U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5038

Prepared in cooperation with the National Park Service and Amistad National Recreation Area

Water Quality and the Composition of Fish and 

Macroinvertebrate Communities in the Devils and 

Pecos Rivers In and Upstream from the Amistad 

National Recreation Area, Texas, 2005–7
Cover Left. Dolan Falls on the Devils River, Texas.

Cover Right. Photo was taken where the International Boundary and Water Commission (IBWC) gaging station near Langtry is located. The 

wier dam where the gage sensor is located is in the picture.
Water Quality and the Composition of Fish 

and Macroinvertebrate Communities in the 

Devils and Pecos Rivers In and Upstream 

from the Amistad National Recreation 

Area, Texas, 2005–7

By J. Bruce Moring

Prepared in cooperation with the National Park Service and Amistad 

National Recreation Area

Scientific Investigations Report 2012–5038

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: 2012

This and other USGS information products are available at http://store.usgs.gov/

U.S. Geological Survey

Box 25286, Denver Federal Center

Denver, CO 80225

To learn about the USGS and its information products visit http://www.usgs.gov/

1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

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:

Moring, J.B., 2012, Water quality and the composition of fish and macroinvertebrate communities in the Devils and 

Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2005-7: U.S. Geological Survey 

Scientific Investigations Report 2012–5038, 70 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

Purpose and Scope .............................................................................................................................4

Description of Study Area ...................................................................................................................4

Methods of Investigation..............................................................................................................................5

Collection and Analysis of Water-Quality Samples.........................................................................6

Collection and Processing of Fish and Macroinvertebrate Samples ..........................................7

Fish Community Surveys and Processing of Samples....................................................................8

Macroinvertebrate Community Surveys and Processing of Samples.........................................8

Quality Control.......................................................................................................................................8

Water Quality in the Devils and Pecos Rivers ......................................................................................30

Total Dissolved Solids ........................................................................................................................30

Chloride.................................................................................................................................................30

Sulfate ..................................................................................................................................................30

Ammonia Plus Organic Nitrogen......................................................................................................30

Nitrate Plus Nitrite Nitrogen .............................................................................................................33

Orthophosphate and Total Phosphorus...........................................................................................33

Selenium...............................................................................................................................................33

Pesticides.............................................................................................................................................33

Composition of Fish and Macroinvertebrate Communities in the 

Devils and Pecos Rivers ......................................................................................................33

Fish Communities................................................................................................................................34

Devils River.................................................................................................................................34

Pecos River.................................................................................................................................34

Comparison between the Devils and Pecos Rivers ...................................................34

Macroinvertebrate Communities .....................................................................................................42

Summary .......................................................................................................................................................63

References....................................................................................................................................................67

Appendix 1. Laboratory recovery of surrogate compounds from four sets analyzed 

concurrently with water-quality samples from U.S. Geological Survey stations 

08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 

Pecos River near Langtry, Tex., in the Amistad National Recreation Area, 2005 ................70
iv

Figures

1. Map showing location of study area .......................................................................................3

2. Graph showing assessment of similarities among fish communities 

determined by using Non-metric Multi-Dimensional Scaling (first and 

second dimensions) for fish collected in 2006-7 at the Devils and Pecos 

Rivers sites in and upstream from the Amistad National Recreation 

Area, Texas ..................................................................................................................................43

3. Graph showing assessment of similarities among macroinvertebrate 

communities determined by using Non-metric Multi-Dimensional Scaling 

(first and second dimensions) for aquatic insects collected in 2006 from 

sampling sites on the Devils and Pecos Rivers in and upstream from the 

Amistad National Recreation Area, Texas ............................................................................64

Tables

1. Sample-collection sites on the Devils and Pecos Rivers in and upstream 

from the Amistad National Recreation Area, Texas, 2005–07 ...............................................6

2. Concentrations of total dissolved solids, selected major ions, and nutrients 

in water-quality samples collected at U.S. Geological Survey stations 

08449400 Devils River at Pafford Crossing near Comstock, Texas, and 

08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation 

Area, Tex., 2005............................................................................................................................10

3. Concentrations of trace metals in water-quality samples collected at 

U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing 

near Comstock, Texas and 08447410 Pecos River near Langtry, Tex., in the 

Amistad National Recreation Area, Tex., 2005.......................................................................12

4. Concentrations of organic carbon and pesticides in water-quality samples 

collected at U.S. Geological Survey stations 08449400 Devils River at Pafford 

Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., 

in the Amistad National Recreation Area, Tex., 2005 ...........................................................14

5. Concentrations of selected major ions and nutrients measured in water-quality 

samples collected in 2005 at U.S. Geological Survey stations 08449400 Devils 

River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near 

Langtry, Tex., in the Amistad National Recreation Area, with summary statistics 

from samples collected at station 08449400 during 1978–1995 as part of the U.S. 

Geological Survey Hydrologic Benchmark Network (U.S. Geological Survey, 2011), 

and summary statistics from samples collected at station 08447410 during 

1974–2007 as part of U.S. Geological Survey National Stream Quality Accounting 

Network (U.S. Geological Survey, 2010)..................................................................................31
v

6. Presence or absence of fish taxa and total number of fish species collected 

from sites on the Devils and Pecos Rivers in and upstream from the Amistad 

National Recreation Area, Texas, 2006–7...............................................................................35

7. Fish species, number of individual specimens, native status, trophic group, 

tolerance classification, and total number of species collected from the study 

sites along the Devils River in and upstream from the Amistad National 

Recreation Area, Texas, 2006–7 ...............................................................................................36

8. Fish species, number of individual specimens, native status, trophic group, 

tolerance classification, and total number of species collected from the study 

sites along the Pecos River in and upstream from the Amistad National 

Recreation Area, Texas, 2006–7 ...............................................................................................39

9. Number of fish species, selected fish community metrics, and the total 

number of fish collected from the study sites along the Devils and Pecos Rivers 

in and upstream from the Amistad National Recreation Area, Texas, 2006–7 .................42

10. Presence or absence of macroinvertebrate taxa and total number of taxa 

collected from the study sites along the Devils and Pecos Rivers in and 

upstream from the Amistad National Recreation Area, Texas, 2006 .................................45

11. Summary of taxonomic classification and counts of individuals by 

macroinvertebrate taxon collected from the Devils River study sites in and 

upsteam from the Amistad National Recreation Area, Texas, 2006...................................49

12. Summary of taxonomic classification and counts of individuals by 

macroinvertebrate taxon collected from the Pecos River study sites in 

and upstream of the Amistad National Recreation Area, Texas, 2006 ..............................55

13. Selected macroinvertebrae community metrics and indexes from the 

collection of qualitative multihabitat samples at the study sites along the Devils 

and Pecos Rivers in and upstream from the Amistad National Recreation Area, 

Texas, 2006...................................................................................................................................61
vi

Conversion Factors, Acronyms, Abbreviations, and Datum

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

centimeter per year (cm/yr) 0.3937 inch (in/yr)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

square kilometer (km2

) 0.3861 square mile (mi2)

liter per second (L/s) 15.85 gallon per minute (gal/min) 

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

(NAVD 88). 

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

Acronyms

ANRA Amistad National Recreation Area

LRL Laboratory reporting level

NASQAN National Stream Quality Accounting Network

NMDS Non-metric Muldimensional Scaling

NPS National Park Service

TDS Total dissolved solids

USGS U.S. Geological Survey

Abbreviations

mg/kg milligram per kilogram

mg/L milligram per liter

μg/L microgram per liter
Water Quality and the Composition of Fish and 

Macroinvertebrate Communities in the Devils and 

Pecos Rivers In and Upstream from the Amistad 

National Recreation Area, Texas, 2005–7 

By J. Bruce Moring

Abstract 

To gain a better understanding of the water quality and 

status of fish and macroinvertebrate communities, the U.S. 

Geological Survey, in cooperation with the National Park 

Service and Amistad National Recreation Area, completed 

a reconnaissance-level survey of the water quality and fish 

and macroinvertebrate communities in the Devils and Pecos 

Rivers in and upstream from the Amistad National Recreation 

Area in southwest Texas during 2005–7. Water-quality 

conditions during the spring and summer months of 2005 in 

the Devils and Pecos Rivers were assessed at locations just 

upstream from the Amistad National Recreation Area, and 

the composition of fish and macroinvertebrate communities 

were assessed during 2006 and 2007 in and upstream from 

the Amistad National Recreation Area and Amistad Reservoir. 

Water-quality samples were collected at one site on both 

the Devils and Pecos Rivers. Fish and macroinvertebrates 

were collected at the water-quality sampling site on each 

river and at three additional sites on each river. The waterquality constituents of primary concern were total dissolved 

solids, chloride, sulfate, ammonia plus organic nitrogen, 

nitrate plus nitrite, orthophosphate, phosphorus, selenium, 

and selected pesticides. During the spring and summer of 

2005, the concentrations of total dissolved solids ranged from 

208 to 232 milligrams per liter (mg/L) in samples from the 

Devils River compared to 1,460 to 2,390 mg/L in samples 

from the Pecos River. Total dissolved solid concentrations 

measured in samples collected from the Devils River and 

Pecos River did not exceed the proposed State of Texas 

water-quality standard applicable for the segments of each 

river where samples were collected. During the spring and 

summer of 2005, chloride concentrations measured in samples 

collected in 2005 from the Devils River ranged from 11.6 to 

12.9 mg/L, compared to chloride concentrations measured 

in samples collected from the Pecos River, which ranged 

from 519 to 879 mg/L. Chloride concentrations in samples 

collected from the Devils River in 2005 were less than the 

lower quartile (25th percentile) value of 14.0 mg/L reported 

for chloride concentrations in water-quality samples collected 

at the same sampling location during 1978–95 by the U.S. 

Geological Survey as part of the Hydrologic Benchmark 

Network program. The chloride concentrations measured in 

samples collected from the Pecos River during the spring 

and summer of 2005 represented a range of values similar 

to the interquartile range of 548 to 942 mg/L reported for 

samples collected during 1974–2007 at the same sampling 

location by the U.S. Geological Survey as part of the National 

Stream Quality Accounting Network program. None of the 

chloride concentrations measured in samples collected from 

the Devils or Pecos Rivers in 2005 exceeded applicable 

proposed State of Texas water-quality standards for chloride. 

Sulfate concentrations ranged from 7.55 to 8.20 mg/L in 

samples from the Devils River compared to 298 to 503 mg/L 

in samples from the Pecos River. Concentrations of sulfate did 

not exceed applicable proposed State of Texas water-quality 

standards. Ammonia plus organic nitrogen concentrations 

were reported as nitrogen ranged from 0.12 to 0.14 mg/L of 

nitrogen in samples collected from the Devils River compared 

to 0.15 to 0.32 mg/L of nitrogen in samples collected from the 

Pecos River. Ammonia plus organic nitrogen concentrations 

measured in samples collected from the Devils River in 

2005 were less than the lower quartile (25th percentile) 

value of 0.23 mg/L of nitrogen for concentrations in waterquality samples collected at the same sampling location 

during 1978–95 by the U.S. Geological Survey as part of 

the Hydrologic Benchmark Network program. Ammonia 

plus nitrogen concentrations measured in samples collected 

from the Pecos River were similar to the range of historical 

concentrations measured in samples collected from the same 

Pecos River sampling location by the U.S. Geological Survey 

National Stream Quality Accounting Network program. 

Nitrate plus nitrite concentrations in samples from the Devils 

River and Pecos Rivers were within the historical range of 

concentrations for samples collected at the same locations 

on each river. Total phosphorous and orthophosphate 
2 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

concentrations were less than the laboratory reporting levels 

in the water samples from the Devils and Pecos Rivers. None 

of the selenium concentrations measured in samples collected 

during the spring and summer of 2005 from the Devils or 

Pecos Rivers exceeded the Texas Surface Water Quality 

Standards (chronic criterion of 5 μg/L or the acute criterion of 

20 μg/L) established by the State for the protection of aquatic 

life. Concentrations of pesticides in the samples collected from 

the Devils and Pecos Rivers during March–August 2005 were 

very low and not present in detectable amounts (all reported 

concentrations were below laboratory reporting levels). 

The total number of fish species collected was the 

same in the Devils River and Pecos River, but the species 

found in the two rivers varied slightly. The number of fish 

species generally increased from the site farthest upstream 

to the site farthest downstream in the Devils River, and 

decreased between the site farthest upstream and site farthest 

downstream in the Pecos River. The redbreast sunfish was 

the most abundant species collected in the Devils River, and 

the blacktail shiner was the most abundant species collected 

in the Pecos River. Comparing the species from each river, 

the percentage of omnivorous fish species was larger at the 

more downstream sites closer to Amistad Reservoir, and the 

percentage of species tolerant of environmental stressors was 

larger in the Pecos River. The fish community, assessed on 

the basis of the number of shared species among the sites 

sampled, was more similar to the fish community at the other 

sites on the same river than it was to the fish community from 

any other site in the other river. More macroinvertebrate taxa 

were collected in the Devils River than in the Pecos River. 

The largest number of macroinvertebrate taxa were from the 

site second farthest downstream on the Devils River, and the 

smallest numbers of macroinvertebrate taxa were from the 

farthest downstream site on the Pecos River. Mayflies were 

more common in the Devils River, and caddisflies were less 

common than mayflies at most sites. Net-spinning caddisflies 

were more common at the Devils River sites. The combined 

percent of mayfly, caddisfly, and stonefly taxa was generally 

larger at the Pecos River sites. Riffle beetles were the most 

commonly collected beetle taxon among all sites, and waterpenny beetles were only collected at the Pecos River sites. 

A greater number of true midge taxa were collected more 

than any other taxa at the genus and species taxonomic level. 

Non-insect macroinvertebrate taxa were more common at the 

Devils River sites. Corbicula sp. (presumably the introduced 

Asian clam) was found at sites in both rivers, and amphipods 

were more abundant in the Devils River. The Margalef 

species richness index, based on aquatic insect taxa only, was 

larger at the Devils River sites than at the Pecos River sites. 

The Hilsenhoff’s biotic index was largest at the site farthest 

downstream in the Devils River and smallest at the site second 

farthest downstream in the Pecos River. Overall similarity 

among sites based on the number of shared macroinvertebrate 

taxa indicated that each site is more similar to other sites on 

the same river than to sites on the other river. 

Introduction

A treaty between the United States and Mexico in 

1944 authorized the construction of the Amistad Dam on the 

Rio Grande downstream from where the Devils and Pecos 

Rivers flowed into the Rio Grande in Texas (Purchase and 

others, 2001). The Amistad Dam was completed in 1969 

and impounded the Rio Grande, Devils River, and Pecos 

Rivers; at the conservation pool elevation of 1,117 ft (about 

340 m) above the North American Vertical Datum of 1988 

(NAVD 88), the surface area of the reservoir is 65,000 acres 

(about 26,300 hectares) (International Boundary and Water 

Commission, 2011).

The Amistad National Recreation Area was established 

in and near the Amistad Reservoir in November 1990 to 

“provide for outdoor recreational use and to protect the scenic, 

natural, and cultural values of the lands and waters” (Purchase 

and others, 2001). Surface-water resources (impounded 

and flowing) in the Amistad National Recreation Area are 

primarily derived from the Rio Grande, Devils River, and 

Pecos River (fig. 1). The Devils and Pecos Rivers in the 

Amistad National Recreation Area, and the adjacent riparian 

habitat they provide (together referred to as the Devils 

and Pecos River corridors), are important to the National 

Park Service (NPS) in part because of the aquatic life they 

support. The development in 2000 of an international fisheries 

management plan for the Amistad Reservoir and surrounding 

areas (including the Amistad National Recreation Area ) by 

the Secretariat of the Environment, Natural Resources, and 

Fisheries of Mexico; NPS; and Texas Parks and Wildlife 

Department underscored the importance of aquatic life 

(Purchase and others, 2001).

When the Amistad Reservoir reached its conservation 

pool elevation for the first time in 1970, many species of 

fish native to the Rio Grande and its major tributaries (the 

Devils and Pecos Rivers) disappeared from the impounded 

sections of these rivers (Brune, 1981). The Amistad gambusia 

(Gambusia amistadensis) was extirpated from its only known 

habitat when Goodenough Springs, historically the third 

largest spring in Texas with an annual mean discharge of 3,900 

liters per second, was inundated when Amistad Reservoir 

reached conservation pool for the first time (Brune, 1981). 

Of the 65 native species of fish historically documented in 

what is now (2011) the Amistad National Recreation Area, 

16 species might have been locally extirpated because of the 

environmental changes resulting from the impoundment of the 

Rio Grande and its major tributaries by the Amistad Reservoir 

(Lobello, 1976). Many of these native fish species are 

rheophilious or “flow-loving” species of the family Cyprinidae 

(minnows) and are dependent upon flowing sections of a river 

and might not survive in the impounded reservoir waters. For 

example, the Devils River minnow (Dionda diaboli), found in 

the Devils River in and near the Amistad National Recreation 

Area, is federally listed as a threatened species, and the 

blotched gambusia (Gambusia senilis) has not been confirmed 

in the Devils River section of the Amistad National Recreation 
Introduction 3

Satan

Canyon

Dolan

Falls

Turkey Bluff

Canyon

Shumla 

Bend

Rio Grande

Pecos

River

Devils

River

Langtry

Creek

Big

Fielder

Draw

Howards Creek

Oppenheimer Canyon

Lewis Canyon

Deadmans Canyon

Cow

Evans Creek

Red Bluff Creek

West Fork

East Fork Sycamore Creek

Pinto

Creek

Elm

Creek

Dolan Creek

Johnson Draw

Devils River

Buckley

Creek

Buffalo Draw

Dry

Devils River

Big

Canyon

Meyers Canyon

Th urston Canyon Lozier Canyon

Amistad 

Reservoir

Rio

Grande

Creek

Sycamore Creek

Everett 

Canyon

D1

D2

D3

D4

P1

P2

P3

P4

08447410

08449400

VAL VERDE COUNTY

TERRELL COUNTY

CROCKETT COUNTY SUTTON COUNTY EDWARDS COUNTY

K

NI NEY CO

UNTY

Del Rio

Comstock

Pandale

Langtry

2309

2310

102°00’ 101°30' 101°00’ 100°30'

30°00’

29°30'

Big Satan

Creek

Amistad 

Dam

NEW 

MEXICO

TEXAS

Pecos River Basin

Devils River Basin

Location map

Study 

area

0 15 30 MILES

Base modified from U.S. Geological Survey digital data, 0 15 30 KILOMETERS

Rivers, counties, shaded relief, and populated places from 

The National Atlas of the United States

Texas Centric Mapping System—Albers Equal Area

projection, North American Datum of 1983

Elevation for the boundary of 

Amistad National Recreation Area

is 348.7 meters above the North American

Vertical Datum of 1988.

Amistad

Reservoir

Amistad National Recreation 

Area in green with a yellow 1 

kilometer buffer to show

geographic extent.

EXPLANATION

Amistad National Recreation Area

Level III Ecoregions (U.S. Environmental Protection Agency, 2011)

 Chihuahuan Deserts

 Edwards Plateau

 Southern Texas Plains

International boundary

Stream (United States only)

Intermittent stream (United States only)

Texas Commission on Environmental Quality stream segment and number

Fish and macroinvertebrate sampling site — see table 1

U.S. Geological Survey streamflow-gaging station where water-quality samples were collected

D1

2309

08447410

Figure 1. Location of study area. 
4 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Area since the reservoir filled in 1970 (Hubbs and others, 

1991). The Proserpine shiner (Cyprinella proserpina), listed 

as a species of concern (U.S. Fish and Wildlife Service, 1999), 

was confirmed as occurring upstream from the reservoir 

inundation zone on the Devils River (Lobello, 1976) after 

impoundment of the Amistad Reservoir in 1969, but has not 

been observed downstream from the reservoir. 

In addition to the extirpation of some native fish species, 

the proliferation of non-native species is a cause for concern 

for several reasons. Non-native species can degrade the fish 

community by feeding on native fishes and competing with 

them for food and habitat. Non-native species can interbreed 

with closely related native species, and if the non-native 

species is at a selective advantage, the population will 

gradually be phenotypically and genotypically dominated by 

a “pure” non-native species (Moyle and Cech, 1982). Some 

non-native fish species common in the lower Devils River near 

Amistad Reservoir include blue tilapia, smallmouth bass, and 

common carp (Linam and Kleinsasser, 2002). Blue tilapia and 

common carp also inhabit the lower Pecos River (Linam and 

Kleinsasser, 1996). 

Little is known about the status of fish and 

macroinvertebrate communities of the Devils and Pecos 

Rivers in the Amistad National Recreation Area, primarily 

because previous studies focused mostly on the status 

of fish and macroinvertebrates in the Rio Grande in this 

region (International Boundary and Water Commission, 

1994). In this report the term macroinvertebrates refers 

to aquatic insects (macroinvertebrates that have six legs; 

the adults also have wings and antennae) along with other 

macroinvertebrates such as freshwater worms, snails, mites, 

and crayfish. Macroinvertebrates are large enough to be seen 

without the aid of a dissecting scope or hand lens (Pacific 

Northwest Region Water Quality Program, 2011). To gain 

a better understanding of the water quality and the status of 

fish and macroinvertebrate communities, the U.S. Geological 

Survey (USGS), in cooperation with the NPS and the Amistad 

National Recreation Area, completed a reconnaissance-level 

survey of selected water-quality constituents and aquatic biota 

(fish and macroinvertebrates) in the Devils and Pecos Rivers 

in and upstream from the Amistad National Recreation Area 

during 2005–7. The water quality and aquatic biota of the 

Devils River were of primary interest to the USGS and NPS 

because the species of greatest concern (Devils river minnow) 

is unique to this river, and because the Devils River has 

historically been less affected by human activities compared to 

the Pecos River.

Purpose and Scope 

This report presents the results of a reconnaissancelevel survey to characterize the concentrations of selected 

water-quality constituents and the composition of fish and 

macroinvertebrate communities at sites on the Devils and 

Pecos Rivers in and upstream from the Amistad National 

Recreation Area in southwestern Texas by using water-quality 

data collected in 2005, and fish and macroinvertebrate data 

collected during 2006–7. 

Comparisons are made between water-quality data 

collected in 2005 and water-quality data collected at the same 

sites from 1974 through 2007 as part of either the USGS 

Hydrologic Benchmark Network (HBN) program or the 

National Stream Quality Accounting Network (NASQAN) 

program. Concentrations of selected water-quality constituents 

from the two sites sampled in 2005 are also compared 

to State of Texas water-quality criteria. Finally, fish and 

macroinvertebrate communities sampled along the Devils and 

Pecos Rivers in and upstream from the Amistad National 

Recreation Area during 2006–7 are compared by using various 

biological metrics and a nonparametric multivariate statistical 

analysis, Non-metric Multidimensional Scaling (NMDS). 

Description of Study Area

Upstream from the Amistad Reservoir in southwestern 

Texas, the Devils and Pecos Rivers are perennial streams 

with base flows that are sustained by groundwater discharges 

(Purchase and others, 2001). Segments of these rivers are in 

the Amistad National Recreation Area, which includes 15 

kilometers (km) of the Devils River and 24 km of the Pecos 

River when the Amistad Reservoir is at conservation pool 

(fig. 1). The lengths of flowing sections of the Pecos River 

and Devils River change in the Amistad National Recreation 

Area depending on the surface-water elevation of Amistad 

Reservoir. When the water-surface elevations in the reservoir 

are relatively low, the Devils River in the Amistad National 

Recreation Area can be as much as 16 km long and the Pecos 

River as much as 32 km long (Purchase and others, 2001). 

The sampling sites on the Devils River were established in 

river segment 2309; those on the Pecos River were established 

in river segment 2310 (fig.1). Segments 2309 and 2310 

of the Devils and Pecos Rivers, respectively, have been 

assigned State water-quality standards (Texas Commission 

on Environmental Quality, 2010) by the Texas Commission 

on Environmental Quality for many of the water-quality 

constituents discussed in this report.

The Devils River basin is sparsely populated; land 

use is dominated by ranching, and relatively large nutrient 

concentrations in the Devils River are the primary waterquality concern (Mast and Turk, 1999). The relatively large 

nutrient concentrations noted in previous investigations of the 

Devils River are surprising because the watershed is sparsely 

populated and the ranches are not heavily grazed; no evidence 

of upward trends in atmospheric deposition or land-use 
Methods of Investigation 5

related sources was identified that might have explained the 

relatively large nutrient concentrations (Mast and Turk, 1999). 

Ecological concerns for aquatic biota in the Devils River 

include the extirpation (local extinction) of native aquatic 

species after completion of the Amistad Reservoir Dam, 

the effects of nutrient enrichment on aquatic biota, and the 

influence of changes in reservoir elevation on riparian habitat 

for native species (Purchase and others, 2001). 

For the part of the Pecos River basin in Texas (fig. 1), 

rangeland is the predominant land use (Thompson, 2008). 

About 73,000 acres (about 30,000 hectares) (Jensen and 

others, 2006) of the Pecos River basin in Texas are irrigated 

croplands dominated by cotton, small grains, and sorghum; oil 

and natural gas production is the largest industry (Thompson, 

2008). Water-quality and biological concerns in the Pecos 

River within the Amistad National Recreation Area have 

historically been related to increasing salinity concentrations, 

increasing loads of suspended sediment, discharge of waste 

waters from oil and gas production, and agricultural runoff and 

irrigation return flows in the contributing watershed (Linam 

and Kleinsasser, 1996; Purchase and others, 2001). 

The climate of the study area is semi-arid, with an 

average rainfall of about 43 to 46 centimeters per year and 

maximum daily temperatures that range from 18 degrees 

Celsius (°C) in the winter to 36 °C in the summer (National 

Park Service, 2010). The Amistad National Recreation Area 

is in an ecological transition zone between the southern Texas 

Plains, Chihuahuan Desert, and Edwards Plateau ecoregions, 

which enhances biodiversity in the Amistad National 

Recreation Area, particularly for plant species (National Park 

Service, 2010). Riparian zones of the Devils River in the 

Amistad National Recreation Area include native plants such 

as pecan (Carya sp.), live oak (Quercus sp.), and sycamore 

(Platanus sp.). Sections of the riparian zone adjacent to the 

Pecos River in the Amistad National Recreation Area are 

dominated by tamarisk (Tamarix sp.), an exotic invasive plant 

referred to locally as salt cedar (National Park Service, 2010). 

Methods of Investigation

One water-quality sampling site and four fish and 

macroinvertebrate sampling sites were established on both 

the Devils and Pecos Rivers (table 1). Water-quality samples 

were collected in 2005 and fish and macroinvertebrates 

were collected during 2006–7. The water-quality data were 

collected at two streamflow-gaging stations in the Amistad 

National Recreation Area operated by the International 

Boundary and Water Commission (IBWC) and identified 

with USGS station numbers and names in the USGS National 

Water Information System (NWIS) (U.S. Geological Survey, 

2011)—USGS stations 08449400 Devils River at Pafford 

Crossing near Comstock, Tex. (hereinafter the Devils River at 

Pafford Crossing gage [site D2]), and 08447410 Pecos River 

near Langtry, Tex. (hereinafter the Pecos River near Langtry 

gage ] [site P2]) (fig. 1; table 1). Discharge data (mean-daily 

discharge) was obtained from USGS NWIS for the dates that 

water-quality samples were collected at each of the gaging 

stations. The water-quality sampling sites were in the Amistad 

National Recreation Area and near where each river flows 

directly into Amistad Reservoir. The location of each sampling 

site was documented by using a Global Positioning System 

(GPS) unit, digital photographs, and field notes to describe the 

site relative to surrounding landmarks, as well as by plotting 

the site on USGS quadrangle maps or smaller scale site maps 

when necessary.

Water-quality sampling was done in the spring and 

summer because selected constituents, such as nutrients and 

pesticides, might be applied more frequently in upstream 

contributing areas in Texas and New Mexico during the spring 

and summer compared to other times of the year resulting 

in relatively large concentrations of nutrients and pesticides 

in the streams compared to other seasons. Water-quality 

samples were collected at the Devils River near Pafford 

Crossing gage (site D2) in March, May, June and August of 

2005, and in March, April, May, June, and August of 2005 

at the Pecos River near Langtry gage (site P2); the March 

samples collected at site D2 and the March, April, and August 

samples collected at site P2 included quality-control samples. 

Spring and summer also are when fish and macroinvertebrates 

might have heightened sensitivity to changes in water quality 

because many species are reproducing and their offspring 

are developing. For example, the federally threatened Devils 

River minnow (Dionda diaboli) spawn from late winter 

through the summer, and lay non-adhesive eggs that can be 

suspended in the water column (Hubbs, 1951). 

Historical and recent water-quality samples have been 

collected by the USGS at the two sites where water-quality 

data were collected in 2005. The data collected in 2005 were 

compared with historical water-quality data collected as part 

of the USGS HBN program during 1978–95 (U.S. Geological 

Survey, 2011; Mast and Turk, 1999) at the Devils River at 

Pafford Crossing gage (site D2), and with data collected as 

part of the USGS NASQAN program during 1974–2007 at 

the Pecos River near Langtry gage (site P2) (U.S. Geological 

Survey, 2010). Data from samples collected in 2005 were 

compared with data collected and processed similarly as part 

of the USGS HBN or NASQAN program (for example, results 

from filtered samples collected in 2005 were compared with 

results from filtered samples collected as part of the USGS 

HBN or NASQAN programs).
6 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Collection and Analysis of WaterQuality Samples

Depth- and width-integrated composite samples were 

collected and processed in 2005 for water-quality analyses in 

accordance with standard USGS protocols (U.S. Geological 

Survey, variously dated). Some samples were filtered in 

the field within 2 hours of collection. Analyses of filtered 

samples provided concentrations of total dissolved solids, 

major ions, nutrients, trace metals, and pesticides. Samples 

were filtered through 0.45-μm pore-diameter filters with the 

exception of those analyzed for organic carbon and pesticides, 

which were filtered through 0.7-μm pore-diameter filters. 

Reusable bottles and sampling equipment were cleaned with 

Liqui-Nox soap, hydrochloric acid, methanol, and deionized 

water prior to use. When used, preservatives such as nitric 

acid were added to the samples in a preservation chamber. 

Ultrapure nitric acid was added to each bottle for cation or 

trace-element analysis, lowering the pH to 2 or less. Samples 

for temperature-sensitive constituents that could change as a 

result of biological activity were chilled with ice to maintain 

them at 4°C from the time they were collected in the field until 

they were analyzed (U.S. Geological Survey, variously dated). 

All of the samples were shipped for analysis within 24 hours 

of collection to the USGS National Water Quality Laboratory 

in Denver, Colorado. Analytical methods are described in 

Fishman (1993), Fishman and Friedman (1989), Furlong and 

others (2001), Lindley and others (1996), Madsen and others 

(2003), Patton and Truitt (2000), Sandstrom and others (2001), 

U.S. Environmental Protection Agency (1993), and Zaugg and 

others (1995).

Table 1. Sample-collection sites on the Devils and Pecos Rivers in and upstream from the Amistad National Recreation Area, 

Texas, 2005–07.

[USGS, U.S. Geological Survey; Site latitude and longitude correspond to downstream boundary of biological assessment reach at each site; Yes, data-collection 

activity for site; No, no data collected]

Site 

identifier

(fig. 1)

USGS station 

number

USGS station 

name

Site 

latitude 

(decimal 

degrees)

Site 

longitude 

(decimal 

degrees)

Bioassessment 

reach 

length 

(meters)

Waterquality 

sampling

(2005)

Fish 

community 

assessment 

(2006)

Fish 

community 

assessment 

(2007)

Macroinvertebrate 

community 

assessment

(2006)

D1 293894100582901 Devils River 

near Satan 

Canyon, Tex.

29.649 100.972 525 No Yes No Yes

D2 08449400 Devils River 

at Pafford 

Crossing 

near Comstock, Tex.

29.675 101.001 403 Yes Yes Yes Yes

D3 29774610099501 Devils River 

near Turkey 

Bluff Canyon, Tex.

29.775 100.995 407 No Yes No Yes

D4 2988810099601 Devils River 

at Dolan 

Falls, Tex.

29.888 100.996 254 No Yes Yes Yes

P1 294735101232401 Pecos River 

at Shumla 

Bend, Tex.

29.793 101.390 490 No Yes No Yes

P2 08447410 Pecos River 

near Langtry, 

Tex.

29.802 101.442 431 Yes Yes Yes Yes

P3 295945101301501 Pecos River 

near Everett 

Canyon, Tex.

29.996 101.504 520 No Yes No Yes

P4 300737101342201 Pecos River at 

Pandale, Tex.

30.127 101.573 272 No Yes Yes Yes

 
Methods of Investigation 7

The following water-quality constituents were analyzed:

• Total dissolved solids; 

• Major ions—calcium, magnesium, potassium, 

sodium, chloride, fluoride, silica, and sulfate;

• Nutrients— ammonia plus organic nitrogen as 

nitrogen, ammonia as nitrogen, nitrate plus nitrite 

as nitrogen (NO3+NO2 as N), nitrate (NO3), nitrite 

(NO2), phosphorous (P), and orthophosphate (PO4);

• Trace metals—aluminum, barium, beryllium, 

cadmium, chromium, cobalt, copper, iron, lead, 

lithium, manganese, molybdenum, nickel, silver, 

strontium, vanadium, zinc, antimony, arsenic, boron, 

and selenium; and

• Organic carbon and pesticides.

Samples for quality-control purposes were collected 

following USGS protocols (U.S. Geological Survey, variously 

dated) at the Devils River at Pafford Crossing gage (site D2) 

and Pecos River near Langtry gage (site P2) at the same time 

the environmental samples were collected in March at site D2 

and in March, April, and August at site P2. A more extensive 

analysis of samples for polar pesticides and their metabolites 

was done for samples collected at site D2 to provide a more 

complete screening of pesticides in what is considered a 

relatively pristine spring-fed river with no impoundments and 

few land uses in the runoff-contributing area that might affect 

water quality (Purchase and others, 2001). 

The constituents of primary concern are total dissolved 

solids, chloride, sulfate, ammonia plus organic nitrogen, 

nitrate plus nitrite, orthophosphate, phosphorous, selenium, 

and selected pesticides. These constituents are among those of 

greatest concern to the Amistad National Recreation Area in 

previous studies of the Devils and Pecos Rivers (Purchase and 

others, 2001). 

Collection and Processing of Fish and 

Macroinvertebrate Samples

The composition of fish macroinvertebrate communities 

were evaluated by collecting fish and macroinvertebrate 

samples in 2006 at the Devils River at Pafford Crossing gage 

(site D2), and at the Pecos River near Langtry gage (site P2), 

and from three additional sites in or near the Amistad National 

Recreation Area on each river. The three additional sites where 

fish and macroinvertebrates were collected in 2006 from the 

Devils River were USGS stations 293894100582901 Devils 

River near Satan Canyon, Tex. (site D1); 29774610099501 

Devils River near Turkey Bluff Canyon, Tex. (site D3); 

and 2988810099601 Devils River at Dolan Falls, Tex. 

(site D4). The three additional sites in or near the Amistad 

National Recreation Area on the Pecos River where fish 

and macroinvertebrates were collected in 2006 were USGS 

stations 294735101232401 Pecos River at Shumla Bend, Tex. 

(site P1); 295945101301501 Pecos River near Everett Canyon, 

Tex. (site P3); and 300737101342201 Pecos River at Pandale, 

Tex. (site P4) (fig. 1; table 1). Fish community surveys were 

repeated in the spring of 2007 at two sites along the Devils 

River (sites D2 and D4) and two sites on the Pecos River 

(sites P2 and P4). The farthest downstream sites where fish 

and macroinvertebrates were collected (site D1 on the Devils 

Rivers and site P1 on the Pecos River) were in sections of the 

Devils and Pecos Rivers that flow during lower water-surface 

elevations in Amistad Reservoir, but are in backwater during 

periods of higher water-surface elevations in the reservoir. 

The fish and macroinvertebrate communities were 

sampled by using procedures developed for the USGS 

National Water Quality Assessment (NAWQA) Program 

(Moulton and others, 2002; Moring 2002). Reach length at 

each site where fish and macroinvertebrates were collected 

was not determined as a multiple of wetted channel width, 

which is commonly done (Moulton and others, 2002; Texas 

Commission on Environmental Quality, 2007), because this 

approach would have resulted in reach lengths of several 

thousand meters or more at some sites that would not have 

been practical for wading and the collection of fish and 

macroinvertebrates. Instead, each reach defining a sampling 

site was selected to include at least two of the most common 

of the basic geomorphic units associated with rivers—for 

example, riffles, runs, and or pools (Church, 1992)—so 

that each reach had a similar variety of habitat types for 

the sampling of fish and macroinvertebrates allowing for 

more standardized equal-effort sampling and between site 

comparisons. Reach lengths at each sampling site ranged from 

272 to 525 m and are listed in table 1.

The total number of fish species and the number of 

individuals of each fish species were compared in and between 

sites on the Devils and Pecos Rivers. Selected fish community 

metrics including the Menhinick species richness (Ludwig and 

Reynolds, 1988), number of non-native individuals, number 

of tolerant and intolerant species, number of fish representing 

different feeding groups, and taxa were compared among sites 

(Linam and others, 2002). Taxon (singular) or taxa (plural) 

refers to a genetically related group or groups of one or more 

organisms with common characteristics that differentiate 

them as a unit (International Commission on Zoological 

Nomenclature, 2010). 

The overall similarity among the fish communities at 

the eight sampling sites was evaluated by the number of 

shared species observed among each of the sites by using a 

Bray-Curtis similarity matrix (Clarke and Warwick, 2001). 

The Bray-Curtis similarity matrix was based on the number 

of unique fish taxa in common among sites and was used 

as input to a statistical procedure known as Non-metric 

Multidimensional Scaling (NMDS). Euclidean distances 

between objects were determined by using the Bray-Curtis 

similarity matrix values as inputs to the NMDS procedure 

(Field and others, 1982; Clark and Warwick, 2001). Statistica 

Version 7 (StatSoft, 2006) was used to calculate the BrayCurtis similarity matrix and to run the NMDS procedure. The 
8 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

overall similarity among the fish communities at the eight 

sampling sites was illustrated by graphically depicting the 

Euclidean distances between them in two dimensions (Clark 

and Warwick, 2001).

The total number of unique macroinvertebrate taxa, 

number of individuals per unique taxon, and several species 

diversity metrics and indexes (Margalef richness, Hilsenhoff 

biotic, Pielou’s J, and Simpson’s heterogeneity indexes) 

(Ludwig and Reynolds, 1988; Hilsenhoff, 1987), were 

determined for each site. Except for the Margalef richness, 

all of the indexes were determined by The EcoAnalysts, Inc., 

laboratory in Moscow, Idaho (Gary Lester, EcoAnalysts, 

Inc., written commun., 2006). Only the Margalef richness 

and Hilsenhoff biotic index are discussed. The Margalef 

richness index was calculated by using only aquatic insect 

taxa, whereas the other indexes were calculated by using 

all macroinvertebrate taxa. As was done to evaluate the 

fish communities, a Bray-Curtis similarity matrix was also 

used to evaluate the aquatic insect assemblages (number of 

unique aquatic insect taxa only). Aquatic insect assemblages 

are a subset of the macroinvertebrate community; because 

the vast majority of the macroinvertebrates collected were 

aquatic insects, it was deemed most appropriate to use aquatic 

insect assemblages in the Bray-Curtis similarity matrix and 

subsequent NMDS procedure. The number of unique 

aquatic insect taxa in common between sites was evaluated 

with the Bray-Curtis similarity matrix and used as input to 

the NMDS procedure to compare the overall similarity of 

aquatic insect assemblages among sites, and the results of the 

NMDS procedure were displayed graphically as Euclidian 

distances to illustrate the overall similarity among aquatic 

insect assemblages.

Fish Community Surveys and Processing 

of Samples

Following methods described in Moring (2002), the fish 

community at each site was sampled by using a combination 

of electrofishing from boats and barges, wading with backpack 

electrofishing equipment, seining, and trap netting. Fish were 

collected in spring and summer (during March and June) 

when the rivers were relatively accessible for fish sampling; 

streamflow amounts are generally smaller in spring and 

summer in the Devils and Pecos Rivers compared to fall 

and winter, when runoff from storm events is more common 

(U.S. Geological Survey, 2010). By collecting fish in the 

spring and summer, the representativeness of the samples was 

also enhanced because fish are more dispersed during these 

seasons—the higher water temperatures in spring and summer 

enhance fish mobility compared to fall and winter when cooler 

temperatures tend to make fish less active (Lucas and others, 

2008). Two electrofishing passes were made through the reach 

at each sample-collection site by using the most appropriate 

equipment considering river depth and flow velocity. At least 

six seine hauls were equally distributed among the types of 

geomorphic units present at each site. Seines used were a 7.5- 

by 3.0-m, 0.64-cm mesh-size bag seine and a 3.0- by 3.0-m, 

0.17-cm flat-panel seine. Collected fish were placed in aerated 

holding tanks; each species of fish was identified, standard and 

total lengths were measured to the nearest millimeter, and each 

fish was weighed to the nearest gram. 

Macroinvertebrate Community Surveys and 

Processing of Samples

The macroinvertebrate community at each site was 

surveyed in 2006 by the collection of a composite sample 

referred to as a qualitative multi-habitat sample (Moulton 

and others, 2002). Macroinvertebrate community data from 

each sample-collection site were determined by using a 

qualitative multi-habitat sample that is biased to maximize 

the number of taxa collected at each site and not to provide 

quantitative data on the number of taxa per unit area from one 

or more habitat types.

 A 0.05-mm mesh size D-frame shaped net was used 

to collect the macroinvertebrate samples equally distributed 

among habitat types as described in Moulton and others 

(2002). Each macroinvertebrate sample was preserved on site 

in 10-percent phosphate-buffered formalin, and submitted 

to the EcoAnalysts, Inc., laboratory in Moscow, Idaho, for 

identification and enumeration of macroinvertebrate taxa, 

and calculation of the Pielou’s J, Simpson’s heterogeneity, 

and Hilsenoff biotic indexes (Gary Lester, EcoAnalysts, Inc., 

written commun., 2006). 

Quality Control

A water-quality field-blank sample was collected 

March 22, 2005, at the Devils River near Pafford Crossing 

gage (site D2) and analyzed for selected major ions, nutrients, 

trace metals, and pesticides in 2005 to evaluate potential 

contamination from field processing and laboratory handling 

and analysis. Sequential-replicate samples were collected at 

the Pecos River near Langtry gage (P2) on March 8, 2005, 

along with a field-blank sample on April 5, 2005, and a 

field-spike sample on August 2, 2005. Quality-control water 

samples were collected as described in the National Field 

Manual for the Collection of Water-Quality Data 

(U.S. Geological Survey, variously dated) and analyzed 

by the same laboratory following the same methods as the 

environmental samples. 

Calcium exceeded the laboratory reporting level (LRL) of 

0.02 milligrams per liter [mg/L] in the March 2005 field-blank 

sample but was two orders of magnitude less than the calcium 

concentrations of all the environmental samples collected 
Methods of Investigation 9

at the Devils River near Pafford Crossing gage. No other 

concentrations of major ions exceeded laboratory reporting 

levels (LRLs) in the field-blank sample (indicated by less-than 

values in table 2). Trace metal concentrations measured in 

this field-blank sample did not exceed applicable LRLs with 

the exception of nickel (0.12 micrograms per liter [mg/L]; 

LRL of 0.06 μg/L) and zinc (1.6 mg/L; LRL of 0.6 μg/L). 

An estimated vanadium concentration of 0.1 mg/L was less 

than the LRL of 0.14 μg/L (table 3). Nutrients and pesticides 

in this field-blank sample (tables 2 and 4, respectively) did 

not exceed the any of the applicable LRLs. An estimated 

concentration of 0.2 mg/L for organic carbon was detected 

(table 4), but this concentration was several times smaller than 

the concentrations of 1.1 to 1.2 mg/L organic carbon measured 

in the environmental samples from this site. 

In addition to the field-blank sample collected at the 

Devils River at Pafford Crossing gage on March 22, 2005, 

sequential-replicate samples were collected at the Pecos 

River near Langtry gage on March 8, 2005, and analyzed to 

determine the precision of the results for major ions and trace 

metals. The relative percent difference (RPD) was determined 

for each pair of replicate analyses as a measure of variability. 

The relative percent difference (RPD) for each constituent was 

computed by using the equation

RPD = |C1 – C2|/((C1 + C2)/2) x 100, (1)

where 

 C1 is the concentration from the first sample 

in the replicate pair; and 

 C2 is the concentration from the second 

sample in the replicate pair.

 The RPDs for total dissolved solids, major ions, 

nutrients, and trace metals were generally 5 percent or smaller, 

indicating good analytical precision; exceptions were arsenic 

and selenium, which had RPDs of 16.67 and 6.90 percent, 

respectively. The RPDs for arsenic and selenium also indicated 

good analytical precision because the concentrations measured 

in the replicate samples were small (1.1 and 1.3 mg/L for 

arsenic, and 2.8 and 3.0 mg/L for selenium). 

A field-blank and a field-spike (matrix spike) sample 

were collected on April 5, 2005, and August 2, 2005, 

respectively, at the Pecos River near Langtry gage and 

analyzed for selected pesticides; no detectable amounts of 

pesticides were measured in the field-blank samples. The 

recovery rates for the field-spike sample were reviewed; most 

recovery rates were in the acceptable range and recovery 

rates overall were typical for the constituents analyzed (Cary 

Carman, U.S. Geological Survey, oral commun., 2011). To 

evaluate the accuracy of the laboratory analysis of pesticides, 

the insecticides diazinon and alpha-hexochlorocyclohexane 

(alpha-HCH) were added as surrogates to environmental 

samples. The average surrogate recoveries were 106.8 percent 

for diazinon and 96.6 percent for alpha-HCH (appendix 1). 

These surrogate recoveries for diazinon and alpha-HCH are 

within the continuing laboratory calibration verification limits 

of 80- to 120-percent recovery for these insecticides (Duane 

Wydoski, U.S. Geological Survey, National Water Quality 

Laboratory, written commun., 2011). 

For quality control, the fish species identified at each site 

were photographed onsite with a digital camera, and photo 

vouchers were prepared to record observations pertaining 

to each fish in an electronic log book. Photo vouchers are 

maintained by the USGS in Austin, Tex. Fish that could not be 

identified in the field were preserved onsite with 10-percent 

phosphate-buffered formalin and returned to the USGS 

office in Austin for sorting and preliminary identification. 

Verification of all species that were identified and permanent 

curation of all preserved specimens was done by the Curator 

of Fishes at the University of Texas Natural History Collection 

in Austin. 

Macroinvertebrate samples were processed by using a 

300-count procedure. If a macroinvertebrate sample contained 

300 or fewer organisms, all the organisms in the samples were 

sorted, identified to the lowest possible taxon, and counted by 

laboratory personnel. If the sample contained more than 300 

organisms, then a 300-count sub-sampling routine was used 

(Lester, 1999). The sub-sampling routine involved sorting the 

organisms in a tray with a grid overlay, and the organisms in 

randomly selected grids were counted up to 300 organisms. 

If the 300 count was met before the organisms in one grid 

were completely counted, all the organisms in that grid were 

counted. Sub-sampling sorting efficiency was checked by 

a separate laboratory technician who re-sorted the original 

sample and processed 20 percent of the total grids that were 

sampled by the original technician. Sorting efficiency was 

measured as a ratio of the number of organisms counted during 

the initial sorting divided by the number from the sorting of 

20 percent of the grids. If sorting efficiency was 90 percent or 

greater, the sample passed this quality-control check. If less 

than 90 percent, the samples underwent the quality-control 

check again until the 90-percent or better efficiency was 

reached. All of the samples for this study passed the initial 

sorting efficiency check. A reference collection was provided 

by EcoAnalysts, Inc., consisting of at least one specimen 

of each unique taxon identified. The accuracy of taxonomic 

identification was checked by a different taxonomist with the 

contract laboratory by checking the accuracy of 10 percent 

of the taxa in the reference collection to a target similarity of 

identification of at least 90 percent. The reference collection 

from this study passed this quality-control check as well. The 

reference collection is maintained at the USGS office in Austin 

to also provide verifiable taxonomic identification if any of the 

taxa identified in this study are questioned or should need to 

be verified in the future. 
10 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 2. Concentrations of total dissolved solids, selected major ions, and nutrients in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental] Site identifier (fig. 1) Date Sample type code USGS station number USGS station name Daily mean discharge, cubic feet per second Dissolved solids dried at 180°C degrees Celsius, water, filtered, milligrams per liter (Total Dissolved Solids) Calcium, water, filtered, milligrams per liter Magnesium, water, filtered, milligrams per liter Potassium, water, filtered, milligrams per liter D2 3/22/2005 2 08449400 Devils River at Pafford Crossing near Comstock, Tex. 576 <10 0.03 <0.008 <0.16 D2 3/22/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 576 232 64.8 12.9 1.32 D2 5/17/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 417 208 57.9 12.7 1.36 D2 6/29/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 480 214 53.8 12.1 1.22 D2 8/3/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 396 227 58.7 13.8 1.3 P2 3/8/2005 9 08447410 Pecos River near Langtry, Tex. 322 2,250 171 79.8 8.24 P2 3/8/2005 7 08447410 Pecos River near Langtry, Tex. 322 2,240 169 79.9 8.01 P2 4/5/2005 9 08447410 Pecos River near Langtry, Tex. 271 2,390 181 91.2 8.67 P2 4/5/2005 2 08447410 Pecos River near Langtry, Tex. 271 -- -- -- -- P2 5/24/2005 9 08447410 Pecos River near Langtry, Tex. 204 1,780 112 65.3 6.92 P2 5/24/2005 9 08447410 Pecos River near Langtry, Tex. 204 -- -- -- -- P2 6/28/2005 9 08447410 Pecos River near Langtry, Tex. 186 2,110 131 75.7 7.44 P2 8/2/2005 9 08447410 Pecos River near Langtry, Tex. 180 1,460 100 51.9 6.54 P2 8/2/2005 1 08447410 Pecos River near Langtry, Tex. 180 -- -- -- -- Relative Percent Difference for sequential-replicate samples collected March 8,2005 from the Pecos River near Langtry, Tex., station .45 1.18 .13 2.83
Methods of Investigation 11

Table 2. Concentrations of total dissolved solids, selected major ions, and nutrients in water-quality samples collected at U.S.Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued[USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental]

Site 

identifier 

(fig. 1)

Date

Sample 

type 

code

USGS 

station 

number

Chloride, 

water, 

filtered, 

milligrams 

per liter

Fluoride, 

water, 

filtered, 

milligrams 

per liter

Silica, 

water, 

filtered, 

milligrams 

per liter as 

SiO2

Sulfate, 

water, 

filtered, 

milligrams 

per liter

Ammonia 

plus

 organic 

nitrogen, 

water, 

filtered, 

milligrams 

per liter as 

nitrogen

Ammonia, 

water, 

filtered, 

milligrams 

per liter as 

nitrogen

Nitrate 

plus nitrite, 

water, 

filtered, 

milligrams 

per liter as 

nitrogen

Nitrate, 

water, 

filtered, 

milligrams 

per liter

Nitrite, 

water, 

filtered, 

milligrams 

per liter

Ortho

phosphate, 

water, 

filtered, 

milligrams 

per liter

Phosphorus, 

water, 

filtered, 

milligrams 

per liter as 

phosphorus

D2 3/22/2005 2 08449400 <0.20 < 0.10 0.10 <0.18 <0.10 <0.04 <0.06 <0.266 <0.026 <0.018 <0.004

D2 3/22/2005 9 08449400 11.8 .3 13.7 8.20 .12 <.04 1.24 E 5.46 E.016 <.018 <.004

D2 5/17/2005 9 08449400 11.6 .29 15.6 7.55 .13 <.04 1.15 E 5.05 E.013 <.018 E.003

D2 6/29/2005 9 08449400 12.9 .3 15.8 7.99 .14 E.02 .99 4.33 .026 <.018 E.003D2 8/3/2005 9 08449400 12.5 .26 16.6 7.86 .13 E.02 1.02 4.49 .03 <.018 E.003

P2 3/8/2005 9 08447410 819 .86 15.9 472 .15 <.04 1.04 4.61 <.026 <.018 <.004

P2 3/8/2005 7 08447410 830 .83 16.3 473 .15 <.04 1.04 4.59 <.026 <.018 <.004

P2 4/5/2005 9 08447410 879 .89 13.9 503 .22 <.04 .83 E 3.63 E.020 <.018 E.004

P2 4/5/2005 2 08447410 -- -- -- -- -- -- -- -- -- -- --

P2 5/24/2005 9 08447410 623 .87 13.3 364 .32 E.03 .40 1.74 .03 <.018 E.002

P2 5/24/2005 9 08447410 -- -- -- -- -- -- -- -- -- -- --

P2 6/28/2005 9 08447410 795 .87 13.4 443 .29 E.03 .22 E.969 E.016 <.018 E.003

P2 8/2/2005 9 08447410 519 .87 16 298 .29 .04 .29 E 1.24 E.023 <.018 <.004

P2 8/2/2005 1 08447410 -- -- -- -- -- -- -- -- -- -- --

Relative Percent Difference for 

sequential-replicate samples collected March 8,2005 from the Pecos River near Langtry, Tex., station

1.33 3.55 2.48 .21 .00 .00 .00 .43 .00 .00 .00
12 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 3. Concentrations of trace metals in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental] Site identifier (fig. 1) Date Sample type code USGS station number USGS station name Daily mean discharge, cubic feet per second Aluminum, water, filtered, micrograms per liter Barium, water, filtered, micro- grams per liter Beryllium, water, filtered, micrograms per liter Cadmium, water, filtered, micro- grams per liter Chromium, water, filtered, micro- grams per liter Cobalt, water, filtered, micro- grams per liter Copper, water, filtered, micro- grams per liter D2 3/22/2005 2 08449400 Devils River at Pafford Crossing near Comstock, Tex. 576 <1.6 <0.2 <0.06 <0.04 <0.8 <0.014 <0.4 D2 3/22/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 576 E 1.0 117 <.06 0.16 <.8 .139 .4 D2 5/17/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 417 E 1.2 113 <.06 <.04 <.8 .182 .4 D2 6/29/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 480 2.7 106 <.06 <.04 <.8 .14 E.4 D2 8/3/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 396 <1.6 109 <.06 <.04 <.8 .098 E.2 P2 3/8/2005 9 08447410 Pecos River near Langtry, Tex. 322 -- -- -- -- -- -- -- P2 3/8/2005 7 08447410 Pecos River near Langtry, Tex. 322 -- -- -- -- -- -- -- P2 4/5/2005 9 08447410 Pecos River near Langtry, Tex. 271 -- -- -- -- -- -- -- P2 4/5/2005 2 08447410 Pecos River near Langtry, Tex. 271 -- -- -- -- -- -- -- P2 5/24/2005 9 08447410 Pecos River near Langtry, Tex. 204 -- -- -- -- -- -- -- P2 6/28/2005 9 08447410 Pecos River near Langtry, Tex. 186 -- -- -- -- -- -- -- P2 8/2/2005 9 08447410 Pecos River near Langtry, Tex. 180 -- -- -- -- -- -- -- P2 8/2/2005 1 08447410 Pecos River near Langtry, Tex. 180 -- -- -- -- -- -- -- Relative Percent Difference for sequential-replicate samples collected March 8,2005 from the Pecos River near Langtry, Tex., station -- -- -- -- -- -- -- --
Methods of Investigation 13

Table 3. Concentrations of trace metals in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued.[USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, Field spike; 2, Field blank; 7, Sequential replicate; 9, environmental]

Site 

identifier 

(fig. 1)

Date

Sample 

type 

code

Iron, 

water, 

filtered, 

micrograms 

per liter

Lead, 

water, 

filtered, 

micrograms 

per liter

Lithium, 

water, 

filtered, 

micrograms 

per liter

Manganese, 

water, 

filtered, 

micrograms 

per liter

Molybdenum, water, 

filtered, 

micrograms 

per liter

Nickel, 

water, 

filtered, 

micrograms 

per liter

Silver, water, 

filtered, 

micrograms 

per liter

Strontium, 

water, 

filtered, 

micrograms per 

liter

Vanadium, 

water, 

filtered, 

micrograms 

per liter

Zinc, 

water, 

filtered, 

micrograms 

per liter

Antimony, 

water, 

filtered, 

micrograms 

per liter

Arsenic, 

water, 

filtered, 

micrograms 

per liter

Boron, 

water, 

filtered, 

micrograms 

per 

liter

Selenium, 

water, 

filtered, 

micrograms 

per liter

D2 3/22/2005 2 <6 <0.08 <0.6 <0.2 <0.4 0.12 <0.20 <0.40 E.1 1.6 <0.20 <0.2 < 8 <0.4

D2 3/22/2005 9 <6 <.08 4.9 .9 .7 1.07 <.20 472 9.1 5.6 <.20 1.1 72 .5

D2 5/17/2005 9 <6 <.08 5 .6 .7 2.57 <.20 432 8.1 2.3 <.20 1 58 .6

D2 6/29/2005 9 <6 <.08 5.5 .6 .7 1.8 <.20 472 8.5 E.3 <.20 1.1 57 E.4D2 8/3/2005 9 <6 <.08 4.4 .5 .7 2 <.20 473 7.8 1.3 <.20 1.1 46 E.3P2 3/8/2005 9 <18 -- 68.4 -- -- -- -- 3,020 6.9 -- -- 1.1 265 2.8

P2 3/8/2005 7 <18 -- 69.8 -- -- -- -- 3,050 7.1 -- -- 1.3 271 3.0

P2 4/5/2005 9 E 10 -- 77 -- -- -- -- 3,090 6.9 -- -- 1.3 304 3.1

P2 4/5/2005 2 -- -- -- -- -- -- -- -- -- -- -- -- -- --

P2 5/24/2005 9 <18 -- 59.8 -- -- -- -- 2,200 8.5 -- -- 1.4 222 1.2

P2 6/28/2005 9 <18 -- 67.2 -- -- -- -- 2,720 7.2 -- -- 1.2 221 1.2

P2 8/2/2005 9 <18 -- 55.5 -- -- -- -- 1,930 8.3 -- -- 1.6 210 1.0

P2 8/2/2005 1 -- -- -- -- -- -- -- -- -- -- -- -- -- --

Relative Percent Difference 

for sequential-replicate samples collected March 8,2005 from the Pecos River near Langtry, Tex., station

-- -- 2.03 -- -- -- -- .99 2.86 -- -- 16.67 2.24 6.90
14 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Station number USGS Station name Daily mean discharge, cubic feet per second Organic carbon, water, filtered, milligrams per liter 2,4-D methyl ester, water, filtered, recoverable, micrograms per liter 2,4-D, water, filtered, recoverable, micrograms per liter 2,4-DB, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter D2 3/22/2005 2 08449400 Devils River at Pafford Crossing near Comstock, Tex. 576 E.2 <0.016 <0.04 <0.02 D2 3/22/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 576 1.1 <.016 <.04 <.02 D2 5/17/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 417 1.2 <.016 <.04 <.05 D2 6/29/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 480 1.2 <.016 <.04 <.02 D2 8/3/2005 9 08449400 Devils River at Pafford Crossing near Comstock, Tex. 396 1.2 <.016 <.04 <.02 P2 3/8/2005 9 08447410 Pecos River near Langtry, Tex. 322 1.4 -- -- -- P2 3/8/2005 7 08447410 Pecos River near Langtry, Tex. 322 1.3 -- -- -- P2 4/5/2005 9 08447410 Pecos River near Langtry, Tex. 271 0.9 -- -- -- P2 4/5/2005 2 08447410 Pecos River near Langtry, Tex. 271 <.3 -- -- -- P2 5/24/2005 9 08447410 Pecos River near Langtry, Tex. 204 1.7 -- -- -- P2 5/24/2005 9 08447410 Pecos River near Langtry, Tex. 204 -- -- -- -- P2 6/28/2005 9 08447410 Pecos River near Langtry, Tex. 186 1.3 -- -- -- P2 8/2/2005 9 08447410 Pecos River near Langtry, Tex. 180 2.8 -- -- -- P2 8/2/2005 1 08447410 Pecos River near Langtry, Tex. 180 -- -- -- --
Methods of Investigation 15

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date

Sample 

type 

code

2,6-Diethylaniline, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

2-Chloro4-isopropylamino-6-aminos-triazine, 

water, filtered, 

recoverable, 

micrograms 

per liter

2-Chloro6-ethylamino4-aminos-triazine, 

water, filtered, 

recoverable, 

micrograms 

per liter

2-Hydroxy4-isopropylamino6-ethylaminos-triazine, water, 

filtered, recoverable, micrograms 

per liter

3-Hydroxy 

carbofuran, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

3-Ketocarbofuran, 

water, filtered, 

recoverable, 

micrograms 

per liter

Acetochlor, 

water, 

filtered, 

recoverable, 

micrograms 

per liter

Acifluorfen, 

water, filtered 

(0.7 micron 

glass fiber 

filter), 

recoverable, 

micrograms 

per liter

D2 3/22/2005 2 <0.006 <0.006 <0.08 <0.032 <0.008 <0.02 <0.006 <0.028D2 3/22/2005 9 <.006 <.006 <.08 <.032 <.008 <.02 <.006 <.028

D2 5/17/2005 9 <.006 <.006 <.08 <.032 <.008 <.02 <.006 <.028

D2 6/29/2005 9 <.006 <.006 <.08 <.032 <.008 -- <.006 <.028

D2 8/3/2005 9 <.006 <.006 <.08 <.032 <.008 <.02 <.006 <.028

P2 3/8/2005 9 <.006 <.006 -- -- -- -- <.006 --

P2 3/8/2005 7 <.006 <.006 -- -- -- -- <.006 --P2 4/5/2005 9 <.006 <.006 -- -- -- -- <.006 --P2 4/5/2005 2 <.006 <.006 -- -- -- -- <.006 --P2 5/24/2005 9 <.006 <.006 -- -- -- -- <.006 --P2 5/24/2005 9 -- -- <.08 -- -- <.02 -- --P2 6/28/2005 9 <.006 <.006 -- -- -- -- <.006 --P2 8/2/2005 9 <.006 <.006 <.08 -- -- <.02 <.006 --

P2 8/2/2005 1 .089 E.033 -- -- -- -- .125 --
16 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Alachlor, water, filtered, recoverable, micrograms per liter Aldicarb sulfone, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Aldicarb sulfoxide, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Aldicarb, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter alpha-HCH, water, filtered, recoverable, micrograms per liter Atrazine, water, filtered, recoverable, micrograms per liter Azinphos-methyl, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Bendiocarb, water, filtered, recoverable, micrograms per liter D2 3/22/2005 2 <0.005 <0.02 <0.022 <0.04 <0.005 <0.007 <0.050 <0.02 D2 3/22/2005 9 <.005 <.02 <.022 <.04 <.005 <.007 <.050 <.02 D2 5/17/2005 9 <.005 <.02 <.022 <.04 <.005 <.007 <.050 <.02 D2 6/29/2005 9 <.005 <.02 <.022 <.04 <.005 <.007 <.050 <.02 D2 8/3/2005 9 <.005 <.02 <.022 <.04 <.005 <.007 <.050 <.02 P2 3/8/2005 9 <.005 -- -- -- <.005 <.007 <.050 -- P2 3/8/2005 7 <.005 -- -- -- <.005 <.007 <.050 -- P2 4/5/2005 9 <.005 -- -- -- <.005 <.007 <.050 -- P2 4/5/2005 2 <.005 -- -- -- <.005 <.007 <.050 -- P2 5/24/2005 9 <.005 -- -- -- <.005 <.007 <.050 -- P2 5/24/2005 9 -- -- -- <.04 -- -- -- -- P2 6/28/2005 9 <.005 -- -- -- <.005 <.007 <.050 -- P2 8/2/2005 9 <.005 -- -- <.04 <.005 <.007 <.050 -- P2 8/2/2005 1 .118 -- -- -- .129 .119 E.099 --
Methods of Investigation 17

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date

Sample 

type 

code

Benfluralin, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Benomyl, 

water, filtered, 

recoverable, 

micrograms 

per liter

Bensulfuron-methyl, 

water, filtered, 

recoverable, 

micrograms 

per liter

Bentazon, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Bromacil, 

water, filtered, 

recoverable, 

micrograms 

per liter

Bromoxynil, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Butylate, 

water, filtered, 

recoverable, 

micrograms 

per liter

D2 3/22/2005 2 <0.010 <0.022 <0.02 <0.01 <0.02 <0.03 <0.004

D2 3/22/2005 9 <.010 <.022 <.02 <.01 <.02 <.03 <.004

D2 5/17/2005 9 <.010 <.022 <.02 <.01 <.02 <.03 <.004

D2 6/29/2005 9 <.010 <.022 <.02 <.01 <.02 <.03 <.004

D2 8/3/2005 9 <.010 <.022 <.02 <.01 <.02 <.03 <.004

P2 3/8/2005 9 <.010 -- -- -- -- -- <.004

P2 3/8/2005 7 <.010 -- -- -- -- -- <.004

P2 4/5/2005 9 <.010 -- -- -- -- -- <.004

P2 4/5/2005 2 <.010 -- -- -- -- -- <.004

P2 5/24/2005 9 <.010 -- -- -- -- -- <.004

P2 5/24/2005 9 -- -- -- -- -- -- --

P2 6/28/2005 9 <.010 -- -- -- -- -- <.004

P2 8/2/2005 9 <.010 -- -- -- -- -- <.004

P2 8/2/2005 1 .086 -- -- -- -- -- .11
18 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Carbaryl, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Carbaryl, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Carbofuran, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Carbofuran, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Chloramben methyl ester, water, filtered, recoverable, micrograms per liter Chlorimuron- ethyl, water, filtered, recoverable, micrograms per liter Chlorodiamino- s-triazine, water, filtered, recoverable, micrograms per liter Chlorothalonil, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter D2 3/22/2005 2 <0.02 <0.041 <0.016 <0.020 <0.02 <0.032 <0.04 <0.04 D2 3/22/2005 9 <.02 <.041 <.016 <.020 <.02 <.032 <.04 <.04 D2 5/17/2005 9 <.02 <.041 <.016 <.020 <.02 <.032 <.04 <.04 D2 6/29/2005 9 <.02 <.041 <.016 <.020 <.02 <.032 <.04 <.04 D2 8/3/2005 9 <.02 <.041 <.016 <.020 <.02 <.032 <.04 <.04 P2 3/8/2005 9 -- <.041 -- <.020 -- -- -- -- P2 3/8/2005 7 -- <.041 -- <.020 -- -- -- -- P2 4/5/2005 9 -- <.041 -- <.020 -- -- -- -- P2 4/5/2005 2 -- <.041 -- <.020 -- -- -- -- P2 5/24/2005 9 -- <.041 -- <.020 -- -- -- -- P2 5/24/2005 9 -- -- -- -- -- -- <.04 <.04 P2 6/28/2005 9 -- <.041 -- <.020 -- -- -- -- P2 8/2/2005 9 -- <.041 -- <.020 -- -- <.04 <.04 P2 8/2/2005 1 -- E.070 -- E.090 -- -- -- --
Methods of Investigation 19

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date Sample type code

Chlorpyrifos, 

water, filtered, 

recoverable, 

micrograms 

per liter

cis-Permethrin, 

water, filtered 

(0.7 micron glass fiber 

filter), recoverable, 

micrograms per liter

Clopyralid, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms per liter

Cyanazine, 

water, filtered, 

recoverable, 

micrograms 

per liter

Cycloate, 

water, filtered, 

recoverable, 

micrograms 

per liter

Dacthal monoacid, 

water, filtered 

(0.7 micron glass fiber 

filter), recoverable, 

micrograms per liter

DCPA, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, micrograms per liter

D2 3/22/2005 2 <0.005 <0.006 <0.02 <0.018 <0.01 <0.03 <0.003

D2 3/22/2005 9 <.005 <.006 <.02 <.018 <.01 <.03 <.003

D2 5/17/2005 9 <.005 <.006 <.02 <.018 <.01 <.03 <.003

D2 6/29/2005 9 <.005 <.006 <.02 <.018 <.01 <.03 <.003

D2 8/3/2005 9 <.005 <.006 <.02 <.018 <.01 <.03 <.003P2 3/8/2005 9 <.005 <.006 -- <.018 -- -- <.003P2 3/8/2005 7 <.005 <.006 -- <.018 -- -- <.003P2 4/5/2005 9 <.005 <.006 -- <.018 -- -- <.003

P2 4/5/2005 2 <.005 <.006 -- <.018 -- -- <.003

P2 5/24/2005 9 <.005 <.006 -- <.018 -- -- <.003

P2 5/24/2005 9 -- -- -- -- -- -- --

P2 6/28/2005 9 <.005 <.006 -- <.018 -- -- <.003

P2 8/2/2005 9 <.005 <.006 -- <.018 -- -- <.003

P2 8/2/2005 1 .117 .055 -- .092 -- -- .128
20 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Desulfinylfipronil amide, water, filtered, recoverable, micrograms per liter Desulfinylfipronil, water, filtered, recoverable, micrograms per liter Diazinon, water, filtered, recoverable, micrograms per liter Dicamba, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Dichlorprop, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Dieldrin, water, filtered, recoverable, micrograms per liter Dinoseb, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Diphenamid, water, filtered, recoverable, micrograms per liter D2 3/22/2005 2 <0.029 <0.012 <0.005 <0.04 <0.03 <0.009 <0.04 <0.01 D2 3/22/2005 9 <.029 <.012 <.005 <.04 <.03 <.009 <.04 <.01 D2 5/17/2005 9 <.029 <.012 <.005 <.04 <.03 <.009 <.04 <.01 D2 6/29/2005 9 <.029 <.012 <.005 <.04 <.03 <.009 <.04 <.01 D2 8/3/2005 9 <.029 <.012 <.005 <.04 <.03 <.009 <.04 <.01 P2 3/8/2005 9 <.029 <.012 <.005 -- -- <.009 -- -- P2 3/8/2005 7 <.029 <.012 <.005 -- -- <.009 -- -- P2 4/5/2005 9 <.029 <.012 <.005 -- -- <.009 -- -- P2 4/5/2005 2 <.029 <.012 <.005 -- -- <.009 -- -- P2 5/24/2005 9 <.029 <.012 <.005 -- -- <.009 -- -- P2 5/24/2005 9 -- -- -- -- -- -- -- -- P2 6/28/2005 9 <.029 <.012 <.005 -- -- <.009 -- -- P2 8/2/2005 9 <.029 <.012 <.005 -- -- <.009 -- -- P2 8/2/2005 1 E.066 .115 .125 -- -- .14 -- --
Methods of Investigation 21

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date Sample type code

Disulfoton, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Diuron, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

EPTC, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Ethalfluralin, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Ethoprop, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Fenuron, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms per liter

Fipronil 

sulfide, water, 

filtered, 

recoverable, 

micrograms 

per liter

D2 3/22/2005 2 <0.02 <0.01 <0.004 <0.009 <0.005 <0.02 <0.013

D2 3/22/2005 9 <.02 <.01 <.004 <.009 <.005 <.02 <.013

D2 5/17/2005 9 <.02 <.01 <.004 <.009 <.005 <.02 <.013

D2 6/29/2005 9 <.02 <.01 <.004 <.009 <.005 <.02 <.013

D2 8/3/2005 9 <.02 <.01 <.004 <.009 <.005 <.02 <.013

P2 3/8/2005 9 <.02 -- <.004 <.009 <.005 -- <.013

P2 3/8/2005 7 <.02 -- <.004 <.009 <.005 -- <.013

P2 4/5/2005 9 <.02 -- <.004 <.009 <.005 -- <.013

P2 4/5/2005 2 <.02 -- <.004 <.009 <.005 -- <.013

P2 5/24/2005 9 <.02 -- <.004 <.009 <.005 -- <.013

P2 5/24/2005 9 -- <.01 -- -- -- <.02 --

P2 6/28/2005 9 <.02 -- <.004 <.009 <.005 -- <.013

P2 8/2/2005 9 <.02 <.01 <.004 <.009 <.005 <.02 <.013

P2 8/2/2005 1 E.02 -- .1 .084 .099 -- .109
22 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Fipronil sulfone, water, filtered, recoverable, micrograms per liter Fipronil, water, filtered, recoverable, micrograms per liter Flumetsulam, water, filtered, recoverable, micrograms per liter Fluometuron, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Fonofos, water, filtered, recoverable, micrograms per liter Imazaquin, water, filtered, recoverable, micrograms per liter Imazethapyr, water, filtered, recoverable, micrograms per liter Imidacloprid, water, filtered, recoverable, micrograms per liter D2 3/22/2005 2 <0.024 <0.016 <0.04 <0.02 <0.003 <0.004 <0.004 <0.020 D2 3/22/2005 9 <.024 <.016 <.04 <.02 <.003 <.004 <.004 <.020 D2 5/17/2005 9 <.024 <.016 <.04 <.02 <.003 <.004 <.004 <.020 D2 6/29/2005 9 <.024 <.016 <.04 <.02 <.003 <.004 <.004 <.020 D2 8/3/2005 9 <.024 <.016 <.04 <.02 <.003 <.004 <.004 <.020 P2 3/8/2005 9 <.024 <.016 -- -- <.003 -- -- -- P2 3/8/2005 7 <.024 <.016 -- -- <.003 -- -- -- P2 4/5/2005 9 <.024 <.016 -- -- <.003 -- -- -- P2 4/5/2005 2 <.024 <.016 -- -- <.003 -- -- -- P2 5/24/2005 9 <.024 <.016 -- -- <.003 -- -- -- P2 5/24/2005 9 -- -- -- -- -- <.04 -- -- P2 6/28/2005 9 <.024 <.016 -- -- <.003 -- -- -- P2 8/2/2005 9 <.024 <.016 -- -- <.003 -- -- -- P2 8/2/2005 1 .09 E.099 -- -- .126 -- -- --
Methods of Investigation 23

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date Sample type code

Lindane, 

water, 

filtered, 

recoverable, 

micrograms 

per liter

Linuron, 

water, filtered 

(0.7 micron 

glass fiber 

filter), 

recoverable, 

micrograms 

per liter

Linuron, 

water, filtered 

(0.7 micron glass 

fiber filter),

recoverable, 

micrograms 

per liter

Malathion, 

water, filtered, 

recoverable, 

micrograms 

per liter

MCPA, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

MCPB, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Metalaxyl, 

water, filtered, 

recoverable, 

micrograms 

per liter

Methiocarb, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

D2 3/22/2005 2 <0.004 <0.01 <0.035 <0.027 <0.03 <0.01 <0.01 <0.010

D2 3/22/2005 9 <.004 <.01 <.035 <.027 <.03 <.01 <.01 <.010D2 5/17/2005 9 <.004 <.01 <.035 <.027 <.03 <.05 <.01 <.010D2 6/29/2005 9 <.004 <.01 <.035 <.027 <.03 <.01 <.01 <.010D2 8/3/2005 9 <.004 <.01 <.035 <.027 <.03 <.01 <.01 <.010

P2 3/8/2005 9 <.004 -- <.035 <.027 -- -- -- --

P2 3/8/2005 7 <.004 -- <.035 <.027 -- -- -- --

P2 4/5/2005 9 <.004 -- <.035 <.027 -- -- -- --

P2 4/5/2005 2 <.004 -- <.035 <.027 -- -- -- --

P2 5/24/2005 9 <.004 -- <.035 <.027 -- -- -- --

P2 5/24/2005 9 -- -- -- -- -- -- -- --

P2 6/28/2005 9 <.004 -- <.035 <.027 -- -- -- --

P2 8/2/2005 9 <.004 -- <.035 <.027 -- -- -- --

P2 8/2/2005 1 .123 -- E.162 .084 -- -- -- --
24 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Methomyl, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Methyl parathion, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Metolachlor, water, filtered, recoverable, micrograms per liter Metribuzin, water, filtered, recoverable, micrograms per liter Metsulfuron- methyl, water, filtered, recoverable, micrograms per liter Molinate, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter N-(4-Chlorophenyl)- N’-methylurea, water, filtered, recoverable, micrograms per liter D2 3/22/2005 2 <0.020 <0.015 <0.006 <.006 <0.03 <0.003 <0.04 D2 3/22/2005 9 <.020 <.015 <.006 <.006 <.03 <.003 <.04 D2 5/17/2005 9 <.020 <.015 <.006 <.006 <.03 <.003 <.04 D2 6/29/2005 9 <.020 <.015 <.006 <.006 <.03 <.003 <.04 D2 8/3/2005 9 <.020 <.015 <.006 <.006 <.03 <.003 <.04 P2 3/8/2005 9 -- <.015 <.006 <.006 -- <.003 -- P2 3/8/2005 7 -- <.015 <.006 <.006 -- <.003 -- P2 4/5/2005 9 -- <.015 <.006 <.006 -- <.003 -- P2 4/5/2005 2 -- <.015 <.006 <.006 -- <.003 -- P2 5/24/2005 9 -- <.015 <.006 <.006 -- <.003 -- P2 5/24/2005 9 -- -- -- -- <.03 -- -- P2 6/28/2005 9 -- <.015 <.006 <.006 -- <.003 -- P2 8/2/2005 9 -- <.015 <.006 <.006 <.03 <.003 -- P2 8/2/2005 1 -- .111 .12 .074 -- .105 --
Methods of Investigation 25

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date

Sample 

type 

code

Napropamide, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

Neburon, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Nicosulfuron, 

water, filtered, 

recoverable, 

micrograms 

per liter

Norflurazon, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

Oryzalin, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Oxamyl, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

p,p’-DDE, 

water, 

filtered, 

recoverable, 

micrograms 

per liter

Parathion, 

water, 

filtered, 

recoverable, 

micrograms 

per liter

D2 3/22/2005 2 <0.007 <0.01 <0.04 <0.02 <0.01 <0.03 <0.003 <0.010

D2 3/22/2005 9 <.007 <.01 <.04 <.02 <.01 <.03 <.003 <.010

D2 5/17/2005 9 <.007 <.01 <.04 <.02 <.01 <.03 <.003 <.010

D2 6/29/2005 9 <.007 <.01 <.04 <.02 <.01 <.03 <.003 <.010

D2 8/3/2005 9 <.007 <.01 <.04 <.02 <.01 <.03 <.003 <.010

P2 3/8/2005 9 <.007 -- -- -- -- -- <.003 <.010

P2 3/8/2005 7 <.007 -- -- -- -- -- <.003 <.010

P2 4/5/2005 9 <.007 -- -- -- -- -- <.003 <.010

P2 4/5/2005 2 <.007 -- -- -- -- -- <.003 <.010

P2 5/24/2005 9 <.007 -- -- -- -- -- <.003 <.010

P2 5/24/2005 9 -- -- -- -- -- -- -- --

P2 6/28/2005 9 <.007 -- -- -- -- -- <.003 <.010

P2 8/2/2005 9 <.007 -- -- -- -- -- <.003 <.010

P2 8/2/2005 1 .133 -- -- -- -- -- .071 .112
26 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Pebulate, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Pendimethalin, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Phorate, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Picloram, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Prometon, water, filtered, recoverable, micrograms per liter Propachlor, water, filtered, recoverable, micrograms per liter Propanil, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter D2 3/22/2005 2 <0.004 <0.022 <0.011 <0.03 <0.01 <0.025 <0.011 D2 3/22/2005 9 <.004 <.022 <.011 -- <.01 <.025 <.011 D2 5/17/2005 9 <.004 <.022 <.011 <.03 <.01 <.025 <.011 D2 6/29/2005 9 <.004 <.022 <.011 <.03 <.01 <.025 <.011 D2 8/3/2005 9 <.004 <.022 <.011 <.03 <.01 <.025 <.011 P2 3/8/2005 9 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 3/8/2005 7 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 4/5/2005 9 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 4/5/2005 2 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 5/24/2005 9 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 5/24/2005 9 -- -- -- -- -- -- -- P2 6/28/2005 9 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 8/2/2005 9 <.004 <.022 <.011 -- <.01 <.025 <.011 P2 8/2/2005 1 .102 .084 .028 -- .11 .119 .113
Methods of Investigation 27

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site 

identifier 

(fig. 1)

Date

Sample 

type 

code

Propargite, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

Propham, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

Propiconazole, 

water, filtered, 

recoverable, 

micrograms 

per liter

Propoxur, water, 

filtered (0.7 micron 

glass fiber filter), 

recoverable, 

micrograms 

per liter

Propyzamide, 

water, filtered 

(0.7 micron glass 

fiber filter), 

recoverable, 

micrograms 

per liter

Siduron, 

water, filtered, 

recoverable, 

micrograms 

per liter

Simazine, 

water, 

filtered, 

recoverable, 

micrograms 

per liter

Sulfometuronmethyl, water, 

filtered, 

recoverable, 

micrograms 

per liter

D2 3/22/2005 2 <0.02 <0.030 <0.01 <0.008 <0.004 <0.02 <0.005 <0.038

D2 3/22/2005 9 <.02 <.030 <.01 <.008 <.004 <.02 <.005 <.038

D2 5/17/2005 9 <.02 <.030 <.01 <.008 <.004 <.02 <.005 <.038

D2 6/29/2005 9 <.02 <.030 <.01 <.008 <.004 <.02 <.005 <.038

D2 8/3/2005 9 <.02 <.030 <.01 <.008 <.004 <.02 <.005 <.038

P2 3/8/2005 9 <.02 -- -- -- <.004 -- <.005 --

P2 3/8/2005 7 <.02 -- -- -- <.004 -- <.005 --

P2 4/5/2005 9 <.02 -- -- -- <.004 -- <.005 --

P2 4/5/2005 2 <.02 -- -- -- <.004 -- <.005 --

P2 5/24/2005 9 <.02 -- -- -- <.004 -- <.005 --

P2 5/24/2005 9 -- -- -- -- -- -- -- --

P2 6/28/2005 9 <.02 -- -- -- <.004 -- <.005 --

P2 8/2/2005 9 <.02 -- -- -- <.004 -- <.005 --

P2 8/2/2005 1 .09 -- -- -- .116 -- .104 --
28 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)] Site identifier (fig. 1) Date Sample type code Tebuthiuron, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Terbacil, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Terbacil, water, filtered, recoverable, micrograms per liter Terbufos, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Thiobencarb, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Triallate, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Triclopyr, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter Trifluralin, water, filtered (0.7 micron glass fiber filter), recoverable, micrograms per liter D2 3/22/2005 2 <0.02 <0.034 <0.016 <0.02 <0.010 <0.006 <0.03 <0.009 D2 3/22/2005 9 <.02 <.034 <.016 <.02 <.010 <.006 <.03 <.009 D2 5/17/2005 9 <.02 <.034 <.016 <.02 <.010 <.006 <.03 <.009 D2 6/29/2005 9 <.02 <.034 <.016 <.02 <.010 <.006 <.03 <.009 D2 8/3/2005 9 <.02 <.034 <.016 <.02 <.010 <.006 <.03 <.009 P2 3/8/2005 9 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 3/8/2005 7 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 4/5/2005 9 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 4/5/2005 2 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 5/24/2005 9 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 5/24/2005 9 <.026 -- -- -- -- -- -- -- P2 6/28/2005 9 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 8/2/2005 9 <.02 <.034 -- <.02 <.010 <.006 -- <.009 P2 8/2/2005 1 .1 E.056 -- .05 .127 .127 -- .082
Methods of Investigation 29

Table 4. Concentrations of organic carbon and pesticides in water-quality samples collected at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, Tex., 2005—Continued. [USGS, U.S. Geological Survey; --, no data; <, less than; E, estimated; 1, field spike; 2, field blank; 7, sequential replicate; 9, environmental; 2,4-D, 2,4-Dichlorophenoxyacetic acid; 2,4-DB; 2,4-dichlorophenoxybutyric acid; DCPA, Dimethyl tetrachloroterephthalate ; EPTC, S-Ethyl-Dipropylthiocarbamate; MCPA, 2-methyl-4-chlorophenoxyacetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)]

Site identifier (fig. 1) Date Sample type code Caffeine, water, filtered, recoverable, micrograms per liter Reference material or spike lot number

D2 3/22/2005 2 E0.012 --

D2 3/22/2005 9 .02 --D2 5/17/2005 9 .025 --

D2 6/29/2005 9 <.050 --

D2 8/3/2005 9 <.018 --P2 3/8/2005 9 -- --P2 3/8/2005 7 -- --P2 4/5/2005 9 -- --P2 4/5/2005 2 -- 44,048P2 5/24/2005 9 -- --

P2 5/24/2005 9 -- --

P2 6/28/2005 9 -- --

P2 8/2/2005 9 -- --P2 8/2/2005 1 -- 90,508
30 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Water Quality in the Devils and 

Pecos Rivers 

The water-quality constituents of primary concern 

were total dissolved solids, chloride, sulfate, ammonia 

plus organic nitrogen, nitrate plus nitrite, orthophosphate, 

phosphorus, selenium, and selected pesticides. Water-quality 

samples collected at the Devils River at Pafford Crossing 

gage and Pecos River at Langtry gage are referred to in this 

section by the site identifiers of these gages (sites D2 and P2, 

respectively) (fig. 1 and table 1), and results discussed are for 

the environmental samples collected at each site in the spring 

and summer of 2005. 

Total Dissolved Solids

The concentrations of total dissolved solids (TDS) 

were an order of magnitude smaller in the environmental 

samples collected from the Devils River at site D2 compared 

to the concentrations of total dissolved solids measured in 

environmental samples collected from the Pecos River at 

site P2, ranging from 208 to 232 mg/L at site D2 and from 

1,460 to 2,390 mg/L at site P2 (table 2). The higher TDS 

concentrations measured in the samples collected in the Pecos 

River compared to the TDS concentrations measured in the 

samples collected from the Devils River likely reflect some 

contribution to streamflow in the Pecos River of groundwater 

of different salinity characteristics, including relatively less 

saline groundwater with total dissolved solid concentrations 

less than 3,000 mg/L, moderately saline groundwater (3,000 

to 10,000 mg/L total dissolved solids), and highly saline 

groundwater (more than 10,000 mg/L total dissolved solids) 

(Ashworth and Hopkins, 1995) (Purchase and others, 2001). 

Reduced inflows of relatively less saline groundwater 

compared to historical inflow amounts, caused by increases 

in groundwater pumping over time and impoundments on the 

Pecos River in New Mexico (upstream from the study area), 

have also contributed to the relatively high concentrations of 

total dissolved solids observed in the Pecos River (Purchase 

and others, 2001). Dissolved-solids concentrations did not 

exceed the State water-quality standard of 300 mg/L for the 

Devils River segment that includes site D2, nor the proposed 

State water-quality standard of 4,000 mg/L for the Pecos 

River segment that includes site P2 (Texas Commission on 

Environmental Quality, 2010). 

Chloride

Chloride concentrations were an order of magnitude 

smaller in the environmental samples collected from the 

Devils River at site D2 compared to chloride concentrations 

measured in environmental samples collected from the Pecos 

River at site P2, ranging from 11.6 to 12.9 mg/L at site D2, 

and from 519 to 879 mg/L at site P2 (table 2). Chloride 

concentrations measured in samples collected in 2005 at site 

D2 did not exceed the proposed State water-quality standard 

of 50 mg/L for the segment of the Devils River containing 

this sampling site (Texas Commission on Environmental 

Quality, 2010) and were between the minimum (6.9 mg/L) 

and lower quartile (25th percentile) of 14 mg/L reported for 

chloride samples collected at this sampling site as part of 

the USGS HBN program during 1978–95 (U.S. Geological 

Survey, 2011) (table 5). Chloride concentrations measured 

in samples collected in 2005 at site P2 did not exceed the 

proposed State water-quality standard of 1,700 mg/L for the 

Pecos River segment that includes site P2 (Texas Commission 

on Environmental Quality, 2010) and represented a range of 

values similar to the interquartile range of 548 to 942 mg/L 

reported for chloride concentrations by the USGS NASQAN 

program during 1974–2007 (U.S. Geological Survey, 2010; 

table 5). The interquartile range represents the central 50 

percent of the data (Helsel and Hirsch, 2002). 

Sulfate

Sulfate concentrations were an order of magnitude 

smaller in the environmental samples collected during 

March–August 2005 from the Devils River compared 

to sulfate concentrations measured in the environmental 

samples collected during April–August 2005 from the Pecos 

River. Sulfate concentrations ranged from 7.55 to 8.20 mg/L 

at site D2 and from 298 to 503 mg/L at site P2 (table 2), 

concentrations that were somewhat smaller compared to those 

measured in environmental samples for chloride. Sulfate 

concentrations measured in 2005 did not exceed proposed 

State water-quality standards of 50 mg/L and 1,000 mg/L for 

the Devils and Pecos River segments, respectively (Texas 

Commission on Environmental Quality, 2010).

Ammonia Plus Organic Nitrogen

Concentrations of ammonia plus organic nitrogen as 

nitrogen (N) measured in environmental samples collected 

during the spring and summer of 2005 at site D2 were 

less variable compared to those measured at site P2, and 

the concentrations of ammonia plus organic nitrogen as N 

were approximately twice as large at site P2 compared to 

those at site D2 (table 2). Ammonia plus organic nitrogen 

concentrations ranged from 0.12 to 0.14 mg/L of N at site 

D2, and from 0.15 to 0.32 mg/L of N at site P2 (table 2). The 

minimum ammonia plus organic nitrogen concentrations 

(0.12 mg/L of N at site D2 and 0.15 mg/L of N at site P2) 

were measured in environmental samples collected in late 

March 2005 at site D2 and in early March 2005 at site P2. 
Water Quality in the Devils and Pecos Rivers 31

Table 5. Concentrations of selected major ions and nutrients measured in water-quality samples collected in 2005 at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, with summary statistics from samples collected at station 08449400 during 1978–1995 as part of the U.S. Geological Survey Hydrologic Benchmark Network (U.S. Geological Survey, 2011), and summary statistics from samples collected at station 08447410 during 1974–2007 as part of U.S. Geological Survey National Stream Quality Accounting Network (U.S. Geological Survey, 2010).[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; mg/L, milligrams per liter; --, no data; <, less than the value; *, data estimated by using a log-probability regression to predict the values of data 

below the detection limit (U.S. Geological Survey, 2006, p. 102; Helsel and Hirsch, 2002)] 

Site 

identifier 

(fig. 1)

USGS

station 

no.

USGS station 

name

Sample

collection

date

Daily mean 

discharge, 

ft3/s

Chloride, water, filtered,

milligrams per liter

Minimum, 

mg/L

25th 

percentile, 

mg/L

Median, 

mg/L

75th 

percentile, 

mg/L

Maximum, 

mg/L

Number of 

analyses used 

in the summary 

statistics

D2 08449400

Devils River at 

Pafford Crossing near Comstock, Tex.

3/22/2005 576 11.8

6.90 14.0 15.0 16.0 26.0 104

5/17/2005 417 11.6

6/29/2005 480 12.9

8/3/2005 396 12.5

P2 08447410 Pecos River near Langtry, Tex.

3/8/2005 322 819

100 548 720 942 1,500 290

4/5/2005 271 879

5/24/2005 204 623

6/28/2005 186 795

8/2/2005 180 519

Site 

identifier 

(fig. 1)

USGS

station 

no.

USGS station 

name

Sample

collection

date

Daily mean 

discharge, 

ft3/s

Ammonia plus 

organic nitrogen, water, 

filtered, milligrams per 

liter as nitrogen

Minimum, 

mg/L

25th 

percentile, 

mg/L

Median, 

mg/L

75th 

percentile, 

mg/L

Maximum, 

mg/L

Number of 

analyses used 

in the summary 

statistics

D2 08449400

Devils River at 

Pafford Crossing near Comstock, Tex.

3/22/2005 576 0.12

0.10 0.23 0.42 0.62 1.4 40

5/17/2005 417 .13

6/29/2005 480 .14

8/3/2005 396 .13

P2 08447410 Pecos River near Langtry, Tex.

3/8/2005 322 .15

-- *.18 *.26 *.40 *1.4 145

4/5/2005 271 .22

5/24/2005 204 .32

6/28/2005 186 .29

8/2/2005 180 .29
32 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Site identifier (fig. 1) USGS station no. USGS station name Sample collection date Daily mean discharge, ft3/s Nitrate plus nitrite, water, filtered, mg/L as nitrogen Minimum, mg/L 25th percentile, mg/L Median, mg/L 75th percentile, mg/L Maximum, mg/L Number of analyses used in the summary statistics D2 08449400 Devils River at Pafford Cross- ing near Com- stock, Tex. 3/22/2005 576 1.24 0.10 1.2 1.4 1.6 3.9 48 5/17/2005 417 1.15 6/29/2005 480 0.99 8/3/2005 396 1.02 P2 08447410 Pecos River near Langtry, Tex. 3/8/2005 322 1.04 -- *0.19 *0.61 *0.95 *3.2 149 4/5/2005 271 .83 5/24/2005 204 .4 6/28/2005 186 .22 8/2/2005 180 .29 Table 5. Concentrations of selected major ions and nutrients measured in water-quality samples collected in 2005 at U.S. Geological Survey stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation Area, with summary statistics from samples collected at station 08449400 during 1978–1995 as part of the U.S. Geological Survey Hydrologic Benchmark Network (U.S. Geological Survey, 2011), and summary statistics from samples collected at station 08447410 during 1974–2007 as part of U.S. Geological Survey National Stream Quality Accounting Network (U.S. Geological Survey, 2010).—Continued. [USGS, U.S. Geological Survey; ft3/s, cubic feet per second; mg/L, milligrams per liter; --, no data; <, less than the value; *, data estimated by using a log-probability regression to predict the values of data below the detection limit (U.S. Geological Survey, 2006, p. 102; Helsel and Hirsch, 2002)] 
Water Quality in the Devils and Pecos Rivers 33

 Ammonia plus organic nitrogen concentrations as N 

measured in the samples collected from the Devils River 

in 2005 at site D2 were less than the lower quartile (25th 

percentile) value of 0.23 mg/L reported for samples collected 

by the USGS HBN program at this site during 1978–95 

(U.S. Geological Survey, 2011) (table 5). The concentrations 

of ammonia plus organic nitrogen as N measured in 

samples collected at site P2 in 2005 generally were within 

the interquartile range of ammonia plus organic nitrogen 

concentrations as N reported by the USGS NASQAN program 

for samples collected at this site during 1974–2007. The 

largest ammonia plus organic nitrogen concentration measured 

in 2005 (0.32 mg/L of N measured in a sample collected at 

site P2) was smaller than the 75th percentile (0.40 mg/L of N) 

measured in the samples collected by the USGS NASQAN 

program at site P2 during 1974–2007 (table 5). 

Nitrate Plus Nitrite Nitrogen

Nitrate plus nitrite concentrations measured in 2005 

ranged from 0.99 to 1.24 mg/L of N in the environmental 

samples collected at site D2 and from 0.22 to 1.04 mg/L of N 

in the environmental samples collected at site P2 (table 2). The 

highest nitrate plus nitrite concentrations were measured in 

samples collected in the early spring (March 2005 at sites D2 

and P2). Although nitrate plus nitrite concentrations measured 

in 2005 in samples collected at site D2 were within the 

historical range of concentrations for samples collected by the 

USGS HBN program during 1978–95, the 2005 concentrations 

were lower compared to the historical median concentration 

of nitrate plus nitrite (1.4 mg/L of N). The nitrate plus nitrite 

concentrations measured in 2005 in samples collected at site 

P2 generally were within the historical interquartile range 

of nitrate plus nitrite concentrations (0.19 to 0.95 mg/L) 

measured in samples collected as part of the USGS NASQAN 

program (table 5). 

Orthophosphate and Total Phosphorus

Orthophosphate and total phosphorous concentrations 

in water were not detected in samples collected in 2005 from 

sites D2 and P2 at concentrations equal to or larger than the 

laboratory reporting levels (LRLs) for these constituents (the 

LRLs were 0.018 mg/L for orthophosphate and 0.004 mg/L for 

total phosphorous) (table 2). During previous studies by the 

National Park Service, total phosphorous and orthophosphate 

concentrations generally were between 0.01 and 0.03 mg/L at 

site D2 (Purchase and others, 2001).

Selenium

Selenium concentrations at site D2 ranged from 0.3 

μg/L (estimated value) to 0.6 μg/L; two values equal to or 

more than the laboratory reporting level of 0.5 μg/L were 

obtained—values of 0.5 and 0.6 μg/L were measured in 

samples collected in March and May 2005 at site D2. At site 

P2, selenium concentrations ranged from 1.0 μg/L to 3.1 μg/L 

(table 3). None of the selenium concentrations measured in 

samples collected during the spring and summer of 2005 from 

the Devils or Pecos Rivers exceeded the Surface Water Quality 

Standards establish by the State for the protection of aquatic 

life (chronic criterion of 5μg/L or the acute criterion of 20 

μg/L) (Texas Commission on Environmental Quality, 2010). 

In previous sediment studies, selenium values did exceed 

screening guidelines of 2 mg/kg in a different sample medium 

(river-bed sediment samples from the Pecos River) (Purchase 

and others, 2001) and in lake-bed sediment samples collected 

from the Amistad Reservoir (Lee and Wilson, 1997). 

Pesticides

Water-quality samples collected at site D2 during March–

August 2005 were analyzed for 162 pesticides (including both 

polar and non-polar compounds), and samples collected at 

site P2 during April–August 2005 were analyzed for 54 polar 

and non-polar pesticides (table 4). No pesticide concentrations 

were reported at concentrations equal to or larger than the 

laboratory reporting level (LRL) in the environmental samples 

collected at sites D2 or P2. In a previous study, no pesticides 

were reported at concentrations equal to or larger than the 

LRLs in samples collected from the Pecos River downstream 

from site P2 (International Boundary and Water Commission, 

1994), and none were reported at concentrations equal to or 

larger than the LRLs at site P2 between 1996 and 2000 as part 

of the NASQAN program (U.S. Geological Survey, 2010). 

Sites D2 and P2 are downstream from where these rivers 

gain streamflow from springs; the inflows from these springs 

are unlikely to contain appreciable amounts of pesticides. As 

noted in the “Description of Study Area” section, land use in 

the Devils River watershed is dominated by ranches and small 

rural home developments, and these land uses are not likely 

to be a major source of pesticides to the river (Purchase and 

others, 2001). 

Composition of Fish and Macroinvertebrate 

Communities in the Devils and Pecos Rivers 

As explained in the section “Collection and Processing of 

Fish and Macroinvertebrate Samples,” the composition of fish 

and macroinvertebrate communities in the Devils and Pecos 

Rivers were evaluated by collecting fish and macroinvertebrate 

samples in stream reaches at the Devils River at Pafford 

Crossing gage and Pecos River at Langtry gage (sites D2, and 

P2, respectively) and in stream reaches at six additional sites, 

three on each river (fig. 1; table 1). Fish and macroinvertebrate 

community assessments are referred to in this section by the 

site numbers where the fish and macroinvertebrate samples 

were collected (sites D1–D4 on the Devils River and sites 

P1–P4 on the Pecos River) (fig. 1 and table 1). 
34 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Fish Communities

A total of 29 species of fish each was collected during 

2006–7 from both the Devils and Pecos Rivers, and 25 species 

were common to both rivers (tables 6–8). Among the species 

of fish at the Devils River sites, 7 species are non-native 

(introduced), and 22 species are native to the Devils River 

(table 6). At the Pecos River sites, 6 species of fish are nonnative, and 23 species are native to the river (table 6).

Devils River

The species of fish collected in the Devils River varied 

among sites, from a minimum of 17 species (2006 sampling 

only) at site D3 to a maximum of 23 species (2006 and 

2007 samplings combined) at site D2 (table 7). Five species 

collected at site D2 in 2006 were not collected from this 

site in 2007, and four species collected at site D2 in 2007 

were not collected from this site in 2006. Previous fish 

community surveys that found 15 species of fish at the site 

farthest downstream (site D2) (International Boundary and 

Water Commission, 1994) and 18 species at the site farthest 

upstream (site D4) (Linam and Kleinsasser, 2002) differed 

slightly from the number of species collected at sites D2 and 

D4 in this study. The difference in the number of species 

collected in this study compared to the previous studies could 

be because of differences in the types of sampling equipment 

used, fish mobility, or both. Additionally, two surveys were 

done in this study in 2006 and 2007 at sites D2 and D4, and 

only one survey was done in each of the previous studies 

(International Boundary and Water Commission, 1994; Linam 

and Kleinsasser, 2002).

More redbreast sunfish were collected than any other 

species of fish in the Devils River followed by a number of 

species of shiners (family Cyprinidae) including the blacktail 

shiner and prosperine shiner (table 7). The Rio Grande cichlid, 

the only native member of the family Cichlidae in Texas, was 

also abundant at the Devils River sites, particularly the two 

most upstream sites (D3 and D4). Fish species collected in the 

Devils River that were not found at the Pecos River study sites 

included the Devils River minnow, sailfin molly, smallmouth 

bass, spotted bass, and warmouth (tables 6–8). The redbreast 

sunfish, sailfin molly, and smallmouth bass are all introduced 

species that are not native to the Devils River (Hubbs and 

others, 1991). 

Pecos River

Of the 29 species of fish collected from the Pecos River, 

6 species are non-native (introduced) and include the bullhead 

minnow, common carp, sheepshead minnow, inland silverside, 

redbreast sunfish, and redear sunfish (table 8). Considering 

only the 2006 sampling results, the number of fish species 

decreased about 42 percent (from 19 to 11) between the most 

upstream and the sites farthest downstream on the Pecos River. 

When both the 2006 and 2007 sampling results are considered, 

the largest number of species (26) was collected from site 

P4. Previous studies found similar upstream to downstream 

decreases in species richness in the lower Pecos River, with 

13 species documented at site P4 compared to 6 species at site 

P1 (International Boundary and Water Commission, 1994; 

Linam and Kleinsasser, 1996).

 The most abundant species among the Pecos River sites 

were the blacktail shiner followed by the red shiner and central 

stoneroller; however, central stonerollers were collected only 

at site P4 (table 8). These and other members of the family 

Cyprinidae were the most abundant fishes overall among the 

Pecos River sites followed by species of sunfish and bass—all 

of the family Centrarchidae. The redbreast sunfish was the 

most common species of sunfish in both rivers, although less 

abundant in the Devils River. Fish species collected in the 

Pecos River but not in the Devils River include the bullhead 

minnow, red shiner, smallmouth buffalo, rainwater killifish, 

and freshwater drum. 

Comparison between the Devils and 

Pecos Rivers 

Butler and von Guerard (1996) note “salinity, or the 

dissolved-solids concentration, is the measure of salts such 

as sodium chloride, calcium bicarbonate, and calcium sulfate 

that are dissolved in water.” Most freshwater fishes adjust to 

changes in salinity through a physiological process known as 

osmoregulation, and some species are more tolerant that others 

of higher salinity because of their ability to osmoregulate in 

more saline freshwater environments (Moyle and Cech, 1982). 

The percentage of tolerant fish species was larger at the two 

sites farthest upstream on the Pecos River compared to the 

two most upstream sites on the Devils River (table 9). This 

is likely because salinity in the Pecos River has historically 

been higher compared to salinity in the Devils River (Linam 

and Kleinsasser, 1996). The percentage of fish collected at the 

site farthest downstream on each river that were omnivores 

(fish that feed on a mixed diet of plant and animals) was 

considerably larger compared to the percentage of omnivores 

at the more upstream sites. Compared to upstream sites, the 

relatively larger percentage of omnivorous fish species at 

the most downstream sites on the Devils and Pecos Rivers 

might be because of their proximity to the impounded waters 

of Amistad Reservoir where omnivorous species of fish are 

likely more common; fish assemblages in temperate southern 

reservoirs such as Amistad Reservoir typically are dominated 

by large-bodied benthic omnivores (Gido, 2001). The 

percentage of introduced individuals was two to three times 

larger at Devils River sites D2 and D3 compared to Pecos 

River sites P2 and P3 and was influenced by the relatively 

large abundance of the non-native redbreast sunfish and 

smallmouth bass at the Devils River study sites. 
Water Quality in the Devils and Pecos Rivers 35

Table 6. Presence or absence of fish taxa and total number of fish species collected from sites on the Devils and Pecos Rivers in 

and upstream from the Amistad National Recreation Area, Texas, 2006–7.

[Shading indicates individual organisms representing the species of fish that were collected. Taxon (singular) or taxa (plural) refers to a genetically related 

group or groups of one or more organisms with common characteristics that differentiated them as a unit. From International Commission on Zoological 

Nomenclature (2010)]

Family Species Common name Status Devils River Pecos River

Lepisosteidae Lepisosteus osseus Longnose gar Native

Clupeidae Dorosoma cepedianum Gizzard shad Native

Cyprinidae Cyprinella venustus Blacktail shiner Native

Pimphales vigilax Bullhead minnow Introduced

Campostoma anomalum Central stoneroller Native

Cyprinus carpio Common carp Introduced

Dionda diobala Devils River minnow Native

Cyprinella prosperpina Prosperine shiner Native

Cyprinella lutrensis Red shiner Native

Dionda episcopa Roundnose minnow Native

Notropis amabilis Texas shiner Native

Catostomidae Scartomyzon cangestum Gray redhorse Native

Ictiobus bubalus Smallmouth buffalo Native

Carpiodes carpio River carpsucker Native

Characidae Astyanax mexicanus Mexican tetra Native

Ictaluridae Ictalurus punctatus Channel catfish Native

Ictaluridae Pylodictis olivaris Flathead catfish Native

Lucania parva Rainwater killifish Native

Cyprinodontidae Cypreinidon variegatus Sheepshead minnow Introduced

Poecilidae Poecilia latipinna Sailfin molly Introduced

Gambusia affinis Western mosquitofish Native

Atherinopsidae Menidia beryllina Inland silverside Introduced

Percidae Etheostoma grahami Rio Grande darter Native

Cichlidae Cichlasoma cyanoguttatum Rio Grande cichlid Native

Centrarchidae Lepomis macrochirus Bluegill Native

Lepomis cyanellus Green sunfish Native

Micropterus salmoides Largemouth bass Native

Lepomis megalotis Longear sunfish Native

Lepomis auritus Redbreast sunfish Introduced

Lepomis microlophus Redear sunfish Introduced

Micropterus dolomieu Smallmouth bass Introduced

Micropterus punctulatus Spotted bass Native

Lepomis gulosus Warmouth Native

Scianidae Aplodinotus grunniens Freshwater drum Native

Number of species 29 29
36 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 7. Fish species, number of individuals, native status, trophic group, tolerance classification, and total number of species collected from the study sites along the Devils River in and upstream from the Amistad National Recreation Area, Texas, 2006–7. [DN-N, replicate sampling of fish at selected sites in 2007; NA, tolerance classification not available for this species of fish; *, confirmed presence of species but accurate total not available] Family Species Common name Status Trophic Group Tolerance Site identifier and USGS station name No. of indi- viduals from all sites on Devils River D1 D2 D2 D3 D4 D4 Devils River near Satan Canyon, Tex. Devils River at Pafford Crossing near Comstock, Tex. (sample 1) Devils River at Pafford Crossing near Comstock, Tex. (sample 2) Devils River near Turkey Bluff Canyon, Tex. Devils River at Dolan Falls, Tex. (sample 1) Devils River at Dolan Falls, Tex. (sample 2) 06/05/2006 06/06/2006 03/06/2007 06/07/2006 06/08/2006 03/07/2006 Lepisosteidae Lepisosteus osseus Longnose gar Native Piscivore Tolerant 1 3 4 1 9 Clupeidae Dorosoma cepedianum Gizzard shad Native Omnivore Tolerant 6 6 Cyprinidae Cyprinella venustus Blacktail shiner Native Invertivore NA 24 14 7 101 37 53 236 Pimphales vigilax Bullhead minnow Introduced Invertivore NA 0 Campostoma anomalum Central stoneroller Native Herbivore NA 4 2 66 37 109 Cyprinus carpio Common carp Introduced Omnivore Tolerant 1 5 5 11 Dionda diobala Devils River minnow Native Invertivore Intolerant *1 3 1 5 Cyprinella prosperpina Prosperine shiner Native Invertivore NA 18 18 43 16 86 181 Cyprinella lutrensis Red shiner Native Invertivore Tolerant 0 Dionda episcopa Roundnose minnow Native Invertivore Intolerant 4 9 13 Notropis amabilis Texas shiner Native Invertivore NA 3 50 10 5 68 Catastomidae Scartomyzon cangestum Gray redhorse Native Invertivore NA 1 9 11 39 10 28 98

Ictiobus 

bubalus

Smallmouth 

buffalo

Native Omnivore NA 0
Water Quality in the Devils and Pecos Rivers 37

Carpiodes 

carpio

River 

carpsucker

Native Omnivore Tolerant 6 7 13 2 28

Characidae Astyanax 

mexicanus

Mexican tetra Native Invertivore NA 3 21 54 78

Ictaluridae Ictalurus 

punctatus

Channel catfish Native Omnivore Tolerant 22 11 1 6 19 15 74

Pylodictis 

olivaris

Flathead catfish Native Piscivore NA 1 2 7 4 14

Cyprinodontidae Lucania parva Rainwater 

killifish

Native Invertivore NA 0

Cypreinidon 

variegatus

Sheepshead 

minnow

Introduced Omnivore Tolerant 4 1 5

Poecilidae Poecilia 

latipinna

Sailfin molly Introduced Omnivore Tolerant 1 1

Gambusia 

affinis

Western 

mosquitofish

Native Invertivore Tolerant 7 12 9 19 53 100

Atherinidae Menidia 

beryllina

Inland 

silverside

Introduced Invertivore NA 1 1 2

Percidae Etheostoma 

grahami

Rio Grande 

darter

Native Invertivore NA 6 4 1 11

Cichlidae Cichlasoma 

cyanoguttatum

Rio Grande 

cichlid

Native Invertivore NA 2 5 1 25 84 34 151

Centrarchidae Lepomis 

macrochirus

Bluegill Native Invertivore Tolerant 59 21 80

Lepomis 

cyanellus

Green sunfish Native Piscivore Tolerant 1 2 1 1 5

Table 7. Fish species, number of individual specimens, native status, trophic group, tolerance classification, and total number of species collected from the study sites along the Devils River in and upstream from the Amistad National Recreation Area, Texas, 2006–7. —Continued.[DN-N, replicate sampling of fish at selected sites in 2007; NA, tolerance classification not available for this species of fish; *, confirmed presence of species but accurate total not available]

Family Species Common name Status Trophic Group Tolerance 

Site identifier and USGS station name

No. of

individuals

from 

all

sites 

on

Devils 

River

D1 D2 D2 D3 D4 D4

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils River

at Pafford 

Crossing

near 

Comstock, 

Tex. 

(sample 1)

Devils River

at Pafford 

Crossing

near 

Comstock, 

Tex. 

(sample 2)

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, Tex. 

(sample 1)

Devils 

River

at Dolan 

Falls, Tex. 

(sample 2)

06/05/2006 06/06/2006 03/06/2007 06/07/2006 06/08/2006 03/07/2006
38 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Micropterus salmoides Largemouth bass Native Piscivore NA 27 7 1 1 36 Lepomis megalotis Longear sunfish Native Invertivore NA 17 31 9 12 13 5 87 Lepomis auritus Redbreast sunfish Introduced Invertivore NA 79 35 19 109 19 2 263 Lepomis microlophus Redear sunfish Introduced Invertivore NA 36 1 37 Micropterus dolomieu Smallmouth bass Introduced Piscivore Intolerant 5 1 26 21 2 55 Micropterus punctulatus Spotted bass Native Piscivore NA 2 1 3 Lepomis gulosus Warmouth Native Piscivore Tolerant 7 7 Scianidae Aplodinotus grunniens Freshwater drum Native Invertivore Tolerant 0 Number of individuals 301 189 111 437 355 380 1,773 Number of species 19 19 17 17 18 15 29 Table 7. Fish species, number of individual specimens, native status, trophic group, tolerance classification, and total number of species collected from the study sites along the Devils River in and upstream from the Amistad National Recreation Area, Texas, 2006–7.—Continued. [DN-N, replicate sampling of fish at selected sites in 2007; NA, tolerance classification not available for this species of fish; *, confirmed presence of species but accurate total not available] Family Species Common name Status Trophic Group Tolerance Site identifier and USGS station name No. of indi- viduals from all sites on Devils River D1 D2 D2 D3 D4 D4 Devils River near Satan Canyon, Tex. Devils River at Pafford Crossing near Comstock, Tex. (sample 1) Devils River at Pafford Crossing near Comstock, Tex. (sample 2) Devils River near Turkey Bluff Canyon, Tex. Devils River at Dolan Falls, Tex. (sample 1) Devils River at Dolan Falls, Tex. (sample 2) 06/05/2006 06/06/2006 03/06/2007 06/07/2006 06/08/2006 03/07/2006
Water Quality in the Devils and Pecos Rivers 39

Table 8. Fish species, number of individual specimens, native status, trophic group, tolerance classification, and total number of species collected from the study sites along the Pecos River in and upstream from the Amistad National Recreation Area, Texas, 2006–7. [DN-N, replicate sampling of fish at selected sites in 2007; NA, tolerance classification not available for this species of fish]

Family Species Common name Status Trophic Group Tolerance

Site Indentifier and USGS station name

No. of

individuals

from all

sites on

Pecos 

River

P1 P2 P2 P3 P4 P4

Pecos 

River

at Shumla

Bend, Tex.

Pecos 

River

near 

Langtry, 

Tex. 

(sample 1)

Pecos 

River

near 

Langtry, 

Tex. 

(sample 2)

Pecos 

River

near 

Everett

Canyon, 

Tex.

Pecos 

River at 

Pandale, 

Tex.

(sample 1)

Pecos 

River at 

Pandale, 

Tex. 

(sample 2)

06/27/2006 06/28/2006 03/08/2007 06/29/2006 06/22/2006 03/09/2007

Lepisosteidae Lepisosteus 

osseus

Longnose 

gar

Native Piscivore Tolerant 3 2 7 1 13

Clupeidae Dorosoma 

cepedianum 

Gizzard shad Native Omnivore Tolerant 20 1 21

Cyprinidae Cyprinella 

venustus

Blacktail 

shiner

Native Invertivore NA 14 5 368 12 14 8 421

Pimphales 

vigilax

Bullhead 

minnow

Introduced Invertivore NA 10 5 15

Campostoma 

anomalum

Central 

stoneroller

Native Herbivore NA 235 235

Cyprinus carpio Common 

carp

Introduced Omnivore Tolerant 5 1 3 1 2 12

Dionda 

diobala

Devils River 

minnow

Native Invertivore Intolerant 0

Cyprinella 

prosperpina

Prosperine 

shiner

Native Invertivore NA 32 71 44 147

Cyprinella 

lutrensis 

Red shiner Native Invertivore Tolerant 4 57 204 265

Dionda 

episcopa

Roundnose 

minnow

Native Invertivore Intolerant 18 16 4 38

Notropis 

amabilis

Texas shiner Native Invertivore NA 2 8 9 2 21

Catastomidae Scartomyzon 

cangestum

Gray redhorse Native Invertivore NA 1 4 11 2 1 19

Ictiobus 

bubalus

Smallmouth 

buffalo

Native Omnivore NA 4 4

Carpiodes 

carpio

River carpsucker Native Omnivore Tolerant 4 1 1 6
40 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Characidae Astyanax mexicanus Mexican tetra Native Invertivore NA 2 6 2 10 Ictaluridae Ictalurus punctatus Channel catfish Native Omnivore Tolerant 16 4 2 3 7 6 38 Pylodictis olivaris Flathead catfish Native Piscivore NA 2 1 2 6 5 16 Cyprinodontidae Lucania parva Rainwater killifish Native Invertivore NA 1 2 1 4 Cypreinidon variegatus Sheepshead minnow Introduced Omnivore Tolerant 1 8 10 31 50 Poecilidae Poecilia latipinna Sailfin molly Introduced Omnivore Tolerant 0 Gambusia affinis Western mosquito- fish Native Invertivore Tolerant 11 15 14 6 46 Atherinidae Menidia beryllina Inland silverside Introduced Invertivore NA 57 4 61 Percidae Etheostoma grahami Rio Grande darter Native Invertivore NA 2 1 6 1 10 20 Cichlidae Cichlasoma cyanogut- tatum Rio Grande cichlid Native Invertivore NA 1 2 3 14 3 23 Centrarchidae Lepomis macrochirus Bluegill Native Invertivore Tolerant 6 1 2 1 10 Lepomis 

cyanellus

Green sunfish Native Piscivore Tolerant 2 1 3

Micropterus 

salmoides

Largemouth 

bass

Native Piscivore NA 12 3 3 2 1 21

Table 8. Fish species, number of individual specimens, native status, trophic group, tolerance classification, and total number of species collected from the study sites along the Pecos River in and upstream from the Amistad National Recreation Area, Texas, 2006–7.—Continued.[DN-N, replicate sampling of fish at selected sites in 2007; NA, tolerance classification not available for this species of fish]

Family Species Common name Status Trophic Group Tolerance

Site Indentifier and USGS station name

No. of

individuals

from all

sites on

Pecos 

River

P1 P2 P2 P3 P4 P4

Pecos 

River

at Shumla

Bend, Tex.

Pecos 

River

near 

Langtry, 

Tex. 

(sample 1)

Pecos 

River

near 

Langtry, 

Tex. 

(sample 2)

Pecos 

River

near 

Everett

Canyon, 

Tex.

Pecos 

River at 

Pandale, 

Tex.

(sample 1)

Pecos 

River at 

Pandale, 

Tex. 

(sample 2)

06/27/2006 06/28/2006 03/08/2007 06/29/2006 06/22/2006 03/09/2007
Water Quality in the Devils and Pecos Rivers 41

Lepomis megalotis Longear sunfish Native Invertivore NA 3 2 14 22 41

Lepomis auritus Redbreast 

sunfish

Introduced Invertivore NA 20 7 2 20 69 118

Lepomis microlophus Redear sunfish Introduced Invertivore NA 1 1

Micropterus 

dolomieu

Smallmouth 

bass

Introduced Piscivore Intolerant 0

Micropterus 

punctulatus

Spotted bass Native Piscivore NA 0

Lepomis gulosus Warmouth Native Piscivore Tolerant 0

Scianidae Aplodinotus 

grunniens

Freshwater 

drum

Native Invertivore Tolerant 4 4

Number of individuals 135 72 446 246 333 451 1,683

Number of species 11 15 13 22 21 19 29

Table 8. Fish species, number of individual specimens, native status, trophic group, tolerance classification, and total number of species collected from the study sites along the Pecos River in and upstream from the Amistad National Recreation Area, Texas, 2006–7.—Continued.[DN-N, replicate sampling of fish at selected sites in 2007; NA, tolerance classification not available for this species of fish]

Family Species Common name Status Trophic Group Tolerance

Site Indentifier and USGS station name

No. of

individuals

from all

sites on

Pecos 

River

P1 P2 P2 P3 P4 P4

Pecos 

River

at Shumla

Bend, Tex.

Pecos 

River

near 

Langtry, 

Tex. 

(sample 1)

Pecos 

River

near 

Langtry, 

Tex. 

(sample 2)

Pecos 

River

near 

Everett

Canyon, 

Tex.

Pecos 

River at 

Pandale, 

Tex.

(sample 1)

Pecos 

River at 

Pandale, 

Tex. 

(sample 2)

06/27/2006 06/28/2006 03/08/2007 06/29/2006 06/22/2006 03/09/2007
42 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Table 9. Number of fish species, selected fish community metrics, and the total number of fish collected from the study sites along 

the Devils and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006–7. 

[USGS, U.S. Geological Survey; Asterisk indicates fish data were combined for fish surveys done in 2006 and 2007; Sums of species groups will not equal 

total number of species because not all categories of species are represented and categories are not mutually exclusive; Percentages will not equal 100 because 

only selected groups of species and individuals are represented in the table]

Metric

Site identifier and USGS station name

D1 D2* D3 D4* P1 P2* P3 P4*

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils 

River

at Pafford 

Crossing

near 

Comstock, 

Tex.

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, 

Tex.

Pecos 

River

at 

Shumla

Bend, 

Tex.

Pecos 

River

near 

Langtry, 

Tex.

Pecos 

River

near 

Everett

Canyon, 

Tex.

Pecos 

River

at 

Pandale, 

Tex.

Number of species1 19 23 17 19 11 21 22 26

Number of native cyprinid species 1 6 5 6 1 5 5 6

Number of invertivore species 10 12 11 12 5 14 14 16

Number of sunfish species (all species of 

the genus Lepomis sp.)

6 5 3 2 1 3 4 4

Number of intolerant species 0 3 2 3 0 1 1 1

Percent of tolerant species2 36.84 39.13 29.41 15.79 36.36 38.10 40.91 38.46

Percent of omnivorous individuals2 11.63 16.00 1.83 4.63 36.30 1.54 6.10 7.53

Percent of invertivorous individuals2 75.75 75.33 90.62 76.19 54.81 96.72 90.24 59.57

Percent of introduced individuals2 38.87 25.67 7.00 5.99 46.67 5.60 9.35 18.11

Total number of individuals collected 301 300 437 735 135 518 246 784

Menhinick species richness3 1.10 1.33 0.81 0.70 0.95 0.92 1.40 0.93

1

 The total number of species for each site is greater than the sum of the number of species in the metrics included in this table because not all species 

collected are included in the metrics selected. Refer to tables 7 and 8 for data used to calculate the count metrics. 

2

 The percentages calculated in this table are based on the tolerance or intolerance of a species to degraded water-quality conditions or trophic group 

(for example, omnivore or invertivore) as shown in tables 7 and 8.

3

 Menhinick species richness is calculated as the cumulative number of species from a site divided by the square root of the total number of individuals 

collected at the site.

On the basis of the first Non-metric Multidimensional 

Scaling (NMDS) dimension (dimension 1 on the x-axis in 

fig. 2), the fish communities from all sites on a given river 

(determined from the species present at the time of collection 

from either the Devils or Pecos River) were more similar to 

one another than to the fish communities from sites on the 

other river. The second dimension of the NMDS (dimension 

2 on the y-axis in fig. 2) indicates that between the two rivers, 

the fish community from any given site is most similar to 

the fish community at the site on the other river of the same 

downstream order. 

The difference in fish communities between the study 

sites on the Devils and Pecos Rivers could be influenced by 

differences in water chemistry, particularly salinity (Linam 

and Kleinsasser, 1996); differences in zoogeographic history 

between the two river basins; and the fact that impounded 

waters of the Amistad Reservoir have removed the natural 

free-flowing fluvial (riverine) connection between the Devils 

and Pecos Rivers to the Rio Grande. The Pecos River is in 

backwater conditions at its confluence with the Rio Grande 

most of the time. Sites on the Pecos River also are farther from 

the main body of Amistad Reservoir compared to those on 

the Devils River, and the distance of the study sites from the 

reservoir also might influence fish community structure.

Macroinvertebrate Communities

 Totals of 100 and 80 unique macroinvertebrate 

taxa were collected from the Devils and Pecos Rivers, 

respectively (table 10). A unique taxon was represented by 

the presence of one or more individual macroinvertebrate 

organisms at the family or lower taxonomic level 

(International Commission on Zoological Nomenclature, 2010). 
Water Quality in the Devils and Pecos Rivers 43

D1

D2

D3

D4

P1

P2

P3

P4

2

The overall similarity among the fish communities at the eight sampling sites is graphically depicted using Euclidean distances determined from a 

 similarity matrix of common fish taxa between sites, and the distances are displayed in two dimensions that maximizes the separation among sites 

 (Clark and Warwick, 2001). 

In N dimensions, the Euclidean distance between two points p and q is

 √(∑i=1

N (pi

-qi)2) 

where

 pi

(or qi

) is the coordinate of p (or q) in dimension i. 

(Black, 2004)

-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Euclidean distance in dimension 1

1.

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

-0.4

-0.6

-0.8

-1.0

Euclidean distance in dimension 2

EXPLANATION

Sampling site on the Devils River (fig.1)—See table 1

Sampling site on the Pecos River (fig.1)—See table 1 P2

D2

Figure 2. Assessment of similarities among fish communities determined by using Non-metric Multi-Dimensional Scaling (first 

and second dimensions) for fish collected in 2006-7 at the Devils and Pecos Rivers sites in and upstream from the Amistad National 

Recreation Area, Texas.
44 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

For example, one macroinvertebrate identified to the family 

level only would be considered a unique taxon separate from 

any other macroinvertebrates identified to genus or species 

(also considered unique taxa) in the same family at the same 

sampling location. The number of unique macroinvertebrate 

taxa in the Devils River ranged from 34 at site D1 to 

57 at site D2 (table 11). For all of sample-collection sites, 

the largest number of unique macroinvertebrate taxa (57) 

was from site D2 (table 11), and the smallest number of 

unique invertebrate taxa (26) was from site P1 (table 12). 

Unlike with fish, no pattern in the number of unique taxa in 

relation to distance from the Amistad Reservoir was observed 

for macroinvertebrates. 

The number of unique mayfly taxa was similar among 

the Devils and Pecos River sites (tables 11 and 12). But 

mayfly taxa of the family Baetidae were more common in the 

Devils River, and mayfly taxa of the families Emphemeridae, 

Isonychidae, and Leptohyphidae were more common in the 

Devils River. The Baetidae mayfly, Fallceon quilleri, was 

the most abundant mayfly collected overall and occurred 

at all sites; the Baetidae mayfly, Baetodes bibranchius, 

was collected only at site D2. The Letophlebiidae mayfly, 

Tricorythodes sp., was collected at all sites, and was most 

common in the most upstream sampling location, site P4 

(table 12). The Caenidae mayfly, Caenis latipennis, was only 

collected at site P1. 

Caddisfly (Trichoptera) taxa were less abundant 

than mayfly (Ephemeroptera) taxa at all study sites. 

Caddisfly taxa, including net-spinning caddisfly taxa of 

the families Philopotamidae and Hydropsychidae, fingernet caddisflies (Philopotomidae), and snail-case caddisflies 

(Helicopsychidae), were more commonly collected at the 

Devils River sites (table 11). The combined percentage of 

Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa was 

generally about twice as large at the Pecos River sites than at 

the Devils River sites, with the exception of site D2 

(table 13). No stonefly (Plecoptera) taxa were collected in 

the Devils or Pecos River, and the study area is beyond the 

range of distribution for this taxon (Merritt and Cummins, 

1996). Large EPT values can be an indication of less disturbed 

water-quality conditions, so the percent EPT taxa is a 

commonly used metric because it is less variable seasonally 

and perennially than many other metrics such as species 

richness (Lenat and Barbour, 1994).

Damselfly and dragonfly taxa (Odonata) were not 

commonly collected at the Devils and Pecos River study 

sites (tables 10–12). This is probably the result of the chosen 

sampling that is biased toward the collection of more bottomdwelling macroinvertebrates. This bias might explain why 

Odonata nymphs and other taxa that inhabit aquatic vegetation 

(and other taxa that move throughout the streambed rather than 

living exclusively on the river bed) were seldom found in the 

samples (Merritt and Cummins, 1996). The most commonly 

collected odonate was the narrow-winged damselfly, Argia sp., 

which was collected at all sites with the exception of site D1. 

Riffle beetles (Elmidae) were the most commonly 

collected beetle taxon and were the most abundant beetle 

taxon in numbers of individuals collected at all sites (table 

10). Travertine beetles (Lutrochus sp.) were collected at 

several Devils and Pecos River sites. Water-penny beetles 

(Psephenidae) were collected at one Pecos River site (site P4, 

Pecos River at Pandale), where coarser river-bed substrates, 

including large gravel and cobble, were more abundant than 

at the Devils River sites. The flattened shape of water-penny 

larvae (Borror and others, 1989), and the ability of this taxon 

to attach to riverbed substrates, may account for the very small 

number of members of this taxon that were collected by using 

a D-frame net. 

True midge taxa of the family Chironomidae were the 

most taxa-rich macroinvertebrate taxon overall. Twenty-six 

unique true midge taxa (genera or species) were collected at 

the Devils River and Pecos River sites combined (tables 11 

and 12). True midges of the family Chironomidae are often 

the most abundant aquatic insect taxon in aquatic ecosystems, 

frequently accounting for 50 percent or more of total 

macroinvertebrate diversity (Merritt and Cummins, 1996). 

True midge taxa are burrowing organisms requiring finematerial substrates such as sands, silts, and clays to survive 

(Minshall, 1984). The relatively small number of individuals 

collected for each true midge taxon is probably a result of the 

lack of fine-material substrates at the sampling sites on the 

Devils and Pecos Rivers observed during the collection of 

macroinvertebrate samples. 
Water Quality in the Devils and Pecos Rivers 45

Table 10. Presence or absence of macroinvertebrate taxa and total number of taxa collected from the study sites along the Devils 

and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006.

[Shading indicates individual organisms representing the macroinvertebrate taxon were detected. Taxon (singular) or taxa (plural) refers to a genetically 

related group or groups of one or more organisms with common characteristics that differentiate them as a unit. From International Commission on 

Zoological Nomenclature (2010)]

 Class Order Family Genus or species Common name Devils 

River

Pecos 

River

Insecta Ephemeroptera Baetidae Baetodes bibranchius Mayflies

Callibaetis sp.

Camelobaetidius variabilis

Fallceon quilleri

Procloeon sp.

Caenidae Caenis latipennis

Caenis sp.

Ephemeridae Hexagenia sp.

Isonychiidae Isonychia sp.

Leptohyphidae

Leptophlebiidae

Neochoroterpes oklahoma

Thraulodes gonzalesi

Thraulodes sp.

Tricorythodes sp.

Vacupernius packeri

Odonata Coenagrionidae Narrow-winged damselflies

Argia sp.

Enallagma sp.

Libellulidae

Brechmorhoga mendax Common skimmers

Gomphidae Club-tail dragonflies

Erpetogomphus designatus

Erpetogomphus sp.

Calopterygidae Hetaerina americana Broad-winged damselflies

Hetaerina sp.

Corduliidae Macromia illinoiensis Green-eyed skimmers

Hemiptera Naucoridae Ambrysus sp. Creeping water bugs

Cryphocricos hungerfordi

Limnocoris sp.

Coleoptera Elmidae Dubiraphia sp. Rifle beetles

Hexacylloepus sp.

Macrelmis sp.

Macrelmis texanus

Microcylloepus sp.

Neoelmis caesa

Phanocerus sp.

Lutrochidae Lutrochus sp. Travertine beetles
46 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Psephenidae Psephenus sp. Water-penny beetles

Stenelmis sp.

Hydrophilidae Tropisternus sp. Water scavenger beetles

Megaloptera Corydalidae Corydalus sp. Dobsonflies

Diptera Chironomidae Ablabesmyia annulata Midges

Ablabesmyia mallochi

Ablabesmyia sp.

Apedilum sp.

Beardius sp.

Cladotanytarsus sp.

Cryptochironomus sp.

Cryptotendipes sp.

Dicrotendipes sp.

Labrundinia sp.

Larsia sp.

Nanocladius sp.

Parachironomus sp.

Pentaneura sp.

Pentaneurini

Polypedilum flavum

Polypedilum halterale gr.

Procladius sp.

Pseudochironomus sp.

Rheocricotopus sp.

Rheotanytarsus exiguus gr.

Tanytarsus sp.

Thienemanniella sp.

Thienemannimyia gr. sp.

Tvetenia discoloripes gr.

Xenochironomus xenolabis

Diptera Certatopogonidae Atrichopogon sp. Biting midges

Bezzia/Palpomyia sp.

Dasyhelea sp.

Tabanidae Atylotus/Tabanus sp. Deer flies, horse flies

Empididae Balloon flies

Hemerodromia sp.

Simulidae Simulium sp. Black flies

Stratiomyidae Soldier flies

Table 10. Presence or absence of macroinvertebrate taxa and total number of taxa collected from the study sites along the Devils 

and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006.—Continued

[Shading indicates individual organisms representing the macroinvertebrate taxon were detected. Taxon (singular) or taxa (plural) refers to a genetically 

related group or groups of one or more organisms with common characteristics that differentiate them as a unit. From International Commission on 

Zoological Nomenclature (2010)]

 Class Order Family Genus or species Common name Devils 

River

Pecos 

River
Water Quality in the Devils and Pecos Rivers 47

Trichoptera Polycentropodidae Tube-making caddisflies

Cernotina sp.

Neureclipsis sp.

Polyplectropus sp.

Hydropsychidae Cheumatopsyche sp. Net-spinnning caddisflies

Hydropsyche sp.

Smicridea (Smicridea) sp.

Philoptamidae Chimarra sp. Finger-net caddisflies

Helicopsychidae Helicopsyche sp. Snail-case caddisflies

Hydroptilidae Hydroptila sp. Micro-caddisflies

Mayatrichia sp.

Neotrichia sp.

Ochrotrichia sp.

Oxyethira sp.

Leptoceridae Long-horn caddisflies

Nectopsyche sp.

Oecetis avara

Lepidoptera Crambidae Petrophila sp. Semi-aquatic moths

Gastropoda Basommatophora Ancylidae Ferrissia sp. Aquatic snails

Lymnaeidae

Melanoides tuberculata

Physa sp.

Planorbidae

Valvata sp.

Bivalvia Corbicula sp. Basket clams

Sphaeriidae Fingernail clams

Clitellata Naididae Aquatic worms

Pristina sp.

Trombidiformes Mites

Arrenuridae Arrenurus sp.

Hygrobatidae Atractides sp.

Hygrobates sp.

Hydromatidae Hydrodroma sp.

Unionicolidae Koenikea sp.

Neumania sp.

Libertiidae Lebertia sp.

Limnesiidae Limnesia sp.

Limnocharidae Limnochares sp.

Rhyncholimnochares sp.

Table 10. Presence or absence of macroinvertebrate taxa and total number of taxa collected from the study sites along the Devils 

and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006.—Continued

[Shading indicates individual organisms representing the macroinvertebrate taxon were detected. Taxon (singular) or taxa (plural) refers to a genetically 

related group or groups of one or more organisms with common characteristics that differentiate them as a unit. From International Commission on 

Zoological Nomenclature (2010)]

 Class Order Family Genus or species Common name Devils 

River

Pecos 

River
48 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Mideopsidae Mideopsis sp.

Oribatidae Oribatei

Oxidae Oxus sp.

Sperchonidae Sperchon sp.

Torrenticolidae Torrenticola sp.

MalocostracaAmphipoda Hyalellidae Hyalella sp. Amphipods

Ostracoda Ostracods

Decapoda Cambaridae Procambarus sp. Crayfishes

Nematodes

Enopla Hoplonemertea Tetrastemmatidae Prostoma sp. Proboscis worms

Number of unique taxa 100 80

Table 10. Presence or absence of macroinvertebrate taxa and total number of taxa collected from the study sites along the Devils 

and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006.—Continued

[Shading indicates individual organisms representing the macroinvertebrate taxon were detected. Taxon (singular) or taxa (plural) refers to a genetically 

related group or groups of one or more organisms with common characteristics that differentiate them as a unit. From International Commission on 

Zoological Nomenclature (2010)]

 Class Order Family Genus or species Common name Devils 

River

Pecos 

River
Water Quality in the Devils and Pecos Rivers 49

Table 11. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Devils River study sites in and upsteam from the Amistad National Recreation Area, Texas, 2006.[USGS, U.S. Geological Survey; sp., species; Total: Total individuals by taxon for all sites on Devils River]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

D1 D2 D3 D4 

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils 

River

at Pafford 

Crossing

near 

Comstock, 

Tex.

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, Tex.

06/05/2006 06/06/2006 06/06/2006 06/08/2006

Insecta Ephemeroptera Baetidae Baetodes bibranchius Mayflies 0 3 0 0 3 

Insecta Ephemeroptera Baetidae Callibaetis sp. 5 0 0 2 7 

Insecta Ephemeroptera Baetidae Camelobaetidius variabilis 0 1 0 0 1 

Insecta Ephemeroptera Baetidae Fallceon quilleri 1 107 34 53 195 

Insecta Ephemeroptera Baetidae Procloeon sp. 45 9 6 1 61 

Insecta Ephemeroptera Caenidae Caenis latipennis 0 0 0 0 0 

Insecta Ephemeroptera Caenidae Caenis sp. 2 0 0 0 2 

Insecta Ephemeroptera Ephemeridae Hexagenia sp. 3 1 0 0 4 

Insecta Ephemeroptera Isonychidae Isonychia sp. 0 2 1 0 3 

Insecta Ephemeroptera Leptohyphidae 0 4 0 4 8 

Insecta Ephemeroptera Leptophlebiidae 1 0 0 0 1 

Insecta Ephemeroptera Leptophlebiidae Neochoroterpes oklahoma 0 0 0 0 0 

Insecta Ephemeroptera Leptophlebiidae Thraulodes gonzalesi 0 0 0 0 0 

Insecta Ephemeroptera Leptophlebiidae Thraulodes sp. 0 0 0 0 0 

Insecta Ephemeroptera Leptophlebiidae Tricorythodes sp. 22 4 2 13 41 

Insecta Ephemeroptera Leptophlebiidae Vacupernius packeri 0 0 0 2 2 

Insecta Odonata Coenagrionidae Narrow-winged

damselflies

0 0 1 2 3 

Insecta Odonata Coenagrionidae Argia sp. 0 5 16 1 22 

Insecta Odonata Coenagrionidae Enallagma sp. 5 0 0 0 5 

Insecta Odonata Libellulidae 1 0 0 0 1 

Insecta Odonata Libellulidae Brechmorhoga mendax Common skimmers 0 0 0 0 0 

Insecta Odonata Gomphidae Club-tail dragonflies 0 0 0 0 0 

Insecta Odonata Gomphidae Erpetogomphus designatus 0 1 2 0 3 
50 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Insecta Odonata Gomphidae Erpetogomphus sp. 0 0 0 0 0 Insecta Odonata Calopterygidae Hetaerina americana Broad-winged damselflies 0 0 0 0 0 Insecta Odonata Calopterygidae Hetaerina sp. 0 0 3 1 4 Insecta Odonata Corduliidae Macromia illinoiensis Green-eyed skimmers 0 1 0 1 2 Insecta Hemiptera Naucoridae Ambrysus sp. Creeping water bugs 0 4 4 4 12 Insecta Hemiptera Naucoridae Cryphocricos hungerfordi 0 0 0 0 0 Insecta Hemiptera Naucoridae Limnocoris sp. 0 1 0 0 1 Insecta Coleoptera Elmidae Dubiraphia sp. Rifle beetles 1 0 0 0 1 Insecta Coleoptera Elmidae Hexacylloepus sp. 0 29 36 9 74 Insecta Coleoptera Elmidae Macrelmis sp. 0 0 0 1 1 Insecta Coleoptera Elmidae Macrelmis texanus 0 0 0 0 0 Insecta Coleoptera Elmidae Microcylloepus sp. 0 35 22 5 62 Insecta Coleoptera Elmidae Neoelmis caesa 0 0 0 0 0 Insecta Coleoptera Elmidae Phanocerus sp. 0 0 0 1 1 Insecta Coleoptera Lutrochidae Lutrochus sp. Travertine beetles 0 6 7 0 13 Insecta Coleoptera Psephenidae Psephenus sp. Water-penny beetles 0 0 0 0 0 Insecta Coleoptera Psephenidae Stenelmis sp. 0 0 0 0 0 Insecta Coleoptera Hydrophilidae Tropisternus sp. Water scavenger beetles 0 0 1 0 1 Insecta Megaloptera Corydalidae Corydalus sp. Dobsonflies 0 0 0 1 1 Insecta Diptera Chironomidae Ablabesmyia annulata Midges 1 0 0 0 1 

Insecta Diptera Chironomidae Ablabesmyia mallochi 1 0 0 0 1 

Insecta Diptera Chironomidae Ablabesmyia sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Apedilum sp. 0 0 1 0 1 

Table 11. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Devils River study sites in and upsteam from the Amistad National Recreation Area, Texas, 2006.—Continued[USGS, U.S. Geological Survey; sp., species; Total: Total individuals by taxon for all sites on Devils River.]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

D1 D2 D3 D4 

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils 

River

at Pafford 

Crossing

near 

Comstock, 

Tex.

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, Tex.
Water Quality in the Devils and Pecos Rivers 51

Insecta Diptera Chironomidae Beardius sp. 0 0 0 5 5 

Insecta Diptera Chironomidae Cladotanytarsus sp. 2 5 0 0 7 

Insecta Diptera Chironomidae Cryptochironomus sp. 0 1 0 0 1 

Insecta Diptera Chironomidae Cryptotendipes sp. 0 1 0 0 1 

Insecta Diptera Chironomidae Dicrotendipes sp. 0 1 0 0 1 

Insecta Diptera Chironomidae Labrundinia sp. 2 5 0 3 10 

Insecta Diptera Chironomidae Larsia sp. 1 3 7 1 12 

Insecta Diptera Chironomidae Nanocladius sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Parachironomus sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Pentaneura sp. 2 4 5 5 16 

Insecta Diptera Chironomidae Pentaneurini 0 1 0 0 1 

Insecta Diptera Chironomidae Polypedilum flavum 0 0 0 3 3 

Insecta Diptera Chironomidae Polypedilum halterale gr. 0 2 2 1 5 

Insecta Diptera Chironomidae Procladius sp. 2 3 4 3 12 

Insecta Diptera Chironomidae Pseudochironomus sp. 1 3 1 0 5 

Insecta Diptera Chironomidae Rheocricotopus sp. 0 0 0 1 1 

Insecta Diptera Chironomidae Rheotanytarsus exiguus gr. 0 0 0 0 0 

Insecta Diptera Chironomidae Tanytarsus sp. 0 11 3 0 14 

Insecta Diptera Chironomidae Thienemanniella sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Thienemannimyia gr. sp. 0 8 6 0 14 

Insecta Diptera Chironomidae Tvetenia discoloripes gr. 0 0 0 0 0 

Insecta Diptera Chironomidae Xenochironomus xenolabis 0 0 0 0 0 

Insecta Diptera Certatopogoniidae Atrichopogon sp. Biting midges 0 0 0 0 0 

Insecta Diptera Certatopogoniidae Bezzia/Palpomyia sp. 0 4 37 2 43 

Insecta Diptera Certatopogoniidae Dasyhelea sp. 17 43 81 15 156 

Table 11. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Devils River study sites in and upsteam from the Amistad National Recreation Area, Texas, 2006.—Continued[USGS, U.S. Geological Survey; sp., species; Total: Total individuals by taxon for all sites on Devils River.]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

D1 D2 D3 D4 

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils 

River

at Pafford 

Crossing

near 

Comstock, 

Tex.

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, Tex.
52 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Insecta Diptera Tabanidae Atylotus/Tabanus sp. Deer flies, horse flies 0 0 0 1 1 Insecta Diptera Empididae Balloon flies 0 0 0 0 0 Insecta Diptera Empididae Hemerodromia sp. 0 0 1 0 1 Insecta Diptera Simulidae Simulium sp. Black flies 0 1 0 1 2 Insecta Diptera Stratiomyidae Soldier flies 0 0 1 0 1 Insecta Trichoptera Polycentropodidae Tube-net makers 0 0 0 0 0 Insecta Trichoptera Polycentropodidae Cernotina sp. 2 0 0 0 2 Insecta Trichoptera Polycentropodidae Neureclipsis sp. 0 0 1 0 1 Insecta Trichoptera Polycentropodidae Polyplectropus sp. 0 1 0 1 2 Insecta Trichoptera Hydropsychidae Cheumatopsyche sp. Net-spinnning cad- disflies 0 24 0 0 24 Insecta Trichoptera Hydropsychidae Hydropsyche sp. 0 6 6 2 14 Insecta Trichoptera Hydropsychidae Smicridea sp. 0 0 0 0 0 Insecta Trichoptera Philopotamidae Chimarra sp. Finger-net caddis- flies 0 3 1 1 5 Insecta Trichoptera Helicopsychidae Helicopsyche sp. Snail-case caddis- flies 0 0 0 6 6 Insecta Trichoptera Hydroptilidae Hydroptila sp. Micro-caddisflies 0 0 8 1 9 Insecta Trichoptera Hydroptilidae Mayatrichia sp. 0 1 6 0 7 Insecta Trichoptera Hydroptilidae Neotrichia sp. 0 1 3 0 4 Insecta Trichoptera Hydroptilidae Ochrotrichia sp. 0 1 0 6 7 Insecta Trichoptera Hydroptilidae Oxyethira sp. 9 0 3 6 18 Insecta Trichoptera Leptoceridae Long-horn caddisflies 0 0 0 0 0 

Insecta Trichoptera Leptoceridae Nectopsyche sp. 0 1 0 3 4 

Insecta Trichoptera Leptoceridae Oecetis avara 0 0 0 2 2 

Table 11. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Devils River study sites in and upsteam from the Amistad National Recreation Area, Texas, 2006.—Continued[USGS, U.S. Geological Survey; sp., species; Total: Total individuals by taxon for all sites on Devils River.]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

D1 D2 D3 D4 

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils 

River

at Pafford 

Crossing

near 

Comstock, 

Tex.

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, Tex.
Water Quality in the Devils and Pecos Rivers 53

Table 11. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Devils River study sites in and upsteam from the Amistad National Recreation Area, Texas, 2006.—Continued[USGS, U.S. Geological Survey; sp., species; Total: Total individuals by taxon for all sites on Devils River.]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

D1 D2 D3 D4 

Devils 

River

near 

Satan 

Canyon, 

Tex.

Devils 

River

at Pafford 

Crossing

near 

Comstock, 

Tex.

Devils 

River

near 

Turkey

Bluff 

Canyon, 

Tex.

Devils 

River

at Dolan 

Falls, Tex.

Insecta Lepidoptera Crambidae Petrophila sp. Semi-aquatic moths 0 1 4 1 6 

Gastropoda Basommatophora Ancylidae Ferrissia sp. Aquatic snails 0 0 0 1 1 

Gastropoda Basommatophora Lymnaeidae 0 1 0 0 1 

Gastropoda Basommatophora Lymnaeidae Melanoides tuberculata 0 0 0 1 1 

Gastropoda Basommatophora Lymnaeidae Physa sp. 1 6 0 4 11 Gastropoda Basommatophora Planorbidae 1 0 0 0 1 

Gastropoda Basommatophora Planorbidae Valvata sp. 0 0 1 27 28 

Gastropoda Bivalvia Corbiculidae Corbicula sp. Basket clams 0 1 0 1 2 

Gastropoda Bivalvia Sphaeriidae Fingernail clams 1 3 5 3 12 

Clitellata Clitellata Naididae Aquatic worms 0 1 1 0 2 

Clitellata Clitellata Naididae Pristina sp. 0 0 0 0 0 

Clitellata Trombidiformes Mites 1 0 0 1 2 

Clitellata Trombidiformes Arrenuridae Arrenurus sp. 12 2 7 8 29 

Clitellata Trombidiformes Hygrobatidae Atractides sp. 2 0 2 2 6 

Clitellata Trombidiformes Hygrobatidae Hygrobates sp. 0 0 12 8 20 

Clitellata Trombidiformes Hydromatidae Hydrodroma sp. 0 0 1 0 1 

Clitellata Trombidiformes Unionicolidae Koenikea sp. 0 0 0 2 2 

Clitellata Trombidiformes Unionicolidae Neumania sp. 0 2 1 1 4 

Clitellata Trombidiformes Libertiidae Lebertia sp. 1 0 0 0 1 

Clitellata Trombidiformes Limnesiidae Limnesia sp. 0 0 0 3 3 

Clitellata Trombidiformes Limnocharidae Limnochares sp. 1 0 0 0 1 

Clitellata Trombidiformes Limnocharidae Rhyncholimnochares sp. 0 1 2 0 3 

Clitellata Trombidiformes Mideopsidae Mideopsis sp. 15 1 12 0 28 

Clitellata Trombidiformes Oribatidae Oribatei 0 1 0 0 1 Clitellata Trombidiformes Oxidae Oxus sp. 2 0 0 0 2 
54 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 11. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Devils River study sites in and upsteam from the Amistad National Recreation Area, Texas, 2006.—Continued [USGS, U.S. Geological Survey; sp., species; Total: Total individuals by taxon for all sites on Devils River.] Class Order Family Tribe Genus or species Common name USGS site identifier and station name Total D1 D2 D3 D4 Devils River near Satan Canyon, Tex. Devils River at Pafford Crossing near Comstock, Tex. Devils River near Turkey Bluff Canyon, Tex. Devils River at Dolan Falls, Tex. Clitellata Trombidiformes Sperchonidae Sperchon sp. 0 0 0 1 1 Clitellata Trombidiformes Torrenticolidae Torrenticola sp. 4 2 10 3 19 Malocos- traca Amphipoda Hyalellidae Hyalella sp. Amphipods 173 12 2 121 308 Malocos- traca Ostracoda Ostracods 4 3 7 6 20 Malocos- traca Decapoda Cambaridae Procambarus sp. Crayfishes 0 2 0 0 2 Malocos- traca Decapoda Nematodes 0 0 2 0 2 Enopla Hoplonemertea Tetrastemmatidae Prostoma sp. Proboscis worms 0 2 0 0 2 Turbellaria Flatworms 0 3 9 10 22 Total number of organisms 344 391 390 374 1,499 Total number of unique taxa 34 57 48 56 100 
Water Quality in the Devils and Pecos Rivers 55

Table 12. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Pecos River study sites in and upstream of the Amistad National Recreation Area, Texas, 2006.[USGS, U.S. Geological Survey; Total: Total individuals by taxon for all sites on Pecos River. Sites P1 to P4 are used to define sites on the Pecos River as shown in figure 1]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

P1 P2 P3 P4

Pecos 

River

at Shumla

Bend, 

Tex.

Pecos 

River

near 

Langtry, 

Tex.

Pecos River

near 

Everett

Canyon, 

Tex.

Pecos 

River

at 

Pandale, 

Tex.

6/27/2006 6/28/2006 6/29/2006 6/22/2006

Insecta Ephemeroptera Baetidae Baetodes bibranchius Mayflies 0 0 0 0 0 Insecta Ephemeroptera Baetidae Callibaetis sp. 1 0 0 0 1 Insecta Ephemeroptera Baetidae Camelobaetidius 

variabilis

0 1 1 5 7 

Insecta Ephemeroptera Baetidae Fallceon quilleri 1 15 58 59 133 

Insecta Ephemeroptera Baetidae Procloeon sp. 0 0 0 0 0 

Insecta Ephemeroptera Caenidae Caenis latipennis 122 0 0 0 122 

Insecta Ephemeroptera Caenidae Caenis sp. 0 1 0 0 1 

Insecta Ephemeroptera Ephemeridae Hexagenia sp. 0 0 0 0 0 

Insecta Ephemeroptera Isonychiidae Isonychia sp. 0 0 0 0 0 

Insecta Ephemeroptera Leptohyphidae 0 0 0 0 0 Insecta Ephemeroptera Leptophlebiidae 0 0 0 0 0 Insecta Ephemeroptera Leptophlebiidae Neochoroterpes oklahoma 0 4 0 1 5 

Insecta Ephemeroptera Leptophlebiidae Thraulodes gonzalesi 0 40 5 0 45 

Insecta Ephemeroptera Leptophlebiidae Thraulodes sp. 0 0 0 12 12 

Insecta Ephemeroptera Leptophlebiidae Tricorythodes sp. 9 28 37 107 181 

Insecta Ephemeroptera Leptophlebiidae Vacupernius packeri 0 1 0 0 1 

Insecta Odonata Coenagrionidae Narrow-winged

damselflies

0 0 0 0 0 

Insecta Odonata Coenagrionidae Argia sp. 4 3 1 1 9 

Insecta Odonata Coenagrionidae Enallagma sp. 0 0 0 3 3 

Insecta Odonata Libellulidae 0 0 0 0 0 Insecta Odonata Libellulidae Brechmorhoga mendax Common skimmers 0 1 0 0 1 Insecta Odonata Gomphidae Club-tail dragonflies 0 2 4 1 7 

Insecta Odonata Gomphidae Erpetogomphus 

designatus

0 0 0 0 0 
56 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 12. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Pecos River study sites in and upstream of the Amistad National Recreation Area, Texas, 2006.—Continued [USGS, U.S. Geological Survey; Total: Total individuals by taxon for all sites on Pecos River. Sites P1 to P4 are used to define sites on the Pecos River as shown in figure 1] Class Order Family Tribe Genus or species Common name USGS site identifier and station name Total P1 P2 P3 P4 Pecos River at Shumla Bend, Tex. Pecos River near Langtry, Tex. Pecos River near Everett Canyon, Tex. Pecos River at Pandale, Tex. 6/27/2006 6/28/2006 6/29/2006 6/22/2006 Insecta Odonata Gomphidae Erpetogomphus sp. 0 1 0 0 1 Insecta Odonata Calopterygidae Hetaerina americana Broad-winged damselflies 0 0 0 1 1 Insecta Odonata Calopterygidae Hetaerina sp. 0 0 0 0 0 Insecta Odonata Corduliidae Macromia illinoiensis Green-eyed skimmers 0 0 0 1 1 Insecta Hemiptera Naucoridae Ambrysus sp. Creeping water bugs 0 5 1 1 7 Insecta Hemiptera Naucoridae Cryphocricos hungerfordi 0 1 6 2 9 Insecta Hemiptera Naucoridae Limnocoris sp. 0 0 0 5 5 Insecta Coleoptera Elmidae Dubiraphia sp. Rifle beetles 0 0 0 0 0 Insecta Coleoptera Elmidae Hexacylloepus sp. 0 4 19 13 36 Insecta Coleoptera Elmidae Macrelmis sp. 0 0 27 1 28 Insecta Coleoptera Elmidae Macrelmis texanus 0 42 0 0 42 Insecta Coleoptera Elmidae Microcylloepus sp. 5 72 17 14 108 Insecta Coleoptera Elmidae Neoelmis caesa 0 3 8 0 11 Insecta Coleoptera Elmidae Phanocerus sp. 0 0 0 0 0 Insecta Coleoptera Lutrochidae Lutrochus sp. Travertine beetles 0 1 2 0 3 Insecta Coleoptera Psephenidae Psephenus sp. Water-penny beetles 0 0 0 1 1 Insecta Coleoptera Psephenidae Stenelmis sp. 0 5 0 3 8 Insecta Coleoptera Hydrophilidae Tropisternus sp. Water scavenger beetles 0 0 0 0 0 Insecta Megaloptera Corydalidae Corydalus sp. Dobsonflies 0 3 0 1 4 Insecta Diptera Chironomidae Ablabesmyia annulata Midges 0 0 0 0 0 Insecta Diptera Chironomidae Ablabesmyia mallochi 5 0 0 0 5 

Insecta Diptera Chironomidae Ablabesmyia sp. 0 0 0 1 1 

Insecta Diptera Chironomidae Apedilum sp. 24 3 0 0 27 
Water Quality in the Devils and Pecos Rivers 57

Table 12. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Pecos River study sites in and upstream of the Amistad National Recreation Area, Texas, 2006.—Continued[USGS, U.S. Geological Survey; Total: Total individuals by taxon for all sites on Pecos River. Sites P1 to P4 are used to define sites on the Pecos River as shown in figure 1]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

P1 P2 P3 P4

Pecos 

River

at Shumla

Bend, 

Tex.

Pecos 

River

near 

Langtry, 

Tex.

Pecos River

near 

Everett

Canyon, 

Tex.

Pecos 

River

at 

Pandale, 

Tex.

6/27/2006 6/28/2006 6/29/2006 6/22/2006

Insecta Diptera Chironomidae Beardius sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Cladotanytarsus sp. 0 0 0 1 1 

Insecta Diptera Chironomidae Cryptochironomus sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Cryptotendipes sp. 0 0 0 0 0 

Insecta Diptera Chironomidae Dicrotendipes sp. 1 0 0 0 1 

Insecta Diptera Chironomidae Labrundinia sp. 4 0 0 0 4 

Insecta Diptera Chironomidae Larsia sp. 0 2 1 0 3 

Insecta Diptera Chironomidae Nanocladius sp. 0 1 0 0 1 

Insecta Diptera Chironomidae Parachironomus sp. 1 0 0 0 1 

Insecta Diptera Chironomidae Pentaneura sp. 0 0 4 0 4 

Insecta Diptera Chironomidae Pentaneurini 0 0 0 0 0 Insecta Diptera Chironomidae Polypedilum flavum 0 0 0 0 0 

Insecta Diptera Chironomidae Polypedilum halterale gr. 13 0 7 20 40 Insecta Diptera Chironomidae Procladius sp. 7 0 0 0 7 

Insecta Diptera Chironomidae Pseudochironomus sp. 6 0 1 0 7 

Insecta Diptera Chironomidae Rheocricotopus sp. 0 0 0 0 0 Insecta Diptera Chironomidae Rheotanytarsus exiguus

gr.

0 0 0 27 27 

Insecta Diptera Chironomidae Tanytarsus sp. 48 3 4 7 62 

Insecta Diptera Chironomidae Thienemanniella sp. 0 0 0 3 3 Insecta Diptera Chironomidae Thienemannimyia gr. sp. 0 0 6 12 18 

Insecta Diptera Chironomidae Tvetenia discoloripes gr. 0 0 0 1 1 Insecta Diptera Chironomidae Xenochironomus 

xenolabis

1 0 0 0 1 

Insecta Diptera Certatopogoniidae Atrichopogon sp. Biting midges 1 0 0 0 1 

Insecta Diptera Certatopogoniidae Bezzia/Palpomyia sp. 3 6 7 2 18 
58 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 12. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Pecos River study sites in and upstream of the Amistad National Recreation Area, Texas, 2006.—Continued [USGS, U.S. Geological Survey; Total: Total individuals by taxon for all sites on Pecos River. Sites P1 to P4 are used to define sites on the Pecos River as shown in figure 1] Class Order Family Tribe Genus or species Common name USGS site identifier and station name Total P1 P2 P3 P4 Pecos River at Shumla Bend, Tex. Pecos River near Langtry, Tex. Pecos River near Everett Canyon, Tex. Pecos River at Pandale, Tex. 6/27/2006 6/28/2006 6/29/2006 6/22/2006 Insecta Diptera Certatopogoniidae Dasyhelea sp. 70 5 0 0 75 Insecta Diptera Tabanidae Atylotus/Tabanus sp. Deer flies, horse flies 0 2 1 0 3 Insecta Diptera Empididae Balloon flies 0 1 0 0 1 Insecta Diptera Empididae Hemerodromia sp. 0 0 0 0 0 Insecta Diptera Simulidae Simulium sp. Black flies 0 0 0 2 2 Insecta Diptera Stratiomyidae Soldier flies 0 0 0 0 0 Insecta Trichoptera Polycentropodidae Tube-net makers 0 1 0 0 1 Insecta Trichoptera Polycentropodidae Cernotina sp. 6 0 0 0 6 Insecta Trichoptera Polycentropodidae Neureclipsis sp. 0 0 0 0 0 Insecta Trichoptera Polycentropodidae Polyplectropus sp. 0 0 0 0 0 Insecta Trichoptera Hydropsychidae Cheumatopsyche sp. Net-spinning cad- disflies 0 67 4 5 76 Insecta Trichoptera Hydropsychidae Hydropsyche sp. 0 0 0 0 0 Insecta Trichoptera Hydropsychidae Smicridea sp. 0 1 0 0 1 Insecta Trichoptera Philopotamidae Chimarra sp. Finger-net caddis- flies 0 1 18 1 20 Insecta Trichoptera Helicopsychidae Helicopsyche sp. Snail-case caddis- flies 0 0 0 0 0 Insecta Trichoptera Hydroptilidae Hydroptila sp. Micro-caddisflies 0 2 2 9 13 Insecta Trichoptera Hydroptilidae Mayatrichia sp. 0 0 0 0 0 Insecta Trichoptera Hydroptilidae Neotrichia sp. 0 1 0 0 1 Insecta Trichoptera Hydroptilidae Ochrotrichia sp. 0 0 0 0 0 Insecta Trichoptera Hydroptilidae Oxyethira sp. 21 0 4 0 25 Insecta Trichoptera Leptoceridae Long-horn caddisflies 0 2 0 0 2 

Insecta Trichoptera Leptoceridae Nectopsyche sp. 0 0 0 7 7 

Insecta Trichoptera Leptoceridae Oecetis avara 0 0 1 6 7 
Water Quality in the Devils and Pecos Rivers 59

Table 12. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Pecos River study sites in and upstream of the Amistad National Recreation Area, Texas, 2006.—Continued[USGS, U.S. Geological Survey; Total: Total individuals by taxon for all sites on Pecos River. Sites P1 to P4 are used to define sites on the Pecos River as shown in figure 1]

Class Order Family Tribe Genus or species Common name

USGS site identifier and station name

Total

P1 P2 P3 P4

Pecos 

River

at Shumla

Bend, 

Tex.

Pecos 

River

near 

Langtry, 

Tex.

Pecos River

near 

Everett

Canyon, 

Tex.

Pecos 

River

at 

Pandale, 

Tex.

6/27/2006 6/28/2006 6/29/2006 6/22/2006

Insecta Lepidoptera Crambidae Petrophila sp. Semi-aquatic moths 0 1 0 0 1 

Gastropoda Basommatophora Ancylidae Ferrissia sp. Aquatic snails 0 0 0 0 0 

Gastropoda Basommatophora Lymnaeidae 0 0 0 0 0 Gastropoda Basommatophora Lymnaeidae Melanoides tuberculata 0 0 0 0 0 

Gastropoda Basommatophora Lymnaeidae Physa sp. 4 6 24 1 35 

Gastropoda Basommatophora Planorbidae 0 0 0 0 0 Gastropoda Basommatophora Planorbidae Valvata sp. 0 0 0 0 0 

Gastropoda Bivalvia Corbiculidae Corbicula sp. Basket clams 0 2 8 13 23 

Gastropoda Bivalvia Sphaeriidae Fingernail clams 0 0 0 0 0 

Clitellata Naididae Aquatic worms 0 0 2 1 3 

Clitellata Naididae Pristina sp. 0 0 1 0 1 

Arachnida Trombidiformes Mites 0 0 0 0 0 

Arachnida Trombidiformes Arrenuridae Arrenurus sp. 0 0 0 0 0 

Arachnida Trombidiformes Hygrobatidae Atractides sp. 0 0 2 0 2 

Arachnida Trombidiformes Hygrobates sp. 0 0 1 0 1 

Arachnida Trombidiformes Hydromatidae Hydrodroma sp. 2 3 10 0 15 

Arachnida Trombidiformes Unionicolidae Koenikea sp. 0 0 0 0 0 

Arachnida Trombidiformes Neumania sp. 0 0 0 0 0 

Arachnida Trombidiformes Libertiidae Lebertia sp. 0 0 0 0 0 

Arachnida Trombidiformes Limnesiidae Limnesia sp. 0 0 0 0 0 

Arachnida Trombidiformes Limnocharidae Limnochares sp. 0 0 0 0 0 

Arachnida Trombidiformes Rhyncholimnochares sp. 0 0 0 0 0 

Arachnida Trombidiformes Mideopsidae Mideopsis sp. 1 0 0 0 1 

Arachnida Trombidiformes Oribatidae Oribatei 1 0 0 0 1 

Arachnida Trombidiformes Oxidae Oxus sp. 0 0 0 0 0 

Arachnida Trombidiformes Sperchonidae Sperchon sp. 0 0 2 0 2 
60 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Arachnida Trombidiformes Torrenticolidae Torrenticola sp. 0 0 0 0 0 Malocostraca Amphipoda Hyalellidae Hyalella sp. Amphipods 4 1 10 9 24 Malocostraca Ostracoda Ostracods 0 0 11 13 24 Malocostraca Decapoda Cambaridae Procambarus sp. Crayfishes 0 0 0 0 0 Malocostraca Decapoda Nematodes 0 0 1 1 2 Enopla Hoplonemertea Tetrastemmatidae Prostoma sp. Proboscis worms 0 0 0 0 0 Turbellaria Flatworms 0 0 7 0 7 Total number of organisms 356 344 325 374 1,408 Total number of unique taxa 26 40 38 40 80 Table 12. Summary of taxonomic classification and counts of individuals by macroinvertebrate taxon collected from the Pecos River study sites in and upstream of the Amistad National Recreation Area, Texas, 2006.—Continued [USGS, U.S. Geological Survey; Total: Total individuals by taxon for all sites on Pecos River. Sites P1 to P4 are used to define sites on the Pecos River as shown in figure 1] Class Order Family Tribe Genus or species Common name USGS site identifier and station name Total P1 P2 P3 P4 Pecos River at Shumla Bend, Tex. Pecos River near Langtry, Tex. Pecos River near Everett Canyon, Tex. Pecos River at Pandale, Tex. 6/27/2006 6/28/2006 6/29/2006 6/22/2006
Water Quality in the Devils and Pecos Rivers 61

Table 13. Selected macroinvertebrate community metrics and indexes from the collection of qualitative multihabitat samples at the study sites along the Devils and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006.[USGS, U.S. Geological Survey; sp., species; gr., group; EPT, Combined Ephemeroptera, Plecoptera, and Trichoptera taxa]

Metric

USGS station name (and site idenifier) and sample collection date

Devils River

near Satan 

Canyon, Tex. (D1)

06/05/2006

Devils River at 

Pafford Crossing 

near Comstock, 

Tex. (D2)

06/06/2006

Devils River

near Turkey

Bluff Canyon, 

Tex. (D3)

06/07/2006

Devils 

River at 

Dolan Falls, 

Tex. (D4)

06/08/2006

Pecos River at 

Shumla Bend, 

Tex. (P1)

06/27/2006

Pecos River

near Langtry, 

Tex. (P2)

06/28/2006

Pecos River

near Everett

Canyon, Tex. (P3)

06/29/2006

Pecos River at 

Pandale, Tex. 

(P4)

06/22/2006

Dominant taxon Hyallela sp. Fallceon 

quilleri

Dasyhelea sp. Hyalella sp. Caenis

latipennis

Microcylloepus sp. Fallceon 

quilleri

Tricorythodes sp.

2nd dominant taxon Procloeon sp. Dasyhelea sp. Bezzia/

Palpomyia sp.

Fallceon 

quilleri

Dasyhelea sp. Cheumatopsyche sp. Tricorythodes sp. Fallceon 

quilleri

3rd dominant taxon Tricorythodes sp. Microcylloepus sp. Hexacylloepus sp. Valvata sp. Tanytarsus sp. Macrelmis 

texanus

Macrelmis sp. Rheotanytarsus

exiguus gr.

Metrics

Number of total 

unique taxa1

34 57 48 56 26 40 38 40

Percent of indivs. 

as Ephemeoptera2

22.97 33.50 11.03 20.05 36.44 26.16 31.08 49.20

Percent of indivs. 

as Plecoptera2

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Percent of indivs. 

as Trichoptera2

3.20 9.72 7.18 7.49 7.40 21.80 8.92 7.49

Percent of unique taxa 

as EPT taxa2

26.16 43.22 18.21 27.54 43.84 47.97 40.00 56.68

Percent of indivs. 

as Coleoptera2

.29 17.90 16.92 4.28 1.37 36.92 22.46 8.56

Percent of indivs. 

as Clitellata2

.00 .26 .26 .00 .00 .00 .92 .27

Percent of indivs. as 

Baetide2

14.83 30.69 10.26 14.97 .55 4.65 18.15 17.11

Percent of indivs. as Chironomidae2 3.49 12.28 7.44 5.88 30.14 2.62 7.08 19.25Percent of indivs. as Hydropsychidae2 .00 7.67 1.54 .53 .00 19.77 1.23 1.34

Percent of indivs. as 

Odonata2

1.74 1.79 5.64 1.34 1.10 2.04 1.54 1.87

Percent of indivs. as Simuliidae2 .00 .26 .00 .27 .00 .00 .00 .54

Number of unique taxa as 

Coleoptera taxa1

1 3 4 4 1 6 5 5
62 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers Table 13. Selected macroinvertebrate community metrics and indexes from the collection of qualitative multihabitat samples at the study sites along the Devils and Pecos Rivers in and upstream from the Amistad National Recreation Area, Texas, 2006.—Continued. Index USGS station name (and site idenifier) and sample collection date Devils River near Satan Canyon, Tex. (D1) 06/05/2006 Devils River at Pafford Crossing near Comstock, Tex. (D2) 06/06/2006 Devils River near Turkey Bluff Canyon, Tex. (D3) 06/07/2006 Devils River at Dolan Falls, Tex. (D4) 06/08/2006 Pecos River at Shumla Bend, Tex. (P1) 06/27/2006 Pecos River near Langtry, Tex. (P2) (06/28/2006) Pecos River near Everett Canyon, Tex. (P3) 06/29/2006 Pecos River at Pandale, Tex. (P4) 06/22/2006 Indexes Margalef richness (metric)3 4.14 6.84 5.56 7.20 3.41 6.03 4.54 5.67 Hilsenhoff biotic index (index) 7.31 5.67 5.69 6.88 5.77 4.92 5.45 5.03 Pielou's J' (index) 0.58 0.73 0.80 0.71 0.68 0.70 0.83 0.74 Simpson's heterogeneity (index) .72 .89 .92 .86 .82 .88 .93 .87

1 Number of unique taxa for these metrics determined by summing counts of taxa from each site listed in tables 11 and 12. 2 Percentages determind by summing number of individuals collected in these taxa or taxa groups as in tables 11 and 12 and dividing by the total number of individuals collected from each site.3 Margalef richness was calculated by using aquatic insect taxa only. 
Summary 63

Non-insect macroinvertebrate taxa—including 

freshwater worms, snails, mites, and crayfish—were more 

common and abundant at the Devils River study sites. Water 

mites (Trombidiformes) were abundant at the Devils River 

sites. The larger number of unique macroinvertebrate taxa 

at the Devils River sites probably relates to the more saline 

waters of the Pecos River because fewer macroinvertebrate 

taxa are likely tolerant of the higher salinity levels in the Pecos 

River compared to those in the Devils River. A more saline 

environment could be considered a physiological desert for 

many aquatic macroinvertebrates because of the tendency 

for water to move from the invertebrate to the environment 

in response to different osmotic pressures between the two 

(Ward, 1992). Basket clams (Bivalvia) of the genus Corbicula

sp. were collected at two Devils River sites and three Pecos 

River sites (tables 11 and 12), and the largest number of this 

taxon was collected at site P4, the Pecos River at Pandale 

site (table 12). Collected individuals of this genus were not 

identified to species, but most likely were the introduced Asian 

clam, Coribula fluminea. The Asian clam has been collected 

in the Rio Grande downstream from Amistad Reservoir 

(International Boundary and Water Commission, 1994) and 

in the Rio Grande in Big Bend National Park upstream from 

Amistad Reservoir (Moring, 2002). 

The Margalef richness index, which was derived by 

using the total number of aquatic insect taxa (Ludwig and 

Reynolds, 1988), was larger at the Devils River sites than at 

the Pecos River sites (table 13). The Margalef richness index 

normalizes the number of species present to the number 

of individuals collected but does not differentiate between 

those communities that have the same or similar number of 

species and total individuals (Ludwig and Reynolds, 1988). 

The Hilsenhoff biotic index was largest at site D1 (Devils 

River near Satan Canyon site), the site farthest downstream 

on the Devils River, and smallest at site P2 (Pecos River 

near Langtry, Tex.), the site second farthest downstream on 

the Pecos River. The Hilsenhoff biotic index is a community 

metric that combines species diversity and tolerance 

characteristics of microinvertebrate taxa (Hilsenhoff, 1987), 

and the larger the Hilsenhoff index value, generally the 

more impaired the macroinvertebrate community. The large 

Hilsenhoff index values for sites D1 and D4 (the Devils River 

at Dolan Falls site) were weighted by the comparatively large 

number of amphipods of the genus Hyalella sp. (table 11) 

that were collected in these sampling locations. Members 

of this genus generally score as very tolerant to organic 

pollution (Plafkin and others, 1989; Texas Commission on 

Environmental Quality, 2007).

The first dimension in ordination of the NMDS analysis 

of aquatic insects (the only group of macroinvertebrate 

organisms used in the NMDS analysis because the sampling 

method was most favorable for collecting aquatic insects) did 

not separate the sites in a way that could be explained by the 

upstream to downstream stream order (fig. 3). The second 

dimension in ordination of the aquatic insect community by 

using NMDS analysis indicates that each site is more similar 

to the other sites in the same river segment than to any of 

the sites in the other river segment. Unlike the grouping of 

fish (which can be readily identified to the species level), the 

grouping of aquatic insects data and NMDS analysis might be 

influenced by the lack of resolution of all aquatic insect taxa 

to the species level because many of the insects collected were 

in immature larvae or nymph developmental stages that are 

difficult or impossible to identify to species or even genus by 

using external morphological characteristics only. Sites may 

be more or less similar as a result of NMDS analysis if more 

of the aquatic insects collected could have been identified to a 

lower taxonomic level such as genus or species. 

Summary 

When Amistad Reservoir reached its conservation pool 

elevation for the first time in 1970, many species of fish native 

to the Rio Grande and its major tributaries (the Devils and 

Pecos Rivers) disappeared from the newly impounded sections 

of these rivers. Of the 65 native species of fish historically 

documented in what is now the Amistad National Recreation 

Area, 16 species might have become locally extinct because of 

the environmental changes caused by the reservoir. In addition 

to the extirpation of some native fish species, the proliferation 

of non-native species is a cause for concern. To gain a better 

understanding of the water quality and status of fish and 

macroinvertebrate communities, the U.S. Geological Survey 

(USGS), in cooperation with the National Park Service (NPS) 

and Amistad National Recreation Area, did a reconnaissancelevel survey of selected water-quality constituents and aquatic 

biota (fish and macroinvertebrates) in the Devils and Pecos 

Rivers in and upstream from Amistad National Recreation 

Area during 2005–7.

The reconnaissance-level survey of selected water-quality 

constituents was done during the spring (March, April, and 

May) and summer (June and August) of 2005 at sampling sites 

on the Devils and Pecos Rivers—USGS stations 08449400 

Devils River at Pafford Crossing near Comstock, Tex., and 

08447410 Pecos River near Langtry, Tex. (sites D2 and site 

P2, respectively). Water-quality data collected during 2005 

were also compared with water-quality data collected as part 

of the USGS Hydrologic Benchmark Network program during 

1978–95 at site D2 and with water-quality data collected 

as part of the USGS National Stream Quality Accounting 

Network program during 1974–2007 at site P2. Fish and 

macroinvertebrate samples were collected during 2006 from 

the Devils and Pecos Rivers, and fish samples were collected 

again in 2007 at selected sites on both rivers. Fish and 

macroinvertebrate samples were collected at sites D2 and P2 

and at three additional sites on each river.
64 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

D1

D2

D3

D4

P1

P2

P3

P4

EXPLANATION

Sampling site on the Devils River (fig.1)—See table 1

Sampling site on the Pecos River (fig.1)—See table 1 P2

D2

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Euclidean distance in dimension 1

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Euclidean distance in dimension 2

The overall similarity among the fish communities at the eight sampling sites is graphically depicted using Euclidean distances determined from a 

 similarity matrix of common fish taxa between sites, and the distances are displayed in two dimensions that maximizes the separation among sites 

 (Clark and Warwick, 2001). 

In N dimensions, the Euclidean distance between two points p and q is

 √(∑i=1

N (pi

-qi)2) 

where

 pi

(or qi

) is the coordinate of p (or q) in dimension i. 

(Black, 2004)

Figure 3. Assessment of similarities among macroinvertebrate communities determined by using Non-metric Multi-Dimensional 

Scaling (first and second dimensions) for aquatic insects collected in 2006 from sampling sites on the Devils and Pecos Rivers in and 

upstream from the Amistad National Recreation Area, Texas. 
Summary 65

The three additional sites on the Devils River where fish 

and macroinvertebrate samples were collected were USGS 

stations 293894100582901 Devils River near Satan Canyon, 

Tex. (site D1); 29774610099501 Devils River near Turkey 

Bluff Canyon, Tex. (site D3); and 2988810099601 Devils 

River at Dolan Falls, Tex. (site D4). In addition to site P2, fish 

and macroinvertebrate samples were collected from the Pecos 

River at USGS stations 294735101232401 Pecos River at 

Shumla Bend, Tex. (site P1); 295945101301501 Pecos River 

near Everett Canyon, Tex. (site P3); and 300737101342201 

Pecos River at Pandale, Tex. (site P4). Fish community 

surveys were repeated in spring 2007 near two sites along the 

Devils River (sites D2 and D4) and two sites on the Pecos 

River (sites P2 and P4). 

Total dissolved solids (TDS) concentrations were an 

order of magnitude smaller in samples collected during 

March–August 2005 at site D2 in 2005 compared to TDS 

concentrations measured in samples collected during April–

August 2005 at site P2. Total dissolved solid concentrations 

measured at the Devils River site did not exceed the State 

water-quality standard of 300 mg/L for the Devils River 

segment, and TDS concentrations measured in the Pecos River 

at site P2 did not exceed the proposed State water-quality 

standard for TDS of 4,000 mg/L for the segment of the Pecos 

River that includes site P2. 

Chloride concentrations were an order of magnitude 

smaller in samples collected at the Devils River site D2 during 

March–August 2005 compared to those collected at the Pecos 

River site P2 during the same period, ranging from 11.6 to 

12.9 mg/L at site D2, and from 519 to 879 mg/L at site P2. 

Chloride concentrations in the samples collected from the 

Pecos River at site P2 during March–August 2005 represent 

a range of values similar to the interquartile range of 548 to 

942 mg/L for chloride concentrations measured in samples 

collected by the USGS National Stream Quality Accounting 

Network Program during 1974–2007. Chloride concentrations 

did not exceed the proposed State water-quality standard of 

50 mg/L for the Devils River segment that includes site 

D2 or the proposed standard of 1,700 mg/L for the Pecos 

River segment that includes site P2. Sulfate concentrations 

in water-quality samples ranged from 7.55 to 8.20 mg/L at 

site D2 and from 298 to 503 mg/L at site P2 in 2005. Sulfate 

concentrations did not exceed proposed State water-quality 

standards of 50 mg/L and 1,000 mg/L for the Devils and Pecos 

River segments, respectively.

In 2005, ammonia plus organic nitrogen concentrations 

ranged from 0.12 to 0.14 mg/L of nitrogen at site D2 and 

from 0.15 to 0.32 mg/L of nitrogen at site P2. Ammonia plus 

organic nitrogen concentrations were within the historical 

range of concentrations measured in samples by the HBN 

program during 1978–95 at site D2. The ammonia plus 

organic nitrogen concentrations at site P2 in 2005 were 

generally within the historical range of concentrations reported 

by the NASQAN program during 1974–2007. Nitrate plus 

nitrite concentrations ranged from 0.99 to 1.24 mg/L at site 

D2 and from 0.22 to 1.04 mg/L at site P2 in 2005. Although 

nitrate plus nitrite concentrations measured in 2005 in samples 

collected at site D2 were within the historical range of 

concentrations measured in samples collected by the USGS 

HBN program during 1978–95, the 2005 concentrations were 

smaller compared to the historical median concentration 

(1.4 mg/L). The nitrate plus nitrite concentrations measured 

in 2005 in samples collected at site P2 generally were within 

with the historical interquartile range of concentrations 

(0.19 to 0.95 mg/L) measured in samples collected by 

the USGS NASQAN program. Orthophosphate and total 

phosphorous concentrations in water were not detected 

in samples collected in 2005 from sites D2 and P2 at 

concentrations equal to or larger than the laboratory reporting 

levels for these constituents. 

Selenium concentrations measured in samples collected 

at site D2 in 2005 ranged from an estimated value of 

0.3 micrograms per liter (μg/L) to 0.6 μg/L. At site P2, 

selenium concentrations ranged from 1.0 μg/L to 3.1 μg/L 

in the 2005 samples. None of the selenium concentrations 

measured in samples collected during the spring and summer 

of 2005 from the Devils or Pecos Rivers exceeded Texas 

Surface Water Quality Standards (chronic criterion of 5 μg/L 

or the acute criterion of 20 μg/L) established for the protection 

of aquatic life. 

Water-quality samples collected during March–August 

2005 at sites D2 were analyzed for 162 pesticides, and waterquality samples collected during April–August 2005 at site P2 

were analyzed for 54 pesticides. No pesticides were reported 

at concentrations equal to or larger than the laboratory 

reporting levels at sites D2 or P2. 

Among all Devils River sites, 29 species of fish were 

collected. Of these 29 species, 7 are non-native (introduced), 

and 22 are native to the Devils River. The number of species 

collected varied from a minimum of 17 species (2006 

sampling only) at the Devils River near Turkey Bluff site to a 

maximum of 23 species (2006 and 2007 samplings combined) 

as the Devils River at Pafford Crossing site. More redbreast 

sunfish were collected than any other species of fish in the 

Devils River followed by a number of species of minnows 

(Cyprinidae) including the blacktail shiner and prosperine 

shiner. Fish species collected in the Devils River that were 

not found at the Pecos River study sites included the Devils 

River minnow, sailfin molly, smallmouth bass, spotted bass, 

and warmouth. The redbreast sunfish, sailfin molly, and 

smallmouth bass are all introduced species that are not native 

to the Devils River. 
66 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

A total of 29 species of fish was collected from the 

four sites on the Pecos River in and upstream from Amistad 

National Recreation Area. Six of the 29 species collected 

are introduced to the Pecos River, and these include the 

bullhead minnow, common carp, sheepshead minnow, inland 

silverside, redbreast sunfish, and redear sunfish. The number 

of fish species decreased about 42 percent between the site 

farthest upstream and the site farthest downstream on the 

Pecos River based on a comparison of 2006 sampling results. 

The most abundant species among the Pecos River sites was 

the blacktail shiner followed by the red shiner and central 

stoneroller. The redbreast sunfish, as in the Devils River, was 

the most common species of sunfish. Fish species collected 

in the Pecos River that were not collected at study sites on 

the Devils River included the bullhead minnow, red shiner, 

smallmouth buffalo, rainwater killifish, and freshwater drum. 

The percentage of tolerant fish species was larger at the two 

sites farthest upstream on the Pecos River compared to the two 

sites farthest upstream on the Devils River. The percentage of 

non-native or introduced individuals was from two to three 

times larger at two of the Devils River sites compared to two 

of the Pecos River sites and was influenced by the relatively 

large abundance of the non-native redbreast sunfish and 

smallmouth bass at the Devils River study sites. 

The similarity of fish communities was assessed by the 

number shared species among each of the sites sampled. In 

this study, Non-metric Multidimensional Scaling (NMDS) 

was used to determine Euclidean distances between objects 

by using an input fish species similarity matrix (Bray-Curtis 

similarity matrix), and these distances were displayed 

graphically by using two NMDS dimensions. On the basis 

of the first NMDS dimension, the fish communities from a 

given site on either the Devils or Pecos Rivers (determined 

from the species present at the time of collection) were more 

similar to the fish communities at other sites on the same river 

than they were to fish communities at any of the sites on the 

other river. The second dimension of the NMDS (dimension 

2 on the y-axis), indicates that between the two rivers, the fish 

community of any site is most similar to the fish community at 

the site on the other river that is in the same downstream order. 

The difference in fish communities between the study 

sites on the Devils and Pecos Rivers could be influenced 

by differences in water chemistry, particularly salinity; 

differences in zoogeographic history between the two river 

basins; and the fact that impounded waters of Amistad 

Reservoir have removed the natural free-flowing fluvial 

(riverine) connection between the Devils and Pecos Rivers to 

the Rio Grande. The Pecos River is in backwater conditions 

at its confluence with the Rio Grande most of the time. Sites 

on the Pecos River also are farther from the main body of 

Amistad Reservoir compared to those on the Devils River, 

and the distance of the study sites from the reservoir also 

might influence fish community structure.

Totals of 100 and 80 unique macroinvertebrate taxa 

were collected in the Devils and Pecos River, respectively. 

The number of unique macroinvertebrate taxa ranged in 

the Devils River from 34 at the Devils River near Satan 

Canyon site to 57 at Devils River at Pafford Crossing site. 

Considering the sites on both rivers, the largest number of 

unique macroinvertebrate taxa (57) was from the Devils 

River at Pafford Crossing site, and the smallest number of 

unique macroinvertebrate taxa (26) was from the Pecos River 

at Shumla Bend site. No pattern in the number of unique 

macroinvertebrate taxa in relation to distance from Amistad 

Reservoir was observed. Caddisfly (Trichoptera) taxa were 

less abundant than mayfly (Ephemeroptera) taxa in all study 

sites. The combined percentage of Ephemeroptera, Plecoptera, 

and Trichoptera taxa was generally about twice as large in the 

Pecos River than the Devils River with the exception of the 

Devils River at Pafford Crossing site. Damselfly and dragonfly 

taxa (Odonata) were not commonly collected in the Devils 

and Pecos study sites. Riffle beetles (Elmidae) were the most 

commonly collected beetle taxon and were the most abundant 

beetle taxon in numbers of individuals collected at all sites. 

True midge taxa of the family Chironomidae were the most 

taxa rich macroinvertebrate taxon overall. Twenty-six unique 

true midge taxa (genera or species) were collected at the Devil 

River and Pecos Rivers sites combined. A clam, most likely 

the introduced Asian clam, was collected at two sites on the 

Devils River and three sites on the Pecos River. The Margalef 

richness index, which was derived by using the relative 

abundance of aquatic insect taxa, was larger at the Devils 

River sites than at the Pecos River sites. The Hilsenhoff biotic 

index was largest at site D1 (Devils River near Satan Canyon 

site), the site farthest downstream on the Devils River, and 

smallest at site P2 (Pecos River near Langtry, Tex.), the site 

second farthest downstream on the Pecos River. Non-insect 

macroinvertebrate taxa—including freshwater worms, snails, 

mites, and crayfish—were more common and abundant at the 

Devils River study sites, and amphipods were more abundant 

at the Devils River sites. 

The first dimension in ordination of the NMDS analysis 

of aquatic insect taxa did not separate the sites in a way that 

could be explained by the upstream to downstream stream 

order. The second dimension in ordination of the aquatic insect 

community by using NMDS analysis indicates that each site is 

more similar to the other sites on the same river segment than 

to any of the sites on the other river segment.
References 67

References

Ashworth, J.B., and Hopkins, Janie, 1995, Aquifers of Texas: 

Texas Water Development Board, Report 345, 69 p.

Barker, R.A., Bush, P.W., and Baker, E.T., Jr., 1994, Geologic 

history and hydrogeologic setting of the Edwards-Trinity 

aquifer system, west-central Texas: U.S. Geological Survey 

Water-Resources Investigations Report 94-4039, 51 p.

Black, P.E., 2004, Euclidean distance: Dictionary of 

algorithms and data structures [online], Black, P.E., ed., 

U.S. National Institute of Standards and Technology, 

accessed January 25, 2012, at http://www.nist.gov/dads/

HTML/euclidndstnc.html.

Borror, D.J., Triplehorn, C.A., and Johnson, N.F., 1989, An 

introduction to the study of insects: Philadelphia, Pa., 

Saunders College Publishing, 875 p.

Brune, Gunnar, 1981, Springs of Texas, volume 1: Fort 

Worth, Tex., Branch-Smith, Inc., 566 p.

Butler, D.L., and Von Guerard, P.B., 1996, Salinity in the 

Colorado River in the Grand Valley, western Colorado, 

1994–95: U.S. Geological Survey Fact Sheet 215-96, 

accessed March 25, 2011, at http://pubs.usgs.gov/fs/

fs-215-96/.

Church, M., 1992, Channel morphology and typology—

Chapter 6, in Calow, P., and Petts, G.E. (eds.), The 

Rivers Handbook—Volume I: London, Blackwell 

Scientific, p. 126-143. 

Clarke, K.R., and Warwick, R.M., 2001, Change in marine 

assemblages—An approach to statistical analysis and 

interpretation (2nd ed.): Plymouth, United Kingdom, 

PRIMER-E Ltd.

Field, J.G., Clarke, K.R., Warwick, R.M., 1982, A practical 

strategy for analyzing multispecies distribution patterns: 

Marine Ecology, v. 12, p. 42-58.

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey 

Open-File Report 93–125, 217 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of pesticides in 

water by graphitized carbon-based solid-phase extraction 

and high-performance liquid chromatography/mass 

spectrometry: U.S. Geological Survey Water-Resources 

Investigations Report 01–4134, 73 p.

Gido, K.B., 2001, Feeding ecology of three omnivorous 

fishes in Lake Texoma (Oklahoma-Texas): The 

Southwestern Naturalist, v. 46, no. 1, p. 23-33.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 4, chap. A3, 510 p. 

(Also available at http://pubs.usgs.gov/twri/twri4a3/.)

Hilsenhoff, W.L., 1987, An improved biotic index of organic 

stream pollution: Great Lakes Entomology, v. 20, p. 31-39.

Hubbs, Clark, 1951, Observations on the breeding of Dionda 

episcopa serena in the Nueces River, Texas: Texas Journal 

of Science, v. 3, p. 490-492.

Hubbs, Clark, Edwards, R.J, and Garrett, G.P, 1991, An 

annotated checklist of the freshwater fishes of Texas, with 

keys to identification of species: The Texas Journal of 

Science, supplement, v. 43, no. 4, 53 p. 

International Boundary and Water Commission, 1994, 

Binational study regarding the presence of toxic substances 

in the Rio Grande/Rio Bravo and its tributaries along the 

boundary portion between the United States and Mexico: 

246 p., accessed March 31, 2011, at http://www.epa.gov/

region6/water/ecopro/binattoxics.pdf.

International Boundary and Water Commission, 2011, 

Amistad Dam and power plant, Del Rio, Texas: accessed 

September 28, 2011, at http://www.ibwc.gov/Organization/

Operations/Field_Offices/amistad.html.

International Boundary and Water Commission, 2011, 

Rio Grande historical mean daily discharge data: accessed 

10 November, 2011, at http://www.ibwc.state.gov/Water_

Data/histflo1.htm.

International Commission on Zoological Nomenclature, 2010, 

Standards, sense, and stability for animal names in science: 

accessed October 5, 2010, at http://www.iczn.org.
68 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

Jensen, Richard, Hatler, William, Mecke, Michael, and Hart, 

Charles, 2006, The influences of human activities on the 

waters of the Pecos Basin of Texas—A brief overview: 

Texas Water Resources Institute Report SR-2006-03, 40 

p., accessed October 5, 2010, at http://twri.tamu.edu/

publications/reports/2006/sr-2006-03.

Lee, R.W., and Wilson, J.T., 1997, Trace elements and 

organic compounds associated with riverbed sediments in 

the Rio Grande/Rio Bravo Basin, Mexico and Texas: U.S. 

Geological Survey Fact Sheet FS-098-97, 6 p., accessed 

October 5, 2010, at http://pubs.usgs.gov/fs/1997/fs-098-97/.

Lenat, D.R., and Barbour, M.T., 1994, Using benthic 

macroinvertebrate community structure for rapid, 

cost-effective, water quality monitoring—Rapid 

bioassessment, in Loeb, S.L. and Spacie, A., eds., 

Biological monitoring of aquatic systems: Boca Raton, 

Fla., Lewis Publishers, p. 187-215.

Lester, G., 1999, Laboratory methods for the processing of 

invertebrate samples: Moscow, Idaho, Ecoanalysts Inc., 4 p.

Linam, G.W., and Kleinsasser, L.J., 1996, Relationships 

between fishes and water quality in the Pecos River, 

Texas: River studies report no. 9, Texas Parks and 

Wildlife Department, 11 p.

Linam, G.W., and Kleinsasser, L.J., 2002, Regionalization of 

the index of biotic integrity for Texas streams: River studies 

report no. 17, Texas Parks and Wildlife Department, 26 p.

Lindley, C.E., Stewart, J.T., and Sandstrom, M.W., 1996, 

Determination of low concentrations of acetochlor in 

water by automated solid-phase extraction and gas 

chromatography with mass selective detection: Journal of 

AOAC International, v. 79, no. 4, p. 962–966.

Lobello, R. L., 1976, Vertebrates of the Lake Amistad National 

Recreation Area, Texas: Alpine, Texas, Department of 

Biology, Sul Ross State University master’s thesis, 165 p.

Ludwig, J.A., and Reynolds, J.F., 1988, Statistical ecology: 

New York, John Wiley, 337 p.

Lucas, M.C., Mercer, T., Peirson, G., Frear, P.A., 2008, 

Seasonal movements of coarse fish in lowland rivers 

and their relevance to fisheries management, in Cowx, 

I.G., ed., Management and Ecology of river fisheries, 

chap. 7: Oxford, United Kingdom., Blackwell Science 

Ltd., p. 87–100.

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, 

Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—A method supplement 

for the determination of fipronil and degradates in water by 

gas chromatography/mass spectrometry: U.S. Geological 

Survey Open-File Report 02–462, 11 p. 

Mast, M.A., and Turk, J.T., 1999, Environmental 

characteristics and water quality of hydrologic benchmark 

network stations in the Midwestern United States, 1963-95: 

U.S. Geological Survey Circular 1173-B, 130 p.

Merritt, R.W., and Cummins, K.W., 1996, An introduction 

to the aquatic insects of North America: Berkeley, Calif., 

Kendall/Hunt Publishing, 771 p.

Minshall, G.W., 1984, Aquatic insect-substratum relationships, 

in Resh, V. H., and Rosenberg, D.M. (eds.), The ecology of 

aquatic insects: New York, Praeger, p. 358-400.

Moring, J.B., 2002, Baseline assessment of instream 

and riparian zone biological resources on the Rio Grande 

in and near Big Bend National Park, Texas: U.S. 

Geological Survey Water-Resources Investigation 

Report 02-4106, 33 p.

Moulton, S.R., Kennen, J.G., Goldstein, R.M., and 

Hambrook, J.A., 2002, Revised protocol for sampling algal, 

invertebrate, and fish assemblages as part of the National 

Water-Quality Assessment Program: U.S. Geological 

Survey Open-File Report 02-150, 75 p.

Moyle, P.B., and Cech, J.J., 1982, Fishes—An introduction 

to ichthyology: Englewood Cliffs, New Jersey, PrenticeHall, 593 p.

National Park Service, 2008, Geologic resource evaluation 

scoping summary—Amistad National Recreation Area, 

Texas: accessed April 11, 2011, at http://www.nature.nps.

gov/geology/inventory/publications/s_summaries/AMIS_

GRE_scoping_summary_2008-0922.pdf.

National Park Service, 2010, Amistad—Nature and science: 

accessed December 13, 2010, at http://www.nps.gov/amis/

naturescience/index.htm.

Pacific Northwest Region Water Quality Program, 2011, 

What are macroinvertebrates: accessed November 2, 2011, 

at http://ww.pnwwaterweb.com.

 Patton, C.J., and Truitt, E.P., 2000, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory—Determination of ammonium plus organic 

nitrogen by a Kjeldahl digestion method and an 

automated photometric finish that includes digest 

cleanup by gas diffusion: U.S. Geological Survey 

Open-File Report 00–170, 31 p.

Plafkin, J.L., Barbour, M.T., Porter, K.D., Gross, S.K., and 

Hughes, R.M., 1989, Rapid bioassessment protocols for 

use in streams and rivers—Benthic macroinvertebrates 

and fish: Washington, D.C., U.S. Environmental 

Protection Agency, Office of Water Regulations and 

Standards, EPA 440/4-89/001, 196 p.
References 69

Purchase, C.E., Larson, D., Flora, M.D., and Reber, 2001, 

Amistad National Recreation Area, Texas—Water resources 

scoping report: National Park Service Technical Report 

NPS/NRWRD/NRTR-2001/295, 92 p.

Rowe, G.L., Jr., Belitz, Kenneth, Essaid, H.I., Gilliom, R.J., 

Hamilton, P.A., Hoos, A.B., Lynch, D.D., Munn, M.D., 

and Wolock, D.W., 2010, Design of cycle 3 of the National 

Water-Quality Assessment Program, 2013–2023—Part 

1—Framework of water-quality issues and potential 

approaches: U.S. Geological Survey Open-File Report 

2009–1296, 54 p., accessed online November 6, 2011, at 

http://pubs.usgs.gov/of/2009/1296/pdf/OF09-1296.pdf.

Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and 

Schroeder, M.P., 2001, Methods of analysis by the 

U.S. Geological Survey National Water Quality 

Laboratory—Determination of moderate-use pesticides 

and selected degradates in water by C-18 solid-phase 

extraction and gas chromatography/mass spectrometry: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4098, 70 p. 

StatSoft, Inc., 2006, STATISTICA for Windows and Windows 

95/98/NT: Tulsa, Okla., StatSoft, Inc.

Texas Commission on Environmental Quality, 2007, Surface 

water quality monitoring procedures, volume 2: Methods 

for collecting and analyzing biological assemblage and 

habitat data: RG-416, 202 p.

Texas Commission on Environmental Water Quality, 2010, 

Texas Surface Water Quality Standards: Rule Project 

Number 2007-002-307-PR, 286 p.

Thompson, W., 2008, Economic impacts of salinity control 

measures for the Upper Pecos River Basin of Texas: 

Texas Water Resources Institute Technical Report, 42 p.

U. S. Environmental Protection Agency, 1993, Method 

365.1, Determination of phosphorus by semi-automated 

colorimetry revision 2.0—Methods for the determination 

of inorganic substances in environmental samples: 

Cincinnati, Ohio, U.S. Environmental Protection Agency, 

Office of Research and Development, Environmental 

Monitoring Systems Laboratory, 17 p.

U. S. Environmental Protection Agency, 2011, Level III 

ecoregions of the continental United States (revised 

December 2011)—GIS data: Durham, N.C., U.S. 

Environmental Protection Agency, National Health and 

Environmental Effects Research Laboratory, accessed 

December 7, 2011, at http://www.epa.gov/wed/pages/

ecoregions.htm.

U.S. Fish and Wildlife Service, 1999, Federally listed as 

threatened and endangered species of Texas (Val Verde 

County List): Austin Ecological Services Field Office, 

Austin, Texas.

 U.S. Geological Survey, variously dated, National field 

manual for the collection of water-quality data: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 9, chaps. A1-A9, available online 

at http://pubs.water.usgs.gov/twri9A/.

U.S. Geological Survey, 2006, User’s manual for the 

National Water Information System of the U.S. Geological 

Survey water-quality system: U.S. Geological Survey 

open-file report, version 4.4., accessed November 28, 2011, 

at http://pubs.usgs.gov/of/2006/1145/pdf/qw_complete.pdf.

U.S. Geological Survey, 2010, National Stream Quality 

Accounting Network: accessed on December 13, 2010, 

at http://water.usgs.gov/nasqan/.

U.S. Geological Survey, 2011, National Water Information 

System: accessed in March 2011 at http://waterdata.usgs.

gov/tx/nwis/.

Ward, J.V., 1992, Aquatic insect ecology, 1, Biology and 

habitat: Hoboken, N.J., John Wiley and Sons, Inc., 456 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—Determination 

of pesticides in water by C-18 solid-phase extraction and 

capillary-column gas chromatography/mass spectrometry 

with selected-ion monitoring: U.S. Geological Survey 

Open-File Report 95–181, 60 p.
70 Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers

[Values shown in percent. Alpha-HCH, alpha-hexachlorocyclohexanet]

Surrogate compound Set 1 Set 2 Set 3 Set 4 Average recovery

Diazinon 114.0 93.9 116.0 104.0 106.8

alpha-HCH 88.7 96.9 107.0 93.6 96.6

Prepared by the USGS Lafayette Publishing Service Center

Appendix 1. Laboratory recovery of surrogate compounds from four sets

analyzed concurrently with water-quality samples from U.S. Geological Survey 

stations 08449400 Devils River at Pafford Crossing near Comstock, Texas, and 

08447410 Pecos River near Langtry, Tex., in the Amistad National Recreation 

Area, 2005.
Moring, J. B.—Water Quality and the Composition of Fish and Macroinvertebrate Communities in the Devils and Pecos Rivers In and Upstream from the 

Amistad National Recreation Area, Texas, 2005–7 —SIR 2012–5038

Printed on recycled paper