A

U.S. Department of the Interior

U.S. Geological Survey

Priority-Pollutant Trace Elements in

Streambed Sediments of the

Cook Inlet Basin, Alaska, 1998–2000

Water-Resources Investigations Report 02-4163

Prepared as part of the

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM
Cover photograph: Costello Creek at the mouth of Camp Creek, Denali National Park and Preserve, Alaska. 

(Photograph by Timothy P. Brabets, U.S. Geological Survey.) 
U.S. Department of the Interior

U.S. Geological Survey

Priority-Pollutant Trace Elements in 

Streambed Sediments of the 

Cook Inlet Basin, Alaska, 1998–2000

By STEVEN A. FRENZEL

Water-Resources Investigations Report 02–4163

Prepared as part of the 

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Anchorage, Alaska 

2002
U. S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

The 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 may be purchased from: 

District Chief U.S. Geological Survey 

U.S. Geological Survey Branch of Information Services 

4230 University Drive, Suite 201 Box 25286 

Anchorage, AK 99508-4664 Denver, CO 80225-0286

Internet URLs:

Alaska Water Resources: http://ak.water.usgs.gov

Cook Inlet Basin NAWQA: http://ak.water.usgs.gov/Projects/Nawqa/

National NAWQA: http://water.usgs.gov/nawqa/nawqa_home.html
iii

FOREWORD

The U.S. Geological Survey (USGS) is 

committed to serve the Nation with accurate and 

timely scientific information that helps enhance and 

protect the overall quality of life, and facilitates 

effective management of water, biological, energy, 

and mineral resources. Information on the quality 

of the Nation’s water resources is of critical interest 

to the USGS because it is so integrally linked to the 

long-term availability of water that is clean and safe 

for drinking and recreation and that is suitable for 

industry, irrigation, and habitat for fish and wildlife. 

Escalating population growth and increasing 

demands for the multiple water uses make water 

availability, now measured in terms of quantity and 

quality, even more critical to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. Shaped by and coordinated with ongoing 

efforts of other Federal, Tribal, State, and local 

agencies, the NAWQA Program is designed to 

answer: What is the condition of our Nation’s 

streams and ground water? How are the conditions 

changing over time? How do natural features and 

human activities affect the quality of streams and 

ground water, and where are those effects most 

pronounced? By combining information on water 

chemistry, physical characteristics, stream habitat, 

and aquatic life, the NAWQA Program aims to 

provide science-based insights for current and 

emerging water issues. NAWQA results can 

contribute to informed decisions that result in 

practical and effective water-resource management 

and strategies that protect and restore water quality.

Since 1991, the NAWQA Program has 

implemented interdisciplinary assessments in more 

than 50 of the Nation’s most important river 

basins and aquifers, referred to as Study Units. 

Collectively, these Study Units account for more 

than 60 percent of the overall water use and 

population served by public water supply, 

and are representative of the Nation’s major 

hydrologic landscapes, priority ecological 

resources, and agricultural, urban, and natural 

sources of contamination.

Each assessment is guided by a nationally 

consistent study design and methods of sampling 

and analysis. The assessments thereby build local 

knowledge about water-quality issues and trends in 

a particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multiscale approach helps to determine if certain types of 

water-quality issues are isolated or pervasive, and 

allows direct comparisons of how human activities 

and natural processes affect water quality and 

ecological health in the Nation’s diverse geographic 

and environmental settings. Comprehensive 

assessments on pesticides, nutrients, volatile 

organic compounds, trace metals, and aquatic 

ecology are developed at the national scale through 

comparative analysis of the Study-Unit findings.

The USGS places high value on the 

communication and dissemination of credible, 

timely, and relevant science so that the most recent 

and available knowledge about water resources can 

be applied in management and policy decisions. 

We hope this NAWQA publication will provide 

you the needed insights and information to meet 

your needs, and thereby foster increased awareness 

and involvement in the protection and restoration of 

our Nation’s waters. 

The NAWQA Program recognizes that a 

national assessment by a single program cannot 

address all water-resource issues of interest. 

External coordination at all levels is critical for a 

fully integrated understanding of watersheds and 

for cost-effective management, regulation, and 

conservation of our Nation’s water resources. 

The Program, therefore, depends extensively on 

the advice, cooperation, and information from other 

Federal, State, interstate, Tribal, and local agencies, 

non-government organizations, industry, academia, 

and other stakeholder groups. The assistance and 

suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water
This page intentionally blank
v

CONTENTS

Foreword ..................................................................................................................................................................................... iii

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

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

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

Sample Collection and Analysis .........................................................................................................................................3

Data Analysis ......................................................................................................................................................................3

Results ...........................................................................................................................................................................................4

Discussion .....................................................................................................................................................................................9

Priority-Pollutant Trace Element Concentrations ...............................................................................................................9

Potential Toxicity ..............................................................................................................................................................10

Summary .....................................................................................................................................................................................11

References Cited .........................................................................................................................................................................12

FIGURES

Figure 1. Map showing Cook Inlet Basin, Alaska, and location of streambed sediment sampling sites......................................2

Figure 2. Graphs showing concentrations of priority-pollutant trace elements in streambed sediment samples 

from the U.S. Geological Survey’s Cook Inlet Basin National Water-Quality Assessment Study 

Unit and from reference streams and streams in urban and mining areas sampled nationally for 

the U.S. Geological Survey National Water-Quality Assessment program, 1992 ........................................................7

Figure 3. Graphs showing cumulative frequency plots for priority-pollutant trace elements in streambed 

sediments from the U.S. Geological Survey’s Cook Inlet Basin National Water-Quality 

Assessment Study Unit ..................................................................................................................................................8

TABLES

Table 1. Guidelines for trace element concentrations, in micrograms per gram, dry weight ......................................................4

Table 2. Concentrations, in micrograms per gram dry weight, of priority-pollutant trace elements in 

streambed sediments finer than 0.063 millimeters in the Cook Inlet Basin, Alaska, 1998 to 2000 ..............................5

Table 3. Statistical significance of comparisons of trace element concentrations from the 

U.S. Geological Survey’s Cook Inlet Basin National Water-Quality Assessment 

(NAWQA) Study Unit and national NAWQA samples, grouped by dominant land use..............................................8

Table 4. Mean percentage of streambed sediment in selected size classes from sites in Anchorage, Alaska .............................9
vi

CONVERSION FACTORS AND VERTICAL DATUM

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

°F = (1.8 × °C) + 32

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a 

geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, 

formerly called Sea Level Datum of 1929.

Concentrations of trace elements in sediment are given in micrograms per gram (mg/g), which is equivalent to 

parts per million.

MAPPING SOURCES:

Base map modified from U.S. Geological Survey 1:250,000 State base maps. 

U.S. Geological Survey Digital Line Graphs published at 1:2,000,000. 

Publication projection is Albers Conical Equal Area. 

Standard parallels are 55°00’ and 65°00’, central meridian –154°00’, latitude of project origin 50°00’.

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in)

kilometer (km) 0.6214 mile

Area

square kilometer (km2) 0.3861 square mile (mi2)

Mass

gram (g) 0.03527 ounce, avoirdupois
1

Priority-Pollutant Trace Elements in Streambed Sediments 

of the Cook Inlet Basin, Alaska, 1998–2000

By Steven A. Frenzel

Abstract

Trace element concentrations in 48 streambed sediment samples collected at 47 sites in 

the Cook Inlet Basin, Alaska, were compared to 

concentrations from studies in the conterminous 

United States using identical methods and to 

Probable Effect Concentrations. Concentrations 

of arsenic, chromium, mercury, and nickel in the 

0.063-mm size fraction of streambed sediments 

from the Cook Inlet Basin were elevated relative to 

reference sites in the conterminous United States. 

Concentrations of cadmium, lead, and zinc were 

highest at the most urbanized site in Anchorage 

and at two sites downstream from an ore body 

in Lake Clark National Park and Preserve. At 

least 35 percent of the 48 samples collected in 

the Cook Inlet Basin exceeded the Probable Effect 

Concentration for arsenic, chromium, or nickel. 

More than 50 percent of the samples were considered to have low potential toxicity for cadmium, 

lead, mercury, nickel, selenium, and zinc. A 

Probable Effect Concentration quotient that

reflects the combined toxicity of arsenic, cadmium, 

chromium, copper, lead, mercury, nickel, and zinc 

was exceeded in 44 percent of the samples from 

the Cook Inlet Basin. The potential toxicity was 

high in the Denali and Lake Clark National Parks 

and Preserves where organic carbon concentrations in streambed sediments were low. However, 

potential toxicity results should be considered in 

context with the very small amounts of fine-grained 

sediment present in the streambed sediments of the 

Cook Inlet Basin. 

INTRODUCTION

The U.S. Geological Survey’s (USGS) National 

Water-Quality Assessment (NAWQA) program 

began full-scale implementation in 1991; in the first 

decade of the program, studies were conducted that 

included parts of all 50 states. The Cook Inlet Basin 

Study Unit investigation began in 1997. The basin 

includes numerous drainages into Cook Inlet in southcentral Alaska, (fig.1). Analysis of streambed sediments 

for trace element concentrations is one aspect of the 

integrated assessment of water quality in the NAWQA 

program (Gurtz, 1994). The Cook Inlet Basin Study 

Unit sampling network was designed to assess the 

occurrence of trace elements in the Cook Inlet Basin 

and to define their distribution in the parts of Denali 

and Lake Clark National Parks and Preserves within the 

basin. Sites also were sampled in Anchorage, the largest 

city in the basin (population about 256,000 in 2000), 

as part of a study of water quality along an urban 

gradient. This report describes the analysis of prioritypollutant trace element concentrations in streambed 

sediment samples collected in the Cook Inlet Basin 

during 1998 to 2000.

The environmental setting of the 101,800 square 

kilometer Cook Inlet Basin Study Unit has been described 

in detail by Brabets and others (1999). Typically, 

lowlands in the basin are underlain predominantly by 

alluvial or glacial deposits, whereas uplands are more 

commonly underlain by metamorphic or igneous rock. 

Sites sampled for streambed sediments and discussed in 

this report were most often located in lowland settings. 

Many of the drainages, however, include upland areas and 

glaciers. Mining and processing of ore have a large potential for introducing trace elements to nearby water bodies. 
2

Study

unit

ALASKA

Katmai National Park

and Preserve

Lake Clark

National Park

and Preserve

Denali

National Park

and Preserve

Significant coal deposits

Water

Glaciers

EXPLANATION

60 ̊ 

154 ̊ 

63 ̊

152 ̊ 146 ̊

63 ̊

COOK INLET

75 100 MILES

100 KILOMETERS

50

75

25

25 50

0

0

National park

7 Streambed sediment sampling

 site location and number

 (see table 2)

59

66 23

27

29

65

64

61 60

63 69

16 55

54

53

7

51

62

68

67

108

107 106

105

103 102

101

41

50

44

57 96

97

98

58

95

100

99

104

52

112

113

110 

111

115 

116

117

Kenai

River

Susitna River

Matanuska

Talkeetna

River

River

River

Deshka River

Kamishak

 River

Skilak

Lake

Susitna

Ninilchik

 River

Palmer

Talkeetna

Tyonek Anchorage

Soldotna

Ninilchik

Cooper

Landing

Figure 1. Cook Inlet Basin, Alaska, and location of streambed sediment sampling sites. (Refer to http://ak.water.usgs.gov/Projects/Nawqa/

water-sites.htm for the location and names of all Cook Inlet Basin National Water-Quality Assessment (NAWQA) surface-water sites.)
3

Precious metals have been mined at small scales throughout the basin. Large-scale mining does not currently 

exist in the Cook Inlet Basin, although exploratory gold 

mining exists in the Johnson River Basin in Lake Clark 

National Park and Preserve on the west side of Cook 

Inlet. The ore (gold, lead, and zinc) body in the Johnson 

River Basin is drained by East Fork Ore Creek, a tributary to Ore Creek. Coal deposits are more economically 

important in the Cook Inlet Basin than are precious 

metals. Coal has been mined at a relatively small scale 

from an area now contained in Denali National Park and 

Preserve (hereinafter called the Denali area). From 1940 

to 1954, 64,000 tons of coal were produced from Dunkle 

Mine in the Costello Creek Basin. An estimated 8 million 

tons of coal remain in the upper Costello and Colorado 

Creek Basins (National Park Service, 1983). Coal mining 

has been proposed for the area drained by Moose Creek 

near Palmer. On the west side of Cook Inlet, industry 

sources have identified more than 750 million tons of 

economically extractable coal (Nelson, 1985).

METHODS

Sample Collection and Analysis

Streambed sediment samples were collected from 

depositional areas accessible by wading in the selected 

stream reaches. Typically, these depositional areas were 

along channel margins or bar formations. The surficial 

2 cm of sediment was collected from several areas and 

composited to form a large sample volume from which 

material was removed and sieved using a 0.063-mm 

nylon mesh (Shelton and Capel, 1994). Sediments were 

digested in strong acid prior to analysis by the USGS 

National Water-Quality Laboratory in Lakewood, 

Colorado. Concentration data were reported on a dryweight basis.

Streambed sediments were collected at sites in 

Anchorage for determination of particle-size distribution 

in conjunction with a study of benthic invertebrates 

and fish communities. Three samples were collected 

from riffles at each of 12 sites by lowering a 15-cm 

diameter enclosure to the streambed and excavating the 

sample within the enclosure. This technique eliminated 

currents that would carry away fine-grained sediments. 

Streambed sediments were dried at 70°C, sieved, and 

weighed by size class. A geometric mean of the three 

samples was determined and presented for five size 

classes, including the less than 0.063-mm size fraction.

Data Analysis

Although concentrations of 44 elements were 

determined for the streambed sediment samples, only 

the results for 9 trace elements are discussed here. 

Those trace elements, arsenic, cadmium, chromium, 

copper, lead, mercury, nickel, selenium, and zinc, 

are listed as priority pollutants (U.S. Environmental 

Protection Agency, 1994). Trace element concentrations 

from the Cook Inlet Basin Study Unit were not normalized for organic carbon content in the streambed sediments for comparisons with data from other NAWQA 

study units and the determination of background concentrations. Analysis of 541 streambed sediment samples 

collected during previous NAWQA studies showed that 

sieving the samples removed most of the background 

differences in the samples, making further “normalization” unnecessary (Rice, 1999). However, for comparing 

data from the Cook Inlet Basin Study Unit to toxicity 

guidelines, data were normalized for organic carbon 

concentrations (dry weight) to equate to the sediment 

quality guidelines (SQGs) described by MacDonald 

and others (2000). Organic carbon in the streambed 

sediments likely affects the bioavailability of trace 

elements such that sediments containing relatively high 

concentrations of organic carbon will have a lower 

potential toxicity than sediments with lower organic 

carbon concentrations and identical trace element concentrations.

Cook Inlet Basin Study Unit samples were compared with samples collected by identical methods in 46 

other NAWQA study units throughout the United States 

between 1992 and 2000. Those comparisons were made 

after stratification of the NAWQA sites into the following land use groups: (1) reference (relatively undisturbed 

basins) and forest, (2) mining, and (3) urban, residential, 

and commercial. Land use categories used in this study 

differ from those used by Rice (1999) in a study of trace 

element concentrations from streambed sediment samples collected for the NAWQA program from 1992 to 

1996. Our urban category also included sites classified 

as residential and commercial, whereas Rice’s urban 

category did not. Comparisons between Cook Inlet 

Basin Study Unit samples and national NAWQA 

samples in the three land use categories were done using 

boxplots and a Wilcoxon rank-sum test. Computed 

p-values less than 0.05 indicated a significant difference 

in a given comparison.
4

Cumulative-frequency plots were used to 

determine background concentrations by locating a 

sharp upward break in the cumulative-frequency 

distribution, which would indicate an anthropogenic 

affect within the Cook Inlet Basin Study Unit (Velz, 

1984). For purposes of plotting, concentrations less 

than the minimum reporting limits for the analytical 

method were assigned a value of one-half the 

reporting limit. A smoothing function was applied 

to reduce noise in the data.

Concentrations of trace elements, excluding 

selenium, were compared to consensus-based SQGs 

(MacDonald and others, 2000). Those guidelines 

were developed from studies that typically use bulk 

sediment samples rather than the fine-grained fraction 

sampled by the NAWQA program. The SQGs 

identify a Threshold Effect Concentration (TEC) 

below which sediment-dwelling organisms are 

unlikely to be adversely affected and a Probable Effect 

Concentration (PEC) above which toxicity is likely 

(MacDonald and others, 2000). These values were 

determined by matching sediment chemistry and 

toxicity data from field studies. MacDonald and others 

(2000) did not determine a PEC for selenium. For that 

element, Van Derveer and Canton (1997) suggested 

a no effect level of 2.5 μg/g (10th percentile of effects) 

and a toxicity level of 4 μg/g (100th percentile of 

effects).

Guideline concentrations from MacDonald and 

others (2000) and Van Derveer and Canton (1997) 

used in this report are shown in table 1. Additionally, 

the toxicity of the combined trace element concentrations was assessed by the method of MacDonald 

and others (2000). They found that when the sum of 

normalized concentrations was divided by the number 

of constituents used in the calculation, a resulting 

value of 0.5 was a threshold that defined toxicity. 

Sediments with mean PEC quotients of less than 

0.5 accurately predicted the absence of toxicity in 

83 percent of the samples they examined. Mean 

PEC quotients greater than 0.5 accurately predicted 

toxicity in 85 percent of the samples. However, their 

mean PEC quotients included organic contaminants 

as well as trace elements. Our calculation of mean 

PEC quotient was done for the priority-pollutant trace 

elements, excluding selenium. 

Table 1. Guidelines for trace element concentrations, in micrograms 

per gram, dry weight

Element

Low 

potential 

for toxicity

High 

potential 

for toxicity

Arsenic (As) 9.79 a

a Threshold Effect Level (TEC: MacDonald and others, 2000).

33 b

b Probable Effect Level (PEC: MacDonald and others, 2000).

Cadmium (Cd) .99 a 4.98 b 

Chromium (Cr) 43.4 a 111 b 

Copper (Cu) 31.6 a 149 b 

Lead (Pb) 35.8 a 128 b 

Mercury (Hg) .18 a 1.06 b 

Nickel (Ni) 22.7 a 48.6 b 

Selenium (Se) 2.50 c

c 10th percentile of effects (Van Derveer and Canton, 1997).

4.00 d

d 100th percentile of effects (Van Derveer and Canton, 1997).

Zinc (Zn) 121 a 459 b 

RESULTS

Relatively high trace element concentrations 

occurred at highly urbanized sites, in the Denali area, 

and at sites downstream of an ore body in Lake Clark 

National Park and Preserve (table 2). Low concentrations were found in Hidden Creek, in the Talkeetna 

and Kamishak Rivers, and at sites in Anchorage with 

low population density. 

Cook Inlet Basin Study Unit concentration data 

were compared to concentrations in samples collected 

during other NAWQA studies at sites in specific land 

use categories with varying results (fig. 2, table 3). 

Mercury and nickel concentrations were statistically 

similar to those in other NAWQA samples from sites 

downstream from urban and mining areas. Arsenic 

concentrations were statistically similar to concentrations from sites in areas with a mining-dominated land 

use, whereas chromium concentrations were similar to 

those at sites in urban areas. Zinc concentrations 

were statistically similar to concentration at sites 

representing reference, or background conditions. 

Samples from Cook Inlet Basin Study Unit sites 

were similar to those in other NAWQA studies 

for all land use categories with respect to selenium 

concentrations and were statistically different with 

respect to cadmium, copper, and lead concentrations.
5

Table 2. Concentrations, in micrograms per gram dry weight, of priority-pollutant trace elements in streambed sediments finer than 0.06Cook Inlet Basin, Alaska, 1998 to 2000[Site no. refers to site number in figure 1; latitude/longitude are given in °, degrees; ’, minutes; ”, seconds; As, arsenic; Cd, cadmium; Cr, chromium; Cu, copper; Pb, Se, selenium; Zn, zinc; organic carbon in percent; values in bold are concentrations that when normalized to 1 percent organic carbon, exceed Probable Effect Concemean PEC quotient, indicate toxicity for the sum of trace elements, excluding selenium (MacDonald and others, 2000); St., Street; Dr., Drive; Hwy., Highway; Pkwyrefer to http://ak.water.usgs.gov/Projects/Nawqa/ water-sites.htm for the location and names of all Cook Inlet Basin National Water-Quality Assessment (NAWQA) s

Site 

no. Site name Latitude Longitude As Cd Cr Cu Pb Hg Ni 

Municipality of Anchorage

23 South Fork Campbell Creek near Anchorage 61°10’02” 149°46’14” 10 .2 100 50 11 .81 44 27 Chester Creek at Arctic Blvd. (1998) at Anchorage 61°12’19” 149°53’43” 23 1.2 120 60 90 .18 64 27 Chester Creek at Arctic Blvd. (1999) at Anchorage 61°12’19” 149°53’43” 26 1.0 120 64 110 .17 50 29 Ship Creek below power plant at Elmendorf Air Force Base 61°13’29” 149°50’39” 11 .2 110 61 15 .16 46 59 Rabbit Creek at Hillside Dr. near Anchorage 61°05’51” 149°43’52” 7.7 .2 72 47 10 .34 32 60 Rabbit Creek at East 140th Ave. near Anchorage 61°05’41” 149°47’14” 7.9 .2 85 43 10 .29 35 61 Rabbit Creek at Porcupine Trail Rd. near Anchorage 61°05’15” 149°49’06” 7.6 .2 91 45 11 .36 36 62 Little Rabbit Creek at Nickleen St. near Anchorage 61°04’21” 149°43’26” 6.2 0.2 62 44 10 0.21 28 63 Little Rabbit Creek at Goldenview Dr. near Anchorage 61°04’54” 149°46’20” 8.8 .3 63 41 10 .25 30 64 Campbell Creek at New Seward Hwy. near Anchorage 61°10’33” 149°51’23” 9.6 .2 99 40 11 .61 40 65 Campbell Creek at C St. near Anchorage 61°08’55” 149°53’03” 9.1 .3 110 49 17 .33 62 66 South Branch of South Fork Chester Creek at Tank Trail 

near Anchorage

61°11’25” 149°42’13” 15 .2 81 38 10 .16 29 

67 South Branch of South Fork Chester Creek 

at Boniface Pkwy. near Anchorage

61°11’23” 149°46’33” 15 .7 110 53 61 .17 47 

68 Ship Creek at Glenn Hwy. near Anchorage 61°14’20” 149°41’32” 10 .2 95 48 11 .18 43 69 Little Rabbit Creek (at Old Seward Hwy.) near Anchorage 61°04’42” 149°48’36” 7.6 .2 64 37 10 .22 31 

Denali National Park and Preserve area

57 Colorado Creek near Colorado 63°16’29” 149°35’20” 44 .5 220 59 15 .18 130 58 Costello Creek near Colorado (Site no. 6310181493237) 63°16’18” 149°32’37” 23 .3 170 64 16 .23 98 95 Camp Creek at mouth near Colorado 63°16’12” 149°31’33” 49 .5 110 35 27 .24 42 96 Costello Creek below Camp Creek near Colorado 63°16’09” 149°31’34” 25 .3 140 55 18 .16 70 97 Crystal Creek at mouth near Talkeetna 62°50’12” 150°18’27” 10 .2 24 16 20 .02 11 98 Coffee River above Crystal Creek near Talkeetna 62°50’14” 150°18’32” 9.1 .2 10 10 22 <.02 6 99 Bear Creek near Talkeetna 62°38’34” 150°54’33” 42 .5 140 59 17 .03 81 

100 Wildhorse Creek near Talkeetna 62°39’20” 150°54’03” 56 1.9 120 48 17 .08 56 101 Long Creek near Talkeetna 62°35’10” 150°45’04” 46 .2 79 26 10 .04 32 102 Hidden Creek near Talkeetna 62°35’30” 151°11’29” 3.3 <.1 3 3 25 <.02 <2 103 Snowslide Creek at mouth near Talkeetna 62°33’24” 151°32’16” 1.7 .4 10 11 76 <.02 6 104 Cripple Creek above Snowslide Creek near Talkeetna 62°33’25” 151°32’18” 8.7 .3 68 26 20 <.02 37 105 Cascade Creek at mouth near Talkeetna 62°25’22” 151°59’22” 88 .2 87 48 13 <.02 49 
6

Denali National Park and Preserve area—Continued

106 Fourth of July Creek at mouth near Talkeetna 62°19’36” 151°58’27” 26 0.3 150 49 16 0.02 80 107 Morris Creek at mouth near Talkeetna 62°17’59” 152°41’05” 30 .2 150 47 14 .07 94 108 Kichatna River above Morris Creek near Talkeetna 62°18’00” 152°41’06” 16 <.1 29 13 33 .02 17 

Johnson River Basin—Lake Clark National Park and Preserve

52 Johnson River above Lateral Glacier near Tuxedni Bay 60°05’41” 152°54’38” 16 .2 66 75 4 .13 17 

110 Kona Creek 3 miles above mouth above Lateral Glacier 

near Tuxedni Bay

60°08’26” 152°55’44” 19 <.1 38 56 6 .75 11 

111 Kona Creek 2.5 miles above Lateral Glacier 

near Tuxedni Bay

60°08’03” 152°55’24” 18 .1 42 57 5 .16 11 

112 Kona Creek tributary above Lateral Glacier 

near Tuxedni Bay

60°06’35” 152°55’09” 18 <.1 77 47 4 .10 25 

113 Kona Creek 0.8 miles above mouth above Lateral Glacier 

near Tuxedni Bay

60°06’36” 152°55’14” 16 .4 48 63 17 .28 14 

115 East Fork Ore Creek near mouth near Johnson Glacier 

near Tuxedni Bay

60°07’15” 152°57’28” 34 <.1 41 54 <1 .53 15 

116 North Fork Ore Creek near mouth near Johnson Glacier 

near Tuxedni Bay

60°07’13” 152°57’40” 64 4.3 14 76 230 .93 4 

117 Ore Creek near mouth near Johnson Glacier 

near Tuxedni Bay

60°06’58” 152°58’14” 44 4.6 23 92 180 .28 8 

Miscellaneous basins

7 Ninilchik River at Ninilchik 60°02’54” 151°39’54” 30 .2 50 14 8 .05 20 

16 Kenai River at Soldotna 60°28’39” 151°04’46” 23 .3 84 36 15 .03 42 41 Talkeetna River near Talkeetna 62°20’49” 150°01’01” 5.2 <.1 38 27 7 .04 18 44 Deshka River near Willow 61°46’05” 150°20’13” 50 .3 67 26 12 .05 29 50 Moose Creek near Palmer 61°41’00” 149°02’36” 23 .3 84 74 16 .20 40 51 Kamishak River near Kamishak 58°57’50” 154°10’11” 8.9 .1 78 38 7 .04 29 53 Kenai River below Russian River near Cooper Landing 60°29’07” 150°00’35” 17 .3 110 46 16 .07 52 54 Kenai River at Jim's Landing near Cooper Landing 60°28’55” 150°06’36” 11 .3 110 45 17 .09 54 55 Kenai River below Skilak Lake outlet near Sterling 60°28’00” 150°35’56” 9.3 .2 82 41 13 .07 42 

Percentage of sites with low potential toxicity 40 83 48 46 75 73 50 Percentage of sites with high potential toxicity 40 6 40 15 12 6 35 

Table 2. Concentrations, in micrograms per gram dry weight, of priority-pollutant trace elements in streambed sediments finer than 0.06

Cook Inlet Basin, Alaska, 1998 to 2000—Continued

[Site no. refers to site number in figure 1; latitude/longitude are given in °, degrees; ’, minutes; ”, seconds; As, arsenic; Cd, cadmium; Cr, chromium; Cu, copper; Pb, 

Se, selenium; Zn, zinc; organic carbon in percent; values in bold are concentrations that when normalized to 1 percent organic carbon, exceed Probable Effect Conce

mean PEC quotient, indicate toxicity for the sum of trace elements, excluding selenium (MacDonald and others, 2000); St., Street; Dr., Drive; Hwy., Highway; Pkwy

refer to http://ak.water.usgs.gov/Projects/Nawqa/ water-sites.htm for the location and names of all Cook Inlet Basin National Water-Quality Assessment (NAWQA) s

Site 

no. Site name Latitude Longitude As Cd Cr Cu Pb Hg Ni 
7

.01

.1

1

.05

.5

5

 CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 183 176 145

Mercury

1

10

100

5

50

500

CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 183 181 146

Nickel

0.1

1

10

0.5

5

CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 183 180 145

Selenium

10

100

1,000

10,000

5

50

500

5,000

50,000

CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 183 180 146

Zinc

48 Number of observations

90th percentile

75th percentile

Median

25th percentile

10th percentile

Sample not included in 

 the 10-90 percentile 

 range

EXPLANATION

1

100

5

10

50

200

CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 183 178 145

Arsenic

0.1

1

10

100

0.5

5

50

200

CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 182 180 137

Cadmium 1

10

100

1,000

5

50

500

5,000

CONCENTRATION, (μg/g)

48 183 180 146

COOK REFERENCE URBAN MINING

Chromium

10

100

1,000

5

50

500

CONCENTRATION, (μg/g)

48 183 180 146

COOK REFERENCE URBAN MINING

Copper

10

100

1,000

10,000

5

50

500

5,000

CONCENTRATION, (μg/g)

COOK REFERENCE URBAN MINING

48 183 181 144

Lead

Figure 2. Concentrations of priority-pollutant trace elements in streambed sediment samples from the U.S. Geological Survey’s (USGS) 

Cook Inlet Basin (COOK) National Water-Quality Assessment (NAWQA) Study Unit and from reference streams and streams in urban 

and mining areas sampled nationally for the USGS NAWQA program, 1992. (μg/g, micrograms per gram)
8

Table 3. Statistical significance of comparisons of trace element 

concentrations from the U.S. Geological Survey’s Cook Inlet Basin 

(COOK) National Water-Quality Assessment (NAWQA) Study Unit 

and national NAWQA samples, grouped by dominant land use 

[vs., versus; p, probability; <, less than; =, equals; Wilcoxon rank-sum test; 

COOK, n=48; Reference, n=183; Urban, n=178; Mining, n=145]

Element

COOK 

vs.

Reference 

COOK 

vs. 

Urban 

COOK 

vs. 

Mining 

Arsenic p < 0.001 p < 0.001 p = 0.430

Cadmium p = 0.004 p < 0.001 p < 0.001

Chromium p = 0.007 p = 0.890 p = 0.010

Copper p < 0.001 p < 0.001 p < 0.001

Lead p < 0.001 p < 0.001 p < 0.001

Mercury p = 0.002 p = 0.347 p = 0.566

Nickel p = 0.020 p = 0.938 p = 0.185

Selenium p = 0.678 p = 0.318 p = 0.182

Zinc p = 0.092 p < 0.001 p < 0.001

Cadmium

CONCENTRATION, (μg/g)

CUMULATIVE FREQUENCY

10 50 70 90 30 1

0.1

1

10

116 117

27

67

27

95

27 Sample and site number

Sample

COOK background level (0.40 μg/g)

0.05

0.5

5

100

57 99

Lead

CONCENTRATION, (μg/g)

CUMULATIVE FREQUENCY

10 50 70 90 30

1

10

100

500

116

117

27

67

27

COOK background level (21 μ 95 g/g)

27 Sample and site number

Sample

98

103

108

102

Zinc

27 Sample and site number

Sample

CONCENTRATION, (μg/g)

CUMULATIVE FREQUENCY

10 50 70 90 30

10

1,000

2,000

116

117

27

67

27

COOK background level (190 μg/g)

50

100

500

0.01

0.1

0.05

1

0.5

5

10

50

100

500

CONCENTRATION, (μg/g)

CUMULATIVE FREQUENCY

10 50 70 90 30

Arsenic

Chromium

Copper

Mercury

Nickel

Selenium

Figure 3. Cumulative frequency plots for priority-pollutant trace elements in streambed sediments from the U.S. Geological Survey’s 

Cook Inlet Basin (COOK) National Water-Quality Assessment Study Unit. (μg/g, micrograms per gram; refer to figure 1 and table 2 for 

site information)

Background levels could be determined from 

cumulative-frequency plots for cadmium (0.40 μg/g), 

lead (21 μg/g), and zinc (190 μg/g; fig. 3). Arsenic 

(range 1.7–88 μg/g), chromium (range 3–220 μg/g), 

copper (range 3–92 μg/g), nickel (range < 2–130 μg/g), 

and selenium (range < 0.1–5.8 μg/g) concentrations 

did not have a distinct break point indicative 

of an anthropogenic effect (fig. 3). Cadmium 

(range < 0.1–4.6 μg/g), lead (range < 1–230 μg/g), 

and zinc (range 16–1,800 μg/g) concentrations 

were higher than the background level for the 

Cook Inlet Basin Study Unit at sites in the most 

urbanized basin (fig. 1, table 2, sites 27 and 67), 

downstream from an ore body (sites 116 and 117), 

or downstream from an old coal mine (site 95).
9

The potential toxicity of individual prioritypollutant trace elements from the less than 0.063-mm 

size fraction of streambed sediments was low in at 

least 50 percent of the samples for cadmium, lead, 

mercury, nickel, selenium, and zinc (table 2). High 

potential toxicity was determined in at least 35 percent of the samples for arsenic, chromium, and nickel. 

Cadmium, lead, and selenium had high potential toxicity in a very low percentage of samples. The mean 

PEC quotient, which reflects the combined toxicity 

of trace elements in the streambed sediment (excluding 

selenium) indicated that 56 percent of the samples 

would be classified as not toxic, and 44 percent of the 

samples would be classified as toxic. 

Particle-size analysis of streambed sediment 

samples collected from riffles at sites in Anchorage, 

except for Ship Creek (sites 29 and 68), showed that 

the less than 0.063-mm size fraction composed less 

than 0.01 to only 16 percent of the material by weight 

for all samples (not shown); the geometric mean of 

samples collected at individual sites was typically 

less than 0.01 percent (table 4). Although particlesize analyses were done for only a few sites, the 

relative magnitude of the percent of fine-grained 

sediment in riffles at other sites can be inferred from 

these data.

Table 4. Mean percentage of streambed sediment in selected 

size classes from sites in Anchorage, Alaska

[For site no. information refer to table 2 and figure 1; mm, millimeter; 

values are geometric means of three samples from riffles at each site; 

<, less than]

Site no. 64 mm 64 mm 2 mm 0.5 mm 0.063 mm

23 55.26 12.42 2.48 .32 < .01

59 66.75 17.44 4.59 .60 < .01

60 57.74 15.82 3.77 .49 < .01

61 64.36 16.79 3.65 .56 .01

62 64.80 22.24 8.03 2.13 0.03

63 57.36 16.62 4.81 .85 .01

64 69.72 17.75 3.88 .50 < .01

65 53.28 13.71 3.25 .33 < .01

66 51.12 13.95 3.41 .37 < .01

67 45.99 11.54 3.15 .37 < .01

69 65.24 15.05 4.11 .60 < .01

DISCUSSION

Priority-Pollutant Trace Element Concentrations

Trace element concentrations can be elevated 

in streambed sediments as a result of anthropogenic 

activities, such as mining or industrial/urban 

development, or as a result of natural geologic factors. 

Data from previous NAWQA studies have shown 

that median concentrations of chromium, copper, 

lead, nickel, and zinc were higher at sites downstream 

of urban areas than at nonurban sites (Rice, 1999). 

However, Rice (1999) combined many land use categories into a nonurban group. Our comparison of urban 

and mining sites sampled in the NAWQA program 

showed that chromium, copper, lead, mercury, and 

zinc had higher median concentrations at urban sites. 

A gradient of urbanization in Anchorage (sites 23, 27, 

29, 59–69) sampled during this study included basins 

with population density less than 100 persons/km2

(sites 23, 59, 62–63, 66) as well as basins with over 

500 persons/km2 (sites 27, 65, 67). Concentrations of 

cadmium, lead, and zinc increased markedly at the most 

highly urbanized sites (sites 27 and 67). 

Two samples collected at Chester Creek at Arctic 

Boulevard (site 27) had two of the three highest concentrations from sites sampled in Anchorage for seven of 

the nine priority-pollutant trace elements. Additionally, 

antimony, iron, manganese, silver, and tin were higher 

at Chester Creek at Arctic Boulevard than at other sites 

in Anchorage (U.S. Geological Survey, 2000). Sites in 

Anchorage had low arsenic concentrations relative to 

other parts of the Cook Inlet Basin. However, the 

arsenic concentration was 23 and 26 μg/g in 1998 

and 1999, respectively, at Chester Creek at Arctic 

Boulevard (site 27). That site was the most urbanized 

site, in terms of population and road densities, sampled 

in Anchorage. The second most urbanized site, South 

Branch of South Fork Chester Creek at Boniface Parkway (site 67), had an arsenic concentration of 15 μg/g. 

All other sites in Anchorage had arsenic concentrations 

of 10 μg/g or less. Cadmium, lead, and zinc concentrations at the two downstream Chester Creek sites 

were much greater than at other Anchorage sites, but 

were lower than concentrations at two sites near an 

ore body in the Johnson River Basin (sites 116 and 117). 
10

The elevated lead and zinc concentrations in the 

Chester Creek Basin were consistent with results from 

similar locations sampled in the 1980s (Brabets, 1987). 

Lead and zinc often are associated with urbanized 

areas and were elevated at many urban sites sampled 

in the NAWQA program (Callender and Rice, 2000; 

Kroening and others, 2000).

Although large-scale precious metal mining does 

not exist presently in the Cook Inlet Basin, small exploratory claims are abundant. Most claims are for gold 

mines, but a variety of mineral deposits are present, 

and arsenopyrite occurs widely. Arsenic concentrations 

in Cook Inlet Basin Study Unit streambed sediments 

tended to be higher than for the areas sampled for the 

NAWQA program in the conterminous United States. 

However, naturally high concentrations are not unprecedented. In the Upper Colorado River Basin NAWQA 

Study Unit, unmined sites had arsenic concentrations 

as high as 62 μg/g, whereas mined sites had arsenic 

concentrations as high as 180 μg/g (Deacon and 

Driver, 1999). Basins sampled in the Denali area 

contain bedrock formations of basalt, argillite, and 

chert that contain numerous metal deposits (National 

Park Service, 1983). Many abandoned exploratory 

mines exist in the southern part of the Denali area, 

and arsenopyrite is commonly associated with those 

mines.

Cadmium, copper, lead, and zinc concentrations 

were elevated at two sites (sites 116 and 117) downstream of an ore body and at two urban sites (sites 27 

and 67). Those trace elements often are elevated in mining areas (Heiny and Tate, 1997; Deacon and Driver, 

1999) and in urban runoff (Rice, 1999; Callender 

and Rice, 2000). Although most sites sampled in the 

Cook Inlet Basin are in essentially undeveloped 

areas, mercury and nickel concentrations were 

statistically similar to those in samples from urban 

and mining-dominated basins in other NAWQA 

study units. Additionally, arsenic concentrations 

from the basin were similar to those from miningdominated sites in other NAWQA studies, and 

chromium concentrations were similar to those at 

urban-dominated NAWQA sites. However, arsenic, 

chromium, mercury, and nickel concentrations from 

the Cook Inlet Basin did not show a break in the cumulative frequency plots that would indicate an anthropogenic effect. Mercury concentrations in Anchorage 

generally were larger than those measured in a study 

of mercury associated with mining activities in the 

Sacramento River Basin that used methods similar to 

those used in this study (Domagalski, 1998). Sources 

of mercury in the Anchorage area are unknown, but may 

be a combination of natural geologic and atmospheric 

sources.

Chromium and nickel concentrations in the 

Cook Inlet Basin were highest from sites in the Denali 

area and from the most urbanized site (site 27) in 

Anchorage. Chromium and nickel concentrations in 

streambed sediments in the Denali area may be 

indicative of the metamorphic and igneous bedrock 

in that area (Silberling and others, 1994). In contrast, 

relatively low concentrations of chromium and nickel 

in the Johnson River Basin likely are indicative of the 

sample location’s proximity to the Alaska–Aleutian 

Range Batholith, which contains little chromium and 

nickel (Waythomas and others, 2000). 

Potential Toxicity 

Given that NAWQA methods specify a 0.063-mm 

size fraction and strong acid digestion, any implied 

toxicity concerns from these data should be considered 

in that context: Larger-grained sediments likely contain 

lower trace element concentrations than the 0.063-mm 

fraction (Horowitz, 1991), whereas strong acid digestion may result in an overestimation of bioavailability. 

However, a direct comparison to the PEC guidelines 

developed by MacDonald and others (2000) showed 

an exceedance of the PEC in at least 35 percent of the 

samples from the Cook Inlet Basin with respect to 

arsenic, chromium, and nickel. Low toxicity, as indicated by the TEC guidelines, was exceeded by more 

than 50 percent of the samples from the basin for 

arsenic, chromium, copper, and zinc. The success of the 

SQGs in predicting toxicity was tested by MacDonald 

and others (2000). They found that except for mercury, 

the TEC and PEC concentrations were successful 

in differentiating between low and high occurrences of 

toxicity. Mercury showed incidences of toxicity in 

nearly 66 percent of samples with concentrations below 

the TEC, 70 percent of samples with concentrations 

between the TEC and PEC, and 100 percent of samples 

with concentrations higher than the PEC (MacDonald 

and others, 2000).
11

Potential toxicity for sediment-dwelling organisms exists in some areas of the Cook Inlet Basin 

study, particularly in the areas of Denali and Lake 

Clark National Parks and Preserves. The relatively 

low amounts of organic carbon in the streambed 

sediments from those areas increased the potential 

toxicity. For example, concentrations of all of the 

priority-pollutant trace elements were relatively low 

at Snowslide Creek (site 103) in the Denali area, yet 

the toxicity potential at that site was considered high 

for chromium, copper, lead, nickel, and zinc because 

the organic carbon concentrations was just 0.07 percent. 

In Anchorage, Chester Creek at Arctic Boulevard 

(site 27) had concentrations of cadmium, lead, and 

zinc that were elevated above a background level 

for the Cook Inlet Basin Study Unit and were higher 

than most sites in the Denali and Lake Clark areas, yet 

because the organic carbon concentration was about 

6 percent the toxicity potential was low.

Streambed sediment data collected in the Cook 

Inlet Basin during 1998 and included in this report 

(sites 7, 16, 23, 27, 41, 44, 50–55, and 57–58) were 

also discussed by Frenzel (2000). In that report, the 

trace element concentrations were compared to guidelines for bulk sediment (Canadian Council of Ministers 

of the Environment, 1999) and were not normalized 

for organic carbon. Frenzel (2000) found that the 

Canadian guidelines were exceeded in 57 percent 

of the streambed sediment samples for arsenic, 43 percent of the samples for chromium, and 7 percent of 

the samples for zinc. None of the samples exceeded the 

Canadian guidelines for the other six priority-pollutant 

trace elements. 

The mean PEC quotient was effective in defining 

overall sediment toxicity in more than 170 samples 

examined by MacDonald and others (2000). When 

applied to streambed sediments in the Cook Inlet 

Basin Study Unit, 44 percent of the samples would be 

classified as toxic. Therefore, concerns of potential 

toxicity to salmonid eggs and fry could exist where 

fine-grained sediments are abundant and trace element 

concentrations exceed PECs. Erosional areas of the 

streambed, such as riffles, where salmonid eggs 

typically are deposited and incubated, contained little 

of the finest-grained sediments—less than 0.01 percent of the sediment matrix was finer than 0.063 mm. 

However, fine-grained sediments are more abundant 

in depositional areas such as pools and sloughs, 

which are preferred rearing habitat for many salmonid 

fry. 

Because of the minute amount of fine-grained 

sediments in riffles, toxicity of trace elements in 

streambed sediments likely is low for salmonid eggs, 

despite concentrations that may exceed the PEC. 

However, since finer-grained sediments are more 

abundant in pools and sloughs, they may present 

greater toxicity for salmonid fry rearing in those areas. 

No concomitant biological data were collected to verify 

whether toxicity actually exists where a high potential 

toxicity is indicated.

SUMMARY

Concentrations of arsenic, chromium, mercury, 

and nickel in streambed sediments of the Cook Inlet 

Basin National Water-Quality Assessment (NAWQA) 

Study Unit were greater than concentrations in samples 

from reference areas sampled for the U.S. Geological 

Survey’s NAWQA program in the conterminous 

United States. Chromium and nickel concentrations 

were highest in the Denali area, while mercury concentrations were highest in the Lake Clark National Park 

and Preserve and in the Municipality of Anchorage. 

Arsenic concentrations were high in both Denali area 

and Lake Clark National Park Preserve. Concentrations 

of cadmium, lead, and zinc were highest at the most 

urbanized site in Anchorage and at two sites downstream from an ore body in Lake Clark National Park 

and Preserve. 

At least 35 percent of the 48 samples collected in 

the Cook Inlet Basin Study Unit had high potential toxicity for arsenic, chromium, or nickel. The potential 

toxicity was high in the Denali area and Lake Clark 

National Park and Preserve, where organic carbon concentrations in streambed sediments were low. Potential 

toxicity results should be considered in context with the 

very small amounts of fine-grained sediment present in 

the streambed sediments of the Cook Inlet Basin. To 

more accurately assess the toxicity of trace elements 

in the streambed sediments, measures of the aquatic 

communities are needed.
12

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Printed on recycled paper

Frenzel —Priority-Pollutant Trace Elements in Streambed Sediments of the Cook Inlet Basin, Alaska, 1998–2000 — Water-Resources Investigations Report 02-4163