Monitoring of Inorganic Contaminants 

Associated With Irrigation Drainage 

in Stillwater National Wildlife Refuge 

and Carson Lake, West-Central 

Nevada, 1994-96 

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U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 00-4173 

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.U58w .5. FISH AND WILDLIFE SERVICE 

no.00-4173 UREAU OF RECLAMATION 7 1- 

2000 UREAU OF INDIAN AFFAIRS 
LIBRARY 

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BUREAU OF RECLAMATION DENVER L BRARY 

II 11 11 11 111 11111 I I I 111 1111111 II 

92074207 

Monitoring of Inorganic Contaminants Associated 

With Irrigation Drainage in Stillwater National 

Wildlife Refuge and Carson Lake, 

West-Central Nevada, 1994-96 

By PETER L. TUTTLE, RAY J. HOFFMAN, STANLEY N. WIEMEYER, 

and JOHN F. MIESNER 

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 00-4173 

Prepared in cooperation: 

U.S. GEOLOGICAL SURVEY 

U.S. FISH AND WILDLIFE SERVICE 

BUREAU OF RECLAMATION 

BUREAU OF INDIAN AFFAIRS 

Carson City, Nevada 

2000 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

CHARLES G. GROAT, Director 

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government 

For additional information Copies of this report can be 

contact: purchased from: 

District Chief U.S. Geological Survey 

U.S. Geological Survey Information Services 

333 West Nye Lane, Room 203 Building 810 

Carson City, NV 89706-0866 Box 25286, Federal Center 

Denver, CO 80225-0286 

email: GS-W-NVpublic-info@usgs.gov 

http://nevada.usgs.gov 
CONTENTS 

Abstract 1 

Introduction 2 

Background 2 

Purpose and Scope 4 

Acknowledgments 5 

Environmental Setting 5 

Previous Contaminant Studies 5 

Carson River Mercury 5 

Agricultural Drainage 7 

Sample Collection, Measurement, and Analysis 9 

Drains and Canals Entering Wetlands 9 

Sampling Sites 9 

Drainflow Measurements 9 

Water-Quality Measurements, Water-Sample Collection, and Laboratory Analyses 11 

Statistical Analyses 11 

Quality Control 11 

Wetlands 12 

Sampling Sites and Sampled Media 12 

Water-Quality Measurements, Sample Collection, and Laboratory Analyses 12 

Quality Control 13 

Toxicity Tests 13 

Remote Sensing of Wetland Habitats 14 

Aquatic Invertebrate Community 14 

Fish-Community Structure and Condition 14 

Surveys of Bird Use of Wetlands 15 

Statistical Analyses 15 

Results and Discussion of Monitoring Program 15 

Water Supply 15 

Drains Entering Wetlands of Stillwater National Wildlife Refuge 16 

S Line Canal 16 

Stillwater Slough 19 

Paiute Diversion Drain Below TJ Drain 19 

Stillwater Point Reservoir Diversion Canal 19 

Drains Entering Wetlands of Carson Lake 19 

Carson Lake Drain 20 

Rice Ditch 20 

L Drain 20 

L 12 Drain 20 

Loads of Dissolved Solids and Boron 21 

Dissolved Solids 21 

Stillwater National Wildlife Refuge 21 

Carson Lake 21 

Boron 21 

Stillwater National Wildlife Refuge 21 

Carson Lake 24 

CONTENTS III 
Evaluation of Load-Measurement Uncertainty Associated With Frequency of Data Collection in Agricultural Drains 

Concentrations and Loads of Total Mercury 

Stillwater Slough 

Stillwater Point Reservoir Diversion Canal 

Physical, Chemical, and Biological Characteristics of Water, Bottom Sediment, and Biota in Wetlands 

Field Measurements of Dissolved Oxygen, pH, and Specific Conductance 

Dissolved Oxygen 

pH 

Specific Conductance 

Trace Elements 

Concentrations in Sampled Media 

Aluminum 

Arsenic 

Boron 

Mercury 

Selenium 

Other Trace Elements 

Lead 

Molybdenum 

Zinc 

Interactive Effects of Trace Elements 

Biological Implications of Contaminants of Concern 

Wetland Communities 

Aquatic-Invertebrate Communities 

Vertebrate Communities 

Fish Communities 

Bird Communities 

Wetland Habitat 

Irrigation-Induced Effects on Ecosystem 

Summary and Conclusions 

Wetland Water Supply 

Wetland-Habitat Conditions 

References Cited 

Figures 

1. Geographic setting of study area, west-central Nevada 

2. Locations of drains entering Stillwater National Wildlife Refuge, other hydrologic features, and sampling 

sites 

3. Surface-water and bottom-sediment sampling sites in and near Carson Lake 

4. Mean boron concentrations and ranges in sediment and pondweed collected from Dry Lake in Stillwater 

National Wildlife Refuge, west-central Nevada, 1992-96 

5. Relations between arsenic concentrations, in wetland water and in sediment, and nektonic-invertebrate 

community metrics 

6. Relations between mercury concentrations in wetland sediment and benthic- and nektonic-invertebrate taxa 

richness 

7. Fish species composition in four wetlands in Lahontan Valley, Nevada, 1995-96 

 24 

 24 

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 25 

 26 

 26 

 26 

 26 

 26 

 28 

 28 

 28 

 30 

 30 

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8 

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IV Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Tables 

1. Selected regulatory standards applicable to designated waters in Nevada as of 1996 6 

2. Threatened, endangered, or candidate species and species of concern associated with wetlands in Lahontan 

Valley, Nevada 7 

3. Measurement sites on agricultural drains entering and in wetlands Stillwater National Wildlife Refuge 

and Carson Lake, Nevada, 1994-96 9 

4. Linear-regression equations of dissolved-solids and boron concentrations in relation to specific conductance 

for drains entering Stillwater National Wildlife Refuge and Carson Lake, Nevada, 1986-96 12 

5. Number of samples of water, sediment, detritus, and biota collected for trace-element concentrations in four 

wetlands in Lahontan Valley, Nevada, 1994-96 13 

6. Streamflows released from Lahontan Reservoir 16 

7. Statistical summary of instantaneous drainflow and concentrations of dissolved solids and dissolved trace 

elements at seven drain sites where water enters wetlands of Stillwater National Wildlife Refuge and of 

Carson Lake, March—October 1994-96 17 

8. Estimated seasonal loads of dissolved solids in drains entering Stillwater National Wildlife Refuge and 

Carson Lake, servicing agricultural areas near Fallon, Nev., 1994-96 22 

9. Estimated seasonal loads of dissolved boron in drains entering Stillwater National Wildlife Refuge and 

Carson Lake, servicing agricultural areas near Fallon, Nev., 1994-96 23 

10. Comparison of continuous-recording and periodic onsite measurements of annual dissolved-solids loads in 

agricultural drains entering Stillwater National Wildlife Refuge, Nevada 25 

11. Field measurements of temperature, dissolved-oxygen concentration and saturation, pH, and specific 

conductance in four wetlands in Lahontan Valley, Nevada, June—July 1994-96 27 

12-16. Concentrations in unfiltered water, sediment, and biological samples collected from four wetlands in 

Lahontan Valley, Nevada, April—August 1994-96: 

12. Aluminum 29 

13. Arsenic 31 

14. Boron 32 

15. Mercury 35 

16. Selenium 37 

17. Benthic invertebrates in bottom-sediment samples from four wetlands in Lahontan Valley, Nevada, 1994-96 41 

18. Nektonic invertebrates in samples from four wetlands in Lahontan Valley, Nevada, 1994-96 42 

19. Population density and taxa richness, evenness, and heterogeneity for benthic and nektonic invertebrates 

collected from four wetlands in Lahontan Valley, Nevada, 1994-96 43 

20. Length, weight, and Fulton's condition factor for selected fish types, representing different size classes, 

collected from four wetlands in Lahontan Valley, Nevada, 1995-96 47 

21. Index of Biological Integrity metrics and scores as modified to assess fish assemblages in four wetlands in 

Lahontan Valley, Nevada, 1994-96 48 

22. Avian species along established transects in four wetlands in Lahontan Valley, Nevada, July—September 1995 

and May—September 1996 49 

23. Area of wetlands, Stillwater National Wildlife Refuge and Carson Lake, Nevada, August—September 1994-96 53 

TABLES V 
	 	

CONVERSION FACTORS, WATER-QUALITY UNITS, VERTICAL DATUM, AND ACRONYMS 

Multiply By To obtain 

cubic foot per second (ft3/s) 0.02832 cubic meter per second 

foot (ft) 0.3048 meter 

inch (in.) 25.4 millimeter 

mile (mi) 1.609 kilometer 

ounce (oz) 29.57 milliliter 

pound (lb) 0.4536 kilogram 

pound per day (lb/d) 0.4536 kilogram per day 

square mile (mil) 2.590 square kilometer 

ton 907.2 kilogram 

ton per day (ton/d) 907.2 kilogram per day 

Temperature: Degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) by using the formula °F = [1.8(°C)]+32. 

Degrees Fahrenheit can be converted to degrees Celsius by using the formula °C = 0.556(°F-32). 

Water-quality units used in this report: 

mg/L milligrams per liter 

μgig micrograms per gram 

ptg/L micrograms per liter 

μS/cm microsiemens per centimeter at 25 degrees Celsius 

Concentrations of trace elements in unfiltered water are expressed in micrograms per liter; trace-element concentrations in bottom sediment 

and biological samples are expressed in micrograms per gram on a dry-weight basis unless otherwise indicated herein. 

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called 

"Sea-Level Datum of 1929"), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada 

ANOVA Analysis of Variance 

IBI Index of Biological Integrity 

NDEP Nevada Division of Environmental Protection 

NDW Nevada Division of Wildlife 

NIWQP National Irrigation Water Quality Program 

NWR National Wildlife Refuge 

USDI U.S. Department of the Interior 

USFWS U.S. Fish and Wildlife Service 

USGS U.S. Geological Survey 

WMA Wildlife Management Area 

VI Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Monitoring of Inorganic Contaminants Associated With 

Irrigation Drainage in Stillwater National Wildlife Refuge 

and Carson Lake, West-Central Nevada, 1994-96 

By Peter L. Tuttlel, Ray J. Hoffman2, Stanley N. Wiemeyer', and John F. Miesnerl 

Abstract 

In 1994, the U.S. Geological Survey and the U.S. 

Fish and Wildlife Service initiated a 3-year drainwater- and wetland-monitoring program in Lahontan 

Valley, Nevada, as part of the National Irrigation Water 

Quality Program of the U.S. Department of the Interior. 

The purpose of the monitoring was to (1) develop a 

long-term hydrologic and biologic data base, (2) provide a baseline to evaluate the effects of Federal activities on water quality, wetland quality, and biota in the 

area, and (3) identify progress toward remediation of 

contaminant concerns in Lahontan Valley wetlands. 

Specific data collected included drain-water quantity 

and quality; trace-element concentrations in water, sediment, and biological samples from wetlands; aquaticinvertebrate and fish diversity and relative abundance 

in wetlands; fish condition; bird use of wetlands; acreage of major wetland habitat types; and toxicity of 

water to test organisms. 

Consistent with previous National Irrigation 

Water Quality Program investigations, some inorganic 

contaminants exceeded applicable beneficial-use criteria or levels of biological concern during 1994-96. 

Water flowing in some agricultural drains into the wetlands contained concentrations of dissolved boron and 

molybdenum and total mercury that frequently 

exceeded applicable beneficial-use criteria. Loads 

of dissolved solids, boron, and mercury were greatest 

during the irrigation season coincident with increased 

flow. In the wetlands of Stillwater National Wildlife 

Refuge, aluminum, arsenic, boron, lead, mercury, 

molybdenum, and zinc in unfiltered water samples 

1U.S. Fish and Wildlife Service 

2U.S. Geological Survey 

exceeded State and(or) Federal criteria for the protection of designated beneficial uses of water; arsenic and 

mercury in sediment exceeded potentially toxic levels; 

and aluminum, boron, mercury, and zinc in biological 

tissues exceeded levels associated with lethal or sublethal effects on fish and wildlife. Concentrations of selenium generally were below levels of biological concern 

in all sample media. 

Invertebrate-community species composition and 

community structure varied among wetlands and 

among years. Dominant invertebrate taxa were classified as moderately to highly tolerant of pollutants. Concentrations of arsenic, boron, and molybdenum in 

unfiltered water and arsenic, mercury, and possibly 

selenium in sediment collected from wetlands correlated with effects on aquatic invertebrate communities. 

Fish species assemblages, which consisted of one 

native species and four introduced species, also varied 

among years and among wetlands. Fish species present 

were classified as moderately tolerant to tolerant of 

pollutants. Measures of fish condition were inconsistent among species and among wetlands. The presence 

of larval fish suggested successful fish reproduction in 

Lahontan Valley wetlands. Bird use of wetlands also 

varied among wetlands and among years. 

Wetland-habitat acreage increased over the 

course of this investigation. The increase was attributed to regional climatic patterns and the increase of 

water flow to wetlands during the 1994-96 study. Corresponding to increased water inflow, the areal extent 

of open water and associated emergent-vegetation habitats also increased. 

Specific conductance, a surrogate measure of dissolved-solids concentration, appeared to be a useful 

variable to monitor the levels of salinity and certain 

potentially toxic trace elements in drains and wetlands 

of Lahontan Valley. 

Abstract 1 
INTRODUCTION 

Background 

For the past decade or so, irrigation-induced 

water-quality problems have been of increasing concern. For example, research by the U.S. Fish and Wildlife Service (USFWS) in the Western United States has 

related incidents of aquatic-bird and fish mortality, 

embryo teratogenesis, and reproductive failures to high 

concentrations of selenium in irrigation drain water 

(Presser and Ohlendorf, 1987; Seiler and others, 1999). 

These adverse effects on fish and wildlife were first 

identified in 1983 at Kesterson National Wildlife Refuge (NWR) in western San Joaquin Valley of California, where irrigation drain-water was impounded 

(National Research Council, 1989). The embryonic 

abnormalities at Kesterson NWR were ultimately 

linked to a combination of human-caused and natural 

phenomena, specifically by the application of irrigation 

water to soil naturally rich in selenium. In this instance, 

selenium as selenate was leached from the soil profile 

and transported to the surface by subsurface drainage 

and eventually entered the food chain. 

In response to widespread concern about the 

nature and extent of contamination problems associated with irrigation drainage, the U.S. Department of 

the Interior (USDI) developed the Irrigation Drainage 

Program in 1985, later renamed the National Irrigation 

Water Quality Program (NIWQP), and formed an interbureau Task Group on Irrigation Drainage. This 

group's charge is to address irrigation-induced waterquality problems in areas where USDI has management responsibilities, including (1) irrigation or drainage facilities constructed or managed by USDI, (2) 

NWR's that receive irrigation drainage water managed 

by USDI, and (3) areas that receive water from USDIfunded projects and that are used by migratory birds 

and (or) endangered species. NIWQP is a five-phase 

program: 

• Phase One: data compilation to identify potential problem areas; 

• Phase Two: onsite reconnaissance investigation of water, bottom sediment, and biota in 

identified areas; 

• Phase Three: detailed study of selected areas 

where further assessment was warranted; 

• Phase Four: formulation of a written plan of 

action to correct identified adverse effects of 

irrigation drainage; and 

• Phase Five: implementation of the corrective 

action to eliminate or alleviate the identified 

problems. 

Phases One through Three are largely the responsibility of the U.S. Geological Survey (USGS) and 

USFWS, whereas Phases Four and Five are largely the 

responsibility of the Bureau of Reclamation. In 1986, 

9 areas that warranted immediate reconnaissance-level 

investigation were identified by the Task Group, and 

later, 17 other areas were added. All 26 study areas are 

in the Western United States. 

Stillwater NWR in Lahonton Valley of westcentral Nevada (fig. 1) was one of the initial nine highpriority areas selected for immediate reconnaissance 

investigation. The results of that study revealed that 

concentrations of potentially toxic trace elements 

(arsenic, boron, mercury, and selenium) and dissolved 

solids likely pose a threat to human health, fish, and 

wildlife in areas that receive irrigation drainage (Hoffman and others, 1990). Because the reconnaissance 

investigation was not designed to determine cause-andeffect relations, a detailed study (Phase Three) of the 

source, transport, and fate of contaminants began in 

water year 1988. The results of the detailed study indicated that fish and wildlife in the historic wetlands of 

Lahontan Valley were affected adversely by elevated 

concentrations of naturally occurring trace elements 

that were mobilized in the shallow alluvial aquifer by 

flood-irrigation practices in the area of the Newlands 

Project, a USDI-sponsored irrigation project (Rowe 

and others, 1991; Lico, 1992; Hallock and Hallock, 

1993; Hoffman, 1994). These waterborne constituents 

flowed downslope in the subsurface or by drainflow 

and eventually entered the wetlands and were concentrated further by evaporation and transpiration. Water 

from some agricultural drains was acutely toxic to 

aquatic organisms. The drains in the agricultural area, 

which eventually discharge to wetlands, were also 

implicated as sites of uptake of selenium and mercury 

by aquatic organisms. Other contaminants of concern, 

either singly or in combination, were arsenic, boron, 

lithium, molybdenum, and perhaps uranium. 

In 1990, Congress enacted the Truckee—Carson— 

Pyramid Lake Water Rights Settlement Act (Title II of 

Public Law 101-618) to resolve conflicts associated 

2 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
		

120° 119°30' 119° 118°30' 

1 

rJ 

40° 

In 2 

STILLWATER 

FERNLEY 

WILDLIFE 

MANAGEMENT 

WILDLIFE 

MANAGEMENT 

AREA 

AREA 

Massie 

Slough 

Stillwater "- -`Marsh'- 

Mahala 

RENO River Fernley Slough SODA 

< cP,5 "LAKE 

39°30' LAHONTAN 

DAM 

 q3.,Z 

River 

—AREA OF 

FIGURE 2 

0 LAHONTAN 

RESERVOIR 

Newlands / 

Project 

area 

FALLON INDIAN 

RESERVATION STILLWATER 

NATIONAL 

WILDLIFE 

z 

Comstock 

Mining District 

Virginia CiA) 

Dayton 

River 

AREA OF — 

FIGURE 3 

(9 

CARSON 

LAKE 

C5-0 

REFUGE 

Carson 

City 

/0 10 20 MILES 

39° 9 0 10 20 KILOMETERS 

Base from U.S. Geological Survey digital data,1:100,000, 1970-85 

Albers Equal-Area Conic projection 

Standard parallels 29°30' and 45°30', central meridian -119°00' 

EXPLANATION AREA 

OF 

FIGURE Wetlands—Includes some open water 

not seperately mapped 

Open water 

Playa or dry or intermittent lake 

Boundary of Wildlife Management Area or 

National Wildlife Refuge 

Figure 1. Geographic setting of study area, west-central Nevada. 

with increasing water demands in the Truckee River the Stillwater NWR, Carson Lake, and the Paiute— 

and Carson River Basins. Restoration and protection of Shoshone Indian Reservation at Fallon. Section 206 

ecologically important wetlands in Lahontan Valley also authorized the Secretary " * * * to take such 

was one of many competing uses of water. Section 206 actions as may be necessary to prevent, correct, or mitof the law authorized and directed the Secretary of the igate for adverse water quality and fish and wildlife 

Interior, in conjunction with the State of Nevada and habitat conditions attributable to agricultural drain 

other parties, to acquire sufficient water and water water originating from lands irrigated by the Newlands 

rights to restore and maintain a long-term average of Project * * * " However, the law also provided for the 

25,000 acres of wetland habitat in Lahontan Valley. disposal of agricultural drain water into Stillwater 

Acquired water would be used to support wetlands in NWR wetlands. 

INTRODUCTION 3 
The USFWS began acquisition of water rights 

under a 1991 "Environmental Assessment and Finding 

of No Significant Impact," which provided for the 

acquisition of up to 20,000 acre-ft of water rights from 

the Newlands Project area. The "Final Environmental 

Impact Statement" for the Federal Water Rights Acquisition Program was completed in 1996 (U.S. Fish and 

Wildlife Service, 1996a). Based on analysis of water 

requirements of various wetland habitat types, the 

USFWS estimated that 125,000 acre-ft of water was 

needed to achieve the goal of 25,000 acres of wetland 

habitat. The "Record of Decision" for water-rights 

acquisition was signed in November 1996. To achieve 

that goal, the chosen alternative relies on the acquisition of rights to 75,000 acre-ft of water from the Carson 

Division of the Newlands Project and the remaining 

50,000 acre-ft from the Carson River corridor upstream 

from Lahontan Reservoir, operational spills from 

Lahontan Reservoir, treated sewage effluent, water 

conserved on lands managed by the U.S. Navy, and 

pumping of ground water near the wetlands. This alternative was chosen because it fulfilled the mandate 

under Section 206(a)(1) of the law and because it minimized possible adverse effects on farmlands, the local 

agricultural community, And local ground-water 

recharge. Under the chosen alternative, an estimated 

19,700 acre-ft of Newlands Project drain water would 

be used to attain the target of 25,000 acres of wetland. 

Water-quality criteria and water-management practices 

to minimize contaminant accumulation in wetlands 

will be addressed in the Stillwater NWR "Comprehensive Conservation Plan" being prepared by the 

USFWS. 

As of August 1998, approximately 29,000 acre-ft 

of irrigation water rights have been purchased by 

USDI, the State of Nevada, and other entities. Acquisition of the full amount of water needed to restore and 

support 25,000 acres of wetlands is not expected to be 

complete for 15 to 20 years hence. 

Purpose and Scope 

Federal activities in Lahontan Valley, including 

the acquisition of water for wetlands and changes in 

water use within the Newlands Project, are expected 

to have positive effects on water quantity and quality 

within the Valley wetlands. Because the type and magnitude of hydrologic changes in the area and the resulting effects on fish, wildlife, and their habitat are 

uncertain, the NIWQP coordinators indefinitely 

suspended the Phase Four remedial-planning activities. 

Additional information was needed to evaluate longterm changes associated with other ongoing activities. 

Therefore, the coordinators authorized and funded an 

environmental monitoring program described herein. 

The objectives of the program are to 

• develop a long-term hydrologic and biologic 

data base for NIWQP; 

• evaluate the effects of ongoing Federal activities on water quality, wetland quality, and biota 

in the area; and 

• identify progress toward remediation of contaminant concerns in Lahontan Valley wetlands. 

From 1994 through 1996, USGS and USFWS 

scientists collected physical, chemical, and biological 

data from surface water at the distal end of the Newlands Project. USGS hydrologists were responsible for 

collecting data on water quantity and quality from eight 

sites on principal drains entering wetlands of Stillwater 

NWR and Carson Lake. These data consisted of (1) 

instantaneous field measurements of drainflow, water 

temperature, specific conductance, pH, and dissolved 

oxygen, (2) continuous measurements of drainflow, 

water temperature, and specific conductance at selected 

sites, and (3) concentrations of dissolved solids; dissolved arsenic, boron, lithium, molybdenum; and, at 

selected sites, total mercury. These data were published 

by the USGS in the annual water-data reports for water 

years 1994-96 (Clary and others, 1995; Baurer and 

others, 1996; Bostic and others, 1997). 

USFWS biologists were responsible for collecting hydrologic and biologic data from four representative wetlands, in Lahontan Valley: Dry Lake, Lead 

Lake, Stillwater Point Reservoir in Stillwater NWR, 

and Sprig Pond wetland unit of Carson Lake (hereafter 

may be referred to as Sprig Pond only). These data 

included (1) trace-element concentrations in water, 

sediment, and biological samples from wetlands, 

(2) aquatic-invertebrate and fish diversity and relative 

abundance, and fish condition, (3) bird use of wetlands, 

(4) areas of major wetland habitat types, and (5) toxicity of water to test organisms. These data are available 

from the U.S. Fish and Wildlife Service (1340 Financial Boulevard, Suite 234, Reno, NV 89502-7147) 

and in "data table" on the Internet at 

<http://www.usbr.goviniwqp/datasyn.html>. 

This report presents an evaluation of the data 

collected during the 1994-96 monitoring program. 

4 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Acknowledgments 

The authors of this report deeply appreciate the 

assistance provided by Damian Higgins, William 

Henry, Robert Bundy, and Robert Flores, of the 

USFWS, and by Rita Whitney, formerly of the USGS, 

for data collection and data compilation. The initial 

manuscript was improved greatly by critical-review 

comments by Kevin Kilbride, USFWS; James Yahnke, 

Bureau of Reclamation; Thomas Strekal, Bureau of 

Indian Affairs; and Frank Rinella, USGS. 

ENVIRONMENTAL SETTING 

A generalized description of the study area, 

including discussion of history, geology, soils, hydrology, and local climate, were provided by Hoffman and 

others (1990, p. 3-15) and Hoffman (1994, p. 4-7). 

The wetlands of Stillwater NWR and Carson 

Lake are designated "Class C" waters of the State 

(Nevada Administrative Code 445A.126), which 

include "waters or portions of waters located in areas of 

moderate-to-urban human habitation, [where] industrial development is moderate, agricultural practices 

are intensive, and the watershed is considerably altered 

by man's activity." Beneficial uses for Class C waters 

include "municipal and domestic supply, after complete treatment; irrigation; watering of livestock; 

aquatic life; propagation of wildlife; recreation involving contact with the water; recreation not involving 

contact with the water; and industrial supply." Applicable water-quality standards are listed in table 1. 

Lahontan Valley is one of the most valuable wildlife areas in the State. The value of the wetlands is 

largely attributed to their expanse and diversity, which 

provide habitat for the largest and most diverse assemblage of migratory and wetland-dependent birds in 

Nevada. Habitat diversity in and wildlife use of Lahontan Valley were described by Thompson and Merritt 

(1988) and U.S. Fish and Wildlife Service (1996a). 

One endangered, one threatened, and one candidate 

bird species for listing as endangered or threatened 

under the Endangered Species Act of 1973 (16 United 

States Code—Annotated §§ 1531 to 1544) have been 

identified in Lahontan Valley (table 2). As many as 

70 bald eagles (Haliaeetus leucocephalus), a threatened species, commonly winter in Lahontan Valley, 

and as many as 70 were reported in recent years. In 

1997 and 1998, a pair of bald eagles nested at Lahontan 

Reservoir. Endangered american peregrine falcons 

(Falco peregrinus anatum) have been observed in 

Lahontan Valley but are considered uncommon 

migrants in the area (Herron and others, 1985, p. 65). 

Similarly, mountain plovers (Charadrius montanus), a 

candidate for listing as endangered or threatened, have 

been sighted only rarely in Lahontan Valley. Of the 19 

species of concern (formerly candidates) that have 

been sighted in Lahontan Valley, 15 commonly are 

found in wetlands. 

Under the Truckee—Carson—Pyramid Lake Water 

Rights Settlement Act of 1990, Stillwater NWR was 

expanded to 77,520 acres. Of this acreage, the USFWS 

estimates that about 14,000 acres will become semipermanent wetland habitat when sufficient water eventually is acquired. However, because of the dynamic 

nature of wetlands in the Great Basin, owing to human 

activities and natural climate variability, actual wetland 

acreage probably will fluctuate. Among other objectives, the refuge is managed for restoration and maintenance of natural biological diversity and for conservation and management of fish, wildlife, and their 

habitat. 

PREVIOUS CONTAMINANT STUDIES 

Carson River Mercury 

From 1859 to 1900, mercury amalgamation was 

used in the milling of gold and silver ore from the Comstock Mining District in the Virginia Mountain Range 

approximately 70 mi west of Stillwater NWR (Smith, 

1943). As many as 186 mills, most of which were 

located near Virginia City and along the Carson River 

between Carson City and Dayton (fig. 1), were in operation during this period (Ansari, 1989). Nearly 7,500 

tons of imported elemental mercury may have been 

"lost" during milling operations (Bailey and Phoenix, 

1944). An unquantified, but probably substantial, 

amount of mercury entered the river by fluvial processes. Extensive contamination of pre-1900 river 

channels indicates that a substantial amount of mercury 

entered Lahontan Valley prior to construction of 

Lahontan Dam in 1916 (Hoffman, 1994). However, 

Hoffman and Taylor (1998) demonstrated that transport of mercury into Lahontan Valley is continuing, at 

least during major floods. An unquantified, but small, 

amount of mercury is found naturally in the Carson 

River Basin. 

ENVIRONMENTAL SETTING 5 
Table 1. Selected regulatory standards applicable to designated waters in Nevada as of 1996 

[—, no standard] 

Regulatory standard 

Constituent 

(reporting unit) Municipal Aquatic Watering of Propagation or domestic Irrigation life livestock of wildlife supply 

pH (standard units) 5.0-9.0 6.5-9.0 4.5-9.0 6.5-9.0 7.0-9.2 

Dissolved solids (milligrams per liter) 1,000 3,000 

Chloride (milligrams per liter) 400 1,500 1,500 

Aluminum (micrograms per liter) 287 

Arsenic (micrograms per liter) 50 3'4180 100 200 

Barium (micrograms per liter) 1,000 

Beryllium (micrograms per liter) 0 100 

Boron (micrograms per liter) 750 5,000 

Cadmium (micrograms per liter) 5 (4.5) 10 50 

Chromium (micrograms per liter) 50 (4.5) 100 1,000 

Copper (micrograms per liter) (4,5) 200 500 

Fluoride (micrograms per liter) 1,000 2,000 

Iron (micrograms per liter) 1,000 5,000 

Lead (micrograms per liter) 50 (4.5) 5,000 100 

Manganese (micrograms per liter) 200 

Mercury (micrograms per liter) 2 .012 10 

Molybdenum (micrograms per liter) 19 

Nickel (micrograms per liter) (4,5) 13.4 200 

Selenium (micrograms per liter) 50 5 20 50 

Uranium (micrograms per liter) 620 

(4,5) Zinc (micrograms per liter) 2,000 25,000 

1From Nevada Administrative Code 445A.119 and 445A.144 except as noted. 

2Aquatic-life criterion recommended by U.S. Environmental Protection Agency (1998). 

3Arsenic 96-hour average standards for aquatic life are specific for As'-3. 

4Standard applies to dissolved fraction only. 

5Standards for aquatic life are based on water hardness, expressed as milligrams per liter of CaCO3. Formulae for 96-hour average standards 

for specific elements are as follows: 

Cadmium: 0.85 exp[0.7852 ln(hardness) — 3.490] 

Chromium: 0.85 exp[0.8190 1n(hardness) + 1.561] 

Copper: 0.85 exp[0.8545 ln(hardness) — 1.465] 

Lead: 0.25 exp[I.273 ln(hardness) — 4.705] 

Nickel: 0.85 exp[0.8460 ln(hardness) + 1.1645] 

Zinc: 0.85 exp[0.8473 ln(hardness) + 0.7614] 

6Proposed maximum contaminant level for drinking water. 

Elevated mercury concentrations were docu- milling activities upstream, mercury-contaminated 

mented for water, sediment, and biological tissue in the sediments have been distributed widely throughout 

lower Carson River Basin (Van Denburgh, 1973; Rich- Lahontan Valley by way of canals, laterals, and drains 

ins and Risser, 1975). The contamination extended to throughout the valley. For example, mercury concenthe historic wetlands in Lahontan Valley (Cooper and tration in various sampled media are elevated in Stillothers, 1985, p. 55-57; Hoffman and others, 1990). water Point Reservoir. Constructed in the 1940's, the 

Although elevated mercury concentrations in the reservoir primarily received agricultural drainage by 

lower Carson River Basin are attributed to historic ore- way of the Stillwater Point Reservoir Diversion Canal 

6 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Table 2. Threatened, endangered, or candidate species and species of concern associated with wetlands in Lahontan 

Valley, Nevada 

Species or subspecies 

(and common name) Federal status Primary habitat 

Mammals 

Brachylagus idahoensis (pygmy rabbit) 

Euderma maculatum (spotted bat) 

Myotis ciliolabrum (small-footed myotis) 

Myotis evotis (long-eared myotis) 

Myotis thysanodes (fringed myotis) 

Myotis volans (long-legged myotis) 

Myotis yumanensis (yuma myotis) 

Plecotus townsendii pallescens (pale townsend big-eared bat) 

Plecotus townsendii townsendii (townsend's big-eared bat) 

Accipiter gentilis (northern goshawk) 

Athene cunicularia hypugea (western burrowing owl) 

Buteo regalis (ferruginous hawk) 

Charadrius alexandrinus (snowy plover) 

Charadrius montanus (mountain plover) 

Chlidonias niger (black tern) 

Falco peregrinus anatum (american peregrine falcon) 

Haliaeetus leucocephalus (bald eagle) 

Ixobrychus exilis (least bittern) 

Plegadis chihi (white-faced ibis) 

Clemmys marmorata marmorata (northwestern pond turtle) 

Limenitus archippus lahontani (nevada viceroy) 

Oryctes nevadensis (nevada oryctes) 

system (fig. 2). Elevated mercury concentrations in 

edible tissue prompted the State of Nevada to issue 

consumptive advisories for game fish in the lower Carson River Basin (Cooper and others, 1985) and one 

species of waterfowl (northern shoveler, Anas clypeata) in Carson Lake (Hallock, Burge, and Tuttle, 

1993b). 

Concern for human health and environmental 

quality prompted the U.S. Environmental Protection 

Agency to list the Carson River Mercury Site in 1990 

on its National Priority List under the Comprehensive 

Environmental Response, Compensation, and Liability 

Act of 1980. The site includes approximately 100 mi of 

the lower Carson River, including Stillwater NWR 

(U.S. Environmental Protection Agency, 1991, p. 1). 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Birds 

Species of concern 

Species of concern 

Species of concern 

Species of concern 

Candidate species 

Species of concern 

Endangered species 

Threatened species 

Species of concern 

Species of concern 

Reptiles 

Species of concern 

Invertebrates 

Species of concern 

Plants 

Species of concern 

Riparian areas 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Wetlands, uplands, agricultural fields 

Uplands 

Uplands 

Uplands 

Wetlands 

Uplands, agricultural fields 

Wetlands 

Wetlands, uplands, agricultural fields 

Wetlands, riparian areas, uplands, agricultural fields 

Wetlands 

Wetlands, agricultural fields 

Wetlands, riparian areas 

Riparian areas 

Uplands 

Agricultural Drainage 

The NIWQP scientific activities were begun in 

1986 in Lahontan Valley. Findings of the reconnaissance investigation were described by Hoffman and 

others (1990). Rowe and others (1991) presented physical, chemical, and biological data generated by subsequent NIWQP detailed studies during 1987-89. On the 

basis of these data, Lico (1992) interpreted physical 

and geochemical characteristics of the detailed study 

area, Hallock and Hallock (1993) interpreted biological 

aspects, and Hoffman (1994) summarized the detailed 

studies. 

In 1990, the USFWS instituted a monitoring program in Stillwater NWR to assess implications of inorganic contaminants for fish, wildlife, and human health 

PREVIOUS CONTAMINANT STUDIES 7 
118°40' 118° 30' 

I I --r - — 

CARSON (SINK STILLWATER NATIONAL 

WILDLIFE REFUGE 

..<' STILLWATER 

39°40 WILDLIFE 

MANAGEMENT 

AREA 

fir, 

C 

JON GP~p~ Q`. LINE 

0 

,Ei ,e 

,-,,. I, 441 r-- / I J PAIUTE' ', eL DRAIN' 

17 1 

, , KENT 

I DR SAGOUSPE 

2 I 1114 DAM Tc 

cc 

0 Stillwateir, 1 

FALLON U.1 1- I INDIAN 

39 RESERVATION °30' al _ _( 

L_ 

3 MILES 

STILLWATER POINT 3 KILOMETERS 

RESERVOIR - -- 

DIVERSION CANAL 

Base from U.S. Geological Survey digital data,1:100,000, 1970-85 

Albers Equal-Area Conic projection 

Standard parallels 29°30' and 45°30', central meridian -119°00' 

EXPLANATION 

Open water 

Wildlife Management Area and National Wildlife Refuge—Privately 

held lands (mostly the Canvasback Gun Club) shown in dark gray 

Sample site—Number used in report 

Drain water V4 

All Wetland 

Figure 2. Locations of drains entering Stillwater National Wildlife Refuge, other hydrologic features, and sampling sites 

(table 3). Extent of Stillwater National Wildlife Refuge as existing in 1997 (U.S. Fish and Wildlife Service, written commun., 

1997). 

8 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
and to assess changes in inorganic-contaminant concentrations in wetlands replenished by freshwater and 

agricultural drainage water (Tuttle and others, 1996). 

Dissolved solids, as measured by specific conductance, 

and 12 of 19 chemical elements monitored during the 

study exceeded levels of concern in 10 percent or more 

of the water, sediment, and(or) biological samples. Dissolved solids and aluminum, arsenic, boron, mercury, 

and zinc commonly exceeded concentrations associated with adverse biological effects. Chromium, copper, iron, lead, molybdenum, and selenium were found 

at levels of biological concern. Mercury, which 

exceeded recommended levels for human consumption 

in fish and waterfowl, was the only element that 

appeared to pose a direct threat to human health. 

Lico and Pennington (1997) found that concentrations of dissolved solids and trace elements of concern were generally higher in the nonirrigation season 

in the Carson Division of the Newlands Project. However, because drainflows were higher, contaminant 

loads were greater during the irrigation season. The 

largest loads were delivered to Stillwater NWR. 

Arsenic, boron, and molybdenum concentrations in 

drain water commonly exceeded Nevada water-quality 

standards. Five identified areas near the perimeter of 

the Carson Division of the Newlands Project appeared 

to contribute proportionally greater loads of inorganic 

contaminants to drain water than did other areas investigated. 

SAMPLE COLLECTION, MEASUREMENT, 

AND ANALYSIS 

This monitoring effort involved independent 

sample collection, processing, and laboratory analysis 

by the USGS and USFWS. The particular techniques of 

sample collection, measurement, and analysis used by 

the two agencies are described in the next two sections: 

"Drains Entering Wetlands" presents USGS methods, 

and "Wetland Monitoring," USFWS methods. 

Drains and Canals Entering Wetlands 

Sampling Sites 

The overall monitoring program consisted of collecting trace-element data on water, sediment, and biological samples from wetlands and related data on 

water from principal drains that enter the wetlands. 

The data-collection procedures used during the monitoring phase of NIWQP were essentially identical to 

those used during other NIWQP studies, from 1986 to 

the present. A principal drain is defined herein as a 

drain that represents a significant component of total 

flow to a wetlands and(or) was shown by previous 

work to transport high concentrations of potentially 

toxic constituents. Eight drain-water sampling sites 

were selected for their proximity to the wetlands without established backwater. These sites include three 

drains to Stillwater NWR, one irrigation-water delivery 

canal (S Line) that empties into Stillwater NWR, and 

four drains to Carson Lake. For this report, S Line 

Canal may be considered a drain (table 3; figs. 2 and 3). 

Drainflow Measurements 

Drainflow quantity was determined by using the 

procedures described by Rantz and others (1982a). 

Electromechanical instruments to continuously record 

drainflow were installed at Paiute Diversion Drain 

below TJ Drain, Stillwater Point Reservoir Diversion 

Canal and S Line Canal. These instruments were 

checked periodically and recalibrated by onsite current-meter measurements. Computation of time-series 

drainflow measurements for these three sites was performed by using the procedures described by Rantz and 

others (1982b). For the five stations (table 3) without 

Table 3. Measurement sites on agricultural drains 

entering and in wetlands in Stillwater National 

Wildlife Refuge and Carson Lake, Nevada, 1994-96 

Measurement Agricultural drain or wetland site1'2 

Stillwater National Wildlife Refuge' 

1 S Line Canal 

2 Stillwater Slough 

3 Paiute Diversion Drain below TJ Drain 

4 Stillwater Point Reservoir Diversion Canal 

9 Dry Lake 

10 Lead Lake 

11 Stillwater Point Reservoir 

Carson Lake2 

5 Carson Lake Drain 

6 Rice Ditch 

7 L Drain 

8 L 12 Drain 

12 Sprig Pond 

1See figure 2. 

2See figure 3. 

SAMPLE COLLECTION, MEASUREMENT, AND ANALYSIS 9 
118° 45' 

-1.0.11111i•1 

FALLON 

30° 25' 

COQ 

30° 20' 

1 2 MILES 

1 2 KILOMETERS L __ Base from U.S. Geological Survey digital data,1:100,000,1970-85 

Albers Equal-Area Conic projection 

Standard parallels 29°30' and 45°30% central meridian -119'00' 

EXPLANATION 

Open water 

Wetland 

Sampling site—Number used in report 

8 7 Drain water 

12A Wetland 

Figure 3. Surface-water and bottom-sediment sampling sites (table 3) in and near Carson Lake. 

Diagonal Drain is informal local name that includes Lower Diagonal and Upper Diagonal Drains. 

Carson Lake Drain is also known locally as Cabin Drain. 

10 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
continuously recording apparatus, drainflow was measured by using a current meter at the time of visit, usually monthly. Additional current-meter measurements 

of instantaneous drainflow to Carson Lake were made 

by the Bureau of Reclamation as part of another program. (Any onsite field measurements made by a 

hydrographer are called instantaneous herein). 

Water-Quality Measurements, Water-Sample 

Collection, and Laboratory Analyses 

Onsite determinations of specific conductance, 

temperature, barometric pressure, dissolved oxygen, 

pH, carbonate, bicarbonate, and total alkalinity, were 

measured according to the methods described by Wilde 

and Radtke (1998). Instruments for continuously 

recording specific conductance, a surrogate measure of 

dissolved-solids concentration, were used at the four 

drains entering Stillwater NWR and two drains entering Carson Lake (Carson Lake Drain and Rice Ditch). 

The instruments were maintained according to procedures described by Gordon and Katzenbach (1983). As 

with the drainflow monitors, these instruments were 

checked periodically and recalibrated onsite. Waterquality samples from the drains were collected and processed by the procedures described by Ward and Harr 

(1990) and Horowitz and others (1994). Arsenic, 

boron, lithium, and molybdenum were determined in 

water samples from all sites. The samples were filtered 

through a 0.45-micrometer-pore-size prerinsed filter 

(operationally defined as "dissolved") and then acidified to pH2 by adding concentrated nitric acid. Water 

samples for mercury determinations were collected at 

two sites, Stillwater Point Reservoir Diversion Canal 

and Stillwater Slough. Chemical analysis for mercury 

was done on whole-water samples that had been collected in acid-rinsed glass bottles and acidified immediately after collection by adding concentrated 

potassium dichromate/nitric acid. All drain-water samples were sent to the USGS National Water Quality 

Laboratory in Denver, Colo., for chemical analyses 

using the procedures described by Fishman and Friedman (1989) and Fishman (1993). 

Statistical Analyses 

Statistical data analysis generally was based on 

procedures described by Helsel and Hirsch (1992). 

Techniques to estimate missing specific conductance 

and boron concentrations included direct substitution, 

linear interpolation, and regression analysis, or a combination of the three depending on the length of missing record and other data. With the exception of L 12 

Drain (table 3), measurements of specific conductance 

and dissolved-solids concentration were plotted for all 

sites to establish regression equations for each site. 

Because of the lack of measured dissolved-solids data 

for L 12 Drain during 1994, specific-conductance values were multiplied by a coefficient of 0.61, the mean 

of dissolved-solids coefficients (table 4), to obtain an 

equivalent dissolved-solids concentration for that year 

(Hem, 1985, p. 66-69). As with dissolved-solids concentration, a regression equation was developed for 

specific conductance and boron for each site, including 

L 12 Drain. Specific conductance was plotted as the 

independent variable, and dissolved-solids or boron 

concentration as the dependent variable. For each of 

the linear regressions, an equation was developed to 

estimate a dissolved-solids or boron concentration for a 

given specific-conductance measurement. The regression equations (table 4) were then used to compute the 

monthly mean dissolved-solids or boron concentrations from the monthly mean specific-conductance values, which were determined from the continuous 

specific-conductance record. Residuals from each 

regression were plotted versus the predicted values. 

Because neither curvature nor changing variance was 

observed, the simple-regression models appear to 

be good representations (Helsel and Hirsch, 1992, 

p. 221-263). Daily loads of dissolved solids and boron 

for Stillwater Slough and the four drains entering Carson Lake are the mathematical product of instantaneous flow, and instantaneous concentration. Load data 

were divided between the 5-month nonirrigation season and the 7-month irrigation season. Because the two 

seasons are unequal in length, daily loads also were 

calculated. 

Seasonal load determinations for arsenic, lithium, 

and molybdenum were not attempted because of the 

known poor relation between concentrations of these 

trace elements and concentrations of dissolved solids in 

the study area (Lico and Pennington, 1997, p. 19-21). 

Quality Control 

Quality control of drainflow measurements consisted of current-meter spin tests, independent checks 

of arithmetic computations, and complete analysis of 

the station records for the measurement period. Quality 

control of drain-water samples in the field consisted of 

SAMPLE COLLECTION, MEASUREMENT, AND ANALYSIS 11 
	 	

Table 4. Linear-regression equations of dissolved-solids and boron concentrations in relation to specific conductance for 

drains entering Stillwater National Wildlife Refuge and Carson Lake, Nevada, 1986-96 

[S, specific conductance per centimeter at 25 degrees Celsius. -, not calculated] 

Coefficient of Coefficient of Dissolved solids Number of Dissolved boron Number of Agricultural drain determination , determination, (milligrams per liter) samples (micrograms per liter) r2 samples r2 

Stillwater National Wildlife Refuge 

S Line Canal (0.579 S) + 15.1 99.7 

Stillwater Slough (0.618 S) - 39.9 99.6 

Paiute Diversion Drain below Ti Drain (0.687 S) - 295 99.3 

Stillwater Point Reservoir Diversion Canal (0.624 S) - 35.1 99.6 

Carson Lake 

Carson Lake Drain (0.611 S) - 4.9 99.0 

Rice Ditch (0.598 S) + 8.6 99.1 

L Drain (0.569 S) + 33 99.3 

(1 ) L 12 Drain 

1See section titled "Drains Entering Wetlands of Carson Lake" in text. 

equipment blanks, field blanks, and replicate samples 

(Horowitz and others, 1994). For statistical summaries, 

only one value from replicate samples was used to preclude biasing the data set. The results of the qualitycontrol samples, published by the USGS in the annual 

water-data reports for water years 1994-96 (Clary and 

others, 1995; Bauer and others, 1996; Bostic and others, 1997), indicate that inadvertent contamination of 

the environmental samples either did not occur or was 

inconsequential considering the elevated ambient concentrations found in the study area. The published 

results also indicate that the replicate data show acceptable precision; the respective constituent concentrations were for the most part nearly identical. Qualitycontrol practices of the USGS National Water Quality 

Laboratory were described by Pritt and Raese (1995). 

Wetlands 

Sampling Sites and Sampled Media 

Sampling sites included Dry Lake (no. 9), Lead 

Lake (no. 10), and Stillwater Point Reservoir (no. 11) 

in Stillwater NWR and the Sprig Pond unit (no. 12) in 

Carson Lake (figs. 2 and 3). Data were collected from 

May through July each year. Within each study wetland, water-quality measurements and samples of sediment, detritus, vegetation, and invertebrates were 

collected for trace-element residue analysis from five 

randomly selected locations within a permanent study 

10 (1.10 - 100 94.8 11 

22 (1.00 S)+ 97 99.4 21 

18 (0.868 S) - 360 98.4 17 

20 (1.04 S)+ 6.2 99.5 16 

22 (1.69 S) - 537 96.7 21 

17 (1.20 S) - 168 97.8 17 

19 (1.10 S) - 103 98.8 19 

(1.08 S) - 123 93.8 13 

plot that measured 327 by 327 ft. Water samples were 

collected at three of these locations. Fish and bird 

samples were collected as near as possible to the study 

plot. Numbers of each sampled media collected during 

each year of the monitoring program are listed in 

table 5. 

Water-Quality Measurements, Sample Collection, 

and Laboratory Analyses 

Wetland water-quality measurements of specific 

conductance, pH, temperature, and dissolved oxygen 

were made onsite by using standard meters, probes, 

and electrodes. Temperature was measured by using a 

hand-held thermometer. Whole (unfiltered) water was 

hand dipped in the middle of the water column using 

250-ml plastic bottles and acidified to pH<2.0. Sediment and detritus were collected by using a 2-in-diameter coring device and then placed in a precleaned 500-

ml plastic container. Sediment samples included the 

top 2 in. of the core, whereas detritus samples included 

only the top 0.75 in. Each sediment and detritus sample 

consisted of a composite of five subsamples that were 

thoroughly mixed by using a stainless-steel knife. 

Pondweed (Potamogeton spp.) samples were collected 

by hand. Hemiptera samples were collected by using a 

kick net, placed in precleaned 500-ml plastic containers, and later sorted from unwanted debris in the laboratory. Fish were collected by using unbaited minnow 

traps and hoop nets. The fish were put in plastic bags 

and later processed. American coot (Fulica americana) 

12 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
		

		

			 			

	 	 		

			 		

			 		

				

		

		 		

		 				

			 		

			 			

Table 5. Number of samples of water, sediment, detritus, and biota collected for trace-element concentrations in four 

wetlands in Lahontan Valley, Nevada, 1994-96 

[—, no sample collected] 

Number of Samples 

Wetland Year Bottom Coot Avocet Coot Avocet Water Detritus Pondweed Hemiptera Fish sediment egg egg liver liver 

Stillwater National Wildlife Refuge 

Dry Lake: 

1994 3 5 5 4 2 5 3 

1995 3 5 5 5 4 4 5 5 

1996 3 5 5 5 5 5 6 5 5 2 

Lead Lake: 

1994 3 5 5 5 5 2 5 

1995 3 5 5 5 2 1 5 5 

1996 3 5 5 5 5 5 7 3 5 3 

Stillwater Point Reservoir: 

1994 3 5 5 2 5 5 5 5 5 

1995 3 5 5 5 1 5 5 5 

1996 3 5 5 5 1 5 3 1 5 

Carson Lake 

Sprig Pond: 

1994 3 5 5 5 2 5 5 5 5 

1995 3 5 5 5 2 5 5 5 5 4 

1996 3 5 5 5 4 5 8 5 5 

and american avocet (Recurvirostra americana) eggs copper, iron, lead, magnesium, manganese, molybdewere collected by hand and placed in a carton, stored num, nickel, strontium, vanadium, and zinc were deteron ice in the field, and later opened by using precleaned mined by inductively coupled plasma-emission 

stainless-steel instruments in the laboratory. Embryos spectroscopy. 

were inspected for gross abnormalities. Juvenile coots 

and avocets were collected by using a shotgun and steel Quality Control 

shot and were placed in plastic bags. Livers from the Interlaboratory quality-control techniques birds were removed later in the laboratory. Preflighted included the use of procedural blanks, duplicate sam- juveniles were collected to study exposure to, and ples, spiked samples, and reference materials. Quality accumulation of, trace elements that occur in the study control and laboratory performance at the Environmen- wetlands. All samples were stored on ice in the field. tal Trace Substances Research Center were assessed Sediment, detritus, and biological samples were placed and approved by the U.S. Fish and Wildlife Service in precleaned glass jars with Teflon-lined closures in (1990, p. 6.6); laboratory performance was within the the field or laboratory and subsequently were frozen. prescribed precision range. All chemical analyses were done by the Environmental Trace Substances Research Center, Columbia, Toxicity Tests Mo., by methods described by U.S. Fish and Wildlife 

Service (1990, p. 3.9). Arsenic and selenium concen- During 1994-96, Microtox toxicity testing was 

trations were determined by hydride-generation used to assess toxicity of all water samples. Microtox 

atomic-absorption spectroscopy. Mercury concentra- testing provides a rapid assessment (5- and 15-minute 

tions were determined by cold-vapor atomic-absorp- procedures) of the relative toxicity of water samples 

tion spectroscopy. Concentrations of aluminum, by using a strain of photoluminescent marine bacteria, 

barium, beryllium, boron, cadmium, chromium, Photobacterium phosphoreum, as a test organism. 

SAMPLE COLLECTION, MEASUREMENT, AND ANALYSIS 13 
The Microtox instrument measures bacterial luminosity, which is assumed to be a measure of metabolic 

activity. A decrease in luminosity after exposure of the 

bacteria to a water sample is interpreted as a depression 

in metabolic activity and therefore provides an indicator of toxic response. Toxicity is expressed as the 

median concentration eliciting a 50-percent reduction 

in light output (EC50); an EC50of 100 percent or 

greater indicates that no effect on metabolic activity 

(and hence no toxicity) was observed in an undiluted 

sample. Procedures for Microtox assessment of water 

samples were described by Henry and Hickey (1991, p. 

7). Wetland water samples used for Microtox testing 

were collected at the same time and locations as wetland water collected for trace-element analysis. 

Remote Sensing of Wetland Habitats 

Aerial photographs (1:12,000 scale), taken in 

August 1994, August 1995, and September 1996, were 

used to quantify wetland plant habitats and open water 

in Stillwater Marsh, including Canvasback Gun Club 

lands (fig. 2), and Carson Lake. The plants in wetland 

habitats include emergent vegetation, such as cattails 

(Typha spp.) and bulrush (Scirpus spp.), and wetmeadow vegetation, such as rushes (Juncus spp.) and 

saltgrass (Distichlis spp.). Color aerial photographs 

taken in 1994 provide poor definition of habitat types; 

infrared photographs taken in subsequent years better 

define the areas. Areal extent of wetland plant habitats 

and open water were determined by using a commercial computer software program to digitize both the 

natural color and infrared aerial photographs. 

Aquatic Invertebrate Community 

Benthic and nektonic invertebrates were collected at locations where the samples of sediment for 

chemical analysis were collected. Benthic invertebrates were collected by using a coring sampler. Each 

sample consisted of a composite of 10 sediment samples collected at a depth of 2 in. Samples were sieved 

through an 800-μm nylon mesh. Nektonic invertebrates were collected by using a kick net, which had an 

opening measuring 8 by 18 in. and an 800-μm mesh 

size. Nektonic invertebrates were collected by towing 

the kick net along ten 3-ft transects in the middle of the 

water column. Benthic and nektonic samples were 

stored in 500-m1 plastic containers on ice in the field 

and transported to the laboratory, where they subsequently were frozen. The samples later were thawed for 

processing. Invertebrates were removed from debris, 

placed in 70-percent ethyl alcohol, and tentatively 

identified to family level. Taxonomic classification initially was based on Pennak (1989) and later was modified to conform to the federal standard data base, the 

Interagency Taxonomic Information System (accessible via URL <http://www.itis.usda.gov>). Taxa richness, heterogeneity, and evenness were calculated by 

methods described by Newman (1995, p. 293-300). 

Fish-Community Structure and Condition 

Passive fish-capture techniques (trapping) were 

used to collect fish because the electroshocking was 

ineffective in highly conductive water and the seining 

was hampered by the high densities of emergent and 

submergent vegetation. In all three years,,42-by-22-cm 

oval minnow traps with 3-cm openings were used. In 

each wetland each year, at least 15 traps were set to collect fish for a minimum of 24 hours. In 1996, 1-cmmesh hoop nets also were used in each wetland; they 

were set for a minimum of 50 hours and checked at 

24-hour intervals. Because of inconsistent methodologies, fish-capture data from 1994 were not included in 

the data analysis. 

All captured fish were identified to species and 

counted. As many as 50 fish from each wetland were 

measured and weighed and examined for gross external 

aberrations. Fulton's condition factor was used to provide a relative measure of well-being of a selected size 

group of representative fish from each wetland (Anderson and Gutreuter, 1983, p. 294-295). 

Modified Index of Biological Integrity (IBI) 

methodologies were used to assess the condition of the 

fish community in study wetlands. IBI methodologies 

were developed to provide a reproducible method for 

assessing conditions of stream fish (Miller and others, 

1988; Plafkin and others, 1989). Because of obvious 

differences between stream and wetland fish communities, the use of IBI methodologies herein is intended 

solely for comparisons of fish-community condition 

among the four study wetlands and to provide a baseline for future comparisons. To calculate IBI scores, 

nine measures (metrics) related to fish-species composition, trophic status, and fish abundance and condition were adapted from Miller and others (1988, p. 

14-15) and Plafkin and others (1989, p. 7.12-7.20): 

(1) number of native fish species, (2) number of benthic fish species, (3) proportion of tolerant individuals, 

14 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
(4) proportion of omnivores, (5) proportion of insectivores, (6) proportion of top carnivores, (7) total fish 

abundance, (8) proportion of introduced fishes, and (9) 

proportion of fish with anomalies. Scoring ranges for 

the metrics generally are according to Plafkin and others (1989, p. 7.8). Scoring of the metric for analysis of 

total fish abundance was adapted from 1BI methodologies developed for northern California (Miller and others, 1988, p. 15). Tolerance and trophic status of 

introduced fishes were obtained from Plafkin and others (1989, app. D). Tui chub was classified as tolerant 

of poor-quality water and omnivorous (Sigler and 

Sigler, 1987, p. 168). Because of capture methods used 

by USFWS biologists during 1994-96, fin erosion was 

not considered an anomaly. 

Surveys of Bird Use of Wetlands 

Data on bird use of wetlands were collected using 

point-control methodology (Bibby and others, 1992) 

along one 3,300-ft permanent transect established in 

each of the four wetlands. Each transect consisted of 

five points spaced linearly at 660-ft intervals. Surveys 

were initiated within 30 minutes after sunrise; 10 minutes was allocated for observation at each point. The 

transects were sampled monthly on or near the 15th of 

the month; only one transect was sampled during any 

sampling day. Sample sessions were July-September 

1995 and May-September 1996. All bird species either 

seen or heard at each point were documented for year, 

wetland, month, and transect point. 

Statistical Analyses 

Trace-element concentrations for all sampled 

media were transformed to common logarithms to 

improve homogeneity of variance, and geometric 

means were calculated when a trace element was 

detected in at least 50 percent of the samples within 

a given wetland and year. A value equal to one-half the 

analytical reporting limit was assigned to samples 

for which a specific trace element was less than the 

analytical reporting limit. 

Two-way analysis of variance (ANOVA) and 

Tukey's multiple-comparison tests were used to examine relations among wetlands and years of sampling for 

trace-element concentrations in unfiltered water, sediment, detritus (1995-96 only), vegetation, and coot 

eggs and livers. If the interaction terms were statistically significant, one-way ANOVA was performed to 

assess among-year differences within each wetland. 

Because of limited sample numbers in some wetlands 

and years, two-way ANOVA was not attempted for 

hemipterans, fish, and avocet eggs and livers. However, one-way ANOVA was used to assess among-wetlands differences and among-year differences within 

each wetland. Statistical tests were only performed for 

media and for years for which three or more samples 

were available. Two-way ANOVA and Tukey's multiple-comparison test also were used to examine relations among wetlands for invertebrate communities. 

Again, if interaction terms were significant, one-way 

ANOVA was performed for wetlands and for years. 

Pearson's chi-square test (correlation coefficient) 

was used to examine relations between trace-element 

concentrations in unfiltered water, sediment, detritus, 

and aquatic vegetation and invertebrates. Because fish 

and bird species were not relegated to specific sampling points within each wetland, arithmetic means 

were used to examine relations among residue concentrations in these and other media. 

RESULTS AND DISCUSSION OF 

MONITORING PROGRAM 

The primary purpose of monitoring selected wetlands and agricultural drains entering the wetlands in 

Lahontan Valley during 1994-96 was to establish an 

adequate baseline to enable assessment of future trends 

in water quantity, water and habitat quality, and traceelement contamination. The abundant baseline information on water quantity and quality, trace-element 

concentrations in abiotic and biotic wetland components, toxicity of water, and abundance and distribution 

of wetland vegetation, invertebrate, fish, and bird life 

generated during the Lahontan Valley wetland monitoring provides insight to the current status of the 

valley's wetland system. 

Water Supply 

The principal water supply for irrigation in the 

Newlands Project area in Lahontan Valley is Lahontan 

Reservoir. Constructed in 1915 and filled in 1916, the 

reservoir has a maximum storage capacity of about 

317,000 acre-ft with flashboards and an operational 

capacity of about 295,000 acre-ft without flashboards 

(Carol Grenier, Bureau of Reclamation, 1998, written 

RESULTS AND DISCUSSION OF MONITORING PROGRAM 15 
commun.). Historically, the irrigation season in the 

area has been from March 15 through November 15. 

However, most releases from the reservoir—about 88 

percent of total annual flow—have been from April 1 

through October 31. For this report, the irrigation season is defined as the 7-month period from April 

through October. 

A comparison of period-of-record monthly mean 

streamflow (1966-96) with calendar year 1994, 1995, 

and 1996 irrigation season is listed in table 6. These 

data show that releases from the reservoir during the 

1994-96 irrigation seasons ranged from about 60 to 

130 percent of the long-term average, thus representing 

a fairly wide range of flow conditions within which to 

interpret the environmental data collected during the 

3-year monitoring program, during which the greatest 

irrigation-season flow was in 1995. During the 1994, 

1995, and 1996 water years (October through September), total flow from the reservoir was about 230,000, 

410,000, and 450,000 acre-ft, respectively, compared 

to the long-term (1967-96) average of about 370,000 

acre-ft/yr. For the period 1975-87, on average, about 

46 percent (range, 23 to 59 percent) of the water 

released annually from Lahontan Reservoir actually 

reached farm headgates owing to operational spills and 

conveyance loss (Maurer and others, 1994, p. 20). During the nonspill years 1988-92, after implementation 

of the 1988 Bureau of Reclamation Operating Criteria 

and Procedures, about 59 percent of released water 

reached farm headgates (Carol Grenier, Bureau of Reclamation, written commun., 1998). Of the water available for irrigation, about 35 percent reaching the 

headgates subsequently is discharged to downstream 

wetlands as irrigation return flow. 

Table 6. Streamflows released from Lahontan Reservoir 

[Streamflows were measured at U.S. Geological Survey gaging station about 1.1 mile 

downstream from Lahontan Dam, west of Fallon, Nev.] 

Monthly mean streamflow Irrigation season' 

(April—October) (cubic feet per second) (acre-feet) 

1966-1996 770 47,000 

1994 470 28,000 

1995 1,000 60,000 

1996 860 52,000 

'Historically, irrigation season in Lahontan Valley is March 15—November 15, but 

majority of releases from Lahontan Reservoir—about 88 percent of total annual flow— 

are during April 1-October 31. Irrigation season is defined herein as 7-month period 

April—October. 

Drains Entering Wetlands of Stillwater 

National Wildlife Refuge 

Of the principal drains to Stillwater NWR, the 

ones that were monitored are S Line Canal, Stillwater 

Slough, Paiute Diversion Drain (called Paiute Drain by 

the USGS (Clary and others, 1995; Bauer and others, 

1996; Bostic and others, 1997), and Stillwater Point 

Reservoir Diversion Canal (fig. 2). For all sites, the 

maximum constituent concentrations almost always 

were in water samples collected prior to irrigation in 

the spring. None of these sites exactly match those 

reported by Rollins (1965), thus meaningful comparisons of historic dissolved-solids concentrations (1959-

62) to those presented herein cannot be made. With the 

exception of mercury, statistical summaries of measurements made during each site visit are listed in table 

7. (For discussion of mercury, see section "Concentrations and Loads of Total Mercury.") 

S Line Canal 

This site is along Hunter Road about 2 mi northeast of the community of Stillwater, Nev. (fig. 2), and 

was instrumented with continuous-flow and specificconductance recorders. The USFWS used the site to 

study the effects of the influx of irrigation water (500 

mg/L dissolved solids) on the ecology of Dry Lake during its inundation. Water-quality data from the S Line 

site also can be used as a reference with which to make 

comparisons with drain-water quality in the study area. 

Although annual median flows in S Line were virtually 

identical for the 3 years, a substantial decrease in concentration of dissolved solids and trace elements was 

recorded in 1995 and 1996 compared to 1994 (table 7). 

The higher concentrations in 1994 probably reflect the 

combined effects of evaporative concentration in 

Lahontan Reservoir (source water for irrigation in the 

Fallon area), which received little natural runoff during 

the 1993-94 water years, and reduced inflow to the reservoir, hence less streamflow available for dilution. 

For example, the median dissolved-solids concentration of 240 mg/L measured in the Carson River just 

downstream from Lahontan Dam for the sampling 

period March—October 1994 was about 74 percent 

greater than the concentrations for the same time 

period in 1995 and 1996, with medians of 137 mg/L 

and 138 mg/L, respectively. None of the recorded 

water-quality data for S Line exceeded existing 

beneficial-use criteria. 

16 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
		

			

		

		

		

			

		

		

		

		

		

		

		

		

		

			

		

		

		

				

		

		

		

	 		

		

		

				

				

			

		

			

		

			

		

			

		

		

		

		

Table 7. Statistical summary of instantaneous drainflow and concentrations of dissolved solids and dissolved trace 

elements at seven drain sites where water enters wetlands of Stillwater National Wildlife Refuge and of Carson 

Lake, March-October, 1994-96 

[n, number of measurements. —, no criterion or otherwise not applicable] 

Agricultural Calendar Summary 

drain year statistics 

Drainflow 

(cubic feet 

per second) 

Dissolved solids1 

(milligrams 

per liter) 

Arsenic2 

(micrograms 

per liter) 

Boron3 

(micrograms 

per liter) 

Lithium 

(micrograms 

per liter) 

Molybdenum4 

(micrograms 

per liter) 

Stillwater National Wildlife Refuge 

S Line Canal: 

1994 Median 23 292 24 425 39 8.5 

Range 0.63-29 261-400 19-29 370-600 29-46 7-14 

Exceedances5 — (n=6) 0 (n=6) 0 (n=6) 0 (n=6) — (n=6) 0 (n=6) 

1995 Median 22 174 12 180 20 6 

Range 6.6-32 168-238 10-15 170-330 20-40 6-6 

Exceedances5 — (n=6) 0 (n=6) 0 (n=5) 0 (n=5) — (n=5) 0 (n=5) 

1996 Median 22 183 12 172 16 6 

Range 0.08-29 156-216 8-17 160-223 10-20 4.8-7.2 

Exceedances5 — (n=6) 0 (n=6) 0 (n=8) 0 (n=8) — (n=8) 0 (n=8) 

Stillwater Slough: 

1994 Median 3.2 1,180 42 2,250 145 8.5 

Range 1.9-12 680-1,740 38-48 1,200-3,100 85-220 10-29 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 8 (n=8) — (n=8) 7 (n=8) 

1995 Median 12 872 35 1,500 100 18 

Range 14-16 658-5,520 30-53 1,100-8,000 80-270 16-58 

Exceedances5 — (n=9) 2 (n=9) 0 (n=9) 9 (n=9) — (n=9) 4 (n=9) 

1996 Median 15 746 31 1,120 76 16 

Range 11-22 594-1,140 28-47 910-1,710 60-97 14-23 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 8 (n=8) — (n=8) 3 (n=8) 

Paiute Diversion Drain below TJ Drain: 

1994 Median 0.32 6,190 170 9,300 320 320 

Range 

Exceedances5 

0.07-3.8 

— (n=7) 

970-10,900 

5 (n=7) 

36-210 

6 (n=7) 1,300-14,000 

7 (n=7) 

77-510 

— (n=7) 

34-900 

7 (n=7) 

1995 Median 7.7 1,320 29 1,500 100 41 

Range 

Exceedances5 

0.12-16 

— (n=7) 

818-13,700 

2 (n=7) 

22-180 

6 (n=7) 1,000-17,000 

7 (n=7) 

70-510 

— (n=7) 

21-540 

7 (n=7) 

1996 Median 18 1,010 23 1,080 55 33 

Range 1.7-77 404-9,650 10-130 440-11,000 30-380 15-280 

Exceedances5 — (n=8) 2 (n=8) 0 (n=8) 5 (n=8) — (n=8) 7 (n=8) 

Stillwater Point Reservoir Diversion Canal: 

1994 Median 13 633 64 1,450 58 31 

Range 1.7-32 476-1,950 43-130 840-3,300 49-80 24-69 

Exceedances5 — (n=12) 0 (n=12) 0 (n=12) 8 (n=8) — (n=8) 11 (n=11) 

1995 Median 35 378 34 790 40 23 

Range 0.5-133 262-5,990 15-300 380-9,900 30-120 9-130 

Exceedances5 — (n=8) 2 (n=8) —6(n=8) 4 (n=8) — (n=8) 5 (n=8) 

1996 Median 38 494 40 740 38 20 

Range 

Exceedances5 

13-157 

— (n=8) 

164-1,240 

0 (n=8) 

11-71 

0 (n=8) 

190-2,000 

4 (n=8) 

20-60 

— (n=8) 

5-47 

4 (n=8) 

RESULTS AND DISCUSSION OF MONITORING PROGRAM 17 
Table 7. Statistical summary of instantaneous drainflow and concentrations of dissolved solids and dissolved trace 

elements at seven drain sites where water enters wetlands of Stillwater National Wildlife Refuge and of Carson 

Lake, March-October, 1994-96—Continued 

Drainflow Dissolved solids1 Arsenic2 Boron3 Lithium Molybdenum4 Agricultural Calendar Summary (cubic feet (milligrams (micrograms (micrograms (micrograms (micrograms drain year statistics per second) per liter) per liter) per liter) per liter) per liter) 

Carson Lake 

Carson Lake Drain: 

1994 Median 9.0 705 58 1,550 52 30 

Range 0.72-25 456-2,560 43-200 710-7,000 44-100 21-170 

Exceedances5 — (n=8) 0 (n=8) —6(n=8) 7 (n=8) — (n=8) 7 (n=7) 

1995 Median 14 519 41 970 50 25 

Range 2.1-26 430-892 33-120 700-1,800 40-70 15-46 

Exceedances5 — (n=8) 0 (n=8) 0 (n=7) 4 (n=8) — (n=7) 6 (n=7) 

1996 Median 18 678 56 1,240 53 29 

Range 6-35 488-860 33-92 820-1,800 39-60 20-44 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 8 (n=8) — (n=8) 8 (n=8) 

Rice Ditch: 

1994 Median 0.62 478 36 730 54 14 

Range 0.06-9.1 299-654 21-55 420-1,100 38-66 8-22 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 5 (n=8) — (n=8) 3 (n=8) 

1995 Median 5 277 19 390 40 9 

Range 0.14-35 242-702 17-92 290-1,130 30-70 9-37 

Exceedances5 — (n=7) 0 (n=7) 0 (n=7) 2 (n=7) — (n=7) 2 (n=7) 

1996 Median 1.3 284 20 409 25 11 

Range 0.02-14 190-400 12-30 190-660 20-40 7.1-23 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 0 (n=8) — (n=8) 1 (n=8) 

L Drain: 

1994 Median 5.6 503 44 800 53 • 18 

Range 2.1-22 348-671 27-78 470-1,100 42-66 10-25 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 4 (n=8) — (n=8) 4 (n=8) 

1995 Median 33 356 24 360 35 9 

Range 9.8-105 220-486 7-70 120-790 12-60 4-19 

Exceedances5 — (n=7) 0 (n=8) 0 (n=8) 1 (n=8) — (n=8) 1 (n=8) 

1996 Median 28 314 26 437 28 14 

Range 15-61 186-466 12-34 210-712 13-40 6.6-17 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 0 (n=8) — (n=8) 0 (n=8) 

L 12 Drain: 

71995 Median 9 181 11 345 26 6 

Range 4-29 124-315 7-31 120-490 12-40 4-13 

Exceedances5 — (n=7) 0 (n=7) 0 (n=6) 0 (n=6) — (n=6) 0 (n=6) 

1996 Median 8.6 194 14 206 19 6.6 

Range 1.2-18 139-372 9-26 113-520 13-32 4.3-11 

Exceedances5 — (n=8) 0 (n=8) 0 (n=8) 0 (n=8) — (n=8) 0 (n=8) 

1Beneficial-use criteria for dissolved solids: Nevada standard for watering of livestock is 3,000 milligrams per liter (State of Nevada, 1997, art. 445A.119). 

Effect criterion for ducklings when no source of fresh water is available is 5,000 milligrams per liter (Mitcham and Wobeser, 1988, p. 45). 

2Beneficial-use criterion for arsenic: Nevada chronic (96-hour) aquatic-life standard as As+3is 180 micrograms per liter (State of Nevada, 1997, art. 

445A.144). 

3Beneficial-use criteria for boron: Nevada standard for watering of livestock is 5,000 micrograms per liter (State of Nevada, 1997, art. 445A.144). Nevada 

standard for irrigating sensitive crops is 750 micrograms per liter (State of Nevada, 1997, art. 445A.144). 

4Beneficial-use criterion for molybdenum: Nevada aquatic-life standard is 19 micrograms per liter (State of Nevada, 1997, art. 445A.144). 

5Number of exceedances (out of n measurements) of most stringent, respective beneficial-use criterion. 

6Arsenic speciation was not done as part of monitoring program for this site and year. 

7Site not established until 1995. 

18 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Stillwater Slough 

This site is located where the slough flows 

beneath Stillwater Road, about 5 mi upstream from its 

discharge to the historic wetlands of the Canvasback 

Gun Club, a privately owned facility virtually surrounded by Stillwater NWR. This site was not considered optimal, but access to the foriner USGS gaging 

station (Stillwater Slough Cutoff), about 3 mi downstream, was denied by private landowners for much 

of the 1994-96 monitoring period. Although the alternate site was instrumented with a continuous specificconductance recorder, it probably greatly underestimates the flow, hence the load of dissolved constituents, to receiving wetlands during the irrigation season. 

After access to the former gaging station eventually 

was allowed, hydrologic data collected at the two sites 

could be compared: For example, on August 13, 1996, 

instantaneous flow increased downstream from 15 to 

32 ft3/s, dissolved-solids concentration from 594 to 

662 mg/L, and overall instantaneous dissolved-solids 

load from 24 to 57 ton/d. These increases probably 

were the result of a number of drain inputs between the 

two sites, Kent Drain in particular. As drainflow 

increased throughout the monitoring program, measured water-quality data showed corresponding 

decreases in concentration. During the 3-year monitoring period, the highest concentrations were recorded in 

1995 (table 7). Beneficial-use criteria for boron and 

molybdenum were exceeded in individual samples for 

most of the recorded observations during 1994-96. The 

number of individual exceedences for molybdenum, 

however, decreased each successive year. The median 

molybdenum concentrations in 1995 and 1996 were 

less than the 19 gg/L beneficial-use criterion. 

Paiute Diversion Drain Below TJ Drain 

The Paiute Diversion Drain site is about 1,000 ft 

and 3,000 ft downstream from the respective confluences of TJ Drain and D Line Canal.3The combined 

flow enters Lead Lake. During 1994-96, the site was 

instrumented with continuous-flow and specific-con3D Line Canal is defined herein as the distributary system 

originating at Sagouspe Dam diversion on the lower Carson River, 

interconnecting the several water bodies that comprise the Indian 

Lakes and terminating at the confluence of Paiute Diversion Drain 

near the northwest boundary of Stillwater NWR (figs. 1 and 2). 

ductance recorders. In 1994, the annual flow was 

entirely from TJ Drain, whereas in 1995 and 1996, 

water from this site may have included water from all 

three drains (table 7). With increased flow from Paiute 

Diversion Drain and(or) D Line Canal in succeeding 

years, the chemical quality of the water showed a 

decided improvement in terms of reduced concentrations. Maximum concentrations, however, remained 

relatively high in 1995 and 1996 and commonly corresponded with water samples collected immediately 

before the irrigation season. Of the constituents measured, boron and molybdenum concentrations 

remained elevated during the 3 years of monitoring; 

most samples exceeded beneficial-use criteria. Of the 

sites monitored in Stillwater NWR, Paiute Diversion 

Drain typically represented the poorest quality in terms 

of maximum concentrations of dissolved solids and 

trace elements. 

Stillwater Point Reservoir Diversion Canal 

This site, known locally as Diagonal Drain, is 

about 1 mi upstream from Stillwater Point Reservoir, 

a principal water-storage facility for Stillwater NWR. 

During 1994-96, the site was instrumented with both 

continuous-flow and specific-conductance recorders. 

This site receives an unquantified mixture of treated 

municipal sewage, shallow ground-water seepage, irrigation return flow and, at times, irrigation water. 

Median instantaneous drainflow increased during each 

successive year; the largest increase, nearly 200 percent, was from 1994 to 1995 (table 7). Dissolved-solids 

concentration was relatively low (less than 650 mg/L) 

during all years. Of the four trace elements shown in 

table 7, boron and molybdenum exceeded beneficialuse criteria in a large percentage of water samples, 

whereas arsenic and lithium did not. 

Drains Entering Wetlands of Carson Lake 

Of the principal drains to Carson Lake, the ones 

that were monitored are Carson Lake Drain, Rice 

Ditch, L Drain, and L 12 Drain (fig. 3). 

L 12 Drain was included in the program in 1995 

when Holmes Drain was discontinued because of backwater conditions that made the data unreliable. Carson 

Lake Drain and Rice Ditch were instrumented only 

with continuous specific-conductance recorders. 

RESULTS AND DISCUSSION OF MONITORING PROGRAM 19 
Carson Lake Drain 

This drain, also known locally as Cabin Drain, 

flows into the Sprig Pond unit of Carson Lake. Drainflow was measured periodically by field personnel of 

the Bureau of Reclamation and the USGS by using current meters. Median instantaneous drainflow increased 

56 percent from 1994 to 1995 and 29 percent from 

1995 to 1996 (table 7). Dissolved-solids concentrations 

decreased 26 percent from 1994 to 1995 yet increased 

30 percent from 1995 to 1996. In spite of the overall 

increase in median flow during 1994-96, the median 

concentrations of dissolved solids and selected trace 

elements did not show a concomitant decrease; in 

1996, they were nearly the same as those in 1994. A 

review of the 1994-96 continuous specific-conductance data indicates that the recorded daily concentrations of dissolved solids were highest (maximum about 

2,400 mg/L) in February and March 1994, just prior to 

the irrigation season. An in-depth comparison of the 

continuous dissolved-solids data with the data shown 

in table 7 for the same time period reveals a discrepancy between the two records. The continuous-record 

data show a successive decline in average daily values 

from year to year as might be expected considering the 

apparent increase of drainflow evident in the periodic 

measurements. For example, median dissolved-solids 

concentrations for the continuous record were about 

800 mg/L in 1994, 500 in 1995, and 300 in 1996. The 

continuous record probably is the more accurate of the 

two records. Infrequent measurements of dynamic 

environmental systems increase uncertainty or analytical error. Of the water-quality constituents measured, 

boron and molybdenum consistently exceeded the 

more restrictive beneficial-use criteria (table 7) for 

each during each of the 3 years of monitoring. 

Rice Ditch 

Rice Ditch, also known locally as Rice Drain, 

feeds mainly the north-central wetland units of Carson 

Lake and was instrumented with only a continuous specific-conductance recorder. Drainflow was measured 

periodically by the Bureau of Reclamation and the 

USGS. Median periodic drainflow for Rice Ditch 

increased substantially (about 700 percent) in 1995 

compared to 1994 (table 7). For that same period, all 

monitored water-quality constituents showed a corresponding decrease in median concentration, presumably owing to dilution. The median flow in 1996 

decreased nearly 300 percent from the 1995 sampling 

period, and, with the exception of lithium, concomittant slight increases in concentration of all monitored 

constituents were observed. Examination of the annual, 

continuous specific-conductance data for the 3-year 

monitoring period shows that the highest mean daily 

dissolved-solids concentrations (about 650 mg/L) typically did not occur during the irrigation season; the 

lowest mean concentrations (about 280 mg/L) occurred 

during the irrigation season. Of the individual constituents measured, boron and molybdenum exceeded beneficial-use criteria during the 3-year monitoring period. 

Boron met or exceeded the Nevada standard for irrigating sensitive crops in 62 percent of the samples in 

1994, 29 percent in 1995, and none in 1996. Molybdenum exceeded the standard in 38 percent of the samples 

in 1994, 29 percent in 1995, and 12 percent in 1996. 

L Drain 

L Drain, at the north-central perimeter of Carson 

Lake, discharges to West Lee Drain and East Lee Drain 

for distribution to western and eastern parts of the lake. 

Median drainflow for L Drain increased substantially 

(nearly 500 percent) in 1995 compared to 1994, with a 

corresponding decrease in median concentration of all 

measured water-quality constituents (table 7). Median 

drainflow decreased about 15 percent from 1995 to 

1996. In general, median arsenic, boron, and molybdenum concentrations decreased substantially in 1995 

and 1996 compared to 1994. In terms of median dissolved-solids concentrations (about 500 mg/L or less), 

the water quality met applicable beneficial-use standards. Only boron and molybdenum occasionally 

exceeded beneficial-use criteria; exceedences (50 percent for each constituent) were greatest in water samples collected in 1994, a water-short year. 

L 12 Drain 

L 12 Drain connects to East Ditch (fig. 3) for distribution of drainflow along the east margin of Carson 

Lake. This station was added to the monitoring network in 1995 when Holmes Drain was discontinued 

owing to backwater effects. Drainflow, about 9 ft3/s, 

varied little between the 1995 and 1996 irrigation seasons (table 7). Median concentrations of dissolved solids, arsenic, and molybdenum also showed relatively 

little change between the 2 years. Median concentrations of boron and lithium, however, were 40 and 27 

percent less, respectively, in 1996 than in 1995. Median 

dissolved-solids concentrations for 1995 and 1996 

20 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
were only about 20 and 30 percent greater, respectively, than that measured in irrigation water immediately downstream from Lahontan Reservoir during the 

same time period. 

Loads of Dissolved Solids and Boron 

Loads of dissolved solids and boron entering 

Stillwater NWR and Carson Lake were calculated 

1994-96 (tables 8 and 9). Because of the lack of correlation of dissolved-solids concentration or drainflow 

with the three other measured trace elements—arsenic, 

lithium, and molybdenum—load estimates were not 

calculated for these constituents. Information on loading of persistent chemical constituents is important for 

terminal wetlands, where discharge is only by evapotranspiration, because of the tendency for dissolvedsolids concentration to increase over time during seasons of minimal inflow. Load information also is 

important in making relative comparisons of loads 

among measured drain systems; the movement of large 

volumes of mineralized water can result in considerable contaminant transport even if the concentration of 

contaminants in solution is relatively low. Load data 

presented herein are divided between the 5-month nonirrigation season and the 7-month irrigation season. 

The loads for Stillwater Slough and the four drains 

entering Carson Lake are calculated solely from periodic instantaneous measurements and are given in 

terms of pounds or tons per day. (For a discussion of 

uncertainty in the determination of seasonal loads 

based solely on instantaneous measurements, see section "Evaluation of Load-Measurement Uncertainty 

Associated With Frequency of Data Collection in Agricultural Drains.") The loads calculated herein may not 

correspond to those reported earlier by Lico and Pennington (1997) because of differences in measurement 

location and calculation method. 

Dissolved Solids 

Stillwater National Wildlife Refuge 

For the two sites in Stillwater NWR that were 

monitored annually, Paiute Diversion Drain below TJ 

Drain and Stillwater Point Reservoir Diversion Canal, 

the loads of dissolved solids were greatest during the 

irrigation season for each of the 3 years (table 8). The 

seasonal difference in loading rate undoubtedly is due 

to increased drainflow during the irrigation season. 

Other drain sites not similarly equipped to measure 

flows all year probably would reflect a similar seasonal 

trend (Lico, 1992; Lico and Pennington, 1997). 

During 1995 and 1996, Paiute Diversion Drain 

delivered the greatest annual load of dissolved solids of 

the four principal drains entering Stillwater NWR. The 

annual load of dissolved solids delivered by this drain 

was about 2,700 tons in 1994, 20,000 in 1995, and 

37,000 in 1996. During 1995 and 1996, the dissolvedsolids load in Paiute Diversion Drain surpassed that 

delivered by Stillwater Point Reservoir Diversion 

Canal for the first time since 1986 (Lico, 1992, p. 18-

20; Hoffman, 1994, p. 15-17). Of the four principal 

drains to Stillwater NWR, S Line delivered the least 

dissolved-solids load: about 1,100 tons in 1994, 1,900 

in 1995, and 1,800 in 1996. These results are not unexpected because of the relatively low dissolved-solids 

concentrations in S Line compared to the other sites. 

Much of the water that passes the S Line site is goodquality water entering the Dry Lake (fig. 3) wetland, 

where USFWS biologists are evaluating the ecological 

effects of a wetland that receives limited, if any, agricultural return flow. 

Carson Lake 

Of the four monitored drains entering Carson 

Lake, Carson Lake Drain and L Drain delivered the 

greatest mean loads of dissolved solids to the Carson 

Lake wetlands (table 8). These two drains delivered a 

combined mean load of 53 tons/d (or 77 percent of the 

mean total daily load) in 1995 and 55 tons/d (or 87 percent) in 1996. The dissolved-solids loads delivered by 

Rice Ditch and by L 12 Drain were relatively low and 

ranged from about 4 to 13 percent of the mean total 

daily load delivered to Carson Lake by the four drains. 

Boron 

Stillwater National Wildlife Refuge 

The overall trend of boron loads (table 9) generally parallels that for dissolved solids; this trend is consistent with the strong positive relation of boron with 

dissolved solids recognized by Hoffman and others 

(1990, p. 36) and by Lico and Pennington (1997, p. 6). 

As for dissolved-solids loads, the largest boron loads 

were delivered to Stillwater NWR during the irrigation 

season. Also, beginning in 1995, the boron loads passing Paiute Diversion Drain during the irrigation season 

exceeded those measured at Stillwater Point Reservoir 

Diversion Canal. The annual load of boron delivered 

by Paiute Diversion Drain below TJ Drain was about 

7,000 lb in 1994, 51,000 in 1995, and 95,000 in 1996. 

RESULTS AND DISCUSSION OF MONITORING PROGRAM 21 
	 	

Monitoring ofInorganic C

ontaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 

Table 8. Estimated seasonal loads of dissolved solids in drains entering Stillwater National Wildlife Refuge and Carson Lake, servicing agricultural areas near Fallon, 

Nev., 1994-96 

[a, number of measurements. —, no data or not applicable] 

Seasonal loads of dissolved solids 

(tons) 

Nonirrigation season, November—March Irrigation season, April—October 

Agricultural drain 1994 1995 1996 1994 1995 1996 

Total Mean Total Mean Total Mean Total Mean daily load Total Mean daily load Total Mean daily load 

seasonal daily seasonal daily seasonal daily seasonal (and range, seasonal (and range, seasonal (and range, 

load load load load load load load for n) load for n) load for n) 

Stillwater National Wildlife Refuge 

S Line Canal1-2 1,100 5.8 1,900 10 1,800 10 

Stillwater Slough3 13 30 33 

(7.2-24, n=7) (19-64, n-8) (25-42, n=7) 

Paiute Diversion Drain below TJ Drain" 51,000 8.6 920 6.1 9,400 63 1,700 8.1 19,000 89 28,000 132 

Stillwater Point Reservoir Diversion Canals 3,100 21 1,200 7.9 7,800 52 5,400 25 12,000 55 12,000 58 

Carson Lake 

Carson Lake Drain3'6 22 20 34 

(13-48, n=7) (6.4-31, n=7) (27-46, n=7) 

Rice Ditch3 3 78.7 4.2 

(0.09-7.4, n=7) (0.07-26, n=6) (0.02-10, n=7) 

L Drain3 10 733 21 

(4.4-21, n=7) (16-62, n=6) (8.8-45, n=7) 

L 12 Drain3 7,86.7 2.6 

(2.5-16, n=7) (0.40-4.2, n=7) 

IEstimated from continuous recordings of drainflow and specific conductance using linear regression equations in table 4.. 

2No flow in canal during nonirrigation season, 1994-96. 

3Means of instantaneous onsite measurements during irrigation season. 

4Drainflow during 1994 represents TJ Drain flow; drainflow during 1995-96 represents combined flow from TJ Drain, D Line, and Paiute Diversion Drain. 

5Data for November through February only; zero flow recorded for March. 

6Known locally as Cabin Drain. 

7Data collected in April 1995 not used in calculation because measurement preceded irrigation. 

8Data collection did not begin until March 1995. 
	 	

Table 9. Estimated seasonal loads of dissolved boron in drains entering Stillwater National Wildlife Refuge and Carson Lake, servicing agricultural areas near 

Fallon, Nev., 1994-96 

[n, number of measurements. —, no data or not applicable] 

Seasonal loads of boron 

(pounds) 

Nonirrigation season, November—March Irrigation season, April—October 

Agricultural drain 1994 1995 1996 1994 1995 1996 

Total Mean Total Mean Total Mean Total Mean daily load Total Mean daily load Total Mean daily load 

seasonal daily seasonal daily seasonal daily seasonal (and range, seasonal (and range, seasonal (and range, 

load load load load load load load for n) load for n) load for n) 

RESULTS ANDDISCUSSION OF MONITORING PROGRAM 

Stillwater National Wildlife Refuge 

S Line Canal1 '2 3,000 17 4,600 25 1,800 10 

Stillwater Slough3 55 105 98 

(30-50, n=7) (60-194, n=8) (71-125, n=7) 

Paiute Diversion Drain below TJ Drain" 5 2,600 22 2,300 15 24,000 159 4,400 20 49,000 230 71,000 320 

Stillwater Point Reservoir Diversion Canal1 11,000 72 4,100 27 28,000 180 20,000 92 44,000 200 44,000 210 

Carson Lake 

Carson Lake Drain3'6 98 70 119 

(50-283, n=7) (29-110, n=7) (58-155, n=7) 

Rice Ditch3 8.4 721 11 

(0.3-25, n=7) (0.1-66, n=6) (0.07-27, n=7) 

L Drain3 31 780 65 

(15-55, n=7) (45-158, n=6) (17-99, n=7) 

L 12 Drain3 7,820 10 

(5-47, n=7) (1.4-20, n=7) 

"Estimated from continuous recordings of drainflow and specific conductance using linear regression equations in table 4. 

2No flow in canal during nonirrigation season, 1994-96. 

3Mean of instantaneous onsite measurements during irrigation season. 

4Drainflow during 1994 represents TJ Drain flow; drainflow during 1995-96 represents combined flow from TJ Drain, D Line, and Paiute Diversion Drain. 

5Data for November through February only; zero flow recorded for March. 

6Known locally as Cabin Drain. 

7Data collected in April 1995 not used in calculation because measurement preceded irrigation. 

8Data collection did not begin until March 1995. 

Al W 
Stillwater Point Reservoir Diversion Canal delivered 

about 31,000 lb in 1994, 48,000 in 1995, and 72,000 in 

1996. These two drains typically transport the majority 

of boron to Stillwater NWR. The estimated daily boron 

load passing the Stillwater Slough site during the irrigation season also is relatively large (fig. 2). This site is 

downstream from an area where water from thermal 

wells is used in and near the community of Stillwater, 

Nev. Leakage at land surface from some thermal wells 

is known to enter Stillwater Slough. The mean concentration of dissolved boron in deep thermal waters in the 

Stillwater, Nev., area is 16,000 μg/L (Morgan, 1982, 

p. 55). 

Carson Lake 

Similar to boron loads in agricultural drain water 

entering Stillwater NWR, the boron loads entering Carson Lake varied during the irrigation season from year 

to year in response to variations in drainflow. As in the 

case of dissolved-solids loads, the largest boron loads 

(greater than 70 percent) were delivered to Carson 

Lake by Carson Lake Drain and L Drain combined. 

During the irrigation season, Carson Lake Drain transported 98 lb/d in 1994, 70 in 1995, and 119 in 1996; 

and L Drain transported 31 lb/d in 1994, 80 in 1995, 

and 65 in 1996. Of the four monitored sites, Carson 

Lake Drain typically transported the greatest load of 

boron (table 9) in 1994 and 1996; in 1995, L Drain 

delivered the largest. Carson Lake Drain discharges to 

the Sprig Pond unit of Carson Lake. L Drain delivered 

a notably increased boron load in 1995 and 1996 compared to 1994. The increase, slightly greater than 100 

percent, corresponded to an increase in median drainflow (table 9). 

EVALUATION OF LOAD-MEASUREMENT 

UNCERTAINTY ASSOCIATED WITH 

FREQUENCY OF DATA COLLECTION IN 

AGRICULTURAL DRAINS 

Each of two hydrologically dissimilar drainflow 

sites were equipped with a continuously recording gage 

for drainflow and for specific conductance (dissolvedsolids concentration). This instrumentation allowed 

comparison of load calculations at 15-minute intervals 

with monthly samples at the two sites. Such a comparison can shed light on the amount of uncertainty or 

error that is associated with frequency of data collection for dissolved constituents in agricultural drains. 

Previous investigators (Dolan and others, 1981; 

Miertschin, 1986) made similar comparisons, but their 

examinations involved analysis of concentration of 

suspended particulate matter and mean daily flow of 

natural streams. 

For the uncertainty analysis (table 10), the continuous record is considered the true record. The corresponding periodic record is comprised of instantaneous 

data collected about every 30 days. The percent differences between the continuous and instantaneous 

records (table 10) show that periodic measurements 

may substantially overestimate or underestimate the 

annual load of dissolved solids passing some sites and 

that these periodic estimates for Paiute Diversion Drain 

appeared to be less accurate than that for Stillwater 

Point Reservoir Diversion Canal. The principal reason 

for the underestimation and the lesser accuracy is the 

greater variability of daily drainflow at Paiute Diversion Drain, which can be extreme at times (Hoffman, 

1994, p. 14), coupled with episodic flow events missed 

by the periodic instantaneous data. 

The 1994-96 monitoring program was enhanced 

technically by the use of continuous-recording instruments on selected drains that exhibited highly variable 

flow rates. The degree of accuracy of the loading information for variable flow regimes is directly proportional to frequency of data collection for the time 

period of interest. 

Concentrations and Loads of Total Mercury 

Whole-water samples for total-mercury determinations were collected at Stillwater Slough and Stillwater Point Reservoir Diversion Canal during calendar 

years 1994-96. At the other sites, such samples were 

collected only during 1994. In December 1994, the 

data were evaluated for possible refinement of the 

overall monitoring program. With the exception of 

Stillwater Slough and Stillwater Point Reservoir Diversion Canal, most of the mercury data at the other sites 

were below the USGS minimum reporting level (0.1 

μg/L). Therefore the decision was made to cease collecting total-mercury samples at the other sites. 

Because of the poor correlation of total mercury with 

drainflow or with other water-chemical data collected 

as part of the monitoring program, predictive regression equations for mercury concentration could not be 

developed. The results presented below (in the next 

two sections) are statistical summaries of mercury concentrations and loads for instantaneous samples. 

24 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Table 10. Comparison of continuous-recording and periodic onsite measurements of annual 

dissolved-solids loads in agricultural drains entering Stillwater National Wildlife Refuge, Nevada 

[Annual load of dissolved solids: Values rounded to two significant figures] 

Annual load of dissolved solids 

Agricultural drain Water 

year 

A 

Continuous 

record' 

B 

Instantaneous 

record2 

C 

Difference between 

continuous and 

(tons) (tons) instantaneous records3 

(percent) 

Paiute Diversion Drain below Ti Drain 41994 2,700 5,400 100 (+) 

1995 20,000 7,500 62 (—) 

1996 37,000 21,000 43 (—) 

Stillwater Point Reservoir Diversion Canal 1994 8,500 9,400 11 (+) 

1995 13,000 13,000 0 

1996 20,000 15,000 25 (—) 

'Continuous recording of flow and specific conductance (as surrogate for dissolved-solids concentration). Annual load of dissolved 

solids calculated by summing products of tons per day by number of days per month. (Tons per day calculated by multiplying daily mean 

flow times daily mean dissolved-solids concentration times 0.0027.) 

2lnstantaneous measurement of flow and specific conductance (as surrogate for dissolved-solids concentration) on 15th day of each 

month. Annual load calculated by summing products of tons per day by number of days per month. (Tons per day calculated by 

multiplying instantaneous flow times instantaneous dissolved-solids estimate times 0.0027.) 

3Calculated by formula C = 100 (B — A) / A. Signs in parentheses indicate if instantaneous data overestimated (+) or underestimated 

(—) value. 

4Zero flow recorded for March. 

Stillwater Slough 

The highest sampled concentrations of total mercury in drain, water during the 1994-96 irrigation seasons, measured at the Stillwater Slough site, were 

relatively high compared to background sites sampled 

in a previous investigation (Hoffman and others, 1990). 

The median concentration of total mercury in Stillwater Slough during 1994-96 was 0.7 μg/L (n=21); values ranged from less than 0.1 to 3.5 μg/L. Of the 21 

values, 3 were below the USGS minimum reporting 

level, 0.1 μg/L; 2 exceeded the 1-hour average (acute) 

Nevada standard for the protection of aquatic life, 2.0 

μg/L; and 18 are known to have exceeded the 96-hour 

average (chronic) standard, 0.012 μg/L. (The chronic 

standard, however, is an order of magnitude lower than 

the minimum reporting level). 

Stillwater Slough, a natural channel during the 

Comstock mining era in the 1800's probably delivered 

mercury-contaminated overflow from Carson Lake to 

the Stillwater wetlands (Hoffman, 1994, p. 8-11). This 

former flow-through system presumably allowed mercury bound to fluvial sediment to be deposited along 

the Stillwater Slough during the 1800's, when mercury 

was used in the milling of precious metals from the 

Comstock Lode. A sample of bottom sediment collected from the slough in 1987 contained 14 μgig of 

mercury, dry weight (Hoffman and others, 1990, p. 

113); another in 1988 contained 10 μgig (Rowe and 

others, 1991, p. 163). Background concentrations in 

minimally contaminated bottom sediments typically 

are less than 1 μg/g, dry weight. Bottom sediments may 

be resuspended in the water column by a sufficient 

increase in water velocity and churning of sediments 

by the action of fish such as carp. 

During the 1994-96 monitoring period, instantaneous total-mercury loads in Stillwater Slough ranged 

from less than 0.01 to 0.38 lb/d (median, 0.02 lb/d). 

Stillwater Point Reservoir Diversion Canal 

At this site during the 1994-96 irrigation seasons, 

the total-mercury concentration ranged from less than 

0.1 to 0.8 μg/L; the median value was 0.4 μg/L (n=20). 

Of the 20 values, 2 were below the USGS minimum 

reporting level, 0.1 μg/L; at least 18 exceeded the 

chronic standard, 0.012 μg/L, and none exceeded the 

Nevada acute standard, 2.0 μg/L. Instantaneous totalmercury loads for the 3-year period ranged from less 

than 0.004 to 0.30 lb/d; the median value was 0.06 lb/d. 

The substantially greater median total-mercury load 

measured at Stillwater Point Reservoir Diversion 

EVALUATION OF LOAD-MEASUREMENT UNCERTAINTY ASSOCIATED WITH FREQUENCY OF DATA COLLECTION 25 
Canal (200-percent difference) relative to Stillwater 

Slough undoubtedly was due to the typically higher 

flow rates at the canal site. Regulations allow for 1- and 

96-hour average-concentration limits to be exceeded 

only once every 3 years (U.S. Environmental Protection Agency, 1986). 

PHYSICAL, CHEMICAL, AND 

BIOLOGICAL CHARACTERISTICS OF 

WATER, BOTTOM SEDIMENT, AND BIOTA 

IN WETLANDS 

Field Measurements of Dissolved Oxygen, pH, 

and Specific Conductance 

Dissolved Oxygen 

Dissolved-oxygen (DO) concentrations, along 

with other water-quality properties, generally were 

measured in the late morning to early afternoon hours 

(typically during 10:00 a.m. to 3:00 p.m.). DO measurements at these times of day may be biased toward 

moderate to high values because oxygen typically is 

released by photosynthetic processes during this time 

period and because no nighttime measurements were 

made. In most surface water, DO concentration varies 

somewhat predictably over a 24-hour period in 

response to physical, chemical, and (primarily) biological factors. Minimum DO concentrations typically are 

observed at dawn after the period of darkness when 

oxygen uptake (respiration) by aquatic organisms 

exceeds DO production by aquatic plants. As the day 

proceeds, DO concentrations gradually increase to a 

maximum near midafternoon, when DO production 

greatly exceeds respiration, and then gradually 

decrease until dawn of the next day. DO concentrations 

exceeding 100-percent saturation are indicative of high 

primary productivity by aquatic plants. For example, 

high daytime productivity at Dry Lake in Stillwater 

NWR and in the Sprig Pond unit of Carson Lake (table 

11) suggests that DO concentrations at these sites may 

be depressed during hours of darkness when oxygen 

uptake by respiratory processes exceeds oxygen production. Conversely, moderate to low concentrations 

during 10:00 a.m. to 3:00 p.m. in Lead Lake may 

indicate relatively lower productivity. The reason for 

the decline in DO concentrations in Stillwater Point 

Reservoir over the 3-year study is unknown. Low DO 

concentrations may adversely affect aquatic organisms, 

particularly fish (Herman and Meyer, 1990). 

pH 

The measured pH values indicate that the wetland 

waters are alkaline (table 11). The highest values were 

measured in Dry Lake, and the lowest in Stillwater 

Point Reservoir. The pH measured in Dry Lake during 

1994-95 exceeded the upper permissible pH limit of 

9.0 for most beneficial uses (table 1). 

Specific Conductance 

Mean annual specific conductance, an indirect 

measure of dissolved-solids concentration, in the study 

wetlands ranged from 575 μS/cm at 25°C in Stillwater 

Point Reservoir in 1995 to 14,000 μS/cm in Lead Lake 

in 1994 (table 11). The maximum value corresponded 

to lower water levels in Lead Lake during that year. 

Specific conductance was consistently lowest in Stillwater Point Reservoir, succeeded by Dry Lake. 

Based on the regression equations listed in table 

4, dissolved-solids concentrations exceeded the 

Nevada water-quality standard for watering of livestock at only one site; Lead Lake in 1994. Watering of 

livestock is a designated beneficial use of wetland 

water in Lahontan Valley. Presently Nevada does not 

have dissolved-solids standards for aquatic life or for 

propagation of wildlife. Because dissolved-solids tolerance of submergent and emergent plants and aquatic 

vertebrates and invertebrates varies widely, species 

composition shifts with changing concentrations 

(Stewart and Kantrud, 1971, p. 3). Elevated dissolvedsolids concentrations may affect bird species as well. 

When relegated to water with a specific conductance 

greater than 20,000 RS/cm, ducklings died (Mitcham 

and Wobeser, 1988, p. 49). Ducklings relegated to 

water with a specific conductance in the range 7,500 to 

20,000 μS/cm suffered sublethal effects on growth, 

feathering, and other physiological functions. Weight 

gain of ducklings reared on water with a specific conductance greater than 4,000 RS/cm was depressed. 

Mean specific conductance in Lead Lake in 1994 was 

14,000 RS/cm. 

26 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
Table 11. Field measurements of temperature, dissolved-oxygen concentration and saturation, pH, and 

specific conductance in four wetlands in Lahontan Valley, Nevada, June-July 1994-96 

[—, not applicable] 

Wetland 

Dry Lake: 

Year 

1994 

Statistics 

Mean 

Range 

Water 

temperature 

(degrees 

Celsius) 

Dissolved oxygen 

Concentration 

(milligrams 

per liter) 

Saturation 

(percent) 

Stillwater National Wildlife Refuge 

25 15.5 217 

25-26 13.4-16.8 186-238 

pH 

(units) 

9.6 

9.5-9.8 

Specific 

conductance 

(microsiemens 

per centimeter at 

25°C) 

593 

580-610 

1995 Mean 

Range 

28 12.9 189 9.1 1,610 

Lead Lake: 

1996 Mean 

Range 

29 

29-30 

9.8 

9.5-10.3 

147 

142-157 

7.5 1,080 

900-1,210 

1994 Mean 

Range 

27 

26-29 

9.3 

7.7-11.1 

135 

109-166 

8.4 

8.3-8.5 

14,000 

1995 Mean 

Range 

21 4.4 

4.0-4.9 

56 

52-66 

7.9 

7.7-8.1 

2,400 

1996 

Stillwater Point Reservoir: 

Mean 

Range 

26 

25-27 

5.8 

4.5-7.3 

83 

63-103 

8.4 

8.2-8.5 

3,920 

3,900-3,950 

1994 Mean 

Range 

25 

24-28 

11.6 

7.7-14.8 

162 

105-202 

8.3 

8.0-8.6 

1,060 

1,010-1,080 

1995 Mean 

Range 

23 

22-23 

6.1 

5.8-6.4 

81 

78-84 

7.6 

7.5-7.7 

575 

550-600 

Sprig Pond: 

1996 Mean 

Range 

17 

15-18 

3.0 

1.7-4.5 

Carson Lake 

35 

21-51 

7.5 

7.4-7.5 

787 

750-810 

1994 Mean 

Range 

24 

23-26 

11.8 

10.2-14.3 

163 

145-192 

8.4 1,710 

1,650-1,800 

1995 Mean 

Range 

25 7.3 

6.6-7.8 

101 

92-109 

8.5 

8.3-8.6 

1,550 

1,250-1800 

1996 Mean 

Range 

30 

27-32 

10.9 

7.4-16.8 

163 

107-264 

8.7 

8.5-9.0 

1,120 

1,050-1,200 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 27 
Trace Elements 

Concentrations In Sampled Media 

Aluminum 

Aluminum previously was identified as a concern 

in water and in avian diet (aquatic vegetation and invertebrates) during contaminants monitoring of wetlands 

in Stillwater NWR (Tuttle and others, 1996, p. 14-17). 

Aluminum concentrations commonly exceeded Federal water-quality criteria in unfiltered water samples 

collected from wetlands. In some cases, exceedences 

were by orders of magnitude. Comparisons of total and 

dissolved samples indicated that most aluminum was 

not in a dissolved phase (Hoffman and others, 1990, p. 

99-100). Aluminum concentrations in a large percentage of food-chain organisms also exceeded levels associated with lethal and sublethal effects on waterfowl 

(Tuttle and others, 1996). Elevated aluminum in wetlands not receiving agricultural drainage suggests that 

aluminum may be naturally elevated in soils and wetlands in Lahontan Valley. 

During 1994-96, aluminum was detected in all 

wetland water, sediment, detritus, pondweed, hemipteran, and fish samples; in 79 percent of the coot eggs 

and 91 percent of the avocet eggs; and in 31 percent of 

the juvenile-coot livers and 38 percent of the juvenileavocet livers. Concentrations in most sampled media 

varied among study wetlands and years (table 12). 

Aluminum concentrations in water and sediment 

did not correlate with pH or specific conductance. Concentrations in water did not correlate with concentrations in sediment, detritus, pondweed, or hemipterans. 

Aluminum concentrations in sediment correlated 

with concentrations in detritus (p<0.001, r2= 0.322), 

hemipterans (p<0.001, r2= 0.383), and pondweed 

(p = 0 .037, r2= 0.073), although r2was low for pondweed. Geometric-mean concentrations in unfiltered 

wetland water, sediment, and food-chain organisms did 

not correlate with mean concentrations in bird eggs. 

During 1994-96, aluminum concentrations in all 

unfiltered wetland-water samples exceeded the Federal 

criterion, 87 Kg/L (U.S. Environmental Protection 

Agency, 1998). High aluminum concentrations in 

water generally corresponded to observed water turbidity, which apparently increased during windy conditions. Toxicity of aluminum in water varies considerably with aluminum species and complexation (Sparling and Lowe, 1996, p. 2). Speciation of aluminum is 

affected by several environmental variables, particularly pH. In the pH range 6.0 to 8.0, aluminum has a 

low solubility and is considered to be biologically inactive. Aluminum solubility increases in more alkaline 

solutions (pH>8.0), but the biological implications are 

poorly understood. 

The biological implications of aluminum in sediments also are uncertain. The correlation between aluminum in sediment and aquatic vegetation, however, 

suggests that sediment serves as a source of the aluminum in vegetation. 

Bird species may be affected adversely by excessive aluminum in diet (Sparling, 1990). Aluminum 

concentrations in 28 percent of the vegetation samples 

and in 14 percent of the hemipteran samples exceeded 

a dietary concentration associated with reduced growth 

and behavioral effects in waterfowl, 5,000 μg/g, and 

concentrations in 12 percent of the vegetation samples 

exceeded a dietary concentration associated with 

reduced survival, 10,000 μ,g/g. Exceedences occurred 

in all wetlands except Dry Lake. Although aluminum 

in organisms that are typical of the avian food chain 

exceeded concentrations of concern, aluminum generally was not elevated in bird eggs and livers. Aluminum toxicosis in birds may be attributed to the 

formation of insoluble phosphates in the gastrointestinal tract and tissues and the subsequent interference 

with phosphate metabolism (Sparling, 1990; Sparling 

and Lowe, 1996). In such cases, aluminum in bird eggs 

and liver tissues may not be elevated. The correlation 

of aluminum concentration in sediment with concentration in pondweed and hemipterans suggests that sediment was the source of aluminum in organisms in the 

potential avian diet. Ingestion of plants or invertebrates 

by birds may result in potentially hazardous exposure 

to aluminum. 

28 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
		

		

		

		

			

		

		

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICSOF WATER, BOTTOM SEDIMENT, AND BIOTA 

Table 12. Aluminum concentrations in unfiltered water, sediment, and biological samples collected from four wetlands in Lahontan Valley, Nevada, 

April-August 1994-96 

[Geometric-mean (and range) data from U.S. Fish and Wildlife Service. Within each wetland for particular sample medium or type, geometric means having same appended letter (a or b) are not significantly different (p<0.05) across years; correspondingly, differing appended letters indicate significant difference between geometric means. -, no data available or not applicable. <, used with sample mean, indicates 

that value for more than half of samples was less than analytical detection limit; used with range, indicates that value for at least one sample was less than detection limit. In cases where analytical detection limit 

varied, maximum limit is given] 

Total Aluminum in Aluminum in biological samples 

aluminum in bottom-sediment (micrograms per gram) 

Wetland Year water samples samples 

(micrograms (micrograms Coot Avocet Coot Avocet Detritus Pondweed Hemiptera Fish per liter) per gram) egg egg liver liver 

Stillwater National Wildlife Refuge 

Dry Lake: 

1<5 1<5 1994 373 a 19,722 a 1,492 a,b 486 a 8 a 

(280-450) (17,540-20,310) (-) (907-2,611) (195-1,214) (-) (8-9) (-) (-) 

1.<5 1995 22,380 b 29,027 b 29,430 a 1,941 b 200 a 44a 8 a 

(13,200-36,600) (19,570-35,680) (25,040-33,990) (1,780-2,200) (128-256) (41-48) (<5-11) (-) (<5-5) (-) 

111 1<5 1.<5 1996 3,070 a 31,992 b 30,736 a 892 a 388 a 299 b 53 b 

(2,440-4,120) (28,820-35,030) (27,060-32,210) (650-1,400) (343-440) (152-493) (12-84) (7-24) (<5-5) (<5-5) 

Lead Lake: 

113 1<5 1994 5,620 a 19,764 a 1,905 a 926 b 7 a 

(2,900-8,720) (13,830-25,680) (-) (1,230-2,710) (403-1,316) (6-9) (6-19) (-) (-) 

1<5 1995 437 b 31,660 b 31,558 b 6,447 b 11,624 1<5 

(230-790) (27,160-35,530) (27,890-36,150) (5,400-10,390) (1,527-1,721) (<5-15) (-) (<5-21) (-) 

1996 1,590 b 25,939 a,b 24,999 a 805 a 131 a 19 b 112 116 1<5 

(1,430-1,900) (24,650-26,800) (24,190-25,310) (302-848) (81-300) (11-27) (6-20) (7-23) (-) 

Stillwater Point Reservoir: 

1994 793 a 16,556 a 10,296 b 19,004 160 a 6a 18 8a 

(390-1,380) (11,620-20,360) (-) (4,530-17,600) (7,710-10,300) (101-244) (5-7) (5-9) (<5-23) (<5-40) 

1.<5 1.<5 1995 600 a 26,630 b 27,183 a 5,064 a,b 1422 104 a 

(265-1,230) (24,000-29,380) (23,540-30,390) (3,310-6,200) (-) (47-150) (<5-8) (-) (-) 

1996 293 a 25,343 b 24,509 a 1,600 a 1850 190 a 16 b 17.3 11 a 

(95-630) (20,430-27,080) (13,440-28,450) (459-1,700) (-) (88-549) (9-26) (-) (<5-33) 

Carson Lake 

Sprig Pond: 

1.<5 1994 7,800 b 22,510 a 14,839 b 4,787 b 169 9 a 9 a 8 a 

(5,400-11,400) (19,300-27,010) (-) (7,740-24,290) (2,550-7,080) (60-79) (7-16) (9-10) (<5-9) (<5-14) 

1<5 1<5 1<5 1<5 1995 457 a 34,590 b 31,481 a 1,166 a 1562 1116 

(270-610) (32,510-36,290) (28,040-35,540) (477-2,200) (558-566) (37-382) (<5-5) (<5-6) (-) (-) 

1996 1,060 a 34,425 b 30,521 a 1,744 a 335 a 15 b 18 b 1<5 32a 

(740-1,510) (32,130-36,590) (27,990-32,470) (1,120-3,260) (187-550) (-) (10-20) (8-42) (<5-72) (<5-137) 

1Analysis of variance was not attempted because of inadequate sample size or large number of samples having concentrations less than analytical detection limit. 

113 
Arsenic 

Earlier NIWQP investigations in Lahontan Valley 

revealed that arsenic concentrations in water collected 

from agricultural drains and from wetlands that 

received irrigation drainage commonly exceeded standards for applicable beneficial uses and exceeded a 

concentration associated with toxicity to amphibians 

(Hoffman and others, 1990, p. 33). Concentrations 

were typically highest just prior to or during the early 

part of irrigation seasons. Arsenic concentrations in 

aquatic vegetation from several drain-water sites 

exceeded levels associated with effects on growth, 

development, and physiology in mallard (Anas platyrhynchos) ducklings. Fish collected from some sites 

contained concentrations associated with decreased 

growth and survival of bluegill (Lepomis macrochirus). Arsenic concentrations in invertebrates and bird 

livers from Stillwater WMA and Carson Lake were 

below levels of concern. 

During 1994-96, arsenic was detected in all unfiltered water, sediment, detritus, and vegetation samples; 

in 78 percent of the hemipterans and 57 percent of the 

fish; in 19 percent of the coot eggs but in none of the 

avocet eggs; and in 62 percent of the coot livers and 13 

percent of the avocet livers (table 13). Arsenic concentrations in unfiltered water positively correlated with 

specific conductance (p<0.001, r2= 0.736) but not with 

pH. Although r2 values were low, arsenic concentrations in unfiltered water correlated with concentrations 

in sediment (p = 0.036, r2= 0.123) and in pondweed 

(p = 0.019, r2= 0.153). Concentrations in sediment 

were weakly correlated with concentrations in pondweed (p = 0.011, r2= 0.106). Concentrations in pondweed were correlated with concentrations in invertebrates (p = 0.008, r2= 0.169). Geometric-mean arsenic 

concentrations in invertebrates correlated with mean 

concentrations in fish (p = 0.014, r2= 0.662). Geometric-mean concentrations in water, sediment, or dietary 

organisms did not correlate with mean concentrations 

in bird eggs or livers. 

Arsenic concentrations in unfiltered water samples collected from Sprig Pond, Lead Lake, and Stillwater Point Reservoir during 1994-96 consistently 

exceeded standards for applicable beneficial uses (table 

1) and also exceeded concentrations associated with 

toxicity to amphibian embryos and larvae, 40 μg/L 

(U.S. Environmental Protection Agency, 1985a, p. 15), 

and toxicity to fish, 40 ps/L (Birge and others, 1979a, 

p. 523). Arsenic in sediments from all wetland units 

exceeded potentially toxic concentrations for sensitive 

benthic invertebrates, 6 μg/g, and arsenic concentrations in sediment from Lead Lake in 1995 exceeded 

a level associated with a broader range of toxicity, 

33 μgig (Persaud and others, 1993, p. 3). 

Mean arsenic concentrations in pondweed and 

invertebrates were less than avian-diet effect levels, 

30 μg/g (Camardese and others, 1990, p. 793). Also, 

concentrations in bird eggs and livers were below levels of concern (Stanley and others, 1994). Because 

concentrations in whole fish and bird livers were substantially lower than concentrations in potential foodchain organisms, arsenic in Lahontan Valley wetlands 

does not appear to magnify in food chains or concentrate in higher organisms. 

Boron 

Boron concentrations in water collected from 

agricultural drains and from wetlands receiving irrigation drainage in previous NIWQP investigations in 

Lahontan Valley commonly exceeded standards for 

applicable beneficial uses and were at a level associated with low-level fish toxicity (Hoffman and others, 

1990, p. 34). Boron concentrations in water correlated 

with specific conductance, and concentrations tended 

to be higher before or in the early part of the irrigation 

season. Boron in a majority of aquatic-vegetation samples exceeded the avian-diet effect level. Concentrations in juvenile-bird livers collected in 1986 exceeded 

a level associated with reduced hatching success and 

juvenile survival. Boron concentrations in bird eggs 

and juvenile-bird livers collected in other years were 

generally lower but exceeded concentrations associated with reduced growth rate. 

During 1994-96, boron was detected in all unfiltered wetland water, sediment, detritus, vegetation, and 

invertebrate samples; in 86 percent of the fish; in 53 

percent of the coot eggs and 56 percent of the avocet 

eggs; and in 95 percent of the coot livers and 91 percent 

of the avocet livers (table 14). Boron concentrations in 

30 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICSOFWATER, BOTTOMSEDIMENT, AND BIOTA 

Table 13. Arsenic concentrations in unfiltered water, sediment, and biological samples collected from four wetlands in Lahontan Valley, Nevada, April-August 

1994-96 

[Geometric-mean (and range) data from U.S. Fish and Wildlife Service. Within each wetland for particular sample medium or type, geometric means having same appended letter (a through c) are not significantly different (p<0.05) across years; correspondingly, differing appended letters indicate significant difference between geometric means. -, no data available or not applicable. <, used with sample mean, indicates that value for more than 

half of samples was less than analytical detection limit; used with range, indicates that value for at least one sample was less than detection limit. In cases where analytical detection limit varied, maximum limit is given] 

Total Arsenic in Arsenic in biological samples 

arsenic in bottom-sediment (micrograms per gram) 

Wetland Year water samples 

(micrograms 

per liter) 

samples 

(micrograms 

per gram) Detritus Pondweed Hemiptera Fish Coot 

egg 

Avocet 

egg 

Coot 

liver 

Avocet 

liver 

Stillwater National Wildlife Refuge 

Dry Lake: 

1994 31 a 17.0 a 6.4 a 1 1.0 - 10.6 - 0.8a 1.<0.5 

(31-32) (14-18) (-) (4.5-8.5) (<1.0-1.4) (-) (<0.5-1.3) (-) (0.7-1.0) (-) 

1995 7 b 14.0 a 13.5 a 3.2 a l <0.5 1.0 a 1<0.5 - 1<0.5 - 

(29-58) (10-18) (11-16) (1.2-9.8) (<0.5-0.5) (0.5-1.9) (<0.5-0.5) (-) (-) (-) 

1996 32 a 15.1 a 14.0 a 3.7 a '<co 1.2 b 1<0.5 1<0.5 0.7 a 10.4 

(25-36) (13-18) (12-19) (1.4-6.2) (<0.9-1.8) (<0.8-2.5) (<0.5-0.6) (-) (<0.5-1.9) (<0.5-0.5) 

Lead Lake: 

1994 175 b 25.9 b - 15.7 a 2.1 b - 1<0.5 1<0.5 - l<0.5 

(172-177) (24-28) (-) (13.4-19.0) (1.9-2.4) (-) (<0.5-0.7) (-) (-) (-) 

1995 40 a 31.2 c 20.7 a 20.7 b 1

4.8 11.3 1<0.5 - 1

<0.5 - 

(35-48) (25-35) (19-24) (19.2-21.8) (4.6-5.1) (-) (-) (-) (<5-1.2) (-) 

1996 133 b 20.0 a 18.3 a 20.3 b 1.8 a 10.9 1<0.5 1<0.5 11.0 1<0.5 

(131-135) (18-24) (18-21) (16.8-26.0) (1.6-2.1) (<0.9-1.5) (<0.5-0.7) (-) (0.7-1.6) (-) 

Stillwater Point Reservoir: 

1994 73 c 13.6 a - 18.2 b 19.0 12.5 1<0.5 l<0.5 1<0.5 1<0.5 

(71-74) (11-17) (-) (12.5-27.2) (8.5-9.5) (1.8-4.4) (<0.5-0.9) (-) (<0.5-1.5) (<0.5-1.5) 

1995 24 a 11.0 a 19.6 b 11.4 a 1<0.5 1<0.5 1<0.5 - 0.6 a - 

(21-27) (7-16) (8-19) (8.4-15.3) (-) (<0.5-1.3) (-) (-) (<0.5-1.1) (-) 

1996 43 b 16.3 a 12.6 a 11.9 a,b 15.2 1<0.9 10.4 1

<0.5 0.6 a - 

(43-43) (11-19) (10-28) (9.3-15.4) 

Carson Lake 

(-) (<0.9-2.2) (<0.5-0.6) (-) (<0.5-0.9) (-) 

Sprig Pond: 

1994 81 b 17.6 a 16.4 b 9.2 b 14.8 1.<0.5 1<0.5 10.5 1<0.5 

(75-86) (15-20) (-) (14.1-17.7) (6.6-18.1) (4.0-5.6) (-) (-) (<0.5-1.2) (<0.5-0.5) 

1995 48 a 20.9 b 20.2 a 6.4 a 10.5 1.<0.5 1. <0.5 1.<0.5 0.4 a 1<0.5 

(43-50) (19-23) (20-21) (4.3-12.8) (<0.5-1.0) (-) (-) (-) (<0.5-0.8) (-) 

1996 60 a 18.1 a 17.8 a 21.1 b 2.8 a - 1<0.5 1<0.5 0.6 a 1<0.5 

(61-75) (17-20) (16-19) (15.6-27.7) (1.3-4.8) (-) (<0.5-0.5) (-) (<0.5-0.8) (-) 

lAnalysis of variance was not attempted because of inadequate sample size or large number of samples having concentrations less than analytical detection limit. CA) 
		 		

			

	 	

		 		

					

			

	 	

						

		

	 	

						

	 	

		 		

		

		

		

		

		

		

		 		

						

		

				

			 		

Monitoring ofInorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 

Table 14. Boron concentrations in unfiltered water, sediment, and biological samples collected from four wetlands in Lahontan Valley, Nevada, April-August 

1994-96 

[Geometric-mean (and range) data from U.S. Fish and Wildlife Service. Within each wetland for particular sample medium or type, geometric means having same appended letter (a through c) are not significantly different (p<0.05) across years; correspondingly, differing appended letters indicate significant difference between geometric means. -, no data available or not applicable. <, used with sample mean, indicates that value for more than 

half of samples was less than analytical detection limit; used with range, indicates that value for at least one sample was less than detection limit. In cases where analytical detection limit varied, maximum limit is given] 

Wetland Year 

Total 

boron in 

water samples 

(micrograms per liter) 

Boron in 

bottom-sediment 

samples 

(micrograms 

per gram) Detritus Pondweed Hemiptera 

Boron in biological samples 

(micrograms per gram) 

Fish Coot 

egg 

Avocet 

egg 

Coot 

liver 

Avocet 

liver 

Stillwater National Wildlife Refuge 

Dry Lake: 

1994 743 a 103.3 a 751 b 13.9 a,b 8.7 a 14.6 b 14.5 

(740-750) (88-119) (-) (689-977) (10.4-22.5) (-) (7.4-10.3) (-) (13.3-16.2) (3.0-6.0) 

1995 1,510a 123.2 a 122.8 a 595 a 18.5 b 5.O a 3.6 a 5.O a 

(832-2,090) (81-160) (97-167) (546-646) (14.1-23.1) (4.7-10.1) (<2.0-8.2) (-) (3.6-21.6) (-) 

1996 1,300 a 122.7 a 112.6 a 573 a 11.6 a 10.6 b 2.5 a i

<2.0 4.6 a 1<2.0 

(915-1,590) (108-138) (98-131) (523-626) (10.6-12.6) (7.3-13.2) (<2.0-5.2) (<2.0-3.1) (2.8-7.5) (-) 

Lead Lake: 

1994 110,770 66.9 a 283 b 73.9 b 6.8 b 1<0.5 16.8 

(10,600-10,900) (41-92) (-) (239-303) (59.4-83.2) (-) (2.6-15.7) (-) (-) (4.9-10.8) 

1995 1,600 a 89.5 a,b 87.8 a 74 a 149.7 1 10.6 1<2.0 6.4 a 

(1,390-1,930) (82-100) (80-102) (65-88) (46.7-52.9) (-) (-) (-) (3.2-9.3) (-) 

1996 3,580 b 98.7 b 98.9 a 826 c 14.4 a 18.1 3.3 a 1<2.0 8.0 a 12.0 

(3,560-3,610) (92-104) (95-103) (679-1,010) (12.6-15.8) (5.0-12.0) (2.4-5.9) (-) (6.6-10.6) (<2.0-3.4) 

Stillwater Point Reservoir: 

1994 1,210 c 55.8a 87 a 147.9 12.7 b 4.7a 11.4 5.7a 11.4 

(1,200-1,220) (37-69) (-) (57-115) (45.7-50.3) (11.3-14.1) (3.9-5.4) (0.6-2.3) (2.9-9.0) (0.7-3.0) 

1995 598 a 74.2 a,b 82.2 a 225 b 12.3 7.8 a,b 1<2.0 3.9 a 

(514-648) (64-83) (61-91) (148-256) (-) (3.8-17.9) (<2.0-8.5) (-) (3.2-9.3) (-) 

1996 852 b 86.4 b 70.0 a 399 c 123.5 3.3 a 2.4 a 1<2.0 2.7 a 

(812-875) (65-96) (37-108) (301-497) (-) (<3.5-7.5) (<2.0-3.1) (-) (2.2-3.3) (-) 

Carson Lake 

Sprig Pond: 

1994 2,220 b 62.7a 113 a 48.4 b 115.5 0.8a 1.2a 6.9 b 3.4 a 

(2,180-2,250) (47-85) (-) (71-237) (41.9-51.8) (14.9-16.1) (<0.5-3.0) (<0.5-4.1) (5.3-10.1) (3.0-3.6) 

1995 1,380 a 78.3 a 71.7 a 491 b 118.0 1<2.0 2.8 a,b i<2.0 2.3 a 3.1 a 

(1,190-1,510) (76-81) (63-77) (178-649) (12.8-25.8) (<0.2-6.4) (<2.0-7.9) (-) (<2.0-8.6) (2.5-3.8) 

1996 1,180 a 84.4 a 79.9 a 731 b 10.0 a 4.7 b 5.3 b 4.0 a,b 4.7 a 

(1,050-1,400) (80-89) (76-84) (537-998) (8.7-12.9) (-) (<2.0-13.4) (4.2-8.1) (3.3-5.5) (3.9-6.1) 

lAnalysis of variance was not attempted because of inadequate sample size or large number of samples having concentrations less than analytical detection limit. 
unfiltered water significantly correlated with specific 

conductance (p<0.001, r2= 0.985) but not with pH. 

Boron concentrations in water correlated only with 

concentrations in hemipterans (p<0.001, r2= 0.478). 

Concentrations in sediment correlated with concentration in detritus (p<0.001, r2= 0.545), pondweed 

(p<0.001, r2= 0.236), and hemipterans (p = 0.001, 

r = 0.268). Geometric-mean concentrations of boron in 

water, sediment, and food-chain organisms did not 

correlate with mean concentrations in fish or in bird 

eggs and livers. 

In general, during 1994-96, boron concentrations 

were lower in wetland water, higher in sediment, and 

substantially lower in bird samples than in the earlier 

NIWQP investigations (during the 1980's). During the 

same 3-year period, boron concentrations in wetland 

water consistently exceeded the irrigation-water-quality standard and exceeded concentrations associated 

with low-level toxicity (LC 10, lethal to 10 percent of 

test population) to aquatic vertebrates (Birge and 

others, 1979a, p. 523). As for aluminum, little information regarding the biological implications of boron in 

sediments is available. However, the correlation 

between concentrations of boron in sediment and boron 

in aquatic vegetation suggests that sediment serves as 

a source of the boron in vegetation. 

Elevated boron in diet has been shown to 

adversely affect bird reproduction, growth, and survival (Smith and Anders, 1989). Boron concentrations 

in all pondweed samples and 35 percent of the aquaticinvertebrate samples exceeded a dietary concentration 

associated with reduced weight gain in mallard ducklings, 30 μg/g (Smith and Anders, 1989, p. 945). Concentrations in 58 percent of the pondweed samples 

exceed a 300-μg/g dietary concentration associated 

with reduced hatch weight and reduced weight gain. A 

dietary concentration associated with reduced hatching 

success or duckling survival, 1,000 μg/g, was exceeded 

in only one sample from the Lahontan Valley wetlands. 

A boron concentration associated with reduced weight 

gain in mallard ducklings, 3 μgig (Smith and Anders, 

1989, p. 948), was met or exceeded in 69 percent of 

coot eggs, 81 percent of juvenile livers, 29 percent of 

avocet eggs, and 72 percent of juvenile livers. 

Although boron concentrations exceeded aviandiet effect levels in both pondweed and hemipteran 

samples, aquatic vegetation represented the greatest 

potential for exposure to boron for migratory birds. 

Boron could adversely affect their reproduction and 

survival. As may be expected, a herbivorous bird species (coot) had higher concentrations of boron in eggs 

and livers than an insectivorous species (avocet). 

Boron concentrations in pondweed correlated with 

concentrations in sediment and detritus. However, concentrations in these media did not correlate with concentrations in unfiltered water. The highest boron 

concentrations in sediment and pondweed were consistently found in Dry Lake, which has been managed 

using high-quality irrigation water since 1990. Since 

1992, boron concentrations in sediment and pondweed 

from Dry Lake have increased (fig. 4). 

-. 180 1,000 

a a 

w 

800 

0 >- ct z 

w 120 

w a 

w 

a 

w 

cr.) 

CC 

O 

CC 

100 

600 0 Z 

0 (5 as 

z 

z 

0 

m 

o_ 80 

2 

< 60 

cr 

• O 40 CC 

400 

Z 

z(/) 

0 2 

cc 

0 cc 

m a 

200 0 CC 

20 

z z 0 0 

1992 1993 1994 1995 1996 

YEAR 

EXPLANATION 

Boron in sediment 

Maximum 

-+- Mean 

Minimum 

Boron in Pondweed 

I 

Maximum 

 Mean 

Minimum 

Figure 4. Mean boron concentrations and ranges in sediment 

and pondweed collected from Dry Lake in Stillwater National 

Wildlife Refuge, west-central Nevada, 1992-96. 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 33 
Mercury 

Previous investigators identified elevated mercury concentrations in water and sediment, in the avian 

diet (aquatic vegetation, aquatic invertebrates, and 

fish), and in bird eggs and livers (Hoffman and others, 

1990; Hallock, Burge, and Tuttle, 1993a, b; Tuttle and 

others, 1996). In those investigations, dissolved mercury was detected in more than half of the wetland 

water samples collected in Lahontan Valley. Because 

the chronic aquatic-life standard and effect concentrations were less than the analytical detection limits provided by the laboratories, at least all measured 

concentrations exceeded levels of concern. Mercury in 

bottom sediments from drains and wetlands commonly 

exceeded concentrations associated with toxicity to 

freshwater and estuarine invertebrates. Mercury in 

avian food-chain organisms commonly exceeded concentrations associated with reduced reproduction and 

mallard-duckling behavioral effects. Concentrations in 

whole fish also exceeded these bird effect levels. Mercury in some bird eggs collected in Lahontan Valley 

exceeded concentrations associated with reduced hatch 

rate and juvenile survival. Concentrations in juvenilebird livers commonly exceeded concentrations associated with reduced reproduction and histopathology. In 

addition, mercury exceeded recommended levels for 

human consumption in several fish and waterfowl samples and was therefore the only element that appeared 

to pose a direct threat to human health. 

Mercury was detected in only four unfiltered wetland-water samples, but the detection limits reported 

by the USFWS laboratory were high, ranging from 0.5 

to 1.5 μg/L. Detected concentrations ranged from 0.6 

to 5.2 μg/L (table 15). Mercury, however, was measured in almost all sediment, detritus, invertebrate, fish, 

coot-egg, avocet-egg, coot-liver, and avocet-liver samples collected from all wetlands. Mercury was detected 

in all pondweed samples from Sprig Pond and Lead 

Lake, in 87 percent of the samples from Stillwater 

Point Reservoir, and in 33 percent of the samples from 

Dry Lake. Mercury concentrations in sediment significantly correlated with concentrations in detritus 

(p<0.001, r2 = 0.962), pondweed (p = 0.027, r2= 0.401), 

and invertebrates (p = 0.008, r2= 0.172). Geometricmean concentrations of mercury in sediment and foodchain organisms did not correlate with mean concentrations in bird eggs or livers. 

Mercury concentrations in sampled biological 

media generally were higher in 1994-96 than were 

found during the earlier NIWQP investigations 

(1980's), particularly in Stillwater NWR. The chronic 

aquatic-life standard for mercury, 0.012 μg/L, is substantially lower than the detection limits reported by 

the USFWS laboratory for mercury in water, 0.5 to 1.5 

μg/L; therefore, at a minimum, the four wetland water 

samples collected during 1994-96 that had detectable 

concentrations of mercury exceeded the chronic 

aquatic-life standard. Similarly, all samples with 

detectable mercury concentrations exceeded an effect 

level for fish, 0.1 μg/L (Birge and others, 1979b, p. 

635). Mercury concentrations in the Carson River correlate with suspended-solid concentrations in the water 

column, and suspended-solids concentrations are positively correlated with river flows exceeding 500 ft3/s 

(Cooper and others, 1985; Bonzongo and others, 

1996). With the exception of Sprig Pond, mercury concentrations were higher in livers of juvenile avocets 

than in those of juvenile coots. Elevated concentrations 

in coot eggs may be from increased consumption of 

insects by females during egg production to acquire 

sufficient protein (Fredrickson and Taylor, 1982). 

Mercury in bottom sediment from all wetlands 

exceeded an estimate of the background mercury concentration in Lahontan Valley prior to mercury contamination less than 1 μg/g, dry weight. Mercury 

concentrations in most sediment samples exceeded 

effect concentrations for sensitive freshwater invertebrates, 0.2 μg/g (Persaud and others, 1993, p. 3) and 

estuarine and coastal marine invertebrates, 0.15 μgig 

(Long and Morgan, 1991, p. 46). Concentrations in 

Lead Lake and Sprig Pond sediments exceeded a 

severe-effect level for aquatic sediments, 2.0 μgig 

(Persaud and others, 1993). 

At relatively low dietary concentrations, mercury 

can affect bird reproduction and survival. Mercury concentrations in all the fish and hemipteran samples and 

in 47 percent of the pondweed samples collected during 1994-96 met or exceeded an avian dietary concentration associated with reduced reproduction in 

successive generations of mallards, 0.5 μg/g (Heinz, 

1979, p. 400). Concentrations in 30 percent of the 

invertebrate samples exceeded a dietary concentration 

associated with reduced reproduction in a single generation of black ducks and lesions in nerve tissue of 

hatchlings, 3.0 μgig (Finley and Stendell, 1978, p. 61). 

A dietary concentration associated with histopathology 

in bird species, 1.1 μgig (Nicholson and Osborn, 1984), 

34 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
			 			

		

Table 15. Mercury concentrations in unfiltered water, sediment, and biological samples collected from four wetlands in Lahontan Valley, Nevada, April-August 1994-96 

[Geometric-mean (and range) data from U.S. Fish and Wildlife Service. Within each wetland for particular sample medium or type, geometric means having same appended letter (a through c) are not significantly different (p<0.05) across years; correspondingly, differing appended letters indicate significant difference between geometric means. -, no data available or not applicable. <, used with sample mean, indicates that value for more than half of samples was less than 

analytical detection limit; used with range, indicates that value for at least one sample was less than detection limit. In cases where analytical detection limit varied, maximum limit is given] 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMEN

T, AND BIOTA 

Total Mercury in Mercury in biological samples 

mercury in bottom-sediment (micrograms per gram) 

Wetland Year water samples samples 

(micrograms (micrograms Coot Avocet Coot Avocet Detritus Pondweed Hemiptera Fish per liter) per gram) egg egg liver liver 

Stillwater National Wildlife Refuge 

Dry Lake: 1 1994 1<1.1 0.2 a 1<0.2 3.0 b 3.4 b 18.6 b 8.1 

(-) (-) (-) (<0.2-0.2) (2.8-3.2) (-) (1.6-7.6) (-) (4.6-53.1) (2.5-20.2) 

1995 1<0.5 0.2 a 0.2 a 10.1 1.3 a 1.4 a 0.8 a 3.8 a 

(-) (0.1-0.3) (0.1-0.3) (<0.1-0.2) (0.7-2.4) (1.1-1.2) (0.5-1.3) (-) (3.0-5.4) (-) 

1<1.5 11.5 1996 0.2 a 0.2 a 1<0.2 2.3 b 1.4 a 1.0 a 2.5 a 19.2 

(-) (<0.1-0.3) (0.1-0.2) (-) (2.1-2.5) (1.2-1.8) (0.8-1.3) (0.9-3.2) (1.6-4.6) (3.0-32.6) 

Lead Lake: 

1994 12.7 12.3 a 1.3 a 6.2 b 22.1 c 122.4 21.8 b 

(<1.1-5.2) (10.9-14.6) (-) (1.1-1.7) (5.4-7.0) (-) (18.4-26.5) (21.8-23.1) (-) (15.1-45.6) 

1<0.5 13.4 1995 27.3 b 21.9 b 3.1 b 12.2 5.8 b 16.7 b 

(-) (24.3-30.4) (17.7-25.9) (2.0-5.1) (2.9-4.1) (2.2-2.2) (2.6-13.5) (-) (12.5-20.4) (-) 

1996 1<1.5 10.1 a 9.5 a 0.3 a 2.1 a 11.2 3.0 a 12.7 4.5 a 6.5 a 

(-) (7.5-11.2) (7.0-11.7) (0.2-0.3) (1.7-2.7) (0.7-1.6) (2.5-4.1) (2.1-4.6) (1.7-11.0) (6.1-7.0) 

Stillwater Point Reservoir: 

15.2 1994 1<1.1 1.5 a 0.9 a 11.8 1.2 a 1.8 a 4.4 a 19.6 

(-) (1.3-1.9) (-) (0.6-1.4) (1.5-2.6) (0.8-2.3) (0.5-4.0) (4.2-9.5) (1.7-9.8) (5.8-13.8) 

1<0.5 1995 1.4 a 1.6 a 0.3 a 12.6 3.7 b 2.3 a 8.7 a 

(-) (0.1-2.2) (0.8-2.0) (0.2-0.5) (2.6-2.6) (2.7-5.3) (0.7-4.8) (-) (4.2-25.7) (-) 

1996 1<1.5 1.7 a 0.5 a 0.1 a 10.5 2.2 a,b 2.9 a 12.1 10.3 a 

(-) (1.0-2.1) (0.1-2.1) (<0.2-0.5) (-) (1.8-2.7) (1.5-5.9) (-) (6.7-12.4) (-) Carson Lake 

Sprig Pond: 1 12.3 1994 <1.1 5.4a 3.4 b 2.2 b 8.7 b 2.2 a 11.9a 11.8 a 

(<1.1-1.7) (4.5-6.0) (-) (2.3-5.3) (1.7-2.4) (2.0-2.7) (5.6-13.2) (1.3-2.8) (5.6-15.8) (9.6-14.7) 

' 1995 1<0.5 8.6 b 10.9 b 0.3 a 10.8 13.0 3.3 a 2.4 a 10.1 a 7.3 a 

(<0.5-0.6) (5.0-11.0) (9.7-12.0) (0.1-0.7) (10.7-10.8) (2.2-4.5) (2.2-7.4) (1.5-3.2) (4.2-32.2) (6.5-9.9) 

1996 1<1.5 5.7 a 5.9 a 0.6 a 1.2 a 2.7 a 2.1 a 6.4 a 6.1 a 

(-) (5.0-6.0) (5.3-6.6) (0.4-0.9) (1.0-1.6) (-) (2.1-6.3) (0.9-5.4) (3.6-8.8) (2.3-25.9) 

lAnalysis of variance was not attempted because of inadequate sample size or large number of samples having concentrations less than analytical detection limit. 

ffl 
was met or exceeded in 90 percent of the hemipterans, 

89 percent of the fish, and 28 percent of the pondweed 

samples. Through a literature review, Zillioux and others (1993, p. 2260) estimated that the significant toxiceffects threshold concentration for most aquatic bird 

eggs was in the range 1.0 to 3.6 μg/g, wet weight. At 

such concentrations, behavioral effects became apparent, whereas at about 5 μg/g, wet weight, reduced 

hatching success and hatchling survival was evident. 

Overall, concentrations in 33 percent of the aquatic 

bird eggs examined during 1994-96 exceeded 1.0 

μg/g, wet weight, and 5 percent exceeded 5.0 lig/g, wet 

weight. Zillioux and others (1993, p. 2260) also estimated a conservative liver-threshold concentration of 5 

μ,g/g, wet weight, for major toxic effects in aquatic 

birds. During 1994-96, concentrations in 13 percent of 

the bird livers exceeded this threshold. Mercury concentrations in 82 percent of the bird livers exceeded 1.0 

μg/g, wet weight, a concentration associated with 

behavioral effects. 

Mercury contamination in Lead Lake is of particular concern. Mercury concentrations in all eggs collected from this wetland in 1994 exceeded a 

concentration associated with embryotoxicity. Mercury concentrations in samples of livers of juvenile 

avocets collected from Lead Lake during 1994 ranged 

from 3.8 to 11.4 μg/g, wet weight. Three samples 

exceeded concentrations associated with major toxic 

effects in waterfowl. The absence of juvenile coots in 

this wetland during that year may have resulted from 

embryotoxicity or poor hatchling survival associated 

with elevated mercury. Concentrations decreased in all 

media examined during 1994-96. Elevated mercury 

concentrations have been noted in fish and other biota 

in the first few years after inundation of newly constructed reservoirs (Bodaly and others, 1984). 

Increased methylation, mobility, and bioavailability of 

mercury resulting from the inundation of Lead Lake, 

which had been dry from 1989 to 1993, may have 

accounted for increased mercury concentrations in 

1994 and 1995. 

Selenium 

Previous studies in Lahontan Valley identified 

selenium as a concern because of concentrations found 

in potential avian diet (invertebrates and fish) and in 

bird livers (Hoffman and others, 1990; Tuttle and others, 1996). Selenium concentrations in filtered water 

were commonly below the USGS reporting limit of 1.0 

Kg/L, and sample concentrations exceeding the reporting limit were less than concentrations associated with 

adverse effects on fish and wildlife. Also, concentrations in more than half the sediment samples were less 

than the USGS reporting limit of 0.1 μg/g dry weight, 

and the samples exceeding the reporting limit generally 

were consistent with selenium-normal environments. 

However, selenium commonly was elevated in foodchain organisms and in bird tissues. Concentrations in 

invertebrates collected from Stillwater Marsh and Carson Lake generally were less than concentrations associated with increased risk to fish and birds. Selenium 

residues in whole fish seldom exceeded concentrations 

of concern. Selenium in biological media tended to be 

higher in samples from Fernley WMA and from 

Massie and Mahala Sloughs (fig. 1) than in samples 

from other areas. Avian eggs contained residues below 

those associated with teratogenesis or embryonic mortality (Lemly, 1996). Concentrations in bird livers generally were below those associated with reproductive 

effects, and concentrations in waterfowl muscle and 

whole fish were below the Nevada criterion for human 

consumption. 

During 1994-96, selenium concentrations in 

unfiltered wetland water were less than detection limits 

in all water samples. Selenium was detected in 65 percent of the sediment, 27 percent of the detritus, 7 percent of the vegetation, 70 percent of the invertebrate, 

and 81 percent of the fish samples; in all avocet eggs 

and all but one of the coot eggs; and in coot and avocet 

livers (table 16). Because selenium concentrations in 

the majority of water, detritus, and vegetation samples 

were less than the detection limits, statistical relations 

were not examined for these media. Selenium concentrations in sediment significantly correlated with concentrations in hemipterans (p = 0.041, r2= 0.355). 

Geometric-mean concentrations of selenium in sediment correlated with mean concentrations in coot livers 

(p = 0.002, r2 = 0.619). 

During 1994-96, selenium concentrations in bird 

livers were lower than those found in previous NIWQP 

investigations. Concentrations in other media in which 

selenium was detected and for which matched samples 

were available were not substantially different. 

Although selenium was not detected in unfiltered wetland water, the detection limits reported by the USFWS 

laboratory (5 to 6 pg/L), exceeded waterborne concentrations associated with long-term adverse effects in 

fish and wildlife populations, 2.0 Kg/L (Lemly, 1996, p. 

432). A selenium concentration of 1.0 μgig in sediment 

36 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
		

		

	 	 	

	 	

		

		

		

		 			

		

Table 16. Selenium concentrations in unfiltered water, sediment, and biological samples collected from four wetlands in Lahontan Valley, Nevada, April-August 1994-96 

[Geometric-mean (and range) data from U.S. Fish and Wildlife Service. Within each wetland for particular sample medium or type, geometric means having same appended letter (a through c) are not significantly different (p<0.05) across years; correspondingly, differing appended letters indicate significant difference between geometric means. -, no data available or not applicable. <, used with sample mean, indicates that value for more than half of samples was less than 

analytical detection limit; used with range, indicates that value for at least one sample was less than detection limit. In cases where analytical detection limit varied, maximum limit is given] 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARAC

TERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 

Wetland Year 

Total 

selenium in 

water samples 

(micrograms 

per liter) 

Selenium in 

bottom-sediment 

samples 

(micrograms 

per gram) Detritus Pondweed Hemiptera Fish Coot 

egg 

Selenium in biological samples 

(micrograms per gram) 

Avocet 

egg 

Coot 

liver 

Avocet 

liver 

Stillwater National Wildlife Refuge 

Dry Lake: 

1994 1<6.0 11.0 1<1.0 1.8 a 10.7 7.3 b 1

7.9 

(-) (0.8-1.1) (-) (1.3-2.6) (-) (<0.5-1.8) (-) (4.5-9.9) (5.8-9.4) 

1995 1 <5.0 1<1.0 1<0.5 2.2 b 1<0.5 11.5 2.2 a 

(-) (-) (2.2-2.3) (-) (1.4-1.7) (-) (1.6-3.5) 

1996 1 <5.6 1 <0.5 1<1.0 1.6 a 11.1 11.4 13.0 2.2 a 

(-) (<0.5-0.7) (-) (1.5-1.9) (<0.9-2.0) (1.0-1.9) (2.3-4.5) (1.7-2.6) 

Lead Lake: 

1994 1.7 b 1<1.0 3.2 b 1.5 a 13.0 6.8 a 

(-) (1.5-2.0) (-) (-) (3.0-3.8) (1.3-1.7) (2.9-3.0) (-) (2.1-11.3) 

1995 1<5.0 1.0 a 1<1.0 1<0.5 1 2.1 2.3 b 3.9 a 

(-) (<1.0-1.3) (<1.0-1.1) (<0.5-0.7) (-) (1.7-3.4) (-) (3.3-4.5) (-) 

1996 1 <5.6 0.9 a 10.6 1<1.0 1.8 a 1.9 a,b 12.6 4.4 a 9.7 a 

(0.6-1.1) (<0.5-0.9) (-) (1.0-2.1) (1.7-2.2) (2.4-2.9) (3.2-7.7) (9.2-10.0) 

Stillwater Point Reservoir: 

1994 1.<5.6 1 0.8 1<1.0 1<1.0 1.6 b 1.4 a 13.8 2.6 a,b 18.4 

(-) (0.6-1.0) (-) (<1.0-1.5) (-) (1.4-1.9) (0.7-2.8) (2.8-4.8) (1.6-3.3) (6.0-11.4) 

1995 1<5.0 1<1.0 10.6 1<0.5 11.4 2.1 b 1.9 a 2.1 a 

(-) (-) (<0.5-1.0) (-) (-) (1.4-2.7) (1.7-2.1) (-) (1.6-3.8) 

1996 t<5.6 10.7 1<1.0 1<1.0 1<0.9 0.7 a 1.9 a 15.0 3.7 b 

(-) (0.6-0.9) (-) (-) 

Carson Lake 

(<0.9-1.2) (1.2-2.7) (-) (3.2-4.6) (-) 

Sprig Pond: 

1994 1<6.0 10.7 1<1.0 1<1.0 1.9 b 2.1 a 4.5 b 6.1 b 

(-) (0.5-1.3) (-) (<1.0-1.0) (-) (1.7-2.2) (1.5-2.7) (1.7-7.5) (3.0-8.8) 

1995 1<5.0 1<1.0 1<1.0 1<0.5 11.5 1.4 a 1.6 a 2.1 a 3.2 a 

(-) (-) (-) (-) (-) (1.2-1.6) (1.1-2.4) (1.6-2.6) (2.9-3.4) 

1996 1<5.6 10.5 1<0.5 1<1.0 1<0.8 1.3 a 1.5 a 2.5 a 4.3 a,b 

(-) (<0.5-0.8) (<0.5-0.7) (-) (-) (-) (0.9-1.8) (1.2-1.9) (2.0-2.9) (3.3-6.4) 

1Analysis of variance was not attempted because of inadequate sample size or large number of samples having concentrations less than analytical detection limit. 
is the minimum concentration associated with effects 

on bird reproduction, and 4.0 μg/g is associated with 

severe effects (U.S. Department of the Interior, 1998, p. 

153). Mean selenium concentrations in sediment from 

Dry Lake in 1994 and from Lead Lake in 1994 and 

1995 exceeded 1.0 μg/g. No selenium concentrations 

in individual sediment samples exceeded 4.0 μg/g. 

With the exception of hemipteran samples collected 

from Lead Lake in 1994 (3.0 to 3.8 μg/g), selenium 

concentrations in organisms that are part of the avian 

diet were less than a selenium concentration of concern, 3.0 μg/g (Skorupa and others, U.S. Fish and Wildlife Service, written commun., 1996). Geometric-mean 

selenium concentrations in coot eggs, at less than 3.0 

μg/g, were within the range of normal concentrations 

of selenium in aquatic bird eggs (Skorupa and Ohlendorf, 1991, p. 362). The geometric-mean concentration 

in avocet eggs collected from Stillwater Point Reservoir exceeded this concentration but was below the 

lower boundary of mean selenium concentrations in 

eggs associated with impaired egg hatchability among 

shorebirds, 8.0 μg/g. Also, concentrations in livers of 

juvenile avocets and coots were below concentrations 

associated with reproductive impairment (Heinz, 1996, 

p. 452). 

Other Trace Elements 

Lead 

The Nevada water-quality standard for lead for 

protection of aquatic life is based on water hardness 

(Nevada Administrative Code 445.1339). For wetlands 

in Lahontan Valley, Hoffman and others (1990, p. 29) 

reported a median hardness of 440 mg/L as CaCO3, 

which equates with a 96-hour average lead standard of 

5.2 μg/L. During 1994-96, lead concentrations 

exceeded detection limits (6 to 11 μg/L) reported by the 

USFWS laboratory in 11 percent of the wetland water 

samples. All detected concentrations, ranging from 6 to 

15 μg/L, exceeded the chronic aquatic-life standard 

(table 1). Although detected concentrations exceeded 

concentrations associated with low-level reproductive 

impairment in Daphnia magna (U.S. Environmental 

Protection Agency, 1985b), they were well below levels associated with lethal or sublethal effects on fish at 

elevated water hardness (Eisler, 1988, p. 61-64). Similarly, lead concentrations in sediment were below levels associated with toxicity to freshwater invertebrates, 

31 μg/g (Persaud and others, 1993, p. 3) and estuarine 

and coastal marine invertebrates, 35 μg/g (Long and 

Morgan, 1991, p. 40). 

Molybdenum 

The Nevada water-quality standard for molybdenum for the protection of aquatic life is 19 μg/L. During 1994-96, 23 percent of the detected concentrations 

in wetland water samples, ranging from 10 to 80 μg/L, 

exceeded the Nevada aquatic-life standard. Low-level 

mortality (LC1) of rainbow trout was found at a molybdenum concentration of 28 μg/L, and a higher level of 

mortality (LC50) at concentrations exceeding 790 μg/L 

(Birge and others, 1979a, p. 523). Molybdenum concentrations during 1994-96 were well below levels 

associated with higher levels of mortality. Molybdenum also was below concentrations associated with 

aquatic-invertebrate mortality (Eisler, 1989, p. 28). 

Zinc 

Zinc was detected in 48 percent of the wetland 

water samples. The highest concentrations were in 

samples from Dry Lake. Zinc was not detected in samples from Stillwater Point Reservoir. Similar to lead 

toxicity, zinc toxicity to aquatic organisms correlates 

inversely with water hardness (U.S. Environmental 

Protection Agency, 1987). Standards for the protection 

of aquatic life are based on water hardness. Zinc concentrations observed during 1994-96 were below the 

chronic aquatic-life standard, 316 μg/L, calculated for 

the mean water hardness of Lahontan Valley wetlands 

(Hoffman and others, 1990, p. 29). Although zinc concentrations in pondweed (20-828 μg/g) and hemipterans (99-323 μg/g) were below dietary concentrations 

associated with reduced survival of mallards, 3,000 

μg/g (Gasaway and Buss, 1972), concentrations in 23 

percent of the pondweed and in 40 percent of the hemipteran samples exceeded a dietary concentration associated with immunosuppression in domestic chickens, 

178 μg/g (Stahl and others, 1989). 

Interactive Effects of Trace Elements 

The combined effects of elevated contaminants 

measured in this study on fish, wildlife, and their habitat are largely uncertain. Although the combined 

effects of contaminants were not examined directly 

during this monitoring program, previous investigations demonstrated that water collected from selected 

agricultural drains and wetlands in Lahontan Valley 

was toxic to freshwater and saltwater fish larvae and 

invertebrates (Dwyer and others, 1992; Ingersoll and 

others, 1992; Finger and others, 1993; Lemly and 

38 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
others, 1993). Mortality occurred over a broad range of 

specific conductance. Although no single trace element 

exceeded toxic concentrations, Finger and others 

(1993, p. 37) noted that water samples that were toxic 

to fish and invertebrates contained elevated arsenic, 

boron, lithium, and molybdenum concentrations 

compared to background sites. During 1994-96, 

specific conductance and concentrations of arsenic, 

boron, and molybdenum in water samples collected 

from Dry Lake were below the ranges associated with 

toxicity as reported by Finger and others (1993, p. 26). 

Concentrations of lithium were not determined for 

these samples. Concentrations of arsenic, boron, and 

molybdenum in Sprig Pond and Stillwater Point Reservoir were near the lower end of the range associated 

with toxicity. For all 3 years, concentrations of these 

three constituents in Lead Lake exceeded levels associated with toxicity. 

Assessment of toxicity using 5- and 15-minute 

Microtox procedures indicated that unfiltered water 

collected from Dry Lake in 1995 and Lead Lake in 

1996 elicited a reduction in metabolic activity of Photobacterium phosphoreum. No other sample indicated 

toxicity (EC50>100 percent for all 5- and 15-minute 

observations). In 1995, although Dry Lake water 

apparently indicated toxicity (EC50=83 percent), the 

95-percent confidence interval was wide (from 3 to 

greater than 100 percent) and metabolic response 

across the range of dilutions was inconsistent. Thus the 

observed response was likely due to error in the methodology rather than actual toxicity. Microtox testing 

indicated that water samples collected from Lead Lake 

in 1996 were toxic (EC50=23 percent and 22 percent 

for 5- and 15-minute observations, respectively). In 

1996, pH, specific conductance, and trace-element concentrations in Lead Lake generally were lower than 

concentrations found in 1994, when no metabolic 

depression was observed in the Microtox assays. This 

difference suggests that the observed toxicity to test 

organisms was not caused by these constituents. 

The toxicity of individual trace elements to birds 

may be altered in the presence of other trace elements. 

Interactions between mercury and selenium have been 

documented extensively (U.S. Department of the Interior, 1998). Several investigators have noted antagonistic interactions: The toxicity of one or both elements is 

decreased in the presence of the other. However, other 

investigators found synergistic interactions—little 

toxic interaction or increased toxicity. Some of the discrepancy may stem from the various chemical forms of 

selenium and mercury examined in the individual 

studies. In a study administering environmentally relevant forms of mercury (as methylmercury chloride) 

and selenium (as selenomethionine) in diet, antagonistic interaction was evident when survival of adult mallards was examined, but synergistic interaction was 

evident when adverse reproductive effects (for example, reduced egg production, teratogenic effects, and 

reduced duckling survival) were considered (Heinz and 

Hoffman, 1998). Although the concentration of methylmercury chloride administered in that study (10 ug/g) 

was within the upper range of concentrations in potential avian-diet organisms found in this and other studies 

in Lahontan Valley (Rowe and others, 1991; Tuttle and 

others, 1996), concentrations of selenium in avian-diet 

organisms typically are well below the level associated 

with adverse effects by Heinz and Hoffman (1998). 

Earlier investigators noted interactive effects 

from contaminants in agricultural drainage. Hoffman 

and others (1991) examined growth and biochemical 

effects in mallard ducklings maintained on diets containing boron and selenium separately and in combination. Adverse effects were more pronounced when 

these elements were administered concurrently and 

when diets contained reduced protein. Conversely, 

Stanley and others (1994) found that arsenic alleviated 

some adverse effects of selenium when both were 

administered to mallard ducklings in their diet. However, Fairbrother and others (1994) identified impaired 

immune system function in avocet chicks collected 

from areas with elevated concentrations of arsenic, 

boron, and(or) selenium. 

Biological Implications of Contaminants of 

Concern 

Previous investigations in Lahontan Valley identified concerns with dissolved-solids concentrations in 

water and the trace elements aluminum, arsenic, boron, 

chromium, mercury, selenium, and zinc in one or more 

biotic or abiotic media (Hoffman and others, 1990, p. 

75; Tuttle and others, 1996, p. 57). Exposure pathways 

and potential biological effects of the various trace elements differ. Elevated trace-element concentrations 

may produce a variety of effects in wetland species and 

communities. Effects may stem from direct toxicity of 

water and sediment or from exposure of higher organisms to elevated trace-element concentrations through 

food chains. Concentrations of agricultural-drainagePHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 39 
related trace elements found in Lahontan Valley are 

within the range of concentrations associated with a 

variety of direct and indirect effects on fish and wildlife, including altered behavior (Kania and O'Hara, 

1974; Heinz, 1979); biochemical and histological 

effects (Nicholson and Osborn, 1984), immunosuppression (Fairbrother and Fowles, 1990); decreased 

reproduction, malformation of embryos, and mortality 

(Heinz, 1996). Interactive effects of trace elements also 

may modify toxicity and organism response (Hoffman 

and others, 1991; Stanley and others, 1994). Trace-element effects at higher levels of biological organization 

are more difficult to quantify. However, agricultural 

development and associated drain water also have been 

linked to effects on biological communities, such as 

loss of habitat variability (Kerley and others, 1993, p. 

20) and reduced species abundance and diversity 

(Dileanis and others, 1996, p. 63). These communitylevel effects may have been due to increased salinity, 

elevated trace-element concentrations, or both. 

Wetland Communities 

Measures of community structure, such as species diversity and species dominance, are commonly 

used indicators of stress in biological communities 

(Landis and Yu, 1995, p. 208). Water-quality properties 

can affect aquatic-invertebrate- and fish-community 

structure (Plafkin and others, 1989, p. 2.1). In general, 

decreased species diversity or dominance by one or 

few taxa are interpreted as effects of environmental 

stress. However, examples of increased species diversity or decreased species dominance resulting from 

contaminant exposure have been observed. Additionally, such indices disregard inherent dynamic and stochastic properties of an ecosystem, and it may be 

difficult to distinguish normal community dynamics 

from contaminant-induced effects. However, community-structure indices may be used effectively to assess 

community-structure similarity and change over time 

(Newman, 1995, p. 284). Therefore, aquatic-invertebrate and fish composition and other community characteristics were assessed to provide a reference for 

future changes in wetland-community structure. 

Aquatic-Invertebrate Communities 

Several indices are available to characterize 

invertebrate community structure (Newman, 1995, p. 

284). Taxa richness, or the number of taxa in a given 

community, is the most basic measure of community 

structure. Taxa evenness, or the equitability of abundances among species in a community, measures community dominance by one or few taxa. Taxaheterogeneity or species-diversity indices incorporate 

both taxa richness and evenness to provide a measure 

of community composition in relation to the diversity 

and abundance of taxa. Shannon's Index provides a 

measure of heterogeneity. 

Invertebrate taxa collected in Lahontan Valley 

represent at least 6 classes, 15 orders, and 35 families. 

Insecta, encompassing 7 orders and 24 families, was 

the dominant class. In benthic samples, 17 taxa were 

identified (table 17). Chironomid larvae, identified in 

all lakes and all seasons, were generally the most abundant benthic organisms. Other common benthic organisms include ostracods, water boatmen (Corixidae), 

and physid (Physidae) and planorbid (Planorbidae) 

snails. In nektonic samples, 32 taxa were identified 

(table 18); however, 4 of the 32 taxa typically are not 

found in the water column and were thought to have 

been dislodged from aquatic plants during sample collection. Therefore these organisms were excluded from 

calculation of nektonic-community measures. Nektonic taxa dominance shifted between years and wetlands. Daphnia, mayflies (Baetidae), damselflies 

(Coenagriidae), water boatmen, and backswimmers 

(Notonectidae) were the most abundant nektonic invertebrates. The high population density of Daphnia spp. 

(5,000 to 25,000 individuals per sample) in 1995 

skewed the measures of community structure. To 

enable a more meaningful comparison of community 

measures for other taxa among years, Daphnia spp. 

were excluded in the calculation of taxa heterogeneity 

and taxa evenness and in subsequent statistical comparisons. 

The greatest mean density of benthic invertebrates was found in Lead Lake (table 19); this wetland 

also had the lowest taxa richness, evenness, and heterogeneity. Additionally, densities varied substantially 

between years. Although mean densities were lower, 

mean taxa richness, evenness, and heterogeneity in 

Sprig Pond were not significantly different from those 

in Lead Lake. In both wetlands, chironomids dominated the benthic-invertebrate community. Taxa richness, evenness, and heterogeneity were greatest in 

Stillwater Point Reservoir succeeded by Dry Lake 

(table 19). Although chironomids also were the dominant benthic invertebrates in these wetlands, other taxa 

were represented better. 

40 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OFWATER, BOTTOM SEDIMENT, AND BIOTA 

Table 17. Benthic invertebrates in bottom-sediment samples from four wetlands in Lahontan Valley, Nevada, 1994-96 

[Benthic invertebrates: Arranged by phylum. Values are estimated means ± standard deviations for unit area of bottom sediment; totals are for all phyla for given wetland in particular year. n, number of samples. —, taxon or taxa not observed] 

Benthic invertebrates in Carson Lake Benthic invertebrates in Stillwater National Wildlife Refuge (number per square meter (number per square meter ± standard deviation) ± standard deviation) 

Class Order Family or subclass Dry Lake Lead Lake Stillwater Point Reservoir Sprig Pond unit 

1994 1995 1996 1994 1995 1996 1994 1995 1996 1994 1995 1996 

(n=5) (n=2) (n=5) (n=4) (n=4) (n=5) (n=5) (n=2) (n=5) (n=3) (n=4) (n=3) 

Nemertea 

(unknown) (unknown) (unknown) 140+102 100+100 

Nematomorph a 

(unknown) (unknown) (unknown) 20+40 

Arth ropod a 

Ostracoda Podocopa (unknown) 600+167 100+100 20+40 100+100 

Arachnida Trombidiformes Hydrachnidae 20+40 160+320 

Insecta Ephemeroptera Baetidae 40+50 140+230 

Odonata Coenagrionidae 60+80 40+50 — 80+116 — — 

Heteroptera Corixidae 20+40 80+75 100+120 80+100 1,500+3,000 75+80 30+45 

Notonectidae 60+50 50+50 60+50 80+120 20+40 — 

Lepidoptera Nepticulidae 30+45 

Coleoptera Georyssidae 20+40 — 

Staphylinidae — — 30+50 

Diptera Chironomidae 60+120 800+400 3,300+2,330 7,210+1,890 5,460+440 1,060+310 600+490 1,450+450 1,340+1,820 1,330+1,670 2,450+2,250 30+50 

Ephydridae 50+50 — 

Tabanidae 20+40 20+40 20+40 30+50 

Mollusca 

Gastropoda Basommatophora Lymnaeidae — — — 20+40 — — 200+140 

Physidae 80+70 120+70 1,750+2,240 550+950 260+260 400+200 800+0 880+490 130+190 150+190 1,300+1,500 

Planorbidae 20+40 20+40 — 50+50 1,800+2,830 430+330 

Totals 940 950 3,660 9,060 6,010 1,440 1,280 2,550 5,940 1,490 2,680 2,050 
Table 18. Nektonic invertebrates in samples from four wetlands in Lahontan Valley, Nevada, 1994-96 

[Nektonic invertebrates: Arranged by phylum. Values are estimated means + standard deviations for unit volume of water; totals are for all phyla for given wetland in particular year. n, number of samples. —, taxon or taxa not observed] 

Monitoring ofInorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 

Nektonic invertebrates in Stillwater National Wildlife Refuge 

(number per cubic meter ± standard deviation) 

Nektonic invertebrates in Carson Lake 

(number per cubic meter 

± standard deviation) 

Class 

or subclass Order Family Dry Lake Lead Lake Stillwater Point Reservoir Sprig Pond unit 

1994 1995 1996 1994 1995 1996 1994 1995 1996 1994 1995 1996 

(n=5) (n=2) (n=5) (n=4) (n=1) (n=5) (n=5) (n=3) (n=5) (n=5) (n=3) (n=5) 

Nemertea 

(unknown) (unknown) (unknown) 0.2+0.4 

Arthropoda 

Ostracoda Podocopa (unknown) 0.4+0.5 1.6+1.6 0.4+0.5 

Malacostraca Amphipoda (unknown) 0.5+0.5 0.2+0.5 0.4+0.5 

Arachnida Trombidiformes Hydrachnidae 19.7+8.5 0.5+0.5 6.2+4.7 1.1+1.3 1.1+0 7.5+5.5 1.5+0.9 0.6+0.9 0.4+0.5 0.2+0.5 

Araneae Pisauridae 0.2+0.4 0.4+0.5 

Araneidae 1.1+0.9 0.2+0.4 

Insecta Ephemeroptera Baetidae 8.8+14.0 42.4+39.8 0.9+1.7 4.9+1.6 3.2+3.8 13.5+19.9 0.9+1.7 9.4+9.3 

Caenidae 0.2+0.4 1.7+2.5 

Odonata Coenagriidae 22.3+13.3 8.0+0.5 16.1+17.6 — 11.6+22.6 5.4+4.2 7.9+3.1 2.4+2.5 0.2+0.4 0.4+0.5 41.3+31.7 

Gomphidae 0.2+0.4 

Libellulidae 1.1+2.1 0.4+0.5 

Heteroptera Corixidae 14.4+22.9 14.5+11.2 155.3+11.2 249.5+78.8 3.2+0 19.7+8.9 88.5+41.6 20.3+7.2 203.1+319.1 31.3+12.8 39.3+8.1 6.2+8.0 

Gerridae 0.7+1.0 0.2+0.4 

Mesoveliidae 0.4+0.5 1.8+2.5 0.2+0.4 

Notonectidae 104.5+36.2 23.0+8.0 194.9+50.5 15.5+7.4 — 108.2+42.6 9.0+8.7 5.1+6.6 2.1+1.9 5.4+4.4 18.4+16.4 

Trichoptera Phryganeidae 2.8+1.7 

Lepidoptera Noctuidae 0.2+0.4 

Pyralidae 1.1+0.9 

Coleoptera Gyrinidae 0.2+0.4 0.2+0.4 

Haliplidae 0.2+0.4 0.2+0.4 

Staphylinidae 0.4+0.9 0.9+1.0 

Diptera Ceratopogonidae 1.4+2.0 0.2+0.4 

Chironomidae 0.9+1.3 8.6+1.1 1.1+0.7 1.9+1.2 3.2+0 0.2+0.4 3.0+1.8 46.4+41.4 16.3+21.5 0.9+1.0 14.6+11.1 0.4+0.9 

Culicidae 17.5+15.1 

Ephydridae 1.7+1.6 2.9+4.0 

Stratiomyidae 1.1+0 0.2+0.4 0.7+1.0 

Syrphidae 1.9+3.3 1.4+1.3 

Tabanidae 3.0+3.4 

Totals 172.7 56.7 419.4 268.0 8.6 148.1 117.8 104.4 241.6 38.6 63.7 78.4 
		

Although the mean density of nektonic inverte- but one wetland (Dry Lake) were similar to concentrabrates (excluding Daphnia spp.) was greatest in Dry tions previously associated with toxicity to aquatic 

Lake, it varied between years. Densities were more organisms in Lahontan Valley (Finger and others, 

consistent in other wetlands. Taxa richness was great- 1993, p. 26). These three constituents generally correest in Stillwater Point Reservoir, and taxa heterogene- late with measurements of specific conductance. 

ity was greatest in Stillwater Point Reservoir and Dry Molybdenum in water correlated with reduced nekLake. Taxa richness and heterogeneity were lowest in tonic taxa richness (p = 0.024, r2= 0.416). Reduced 

Lead Lake. Apart from the temporary dominance of nektonic taxa heterogeneity correlated with dissolved Daphnia spp. in 1995, hemiptera generally were the solids as specific conductance (p = 0.003, r2= 0.591), 

dominant taxa in all wetlands. arsenic (p<0.001, r2= 0.756; fig. 5), and boron 

During 1994-96, concentrations of arsenic, (p = 0.001, r2= 0.658) in water. Although above the 

boron, and molybdenum in unfiltered wetland water chosen level of significance (p50.05), reduced nektonic 

generally were below levels associated with adverse taxa richness also appeared to correlate weakly with 

effects on aquatic invertebrates. However, concentra- dissolved solids (p = 0.060, r2= 0.311) and with boron 

tions of these constituents in unfiltered water from all (p = 0.075, r2= 0.284). Measures of invertebrateTable 19. Population density and taxa richness, evenness, and heterogeneity for benthic and nektonic invertebrates 

collected from four wetlands in Lahontan Valley, Nevada, 1994-96 

[Density: Estimates for benthic invertebrates are per unit area of bottom sediment, and for nektonic, per unit volume of water. Taxa richness, evenness, and 

heterogeneity are unitless ratios] 

Benthic invertebrates Nektonic invertebrates 

Wetland Density Density 

and year (number Taxa Taxa Taxa (number Taxa Taxa Taxa 

per square richness evenness heterogeneity per cubic richness evenness heterogeneity 

meter) meter) 

Stillwater National Wildlife Refuge 

Dry Lake: 

1994 940 9 0.35 1.35 173 12 0.19 1.27 

1995 950 3 .18 .54 57 9 .31 1.47 

1996 3,660 7 .09 .48 419 11 .16 1.20 

Mean annuals 1,850 a 6.3 b .21 b .79 b 216 c 10.7 b .22 a,b 1.31 c 

Lead Lake: 

1994 9,060 3 0.09 0.55 268 6 0.06 0.40 

1995 6,010 2 .06 .31 9 5 .60 1.26 

1996 1,440 7 .20 .88 148 9 .14 .89 

Mean annual' 5,503 c 4.0 a .12 a .58 a 190 b,c 6.7 a .27 b .85 a 

Stillwater Point Reservoir: 

1994 1,280 7 0.32 1.32 118 16 0.17 1.07 

1995 2,550 6 .28 1.09 104 17 .29 1.66 

1996 5,940 10 .28 1.61 242 12 .20 1.22 

Mean annuals 3,310 b 7.7 c .29 c 1.34 c 154 b 15 c .22 a,b 1.32 c 

Carson Lake 

Sprig Pond: 

1994 1,490 3 0.11 0.40 39 11 0.15 0.76 

1995 2,680 3 .07 .34 64 10 .22 1.12 

1996 2,050 7 .27 1.11 78 11 .22 1.32 

Mean annuals 2,073 a 4.3 a .15 a .62 a 60 a 10.7 b .20 a 1.07 b 

IWithin each metric, mean-annual values having same appended letter (a through c) are not significantly different (p<0.05) across wetlands; correspondingly, 

differing appended letters indicate significant difference between mean-annual values. 

2Taxa richness was based on all species identified in samples. However, taxa not normally expected in benthic samples (such as Daphnia spp.) or in nektonic 

samples (such as gastropods) were excluded from calculation of taxa evenness and heterogeneity. To assist in interpretation, Daphnia spp. were also excluded from 

calculation of these metrics in nektonic samples. 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 43 
community structure did not correlate with aluminum 

in water. The infrequency of detection of lead, mercury, 

and selenium in wetland water precluded meaningful 

statistical interpretation. Other studies have implicated 

these constituents in water with adverse effects on 

aquatic organisms at concentrations where lower levels 

of detection were reported than during the 1994-96 

monitoring program (see section "Concentrations in 

Sampled Media," under "Trace Elements"). Therefore, 

the potential for these elements in water to produce 

adverse effects on aquatic invertebrates and community structure in the Lahontan Valley wetlands remains 

uncertain. 

Bottom sediments having elevated concentrations of trace elements also have been associated with 

adverse effects on aquatic invertebrates, including 

shifts in community structure (Moore and others, 1991; 

Suchanek and others, 1995). During 1994-96, arsenic 

and mercury concentrations in sediment exceeded concentrations associated with effects on benthic invertebrates. Arsenic concentrations in sediment correlated 

directly with reduced taxa evenness (p = 0.034, 

r2= 0.376) and inversely with abundance (p = 0.034, 

r2= 0.376) in benthic invertebrates (fig. 5). Although 

the selected level of significance was exceeded, arsenic 

concentrations in sediment also appeared to be correlated weakly with reduced benthic-invertebrate taxa 

richness (p = 0.086, r2= 0.266) and heterogeneity 

(p = 0.099, r2= 0.248). Arsenic concentrations in sediment also correlated with reduced nektonic-invertebrate taxa richness (p<0.001, r2= 0.737). 

Mercury concentrations in bottom sediment correlated with reduced benthic-invertebrate taxa evenness (p = 0.044, r2= 0.346). Concentrations of mercury 

in sediment more weakly correlated with reduced 

benthic-invertebrate abundance (p = 0.094, r2= 0.225), 

taxa richness (p = 0.052, r2= 0.326), and taxa heterogeneity (p = 0.090, r2= 0.260; fig. 6). Concentrations 

of mercury in sediment also correlated with reduced 

nektonic-invertebrate taxa richness (p = 0.006, 

r2= 0.553). The correlation between mercury concentrations in sediment and reduced nektonic-invertebrate 

taxa evenness approached significance (p = 0.053, 

r2= 0.325). Elevated concentrations of mercury in bottom sediment have been shown to cause adverse effects 

on benthic-invertebrate community structure, including decreased benthic-community heterogeneity, such 

as was measured in Clear Lake, Calif., by Suchanek 

and others (1995), using Shannon's Index. 

Selenium concentrations in bottom sediment correlated with reduced benthic-invertebrate abundance 

(p = 0.037, r2= 0.366) and nektonic-invertebrate heterogeneity (p = 0.011, r2= 0.492). However, these correlations were weakened because the concentration of 

selenium was below analytical detection limits in 35 

percent of the samples. 

Published information on biological-effect concentrations of aluminum and boron in bottom sediment 

is sparse. However, concentrations of these two elements in sediment did not correlate with measures of 

benthic- or nektonic-invertebrate community structure. 

Vertebrate Communities 

Fish Communities 

Active fish-collection methods can be difficult to 

apply, so passive collection methods (traps) were used. 

Because passive sampling techniques may be selective 

for fish species and size (Hubert, 1983), fish captured 

during this investigation may not be entirely representative of species assemblage or population-size distribution within each wetland. For example, mosquitofish 

(Gambusia affinis), which tend to be small and slender, 

were observed in shallow backwater areas in all wetlands, but were rarely captured or retained in minnow 

traps. Therefore, it was deemed inappropriate to report 

capture success or size distributions for this species. 

One native fish species—tui chub (Gila 

bicolor)—and four nonnative fish species—common 

carp (Cyprinus carpio), pumpkinseed (Lepomis gibbosus), fathead minnows (Pimephales promelas), and 

mosquitofish—were identified in the four study wetlands. Based on capture efficiencies, fish appeared to be 

most abundant in Lead Lake and Dry Lake, and species 

assemblages were very similar in the two wetlands (fig. 

7). Overall, the smallest number of fish were captured 

in Sprig Pond despite more-intensive efforts with minnow traps, hoop nets, and gill nets set at several locations around the wetland. 

Because of low fish-catch rates, little can be 

deduced from fish data. In general, fish appeared to be 

in good health, with no external or encysted parasites, 

external fungus or lesions, hemorrhaging, or tumors. 

Spinal deformations were noted in two fathead minnows from Lead Lake; however, these represented less 

than 1 percent of the samples. Fin erosion, seen on a 

number offish from all wetlands, may have been due to 

the capture techniques (fish traps), which required 

holding and concentrating fish in the traps for 24 hours 

or more. 

44 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
• 

• • 

• 

• 

• • • 

• • 

• 

• 

• 

• 

• 

• 

• • 

• 

• 

• 

• • 

			

A B 

20 

18 /0.164 -, p<0.000 - 

TAXA RICHNESS 

r 2=0.184 r 2=0.737 

16 • • _ 

_ - 

12 • • 

10 • • _ 

8 

6 • • 

14 

_ 

4 

2 

0 

C 

10.0 

D 

0.9 p=0.083 _ p=0.148 _ 

r 2=0 .270 r2=0.217 

0.8 

TAXA EVENNESS 

0.7 

0.6 • • - 

0.5 _ - 

0.4 

0.3 

0.2 

0.1 

0 

- 

• • 

• 

• S. 

• • 

• • 

• 

• 

-• 

-

• 

Ilb• • 0 s 5 

• • 

• 

E F 

2.0 

1.8 p<0.000 - p=0.118 

r 2=0.753 r2=0.227 _ 

HETEROGENEITY 

1.6 _ 

1.4 

• • iL • w • 0

•4) • 

1.2 

1.0 

0.8 • 

- 

_ 

0.6 - 

0.4 • • 

0.2 

0 

0 25 50 75 100 125 150 175 200 10 15 20 25 30 35 

ARSENIC IN WATER, ARSENIC IN SEDIMENT, 

IN MICROGRAMS PER LITER IN MICROGRAMS PER GRAM 

Figure 5. Relations between arsenic concentrations, in wetland water and in sediment, and nektonicinvertebrate community metrics (unitless ratios). 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 45 
TAXA RICHNESS 

20 

0 0 

15 

- -0- 

-aa__ ..... 10 D 0 o 

• • • 0 

5 

• • • • 

0 

0 5 10 15 20 25 30 

MERCURY IN SEDIMENT, IN MICROGRAMS PER GRAM 

EXPLANATION 

Nektonic invertebrates (p = 0.006; r 

2 = 0.553) 

o Data point 

Trend in data 

Benthic invertebrates (p = 0.052; r 

2 = 0.326) 

• Data point 

Trend in data 

Figure 6. Relations between mercury concentrations in wetland sediment and benthic- and 

nektonic-invertebrate taxa richness (unitless ratios), showing regression lines or trends in 

data. 

Environmental stress can affect growth rate and 

general condition of fish. Numerical condition factors, 

such as Fulton's condition factor, provide a measure of 

relative nutritional state or well-being of individual fish 

and populations (Anderson and Gutreuter, 1983, p. 

294). Such factors also may be used to compare relative condition of populations and for monitoring environmental changes over time (Ney, 1993, p. 140). In 

general, the condition factor is smaller in individuals 

whose weight-to-length ratio is less than expected, possibly because of a poorer overall nutritional state. 

Because length-weight relationships are species dependent, interspecific comparisons may not be appropriate. 

Similarly, length-weight relationships may vary with 

fish age and season. Fish condition, as determined by 

Fulton's condition factor, was inconsistent among wetlands and species (table 20). For example, no statistical 

difference in Fulton's condition factor was found 

between tui chub from Dry Lake and those from Lead 

Lake. However, Fulton's condition factor was significantly greater for pumpkinseeds and significantly 

smaller for fathead minnows collected from Dry Lake 

when compared to those from Lead Lake. 

Because of low fish catches regardless of wetland 

or year, statistical relations between contaminant concentrations and fish abundances and condition were not 

examined. 
	 

 

					 		

		

		

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICSOF WATER, BOTTOM SEDIMENT, AND BIOTA 

r- 71 SPECIES COMPOSITION, IN PERCENT 

Z =CI 

C 0 C 01 co CD 0 0 O O O O O O 0 O 0 0 3 R. 7131 

CT A) ..,, 

CD Z . -"' 

0 < m ..., 2.) -th-• II ii: co = - Co N "0 

.-0.' CTI, < 2. 5co ,:„ . sl) a I. II 

-a -...a IIm co co 

(15 co -0 u. cn Coo c4 RI-cri r.n. -i r) ''t '71 V 

__ 5-:. E. ..C.D rm F.L. R. 

• 9) `5' II 

a) 

5' . r Cs co cr 

3911da1 3d1141IM 

1VNOLLVN 1:131V/V\1111S 

(-D cp 5 a .= o 

N 

CD 

C -0 w ro o_ 7C CI) 

m 0 co •=,a CO 

z 

Table 20. Length, weight, and Fulton's condition factor for selected fish species, representing different size classes, collected from four wetlands in Lahontan 

Valley, Nevada, 1995-96 

[—, no data] 

Fathead minnow Pumpkinseed1 Carp1 Tui chubs 

Mean Mean Mean Mean Wetland Mean length Mean weight Fulton's Mean length Mean weight Fulton's Mean length Mean weight Fulton's Mean length Mean weight Fulton's 

(inches) (ounces) condition (inches) (ounces) condition (inches) (ounces) condition (inches) (ounces) condition 

factor factor factor factor 

Stillwater National Wildlife Refuge 

21.3 Dry Lake 2.5+0.2 0.11+0.03 1.3+0.2 a 1.9+0.9 0.15+0.28 1.9+0.4 b 2

2.6 20.13 2.2+0.3 0.07+0.02 1.2+0.2 b 

Lead Lake 2.0+0.1 0.08+0.02 1.7+0.1 b 1.8+0.4 0.06+0.05 1.7+0.2 a 3.3+0.9 0.39+0.29 1.5+0.1 a 2.1+0.1 0.05+0.1 1.2+0.1 b 

Stillwater Point 1.9+0.3 0.07+0.03 1.7+0.2 a 2.9+0.4 0.27+0.11 1.9+0.5 a 1.9+0.1 0.04+0.01 0.9+0.1 a 

Reservoir 

Carson Lake 

Sprig Pond 3.0+0.4 0.34+0.13 b 2.0+0.2 a 

1Mean Fulton's condition factors having same appended letter (a through c) are not significantly different (p<0.05); correspondingly, differing appended letters indicate significant difference between factors. 

2Single fish sample. 
The 1131, a community-condition index based on 

as many as 12 metrics related to fish-community taxonomic and trophic structure, abundance, and general 

health, was developed to assess the relative condition 

of stream fish communities (Plafkin and others, 1989). 

Although the IBI was not developed for palustrine fish 

communities, several of the metrics are applicable to 

the marsh habitat. Because IBI methodologies were 

designed to provide a reproducible fish-community 

indexing tool, these metrics may be useful in the future 

assessment of relative status and trends in Lahontan 

Valley wetland fish communities. Therefore, scoring 

listed in table 21 is provided only for comparison of 

fish-community condition in the four study wetlands 

and to provide a basis for future comparisons. 

Community-condition scores were similar for 

Dry Lake, Lead Lake, and Stillwater Point Reservoir 

and were slightly lower for Sprig Pond (table 21). Scoring was affected strongly by depauperate fish communities, the dominance of tolerant species, and the 

indiscriminate dietary habits of the representative 

fishes. Fish communities in these wetlands possess 

many of the characteristics of a degraded fishery, 

including limited species diversity, predominance of 

tolerant species, skewed trophic structure, and lack of 

piscivorous fishes (Plafkin and others, 1989, p. 7-8). 

Although not reflected in the 1131 score, age structure in 

all ponds was skewed toward younger individuals. The 

predominance of younger fish in Lead Lake is likely 

attributable to recent recolonization after desiccation 

(or near desiccation) in the early 1990's. It is uncertain 

if lack of larger individuals in other wetlands, which 

have received more reliable water supplies for longer 

periods, reflects recent recolonization, sampling bias, 

or poor survival among adults. 

Bird Communities 

During the eight sampling sessions combined, 79 

bird species were observed (table 22). The highest 

numbers of birds were observed at Sprig Pond and the 

lowest at Dry Lake. However, differences in habitat 

types and visibility among transects are reflected in the 

numbers and species observed. Green-winged teal, cinnamon teal, mallard, yellow-headed blackbird, barn 

swallow, american white pelican, american coot, american avocet, black-crowned night heron, white-faced 

ibis, and marsh wren were generally the most abundant 

species in each wetland. No threatened or endangered 

birds (table 2) were observed during the surveys, and 

white-faced ibis and black tern were the only observed 

species of concern. White-faced ibis were seen in all 

study wetlands but were most common in Sprig Pond 

and Stillwater Point Reservoir. Few black terns were 

found in Sprig Pond and Lead Lake. 

Table 21. Index of Biological Integrity metrics and scores as modified to assess fish assemblages in four wetlands in 

Lahontan Valley, Nevada, 1994-96 

[Score: Ranking based on percentage similarity between calculated and reference-site values, used in bioassessments (Plafkin and others, 1989)] 

Stillwater National Wildlife Refuge Carson Lake 

Scoring criteria 

(percent) 

Index of Biological Integrity 

metrics 

For 

score 

of 5 

Species richness and composition metrics: 

Native fish species > 67 

Benthic fish species > 67 

Tolerant individuals 1 < 10 

Trophic-composition metrics: 

Omnivores <10 

Insectivores > 45 

Main carnivores >5 

Fish abundance and condition metrics: 

Dry Lake 

For For Actual score score Score (count) of 3 of 1 

33-67 < 33 20 

33-67 < 33 0 

10-25 > 25 86 

10-25 > 25 86 1 

20-45 < 20 14 1 

1-5 <1 0 1 

Lead Lake Stillwater Point 

Reservoir Sprig Pond unit 

Actual 

(count) Score Actual 

(count) Score Actual 

(count) Score 

20 1 25 0 

0 1 0 0 

86 1 75 100 

86 1 75 1 100 1 

14 1 25 3 0 1 

0 1 0 1 0 1 

All fish 

Introduced fishes 2 

Fish showing anomalies 3 

Abundant Common Rare 

< 33 33-67 > 67 

< 1 1-5 <5 

Total scores 

Abundant 

76 

0 

5 

1 

5 

17 

Abundant 

76 

0 

5 

1 

5 

17 

Common 

73 

0 

3 

1 

5 

17 

Rare 

100 

0 

1 

1 

5 

13 

1Does not include mosquitofish. 

2Plaflcin and others (1989). 

3Does not include fin damage. 

48 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 

Table 22. Avian species along established transects in four wetlands in Lahontan Valley, Nevada, July—September 1995 and May—September 1996 

[Avian species: Arranged by taxonomic order. n, number of observation periods. species not observed; <, less than; ?, separate species not identified] 

Sightings of avian species 

in Carson Lake Sightings of avian species in Stillwater National Wildlife Refuge (mean number per (mean number per period of observation ± standard deviation) period of observation 

Avian species ± standard deviation) Family (and common name) 

Dry Lake Lead Lake Stillwater Point Reservoir Sprig Pond unit 

1995 1996 1995 1996 1995 1996 1995 1996 

(n=3) (n=5) (n=3) (n=5) (n=3) (n=5) (n=3) (n=5) 

Podicipediformes 

Podicipedidae Aechmophorus occidentalis (western grebe) 17+6 213+30 91+18 38+30 38+24 34+9 31+47 

Podiceps nigricollis (eared grebe) <1+<1 1+1 47+23 31+18 13+19 2+1 8+6 2+5 

Podilymbus podiceps (pied-billed grebe) 1+2 8+4 4+2 2+1 7+5 4+2 2+1 

Pelecaniformes 

Pelecanidae Pelecanus erythrorhynchos (american white pelican) 20+13 16+12 53+54 456+250 9+8 103+83 58+45 165+111 

Phalacrocoracidae Phalacrocorax auritus (double-crested cormorant) <1+<1 36+26 58+51 

Anseriformes 

Anatidae ?(duck species) 715+523 178+262 183+130 141+124 35+50 513+393 562+405 191+191 

Aix sponsa (wood duck) <1+<1 <1+1 

Anas acuta (northern pintail) 41+30 27+37 8+3 5+3 11+9 6+9 33+23 4+6 

Anas americana (american wigeon) 25+35 15+30 3+4 5+9 2+2 <1+1 2+4 

Anas clypeata (northern shoveler) 4+4 2+2 1+1 18+14 <1+1 3+2 4+3 1+1 

Anas crecca (green-winged teal) 47+51 5+9 201+270 23+22 9+13 4+4 57+50 3+5 

Anas cyanoptera (cinnamon teal) 25+25 23+19 37+20 56+63 17+4 61+64 257+209 63+59 

Anas discors (blue-winged teal) 9+6 <1+1 <1+<1 3+4 <1+<1 

Anas platyrhynchos (mallard) 71+37 48+33 15+9 29+31 25+2 476+752 63+34 38+43 

Anas strepera (gadwall) 32+25 21+13 64+35 63+36 7+<1 31+22 21+22 13+13 

Aythya americana (redhead) 16+15 11+18 30+14 24+19 56+47 18+20 14+9 22+28 

Aythya collaris (ring-necked duck) <1+<1 — 

Aythya valisineria (canvasback) 2+2 1+1 <1+1 1+1 — 

Branta canadensis (canada goose) 2+1 15+22 10+13 8+11 61+43 3+3 22+15 31+37 

Bucephala albeola (bufflehead) <1+<1 <1+<1 — 

Oxyura jamaicensis (ruddy duck) 1+1 2+2 61+44 60+89 13+18 8+8 9+10 9+7 
o Table 22. Avian species along established transects in four wetlands in Lahontan Valley, Nevada, July—September 1995 and May—September 1996—Continued 

Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 

Sightings of avian species 

Family Avian species 

(and common name) 

Sightings of avian species in Stillwater National Wildlife Refuge 

(mean number per period of observation ± standard deviation) 

in Carson Lake 

(mean number per 

period of observation 

± standard deviation) 

Dry Lake Lead Lake Stillwater Point Reservoir Sprig Pond unit 

1995 1996 1995 1996 1995 1996 1995 1996 

(n=3) (n=5) (n=3) (n=5) (n=3) (n=5) (n=3) (n=5) 

Accipitridae Buteojamaicensis (red-tailed hawk) 

Circus cyaneus (northern harrier) 3+3 

Falconiformes 

1+1 <1+1 <1+1 1+1 

<1+<1 

1+1 1+1 2+2 

Falconidae 

Phasianidae 

Ardeidae 

Falco mexicanus (prairie falcon) 

Falco sparverius (american kestrel) 

Callipepla californica (califomia quail) 

Ardea herodias (great blue heron) 

Bubulcus ibis (cattle egret) 

Casmerodius albus (great egret) 

Egretta thula (snowy egret) 

Botaurus lentiginosus (american bittern) 

Nycticorax nycticorax (black-crowned night-heron) 

1+1 

1+1 

5+5 

1+2 

5+3 

Galliformes 

Ciconiiformes 

2+1 

1+2 

1+1 

1+3 

12+11 

2+2 

<1+1 

6+2 

<1 +< 1 

<1+1 

4+1 

<1+1 

3+2 

2+2 

10+3 

<1+1 

1+1 

6+5 

4+1 

60+29 

1+1 

25+6 

5+4 

4+4 

3+3 

31+21 

1+2 

26+17 

4+3 

13+6 

47+28 

43+9 

8+4 

<11-<1 

20+15 

25+18 

2+3 

45+30 

Threskiornithidae 

Rallidae 

Recurvirostridae 

Plegadis chihi (white-faced ibis) 

Fulica americana (american coot) 

Porzana carolina (sora) 

Rallus limicola (virginia rail) 

Himantopus mexicanus (black-necked stilt) 

Recurvirostra americana (american avocet) 

63+43 16+7 

Gruiformes 

151+148 135+160 

<1+<1 1+1 

1±<1 3+2 

Charadriiformes 

5+8 3+3 

4+4 12+15 

33+28 

451+374 

<1+1 

2+2 

6+3 

1,025+727 

<1+<1 

3+2 

5+3 

807+474 

883+560 

4+6 

24+12 

249+224 

722+716 

1+<1 

1+2 

5+9 

14+22 

766+106 

665+298 

2+1 

1+1 

18+19 

49+51 

1567+1421 

263+184 

5+9 

7+4 

1538+1485 

Charadriidae Charadrius vociferus (killdeer) 4+5 1+<1 1+1 1+1 2+2 6+5 6+7 

Scolopacidae ? (sandpiper species) 

? (peep species) 

Actitis macularia (spotted sandpiper) 

Calidris alpina (dunlin) 

Calidris minutilla (least sandpiper) 

Limnodromus spp. (dowitcher species) 11+15 

2+4 

<11-<1 

<1±<1 

15+30 

<1+<1 

<1+<1 

<1+<1 

40+80 

— 

4+4 31+57 

<1+1 

7+12 

30+60 

<1+1 

15+23 

7+12 
Charadriiformes—Continued 

PHYSICAL, CHEMICAL, ANDBIOLOGICALCHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 

Phalaropodidae 

Laridae 

Columbidae 

Strigidae 

Caprimulgidae 

Picidae 

Tyrannidae 

Alaudidae 

Hirundinidae 

Numenius americanus (long-billed curlew) 

Tringa melanoleuca (greater yellowlegs) 

Tringa totanus (redshanks) 

Phalaropus lobatus (red-necked phalarope) 

Phalaropus tricolor (wilson's phalarope) 

Phalaropus spp. (phalarope species) 

? (gull species) 

Chlidonias niger (black tern) 

Larus californicus (california gull) 

Larus delawarensis (ring-billed gull) 

Larus philadelphia (bonaparte's gull) 

Larus pipixcan (franklin's gull) 

Sterna caspia (caspian tern) 

Sterna forsteri (forster's tern) 

Zenaida macroura (mourning dove) 

Asio flammeus (short-eared owl) 

Chordeiles minor (common nighthawk) 

Colaptes auratus (northern flicker) 

Tyrannus verticalis (western kingbird) 

Eremophila alpestris (horned lark) 

? (swallow species) 

Hirundo pyrrhonota (cliff swallow) 

Hirundo rustica (barn swallow) 

Riparia riparia (bank swallow) 

Stelgidopteryx ruficollis (northern rough-winged swallow) 

Tachycineta bicolor (tree swallow) 

Tachycineta thalassina (violet-green swallow) 

<1+<1 

3+3 

<1+<1 

4+5 <1+1 

2+3 3+3 

2+2 3+5 

5+5 

11+15 

3+4 <1+<1 

2+3 1+1 

Columbiformes 

Strigiformes 

Caprimulgiformes 

3+4 1+2 

Piciformes 

Passeriformes 

2+4 

2+4 

3+4 

8+7 4+3 

1+2 

<1+1 

<1+1 

1+2 

8+12 

9+13 

46+56 

5+3 

6+5 

1+1 

31+23 

2+4 

<1+<1 

1+2 

8+13 

<1+1 

5+3 

1+2 

3+3 

3+2 

<1+<1 

1+1 

33+44 

1+1 

1+1 

11+21 

<1+<1 

42+79 

<1+1 

<1+1 

5+5 

1+1 

1+1 

<1+1 

7+8 

1+1 

33+47 

17+24 

176+234 

2+2 

1+1 

1+1 

1+1 

8+15 

2+4 

2+2 

3+3 

1+2 

3+4 

<1+<1 

1+1 

2+3 

2+3 

23+39 

3+3 

33+61 

1+1 

<1+1 

4+7 

1+1 <1+1 

<1+1 

<1+1 

1+1 

2+2 

400+295 5+7 

<1+1 5+6 

6+5 4+3 

9+7 1+1 

<1+1 

<1+1 

<1+1 19+16 

1+2 <1+<1 

<1+<1 

1+3 

18+36 

<1+1 1+3 

3+2 22+41 

2+4 

2+4 

4+8 

cri 
U1 

Table 22. Avian species along established transects in four wetlands in Lahontan Valley, Nevada, July—September 1995 and May—September 1996—Continued 

Monitoring ofInorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 

Sightings of avian species 

Family Avian species 

(and common name) 

Sightings of avian species in Stillwater National Wildlife Refuge 

(mean number per period of observation ± standard deviation) 

in Carson Lake 

(mean number per 

period of observation 

± standard deviation) 

Dry Lake Lead Lake Stillwater Point Reservoir Sprig Pond unit 

1995 1996 1995 1996 1995 1996 1995 1996 

(n=3) (n=5) (n=3) (n=5) (n=3) (n=5) (n=3) (n=5) 

Passeriformes—Continued 

Corvidae Corvus corax (common raven) 1+<1 3+3 1+1 <1+1 1+1 <1+<1 

Pica pica (black-billed magpie) 1+1 1+1 <1+<1 <1+<1 

Troglodytidae Cistothorus palustris (marsh wren) 45+8 33+9 19+10 19+4 21+18 17+11 15+6 29+12 

Laniidae Lanius ludovicianus (loggerhead shrike) 1+1 

Sturnidae Sturnus vulgaris (european starling) 8+16 

Purulidae Geothlypis trichas (common yellowthroat) 1+1 3+6 

Icteridae ? (blackbird species) <1+<1 17+24 

Agelaius phoeniceus (red-winged blackbird) 7+4 46+46 11+9 7+6 2+3 35+26 <1+1 5+4 

Euphagus cyanocephalus (brewer's blackbird) 1+1 <1+1 4+8 1+1 

Molothrus ater (brown-headed cowbird) 1+1 3+5 3+4 <1+1 

Sturnella neglecta (western meadowlark) 5+2 6+3 6+6 2+1 — 2+3 <1+1 <1+<1 

Xanthocephalus xanthocephalus (yellow-headed blackbird) 28+15 17+9 66+61 17+14 48+36 27+20 71+56 82+77 

Fringillidae Amphispiza belli (sage sparrow) 5+5 1+1 1+2 1+2 1+1 2+2 2+2 

Melospiza melodia (song sparrow) 6+4 12+5 8+6 7+3 1+1 2+3 <1-1-<1 

Zonotrichia leucophrys (white-crowned sparrow) 1+2 <1+<1 

Total number of individual birds (all taxa) observed 1,410 717 1,690 2,374 2,436 2,590 3,291 4,287 

Total number of distinct species (all taxa) observed 49 60 41 66 49 66 47 56 
Wetland Habitat 

Dramatic changes in areal extent of the wetlands 

were observed from 1994 to 1996 (table 23). The 

changes were attributed to above-normal precipitation 

and runoff during 1995 and 1996 after below-normal 

precipitation and runoff from the Sierra Nevada in the 

late 1980's and early 1990's during a regional drought. 

As a result of that drought, wetland acreage in Stillwater NWR and Carson Lake had dwindled to about 1,000 

acres during 1992 (William Henry, U.S. Fish and Wildlife Service-Stillwater National Wildlife Refuge, written commun., 1997). Conversely, Carson River flows 

below Lahontan Reservoir were 111 percent of the 

period-of-record mean annual flow volume in 1995 and 

122 percent of the average in 1996. These greater flow 

volumes resulted in an areal expansion of wetlands. 

The majority of the increase was in expansive shallow 

wetlands in areas lower on the hydrologic gradient. 

Water entered the southwestern part of Stillwater NWR 

primarily through two irrigation-water delivery conduits (D Line and S Line Canals) and four major agricultural drains (Stillwater Point Reservoir Diversion 

Canal, Stillwater Slough, Paiute Drain, and Paiute 

Diversion Drain). The initial wetlands included Stillwater Point Reservoir, lakes on Canvasback Gun Club 

lands, and Lead Lake. However, irrigation-quality 

water also has been discharged directly to Dry Lake 

since 1991. Water flowing from the initial wetlands 

flooded sequential wetlands down the hydrologic gradient toward Carson Sink to the northeast. 

During 1994-96, gradual changes in wetland 

plant communities were observed in Stillwater NWR. 

Initial wetlands (higher on the hydrologic gradient) 

were typically deeper (3-6 ft) and more perennial in 

nature. Emergent vegetation, typically hardstem bulrush (Schoenoplectus acutus), was abundant in deeper 

water habitats (greater than 3 ft), whereas cattails 

(Typha spp.) were abundant in shallower habitats. 

Alkali bulrush (Bolboschoenus maritimus) with interspersed sedges and rushes was common around the 

ephemeral perimeter of the wetlands. Pondweed (Potamogeton spp.), primarily sago pondweed (Potamogeton pectinatus), was abundant in open-water habitats. 

Wetlands downgradient from the initial wetlands were 

typically shallower (less than 3 ft) and had narrow 

bands of cattails and alkali bulrush around the periphery. Cattails and hardstem bulrush were less common, 

and alkali bulrush became the dominant emergent plant 

with increased distance from the initial inflow. Similarly, pondweed was the dominant aquatic vegetation 

in open-water habitats in wetlands higher on the hydrologic gradient, but muskgrass (Chara spp.) and widgeongrass (Ruppia maritima) became more abundant 

in wetlands lower on the hydrologic gradient. Recently 

flooded wetlands farthest from the inflows typically 

were very shallow and nearly devoid of emergent and 

aquatic vegetation. 

Table 23. Area of wetlands, Stillwater National Wildlife Refuge 

and Carson Lake, Nevada, August-September 1994-96 

Areal 

(acres) 

Wetland Year 

Open 

water 

Emergent 

vegetation Total 

Stillwater National Wildlife Refuge 

Dry Lake: 

1994 320 40 360 

1995 130 430 560 

1996 760 1,470 2,230 

Lead Lake: 

1994 260 270 530 

1995 530 460 990 

1996 930 1,950 2,880 

Stillwater Point Reservoir: 

1994 190 240 430 

1995 280 1,150 1,430 

1996 470 810 1,280 

Stillwater Marsh areal: 

1994 2,200 2,000 4,200 

1995 4,300 8,200 12,500 

1996 14,700 11,700 26,400 

Carson Lake 

Sprig Pond: 1994 310 1,400 1,710 

1995 700 3,000 3,700 

1996 740 2,670 3,410 

Carson Lake area3: 

1994 1,270 4,130 5,400 

1995 1,880 7,100 8,980 

1996 2,670 7,050 9,720 

1Rounded to nearest 10 acres. 

2lncludes Canvasback Gun Club lands (see fig. 2). 

3Total wetlands area, including Sprig Pond (see fig. 3). 

PHYSICAL, CHEMICAL, AND BIOLOGICAL CHARACTERISTICS OF WATER, BOTTOM SEDIMENT, AND BIOTA 53 
Of the three wetlands on Stillwater NWR 

assessed in the 1994-96 study, the most diverse of wetland plant communities were in the wetlands at Stillwater Point Reservoir. The dominant emergent-vegetation 

species were hardstem bulrush and southern cattail 

(Typha domingensis); alkali bulrush and inland saltgrass (Distichlis spicata) were around the wetland 

perimeter. Hardstem bulrush and southern cattail 

formed dense monotypic stands. Pondweed, primarily 

sago pondweed, was the dominant submergent-plant 

species. Aquatic vegetation was sparse in ephemeral 

areas around much of the wetland perimeter, although 

saltcedar (Tamarix ramosissima), a nonnative plant, 

was encroaching on ephemeral shores near the perimeter. Dry Lake consisted of a large, open water body 

fringed by cattails and alkali bulrush. Pondweed was 

again the dominant aquatic plant throughout the openwater areas. Salt grass was abundant in ephemeral 

areas around the perimeter. Also dominated by open 

water, Lead Lake had narrow bands of hardstem bulrush, alkali bulrush, and cattails fringing much of the 

lake. Emergent communities were more extensive in 

shallow areas toward the east side of the wetland. Saltcedar encroached on ephemeral areas along much of 

the shoreline and shallow areas within the wetland. 

Smotherweed (Bassia hyssopifolia), another nonnative 

plant, also was common around the perimeter. Submergent vegetation was uncommon throughout most of 

this wetland, although localized stands of longleaf 

pondweed (Potamogeton nodosus) were in the sampling area. Plant-community diversity also was relatively high in wetlands and open water of Carson Lake. 

Southern cattail and hardstem bulrush were the dominant emergent-plant species, and pondweed was abundant in open water in northern Sprig Pond. In the 

southern part of the wetland, alkali bulrush was the 

dominant emergent species around the perimeter, and 

muskgrass was abundant in the extensive open-water 

area. 

Irrigation-Induced Effects on Ecosystem 

Irrigation-induced effects on fish and wildlife and 

on their habitat in the Western United States are attributed largely to human modification of natural hydrologic characteristics and wetland processes and water 

supplies (Lemly and others, 1993, p. 2265). These 

modifications typically include the diversion of relatively fresh water prior to its entering wetlands, resulting in the desiccation of some wetlands and the 

alteration of natural hydrologic characteristics of others. In some cases, previously flow-through wetlands 

have become hydrologically isolated and serve as sinks 

in local topographic-low areas. Application of irrigation water to previously arid soils and the discharge of 

irrigation drainage to wetlands has also caused substantial changes in the biogeochemical cycling of many 

major and trace constituents (Lemly and others, 1993). 

Drainage from agricultural areas, including operational 

spills, surface runoff from fields, and subsurface drainage, may constitute a significant percentage of water 

entering wetlands. Agricultural drain water, particularly subsurface drainage, commonly contains elevated 

concentrations of dissolved solids, including a variety 

of major constituents and trace elements, which may 

have been mobilized from soils or local groundwater. 

Evaporative water loss may further concentrate these 

materials in wetlands. Hydrologically isolated wetlands in arid areas of the Western United States are 

particularly susceptible to persistent contaminant accumulation and concentration (Seiler, 1995). Because 

wetland communities are determined largely by hydrologic characteristics and water quality (Mitsch and 

Gosselink, 1986, p. 55 and p. 126), these alterations 

have effected changes in fish and wildlife populations 

and communities. 

Hydrologic characteristics and wetlands processes and water supplies in Lahontan Valley have 

been modified substantially since the beginning of the 

Newlands Project in 1902 (Hoffman and others, 1990; 

Lico, 1992; Kerley and others, 1993; Hoffman, 1994). 

Among the more notable changes were the reduction 

of the amount of water entering and flowing through 

wetlands, shifts in timing and locations of inflow to 

wetlands, increased hydrologic isolation of wetlands, 

greater mobilization of dissolved solids and trace elements from agricultural soils, and degradation of the 

quality of water entering wetlands. Agricultural and 

nonagricultural water consumption, the discharge of 

drain water to wetlands, historic ore-milling activities, 

and wetland-management activities are major contributors to these modifications. Largely because of the 

lack of historical information, the incremental changes 

to the wetland ecosystem are difficult to discern. However, historic descriptions provide evidence that gross 

physical, chemical, and biological conditions in wetlands have changed substantially. 

54 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
The diversity of wetland plant communities in 

Lahontan Valley has declined since the beginning of 

the Newlands Project. On the basis of early accounts, 

Donahue (1993) identified 27 historical wetland plantcommunity types in Lahontan Valley, and in the 

1990's, Bundy and others (1996) identified 21 of them. 

In general, the dominant wetland plants currently 

found in Lahontan Valley are tolerant of saline conditions, whereas some of the historically described 

saline-intolerant communities are no longer found 

(Bundy and others, 1996). 

No historical information on invertebrate communities was found. Currently, dominant invertebrate 

taxa in Lahontan Valley are tolerant of pollutants 

(Plafkin and others, 1989, app. C). Aquatic-invertebrate communities in Lahontan Valley wetlands, particularly in Lead Lake and Sprig Pond, exhibited some 

characteristics consistent with impaired stream systems, including absence of sensitive taxa, dominance 

of tolerant taxa, and low taxa richness. The 1994-96 

monitoring data indicate that invertebrate community 

structure is, at least in part, affected by concentrations 

of dissolved solids, arsenic, boron, and(or) molybdenum in water and concentrations of arsenic and mercury in sediment. 

Although at least 5 native and 15 introduced 

fishes have access to Lahontan Valley wetlands, only 

1 native and 4 nonnative fish species were found in the 

wetlands. Fish communities in Lahontan Valley wetlands also exhibited characteristics consistent with 

impaired stream systems, including low species diversity, skewed trophic structure, and predominance of 

tolerant species (Plafkin and others, 1989). Concentrations of arsenic, boron, and molybdenum in water from 

some wetlands were similar to concentrations associated with toxicity to test organisms (Finger and others, 

1993). In a limited number of water samples, arsenic, 

boron, lead, and mercury exceeded concentrations 

associated with low-level mortality or reproductive 

impairment in sensitive fish (Birge and others, 1979a 

and b). 

Aquatic-bird occurrence, nesting, and reproduction have declined since the beginning of the Newlands 

Project (Kerley and others, 1993); the most noticeable 

decline has been since 1979 (U.S. Fish and Wildlife 

Service, 1996a). Declines have been attributed to wetland loss and degradation. Habitat degradation has contributed to decreased bird foraging and nesting habitat 

and has promoted increased predation through the concentration of predators in fewer or smaller wetland 

areas (Hallock, Janik, and Kerley, 1993, p. 63). Elevated concentrations of some trace elements may also 

affect avian reproduction and survival. Aluminum, 

boron, and mercury in avian food chains were found to 

exceed concentrations associated with sublethal 

effects, and 5 percent exceeded levels associated with 

embryotoxicity. Boron concentrations in a majority of 

the sampled eggs exceeded concentrations associated 

with sublethal effects. The actual effects of these elements on bird diversity and abundance in Lahontan 

Valley are uncertain. 

SUMMARY AND CONCLUSIONS 

The quantity and quality of wetlands in Lahontan 

Valley have declined since the advent of large-scale 

agriculture in the valley in the early 1900's. Recent 

investigations documented dissolved-solids and traceelement concentrations associated with adverse effects 

on fish and wildlife. Under the auspices of the Truckee—Carson—Pyramid Lake Water Settlement Agreement, the Department of the Interior implemented a 

program to acquire rights for water to restore and maintain a part of the historic wetlands in Lahontan Valley. 

Although inflow to wetlands will be restored in part, 

the effects of increased inflow on wetland contamination are uncertain. To establish a baseline for assessment of the benefits of water acquisition to wetland 

contamination, the U.S. Geological Survey and the 

U.S. Fish and Wildlife Service initiated a monitoring 

program in Lahontan Valley. Specific goals of the monitoring were to (1) develop a long-term hydrologic and 

biologic data base for the U.S. Department of the Interior Irrigation Drainage Program, (2) evaluate the 

effects of Federal activities on water quality, wetland 

quality, and biota in the area, and (3) identify progress 

toward the remediation of contaminant concerns in 

Lahontan Valley wetlands. 

During 1994-96, monitoring data were collected 

from seven agricultural drains, one irrigation-water 

delivery canal, and four wetlands. Information generated also provided further insight into the probable current status of the Lahontan Valley wetland system, 

particularly concerning wetland water supply and wetland-habitat conditions. 

SUMMARY AND CONCLUSIONS 55 
Wetland Water Supply Wetland-Habitat Conditions 

• During 1994-96, releases from Lahontan Reservoir ranged from 60 to 130 percent of the 

long-term average. Because of operational 

spills and conveyance losses, only about 23 to 

59 percent of the released irrigation water 

arrived at farm headgates, and about 35 percent of that water eventually entered wetlands 

as agricultural drainage. 

• Maximum dissolved-solids concentrations 

generally were recorded before or very early in 

the irrigation season. Maximum dissolved-solids loads generally were observed during the 

irrigation season, coincident with increased 

flow. 

• Of the monitored drains entering Stillwater 

National Wildlife Refuge, the highest dissolved-solids, boron, and molybdenum concentrations and the greatest number of 

exceedences of Nevada water-quality standards were found in water from the Paiute 

Diversion Drain. The lowest concentrations of 

these constituents were found in water from 

the S Line. No monitored constituents in S 

Line exceeded applicable standards. 

• Of the monitored drains entering Carson Lake, 

the highest dissolved-solids, boron, and 

molybdenum concentrations and the greatest 

number of exceedences of Nevada water-quality standards were found in water from the 

Carson Lake Drain. Concentrations were generally lower in water from other drains. 

• Concentrations of total mercury in drain water 

were generally below the analytical detection 

limit, 0.1 lig/L, in all conduits except Stillwater Slough and Stillwater Point Reservoir 

Diversion Canal. The highest concentrations 

of mercury in the water column were found in 

Stillwater Slough, whereas the highest mercury loads were found in Stillwater Point Reservoir Diversion Canal, which drains into 

Stillwater Point Reservoir. 

• Aquatic-invertebrate and fish communities in 

Lahontan Valley wetlands exhibited some 

characteristics consistent with stream communities affected by pollutants or degraded water 

quality. 

• Mercury represented the greatest threat to fish 

and wildlife in Lahontan Valley wetlands. 

Concentrations in all sampled media exceeded 

concentrations associated with adverse effects 

on wetland organisms. Concentrations in bottom sediment positively correlated with concentrations in food-chain organisms and 

negatively correlated with measures of 

aquatic-invertebrate community structure. Elevated concentrations of mercury in Lahontan 

Valley are attributed to historic ore-milling 

operations; however, drainage has redistributed mercury throughout Lahontan Valley. 

Because sediments act as both a sink for and a 

source of mercury in aquatic systems, the 

acquisition of water is unlikely to mitigate 

mercury contamination. 

• Aluminum concentrations in food-chain 

organisms exceeded concentrations that are 

potentially toxic to birds. Concentrations in 

food chains positively correlated with concentrations in bottom sediment. Concentrations of 

aluminum in sediments likely reflect natural 

soil conditions; therefore, the increased inflow 

of higher quality water is unlikely to reduce 

biological concern regarding aluminum. 

• Arsenic, boron, and molybdenum concentrations in unfiltered wetland water exceeded 

applicable standards and(or) biological-effect 

criteria. Concentrations of these elements were 

similar to concentrations previously associated 

with toxicity to aquatic organisms and negatively correlated with measures of aquaticinvertebrate community structure. Because 

dissolved solids (as specific conductance) positively correlated with concentrations of each 

of these elements, managing wetlands by using 

higher quality water (such as water having 

lower dissolved-solids concentration) might 

reduce the potential for toxicity associated 

with these elements in water and therefore benefit the aquatic ecosystem. 

56 Monitoring of Inorganic Contaminants Associated With Irrigation Drainage, West-Central Nevada, 1994-96 
• Arsenic in bottom sediment in all sampled wetlands exceeded the concentration associated 

with toxicity to sensitive aquatic organisms 

and negatively correlated with measures of 

aquatic-invertebrate community structure. 

Because concentrations in unfiltered water 

positively correlated with bottom sediment, 

supplying wetlands with higher quality water 

may reduce the potential for toxicity. 

• Boron concentrations in food-chain organisms, 

bird eggs, and juvenile-bird livers exceeded 

levels associated with sublethal effects on 

birds. Concentrations were generally higher in 

vegetation and in herbivorous birds. Concentrations in vegetation were positively correlated with bottom sediment. However, because 

concentrations in these media did not correlate 

with concentrations in unfiltered water, it is 

uncertain whether supplying wetlands with 

higher quality water would reduce boron concentrations in bottom sediment. 

• Selenium was not detected in wetland water 

samples or in the bulk of the detritus and vegetation samples. Concentrations in biological 

media were not indicative of adverse effects to 

fish and wildlife, including impaired avian 

reproduction. Although previous National Irrigation Water Quality Program investigations 

identified potentially toxic selenium concentrations in biological samples, this element did 

not appear to represent a threat to fish and 

wildlife during the 1994-96 monitoring program. Because selenium concentrations in 

water were less than the analytical detection 

limit and because concentrations in other 

media correlated poorly with one another, little 

inference may be drawn for water- or wetlandmanagement practices to minimize risks from 

selenium. 

• Specific conductance, a surrogate measure of 

dissolved-solids concentration, appeared to be 

a useful variable to monitor the levels of salinity and potentially toxic trace elements in 

drains and wetlands of Lahontan Valley. 

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