Effects of Mining on Benthic 

Macroinvertebrate Communities 

and Monitoring Strategy

By Chester R. Anderson

Chapter E20 of

Integrated Investigations of Environmental Effects of Historical 

Mining in the Animas River Watershed, San Juan County, Colorado

Edited by Stanley E. Church, Paul von Guerard, and Susan E. Finger

Professional Paper 1651

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract .......................................................................................................................................................853

Introduction.................................................................................................................................................853

Purpose and Scope ..........................................................................................................................854

Acknowledgments ............................................................................................................................854

Methods.......................................................................................................................................................854

Results .........................................................................................................................................................859

Macroinvertebrate Communities in Reference Tributaries .......................................................859

Taxa Richness and Densities of Specific Taxa in the Animas River .........................................859

Evenness of Taxa in the Animas River ...........................................................................................861

Similarity Among Animas River and Reference Tributary Sites ................................................861

Discussion ...................................................................................................................................................861

Proposed Sampling Plan and Analysis ..................................................................................................863

Pre-Remediation Baseline Sampling .............................................................................................863

Post-Remediation Sampling ............................................................................................................865

Statistical Analysis to Assess Effectiveness of Remediation ...................................................865

Summary......................................................................................................................................................871

References Cited........................................................................................................................................871

Appendix. 1997 pre-remediation baseline data (mean number of taxa per square meter) 

[included as file on accompanying CD-ROM; Sole and others, this volume, Chapter G]

Figures

 1. Map showing sample sites in Animas River watershed study area ................................855

 2. Map showing sample sites from study area south to Colorado State line .....................856

 3–8. Diagrams showing:

 3. Number of invertebrate taxa in the major stream Orders (stoneflies, 

 mayflies, true flies, caddis flies, beetles, non-insects) ...............................................860

 4. Densities (number of individuals per square meter) of taxa within 

 major stream Orders (stoneflies, mayflies, true flies, caddis flies, 

 beetles, non-insects) ........................................................................................................862

 5. Densities of taxa within mayfly Order (Ephemeroptera) .............................................864

 6. Densities of taxa within caddis fly Order (Trichoptera)...............................................866

 7. Densities of taxa within stonefly Order (Plecoptera) ..................................................867

 8. Densities of taxa within true fly Order (Diptera) ...........................................................868

 9. Graph showing similarity indices ...........................................................................................869

 10. Graph showing pre-remediation baseline data for a Multiple Site Assessment ..........870

Tables

 1. Sample sites ..............................................................................................................................858

 2. Pre-remediation baseline data for the Animas River canyon ...........................................869
Abstract

The benthic macroinvertebrate community of the Animas 

River watershed study area has been impaired by more than a 

century of hard-rock mining. Currently, remediation of mine 

sites is being done to restore ecosystem health in this watershed. Ecological recovery of the community depends on the 

degree that remediation improves water quality and reduces 

erosion of mill tailings into the river, resulting in improved 

habitat quality. Benthic macroinvertebrate data were collected 

in fall 1996, spring 1997, and fall 1997 to measure existing 

ecosystem health and to evaluate the response of the benthic community to remediation activities. Macroinvertebrate 

samples were obtained from 25 impaired and 11 unimpaired 

sites. Sampling methods were proposed to determine time of 

year, frequency, and location for collection of pre-remediation 

data and to qualitatively and statistically compare those data 

to the post-remediation data. Two methods were proposed: 

(1) a single site assessment where only one sample site exists 

downstream from each remediation site, and (2) a multiple site 

assessment where a minimum three sample sites are used for 

each remediation site. At least 3 years of pre-remediation data 

and 3 years of post-remediation data from the same site must 

be collected to distinguish between the effectiveness of remediation and temporal variation inherent in natural populations. 

If post-remediation data are not significantly different from 

pre-remediation data, then subsequent data collection should 

be delayed until further remediation is completed, the benthos 

has had more time to recover, or macroinvertebrates have had 

more time to recolonize the impaired reaches. If a significant 

difference is evident between pre- and post-remediation data, 

a minimum of 2 years of additional post-remediation data 

should be collected.

Introduction

The Animas River watershed study area has been 

extensively affected by more than a century of hard-rock 

mining, resulting in impaired benthic macroinvertebrate and 

fish communities throughout the watershed. The purpose of 

remediating abandoned mine sites is to restore ecosystem 

health (von Guerard and others, this volume, Chapter B). Two 

indicators of aquatic ecosystem health are species composition 

and species diversity, which researchers can evaluate by determining number of taxa (taxa richness) and relative densities of 

the taxa or the taxa evenness (May, 1988). In general, healthy 

aquatic ecosystems are reflected by high numbers of taxa and 

even taxa distribution across their habitat.

Benthic biological communities include periphyton, 

macroinvertebrates, and some species of fish. Periphyton 

(or biofilm) is composed mostly of the primary producer, 

algae, and grows on top of rocks and other benthic substrates. Benthic macroinvertebrates feed on periphyton, dead 

organic material and a wide range of small organisms, and 

are themselves an important food resource for fish, amphibians, reptiles, birds, and mammals. Of the fish, some species, 

such as suckers and fathead minnows, graze primarily upon 

periphyton. Trout and speckled dace, however, rely primarily 

upon benthic macroinvertebrates for their food.

Acid mine drainage may reduce species diversity in 

stream ecosystems through both acute and chronic mechanisms, including toxicity of metals in stream water, sediment, and interstitial water (Besser and others, this volume, 

Chapter D; Besser and Brumbaugh, this volume, Chapter E18; 

Besser and Leib, this volume, Chapter E19) as well as 

physical effects of metal-bearing precipitates (colloids) on 

aquatic organisms and their habitats (Milhous, this volume, 

Chapter E21).

One of the major goals of the Animas River watershed study was to evaluate the effectiveness of remediation 

(Buxton and others, 1997). Although monitoring water chemistry in streams provides information on exposure concentrations and chemical loading, it does not directly address 

species composition and diversity or the quality of benthic 

community habitat (Karr and others, 1986; Yoder and Rankin, 

1999). Because of the abundance and mobility of benthic 

macroinvertebrates, coupled with their ability to recolonize 

impaired ecosystems, this group of taxa is commonly selected 

for use in monitoring studies of aquatic ecosystem health 

throughout the United States (Davis and others, 1996). The 

methods for collection, analysis, and interpretation of benthic 

macroinvertebrate data are well established through works 

Chapter E20

Effects of Mining on Benthic Macroinvertebrate 

Communities and Monitoring Strategy

By Chester R. Anderson
including the Rapid Bioassessment Protocol (RBP) developed 

for the Environmental Protection Agency (Shackleford, 1988; 

Plafkin and others, 1989; Barbour and others, 1992, 1995, 

1996; Hayslip, 1993), the benthic Index of Biotic Integrity 

(IBI; Kerans and Karr, 1994; Fore and others, 1996), and the 

Invertebrate Community Index (DeShon, 1995). Their use as 

indicators of water and habitat quality has been justified by 

Hutchinson (1993), Karr and Chu (1999), Resh and Jackson 

(1993), and Rosenburg and Resh (1993). In addition, long 

holding times for preserved samples and the establishment of 

voucher collections that may be evaluated by other investigators for quality control are advantageous. Moreover, using 

macroinvertebrates for monitoring and assessing the health of 

an aquatic ecosystem directly addresses the concept of species diversity by recognizing that benthic macroinvertebrates 

integrate a variety of variables of concern over both space 

(such as benthic habitat and water quality) and time (because 

they live in the stream year-round and any ephemeral change 

in water quality will appear in the composition of the macroinvertebrate community). Limitations to the use of macroinvertebrates for monitoring include the relative difficulty of 

sampling. In contrast to invertebrates, periphyton is relatively 

difficult to identify.

Community metrics can be calculated from counts of 

individuals or counts of individual taxa in an ecosystem. Most 

metrics incorporate knowledge of the type of taxa, taxa richness, and relative numbers (evenness). There have been several 

attempts to apply a single number to taxa richness and evenness. The most widely accepted attempt is the Shannon-Weiner 

diversity index. The problem is that such an integrative index 

loses important information and may not wholly define and 

encompass all the intricacies of a macroinvertebrate community 

(Hurlbert, 1971; Purvis and Hector, 2000).

How the community will respond to remediation efforts 

(Stone and Wallace, 1998; O’Neill, 1999) is also unknown. 

The response will depend on existing macroinvertebrate 

communities within the watershed as well as the effect that 

remediation has on water and substrate quality. Potential 

responses include additions of or increasing densities of intolerant taxa and (or) loss of or decreasing densities of tolerant 

taxa. Therefore, descriptions of the macroinvertebrate community data should include species identification and the number 

of taxa as well as relative densities With this information, a 

variety of community metrics may be used to evaluate the 

effectiveness of remediation and to compare pre-remediation 

data to post-remediation data (Resh and others, 1988). 

Because the exact response of the macroinvertebrate community to remediation is unknown, identifying specific metrics 

for the purpose of evaluating the effectiveness of remediation 

cannot be completed until post-remediation data are obtained 

and thoroughly compared to the pre-remediation data. Distinguishing between temporal variability and actual recovery 

of the ecosystem is also necessary to accurately evaluate the 

effectiveness of remediation (Chapman, 1999).

Other processes may also help in evaluation of the effectiveness of remediation and may help identify underlying or 

mechanistic reasons for recovery or lack thereof. They include 

measurements at the suborganismal (for example, bioassays, 

Besser and Leib, this volume) to the ecosystem level (for 

example, nutrient cycles, Stone and Wallace, 1998; Adams 

and others, 2002; Resh and others, 1988). However, such procedures may not be feasible because of their complexity and 

cost. In conjunction with other research, both included in this 

volume and by other agencies, this study is an attempt to meet 

some of the objectives outlined by Michener (1997), Kondolf 

(1995), and Kondolf and Micheli (1995) in assessment of the 

effectiveness of remediation practices.

Purpose and Scope

The primary purpose of this study was to

• Gather benthic macroinvertebrate pre-remediation 

data to evaluate whether mine-site remediation in the 

Animas River watershed study area will increase the 

diversity of benthic macroinvertebrates

• Propose guidelines for conducting post-remediation 

sampling of the benthic community in the Animas 

River

• Propose methods to evaluate the effectiveness of 

remediation using biological data.

Acknowledgments

I acknowledge the help of Dave Gerhardt of the USDA 

Forest Service, San Juan National Forest; William Simon, 

Animas River Stakeholders; and Barbara Horn, Colorado 

Division of Wildlife. Each contributed significantly to 

the design and implementation of this research. The San Juan 

National Forest provided funds, personnel, and equipment for 

the collection and processing of the macroinvertebrate 

samples. Bob Brantlinger and Jamey O’Leary helped considerably in the data collection.

Methods

We used biomonitoring and assessment methods to 

obtain pre-remediation data in 1996 and 1997 at 25 impaired 

and 11 reference sites, from the northernmost headwaters of 

the Animas River (the watershed study area as such) to the 

confluence with the San Juan River (figs. 1 and 2; table 1). 

The pre-remediation data were collected prior to the bulk of 

854 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 855

Elk Cr eek

Molas

Creek

Sout h Fork

Mi neral Creek

Kendall Gulch

Cunning ham

Creek

Boulder Gulch

Eureka Gulch

former

Lake

Emma

Elk Park

Mineral Creek

Animas

River

Cement Creek

Chattanooga

Eureka

Silverton

Animas

Forks

Howardsville

18

19

23

22

24

21

20a-c

11

12

13

14

15

16

17

Deer P ark Creek

EXPLANATION

Localities for invertebrates

Animas River

watershed 

study area

C O L O R A D O

Durango

0

0 1

1 2 MILES

2 KILOMETERS

107o50'30" 107o45' 107o37'30" 107o30'

37o

52'

30"

37o

45'

37o

58'

Animas

River

tributary

Figure 1. Sample sites, Animas River watershed study area, from confluence of Elk Creek north to the headwaters of the study area 

streams. Dot indicates two samples taken at site, one in mainstem upstream of confluence and one in the tributary (see inset in figure).
EXPLANATION

Localities for invertebrates

0 3 5 MILES

0 3 5 KILOMETERS

Durango

37o00' 

Silverton

ANI MAS

CA N YON

Cascade

Creek

Creek

Florida

River

Florida River

River

108o00' 

Base from U.S. Geological Survey

1:100,000 digital line maps, 1989

Cement Creek

Area of figure 1

Animas

River

tributary

107o45' 107o30' 

37o15' 

37o30' 

37o45' 

38o00' 

He rmosa

Animas

Animas Mineral Creek River

Needle

Creek

Lightner

Creek

Animas River

watershed 

study area

C O L O R A D O

Durango

12

11

9

10

7

5

2

1

upstream from confluence 

with San Juan River

8

6

4

3

856 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 857

remediation work (Finger and others, this volume, Chapter F). 

Sites were sampled in fall 1996, and spring and fall 1997. The 

majority of the sample sites were at major tributaries of the 

Animas River where, for the response variable, samples were 

taken from the Animas River immediately upstream from the 

tributaries. These sample sites were chosen for two reasons: 

(1) to use the tributary as a reference and (2) to avoid mixing 

zones. Where tributaries were far apart, especially downstream 

from the Animas River canyon, samples were taken at established sample sites that were not necessarily associated with 

a tributary but where we knew that data had been collected 

previously (Peter Butler, Robert Owen, and William Simon, 

Unpublished report to Colorado Water Quality Control 

Commission, Animas River Stakeholders Group, 2001).

Reference samples were obtained for the purpose of 

measuring potential community metrics given various levels of 

remediation. Each tributary station had similar physical habitat 

features as the associated Animas River stations, such as 

substrate type (granite, sandstone, limestone, for example) and 

composition (boulder, cobble, gravel, for example) but were 

dissimilar in stream order (size) and gradient. At each sample 

site, we also obtained data for benthic habitat.

Field sampling procedures were modeled after the EPA’s 

Rapid Bioassessment Protocol (RBP) for macroinvertebrates. 

Because macroinvertebrate habitat in the Animas River is 

primarily boulder-cobble substrate, the single-habitat approach 

was selected as opposed to the multi-habitat approach. RBP 

protocol emphasizes compositing samples over an area of 

greater than 2 m2

, but the primary goal of RBP is assessment 

of stream ecosystem health. The goal of this research was 

to establish pre-remediation data from which to gauge the 

effectiveness of mine-site remediation. To accomplish this, we 

needed to determine sampling errors and densities of particular taxa. Therefore, instead of compositing the samples as in 

the RBP protocol, we took from 3 to 6 samples from each site. 

The area sampled for each one was limited to an area of 0.5 m 

directly upstream of the net, resulting in an area of 0.25 m2

. 

Because of the high flows and volumes of water found in the 

incised Animas River canyon (sites 8–14, figs. 1 and 2), a 

modified rectangular dip-net was constructed for this research. 

The net had more surface area to allow greater quantities of 

water to flow into and through the net. The opening measured 

23 cm high by 50 cm wide. The net measured 50 cm long 

and had approximately 1,000 cm2 of 500-μm mesh netting. 

Laboratory sample processing of the macroinvertebrate 

samples followed protocols outlined by the National Aquatic 

Monitoring Center (Vinson and Hawkins, 1996). Taxa were 

identified to the lowest possible level (see Appendix, included 

on CD-ROM, Sole and others, this volume, Chapter G), and 

voucher specimens are stored at the USDA San Juan National 

Forest aquatics laboratory.

The total number of taxa per sample site and the means 

of the densities of each taxon per sample site were calculated, 

tabulated, and graphed to determine the pre-remediation 

baseline. Unknown specimens that clearly did not fit in any of 

the other taxonomic categories were not included in calculations of taxa richness. Data were assessed on the basis of 

(1) the composition of a diverse macroinvertebrate community within the Animas River watershed, (2) the total number 

of taxa (taxa richness) for each sample site and how this 

metric varies by river mile within the Animas River and in 

the tributaries, and (3) the relative densities of taxa (number 

of individuals/taxon/m2

) within each of the most important 

lotic (flowing streams and rivers) aquatic groups: true flies 

(Diptera), mayflies (Ephemeroptera), stoneflies (Plecoptera), 

caddis flies (Trichoptera), beetles, and non-insects for both the 

Animas River and tributaries.

Minor modifications were made to the original 1996 

sampling plan. In 1997, the sampling plan included stations 

upstream of and in Hermosa Creek (fig. 2, site 7) and Kendall 

Gulch (site 14, fig. 1 and table 1). Note: Because of the large 

number of springs along the Animas River upstream from 

Molas Creek (site 12T), data from this site were not included 

in the analysis.

Macroinvertebrate communities at impaired sites were 

compared to reference sites using Morisita’s index of similarity and percent similarity index for the following: upstream 

from Cunningham Creek site (site 18) to Cunningham Creek 

at mouth (site 18T), upstream from Boulder Gulch (site 17) 

to Boulder Gulch at mouth (site 17T), upstream from Deer 

Park Creek (site 13) to Deer Park Creek at mouth (site 13T), 

upstream from Elk Creek (site 11) to Elk Creek at mouth 

(site 11T), upstream from Needle Creek (site 10) to Needle 

Creek at mouth (site 10T), upstream from Cascade Creek 

(site 9) to Cascade Creek at mouth (site 9T), upstream from 

Hermosa Creek (site 7) to Hermosa Creek at mouth (site 7T), 

and Mineral Creek upstream from South Fork Mineral Creek 

(site 20a) to South Fork Mineral Creek at mouth (site 20b, 

fig. 1).

Annual variation of pre-remediation data was estimated 

utilizing 1992, 1996, and 1997 data both within the Animas 

River canyon (sites 8–14, figs. 1, 2) and at Mineral Creek 

upstream from South Fork Mineral Creek (site 20a, fig. 1). 

Within the canyon a regression line was fit, utilizing leastsquares analysis, to total taxa data collected at each station 

for each year. At the Mineral Creek site the mean and standard error of the 1992, 1996, and 1997 total taxa data was 

calculated.

Figure 2 (facing page). Sample sites, Animas River watershed 

south of study area to Colorado State line. Sample site 1 on the 

Animas River upstream from the confluence with the San Juan 

River in New Mexico is not shown. Dot indicates two samples 

taken at site, one in mainstem at confluence and another in the 

tributary (see inset in figure).
Table 1. Sample sites.

[Site number (T denotes associated tributary); distance in river miles upstream from confluence of Animas River with San Juan River, N. Mex., see figs. 1 and 2, 

degree of impairment and reference sites]

Site No.1 Site name River distance Impairment

Animas River sites

19 Upstream from Eureka Gulch 82.1 Impaired

18 Upstream from Cunningham Creek 78.2 Impaired

17 Upstream from Boulder Gulch 75.8 Impaired

16 Upstream from Cement Creek 74.2 Impaired

15 Upstream from Mineral Creek 73 Impaired

14 Upstream from Kendall Gulch 72 Impaired

13 Upstream from Deer Park Creek 71.7 Impaired

11 Upstream from Elk Creek 67.4 Impaired

10 Upstream from Needle Creek 61 Impaired

9 Upstream from Cascade Creek 54.7 Impaired

8 Downstream from Bakers Bridge 43.3 Impaired

7 Upstream from Hermosa Creek 38.5 Impaired

6 32nd St. Bridge, Durango 25.8 Impaired

5 Upstream from Lightner Creek 23.5 Impaired

4 Purple Cliffs 21 Impaired

3 Weaselskin Bridge 19 Impaired

2 Upstream from Florida River 17 Impaired

1 Mouth 0.3 Impaired

Animas River tributary sites

19T Eureka Gulch mouth 82 Impaired

18T Cunningham Creek mouth 78.1 Slightly Impaired/Reference

17T Boulder Gulch mouth 74.2 Unimpaired/Reference

13T Deer Park Creek mouth 71.6 Unimpaired/Reference

11T Elk Creek mouth 67.3 Unimpaired/Reference

10T Needle Creek mouth 60.9 Unimpaired/Reference

9T Cascade Creek mouth 54.7 Unimpaired/Reference

7T Hermosa Creek mouth 38.5 Unimpaired/Reference

5T Lightner Creek mouth 23.1 Unimpaired/Reference

2T Florida River mouth 17 Unimpaired/Reference

Cement Creek basin

16T Mouth 74.1 Impaired

22 Downstream from South Fork Cement Creek 80.5 Impaired

23 Upstream from North Fork Cement Creek 81.4 Impaired

24 South Fork Cement Creek Mouth 80.6 Impaired

Mineral Creek basin

15T Mouth 73 Impaired

20a Upstream from South Fork Mineral Creek 76.5 Impaired

South Fork Mineral Creek subbasin

20b Mouth 76.5 Slightly Impaired/Reference

21 South Fork Mineral Creek Forest Service Campground 80.1 Slightly Impaired/Reference

1

See figures 1 and 2.

858 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 859

Results

Macroinvertebrate Communities in Reference 

Tributaries

Data from the unimpaired tributaries, when compared 

with data from the Animas River and Cement and Mineral 

Creeks, showed relatively higher numbers of taxa and densities and an even distribution of the number of taxa within the 

Orders (figs. 3, 4; table 1). Except for South Fork Mineral 

Creek mouth (site 20b, fig. 1) and Lightner Creek mouth 

(site 5T, fig. 2), the communities in the tributaries were dominated by mayflies (fig. 4). As in the Animas River upstream 

from Boulder Gulch, Cunningham Creek at mouth, and 

Boulder Gulch at mouth (sites 17T and 18T, fig. 1; table 1), 

macroinvertebrate communities were dominated by the heptageniid mayflies, Rhithrogena and Epeorus, and the ephemerelid mayfly, Drunella (fig. 5). South Fork Mineral Creek 

at mouth and South Fork Mineral Creek at the United States 

Department of Agriculture (USDA) Forest Service campground (site 21, fig. 1) had fairly diverse and even macroinvertebrate communities reflected in both taxa richness (23 and 

17 respectively) and evenness (fig. 4). Because this tributary, 

as well as Cunningham Creek and lower Boulder Gulch, was 

affected by mineralization, the composition of the macroinvertebrate community of these tributaries may be important in 

determining what community compositions to expect as the 

Animas River macroinvertebrate community recovers. (See 

objective 4, Appendix 6b, Macroinvertebrate Report, Unpub. 

Report to Colorado Water Quality Commission, ARSG, 2001.)

Boulder Gulch is a high-gradient drainage wholly within 

the Silverton caldera. Since this subbasin was set aside as the 

community water supply, essentially no mining activity has 

occurred within the subbasin. The subbasin is underlain by 

propylitically altered bedrock (Bove and others, this volume, 

Chapter E3), and the water quality is good (Wright and others, this volume, Chapter E10). The stream contains a diverse 

assemblage of macroinvertebrates (figs. 3–8). This tributary 

represents the best reference reach for the macroinvertebrate 

community in the caldera. It is easily accessible for sampling, 

and pre-remediation geochemical and biological baseline data 

are available.

A diverse macroinvertebrate community in a tributary 

outside the Silverton caldera was best represented by Deer 

Park Creek (site 13T, fig. 1), 1.3 miles downstream from the 

caldera margin (Yager and Bove, this volume, Chapter E1). 

Deer Park Creek had a relatively large number of taxa (35) 

existing at relatively high densities (1,274 individuals per 

square meter; fig. 3). The numbers of taxa within each Order 

were distributed relatively evenly with a slight dominance by 

mayflies (fig. 4). Within the mayfly Order, there were seven 

taxa dominated by two genera, Rhithrogena and Drunella

(303 and 130/m2

, fig. 5 and Appendix (Sole and others, this 

volume)). Although the density of mayflies in Deer Park 

Creek (533/m2

) was less than in Cunningham Creek (773/m2), 

there were more mayfly taxa in Deer Park Creek (7) than in 

Cunningham Creek (4) as well as more taxa of the other major 

Orders such as caddis flies (fig. 6 and Appendix). In Deer Park 

Creek, there were six taxa of caddis flies dominated by Rhyacophila (Appendix) and seven taxa of stoneflies dominated by 

both Zapada (142/m2

) and a taeniopterygid (120/m2; fig. 7 and 

Appendix). There were relatively few dipterans (fig. 8) in Deer 

Park Creek compared to South Fork Mineral Creek at mouth 

site (20b, fig. 1).

Similarity of macroinvertebrate communities in the 

Animas River mainstem to reference tributaries reflected patterns in taxa richness and evenness in the mainstem (fig. 9) 

except at Hermosa Creek (sites 7 and 7T). Similarity declined 

due to changes in taxa composition in Hermosa Creek at 

mouth compared to other tributaries and the mainstem.

Examples of less diverse and even macroinvertebrate 

communities exist in Cement and Mineral Creeks (sites 20a, 

16T, and 22–24, fig. 1). Both tributaries had relatively few taxa 

(9 and 16 respectively, collected at confluence with Animas 

River) with either low densities (64 and 143/m2

) or communities that were dominated by only one or two taxa (figs. 3 and 

4; Appendix).

Taxa Richness and Densities of Specific Taxa 

in the Animas River

Compared to conditions in Boulder Gulch and other 

reference tributaries, both taxa richness and density of macroinvertebrates in the Animas River upstream from Eureka 

Gulch (site 19, fig. 1) were low, but both metrics increased 

from Eureka Gulch to Boulder Gulch (sites 19 through 17T, 

fig. 1 and fig. 3). The peak in taxa richness and densities 

in the Animas River from the reach upstream of Cunningham 

Creek and Boulder Gulch represented a fairly diverse 

macroinvertebrate community, although not as diverse as the 

communities within either the mouth of Cunningham Creek 

or Boulder Gulch themselves. Taxa richness and densities in 

the Animas River decreased dramatically downstream from 

Boulder Gulch to Mineral Creek. Downstream, the taxa richness in the Animas River increased to previous levels found 

around Cunningham Creek near the confluence with Deer 

Park Creek, but invertebrate densities did not increase substantially until 28 miles downstream at the Downstream from 

Bakers Bridge site (site 8, fig. 2 and fig. 3; table 2). Presumably 

this recovery of the invertebrate community is attributable 

to improved water and habitat quality and changes in toxicity of dissolved metals. Taxa richness more or less levels off 

from Bakers Bridge to the confluence with the San Juan River 

(sites 8 through 1, fig. 2), but densities continue to increase 

downstream to Weaselskin Bridge (site 3, figs. 2, 4).
Tributaries and subbasins

0

5

10

15

20

25

30

35

40

19T 18T 17T 20b 15T 21 20c 16T 13T 11T 10T 9T 7T 5T 2T

SITE NUMBER

Animas mainstem

0

5

10

15

20

25

30

35

40

19 18 17 16 15 14 13 11 10 9 8 7 6 5 4

NUMBER OF TAXA NUMBER OF TAXA

Other Stones Flies Mays Caddis Beetles

860 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 861

Evenness of Taxa in the Animas River

The number of taxa found within each Order of macroinvertebrates is relatively even throughout the Animas River. 

The evenness, however, as illustrated by the number of individuals per taxon/m2

 within the Animas River upstream from 

Cunningham Creek, shows domination by dipterans (240/m2

out of total of 399/m2

; fig. 3 and Appendix). Within the mayfly 

community in the Animas River upstream from Cunningham 

Creek, Rhithrogena (36/m2) and Baetis (27/m2, total mayfly 

density=73/m2

) are dominant (fig. 5 and Appendix). In the 

reach from Eureka Gulch to Boulder Gulch, the composition 

of the mayfly community improves: an increase in taxa richness (from two to four) and densities (from 2.67 to 500/m2

) 

with dominance by Rhithrogena (385/m2

), Baetis (59/m2), 

Epeorus (38/m2

), and Drunella (18/m2). The number of taxa 

of mayflies remains relatively constant throughout the reach 

(fig. 3), but the densities of the mayfly community do not 

recover in the Animas River until south of Durango, 55 mi 

downstream (site 5, fig. 2; fig. 5). Rhithrogena essentially disappears downstream at Cement Creek (site 16, to 0.67/m2

) and 

reappears upstream from Elk Creek (site 11, fig. 1; 9.33/m2) 

reaching a peak density of 42/m2

 at the site upstream from 

Needle Creek (site 10, fig. 2).

Upstream from Boulder Gulch, there is less disparity of 

relative densities of mayflies (500 mayflies per square meter 

compared to 630 total taxa per square meter) between the 

Animas River and its associated tributaries—Cunningham 

Creek (site 18T; 773 / 1,121) and Boulder Gulch (site 17T; 

564 / 1,138)—than there is in the Animas River downstream 

from the confluence with Mineral Creek, where a greater 

disparity exists between relative densities of mayflies in 

the Animas River and associated tributaries—Deer Park, 

Elk, Needle, Cascade, and Hermosa Creeks (figs. 1, 2, 5; 

Appendix). In the Animas River upstream from the confluence 

with Mineral Creek (site 15, fig. 1), dipteran communities were 

dominated by orthoclads and an unknown chironomid, whereas 

associated tributaries, Boulder Gulch and Cunningham Creek, 

had relatively high diversity of true flies (fig. 8).

Downstream from the confluence of Cascade Creek 

(site 9, fig. 2), the number of taxa and their densities increased 

sharply in the Animas River. Upstream from Bakers Bridge 

(site 8, fig. 2), densities of caddis flies (fig. 6) were low 

(84/m2

), dominated by Arctopsyce (75/m2). Downstream 

from Bakers Bridge, additional taxa were found along with 

a dramatic increase in densities (fig. 6). The Animas River 

caddis fly community, when compared to that of tributaries 

such as Boulder Gulch and Deer Park Creek, appeared to be 

reduced more than the other Orders of macroinvertebrates 

(fig. 6). The densities of Brachycentrus increased substantially upstream from Hermosa Creek (site 7, fig. 2), but the 

total number of taxa of caddis flies did not increase in the 

Animas River until downstream from Durango (Appendix). 

Below Bakers Bridge, the Animas River’s setting changes 

dramatically from a steep, incised canyon to a relatively wide 

valley and a meandering stream. Agriculture, gravel mining, 

housing developments as well as urban landscapes dominate 

land use.

Stonefly densities throughout the Animas River were 

low (fig. 7). The communities were dominated by Zapada

upstream from Deer Park Creek with the greatest diversity 

upstream from the confluence with Cement Creek. Downstream from the Mineral Creek confluence, an unknown 

taeniopterigid dominated the stoneflies in the Animas River 

south to Bakers Bridge through the Animas River canyon. 

Relatively high numbers of taxa of stoneflies occurred in the 

Animas River upstream from Boulder Gulch (five), but this 

community was absent in the reach downstream from the confluence with Cement Creek and did not reappear until Needle 

Creek (fig. 7), reflecting the effects of more acidic and metalrich water flowing from Cement and Mineral Creeks into the 

Animas River (Kimball and others, this volume, Chapter E9).

Similarity Among Animas River and Reference 

Tributary Sites

The composition of the macroinvertebrate communities 

in the Animas River when compared to reference tributaries 

utilizing Morisita’s and Percent Similarity Indices revealed 

similar trends to the number of taxa and evenness metrics. 

Similarity peaked upstream of Silverton with a decline at and 

downstream from Silverton, and a recovery of the community 

in the Animas River canyon. At the Hermosa Creek sites (site 7 

versus 7T) a decline in similarity occurred (fig. 9).

Discussion

The rate of recovery of the macroinvertebrate community 

after remediation depends on (1) the rate that water quality 

improves, (2) the rate that the benthos (stream substrate and 

associated organisms and detritus) recovers, and (3) the rate 

of recolonization by macroinvertebrates. Therefore, when and 

how often to conduct post-remediation sampling should depend 

on the rate that all the components (physical, chemical, and 

biological) of impaired segments recover after remediation. 

The processes by which these components recover operate 

along different spatial and temporal scales and may be specific 

to a particular location in the watershed.

Figure 3 (facing page). Number of taxa in the major stream 

Orders (stoneflies, mayflies, true flies, caddis flies, beetles, noninsects) for sample sites in Animas River upstream of tributaries 

(upper graph) and in tributaries (lower graph). Sample stations 

sorted from upstream (left) to downstream (right) on X-axis. 

Sample site with asterisk, reference site. 
Tributaries and subbasins

Animas mainstem

0

500

1,000

1,500

2,000

2,500

3,000

19 18 17 16 15 14 13 11 10 9 8 7 6 5 4 3 2 1

Other Stones Flies Mays Caddis Beetles

0

500

1,000

1,500

2,000

2,500

3,000

19T 18T 17T 20b 15T 21 20c 16T 13T 11T 10T 9T 7T 5T 2T

SITE NUMBER

NUMBER PER SQUARE METER NUMBER PER SQUARE METER

Figure 4. Densities (number of individuals per square meter) of taxa within major stream Orders (stoneflies, mayflies, true 

flies, caddis flies, beetles, non-insects) for sample sites within Animas River upstream of tributaries (upper graph) and within 

tributaries (lower graph).

862 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 863

The assumption is that water quality from remediation 

sites will improve almost immediately after remediation is 

completed, but how long it will take for the sediment quality (Church, Fey, and Unruh, this volume, Chapter E12) and 

the biological community to recover (Besser and others, this 

volume; Milhous, 1998) is unknown. The physical and chemical processes that may affect the recovery of the benthos are 

stream gradient, stream size, frequency and extent of floods, 

and changes in pH and background concentrations of metals 

in the water (Mast and others, this volume, Chapter E7).

Aluminum and iron have many common sources in 

the Cement and Mineral Creek basins (Bove and others, 

this volume), and the substrate of the Animas River has 

been significantly affected by aluminum and iron precipitates 

(Church, Fey, and Unruh, this volume; Kimball and others, 

this volume). These precipitates have coated rock surfaces 

and filled interstitial spaces, reducing the habitat available to 

macroinvertebrates (Parkhurst, 1999; Church, Fey, and Unruh, 

this volume; Milhous, this volume).

Parkhurst and others (1999) found significant relationships between invertebrate metrics and total aluminum, iron, 

and manganese concentrations, but found no such relationship 

with cadmium, copper, and zinc. Iron and aluminum were 

present primarily in the particulate phase, and manganese, 

cadmium, copper, and zinc were present primarily in dissolved 

forms. Their conclusion was that the physical effects of the 

precipitate, not the toxic effects of dissolved metals, were the 

primary reason for the suppression of the benthic macroinvertebrate community. Current research has found correlations 

between dissolved metals that are at or near toxic levels for 

fish and invertebrates, levels of these metals in tissues of fish 

and invertebrates and impacts on populations of trout and 

invertebrates (Besser and others, this volume; Besser and 

Brumbaugh, this volume; Besser and Leib, this volume).

A scenario may be hypothesized wherein the majority 

of sources of mining impacts are eliminated from the Animas 

River and the remaining metals affecting water quality and 

benthic habitat exist only in the benthos. The rate that these 

metals move through the river system and out of the benthos 

will be a function of the depth of contamination and the rate 

that metals are brought to the surface of the benthos. Floods 

will have a greater impact where the stream gradient is high 

and will tend to move metals to depositional areas (margins 

of the streams or pools) and farther down the Animas River 

where the gradient is lower. As metals move downstream, 

they become less available to erosion and their concentrations 

become more dilute.

Chemical processes that govern metal bioavailability of 

the benthos include changes in pH (from ground-water infiltration, surface water, and geology), amount of dissolved metal 

in surface water, and bioaccumulation of primary producers 

(Besser and Brumbaugh, this volume). An increase in the pH 

will reduce the potential for toxic metals to be dissolved from 

the benthos into the water column and will also increase the 

rate of precipitation of most metals, contributing to the toxicity 

of precipitates to benthic organisms (Church, Fey, and Unruh, 

this volume). Suspended precipitates, as colloids or flocculates, will work their way downstream and out of the watershed and are flushed out each year during high flow.

Biological processes may also significantly contribute to 

cleaning up the benthos. Studies have shown that macroinvertebrates can move large quantities of particulates downstream 

through their foraging behaviors (Wallace and Whiles, 1993). 

Therefore, as the macroinvertebrate community recovers 

through time, the rate that metals could move out of the watershed will increase by this mechanism alone. Biological processes will also produce more organic matter that tends to bind 

metals in less toxic, more innocuous or unavailable forms.

Because the adult stages of macroinvertebrates are 

winged and terrestrial, and larvae can easily drift downstream 

into impaired reaches from unimpaired or from less impaired 

reaches of the Animas River and its tributaries where there are 

more diverse communities of macroinvertebrates, colonization 

is most likely not a limiting factor to the rate of recovery of the 

macroinvertebrate community.

Proposed Sampling Plan and Analysis

Pre-Remediation Baseline Sampling

The overall concept of sampling upstream of major 

tributaries and utilizing the mouth of unimpaired tributaries for 

macroinvertebrate reference sites appeared to be adequate and 

sound, and has historical precedence (Clements and others, 

2000; Hughes and others, 1986). In any design of an evaluation of remediation practices, pre-remediation baseline sample 

sites should be located downstream from proposed remediation sites and upstream from significant changes in water or 

habitat quality. For economic reasons, the number of sample 

sites should be kept at a minimum as long as the accuracy and 

efficacy of the program are not compromised. Sample sites 

must be located in segments where, other than remediation, 

no anthropogenic changes occurred to the segments upstream 

from or between the sample stations. For this reason, stations 

downstream from Bakers Bridge should be eliminated from 

the analysis (sites 7–1, fig. 2) because they were subject to a 

variety of anthropogenic disturbances, including non-point 

pollution from erosion, agriculture, livestock, and septic tanks, 

as well as municipal discharge and gravel mining.

Pre-remediation baseline data should include data on 

water chemistry and benthic habitat. Such data will not only 

allow for assessments of particular remediation strategies 

and insight into the mechanisms and underlying processes of 

recovery (Adams and others, 2002), but will also help in decisions on when and where to conduct post-remediation sampling for biological indices.

Both physical accessibility and cost must be considered 

in a decision on which season to sample. High flow, low temperatures, and snow severely inhibit access and limit the efficiency and accuracy of sampling in the Animas River during 
Animas mainstem

0

100

200

300

400

500

600

19 18 17 16 15 14 13 11 10 9 8 7

Baetidae Acentrella Baetidae Baetis Ephemerellidae unknown

Ephemerellidae Drunella Ephemerellidae Ephemerella Heptageniidae Cinygmula

Heptageniidae Epeorus Heptageniidae Rhithrogena Heptageniidae unknown

Siphlonuriidae Ameletus Tricorythidae Tricorythodes

Tributaries and subbasins

0

100

200

300

400

500

600

700

800

900

19T 18T 17T 20b 15T 21 20c 16T 13T 11T 10T 9T 7T

NUMBER PER SQUARE METER NUMBER PER SQUARE METER

SITE NUMBER

864 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 865

Figure 5 (facing page). Densities of taxa within mayfly Order 

(Ephemeroptera) for stations within Animas River upstream of 

tributaries (upper graph) and within tributaries (lower graph).

winter, spring, and late fall. At high flow, difficulty of access is 

compounded by the high gradient in the Animas River canyon 

(Blair and others, 2002). In the spring, a small window opens 

between snowmelt and high flow. If this window is missed due 

to weather or some other circumstance such as accessibility, 

then biomonitoring for that season will not be accomplished. 

In the fall, the sampling window between the time that high 

flow has receded and the time of inhibiting snowfall is much 

larger. Therefore it is suggested that macroinvertebrate sampling be done in the fall. Sampling in the fall, during low flow, 

was and will be necessary for efficiency and consistency of 

results between the pre- and post-remediation sampling.

Post-Remediation Sampling

Post-remediation sampling is important to conduct during 

the same season that the pre-remediation data were gathered, 

and procedures for field sampling, sample processing, and 

taxonomic identification must be exactly the same. Given 

the scarcity of data on how benthic macroinvertebrate communities will react to mine-site remediation, sample processing should include at least a 300-count subsample, and taxa 

should be identified to the lowest possible level. Furthermore, 

if taxonomic unknowns are included in the data analysis, they 

must be systematically used in the same way throughout the 

study period and must be known to not fit into any of the other 

taxonomic classifications.

When and how soon post-remediation sampling occurs 

after remediation is completed must be decided based on when 

and where mine-site remediation occurs (which is governed by 

factors not related to testing the effectiveness of remediation) 

and by the effect that remediation has on water quality. Remediation in the Animas River watershed is currently underway 

and will continue in various amounts in various subbasins 

(William Simon, written commun., 2003). Robert Owens 

(Unpub. water quality and metal loading report, Colo. Dept. 

of Public Health and Environment, 1997) predicted that 

remediation must occur at several sites throughout each 

basin before appreciable reductions in metal loading will be 

detected. Walton-Day and others (this volume, Chapter E24) 

have shown that remediation in Cement Creek will have little 

difference in instream metal loads, but that remediation in 

the Animas River downstream from Eureka could result in 

lowering of toxic metal loads. Therefore, after an appreciable 

amount of remediation has taken place in the Animas River 

basin, the effects of this remediation should be detected in 

changes in the water chemistry, and post-remediation macroinvertebrate sampling should be conducted to demonstrate 

possible improvement in the macroinvertebrate community. 

After there has been remediation throughout the study area, 

post-remediation sampling should take place downstream 

from Silverton. This scenario implies that an adequate preremediation data set for water chemistry exists to detect 

changes in water chemistry (Unpub. report to Colorado Water 

Quality Control Commission, ARSG, 2001).

Statistical Analysis to Assess Effectiveness 

of Remediation

At least 3 years of pre- and post-remediation data is necessary to adequately assess the degree of annual variation of 

the invertebrate community and to determine if the difference 

between the post-remediation and the pre-remediation data is 

significant or is simply within the limits of annual variation 

(Chapman, 1999; O’Neill, 1999). If possible, a better strategy 

would be to sample annually while remediation procedures 

were implemented and sufficiently beyond the remediation 

period until the metrics reach some level of stability. Stations 

used to assess annual variation should include ones that vary 

in degree of impairment, from highly impaired to unimpaired. 

Unimpaired tributaries essentially have saturated macroinvertebrate communities and thus will not vary from year to year 

in the same manner that an impaired stream with only a few 

species will vary. Although not as accurate, year-to-year variation may be defined using historical data as long as the differences in sampling methods, sample processing, and taxonomic 

identification are defined.

Two types of analysis may be performed to evaluate 

the effectiveness of remediation. The analyses may be performed on a number of metrics, including richness, percent 

Ephemeroptera–Plecoptera–Trichoptera genera, percent 

Chironomidae individuals, Hilsenhoff Biotic Index (Plafkin 

and others, 1989), and others. In impaired tributaries where 

the number of stations was limited, it would be necessary to 

assess the effectiveness of remediation using only one sample 

site, a “Single Site Assessment.” Downstream from such a 

site where the tributary enters the Animas River, any changes 

to the tributary due to remediation would be masked by the 

influence of the water chemistry in the Animas River. At 

such sites, pre-remediation baseline means may be calculated 

from three uncomposited samples taken from an equal area of 

benthic habitat and statistically compared to post-remediation 

means. If a significant difference between the pre- and the 

post-remediation means is found, then the difference should 

be compared to and be greater than the annual variation in 

order to imply that the difference is attributable to remediation efforts. Annual variation may be determined by obtaining 

at least 3 years of pre-remediation data and 3 years of postremediation data. Instead of obtaining three uncomposited 

samples from an equal area of benthic habitat, a composited 

sample may be obtained and, from processing the whole sample and through rarefaction analysis (Hurlbert, 1971), means 

and variances may be calculated for each sample site and compared to post-remediation data (for example, ECOSIM, Gotelli 

and Entsminger, 2001).
Animas mainstem

0

100

200

300

400

500

600

19 18 17 16 15 14 13 11 10 9 8 7

Unknown Brachycentridae Brachycentrus Brachycentridae Micrasema

Glossosomatidae Glossosoma Helicophsychidae Helicopsyche Hydrophsychidae Arctopsyche

Hydrophsychidae Cheumatopsyche Hydrophsychidae Hydropsyche Hydroptilidae unknown

Hydroptilidae Hydroptila Lepidostomatidae Lepidostoma Leptoceridae Nectopsyche

Leptoceridae Oecetis Limnephilidae unknown Limnephilidae Ecclisomyia

Uenoidae Neophylax Uenoidae Oligophlebodes Rhyacophilidae Rhyacophila

Rhyacophilidae Neothremma

Tributaries and subbasins

0

20

40

60

80

100

120

19T 18T 17T 20b 15T 21 20c 16T 13T 11T 10T 9T 7T

SITE NUMBER

NUMBER PER SQUARE METER NUMBER PER SQUARE METER

Figure 6. Densities of taxa within caddis fly Order (Trichoptera) for stations within Animas River upstream of tributaries (upper 

graph) and within tributaries (lower graph).

866 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 867

Animas mainstem

0

10

20

30

40

50

60

70

80

90

19 18 17 16 15 14 13 11 10 9 8 7

Unknown Capniidae unknown Chloroperlidae unknown

Chloroperlidae Sweltsa Leuctridae unknown Nemouridae unknown

Nemouridae Zapada Perlidae unknown Perlidae Calineuria

Perlidae Hesperoperla Perlodidae unknown Perlodidae Isoperla

Perlodidae Megarcys Perlodidae Skwala Pteronarcyidae Pteronarcella

Pteronarcyidae Pteronarcys Taeniopterygidae unknown

Tributaries and subbasins

0

50

100

150

200

250

300

350

400

450

500

19T 18T 17T 20b 15T 21 20c 16T 13T 11T 10T 9T 7T

NUMBER PER SQUARE METER NUMBER PER SQUARE METER

SITE NUMBER

Figure 7. Densities of taxa within stonefly Order (Plecoptera) for stations within Animas River upstream of tributaries (upper 

graph) and within tributaries (lower graph).
Animas mainstem

0

50

100

150

200

250

300

19 18 17 16 15 14 13 11 10 9 8 7

Unknown Athericidae Atherix Blephariceridae Bibiocephala

Ceratopogonidae unknown Ceratopogonidae Bezzia Ceratopogonidae Probezzia

Empididae unknown Empididae Chelifera Empididae Clinocera

Empididae Hemerodromia Empididae Oreogeton Empididae Limnophora

Empididae Pericoma Empididae Psychoda Simulidae unknown

Simulidae Prosimulium Simulidae Simulium Tipulidae unknown

Tipulidae Rhabdomastix Tipulidae Antocha Tipulidae Dicranota

Tipulidae Hexatoma Tipulidae Tipula Chironomidae unknown

Chironomidae Chironominae Chironomidae Orthocladiinae Chironomidae Tanypodinae

Tributaries and subbasins

0

100

200

300

400

500

600

19T 18T 17T 20b 15T 21 20c 16T 13T 11T 10T 9T 7T

NUMBER PER SQUARE METER NUMBER PER SQUARE METER

SITE NUMBER

Figure 8. Densities of taxa within true fly Order (Diptera) for stations within Animas River upstream of tributaries (upper graph) 

and within tributaries (lower graph).

868 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 869

An example where a Single Site Assessment is appropriate 

is on Mineral Creek upstream from South Fork Mineral Creek 

(site 20a, fig. 1). South Fork Mineral Creek is similar in size 

to Mineral Creek, and 3.5 miles downstream, Mineral Creek 

drains into the Animas River. Any assessment of remediation 

that occurred in the Mineral Creek drainage at a site downstream from the confluence with South Fork Mineral Creek 

would be masked by the influence of the quantity and quality 

of water from South Fork Mineral Creek. The annual variation 

may be estimated from fall 1992 data collected by the Colorado 

Department of Public Health and Environment and the fall 1996 

and 1997 data collected for this study. The range is from a low 

of 2 taxa in 1992 to a high of 12 taxa in 1997. To assume that 

mine-site remediation has improved the diversity and evenness 

of the macroinvertebrate communities, 3 years of consecutive, 

fall, post-remediation data collected at the same sample sites 

must be statistically different from the pre-remediation data and 

the annual variation. For a Single Site Assessment, the statistical test to determine the effectiveness of mine-site remediation 

is a t-test, thus the necessity of at least three samples.

In the Animas River, where at least three sample sites 

were available to establish pre-remediation data and where 

(1) the tributaries or the Animas River between the stations 

will not have any type of anthropogenic interference other than 

Figure 9. Morisita’s Index of similarity (Cλ) and Percent Similarity between upstream sites in Animas River and associated 

reference tributaries (north is at left, that is, upstream). Mileages coordinated with sites in tables 1 and 2.

5

10

15

20

25

30

35

40

75 70 65 60 55 50 45 40 35

NUMBER OF TAXA

1992 1996 1997

RIVER MILE

Table 2. Pre-remediation baseline data for the Animas River canyon.

[Total number of taxa for macroinvertebrates per square meter by year from upstream of Mineral Creek downstream to Bakers Bridge; distance given in river 

miles upstream from confluence of Animas River with San Juan River, N. Mex.; --, no data]

Sample site Distance

(mi) 1992 1996 1997

Downstream from Bakers Bridge 43.3 -- 30 30

Upstream from Cascade Creek 54.7 15 20 16

Upstream from Needle Creek 61.0 -- 18 12

Upstream from Elk Creek 67.4 13 18 15

Upstream from Deer Park Creek 71.7 -- 5 11

Upstream from Kendall Gulch 72.0 9 -- 12

Upstream from Mineral Creek 73.0 -- 7 7

Regression equation y = –0.3027 ln(x)

+ 31.968

y = –41.10 ln(x)

+ 185.64

y = –24.803 ln(x)

+ 118.24

R2

 value R2 = 0.8248 R2 = 0.8371 R2 = 0.6003
remediation occurring between the time the pre-remediation 

data were collected and the time the post-remediation sampling 

was conducted or (2) a regression line can be fitted to the data 

such that the R 2

 value is not unreasonably high, the effectiveness of remediation may be evaluated using multiple sample 

sites on the Animas River, a “Multiple Site Assessment.” At 

such sample sites, samples may be composited. Examples 

within the Animas River where a Multiple Site Assessment 

may be utilized are in the reach from Eureka Gulch to Boulder 

Gulch (sites 19–17, fig. 1), from Boulder Gulch to Cement 

Creek (sites 17–16, fig. 1), and from Mineral Creek to Bakers 

Bridge (sites 15–8, figs. 1 and 2). Regression lines fitted to the 

pre-remediation data may be compared to post-remediation 

regressions using an analysis such as ANOVA. If a significant difference between the pre- and the post-remediation 

data is found, then the difference must be compared to and 

be greater than the annual variation to imply that the difference is attributable to remediation efforts. For example, in 

the reach from the confluence with Mineral Creek to Bakers 

Bridge (sites 15–8, figs. 1 and 2), regression analysis of the 

data may be fitted to 3 years of pre-remediation data: 1992 

data collected by the Colorado Department of Public Health 

0

10

20

30

40

50

60

70

18 17 13 11 10 9 7

SITE NUMBER

PERCENT SIMILARITY

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

MORISITA'S SIMILARITY INDEX

Percent similarity Morisita's C

Figure 10. Pre-remediation baseline data for a Multiple Site Assessment. Variation of taxa richness within the Animas 

River canyon downstream from Silverton to the upstream from Hermosa Creek site for fall 1992 data collected by Colorado 

Department of Public Health; fall 1996 and fall 1997 data collected by USDA Forest Service, San Juan National Forest, and 

Animas River Stakeholders Group. Three years of consecutive, fall, post-remediation data collected at the same sample sites 

must be statistically different from the pre-remediation data to imply that mine-site remediation has improved diversity of 

macroinvertebrate communities. Variable for Y-axis may include any appropriate population metric.

and Environment and the fall 1996 and 1997 data collected 

for this study (table 2 and fig. 10). To assume that mine-site 

remediation has improved the diversity and evenness of the 

macroinvertebrate communities, 3 years of consecutive, fall, 

post-remediation data collected at the same sample sites must 

be statistically greater than the pre-remediation data. If no 

significant difference is observed between the pre-remediation 

data and the post-remediation data, then either further remediation is required or more time for recovery of the benthos or 

colonization by macroinvertebrates is necessary before more 

post-remediation data are collected. In statistical assessment 

of the effectiveness of remediation, critical statistical values, 

α and β, do not necessarily have to be at the generally accepted 

0.05 and 0.20 but may rather be set by the regulatory process 

and may be more or less stringent (Fleiss, 1981).

For either of these scenarios, composited samples 

should be taken from unimpaired streams to determine the 

degree that impaired communities are becoming more similar 

to unimpaired communities (fig. 10). Unimpaired streams 

are assumed to have healthy macroinvertebrate communities 

and thus accurately represent the goal of stream remediation.

870 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Monitoring Benthic Invertebrate Communities 871

Summary

The primary objectives of establishing pre-remediation 

baseline data were achieved by our obtaining multiple 

uncomposited samples for three sampling dates: fall 1996, 

spring 1997, and fall 1997, from 25 impaired sites in the 

Animas River watershed study area and beyond (figs. 1 and 

2). These samples will allow for a statistical analysis to postremediation data. Multiple, uncomposited samples from 11 reference streams in the watershed were also collected (table 1). 

Specimens have been archived at the USDA Forest Service, 

San Juan National Forest laboratory, and identifications may 

be validated for comparison to post-remediation data. Methods were proposed to evaluate the effectiveness of mine-site 

remediation and to decide when and where to conduct postremediation sampling. The greatest limitation to the use of 

this data set in assessing the success of remediation will be the 

lack of information on temporal variation. A long-term, annual 

sampling program at a variety of sites with differing degrees of 

impairment will be important to an assessment of the effectiveness of future mine-site remediation (Chapman, 1999).

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Smith, J.G., and Stewart, A.J., 2002, Assessing recovery 

in a stream ecosystem—Applying multiple chemical 

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Barbour, M.T., Diamond, J.M., and Yoder, C.O., 1996, Biological assessment strategies—Applications and limitations, in

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Barbour, M.T., and Gerritsen, J., 1996, Subsampling of 

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Blair, R.W., Jr., Yager, D.B., and Church, S.E., 2002, Surficial 

geologic maps along the riparian zone of the Animas River 

and its headwater tributaries, Silverton to Durango, Colorado, with upper Animas River watershed gradient profiles: 

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Buxton, H.T., Nimick, D.A., von Guerard, Paul, Church, S.E., 

Frazier, Ann, Gray, J.R., Lipin, B.R., Marsh, S.P., Woodward, 

Daniel, Kimball, Briant, Finger, Susan, Ischinger, Lee, 

Fordham, J.C., Power, M.S., Bunck, Christine, and Jones, 

J.W., 1997, A science-based, watershed strategy to support 

effective remediation of abandoned mine lands: Proceedings 

of the Fourth International Conference on Acid Rock Drainage, Vancouver, B.C., May 31–June 6, 1997, p. 1869–1880.

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872 Environmental Effects of Historical Mining, Animas River Watershed, Colorado