communities (Davis and others, 

2009). 

Results of the current-conditions study for 2005–08 

indicated that an approximately 33-mile length of the Powder River, from Willow Creek downstream to below Crazy 

Woman Creek (named the middle reach), contained macroinvertebrate and algal communities distinct from those of the 

upper and lower reaches of the Powder River (Peterson and 

others, 2010). For example, macroinvertebrate taxa richness, 

relative abundance, functional feeding group, and tolerance 

metrics, which together are indicative of communitywide 

differences, indicated decreased biological condition in the 

middle reach of the Powder River relative to the upper and 

lower reaches (Peterson and others, 2010). In part because of 

those differences, the ATG adopted a focused paired-site study 

design in 2010 where sample site pairs were located above 

and below known discharges (either direct or via tributaries) 

of CBNG effluent to the Powder River in Wyoming and the 

Tongue River in Montana and Wyoming. The assumption of 

this paired-site study design is that any naturally occurring 

changes or non-CBNG anthropogenic activities would be 

similar between site pairs, so that any appreciable changes in 

macroinvertebrate and/or algal communities that occur within 

the site pair may be attributed to influences from CBNG effluent. In addition, sampling sites were located on the Tongue 

River upstream and downstream of Hanging Woman Creek 

related to potential effects of planned coal development in 

the Hanging Woman Creek drainage. Additional information 

about CBNG development and monitoring is available from 

the BLM at http://www.wy.blm.gov/prbgroup/; the Wyoming 

Department of Environmental Quality (WDEQ) at http://deq.

state.wy.us/wqd/WYPDES_Permitting/WYPDES_cbm/cbm.

asp; and the USGS at http://wy.water.usgs.gov/.

Purpose and Scope 

The purpose of this report is to assess macroinvertebrate 

and algal communities upstream and downstream of CBNG 

discharges in the Powder River structural basin during 2010. 

Macroinvertebrate and algal samples were collected from 

18 sites on the main stem of the Powder River in Wyoming 

and 6 sites on the main stem of the Tongue River in Wyoming 

and Montana. Related data collected in conjunction with the 

biological samples included streamflow discharge, water 

quality (major ions and field measurements), pebble counts, 

and microhabitat associated with biological sample collection 

points. Digital photographs and global positioning system 

(GPS) coordinates also were obtained at each site. 

Location of Sampling Sites

Sampling sites generally were located in pairs upstream 

and downstream of direct discharges or tributaries contributing CBNG effluents to the Powder River and Tongue River 

(table 1; fig. 1). In some cases, the downstream site for one 

pair is also the upstream site for the next pair of sites. The sites 

on the Tongue River upstream and downstream of Hanging 

Woman Creek (sites TR5 and TR6) are an exception because 

their location is related to potential effects of planned coal 

development in the Hanging Woman Creek drainage.

Sample Collection and Laboratory Analysis

Ecological sampling in late July for the Powder River 

and mid-September for the Tongue River was timed to mimic 

seasonal sampling periods on those rivers during 2005–08 

(Peterson and others, 2010). Macroinvertebrate samples were 

collected from multiple riffles (where available) at each site, 

using a Slack sampler (Moulton and others, 2002). Triplicate macroinvertebrate samples (labeled A, B, and C) were 

collected at each site as a measure of variability. Each macroinvertebrate sample was a composite from five areas, each 

defined by a square sampling frame measuring 50 centimeters 

(cm) by 50 cm (0.25 m2), which sums to 1.25 m2 total area per 

sample. Triplicate samples were collected side-by-side among 

one or more riffles until five grabs were collected for all three 

samples (15 total). Each of the triplicate macroinvertebrate 

samples was composited and elutriated separately. Macroinvertebrate samples were preserved in ethanol and sent to the 

Buglab at Utah State University in Logan, Utah, for taxonomic 

identification. Chironomid taxonomy was subcontracted to 

Rhithron Associates, Inc. in Missoula, Mont. 

Algal samples were collected by scraping rocks from riffles in the same general area as the macroinvertebrate samples 

(Moulton and others, 2002). The general procedure was to 

collect five undisturbed rocks near each of the five macroinvertebrate grabs, for a total of 25 rocks per algal sample. Algae 
107° 106° 105°

45°

44°

Creek

Tongue

River 

Reservoir

Lake

 De Smet

Pumpkin Creek

Belle

River

River

Cr

Creek

Clear

Woman

Crazy

River

Creek

Hanging Woman

Powder Little

River

Cr

Cr

Squirrel

S Fk

Powder

Powder

River

Tongue

Youngs

Creek

Badger

Prairie Dog

Creek

Powder

Fourche

Spotted Horse

Creek

Mitchell

Draw

Creek

River

Flying E Cr

Dry Fk Powder River

Willow

Pumpkin Creek

Fourmile Creek

Creek

Beaver

Creek

Burger Draw

Dead

Creek

Horse

Dry

Creek

Wild Horse Creek

Fortification Creek

LX Bar Creek

SA

Creek

Cr

Cottonwood Cr

CAMPBELL COUNTY

JOHNSON

COUNTY

SHERIDAN COUNTY

POWDER

RIVER

COUNTY

BIG HORN

COUNTY

ROSEBUD

COUNTY

WASHAKIE

COUNTY

CR

O

O

K CO

U

NTY

BIG

HORN

COUNTY

WESTO

N CO

U

NTY

CA

RTER CO

U

NTY

Monarch

Kirby

Sussex

Wright

Kaycee

Dayton

Decker

Buffalo

Gillette

Sheridan

Moorhead 06306300

06313590

06313500

06317000

06316400

06306250

MONTANA

WYOMING

Ivy

Joe

192

0 10 20 30 MILES

0 10 20 30 KILOMETERS

TR6 TR5

TR4

TR3

TR2

TR1

PR9

PR8

PR7

PR6

PR5

PR4

PR3

PR2

PR1

PR18

PR16 PR17

PR15

PR14

PR13

PR12

PR11

Base from U.S. Geological Survey digital data, 1999–2004, 1:2,000,000 

Roads from Federal Highway Administration digital data, 2002, 1:100,000 

Albers Equal-Area Conic projection 

Standard parallels 40°N and 60°N, central meridian 106°W 

MONTANA

WYOMING

PR10

Barber 59

50

14

16

90

90

90

25

25

59

39

16

Powder River drainage area

Tongue River drainage area

Powder River structural basin boundary

Aquatic ecology sampling site and number

Streamgage and number

PR1

EXPLANATION

06306300

Figure 1. Location of aquatic ecological sampling sites and selected streamgages on the Powder River and 

Tongue River, Wyoming and Montana, 2010.

Introduction 3
Table 1. Ecological sampling sites on the Powder River and Tongue River, Wyoming and Montana, 2010.

Site 

number 

(fig. 1)

U.S. Geological 

Survey station 

identification 

number

Site name Latitude Longitude Pair number and target

PR1 434631106151901 Powder River above Dry Fork 43.7753 -106.2553 1 - upstream of Dry Fork and Willow CreekPR2 435453106104701 Powder River below Willow Creek 43.9147 -106.1798 1 - downstream of Dry Fork and Willow CreekPR3 440134106100901 Powder River above Pumpkin Creek 44.0264 -106.1691 2 - upstream of Pumpkin CreekPR4 440152106101801 Powder River below Pumpkin Creek 44.0311 -106.1716 2, 3 - downstream of Pumpkin Creek, upstream of Fourmile CreekPR5 440552106094601 Powder River below Fourmile Creek 44.0978 -106.1627 3,4 - downstream of Fourmile Creek, upstream of Beaver CreekPR6 440720106083801 Powder River below Beaver Creek 44.1223 -106.1438 4,5 - downstream of Beaver Creek, upstream of Burger DrawPR7 440919106091401 Powder River below Burger Draw 44.1568 -106.1593 5 - downstream of Burger DrawPR8 441520106084801 Powder River above Dry Creek 44.2556 -106.1468 6 - upstream of Dry CreekPR9 441533106084401 Powder River below Dry Creek 44.2591 -106.1456 6, 7 - downstream of Dry Creek, upstream of Flying E Creek

PR10 441632106071601 Powder River below Flying E Creek 44.2757 -106.1212 7, 8 - downstream of Flying E Creek, upstream of Barber Creek

PR11 441956106090401 Powder River below Barber Creek 44.3322 -106.1510 8 - downstream of Barber Creek

PR12 442538106082001 Powder River below Mitchell Draw 44.4242 -106.1501 8 - downstream of Barber Creek and other effluentPR13 443832106072601 Powder River above Wild Horse Creek 44.6421 -106.1239 9 - upstream of Wild Horse CreekPR14 443927106074401 Powder River below Wild Horse Creek 44.6576 -106.1290 9, 10 - downstream of Wild Horse Creek, upstream of unnamed effluentPR15 444857106030401 Powder River above Ivy Creek 44.8090 -106.0873 10 - downstream of unnamed effluentPR16 445537105590401 Powder River above LX Bar Creek 44.9270 -105.9845 11 - upstream of LX Bar CreekPR17 445601105570201 Powder River below LX Bar Creek 44.9337 -105.9506 11, 12 - downstream of LX Bar Creek, upstream of SA CreekPR18 445728105553701 Powder River below SA Creek 44.9578 -105.9270 12 - downstream of SA Creek

TR1 6306020 Tongue River below Youngs Creek 44.9859 -106.8912 13 - upstream of Fidelity dischargesTR2 445935106505401 Tongue River above Prairie Dog Creek 44.9877 -106.8445 13, 14 - downstream of first Fidelity discharges, upstream of Prairie Dog CreekTR3 445938106490801 Tongue River below Prairie Dog Creek 44.9957 -106.8241 14, 15 - downstream of Prairie Dog CreekTR4 450047106490101 Tongue River above Badger Creek 45.0128 -106.8157 15 - downstream of Fidelity discharges, upstream of Badger CreekTR5 451902106312601 Tongue R above Hanging Woman Creek 45.3190 -106.5257 16 - upstream of Hanging Woman CreekTR6 451924106312201 Tongue R below Hanging Woman Creek 45.3233 -106.5228 16 - downstream of Hanging Woman Creek

4 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Introduction 5

on each rock were scraped using a PVC-ring (about 18.8 cm2

area) to delimit a composite area of 471 cm2

 total per sample. 

Algal samples were preserved in formalin and sent to Rhithron 

Associates, Inc., in Missoula, Mont., for taxonomic identification following standard WDEQ protocols. 

Prior to ecological sampling, cross-sectional measurements of field parameters (specific conductance, pH, dissolved 

oxygen, and water temperature) were recorded at each site to 

ensure that the river was well mixed. Field parameters were 

measured at regular intervals, typically every 5 feet, across 

the stream. If the field parameters indicated the stream was 

not well mixed, the crew moved downstream and repeated 

the cross-sectional measurement process. Depth- and widthintegrated water-quality samples were collected and composited in a churn at each site following standard USGS protocols 

(U.S. Geological Survey, variously dated) and sent to the 

USGS National Water-Quality Laboratory for analysis of 

major ions. Turbidity was measured onsite. Streamflow was 

measured at each site at the time of ecological sampling, following Rantz and others (1982). 

A Wolman pebble count was conducted across riffles at 

each site, along a transect generally from bankfull to bankfull (Wolman, 1954). The exception to the bankfull cross 

section occurred at site PR15, where the riffle habitat was 

confined to a narrow edge along the left bank. The pebble 

count at site PR15 was conducted within the riffle habitat, 

parallel to the left bank. A minimum of 100 particles per site 

were measured for the pebble count. Microhabitat measures 

recorded with each of the macroinvertebrate and algal grabs 

were depth, velocity, riffle embeddedness, and substrate 

class (Moulton and others, 2002). The microhabitat substrate 

class was determined by visually estimating the dominant 

substrate at the grab point and assigning a numeric score of 

3 for sand (>0.063–2 millimeters (mm)), 4 for fine to medium 

gravel (<2–16 mm), 5 for coarse gravel (>16–32 mm), 

6 for very coarse gravel (<32–64 mm), 7 for small cobble 

(<64–128 mm), and 8 for large cobble (<128–256 mm). 

Methods of Data Analysis

Biological community metrics were calculated using 

procedures and attributes described by Cuffney (2003) for 

macroinvertebrates and by Porter (2008) for algae. Macroinvertebrate tolerance scores (Hilsenhoff, 1987; Cuffney, 2003) 

were assigned to one of three ranges: intolerant, greater than 

or equal to (≥) 0 to less than or equal to (≤) 4; moderately 

tolerant, greater than (>) 4 to less than (<) 7; and tolerant, ≥7 

to ≤10. The Shannon diversity index, nitrogen fixation, motility, and benthic-sestonic (substrate-attached and -unattached) 

metrics were computed for the entire algal community (Porter, 

2008). Salinity, nitrogen uptake metabolism, saprobien system, 

and pH tolerance metrics were computed only for the diatom 

community (Van Dam and others, 1994). The relative abundance of halophilic diatoms, those preferring high salinity, 

was calculated from the sum of categories brackish-fresh and 

brackish species, and the relative abundance of nitrogen autotrophs was calculated from the sum of categories autotrophs 

low nitrogen and autotrophs high nitrogen, as described by 

Van Dam and others (1994). 

Statistical comparisons of macroinvertebrate community 

metrics were performed in Spotfire S+ (TIBCO Software Inc., 

2008) at a probability level (p) of 0.05. Following procedures 

described by Helsel and Hirsch (2002), Kruskal-Wallis ranksum tests were used to look for significant differences in metric values within the Powder River group (sites PR1–PR18) 

and the Tongue River group (sites TR1–TR4). Rank-transformed data for groups with significant differences were subsequently tested for differences between sites using analysis of 

variance (ANOVA) and Tukey’s test for multiple comparisons. 

Metrics from sites TR5–TR6 were tested using a Wilcoxon 

rank-sum test appropriate for a pair of sites instead of the 

group tests. 

The Observed/Expected (O/E) models developed by 

the States of Wyoming (Hargett and others, 2005; 2007) and 

Montana (Montana Department of Environmental Quality, 

2006) also were used to evaluate the macroinvertebrate data. 

Application of both O/E models by Peterson and others (2009) 

have shown them to be sensitive for detection of environmental change within the ATG study area. Similar to other 

multivariate predictive models such as RIVPACS (Clarke and 

others, 2003; Moss and others, 1987; Wright and others, 1993) 

and its derivatives, the Wyoming and Montana O/E models 

are statewide macroinvertebrate-based predictive models that 

provide an assessment of biological condition by comparing the macroinvertebrate taxa observed at a site of unknown 

biological condition to the indigenous macroinvertebrate taxa 

expected to occur (probability of occurrence >50 percent) 

in the absence of human stress. Predictor variables, such as 

site latitude and longitude, substrate type, precipitation, air 

temperature, watershed area, elevation and geology were used 

to construct the models. The expected macroinvertebrate taxa 

were derived from an appropriate set of reference sites that 

were minimally or least affected by anthropogenic stress. The 

deviation of the observed from the expected taxa, known as 

the O/E score, is a measure of the compositional similarity 

expressed in units of taxa richness and, thus, is a communitylevel measure of biological condition. Such O/E scores near 1 

imply high biological condition similar to expected conditions, 

whereas O/E scores less than 1 imply some degree of biological degradation as a result of the absence of expected taxa. The 

reference expectations for the Wyoming and Montana invertebrate O/E models were each developed from a network of 

reference sites within the state of origin. Thus the geographic 

application of each model is generally restricted to within the 

state for which it was developed. For these reasons, the Wyoming O/E model was applied only to macroinvertebrate data 

from Powder River sites, whereas Tongue River sites were 

evaluated with the Montana O/E model.

The BrayCurtis (BC) index was calculated from outputs of the invertebrate O/E models to evaluate potential taxa 

replacement issues that might not be captured by the O/E 
6 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

model (Van Sickle, 2008). The BC index allows comparison of 

an observed sample to an expected population based upon the 

same probability of capture scores used in the O/E model. The 

BC index is designed to provide a more accurate evaluation of 

a macroinvertebrate sample because it will not allow the influence of rare or additional taxa to affect the final result. The 

O/E model can be biased when rare or unexpected taxa replace 

common ones. Van Sickle (2008) demonstrated how this could 

result in a good final O/E score when the opposite may be true. 

The BC index ranges between 0 and 1, where 0 is the most 

similar to the expected reference population, and 1 is the score 

for the least similar to reference.

Quality Assurance

Quality assurance for analyses of major ions included 

collection and analysis of quality-control (QC) samples from 

two sites (10 percent of samples). Concentrations of all major 

ions in a blank sample collected at site PR10 were less than 

the laboratory reporting limits with the exception of chloride 

that was three orders of magnitude less than the concentration of chloride in the corresponding environmental sample. 

The other QC sample for major ions was a split collected at 

site PR1. The relative percentage difference (RPD) in constituent concentrations between the environmental (sample 1) and 

the split (sample 2) sample was calculated using the formula: 

RPD = absolute value ((sample 1 – sample 2)/[(sample 1 + 

sample 2)/2]) x 100

The RPD between the environmental and split samples was 

less than 5 percent difference for all of the major ions. 

Quality assurance for pebble counts consisted of triplicate pebble counts at two sites. The D84, or diameter of the 

84th percentile of particles, is presented as an indicator for 

comparison of the triplicates. The RPD between the triplicates 

collected at PR5 was 30, 14, and 44 percent difference, respectively, in the D84 values. The RPD between the triplicates collected at site TR2 was 0, 3.6, and 3.6 percent difference in the 

D84 values. In order to provide a better estimate for data analysis in later sections of this report, the triplicate pebble counts 

were composited at each site, thereby providing a pebble count 

of more than 300 particles for sites PR5 and TR2. 

Taxonomic QC samples for invertebrates were provided 

by the triplicate samples collected at each site. The variation 

among the triplicate samples was analyzed through various 

techniques, such as ANOVA, described in the sections, “Methods of Data Analysis” and “Macroinvertebrate Communities.”

Taxonomic QC samples for algae were collected at 

site PR12 (environmental, split, and replicate samples) and at 

site PR14 (environmental and replicate samples). The algae 

QC samples were compared to the environmental samples 

using BC similarity coefficients (Bray and Curtis, 1957). The 

similarity coefficients of the algae QC samples ranged from 68 

to 73 percent, on a scale from 0 (no similarity) to 100 percent 

(complete similarity). 

Streamflow, Water Quality, and Habitat

Streamflow and water-quality data are available from 

the USGS websites: http://waterdata.usgs.gov/wy/nwis/nwis

for Wyoming and http://waterdata.usgs.gov/mt/nwis/nwis for 

Montana.

Powder River

Streamflow in the Powder River generally was stable 

at the time of sampling. The Powder River was in a normal 

seasonal recession in late July although streamflow was higher 

than long-term median values for the Powder River at Arvada 

(fig. 2). Localized thunderstorms in the Powder River drainage during the evening of July 21 produced a small increase 

(less than 5 percent) in streamflow at Arvada (streamgage 

06317000, between sites PR13 and PR14) on July 22 (fig. 2), 

but data from other streamgages on the Powder River (at Sussex, 06313500, and above Burger Draw, 06313590) did not 

show a similar increase. 

Streamflow in the Powder River exhibited a general 

increase in the downstream direction from 77 cubic feet per 

second (ft3/s) at site PR1 to 146 ft3/s at site PR18 (table 2). An 

abrupt increase in streamflow of 103 ft3/s was noted between 

site PR12 (below Mitchell Draw) and site PR13 (above Wild 

Horse Creek) (fig. 3). Most of the increase in flow between 

sites PR12 and PR13 could be attributed to inflow from Crazy 

Woman Creek (streamgage 06316400), however, about 30 ft3/s 

was not accounted for, considering zero contributions from 

precipitation events either directly or via ephemeral tributaries such as Cottonwood Creek and Fortification Creek. Direct 

discharge of CBNG effluent to the Powder River is unlikely 

to have contributed the remaining 30 ft3/s (Jeremy Zumberge, 

Wyoming Department of Environmental Quality, personal 

commun., 2010). Other potential reasons for the increase of 

30 ft3/s in this reach include alluvial recharge, measurement 

error, or additional flow in Crazy Woman Creek between 

streamgage 06316400 and the confluence with the Powder 

River (2.3 air miles). The increase in streamflow between 

sites PR12 and PR13 in 2010 was in contrast to previous 

work (Ringen and Daddow, 1990, and Peterson and others, 

2010) that documented periods of no flow in the same area. 

The overall decrease in streamflow downstream of site PR14 

(fig. 3) is presumably due to alluvial infiltration, given that the 

reach of the Powder River from Arvada to Moorhead has been 

described as a losing reach (Ringen and Daddow, 1990). 

Specific conductance, alkalinity, and sodium concentrations varied among Powder River sites. Values for those 

constituents were highest at sites PR10–PR12 (fig. 3), from 

below Flying E Creek to below Mitchell Draw. Contributions 
Figure 2. Hydrographs for A, the Powder River at Arvada (streamgage 06317000), July 15–31, 2010, and 

B, the Tongue River at the Montana-Wyoming State Line (streamgage 06306300), September 1–17, 2010. Daily discharge, in cubic feet per second

300

200

100

40

July 15 July 17 July 19 July 21 July 23 July 25 July 27 July 29 July 31

Date

A

Daily discharge, in cubic feet per second

300

200

220

240

260

280

120

140

160

180

100

Sept. 1 Sept. 3 Sept. 5 Sept. 7 Sept. 9 Sept. 11 Sept. 13 Sept. 15 Sept. 17

Date

B

Daily mean discharge

Median daily statistic

EXPLANATION

Streamflow, Water Quality, and Habitat 7
Table 2. Environmental variables associated with biological samples, Powder River and Tongue River, Wyoming and Montana, 2010.

[ft3/s, cubic feet per second; std, standard; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; deg C, degrees Celsius; NTRU, nephelometric 

turbidity ratio units; CaCO3, calcium carbonate; %, percent; mm, millimeter; D50, diameter of the 50th percentile of particles; D84, diameter of the 84th percentile 

of particles; Microhabitat values represent average of five measurements; ft/s, feet per second; <, less than; NA, not available]

Site 

number

Sample 

date

Instaneous 

discharge 

(ft3/s)

Field measurements Major ions 

Dissolved 

oxygen 

(mg/L)

pH 

(std 

units)

Specific 

conductance 

(μS/cm)

Water 

temperature 

(deg C)

Turbidity 

(NTRU)

Calcium 

(mg/L)

Magnesium 

(mg/L)

Potassium 

(mg/L)

Sodium 

adsorption 

ratio

Sodium 

(mg/L)

PR1 7/21/2010 77 8.2 8.3 2,270 21.3 12 149 59.1 9.23 4.64 265 

PR2 7/21/2010 66 7.5 8.3 2,220 27.2 42 140 57.4 8.93 4.64 258 

PR3 7/20/2010 86 8.7 8.2 2,150 19.9 55 137 58.5 8.08 4.57 253 

PR4 7/20/2010 90 7.4 8.2 2,200 28.4 54 136 58.7 8.42 4.60 255 

PR5 7/21/2010 91 7.7 8.2 2,210 23.7 46 138 60.5 8.80 4.76 266 

PR6 7/21/2010 89 7.1 8.3 2,180 27.4 40 128 57.2 8.84 4.99 271 

PR7 7/19/2010 109 7.2 8.2 2,080 28.8 63 121 54.6 8.51 4.83 255 

PR8 7/20/2010 105 7.0 8.3 2,140 27.8 80 123 55.5 8.63 5.09 270 

PR9 7/20/2010 105 8.1 8.3 2,110 19.9 71 122 56.1 8.41 5.01 267 

PR10 7/22/2010 104 8.2 8.3 2,310 23.8 60 117 54.8 10.4 6.25 327 

PR11 7/23/2010 103 8.3 8.2 2,340 20.8 45 104 56.0 11.6 6.78 345 

PR12 7/26/2010 83 9.9 8.1 2,490 30.3 NA 79.9 54.0 12.8 8.31 392 

PR13 7/22/2010 186 6.3 8.4 1,930 21.2 4,030 115 55.5 8.22 4.52 236 

PR14 7/22/2010 206 6.0 8.3 1,880 27.0 1,440 111 53.6 8.37 4.42 226 

PR15 7/27/2010 117 7.4 8.3 2,130 22.2 100 94.6 53.6 9.32 6.24 307 

PR16 7/27/2010 154 7.6 8.5 1,880 24.5 71 102 54.5 8.50 4.86 244 

PR17 7/28/2010 143 7.6 8.5 1,890 21.5 45 98.0 53.5 8.38 5.05 250 

PR18 7/28/2010 146 7.9 8.5 1,950 26.7 76 101 56.3 8.75 5.16 261 

TR1 9/13/2010 135 11.2 8.4 527 18.2 14 42.5 23.4 2.67 .82 26.9 

TR2 9/14/2010 176 9.1 8.4 534 16.0 14 51.0 30.7 2.20 .54 19.6 

TR3 9/14/2010 177 12.3 8.6 592 18.4 13 57.6 35.1 2.71 .65 25.4 

TR4 9/16/2010 119 5.9 8.3 698 14.9 9.2 60.4 36.2 2.94 .99 39.3 

TR5 9/15/2010 283 8.4 8.5 498 18.6 8.8 50.8 29.6 2.13 .50 18.1 

TR6 9/15/2010 283 7.0 8.5 488 17.6 7.2 43.6 24.0 2.60 .82 27.3 

1

Substrate class from Moulton and others (2002).

8 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

of produced water from CBNG activities via Flying E Creek, 

Barber Creek, and other tributaries is a potential source 

because elevated concentrations of these constituents and 

related properties have been reported in CBNG effluent 

(Rice and others, 2000). Specific conductance, alkalinity, and 

sodium concentrations dropped considerably from site PR12 

to site PR13, coincident with the previously described increase 

in streamflow coupled with dilution by lower ionic-strength 

water from Crazy Woman Creek (about 1,200 microsiemens 

per centimeter (μS/cm)). Specific conductance, alkalinity, and 

sodium concentrations increased from site PR14, below Wild 

Horse Creek, to site PR15, above Ivy Creek. For example, 

specific conductance increased from 1,880 μS/cm at site PR14 

to 2,130 μS/cm at site PR15, whereas streamflow decreased, 

consistent with the losing reach described earlier. Water 

produced from CBNG activities is a potential source of the 

elevated constituents at site PR15 but is too small a volume 

of water to result in increased streamflow. Inflow of lower 

specific-conductance water from Clear Creek likely was 

responsible for the decrease in specific conductance, alkalinity, 
Major ions Pebble count Invertebrate and algae microhabitat

Alkalinity 

(mg/L as 

CaCO3

)

Chloride 

(mg/L)

Fluoride 

(mg/L)

Silica 

(mg/L)

Sulfate 

(mg/L)

Dissolved 

solids, sum 

(mg/L)

Less than 

2 mm 

(%)

D50 

(mm)

D84

(mm)

Depth 

(ft)

Embeddedness 

(%)

Velocity 

(ft/s)

Substrate 

class1

208 209 0.72 9.80 731 1,560 56.8 <2 28 0.60 52 1.66 5.8

183 193 .66 9.96 722 1,500 75.5 <2 35 .48 30 1.07 6.0

174 187 .61 9.84 735 1,490 23.6 16.5 54 .71 34 1.79 6.1

162 187 .59 9.92 739 1,490 37 22.6 56 .50 12 1.84 5.2

168 190 .61 9.95 755 1,530 23.1 39 89 1.13 56 2.09 7.1

190 181 .66 9.81 720 1,490 15.1 44 88 .69 52 2.08 6.3

190 158 .62 9.58 677 1,400 15.2 38 95 .66 10 2.03 5.0

204 164 .64 8.91 702 1,450 20.2 13.5 30 .45 40 1.43 5.0

213 162 .63 8.69 699 1,450 80.3 <2 4.5 .25 40 .93 3.1

288 172 .70 9.02 688 1,550 13.8 18 91 .41 43 1.84 7.6

286 172 .68 8.30 666 1,540 23.3 18 50 .62 40 1.78 6.3

305 175 .74 7.26 683 1,590 7.7 20.5 65 .56 50 1.96 7.2

228 106 .53 7.66 660 1,320 36.7 5.2 25 .88 56 1.65 6.2

226 100 .52 7.94 641 1,280 25 20 97 .80 30 2.91 6.2

256 133 .59 8.01 699 1,460 9.4 40 62 .46 42 .89 4.0

230 99.4 .51 6.55 620 1,270 2.7 40 62 .53 37.5 2.45 4.6

242 102 .52 6.51 624 1,290 0 59 106 .58 26 2.58 5.7

244 98.9 .52 6.51 642 1,320 2.9 38 73 .53 36 2.20 4.4

167 2.90 .26 3.36 95.2 297 1.7 32 49 .66 14 1.63 5.4

211 3.32 .26 3.32 80.3 317 4.2 37 55 .64 10 1.82 6.3

213 3.63 .25 4.51 128 385 12.8 28 48 .58 34 1.89 6.0

239 4.50 .35 3.09 147 437 10.7 20 32 .61 34 1.15 5.9

209 3.75 .25 3.81 77.9 312 1 43 88 .79 26 1.40 6.2

166 2.92 .24 3.45 93.7 297 0 42 63 .81 16 1.80 5.4

Table 2. Environmental variables associated with biological samples, Powder River and Tongue River, Wyoming and Montana, 2010.—

Continued

[ft3/s, cubic feet per second; std, standard; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; deg C, degrees Celsius; NTRU, nephelometric 

turbidity ratio units; CaCO3, calcium carbonate; %, percent; mm, millimeter; D50, diameter of the 50th percentile of particles; D84, diameter of the 84th percentile 

Streamflow, Water Quality, and Habitat 9

and sodium downstream of site PR15. Concentrations of other 

major ions in the Powder River, such as sulfate (table 2), did 

not vary as much as alkalinity and sodium. 

Substrate measurements showed variation in the Powder 

River. Substrate size was highly variable among sites in the 

Powder River, as indicated by pebble count D84 ranging from 

-

habitat substrate class scores were also lowest at site PR9 but 

also showed substantial variability between sites (table 2). 
Figure 3. Instantaneous streamflow, water-quality, and habitat measurements from ecological sampling sites on the Powder River, 

July 2010, and the Tongue River, September 2010, Wyoming and Montana. 

0

50

100

150

200

250

0

50

100

150

200

250

300

0

500

1,000

1,500

2,000

2,500

3,000

0

100

200

300

400

500

600

700

800

0

50

100

150

200

250

300

350

0

50

100

150

200

250

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0

50

100

150

200

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300

350

400

450

0

5

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25

30

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45

0

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60

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0

10

20

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80

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100

0

1

2

3

4

5

6

7

8

4.8

5

5.2

5.4

5.6

5.8

6

6.2

6.4

PR1 PR2 PR3 PR4 PR5 PR6 PR7 PR8 PR9 PR10 PR11 PR12 PR13 PR14 PR15 PR16 PR17 PR18 TR1 TR2 TR3 TR4 TR5 TR6

Powder River site number Tongue River site number

Instantaneous streamflow,

in cubic feet per second 

Specific conductance,

in microsiemens

per centimeter 

Alkalinity, in milligrams per

liter as calcium carbonate 

Sodium, in milligrams

per liter

Pebble count,

84th percentile,

in millimeters Substrate class score

10 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Macroinvertebrate Communities 11

Tongue River

The Tongue River was near the long-term median streamflow at the time of ecological sampling, as indicated by data 

from streamgage 06306300 at the state line (fig. 2). Streamflow increased with downstream distance, from 135 ft3

/s at 

site TR1 to 177 ft3/s at site TR3, followed by a decrease to 

119 ft3/s at site TR4 (fig. 3, table 2). Inflows from tributaries 

such as Prairie Dog Creek, irrigation return flows and diversions, and CBNG-produced water contributed to the increase 

between sites TR1 and TR3. Diversions for irrigation might 

have caused the decrease in flow from TR3 to TR4. Streamflow at sites TR5 and TR6, downstream of Tongue River 

Reservoir, was 283 ft3/s. 

Specific conductance upstream from Tongue River Reservoir increased from 527 μS/cm at site TR1 to 698 μS/cm at 

site TR4 (fig. 3). Alkalinity concentrations followed the same 

pattern, increasing from 167 mg/L at site TR1 to 239 mg/L 

at site TR4 (fig. 3). Potential influences to water quality 

of the Tongue River between sites TR1 and TR4 include 

CBNG-produced water, tributary inflow, and irrigation return 

flows and diversions. Specific conductance of Prairie Dog 

Creek (streamgage 06306250) on the date of sampling was 

984 μS/cm and considerably higher than at sites TR2 and 

TR3. Specific conductance at sites TR5 and TR6 was near 

500 μS/cm and lower relative to sites TR1–TR4, likely due to 

the effects of Tongue River Reservoir. Specific conductance 

and sodium concentrations in the Tongue River were much 

lower than those in the Powder River, though alkalinity concentrations were similar (fig. 3). 

Other variations included pebble count and substrate 

class scores. The pebble count D84 ranged from 32 to 55 mm 

at sites TR1–TR4, and from 63 to 88 mm at sites TR5–TR6 

(fig. 3). Microhabitat substrate class scores indicated a different pattern, with minimum scores at sites TR1 and TR6, and 

maximum scores at sites TR2 and TR5. 

Macroinvertebrate Communities

Macroinvertebrate communities of the Powder River are 

discussed separately from those of the Tongue River because 

of differences noted during earlier studies (Peterson and others, 2010) and confirmed from the 2010 samples. For example, 

communities of the Powder River generally contained a higher 

relative abundance of Diptera and lower relative abundance 

of Ephemeroptera and Trichoptera than communities of the 

Tongue River (table 3). Macroinvertebrate taxonomic data 

from 2010 are available at http://wy.water.usgs.gov/projects/

atg/htms/data.htm (accessed October 6, 2011). 

Powder River

Community Metrics

Kruskal-Wallis tests indicated significant (p < 0.05) differences within the Powder River group for metrics including 

taxa richness, relative abundance, functional feeding group, 

and water-quality tolerance. Additional analysis using ANOVA 

and Tukey’s multiple comparison test (table 4) indicated 

significant differences in metric values between some of the 

site pairs upstream and downstream of CBNG effluents and 

tributaries (table 1) as well as between other sites. Differences 

in metric values indicated a decline in biological condition between the upstream and downstream sites in some 

cases, and an increase in other cases. The Powder River was 

divided into three zones for the purposes of discussion. The 

upper reaches include sites PR1–PR9, the middle reaches 

include sites PR9–PR14, and the lower reaches include 

sites PR14–PR18. 

Within the upper reaches of the Powder River, significant 

differences in metric values were noted at site pairs bracketing 

Dry Fork and Willow Creek (sites PR1–PR2), Beaver Creek 

(sites PR5–PR6), and Dry Creek (sites PR8–PR9). Significant differences in relative abundance of Ephemeroptera 

(increases at sites PR1–PR2 and PR8–PR9; table 4 and fig. 

4), Trichoptera (increase at sites PR5–PR6; table 4), Diptera 

(decrease at sites PR5–PR6), and dominant taxon (decrease at 

all three site pairs) are consistent with an increase in biological 

condition using predicted responses to biological perturbation from Barbour and others (1999). The dominant taxon 

at most of the sites on the Powder River was the blackfly 

Simulium. For example, at sites PR5 and PR6, the decrease in 

dominant taxon was from an average of 90 percent Simulium

spp. at PR5, to 62 percent at site PR6. At sites PR8 to PR9, 

the decrease in dominant taxon corresponded to a taxonomic 

shift as well, from an average of 59 percent Simulium spp. at 

site PR8, to 30 percent Saetheria (Chironomidae) at site PR9. 

The relative abundance of filterer-collectors decreased within 

each of the three site pairs (fig. 4). Barbour and others (1999) 

noted that functional feeding group response to perturbation 

is variable, but generalists such as filterer-collectors utilize a 

broader range of food materials than specialists, and thereby 

are more tolerant to perturbation. The observed decreases 

in filterer-collectors therefore are considered an increase in 

biological condition, particularly in combination with the 

increase in scrapers (a feeding specialist) at PR1 to PR2 and 

gatherer-collectors at PR8 to PR9 (table 3), and differences in 

relative abundance of Ephemeroptera, Trichoptera, Diptera, 

and dominant taxon as noted above. 

Some of the site pairs in the upper reaches of the Powder 

River had no significant differences in metric values, including 
Table 3. Macroinvertebrate community metrics, Powder River and Tongue River, Wyoming and Montana, 2010.

[m2, square meter; %, percent]

Sample 

number

Collection 

date

Taxa richness Density, diversity, and relative abundance 

Total 

richness

Ephemeroptera 

richness

Trichoptera 

richness

Diptera 

richness

Density 

(per m2)

Shannon 

diversity

Dominant 

taxon 

(%)

PR1A 7/21/2010 24 6 2 9 3,257 0.84 46 

PR1B 7/21/2010 24 7 4 7 3,061 .76 55 

PR1C 7/21/2010 29 9 5 10 1,791 .95 41 

PR2A 7/21/2010 31 11 4 11 1,099 1.00 31 

PR2B 7/21/2010 30 10 3 12 970 1.18 18 

PR2C 7/21/2010 30 9 5 11 436 1.10 20 

PR3A 7/20/2010 14 5 3 4 656 .33 84 

PR3B 7/20/2010 15 5 2 5 581 .34 84 

PR3C 7/20/2010 13 7 3 2 1,386 .31 85 

PR4A 7/20/2010 18 8 3 4 666 .37 83 

PR4B 7/20/2010 17 5 3 5 652 .35 83 

PR4C 7/20/2010 20 8 3 4 1,490 .36 84 

PR5A 7/21/2010 15 4 3 3 5,046 .18 92 

PR5B 7/21/2010 17 6 3 6 1,331 .23 90 

PR5C 7/21/2010 23 7 3 9 1,509 .30 87 

PR6A 7/21/2010 21 4 3 10 723 .60 65 

PR6B 7/21/2010 24 6 4 8 530 .68 59 

PR6C 7/21/2010 24 5 5 8 802 .65 63 

PR7A 7/19/2010 32 10 4 13 306 .91 49 

PR7B 7/19/2010 25 6 4 11 395 .86 49 

PR7C 7/19/2010 32 7 5 14 610 .57 73 

PR8A 7/20/2010 23 7 3 10 368 .86 42 

PR8B 7/20/2010 22 6 3 9 390 .62 66 

PR8C 7/20/2010 24 6 4 8 703 .58 70 

PR9A 7/20/2010 18 6 1 8 107 .90 40 

PR9B 7/20/2010 21 5 2 11 166 1.00 30 

PR9C 7/20/2010 29 9 3 10 236 1.15 20 

PR10A 7/22/2010 32 7 4 15 621 1.12 22 

PR10B 7/22/2010 32 6 4 16 675 1.00 39 

PR10C 7/22/2010 32 5 4 17 1,096 .91 45 

PR11A 7/23/2010 30 5 4 16 602 1.01 33 

12 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

Pumpkin Creek (sites PR3–PR4), Fourmile Creek (sites PR4–

PR5), and Burger Draw (sites PR6–PR7). Although sites PR2 

to PR3 were not specifically designed as a site pair (table 1), a 

notable decline in biological condition from sites PR2 to PR3 

was indicated by the increase in filterer-collectors and decrease 

in relative abundance of Ephemeroptera (fig. 4), as well as by 

an increase in dominant taxon and decreases in Shannon diversity and relative abundance of intolerant macroinvertebrates 

(table 3). The cause for the decline between sites PR2 and PR3 

is not known. 

Macroinvertebrate communities in the middle reaches 

of the Powder River indicated decline in biological condition. The site pair bracketing Flying E Creek (site PR9–PR10) 

indicated decreases in relative abundance of Ephemeroptera, 

intolerant macroinvertebrates, and gatherer-collectors, and 

an increase in relative abundance of Diptera, all of which 
Density, diversity, and relative abundance Functional feeding groups Tolerance

Ephemeroptera 

(%)

Trichoptera 

(%)

Diptera 

(%)

Chironomidae 

(%)

Predators 

(%)

Gatherercollectors 

(%)

Filterercollectors 

(%)

Scrapers 

(%)

Intolerant 

(%)

26 18 52 6 1 27 69 1 32

24 13 60 5 2 23 71 1 21

27 19 52 8 2 33 62 2 25

31 29 38 6 4 31 61 3 31

36 30 29 14 6 43 43 3 35

40 29 28 7 4 36 50 7 34

11 3 85 1 0 9 91 0 12

9 4 87 3 1 10 89 0 6

7 8 85 0 0 6 94 0 11

7 8 84 1 0 7 91 1 10

8 7 84 1 0 8 91 0 10

5 7 87 3 1 7 90 1 8

1 5 93 1 0 3 97 0 5

3 5 92 1 0 3 95 1 7

2 8 89 2 1 3 94 1 8

4 22 71 5 4 8 86 1 21

4 25 67 7 3 9 83 2 21

5 22 69 5 3 10 83 3 23

10 12 72 22 6 24 60 6 19

6 17 72 22 2 24 64 6 15

4 12 81 8 4 9 81 4 12

7 25 62 20 7 23 69 1 25

6 13 77 11 2 14 82 2 14

5 10 82 12 3 14 80 2 13

27 9 56 48 6 68 23 2 33

22 15 55 41 8 51 36 3 30

25 22 40 27 15 41 35 7 41

9 10 72 44 13 35 42 1 18

8 7 81 38 7 27 57 1 17

2 7 86 38 7 23 59 1 11

3 8 82 47 8 31 44 2 11

Table 3. Macroinvertebrate community metrics, Powder River and Tongue River, Wyoming and Montana, 2010.—Continued

[m2, square meter; %, percent]

Macroinvertebrate Communities 13

typically are associated with a decline in biological condition (Barbour and others, 1999). The site pair bracketing Wild 

Horse Creek (sites PR13–PR14) also indicated a decline in 

biological condition. Between sites PR13 and PR14, the relative abundance of intolerant macroinvertebrates and predators 

decreased, and Diptera relative abundance increased. Although 

sites PR12 and PR13 were not designed as a site pair (table 1), 

several metrics were significantly (p < 0.05) different between 

sites PR12 to PR13 (table 4) which bracket the influx of low 

specific-conductance water described earlier in this report. 

A decline in biological condition from sites PR12 to PR13 

was indicated by increased abundance of filter-collectors and 

decreased abundance of predators, increase in dominant taxon 

percentage and decrease in Shannon diversity, and decrease 

in Diptera taxa richness and Chironomidae abundance. 

Chironomids including Saetheria and Cricotopus spp. were 
Sample 

number

Collection 

date

Taxa richness Density, diversity, and relative abundance 

Total 

richness

Ephemeroptera 

richness

Trichoptera 

richness

Diptera 

richness

Density 

(per m2)

Shannon 

diversity

Dominant 

taxon 

(%)

PR11B 7/23/2010 35 7 5 16 1,336 .87 47 

PR11C 7/23/2010 35 7 5 16 723 1.11 24 

PR12A 7/26/2010 29 4 4 16 364 1.01 36 

PR12B 7/26/2010 32 5 5 15 808 .92 34 

PR12C 7/26/2010 27 2 3 15 1,028 1.00 38 

PR13A 7/22/2010 23 6 3 10 1,762 .62 69 

PR13B 7/22/2010 23 7 5 8 1,726 .46 79 

PR13C 7/22/2010 25 6 4 11 1,317 .67 68 

PR14A 7/22/2010 17 4 4 5 2,010 .31 85 

PR14B 7/22/2010 18 6 3 7 2,609 .27 89 

PR14C 7/22/2010 17 5 2 6 3,173 0.21 91 

PR15A 7/27/2010 35 8 5 15 350 1.20 26 

PR15B 7/27/2010 26 7 2 13 398 1.19 17 

PR15C 7/27/2010 29 7 2 15 570 1.19 19 

PR16A 7/27/2010 25 11 5 4 2,334 .84 37 

PR16B 7/27/2010 22 9 4 4 2,284 .84 39 

PR16C 7/27/2010 16 6 4 2 2,245 .81 36 

PR17A 7/28/2010 21 8 5 3 2,654 .76 40 

PR17B 7/28/2010 20 8 5 3 1,901 .77 38 

PR17C 7/28/2010 21 9 5 2 2,761 .76 35 

PR18A 7/28/2010 24 10 4 4 328 .93 30 

PR18B 7/28/2010 16 7 2 2 210 .79 38 

PR18C 7/28/2010 25 10 3 6 268 .80 36 

TR1A 9/13/2010 29 7 6 7 11,086 .98 29 

TR1B 9/13/2010 29 8 5 9 7,978 1.05 19 

TR1C 9/13/2010 24 5 6 8 6,256 .97 25 

TR2A 9/14/2010 37 8 8 11 6,630 1.20 21 

TR2B 9/14/2010 34 7 7 10 6,896 1.20 17 

TR2C 9/14/2010 31 8 6 6 10,045 1.11 24 

TR3A 9/14/2010 32 8 7 8 5,878 1.15 25 

TR3B 9/14/2010 38 8 7 14 7,198 1.25 17 

TR3C 9/14/2010 34 7 8 11 6,825 1.19 22 

TR4A 9/16/2010 36 6 7 13 15,447 1.11 30 

TR4B 9/16/2010 40 8 6 16 12,447 1.12 29 

TR4C 9/16/2010 31 9 5 10 10,577 1.11 28 

TR5A 9/15/2010 30 6 7 10 8,064 1.13 23 

TR5B 9/15/2010 35 5 9 14 11,921 1.10 32 

TR5C 9/15/2010 35 7 7 11 14,194 1.13 28 

TR6A 9/15/2010 35 7 8 13 2,360 1.17 16 

TR6B 9/15/2010 30 7 8 10 3,556 1.09 24 

TR6C 9/15/2010 33 7 7 12 6,766 1.13 18 

Table 3. Macroinvertebrate community metrics, Powder River and Tongue River, Wyoming and Montana, 2010.—Continued

[m2, square meter; %, percent]

14 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Density, diversity, and relative abundance Functional feeding groups Tolerance

Ephemeroptera 

(%)

Trichoptera 

(%)

Diptera 

(%)

Chironomidae 

(%)

Predators 

(%)

Gatherercollectors 

(%)

Filterercollectors 

(%)

Scrapers 

(%)

Intolerant 

(%)

4 6 86 38 4 29 56 2 9

8 12 71 44 11 40 40 2 18

6 11 76 31 15 27 48 3 11

4 5 87 48 9 37 41 1 8

4 10 80 38 8 24 52 1 12

13 8 76 7 2 15 78 0 19

12 6 81 1 2 12 84 0 17

14 8 75 7 2 17 76 1 21

11 2 87 2 0 12 87 0 11

5 1 93 5 0 7 91 0 7

6 1 92 1 0 6 93 1 7

48 20 22 18 12 59 16 4 53

36 27 32 24 5 54 26 1 42

39 19 36 28 7 60 22 1 42

30 27 38 0 1 32 64 2 52

33 23 40 1 1 34 61 3 49

31 27 36 0 1 34 63 2 46

34 22 41 0 1 33 63 3 51

32 25 38 0 1 32 64 2 53

25 37 35 0 1 24 71 2 55

41 16 38 13 4 52 41 2 52

39 14 41 3 2 41 52 3 44

49 10 38 1 1 47 46 5 54

38 20 31 1 1 44 49 6 51

44 23 21 3 1 52 41 4 58

40 18 30 5 2 50 42 2 43

27 30 9 5 4 50 14 21 71

30 33 12 3 3 43 30 15 66

34 33 10 5 2 50 36 8 70

36 26 16 11 2 49 14 23 65

30 30 15 11 2 46 22 17 64

31 30 14 8 6 48 25 13 67

51 12 28 25 3 64 15 1 35

50 12 32 29 2 60 16 2 33

54 15 25 20 1 65 19 3 38

41 31 15 11 4 53 30 6 61

47 18 16 9 6 61 20 9 70

51 25 8 4 6 63 18 7 75

45 23 17 9 3 55 28 8 54

49 15 16 5 3 62 22 10 66

37 28 11 6 3 57 30 5 69

Table 3. Macroinvertebrate community metrics, Powder River and Tongue River, Wyoming and Montana, 2010.—Continued

[m2, square meter; %, percent]

Macroinvertebrate Communities 15
Table 4. Analysis of variance for macroinvertebrate community metrics, Powder River and Tongue River, Wyoming and Montana, 

2010.

[ --, difference in metric value between sites not significant at p=0.05; D, significant decrease in metric value, I, significant increase in metric value; 

NA, not analyzed (group p > 0.05); *, results based on a Wilcoxon rank sum test]

Site 

numbers

Pair number and 

target

Taxa richness Functional group abundance 

Total 

richness

Ephemeroptera 

richness

Trichoptera 

richness

Diptera 

richness

Predator 

abundance 

(%)

Gatherercollector 

abundance 

(%)

Filterercollector 

abundance 

(%)

Scraper 

abundance 

(%)

Powder River Group 

PR1–PR2 1–Dry Fork and 

Willow Creek

-- -- -- -- -- -- D I 

PR2–PR3 target not assigned 

(table 1)

D -- -- D D D I D 

PR3–PR4 2–Pumpkin Creek -- -- -- -- -- -- -- -- 

PR4–PR5 3–Fourmile Creek -- -- -- -- -- -- -- -- 

PR5–PR6 4–Beaver Creek -- -- -- -- I -- D -- 

PR6–PR7 5–Burger Draw -- -- -- -- -- -- -- -- 

PR8–PR9 6–Dry Creek -- -- -- -- -- I D -- 

PR9–PR10 7–Flying E Creek I -- -- I -- D -- -- 

PR10–PR11 8–Barber Creek -- -- -- -- -- -- -- -- 

PR10–PR12 8–Barber C and other 

treated effluent

-- -- -- -- -- -- -- -- 

PR12–PR13 target not assigned 

(table 1)

-- -- -- D D -- I -- 

PR13–PR14 9–Wild Horse Creek -- -- -- -- D -- -- -- 

PR14–PR15 10–Unnamed effluent I -- -- I I I D -- 

PR16–PR17 11–LX Bar Creek -- -- -- -- -- -- -- -- 

PR17–PR18 12–SA Creek -- -- -- -- -- -- D -- 

Tongue River Group 

TR1–TR2 13–first Fidelity 

discharges

NA NA NA NA NA NA NA -- 

TR2–TR3 14–Prairie Dog 

Creek

NA NA NA NA NA NA NA -- 

TR3–TR4 15–discharges above 

Badger Creek

NA NA NA NA NA NA NA D 

Tongue River—Hanging Woman pair 

TR5–TR6* 16–Hanging Woman 

Creek

-- -- -- -- -- -- -- -- 

16 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

relatively abundant at site PR12, as well as at sites PR7–PR11 

and PR15. Saetheria is a gatherer-collector, and the Cricotopus spp. identified are shredders and omnivores (Merritt and 

Cummins, 1996; Cuffney, 2003), which contributes to the 

difference in relative abundance among functional feeding 

groups at sites PR12 and PR13. Two site pairs (PR10–PR11, 

and PR10–PR12) in the middle reaches of the Powder River 

indicated no significant differences in metric values. Those site 

pairs were designed to bracket Barber Creek and other effluent 

downstream of Barber Creek.

Macroinvertebrate communities in the lower reaches of 

the Powder River indicated either increase in biological condition or no change. At sites PR14–PR15 that bracket unidentified effluents, more than a dozen metrics were significantly 

different (p < 0.05) between the sites (table 4), including an 

increase in relative abundance of Ephemeroptera and decrease 

in filterer-collectors (fig. 4). The average relative abundance of 

intolerant macroinvertebrates was 8 percent at site PR14 and 

46 percent at site PR15. Other metrics that were significantly 

different between sites PR14 and PR15 were increases in total 
Tolerance

Density

Density, diversity, and relative abundance

Number of 

differences 

Intolerant 

abundance 

(%)

Shannon 

diversity

Dominant 

taxon (%)

Ephemeroptera (%)Trichoptera 

(%)

Diptera 

(%)

Chironomidae (%)

Powder River Group

-- D -- D I -- -- -- 5

D -- D I D D I D 13

-- -- -- -- -- -- -- -- 0

-- -- -- -- -- -- -- -- 0

I -- -- D -- I D -- 6

-- -- -- -- -- -- -- -- 0

-- -- I D I -- -- -- 5

D I -- -- D -- I -- 7

-- -- -- -- -- -- -- -- 0

-- -- -- -- -- -- -- -- 0

-- -- D I -- -- -- D 6

D -- -- -- -- -- I -- 3

I D I D I I D I 13

-- -- -- -- -- -- -- -- 0

-- D -- -- I -- -- I 4

Tongue River Group

I NA I NA D I D -- 5

-- NA -- NA -- -- -- I 1

D NA -- NA I D I -- 5

Tongue River—Hanging Woman pair

-- -- -- -- -- -- -- -- 0

Table 4. Analysis of variance for macroinvertebrate community metrics, Powder River and Tongue River, Wyoming and Montana, 

2010.—Continued

[ --, difference in metric value between sites not significant at p=0.05; D, significant decrease in metric value, I, significant increase in metric value; 

NA, not analyzed (group p > 0.05); *, results based on a Wilcoxon rank sum test]

Macroinvertebrate Communities 17

richness, Diptera richness, Shannon diversity, and relative 

abundance of predators, collector-gatherers, Trichoptera, and 

Chironomidae, and decreases in density, dominant taxon, 

and Diptera abundance due to few Simulium spp. individuals. At sites PR17–PR18 that bracket SA Creek, biological 

condition appeared to increase between the sites on the basis 

of decreases in filterer-collector abundance and density, and 

increases in abundance of Ephemeroptera and Chironomidae. 

The site pair that brackets LX Bar Creek (PR16–PR17) indicated no significant changes in metric values. 
Figure 4. Selected macroinvertebrate community metrics from ecological sampling sites, 

A, Powder River and B, Tongue River, Wyoming and Montana, 2010.

0

20

40

60

80

100

Filterer-collectors, in percent

PR1 PR2 PR3 PR4 PR5 PR6 PR7 PR8 PR9 PR10 PR11 PR12 PR13 PR14 PR15 PR16 PR17 PR18

Powder River site number

0

10

20

30

40

50

Ephemeroptera, in percent

30

40

50

60

70

80

A

B

TR1 TR2 TR3 TR4 TR5 TR6

Tongue River site number

Intolerant macroinvertebrates,

in percent

EXPLANATION 

Maximum

Median

Minimum

18 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Macroinvertebrate Communities 19

Observed/Expected Model

Biological condition, as evaluated with the Wyoming 

invertebrate observed/expected (O/E) model, was significantly 

different among sites on the mainstem Powder River (ratio 

of sample variances F = 5.19, p < 0.0001). According to the 

Tukey multiple-comparison rank test, O/E scores were lowest 

at sites PR1 (mean = 0.31) and PR14 (mean = 0.37) whereas 

scores were highest at sites PR2, PR4, PR6, PR7, PR10, PR11, 

PR15, PR16 and PR18 (mean = 0.75) relative to all other sites 

(table 5). Considering the naturally variable environmental 

conditions of plains streams such as the Powder River, the 

variability of the mean O/E scores at each site was very low 

at ±0.06, based on the root mean square error (RMSE) for a 

90 percent confidence interval (Zar, 1984). Intra-sample precision was less than that of the Wyoming O/E model of ±0.17, 

which is precise enough to detect even modest anthropogenic 

disturbance.

A wide range in O/E scores was apparent among Powder River sites (fig. 5). Interspersed within this variability, 

however, were three localized reaches that each displayed a 

decrease preceded by an abrupt increase in biological condition. Biological condition, as described by O/E scores, 

increased from PR1 to PR2, followed by a spatially variable 

yet general decline from PR2 to PR9. A second appreciable 

increase in biological condition occurred between PR9 and 

PR10, followed by the most precipitous and cumulative downstream decline in biological condition along the Powder River 

from PR10 to PR14. Finally, there was an abrupt increase 

in biological condition from PR14 to PR15, followed by a 

marginal downstream decline from PR15 to PR17. Contributions from major tributaries to the Powder River such as Crazy 

Woman and Clear Creeks did not appear to be responsible for 

any of the four appreciable increases in biological condition. 

In fact, the sites that exhibited abrupt increases in biological 

condition each occurred immediately below smaller tributaries 

such as Willow Creek (PR2), Burger Draw (PR7), Flying E 

Creek (PR10), and Joe Creek (PR15).

The uppermost and lowermost sites within each declining 

biological-condition segment, particularly the PR10–PR14 and 

PR2–PR9 segments, corresponded to some of the highest and 

lowest O/E scores according to the Tukey multiple comparison 

rank test. Biological condition declined by 52 percent, 34 percent, and 15 percent from the upstream to downstream extents 

within the PR10–PR14, PR2–PR9 and PR15–PR17 segments, 

respectively. The variable but overall decline in biological 

condition within the PR2–PR9 segment indicates localized 

noncumulative environmental stressors influenced the resident 

biota. This may indicate localized perturbations were spatially 

limited in their extent and/or the declines were offset by other 

factors such as tributary contributions. Localized biological 

condition declines within the PR2–PR9 segment occurred 

above Pumpkin Creek (PR3), below Fourmile Creek (PR5), 

and above Dry Creek (PR8). Localized increases in biological 

condition occurred at sites PR4 (below Pumpkin Creek) and 

PR7 (below Burger Draw). The declining trend in biological 

condition within the remaining two segments, in particular 

segment PR10–PR14, indicates the macroinvertebrate communities were subjected to additive effects of environmental 

stressors with distance downstream. Cumulative inputs from 

smaller tributaries such as Fortification and Wild Horse Creeks 

may contribute to the biological-condition declines within 

those two remaining segments. An absence of expected mayfly 

(Ephemeroptera), beetle (Coleoptera), midge (Diptera) and 

non-insect taxa, among other groups, that were predicted to 

occur with a probability greater than 50 percent, contributed to 

the measured declines in biological condition within these four 

segments of the Powder River. Absence of non-insect water 

mites (Acari) and the moderately tolerant mayfly Tricorythodes played a large role in the decline in the measured biological condition between sites PR10 and PR14. An absence of 

the mayflies Baetis and Tricorythodes, riffle beetles Microcylloepus and Dubiraphia, and/or the tolerant midge Rheotanytarsus relative to the macroinvertebrate community at 

site PR2 indicated a general downstream decline in biological 

condition within the PR2–PR9 segment. Lastly, the marginal downstream decline in biological condition within the 

PR15–PR17 segment was associated with the disappearance 

of Dubiraphia and to some extent the mayflies Caenis and 

Baetis, and in particular Tricorythodes, that are considered 

ubiquitous generalists tolerant to a wide range of environmental stressors but preferring waters with sufficient dissolved 

oxygen, low to moderate nutrient concentrations, and low 

to moderate organic enrichment (Barbour and others, 1999; 

Ward, 1992; Winget and Magnum, 1991). Tricorythodes and 

Baetis generally inhabit stable gravel- or sand-dominated 

channels; are a common component of the macroinvertebrate 

community in plains streams with naturally large sediment 

loads; and in the case of Tricorythodes, may thrive in waters 

with low to moderate levels of human disturbance such as 

during or after periods of increased suspended or accumulated 

sediment (Gray and Ward 1982; Peterson 1990; Ward 1986; 

Ward 1992). Loss of Baetis, and in particular Tricorythodes,

within the PR10–PR14 and PR2–PR9 segments was unexpected considering their tolerances to naturally high sediment 

loads and preferences for fine-gravel/sand-dominated channel 

beds of the Powder River. Caenis are widespread collectorgatherers adapted to residing in fine-sediment-dominated 

habitats, but they are considered to be moderately sensitive to 

environmental stressors (Merritt and Cummins, 1996; Ward, 

1992). Although they generally exhibit patchy distributions 

within stream microhabitats, the decline of Caenis within 

the PR15–PR17 segment is puzzling considering preferable 

physical habitat conditions for this taxon within the segment. 

Microcylloepus and Dubiraphia are associated with lentic and 

lotic habitats, though Dubiraphia has been shown to decrease 

in relative abundance with increased human disturbance 

(Elliott and others, 1997; Merritt and Cummins, 1996). The 

downstream disappearance of Acari within the PR10–PR14 

segment was surprising as this arthropod commonly occurs 

across a broad ecological spectrum of streams. Environmental stress, however, can trigger diapause in Acari and many 
Table 5. Observed/expected scores and analysis of variance among mean scores for macroinvertebrate 

communities, Powder River and Tongue River, Wyoming and Montana, 2010.

[O, observed; E, expected; BC, Bray-Curtis index; Tukey, analysis of variance with Tukey test, letters indicate significant (p 

<0.05) differences in mean O/E scores between sites within Powder River and Tongue River groups]

Sample 

number O E O/E Mean O/E Tukey BC Mean BC

Powder River Group

PR1 3 14 0.21 0.31 C 0.74 0.64

PR1 5 14 .36 .59

PR1 5 14 .36 .59

PR2 7 9 .78 .85 A .27 .24

PR2 9 9 1.00 .18

PR2 7 9 .78 .28

PR3 6 9 .67 .59 B .37 .40

PR3 6 9 .67 .35

PR3 4 9 .44 .48

PR4 7 9 .78 .78 A .28 .28

PR4 6 9 .67 .35

PR4 8 9 .89 .21

PR5 4 9 .44 .56 B .52 .41

PR5 6 9 .67 .33

PR5 5 9 .56 .39

PR6 7 9 .78 .67 A .27 .34

PR6 6 9 .67 .33

PR6 5 9 .56 .43

PR7 7 9 .78 .85 A .30 .25

PR7 9 9 1.00 .15

PR7 7 9 .78 .30

PR8 5 9 .56 .60 B .41 .38

PR8 6 9 .67 .33

PR8 5 9 .56 .41

PR9 4 9 .44 .56 B .52 .42

PR9 5 9 .56 .41

PR9 6 9 .67 .33

PR10 8 9 .89 .78 A .21 .27

PR10 7 9 .78 .27

PR10 6 9 .67 .33

PR11 6 9 .67 .71 A .35 .32

PR11 6 9 .67 .33

PR11 7 9 .78 .27

PR12 6 9 .67 .63 B .33 .36

PR12 6 9 .67 .33

PR12 5 9 .56 .41

PR13 4 9 .44 .56 B .44 .38

20 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Sample 

number O E O/E Mean O/E Tukey BC Mean BC

Powder River Group—Continued

PR13 5 9 0.56 0.36

PR13 6 9 .67 .33

PR14 5 9 .56 0.37 C .36 0.56

PR14 1 9 .11 .85

PR14 4 9 .44 .46

PR15 7 9 .78 .74 A .25 .29

PR15 6 9 .67 .35

PR15 7 9 .78 .27

PR16 6 9 .67 .67 A .30 .29

PR16 7 9 .78 .22

PR16 5 9 .56 .36

PR17 5 9 .56 .63 B .39 .33

PR17 6 9 .67 .30

PR17 6 9 .67 .30

PR18 7 9 .78 .74 A .28 .28

PR18 7 9 .78 .22

PR18 6 9 .67 .35

Tongue River Group

TR1 1 7 0.14 0.32 B 0.76 0.59

TR1 2 7 .28 .61

TR1 4 7 .55 .41

TR2 6 7 .82 .68 A .33 .38

TR2 5 7 .68 .38

TR2 4 7 .55 .43

TR3 6 8 .80 .76 A .33 .35

TR3 5 8 .67 .39

TR3 6 8 .80 .33

TR4 6 8 .79 .70 A .31 .34

TR4 5 8 .66 .36

TR4 5 8 .66 .35

TR5 4 8 .50 .54 AB .42 .40

TR5 4 8 .50 .42

TR5 5 8 .63 .36

TR6 4 8 .50 .50 AB .42 .44

TR6 3 8 .38 .53

TR6 5 8 .63 .36

Table 5. Observed/expected scores and analysis of variance among mean scores for macroinvertebrate 

communities, Powder River and Tongue River, Wyoming and Montana, 2010.—Continued

[O, observed; E, expected; BC, Bray-Curtis index; Tukey, analysis of variance with Tukey test, letters indicate significant (p 

<0.05) differences in mean O/E scores between sites within Powder River and Tongue River groups]

Macroinvertebrate Communities 21
Figure 5. Macroinvertebrate observed/expected model scores from ecological sampling sites, A, 

Powder River and B, Tongue River, Wyoming and Montana, 2010.

A

TR1 TR2 TR3 TR4 TR5 TR6

Tongue River site number

PR1 PR2 PR3 PR4 PR5 PR6 PR7 PR8 PR9 PR10 PR11 PR12 PR13 PR14 PR15 PR16 PR17 PR18

Powder River site number

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Wyoming observed/expected (O/E) model score

B

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Montana observed/expected (O/E) model score

Mininum

EXPLANATION

Maximum

Mean

Mininum

EXPLANATION

Maximum

Mean

22 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Macroinvertebrate Communities 23

insects that could translate to a decline or absence within the 

sampled community. 

Similarities to an expected reference condition as 

measured by the BC index also differed significantly among 

Powder River sites (F = 3.99, p < 0.001) with a spatial pattern opposite that of the O/E scores. The most downstream 

sites of segments PR2–PR9, PR10–PR14 and PR15–PR17 

were more dissimilar (higher BC scores) from reference than 

the upstream sites on those segments. This indicates greater 

taxa replacement with distance downstream within each 

of the three segments. Sites PR1 (mean = 0.64) and PR14 

(mean = 0.56) were the most dissimilar from reference conditions relative to all other sites on the Powder River. In other 

words, 64 percent and 56 percent of the taxa collected at PR1 

and PR14, respectively, replaced those expected to occur at 

these sites according to the model.

The macroinvertebrate communities at PR1 and the most 

downstream sites within the PR2–PR9, PR10–PR14, and to 

a lesser extent the PR15–PR17 segments, were dominated by 

high percentages of collector-filterer and collector-gatherer 

taxa with moderate to high tolerances to environmental stressors. These taxa included midges such as Saetheria sp.; black 

flies (Simulium sp.); and Hydropsyche caddisfly larvae. Dominance of these taxa contributed to the lower O/E and higher 

BC scores at PR1 and at the downstream sites on each of the 

three segments. One anomaly to the dominance of tolerant 

taxa at the downstream sites was the relatively high abundance 

of the clinger mayfly Traverella sp., considered sensitive to 

environmental stressors, at PR17. Its high relative abundance 

likely was associated with the coarser riffle substrate relative to other Powder River sites. In addition, its presence 

reflects the marginal decline in biological condition within 

the PR15–PR17 segment relative to the more pronounced 

downstream decreases in biological condition displayed in the 

other two segments. Collectively, the overall spatial patterns in 

biological condition in 2010 are similar to what was reported 

by Peterson and others (2009; 2010) within the same general 

reaches of the Powder River.

Tongue River

Community Metrics

Macroinvertebrate community metrics indicated a general increase in biological condition from site TR1, near the 

Wyoming-Montana border, to site TR2 that is downstream of 

CBNG-produced water discharges in Montana. From site TR1 

to TR2, increases were noted in Shannon diversity and relative abundance of intolerant macroinvertebrates (fig. 4) and 

Trichoptera, and a decrease was noted in relative abundance 

of Diptera (table 4). The relative abundance of Ephemeroptera 

decreased, however, from an average of 41 percent at site TR1 

to 31 percent at site TR2. Despite the marginal decline, 

Ephemeroptera still constituted a substantial portion of the 

community at site TR2 (table 3) indicating minimal effects due 

to CBNG. Sites TR2 and TR3 are upstream and downstream 

of Prairie Dog Creek, which is a major tributary to the Tongue 

River and receives discharges from CBNG production and 

irrigation-return flows. Among all evaluated metrics, only the 

relative abundance of Chironomidae increased significantly 

(albeit marginally) between sites TR2 and TR3 (table 4). 

Community metrics generally indicated a decline in 

biological condition between sites TR3 and TR4, from downstream of Prairie Dog Creek to upstream of Badger Creek. The 

relative abundance of scrapers, intolerant macroinvertebrates, 

and Trichoptera decreased from site TR3 to TR4, whereas the 

relative abundance of Ephemeroptera and Diptera increased, 

all of which were statistically significant (table 4). The dominant taxon shifted from Fallceon quilleri (average 21 percent) 

at site TR3 to Tricorythodes (average 29 percent) at site TR4, 

which helps explain the marginal increase in relative abundance of Ephemeroptera between the sites.

None of the community metrics were significantly different between sites TR5 and TR6, upstream and downstream 

of Hanging Woman Creek (table 4). The lack of significant 

differences was not surprising, given that these sites were 

sampled to establish a measure of baseline conditions in 

anticipation of future development. 

Observed/Expected Model

The Montana O/E model indicated the biological condition varied significantly between Tongue River sites (F = 4.84, 

p < 0.05; table 5). Site TR1 had the lowest overall scores, 

which were significantly different from scores at all other 

Tongue River sites (fig. 5, table 5). The O/E scores substantially increase at TR2 (above Prairie Dog Creek; mean = 0.68), 

with a slight increase at site TR3 (below Prairie Dog Creek; 

mean = 0.76), followed by a decrease at TR4 (above Badger 

Creek; mean = 0.70). Downstream of the Tongue River Reservoir, sites TR5 (above Hanging Woman Creek; mean = 0.54) 

and TR6 (below Hanging Woman Creek; mean = 0.50) scored 

slightly lower than the TR2 to TR4 group and scored slightly 

higher than the values from samples collected at site TR1. 

Scores at sites TR5 and TR6 were not significantly different 

from any of the other Tongue River sites. These data indicate 

that CBNG discharges do not substantially affect biological 

condition on the mainstem Tongue River. The variability of 

the samples was very low (RMSE = 0.07). This is much lower 

than the error for the Montana O/E model (±0.17). 

The BC index scores for the samples collected on the 

Tongue River followed a trend opposite that to the O/E scores 

(Table 5). The samples collected from site TR1 were the most 

dissimilar from reference (mean = 0.59). This shows that the 

majority (60 percent) of the taxa collected from TR1 replaced 

those taxa expected to be there by the model. The average 

dissimilarity decreased between sites TR2, TR3, and TR4 

(means = 0.38, 0.35, and 0.34, respectively). The BC scores 

trended upward from sites TR5 and TR6 (means = 0.40, 

and 0.44, respectively). The changes in BC scores demonstrated the effect of taxa replacement on the O/E results. 

Taxa collected from some of the Tongue River sites varied 
24 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

substantially from each other. For example, all of the samples 

collected from TR1 were dominated by Simulium sp. and 

Acarina. These taxa were not expected by the O/E model, and 

therefore O/E scores were significantly lower than the others. 

Sites TR2 through TR4 were either dominated by Microcylloepus, Fallceon, or Tricorythodes, respectively. The 

greater abundance of these sensitive taxa contributed to an 

increase in the O/E scores, and a decrease in BC scores. 

Communities at sites TR5 and TR6 were dominated by 

mayflies Fallceon, Microcylloepus, and net-spinning Hydropsychidae. The samples from TR5 and TR6 also contained 

Simulium sp. and water mites. 

Algal Communities

Diatoms (Bacillariophyta) were the predominant phylum 

in algal communities of the Powder River and Tongue River 

(table 6), often comprising 90 percent or more of the identified taxa. A few blue-green cyanobacteria (Cyanophyta) and 

green algae (Chlorophyta) taxa generally were present in 

the samples. Though low in taxa richness, blue-green algae 

commonly dominated in terms of relative abundance. Aside 

from these general patterns, algal communities of the Powder 

River were substantially different from those of the Tongue 

River. For example, red algae (Rhodophyta) were absent from 

the Powder River but present at all Tongue River sites. Taxa 

richness was generally lower in the Powder River (average 

36 taxa per sample) than the Tongue River (average 60 taxa 

per sample). The algal taxonomic data are available online at: 

http://wy.water.usgs.gov/projects/atg/htms/data.htm (accessed 

October 6, 2011). 

Powder River

Blue-green algae dominated the algal communities of the 

Powder River, with an average relative abundance of 66 percent, compared to 33 percent diatoms and 1 percent green 

algae. Diatoms composed a majority of the taxa, however, 

with an average of 33 taxa per sample. 

Algal community composition in the Powder River 

trended in the downstream direction but also varied between 

sites. For example, algal taxa richness and the Shannon diversity index generally increased in the downstream direction 

(fig. 6). Site-to-site variations in taxa richness and diversity 

also occurred that exceeded the standard deviation observed 

in split and replicate samples (table 6) and consequently could 

not be attributed to natural variation or error during sampling 

and analysis. The split and replicate sample data listed in 

table 6 were not used in data analysis except as specified. 

In the upper to middle reaches of the Powder River, 

increases or decreases in taxa richness and diversity generally 

corresponded to increases or decreases in biological condition 

as indicated by the invertebrate communities. For example, 

algal taxa richness and diversity generally increased at 

sites PR1–PR2 (Dry Fork and Willow Creek), sites PR5–PR6 

(Beaver Creek), and sites PR8–PR9 (Dry Creek), and 

decreased at sites PR2–PR3 (downstream of Willow Creek to 

upstream of Pumpkin Creek) and sites PR9–PR10 (Flying E 

Creek), which corresponded to invertebrate community 

changes in the same direction. Maximum values of algal taxa 

richness and diversity generally occurred at sites PR13–PR15 

(fig. 6), coinciding with the inflow of low specific-conductance 

water and inflow from Crazy Woman Creek described earlier, 

but in contrast to a decrease in biological condition of the 

invertebrate communities. The occurrence of maximum values 

for taxa richness and diversity at sites PR13–PR15 might 

reflect disturbance under the intermediate disturbance hypothesis (Grime, 1973) whereby a disturbance (or perturbation) to 

the system causes species diversity to be higher than would be 

present at equilibrium. 

Site-to-site increases and decreases in relative abundance 

of halophilic diatoms (those preferring high salinity) and 

facultative nitrogen heterotrophs (diatoms which need high 

levels of organic nitrogen) in the upper and middle reaches 

of the Powder River generally corresponded inversely to 

increases and decreases in algal taxa richness, diversity, and 

invertebrate community condition; abundances decreased in 

the downstream direction (fig. 6). For example, the relative 

abundance of halophilic diatoms and facultative nitrogen heterotrophic diatoms, which need periodically elevated concentrations of organic nitrogen, increased from sites PR2 to PR3 

and PR12–PR13, whereas invertebrate community condition 

decreased at those site pairs. Obligate nitrogen heterotrophs, 

which need continuously elevated concentrations of organic 

nitrogen, composed less than 10 percent of the diatoms in the 

Powder River except at PR13–PR15 where they composed 

16 to 24 percent (table 6) of the community, which might 

indicate the inflow of low specific-conductance water previously described also contains relatively high concentrations of 

organic nitrogen. 

Alkaliphilic diatoms that prefer pH greater than 7 

generally dominated the diatom communities of the Powder 

River. An exception was site PR17 below LX Bar C, where 

64 percent were alkaliphilic and 28 percent circumneutral (pH 

near 7). This community may be an indicator of less-alkaline 

sources of water in the area.

Algal taxa in the Powder River were motile or adapted 

to living on unstable sediments associated with sedimentation (Porter, 2008). About 40 to 70 percent of the algal taxa 

in the Powder River were motile species, and the number of 

motile taxa appeared to increase in the downstream direction 

(table 6). Algal communities also were predominantly benthic 

forms (living on or attached to substrate). The relative abundance of benthic forms was 79 percent or more at all sites on 

the Powder River except at site PR9 below Dry Creek (49 percent; table 6) where sestonic (unattached) algae, primarily the 

blue-green algae Anabaena, composed 41 percent of the algal 

community. 

Dominant taxa of blue-green algae included Phormidium, 

Leptolyngbya, and nitrogen-fixing Anabaena and Calothrix
Algal Communities 25

that can assimilate atmospheric nitrogen and become more 

common in waters where ratios of nitrogen to phosphorus are 

low (Porter, 2008). The relative abundances of nitrogen-fixers 

were highest at sites PR5 (45 percent), PR9 (38 percent), and 

PR17 (27 percent). The variability in relative abundance of 

nitrogen fixers among sites might be at least partially due to 

the colonial nature of blue-green algae, given that taxa richness of nitrogen fixers was low (0 to 3 taxa per site; table 6) 

and nitrogen-fixing diatoms (Rhopalodiaceae) composed less 

than 1 percent of relative abundance in the diatom community 

at each of the sites on the Powder River.

Powder River diatom communities were dominated 

by Nitzschia inconspicua, Navicula recens, and Nitzschia 

liebetruthii. Together, these three species composed more than 

40 percent of the relative abundance of diatoms at every site 

on the Powder River (http://wy.water.usgs.gov/projects/atg/

htms/data.htm, accessed October 6, 2011). Nitzschia inconspicua is a facultative nitrogen heterotroph in streams of the 

central and western plains that can tolerate elevated nitrogen 

and phosphorus concentrations (Porter, 2008). Navicula recens

is common to prairie creeks and large rivers of southeastern 

Montana characterized by elevated specific conductance 

(3001 μS/cm), alkalinity (262 mg/L), and turbidity (71 NTRU, 

nephelometric turbidity ratio units) (Bahls, 2005). Navicula 

recens also is considered a nutrient increaser, where relative 

abundance increases with increased nutrient concentrations 

(Teply and Bahls, 2005). Nitzschia liebetruthii is considered 

a general nutrient decreaser with a broad tolerance to nutrients although generally decreases with nutrient enrichment 

and high specific conductance (Bahls, 1993; Porter, 2008; 

and Teply and Bahls, 2005). Generally, the upper half of the 

Powder River study area, from sites PR1–PR11, exhibited 

the highest relative abundances of Nitzschia inconspicua and 

Navicula recens, which might reflect varying degrees of nutrient enrichment at those sites.

Tongue River

Tongue River algal communities were dominated by 

diatoms (average relative abundance 46 percent) and bluegreen algae (average 37 percent). Red algae ranged from 4 to 

23 percent relative abundance and were represented entirely 

by Audouinella, an epiphyte on Cladophora that prefers 

fast water velocity (Blinn and Cole, 1991) (table 6). Green 

algae were uncommon in terms of relative abundance in the 

samples, though Cladophora were noted in riffles at all of the 

Tongue River sites. 

Algal communities upstream of Tongue River Reservoir (sites TR1–TR4) were distinctly different from those 

downstream of the reservoir (sites TR5-TR6). Total richness 

averaged 70 taxa at sites TR1–TR4, compared to 38 taxa at 

sites TR5-TR6. Total richness increased from 57 taxa at site 

TR1 below Youngs Creek to 83 taxa at site TR2 above Prairie 

Dog Creek, then decreased to 71 taxa at site TR3 below Prairie 

Dog Creek and at site TR4 above Badger Creek (fig. 6). The 

Shannon diversity index increased with distance downstream 

above the reservoir, from 0.96 at site TR1 to 1.42 at site TR4. 

The increase in algal taxa richness and diversity from site TR1 

to TR2 was consistent with the increase in invertebrate community condition at those sites, but algal taxa richness and 

diversity did not appear to correspond with the decrease in 

invertebrate community condition from site TR3 to TR4. 

The relative abundance of halophilic (high salinity 

conditions) diatoms ranged from 21 to 27 percent upstream 

of Tongue River Reservoir, compared to 55 to 59 percent 

downstream of the reservoir. Although specific conductance at 

the time of sampling was lower at sites TR5-TR6 than at sites 

TR1–TR4 (fig. 3), the higher abundance of halophilic diatoms 

downstream of the reservoir might be a reflection of waterquality conditions during other times of the year. 

Organic nitrogen autotrophs were dominant, in terms 

of relative abundance, throughout the Tongue River, with 

minimal differences upstream and downstream of the reservoir 

(table 6). Alkaliphilic diatoms dominated at all of the sites on 

the Tongue River, with relative abundances of 63 to 72 percent 

at sites TR1–TR4, and 94 percent at sites TR5 and TR6. 

Alkabiontic diatoms, associated with higher pH than alkaliphilic diatoms, composed 26 percent of the diatom community 

at site TR1 and 19 percent at site TR2. The higher relative 

abundance of alkabiontic diatoms at sites TR1 and TR2 was 

not confirmed by pH measurements at the time of sampling 

(table 2) but might be an indicator of higher pH values during 

other times of the year. 

Many algal taxa in the Tongue River were motile, 

representing 20 percent of the community in terms of relative abundance. Communities at sites TR1–TR4 contained 

23 to 38 motile taxa, whereas sites TR5–TR6 contained 11 to 

13 motile taxa (fig. 6). Motile taxa richness increased from 

23 to 38 taxa between sites TR1 and TR2, then decreased to 

30 taxa at site TR3 and 34 taxa at site TR4. The number of 

benthic taxa also was higher at sites TR1–TR4, ranging from 

55 to 78 taxa, than at sites TR5-TR6, which had 33 to 35 benthic taxa.

The relative abundance of nitrogen-fixers was greatest 

at site TR1, below Youngs Creek (39 percent), and site TR6, 

below Hanging Woman Creek (19 percent), compared to less 

than 10 percent at other sites (table 6). Nostoc (blue-green 

algae) and the diatom Epithemia sorex were the most common 

nitrogen fixers (Porter, 2008) in the Tongue River. Epithemia 

sorex prefers a low ratio of nitrogen to phosphorus and often is 

associated with Cladophora and various nitrogen-fixing bluegreen algae (Bahls, 2005). 

The dominant taxa, by relative abundance in the diatom 

communities of the Tongue River, were Epithemia sorex, 

Cocconeis pediculus, and Cocconeis placentula, particularly 

below Tongue River Reservoir (http://wy.water.usgs.gov/

projects/atg/htms/data.htm, accessed October 6, 2011). Epithemia sorex is often found in waters with moderate specific 

conductance (752 μS/cm), alkalinity (226 mg/L), and turbidity 

(23 NTRU) (Bahls, 2005). Cocconeis pediculus and Cocconeis placentula, both epiphytes on Cladophora, have similar 
Table 6. Algal community metrics for the Powder River and Tongue River, Wyoming and Montana, 2010.

[%, percent; E, environmental; S, split; R, replicate]

Site 

number

Sample 

date

Taxa richness and abundance

Diatom 

community 

metrics

Algal taxa 

richness

Diatom 

richness

Diatom 

abundance 

(%)

Blue-green 

algae 

richness

Bluegreen 

algae 

abundance 

(%)

Green 

algae 

richness

Green 

algae 

abundance 

(%)

Red 

algae 

richness

Red 

algae 

abundance 

(%)

Halophilic 

(%)

Environmental samples 

PR1 7/21/2010 20 16 5 2 85 2 10 0 0 91 

PR2 7/21/2010 35 31 11 4 89 0 0 0 0 74 

PR3 7/20/2010 21 17 3 4 97 0 0 0 0 82 

PR4 7/20/2010 32 26 5 5 95 1 0 0 0 73 

PR5 7/21/2010 26 19 4 5 95 2 1 0 0 84 

PR6 7/21/2010 31 27 1 4 99 0 0 0 0 76 

PR7 7/19/2010 26 23 21 3 79 0 0 0 0 75 

PR8 7/20/2010 36 32 14 4 86 0 0 0 0 69 

PR9 7/20/2010 48 45 50 2 48 1 2 0 0 71 

PR10 7/22/2010 22 21 96 0 0 1 4 0 0 79 

PR11 7/23/2010 35 32 32 3 68 0 0 0 0 66 

PR12 7/26/2010 29 26 43 2 54 1 2 0 0 44 

PR13 7/22/2010 46 43 74 3 26 0 0 0 0 51 

PR14 7/22/2010 59 57 77 2 23 0 0 0 0 56 

PR15 7/27/2010 59 56 70 3 30 0 0 0 0 57 

PR16 7/27/2010 39 33 32 5 65 1 3 0 0 67 

PR17 7/28/2010 47 42 22 5 78 0 0 0 0 49 

PR18 7/28/2010 43 39 26 4 74 0 0 0 0 72 

TR1 9/13/2010 57 53 29 3 49 0 0 1 23 27 

TR2 9/14/2010 83 76 32 4 60 2 4 1 4 25 

TR3 9/14/2010 71 65 46 3 37 2 8 1 9 25 

TR4 9/16/2010 71 67 66 2 22 1 1 1 11 21 

TR5 9/15/2010 38 32 48 3 29 2 1 1 22 55 

TR6 9/15/2010 39 33 56 3 25 2 13 1 6 59 

Standard deviation among metrics from environmental, split, and replicate samples 

PR12E 7/26/2010 29 26 43 2 54 1 2 0 0 44 

PR12S 7/26/2010 30 27 34 2 65 1 1 0 0 52 

PR12R 7/26/2010 32 29 50 2 46 1 4 0 0 52 

PR12 standard 

deviation

1.5 1.5 8.1 .0 9.7 .0 1.6 .0 .0 4.3 

PR14E 7/22/2010 59 57 77 2 23 0 0 0 0 56 

PR14S 7/22/2010 59 56 69 2 31 1 0 0 0 53 

PR14 standard 

deviation

0.0 .7 5.7 .0 5.4 .7 .2 .0 .0 1.9 

26 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Diatom 

community 

metrics

Diatom community metrics Algal community metrics

Nitrogen 

autotrophs 

(%)

Facultative 

nitrogen 

heterotrophs 

(%)

Obligate 

nitrogen 

heterotrophs 

(%)

Circumneutral 

pH 

(%)

Alkaliphilic 

(%)

Alkabiontic 

(%)

Shannon 

diversity 

index

Motile 

taxa 

richness

Motile 

abundance 

(%)

Benthic 

taxa 

richness

Benthic 

abundance 

(%)

Nitrogen 

fixer 

taxa 

richness

Nitrogen 

fixers 

(%)

Environmental samples

5 94 2 2 97 0 0.42 9 19 20 100 0 0

24 72 4 1 93 6 .61 18 65 32 98 2 2

18 81 1 1 99 0 .36 12 79 19 99 2 16

24 75 1 1 98 1 .52 14 71 29 86 2 23

13 85 2 2 98 0 .60 11 46 22 92 2 45

28 72 1 3 96 0 .30 14 7 30 100 1 8

25 69 6 3 96 1 .67 13 40 24 100 0 0

26 68 6 4 94 1 .57 20 81 33 93 3 10

28 65 7 11 83 4 .96 30 43 44 49 2 38

21 74 5 4 96 0 .79 15 86 20 100 0 0

34 60 7 13 85 1 .65 15 24 30 99 1 1

61 36 3 5 93 2 .89 17 27 26 99 0 0

27 50 23 11 88 1 1.20 26 61 42 79 1 15

33 50 16 14 81 2 1.25 37 80 56 93 0 0

25 51 24 17 77 1 1.25 37 58 55 95 2 3

23 72 5 4 94 1 1.01 20 44 36 96 2 12

46 47 7 28 64 1 .95 23 28 43 93 2 27

17 75 9 6 92 2 .80 21 72 38 91 1 7

91 5 4 6 66 26 .96 23 21 55 100 5 39

84 10 6 9 68 19 1.08 38 13 78 94 2 6

87 6 7 12 72 4 1.31 30 18 68 100 2 1

85 5 10 15 63 4 1.42 34 41 68 99 2 2

98 1 1 3 94 2 .91 11 23 33 93 3 6

100 0 0 1 94 4 .99 13 6 35 82 3 19

Standard deviation among metrics from environmental, split, and replicate samples

61 36 3 5 93 2 0.89 17 27 26 99 0 0

59 37 4 4 94 2 0.70 17 28 27 99 0 0

66 26 7 3 95 2 0.89 17 37 30 100 0 0

3.8 6.0 2.3 .8 .7 .2 0.11 .0 5.2 2.1 .5 .0 0

33 50 16 14 81 2 1.25 37 80 56 93 0 0

29 52 19 16 80 2 1.24 34 79 55 95 1 0

3.0 1.1 1.9 1.5 .4 .0 .01 2.1 .3 .7 1.1 .7 0

Table 6. Algal community metrics for the Powder River and Tongue River, Wyoming and Montana, 2010.—Continued

[%, percent; E, environmental; S, split; R, replicate]

Algal Communities 27
Figure 6. Algal community metrics for ecological sampling sites on the Powder River and Tongue River, Wyoming and Montana, 2010.

R2 = .47

0

10

20

30

40

50

60

70

Algal taxa richness

R2 = .60

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Shannon diversity index

R2 = .51

0

10

20

30

40

50

60

70

80

90

100

PR1PR2PR3PR4PR5PR6PR7PR8PR9

PR10PR11PR12PR13PR14PR15PR16PR17PR18

PR1PR2PR3PR4PR5PR6PR7PR8PR9

PR10PR11PR12PR13PR14PR15PR16PR17PR18

Relative abundance of halophilic diatoms, 

in percent 

R2 = .41

0

10

20

30

40

50

60

70

80

90

100

Relative abundance of facultative nitrogen 

heterotrophs, in percent 

Powder River site number Powder River site number

Tongue River site number Tongue River site number

0

10

20

30

40

50

60

70

80

90

Algal taxa richness

0

5

10

15

20

25

30

35

40

TR1 TR2 TR3 TR4 TR5 TR6 TR1 TR2 TR3 TR4 TR5 TR6 Motile taxa richness

28 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010
Potential Effects of Water Produced from Coalbed Natural Gas Development on Biological Communities 29

water-quality preferences as Epithemia sorex (Bahls, 2004). 

The presence and relative abundance of these three taxa in 

the Tongue River coincided with their expected water-quality 

affinities. 

Potential Effects of Water 

Produced from Coalbed Natural 

Gas Development on Biological 

Communities

The ecological data presented in this report were collected to assess conditions in the Powder River and Tongue 

River upstream and downstream of known CBNG effluent discharges that enter the rivers directly or via tributaries (table 1), 

with the exception of sites TR5-TR6 that were sampled as a 

baseline for future development. Toxicity of CBNG effluents 

to aquatic life due to elevated sodium bicarbonate concentrations has been described in laboratory toxicity tests and 

in mixing zones within the Tongue River (Parkhurst, 2010; 

Pillard, 2010) and from the Powder River (Farag and others, 

2010). 

Samples of major ions collected in conjunction with 

the biological samples during this study indicated alkalinity 

concentrations were similar in the Tongue River and Powder 

River, ranging from 162 to 305 mg/L as CaCO3 (table 2). 

Alkalinity concentrations were highest at sites PR10–PR12 

(fig. 3). Maximum alkalinity concentrations in the Powder 

River during 2010 were lower than maximum concentrations 

during 2005–08 (Peterson and others, 2010), perhaps due to 

effects of dilution of CBNG effluents by higher streamflow in 

2010. Maximum alkalinity concentrations during 2005–2008 

exceeded 1,000 mg/L and also exceeded the 625-mg/L sodium 

bicarbonate concentration associated with reduced survival 

of fathead minnows (Farag and others, 2010). Given that 

alkalinity and sodium concentrations in this report are reported 

individually, it is beyond the scope of this report to compute 

potential toxicity during 2010. Also, it should be noted that 

biological communities reflect water-quality conditions over 

a longer time period than captured in instantaneous waterquality samples and thereby act as integrators of water quality 

prior to the sampling events. 

Powder River

The Powder River was divided into three zones for 

the purposes of discussion. The upper reaches include 

sites PR1–PR9, the middle reaches include sites PR9–PR14, 

and the lower reaches include sites PR14–PR18. 

Within the upper reaches of the Powder River, macroinvertebrate communities indicated significant differences 

(p <0.05) between site pairs designed to bracket CBNG 

effluents and tributaries (table 1). Potential increases in 

condition of the macroinvertebrate community were evident at three of the site pairs: from upstream to downstream 

of Dry Fork and Willow Creeks (sites PR1–PR2), Beaver 

Creek (sites PR5–PR6), and Dry Creek (sites PR8–PR9). The 

determination of increase in biological condition was based 

on several groups of metrics including functional feeding 

groups, community composition, and dominant taxon or 

diversity (table 4). Conversely, the macroinvertebrate metrics 

indicated a decline in biological condition from sites PR2 to 

PR3. Although sites PR2 and PR3 were not designed as a site 

pair, a relatively large number of metrics (13) were significantly (p < 0.05) different between sites PR2 and PR3 and 

indicated the negative effects of an unidentified influence on 

the macroinvertebrate communities. No significant differences 

in macroinvertebrate metrics were noted at site pairs upstream 

and downstream of Pumpkin Creek (sites PR3–PR4), Fourmile 

Creek (sites PR4–PR5), and Burger Draw (sites PR6–PR7). 

The O/E scores for the upper reaches of the Powder were 

spatially variable and indicated some localized spatial patterns 

similar to those indicated by the macroinvertebrate metrics, 

such as increases in biological condition from sites PR1 to 

PR2 and PR5 to PR6, and a significant decrease at sites PR2 

to PR3. The variable but overall decline in O/E scores in the 

PR2–PR9 segment indicates localized noncumulative environmental stressors influenced the macroinvertebrate communities in 2010. 

Algal community metrics in the upper reaches of the 

Powder River generally supported the macroinvertebrate 

results. For example, algal taxa richness and Shannon diversity increased at sites PR1–PR2, PR5–PR6, and PR8–PR9, 

with the exception of a decrease in diversity at sites PR5–PR6, 

whereas algal taxa richness and diversity decreased from sites 

PR2 to PR3, concurrent with the decline in biological condition noted from the macroinvertebrate results. 

Macroinvertebrate community metrics indicated potential 

decline in biological condition in the middle reaches of the 

Powder River (sites PR9–PR14). Functional feeding groups, 

community composition, tolerance, and diversity or dominant 

taxon indicated declines at designated site pairs upstream 

and downstream of Flying E Creek (sites PR9–PR10) 

and Wild Horse Creek (sites PR13–PR14), as well as at 

sites PR12–PR13 that were not a designated site pair. The 

decline between sites PR12 and PR13 might be associated with the inflow from Crazy Woman Creek (streamgage 

06316400) and other sources as described earlier in this report. 

No significant differences in macroinvertebrate metrics were 

noted at site pairs upstream and downstream of Barber Creek 

(sites PR10–PR11), and other effluents (sites PR11–PR12). 

Macroinvertebrate O/E scores in the middle reaches of 

the Powder River indicated substantial decline in biological condition from site PR10 to PR14. The declining trend 

indicates the macroinvertebrate communities were subjected 

to cumulative effects of environmental stressors with distance 

downstream. 

Algal community metrics supported the macroinvertebrate community decline at sites PR9–PR10, as indicated by 
30 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

decreases in algal taxa richness and diversity, and increases 

in relative abundance of halophilic and nitrogen heterotrophic 

diatoms. Obligate nitrogen heterotrophs, which need continuously elevated concentrations of organic nitrogen, composed 

less than 10 percent of the diatoms in the Powder River except 

at sites PR13–PR15 where they composed 16 to 24 percent. 

The increase in obligate nitrogen heterotrophs indicates the 

influx of water between sites PR12 and PR13 might have contained high concentrations of organic nitrogen. 

Macroinvertebrate communities in the lower reaches 

of the Powder River indicated an increase in biological 

condition from upstream to downstream of CBNG effluents (sites PR14–PR15) and SA Creek (sites PR17–PR18). 

A relatively large number (13) of metrics were significantly 

different (p < 0.05) between sites PR14 and PR15, including 

increases in total richness, diversity, and relative abundance of 

Ephemeroptera, intolerant macroinvertebrates, and collectorgatherers. Four macroinvertebrate metrics were significantly 

different between sites PR17 and PR18, including increases in 

relative abundance of Ephemeroptera and Chironomidae, and 

decreases in filterer-collectors and density. No significant differences in metrics were noted from upstream to downstream 

of LX Bar Creek (sites PR16–PR17).

The O/E scores in the lower reaches of the Powder River 

indicated a substantial increase in biological condition from 

sites PR14 to PR15, and a slight decrease from site PR15 to 

PR17. The O/E scores increased from site PR17 to PR18, indicating an increased biological condition similar to that noted 

in the macroinvertebrate metric results. 

Algal communities of the lower Powder River were 

marked by maximum values of taxa richness and diversity 

at sites PR14 and PR15. Relative abundance of halophilic 

diatoms increased upstream to downstream of SA Creek, coincident with the increase in biological condition noted in the 

macroinvertebrate communities. The algal community below 

LX Bar Creek contained a higher percentage of circumneutral diatoms preferring neutral pH than any of the sites on the 

Powder River that were dominated by alkaliphilic diatoms that 

prefer alkaline pH values, which may indicate contributions of 

less alkaline water. 

Comparison of the 2010 macroinvertebrate communities 

with those sampled in 2005–08 indicated potential temporal 

changes in biological condition in the upper reaches of the 

Powder River (fig. 7). The 2005–08 metrics shown in figure 7 

had significant differences in the middle reaches compared to 

upper and lower reaches, such as the low relative abundance 

of intolerant macroinvertebrates from river miles 283 to 406 

(Peterson and others, 2010). The mean values of metrics 

during 2010 also indicated decreased biological condition in 

the middle reaches of the Powder River; however, the 2010 

change in biological condition occurred at river mile 351, 

downstream of the 2005–08 point of change, potentially 

indicating an increase in biological condition in the vicinity 

of river miles 283 to 351. Changes in the amounts or quality of CBNG effluents in the upper reaches of the Powder 

River might account for differences between the 2005–08 and 

2010 results. Biological condition in the lower Powder River 

increased at river mile 243 during 2005–08 and again at the 

same point in 2010.

Tongue River

Macroinvertebrate community metrics for the Tongue 

River generally indicated an increase in biological condition from site TR1, near the Wyoming-Montana border, to 

site TR2, downstream of some of the CBNG-produced water 

discharges in Montana. Sites TR2 and TR3, upstream and 

downstream of Prairie Dog Creek which receives CBNG and 

irrigation discharges, had relatively few significant differences 

in macroinvertebrate metric values. Several macroinvertebrate 

community metrics indicated a decline in biological condition 

from site TR3 to site TR4, which are upstream and downstream respectively of CBNG production water discharges 

between Prairie Dog Creek and Badger Creek. 

The O/E and BC scores for the macroinvertebrate community at site TR1 were significantly different (p < 0.05) from 

those calculated for sites TR2, TR3, and TR4. The model 

scores calculated from the samples collected from TR5 and 

TR6 were not significantly different from any of the other sites 

but were slightly closer to the expected reference condition 

than TR1 that had the lowest score among the Tongue River 

sites. The scores calculated from site TR3 samples were highest, and therefore closest to the expected condition.

Algal community metrics in the Tongue River indicated 

an increase in total richness and motile taxa richness from 

site TR1 to TR2, consistent with the increase in biological 

condition noted from the macroinvertebrate metrics. Site TR1 

was notable for high relative abundances of nitrogen-fixing 

algae and alkabiontic (high pH) diatoms. Algal metrics at site 

pairs TR2 to TR3 and TR3 to T4 did not appear to change 

substantially between the sites. 

Further Study Needs

The 2010 sampling at site pairs upstream and downstream of CBNG effluents identified specific points where 

changes in biological condition occurred, in addition to confirming the results from 2005–08. Confirmation of the changes 

in condition at specific sites would be beneficial. For example, 

the maximum alkalinity concentrations in the Powder River 

coincided with a reach of declining biological condition, but 

not all site pairs with declines in biological condition had 

high alkalinity concentrations. Biological communities are 

long-term indicators of water-quality change, as they integrate 

responses to both natural and anthropogenic influences over 

time. Given that this is the first year of sampling focused on 

the effect on the mainstem biota from the tributaries, additional continued monitoring of macroinvertebrates, algae, 

and water quality, including nutrients, would provide further 

resolution to the spatial and general temporal patterns identified with this and previous studies. 
Figure 7. Comparison of mean macroinvertebrate metric scores from 2005–08 to mean scores from 

2010, Powder River, Wyoming.

0

10

20

30

40

50

60

Intolerant macroinvertebrates,

in percent

0

20

40

60

80

100

120

Filterer-collectors, in percent

0

10

20

30

40

50

Ephemeroptera, in percent

0

20

40

60

80

100

Diptera, in percent

0

2

4

6

8

10

12

450 400 350 300 250 200

River mile in Powder River

Ephemeroptera richness

2005–08

2010

EXPLANATION

Potential Effects of Water Produced from Coalbed Natural Gas Development on Biological Communities 31
32 Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010

Summary

Ongoing development of coalbed natural gas in the 

Powder River structural basin in Wyoming and Montana led 

to formation of an interagency task group, and a subgroup, 

the Aquatic Task Group (ATG), to address concerns about the 

effects of the resulting production water on biological communities in streams of the area. This study was conducted 

under the direction of the ATG, and in cooperation with the 

Bureau of Land Management, the Montana Department of 

Environmental Quality, the Wyoming Department of Environmental Quality, and the Wyoming Game and Fish Department. Samples of macroinvertebrates, algae, water quality, 

and related measurements were collected at 18 sites on the 

mainstem Powder River and 6 sites on the mainstem Tongue 

River in 2010. Sampling-site locations were selected on a 

paired approach, typically upstream and downstream of direct 

discharge points and tributaries associated with coalbed natural gas development. 

Differences in biological condition among site pairs were 

evaluated using multiple lines of evidence including macroinvertebrate and algal community metrics and observed/

expected (O/E) macroinvertebrate models. Triplicate samples 

of macroinvertebrates were used to test for statistically significant differences among site pairs using metrics including taxa 

richness, taxa relative abundance, functional feeding groups, 

and tolerance, as well as O/E scores. 

The Powder River was divided into three zones for 

the purposes of discussion. The upper reach includes 

sites PR1–PR9, the middle reach includes sites PR9–PR14, 

and the lower reach includes sites PR14–PR18. Biological 

condition in the upper reach of the Powder River was spatially 

variable, but the multiple lines of evidence generally agreed 

about the indication of increase or decrease at given site pairs. 

Invertebrate community metrics and O/E scores, as well as 

algal metrics, indicated a substantial decline in biological condition between sites PR2 and PR3, from downstream of Willow Creek to upstream of Pumpkin Creek. At other site pairs, 

multiple lines of evidence indicate no significant differences 

or an increase in biological condition, such as an increase 

between sites PR5 and PR6, upstream and downstream of 

Beaver Creek. The spatial variability indicates localized noncumulative stressors might be affecting the biota. Biological 

condition, as indicated by macroinvertebrate metrics and O/E 

scores and algal metrics, generally declined in the middle 

reaches of the Powder River, indicating potential cumulative 

effects from CBNG discharges in some of the reaches from 

Flying E Creek to downstream of Wild Horse Creek. The 

middle reaches of the Powder River also contained the highest 

alkalinity concentrations, a potential indicator of toxicity from 

sodium bicarbonate. Inflow of water between sites PR12 and 

PR13, between Barber Creek and Wild Horse Creek, might 

be associated with the corresponding decline in macroinvertebrate community condition and increase in facultative nitrogen 

heterotrophic diatoms. The increase in nitrogen heterotrophs 

indicates that the water contains relatively high concentrations 

of organic nitrogen. Comparison of invertebrate metric results 

from 2010 to those from 2005–08 corroborated previous findings (Peterson and others, 2010) that biological condition in 

the middle reaches of the Powder was lower than in the upper 

or lower reaches. Mean O/E scores in the middle reaches were 

as low as 0.37, indicating substantially decreased biological 

condition compared to the reference condition score of 1.00. 

Biological condition in the lower reaches of the Powder 

River was variable, indicating declines at some site pairs and 

no significant differences or increases at others. The 2010 

macroinvertebrate metrics, O/E scores, and algal metrics 

indicated a substantial increase in biological condition from 

site PR14 to PR15, which is the same reach where biological 

condition increased during 2005–08. 

Biological condition at site pairs on the Tongue River 

showed an increase in one case, near the Wyoming-Montana 

border, and a decrease in another case, near Badger Creek. 

Few significant differences were noted from upstream to 

downstream of Prairie Dog Creek, a major tributary. No significant differences were noted in the Tongue River upstream and 

downstream of Hanging Woman Creek, a site pair related to 

potential development in the Hanging Woman Creek drainage. 

Further study would be beneficial to confirm the patterns 

observed, including increases and decreases in biological condition. An additional year of sampling at the same sites also 

will help pinpoint areas of interest to examine in greater detail. 

Acknowledgments

David Mott, Greg Boughton, Scott Edmiston, Clint 

Masters, and Seth Davidson of the USGS, as well as several 

interns from the BLM, assisted with data collection in 2010. 

Many private landowners and the Anadarko Corporation 

(The Woodlands, Texas), allowed access to sampling sites. 

Colleague reviewers were Kathy Foster and Jill Frankforter. 

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Peterson and others—Assessment of Coalbed Natural Gas Development in Powder and Tongue Rivers, Wyoming and Montana, 2010—OFR 2011–1294