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Selected Geochemical and Biogeochemical 

Studies of the Fortymile River Watershed, Alaska

Professional Paper 1685

U.S. Department of the Interior 

U.S. Geological Survey
Selected Geochemical and Biogeochemical Studies of the 

Fortymile River Watershed, Alaska

Larry P. Gough, Editor

Professional Paper 1685

U.S. Department of the Interior 

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey Information Services 

Box 25286, Denver Federal Center 

Denver, CO 80225

This report and any updates to it are available online at: 

http://pubs.usgs.gov/pp/p1685/

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Cataloging-in-publication data are on file with the Library of Congress (URL http://www.loc.gov/).

COVER Fortymile River near the mouth of Moose Creek. This section of the river, just a few miles west of the 

United States-Canadian border, cuts through supracrustal metasedimentary rocks of the Taylor Mountain assemblage. The geochemical influence of this and other lithologic units on surface-water chemistry and fish-tissue biogeochemistry is the subject of the first two chapters in this report. The brown color of the river water is due to the 

abundance of natural organic matter, which plays a role in the transport and complexation of dissolved metals—the 

subject of the third chapter in this report.

Manuscript approved for publication, October 30,2003 

Produced in the Western Region, Menlo Park, California 

Text edited by George A. Havach 

Layout and design by Sara Boore
Ill

Contents

[Numbers designate chapters]

Introduction ........................................................................................... ...^^ 1

By Larry P. Gough

1. Geochemical Processes and Geologic Framework Influencing Surface-Water and

Sediment Chemistry in the Fortymile River Watershed, East-Central Alaska..................... 3

By Bronwen Wang, Richard B. Wanty, and Jim Vohden

2. Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling

(Thymallus arcticus) in the Lower Fortymile River, Eastern Alaska...................................... 21

By Larry P. Gough, James G. Crock, Robert R. Seal, Bronwen Wang, and 

PhyllisWeber-Scannell

3. Comparative Characteristics of Natural Organic Matter in the Fortymile River, Alaska ............ 45

By Donald L. Macalady, Kaylene Ritter, Aaron D. Redman, and Magnus Skold

4. U.S. Geological Survey Reports on the Fortymile River Watershed — Products of 

Recent Mineral Resources Program Studies.................................................................................... 53

Introduction

By Larry P. Gough

The collection of three papers that follow results from 

hydrologic, geologic, geochemical, and biogeochemical 

studies begun in 1997 in the Forty mile River watershed, 

east-central Alaska. These studies are the latest in a series of 

publications (see bibliography at end of this report), resulting 

from work focused on the mineral-rich Yukon-Tanana Upland 

(YTU) physiographic region (Interior Highlands Ecoregion), 

conducted by the U.S. Geological Survey (USGS)'s Mineral 

Resources Program.

The YTU has a long history related to the mining and 

mineral industry. Placer gold was first discovered in the Fortymile River in 1886, and both alluvial and lode deposits have 

been exploited within the region. The development of low- to 

high-grade, high-tonnage, intrusion-related Au deposits (such 

as Fort Knox, True North, and Pogo) since the early 1990s is 

a new resource that has spurred a resurgence of exploration 

activity. Numerous State and Federal regulations require that 

the degree of potentially adverse environmental impact from 

these exploration and mining activities be quantified, especially for surface-water quality and its influence on the health 

of aquatic biota. By helping to establish regional premining 

baselines, these and other studies will aid regulatory decisions 

at the local, State, and Federal levels, as well as help the mining companies formulate efficient mitigation plans.

The USGS, the Bureau of Land Management, and the 

Alaska Department of Natural Resources are cooperating in 

project work to provide the scientific data for upcoming decisions that involve State and Federal land-use options and their 

regulations. One important question that relates to resource 

development is "what are the regional predevelopment 

geochemical 'signatures' (or baselines) for water and biota, 

and what impact do natural processes have on the variation 

in those 'signatures'"? This question is especially important 

because it applies to trace elements, particularly if those trace 

elements have environmental importance (that is, are metabolically active, possibly even toxic, in plants and animals). By 

understanding the predevelopment baselines, changes suspected to have been caused by human activity can be defined 

and quantified.

The chapters in this report provide a framework for the 

analysis of future, potential changes in geochemical and biogeochemical signatures, because they report the quantitative 

analysis of water, sediment, rocks, and fish tissue. They also 

report on the processes that affect the mobility and bioavailability of certain trace elements. The chapter by Wang and others discusses major- and trace-element chemistry in relation to 

regional lithologic units within the Fortymile River watershed. 

The major-ion chemistry of the waters reflects a rock-dominated aqueous system with but limited interaction with the 

geologic materials of the region. The authors discuss in detail 

the multiple and varied reasons for this apparent paradox. The 

chapter by Gough and others examines the chemistry of fish 

tissue (Arctic grayling) and reports functional biogeochemical 

baseline values and (or) ranges for numerous elements, including mercury. This chapter also examines the nitrogen-, carbon-, 

and sulfur-isotopic composition of fish tissue in relation to 

grayling food sources and trophic position in the food web. 

Finally, the chapter by Macalady and others discusses the role 

of dissolved natural organic matter on the mobility of trace 

elements in waters. Measurements of the copper-complexation 

capacities of these samples confirm that the dissolved organic 

matter has very low metal-binding capacities. The authors 

discuss the importance of this discovery in relation to future 

potential mining activities.

The bibliography at the end of this report lists all the publications that were generated by this project from 1997 to the 

present, some of which are available in their entirety online, 

whereas others may be obtained from the USGS library (URL 

http://library.usgs.gov/) or from USGS Information Services 

(URLhttp://mapping.usgs.gov/esic/to_order.html).

Chapter 1

Geochemical Processes and Geologic Framework 

Influencing Surface-Water and Sediment Chemistry 

in the Fortymile River Watershed, East-Central Alaska

By Bronwen Wang, Richard B. Wanty, and Jim Vohden 1

Contents

Abstract.......................................................................................................... 3

Introduction................................................................................................... 3

Geologic Setting............................................................................................ 4

Methods......................................................................................................... 6

Results .......................................................................................................... 7

Aqueous Chemistry............................................................................ 7

Stream Sediment................................................................................ 8

Rare-Earth Elements.......................................................................... 9

Summary........................................................................................................17

References Cited ..........................................................................................17

Abstract

We have analyzed major, trace, and rare-earth elements 

in water and stream-sediment samples from 33 sites within the 

Fortymile River Basin. The major-ion chemistry of the basin 

is relatively uniform. Stream waters are classified primarily as 

Ca2+ and Mg2+-HCO3-to mixed Ca2+ and Mg2+-HCO3- and SO42- 

type. The major-ion chemistry of the waters reflects a rockdominated aqueous system with but limited interaction with 

the geologic materials of the region. Trace-element concentrations in water are generally low; however, some dissolved 

Cu contents exceeded the freshwater-aquatic-life standard for 

chronic exposure. Stream-sediment As, Cu, Hg, and Zn contents ranged from below the Canadian interim sediment-quality guideline (ISQG) to above the ISQG but below the probable-effects limit (PEL). All the sites exceeded the ISQG for 

Cr, and nine exceeded the PEL; however, what effect, if any, 

these levels might have on the stream biota in this aqueous 

system is unclear. The streams draining metavolcanic rocks 

had the highest Cr contents in sediment, possibly reflecting the 

Cr contents of the mafic metavolcanic rocks.

Total rare-earth-element (REE) concentrations range from 

<0.61 to 15 ng/L and from 103 to 171 mg/kg for aqueous and

'Alaska Department of Natural Resources.

stream-sediment samples, respectively. Total aqueous REE 

concentrations were positively correlated with the amount of suspended colloidal matter but not correlated with the pH of the water.

Introduction

The Fortymile River lies within the "Tintina Gold Belt" 

and is within the Yukon-Tanana Upland physiographic province (fig. 1). Placer gold has been mined in the Fortymile River 

region since 1886 (Mertie, 1938; Yeend, 1996), and gold exploration and development in the Tintina Gold Belt has recently 

expanded because of the discoveries of the Fort Knox, True 

North, and Pogo deposits (Goldfarb and others, 2000). Between 

1997 and 1998, the U.S. Geological Survey and the Alaska 

Department of Natural Resources conducted a cooperative study 

in the Fortymile River watershed to provide background geochemical data for this region. The effects of current placer-mining operations on the Fortymile River and the chemical composition of bedrock, soils, and vegetation in the Fortymile River 

Basin have been reported elsewhere (Crock and others, 1999, 

2000; Wanty and others, 2000; Gamble and others, 2001; Gough 

and others, 2001). In this chapter, we focus on the chemical 

characteristics of surface water and stream sediment within the 

basin, evaluating the major ions, trace elements, and rare-earth 

elements (REEs) in the context of the geologic setting.

Interest in REE mobility in riverine environments has 

increased in recent years. Previously, REEs had been considered 

to be relatively immobile in many geologic environments. With 

advances in analytical-chemical techniques, however, many 

studies have shown REE fractionation during soil development 

and mobility in ground waters, surface waters, and thermal 

springs (Keasler and Liveland, 1982; Cullers and others, 1987; 

Goldstein and Jacobson, 1988; Elderfield and others, 1990; 

Smedley, 1991; Ohlander and others, 1996; Morey and Setterholm, 1997; Banks and others, 1999; Tricca and others, 1999; 

Johannesson and others, 2000). As a result, REE mobility is
Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

now widely accepted, and several studies have used REEs as 

hydrologic tracers (Johannesson and others, 1997; Worrall, 2001).

Brookins (1989) and Wood (1990) reviewed the aqueous 

geochemistry of REEs. With the exception of Ce(IV) and Eu(II), 

all REEs occur in nature in a 3+ oxidation state, and the ionic 

size decreases from La3+ to Lu3+ because of the lanthanide contraction (see Greenwood and Earnshaw, 1984). The lanthanides 

are considered "hard acids" and readily form complexes with 

such hard bases as COf~, PO^, SOf, F', and OH~. The distribution of REEs in water and sediment depends on the distribution 

and fractionation characteristics of the geologic material, the 

preferential dissolution of REEs containing mineral phases 

during weathering, and the formation and presence of secondary 

minerals and colloidal matter (Banks and others, 1999).

REEs are commonly normalized to either chondrite or 

the North American Shale Composite (NASC) (Goldstein 

and Jacobsen, 1988; McLennan, 1989). Such normalization 

smoothes the inherent difference in abundance of the individual elements in the lanthanide series. Chondrite is believed 

to represent the cosmic and bulk-earth abundance, whereas the 

NASC represents the average upper-continental crust. Fractionation during weathering can give rise to normalized patterns that are enriched or depleted in light REEs (LREEs), and 

the redox behavior of Ce and Eu can lead to either positive or 

negative anomalies, depending on environmental conditions.

One measure of the relative fractionation of REEs is 

given by the normalized La/Yb ratio:

(La/Yb)n = (La/Yb)smTlple/(La/Yb)standan,

(La/Yb)n>l indicates LREE enrichment in a sample relative 

to the normalizing component, (La/Yb)n<l indicates relative

LREE depletion, and (La/Yb)n~l indicates little internal REE 

fractionation. Ce and Eu anomalies are expressed herein as 

Ce* and Eu/Eu*, given by Ce*=3Cen/(2Lan+Ndn) and Eu/ 

Eu*=Eun/(SmnxGdn)° 5 , respectively, where the subscript "n" 

denotes the normalized concentration (Goldstein and Jacobsen, 1988; Elderfield and others, 1990).

Geologic Setting

The bedrock geology and geochemistry of the Fortymile 

River area have been discussed in detail elsewhere (Foster 

and others, 1994; Hansen and Dusel-Bacon, 1998; Day and 

others, 2000, 2002; Szumigala and others, 2000a, b; Gamble 

and others, 2001). The major lithologic units in the study area 

compose a supracrustal sequence of volcanic and sedimentary 

rocks that have been intruded by Mississippian biotite tonalite (Day and others, 2002). The metasedimentary and mafic 

metavolcanic rocks were deposited on a continental margin or 

distal to an island-arc complex. Recrystallization of the entire 

package during intense Jurassic deformation and dynamic 

metamorphism almost entirely obscured the original sedimentary fabrics (Dusel-Bacon and others, 1995). A posttectonic 

granitic suite, chemically similar to other volcanic-arc granites, intrudes the entire sequence (Day and others, 2002).

The metasedimentary rocks consist of biotite schist, 

quartzite, and marble. The biotite schist and quartzite constitute end members of a compositional continuum defined 

primarily by the proportion of micaceous material (Gamble 

and others, 2001). The mineralogy of the biotite schist consists 

of quartz+biotiteiwhite micaigarnetihornblende. The marble

area

Figure 1. Sketch map of Alaska, showing location of study area within the 

Tintina Gold Belt and relative to several major gold deposits (dots) and cities 

(asterisks).
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry 5

contains as much as 5 volume percent white mica, biotite, 

amphibole, and (or) pyrite.

The metavolcanic rocks are predominantly basalt; no 

metavolcanic rocks of felsic composition have been observed 

(Day and others, 2002). The mafic metavolcanic rocks contain 

plagioclase+hornblende±biotite±clinopyroxene±garnet±quartz 

and are fine- to medium-grained, dark-green to black amphibolite gneiss, with both a tholeiitic and a tholeiitic to calc-alkaline series (Dusel-Bacon and Cooper, 1999; Day and others, 

2000). Higher Cr and Cu contents were reported in the mafic 

metavolcanic rocks relative to the other rock types (Gamble 

and others, 2001).

The southeastern part of the study area (fig. 1) is largely 

underlain by tonalitic orthogneiss (Steel Creek Dome Orthogneiss) that occurs as interlayers within the supracrustal rocks 

and as small bodies which intrude the sequence (Day and others, 2000, 2002; Gamble and others, 2001). The orthogneiss is

light gray, fine to medium grained, and gneissic and generally 

consists of plagioclase, quartz, biotite, muscovite, and alkali 

feldspar, with accessory apatite, opaque minerals, and zircon 

(Gamble and others, 2001). The tonalitic gneiss is transitional 

in composition from metaluminous to peraluminous.

Day and others (2000) distinguished four basic chondritenormalized REE patterns in the lithologic units of the study 

area (fig. 2). The metasedimentary rocks are LREE enriched 

and have a negative Eu anomaly. The metavolcanic rocks 

exhibit two patterns: one characterized by LREE depletion and 

another by LREE enrichment (referred to as metavolcanic rock 

groups I and II, respectively, by Day and others, 2000). The 

tonalites are LREE enriched and have a small, positive or negative Eu anomaly. In addition, much of the Fortymile River area 

is overlain by loess. LREE concentrations within the loess are 

generally higher than in the bedrock (fig. 2). The loess is LREE 

enriched relative to chondrite, with a negative Eu anomaly.

100

<

cc

111 

o-z. 

O O

HI 

HI

cc

Q 

HI 

N

CC

O

6

CO

cc O

LLJ 

H

CC 

Q-z. 

O

O

10

0.1

••*--• loess/chondrite

•••••• ms/chondrite

• -A- - - mv group I/chondrite

• -A- - - mv group II/chondrite

•-•••• sct/chondrite

A---A* v V

• loess/NASC

• ms/NASC

1 mv group I/NASC

•mv group II/NASC

• sct/NASC

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

Figure 2. Chondrite- or North American Shale Composite (NASC)-normalized rareearth-element (REE) concentrations in bedrock and loess of the Fortymile River Basin, 

eastern Alaska (fig. 1). Bedrock values are mean REE concentrations reported by 

Crock and others (1999) and Day and others (2000); loess values are those of L.P. Gough 

(unpub. data, 1998). ms, metasediment; mv, metavolcanic; set, Steele Creek tonalite.
Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Methods

A total of 33 sites were sampled during June and July

1997 and 1998 (fig. 3). In the text, sites are referred to by 

the creek name. Complete analytical data for these sites were 

reported by Crock and others (1999, 2000); 1997 analytical 

data for anions were omitted from these reports and are listed 

in table 1. Water samples were collected in both 1997 and

1998 at three sites on the North Fork of the Fortymile River, 

Buck Creek, and O'Brien Creek for interannual comparison. 

Major-ion and trace-element chemical analyses are available 

for both water and stream-sediment samples at all sites, but 

REE and Hg analyses are unavailable for the 1997 streamsediment samples. In addition, stream-sediment samples 

were not collected on the tributaries to Uhler Creek or on the 

South Fork or main stem of the Fortymile River.

Details of the sampling and analysis were presented 

by Crock and others (1999, 2000) and Wanty and others 

(2000). In general, water samples were depth- and widthintegrated composite samples filtered through a 0.45-|im

filter. Samples for cation analysis were acidified with 

ultra-high-purity HNO3 . The filtered water samples are 

considered to represent the dissolved metals for comparison 

with the U.S. Environmental Protection Agency's standard; 

however, colloids <0.45 p,m could be present in these 

samples. Measurements of pH, electrical conductivity, temperature, turbidity, and stream discharge were performed 

in the field. Sediment samples were bulk composites from 

active depositional zones within the stream. Several depositional areas were sampled and combined to obtain sufficient 

material for analysis. In the laboratory, sediment samples 

were dried, sieved to minus-80 mesh, and ground before 

analysis by inductively coupled plasma mass spectrometry 

(ICP-MS). Sampling and analytical methods followed 

established standard procedures (Wood, 1976; Fishman 

and Pyen, 1979; Lichte and others, 1987; Meier and others, 

1994). Cations and trace metals were analyzed by ICP-MS 

(Meier and others, 1994); anions were analyzed by ion 

chromatography, following the techniques of Fishman and 

Pyen (1979).

142°00' 141°00'

64°25

EXPLANATION 

D sampled in 1997

O sampled in 1998 

[H sampled in 1997 and 1998 

® North Fork stream sediment 

sampled in1997

Base data for hydrography and roads from USGS 

1: 63,360 scale digital line graphs for Eagle A-1, 

A-2, B-1, B-2, and B-3 quadrangles. Universal 

Transverse Mercator projection, 1927 North 

American Datum.

SMILES

I

01234 5 KILOMETERS

Location of 

study area

Figure 3. Fortymile River Basin, eastern Alaska (fig. 1), showing locations of 1997 and 1998 water- and stream-sediment-sampling sites.
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry

Table 1. Major-anion concentrations in surface water samples from the Fortymile River Basin, eastern Alaska.

[See figures 1 and 3 for locations. Samples collected in 1997, numbered according to Crook and others (1999). All values in milligrams 

per liter; dashes, not measured. 1C, ion chromatography]

Sample

97AK-01 A

97AK-01 B

97AK-06W 

97AK-07W A

97AK-07W B

97AK-08W 

97AK-09W A

97AK-09W B

97AK-10W 

97AK 11 W

97AK 12W

97 AK 13 W

97AK 14W

97AK 15W A

97AK 16W

97AK-18W

Description

Hutchinson Creek ————————————

Bullion Creek ———————————————

Split of Bullion Creek ——————————

Wilson Creek ————————————————

Wilson Creek duplicate —————————— 

Uhler Creek at confluence with the South Fork 

of the Fortymile River.

Uhler Creek at mining operation ——————

Uhler Creek above mining —————————

Unnamed tributary to Uhler Creek — — — — —

Uhler Creek above tributary ——————————

O'Brien Creek ———————————————

North Fork of the Fortymile River above 

confluence with the South Fork.

F

0.09

.13 

.19

.18 

.15

.10

.10 

.09 

.11 

.09 

.14 

.12 

.12

Cl

0.18

.13 

.13

.18 

.14

.19

.10 

.08 

.10 

.07 

.40 

.38 

.83

NO3"

.39 

.42 

.55 

.79 

.73 

.96 

.86 

.87 

.89

1.10 

.75 

.54 

.85 

.39 

8.10 

.31

sor

5 

5 

21 

14 

14 

10 

41 

42 

14

6 

8 

13 

7 

64 

13 

23

Alkalinity 

as CaCO3

87

48 

58 

58 

28 

41 

41 

22

19 

17 

13 

18 

103 

77 

53

Results

Aqueous Chemistry

The major- and trace-element concentrations in water 

samples are listed in table 2. As illustrated by a Piper plot (fig. 

4), the stream waters are classified primarily as Ca2+ and Mg2+- 

HCO;T to mixed Ca2+ and Mg^-HCC^and SO42~type. At seven 

sites—Wilson, Creek, Steel Creek, Smith Creek, Flat Creek, 

Polly Creek, Sam Patch Creek, and an unnamed tributary to 

Uhler Creek—>50 percent of the anionic charge was derived 

from SO42~. The low content of total dissolved solids indicates 

that these waters have not undergone extensive interaction 

with the geologic material of the region. However, the plot of 

Na/(Na+Ca) versus total dissolved solids in the waters lies in 

the general region of rock-dominated systems as defined by 

Gibbs (1970) (fig. 5), indicating that the composition of these 

samples is more rock dominated as opposed to evaporation or 

precipitation dominated. The minimal water-rock interaction 

may be due to short flowpaths, partly owing to the presence 

of permafrost limiting the hydrologic flowpath (Wanty and 

others, 2000).

As, Cd, Cu, Pb, Hg, and Se contents in water are all 

commonly associated with regulatory concerns. As and Se 

contents are below the limits of detection (<3 and <0.2 |Ug/L, 

respectively) in all samples. Hg was detected in two samples: 

at the mouth of Smith Creek (0.005 |Lig/L) and in Steele Creek 

(0.014 |Ug/L), both well below both the aquatic-life-standard 

criteria continuous concentration (CCC) of 0.77 |Ug/L and

the human-health consumption criterion of 0.05 jig/L (U.S. 

Environmental Protection Agency, 1999). The CCC is defined 

as the highest concentration of a material in surface water 

to which an aquatic community can be exposed indefinitely 

without resulting in an unacceptable effect. The Cd content at 

10 sites and the Pb content at 11 sites were above the limits 

of detection, ranging from 0.02 to 0.17 jig/L and from 0.05 to

EXPLANATION 

+1997 tributary samples 

O 1997 North Fork samples 

x 1998 tributary samples 

X 1998 North Fork samples 

n 1998 South Fork sample 

A 1998 main-stem samples

cr

Figure 4. Piper plot of major cations and anions for water 

samples from the Fortymile River and its tributaries, eastern Alaska 

(figs. 1,3).
8 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Table 2. Summary statistics for the major ions and trace elements in water samples from the Fortymile 

River and its tributaries.

[See figures 1 and 3 for locations. Statistics not calculated for elements with censored data]

Element Lower limit Arithmetic 

of detection mean

Geometric 

mean

Geometric 

deviation

Observed 

range

Proportion 

of samples

above

analytical

detection limit

Al(ug/L)-——- - 0.1 208 154.9 2.2 23-839 36:36

As (ug/L)—-—- - 3 — — — <3 0:36

Ba(ug/L)—------ .1 37 32 2 16-76 36:36

Ca(mg/L) ——— .05 17 15 2 5.6-35 36:36

Cd(ng/L)——- - .05 — — — <.02-0.17 10:36

Cl(mg/L)—-—- .01 .27 .20 2.07 .06-0.90 36:36

Co (ng/L)------ .02 .54 .23 3.03 .03-7.02 36:36

Cr(ng/L)—------ 1 2221-5 36:36

Cu (ng/L)------ .5 4.9 4.0 1.7 2-34.9 36:36

F(mg/L)-«—- — .01 .10 .10 1.50 .04-0.19 36:36

Fe(ug/L)——— 10 293 239 2 53-780 36:36

HCO3-(mg/L)—- — 54 41 2 12-125 36:36

Hg(ng/L)——-- .005 — — — <.005-0.014 2:36

K(ug/L)——— .3 816 760 1.45 440-1,700 36:36

Li(ng/L)—------ .1 1.7 .9 3.0 .1-17.9 36:36

Mg(mg/L)~- -— .01 4.4 3.53 2.08 1.2-14.7 36:36

Mn(ng/L)——— .01 20 7 5 .34-163 36:36

Mo (ug/L)——— .02 — — — <.02-1.45 26:33

Na(mg/L)~- —— .01 1.7 1.47 1.68 .76-7.39 36:36

Nb(ng/L)——- .02 — — — <02-0.2 25:36

Ni(ng/L)—------ .1 3.7 2.4 2.3 .6-33.6 36:36

NO3-(mg/L)——- .05 .9 .6 2.2 .1-8.1 36:36

Pb(ng/L)-~ ------ -05 — — — <05-0.2 11:36

Rb(ng/L)-—— .01 .91 .89 1.44 .35-1.81 36:36

Sb(ug/L)——— .1 .21 .2 2.0 .04-0.74 36:36

Sc(ng/L)—------ .1 — — — <.1-1.4 32:36

Se(ng/L)——— .2 — — — <.5 0:36

SiO2 (mg/L)—— .5 5.3 4.9 1.4 3.2-9.3 36:36

SO42-(mg/L) —-- .05 21 16 2 3.3-64 36:36

Sr(ng/L)——— .5 68 58 2 18-134 36:36

Th(ng/L)—------ .005 .18 .16 1.89 .03-0.49 36:36

Ti(ug/L) ——— .1 3.3 2.8 1.8 .7-7.9 36:36

U(ng/L)-—------ .005 .4 .3 2.2 .07-1.21 36:36

V(ng/L)——-— .1 .9 .7 2.0 .2-2.3 36:36

Zn(ug/L)~-——- .5 — — — <.5-50.1 30:36

0.2 |U,g/L, respectively. Cu was detected at all sites at contents 

ranging from 2 to 34.9 mg/L. Aquatic-life criteria for dissolved Cd, Pb, and Cu vary with hardness (U.S. Environmental Protection Agency, 1999), which is calculated from the Ca 

and Mg contents and expressed as milligrams of CaCO3 per 

liter (Greenberg and others, 1985).

The hardness of waters in the Fortymile River Basin 

ranged from 21 and to 137 mg CaCO3/L. The CCC and the 

criteria maximum concentration (CMC, defined as the highest concentration of a material in surface water to which an 

aquatic community can be exposed briefly without resulting in 

an unacceptable effect for freshwater aquatic organisms) were 

calculated for each stream by using their respective hardness.

Cd and Pb contents were below both the CMC and CCC in 

all streams; Cu contents exceeded the CCC and CMC at Twin 

Creek, Bow Creek, Polly Creek, and Discovery Creek (fig. 6).

Stream Sediment

Trace elements in stream sediment may be contained 

in the sediment minerals or adsorbed onto clay, oxides, and 

organic layers. No State or Federal guidelines or standards 

exist for trace-element concentrations in stream sediment; 

however, the Canadian Council of Ministers for the Environment (1999) has adopted Canadian Sediment Quality Guide-
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry

lines for the protection of aquatic life, and guidelines have 

been set for As, Cd, Cr, Cu, Pb, Hg, and Zn. Two levels are 

defined for the total trace-element concentration in a bulk 

stream-sediment sample: the interim sediment-quality guideline (ISQG), where toxicologic effects are expected to be rare; 

and the probable-effect level (PEL), where toxicologic effects 

are expected to occur (table 3).

Major- and trace-element concentrations in stream-sediment samples are listed in table 4. Cd and Pb contents are all 

below the ISQG, whereas As, Cu, Hg, and Zn contents range 

from below to above the ISQG but below the PEL. Cr content 

at all sites exceeded the ISQG and at nine sites exceeded the 

PEL; sediment from streams draining metavolcanic rocks 

generally had a higher Cr content. To understand what, if any, 

effect Cr may be having on the aquatic biota, further work on 

the form and distribution of Cr bioavailability in this aquatic 

system is needed.

Rare-Earth Elements

Total REE concentrations range from <0.61 to 15 jig/L 

and from 103 to 171 mg/kg in water and stream-sediment

10,000

1,000

0.5 

Na/(Na + Ca) RATIO

1.00

Figure 5. Total dissolved solids versus Na/ 

(Na+Ca) ratio for the Fortymile River and its tributaries, eastern Alaska (figs. 1,3). Boomerangshaped envelope approximated from Gibbs (1970).

4.5-

4.0- 

Q

cr 

<3.5H

2.5-

O Q 1.5- 

< ft 1.0

Q 

^0.5H

x

0

Figure 6. Ratio between filtered Cu contents and hardness-adjusted criteria-maximumconcentration (open bars) and criteria-continuous-concentration (solid bar) Cu standards 

(U.S. Environmental Protection Agency, 1999) for water samples from the Fortymile River 

and its tributaries, eastern Alaska. Values greater than 1 exceed hardness-adjusted 

standard. ERA, U.S. Environmental Protection Agency.
10 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

samples, respectively (table 5). The REE concentrations in 

water samples from the Fortymile River area are generally 

higher than those in stream waters reported by other workers (table 6). Chondrite- and NASC-normalized patterns for 

water and stream-sediment samples from the Fortymile River 

Basin are plotted in figures 7 through 9. Both water and 

stream-sediment chondrite-normalized patterns are LREE 

enriched, with slightly negative Ce and Eu anomalies (figs. 

7-9). The small-tributary watersheds have (La/Yb)n values 

ranging from 3.2 to 10.9, Ce* values tanging from 0.44 to 

0.97, and Eu/Eu* values ranging from 0.44 to 0.95 in water 

samples, and (La/Yb)n values ranging from 3.8 to 8.7, Ce* 

values ranging from 0.81 to 0.85, and Eu/Eu* ratios ranging 

from 0.71 to 0.93 in stream-sediment samples (table 5). Water 

samples from the North Fork, South Fork, and main stem of 

the Fortymile River have (La/Yb)n ,Ce*, and Eu/Eu* values in 

the same range as those from the tributaries (table 5). When

Table 3. Interim freshwater sediment-quality guidelines and 

probable-effects levels for selected trace elements in water samples from the Fortymile River and its tributaries, eastern Alaska.

[See figures 1 and 3 for locations. All values in milligrams per kilogram 

dry weight. ISQC, interim sediment-quality guideline (Canadian Council 

of Ministers for the Environment, 1999); PEL, probable-effects level]

Element ISQG PEL

Ac

Cd /-i i ——— -

Cr

Cu— -----

Pb ......_

Hg———

Zn— — -

5 9

.6

•37 o

oc 7

35.0

100

17.0

3.5

90.0

197

91 3

486

315

Table 4. Summary statistics for major-ion and trace-element concentrations in stream-sediment samples from the Fortymile 

River and its tributaries, eastern Alaska.

[See figures 1 and 3 for locations. All values are dry-weight contents]

Element Lower limit 

of detection

Arithmetic 

mean

Geometric 

mean

Geometric 

deviation

Observed 

range

Proportion of samples 

above analytical 

detection limit

Ag (mg/kg) —— 

Al (wt pet) 

As (mg/kg)—— 

Au (mg/kg) ----- 

Ba (mg/kg)——- 

Be (mg/kg)—— 

Bi (mg/kg) —-— 

Ca (wt pet) --—— 

Cd (mg/kg)-—- 

Co (mg/kg)—— 

Cr (mg/kg)—— 

Cs (mg/kg) —— 

Cu (mg/kg)——— 

Fe (wt pet) ——— 

Ge (mg/kg)—— 

Hg (mg/kg) —— 

K (wt pet) —— 

Li (mg/kg) —— 

Mg (wt pet) —— 

Mn (mg/kg) —— 

Mo (mg/kg) —— 

Na(wt pet)——— 

Nb (mg/kg) —— 

Ni (mg/kg) 

Pb (mg/kg) ——- 

P(wtpct)——— 

Rb (mg/kg)—— 

Sb (mg/kg) —— 

Sc (mg/kg) 

Sr (mg/kg) ——— 

Ti (wtpct)——— 

U (mg/kg) —— 

V (mg/kg)—— 

Y (mg/kg)——- 

Zn (mg/kg)——

0.02

.01

.5

.005 

5

.1

.05

.5

.1 

1

.1 

1

.05

.1

.1

.02

.5

.5

.1 

10

.1

.1

.01

.1 

.1

.01

1 

.1

.5

10

.05

.05

1

.01

3

0.34

8.35

7.5

1,061

1.5

0.16

2.8

.3

18

83

3

29

4.9

3.0

1.6

22

2

1,060

.9

2.2

13

23

16

0.1

65

1.3

21

282

0.48

2.2

149

26

107

0.23

8.21

6.8

1,051

1.4

.15

2.7

.2

17

79

3

27

4.8

2.4

1.6

21

2

1,037

.9

2.1

13

29

15

.09

63

.9

20

270

.48

2.1

144

25

105

2.38

1.2

1.5

1.1

1.24

1.45

1.3

1.3

1.3

1.3

1.3

1.4

1.24

1.1

.3 

.3 

.3 

.2 

.3 

.4 

.3 

.5

.3 

2.2

.3 

.24 

.3 

.3

0.07-1.45 

5.46-12

3.4-8

<.005-0.035 

836-1,300

1-3.2

.09-0.55

1.4-5.9

.2-0.4

12-39

49-172

2-4

19-122

3.1-7.7

1.2-6.2

<.02-0.3

.9-2.5

13-37

1.2-3.1

645-1,370

.6-1.8

1.0-4.3

5.8-20

12.6-88

9.4-28

.6-0.14

39-120

.2-5.4

14-33

143-558

.37-0.80

1.4-3.6

87-335

19-46 

79-190

34:34 

34:34 

34:34 

24:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

31:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

34:34 

20:20 

34:34 

34:34 

34:34 

34:34
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry 11

Table 5. Total rare-earth-element concentrations, (La/Yb)n ratios, Ce anomalies (Ce*), and Eu/Eu* ratios for water and 

stream-sediment samples for streams in the Fortymile River Basin, eastern Alaska.

[See figures 1 and 3 for locations. Total rare-earth-element (REE) values: tributary and Fortymile River water samples, micrograms per liter; 

tributary stream-sediment samples, milligrams per kilogram. (LaA'b)n=(LaA'b)samp,e/(LaA'b)stanilmj (Goldstein, 1988); Ce*=3(Ce)n/(2Lan+Nb,1 ) 

(Goldstein, 1988; Elderfield, 1990); Eu/Eu*=Eun/(SmnxGdn)05 (McLennan, 1989)]

Site Total 

REEs

Chondrite normalized

(La/Yb)n Ce* Eu/Eu*

NASC normalized

(La/Yb)n Ce* Eu/Eu*

Tributaries — water

A IHpt* C~**Y(*(*\r

Qii/*t- /"Voot- /I OQ'TA

Riirk Cre-e-\c HQQJtt _________________ -.

frlci/M**!* C**Tf*P\C ................

Flat Crpp-lc —————— ......

Hall Treek ____________________

l-Iiif r*V||v»cr\r» (~*Tf*f*\f ....

\^Vw\c** (~*Tf*P\C .................

O'Qrior* /"Vjajat' /'1OO'7\

O'Rrien Cr?e\c nQQKI _____ ... .. ... ...

Polly Creek ———————————————

^lam Patr^h Prpplr __

Smith Creek ——————— — .—.———......

Cr»r\\i/ f'VApk".. .........

Upper Squaw Gulch ———————————————

Cfppfp C*r(*(*\f ............

T\vin (~*Tf*p\c ...............

Uhler Creek above tributary ——————————

Uhler Creek at mining operation ----——---—----

Uhler Creek at confluence with the South Fork of 

the Fortymile River. 

Uhler Creek 1 mi above mining — — —— —— —

Unnamed tributary to Uhler Creek ————————

0.84 

11.02 

3.05 

1.93 

3.72 

4.25 

3.56 

3.64 

1.34 

3.83 

3.34 

2.31 

12.53 

5.32 

2.85 

.61 

2.81 

9.04 

4.23 

4.33 

2.11 

5.35 

4.28 

15.00 

3.91 

3.48 

3.77 

4.17

3.53 

3.23 

2.10

4.3 

10.6 

5.0 

5.8 

7.1 

10.8 

6.4 

7.4 

4.4 

8.3 

7.7 

6.5 

10.9 

8.6 

5.3 

3.2 

6.6 

9.5 

5.0 

6.0 

6.0 

6.8 

6.3 

10.3 

5.4 

7.9 

7.1 

7.0

6.6 

4.8 

4.0

0.44 

.97 

.62 

.65 

.79 

.53 

.77 

.73 

.56 

.72 

.67 

.60 

.93 

.61 

.74 

.89 

.79 

.90 

.86 

.61 

.63 

.82 

.74 

.83 

.73 

.73 

.75 

.71

.75 

.79 

.58

0.77 

.72 

.58 

.64 

.77 

.44 

.90 

.74 

.73 

.78 

.69 

.66 

.67 

.62 

.95 

.53 

.80 

.77 

.78 

.75 

.93 

.85 

.83 

.64 

.84 

.60 

.69 

.67

.53 

.73 

.77

0.6 

1.6 

.8 

.9 

1.1 

1.6 

1.0 

1.1 

.7 

1.2 

1.1 

1.0 

1.6 

1.3 

.8 

.5 

1.0 

1.4 

.7 

.9 

.9 

1.0 

.9 

1.5 

.8 

1.2 

1.1 

1.1

1.0 

.7 

.6

0.44 

.97 

.62 

.65 

.80 

.53 

.77 

.74 

.56 

.72 

.67 

.59 

.94 

.61 

.74 

.89 

.79 

.90 

.86 

.61 

.64 

.82 

.75 

.85 

.72 

.73 

.74 

.71

.75 

.77 

.57

1.10 

1.03 

.82 

.91 

1.10 

.63 

1.28 

1.05 

1.04 

1.10 

.98 

.94 

.96 

.88 

1.35 

.76 

1.14 

1.09 

1.11 

1.07 

1.32 

1.20 

1.19 

.91 

1.20 

.85 

.98 

.95

.76 

1.04 

1.09

Fortymile River — water

North Fork above confluence with the South Fork 

of the Fortymile River (1997). 

North Fork above confluence with the South Fork 

of the Fortymile River (1998). 

South Fork above confluence with the North Fork 

of the Fortymile River. 

Main stem of the Fortymile River above Polly 

Creek. 

Main stem of the Fortymile River below Moose 

Creek.

0.85 

1.58 

2.94 

2.08 

2.29

6.5 

5.1 

4.2 

4.9 

4.6

0.44 

.48 

.64 

.56

.57

0.65 

.74 

.83 

.93 

.81

1.0 

.8 

.6

.7 

.7

0.44 

.48 

.64

.57 

.57

0.93 

1.05 

1.18 

1.32 

1.15
12 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Table 5. Total rare-earth-element concentrations, (La/Yb)n ratios, Ce anomalies (Ce*), and Eu/Eu* ratios for water and 

stream-sediment samples for streams in the Fortymile River Basin, eastern Alaska—Continued

Site Total 

REEs

Chondrite normalized

(La/Yb)n Ce* Eu/Eu*

NASC normalized

(La/Yb)n Ce* Eu/Eu*

Tributaries — stream sediment

Canyon Creek —————————————— • Discovery Creek ------------------------------

Flat PrpplHall Creek -————————————.

Canyon Creek above Hall Creek ———— • Mariner —————————————————— • Canyon Creek above Mariner Creek ——— • Moose Creek ——————————————— •

NllfJffPt frpplr— -— .._.-.._..___._..._ .____.__.

Polly Creek ________________ •

Qatn Potr>Vi frooU

Smith Creek -—-—-——-—— ——

Snow Creek ———————————————— • Upper Squaw Creek ——————————— •

Qri|iO\x; f~*TP(*\f

Canyon Creek above Squaw ——————— •

Ctpplp rVppl-

. ___ 123 4

... ...... 153.4

......... 132.3

......... 107.9

n« £.

......... 124.7

......... 134.4

......... 103.8

......... 171.9

. ___ 132 3

......... H4.1

......... 117.4

107 1

......... 150.8

......... 124.1

___ 1 77 n

m o

m o

1 1£. O

......... 120.9

7.4 

7.0 

5.8 

3.8 

5.4 

6.4 

6.7 

4.9 

8.7 

6.5 

5.5 

6.2 

5.9 

7.6 

6.7 

5.8 

4.4 

5.7 

6.9 

5.6

0.81 

.83 

.85 

.84 

.81 

.81 

.81 

.81 

.83 

.82 

.83 

.83 

.83 

.82 

.83 

.84 

.82 

.82 

.82 

.82

0.78 

.73 

.84 

.90 

.79 

.81 

.80 

.84 

.71 

.79 

.82 

.83 

.86 

.75 

.84 

.87 

.93 

.78 

.78 

.86

1.1 

1.0 

.8 

.5 

.8 

1.0 

1.0 

.7 

1.2 

.9 

.8 

.9 

.8 

1.1 

1.0 

.8 

.7 

.8 

1.0 

.8

0.81 

.83 

.82 

.82 

.82 

.82 

.83 

.83 

.83 

.81 

.83 

.82 

.83 

.82 

.83 

.84 

.83 

.83 

.82 

.80

1.12 

.73 

1.20 

1.30 

1.12 

1.16 

1.13 

1.20 

.71 

1.13 

.82 

.83 

.86 

.75 

.84 

.87 

1.32 

1.11 

1.12 

1.23

water and stream-sediment samples are normalized to the 

NASC, the resulting patterns range from no REE fractionation 

to LREE enrichment or depletion; the NASC-normalized 

patterns also have negative Ce and negative to positive Eu 

anomalies (figs. 7-9; table 4).

In rivers, colloidal matter and solution pH have been 

observed to affect both the aqueous REE concentrations and 

normalized patterns (Goldstein and Jacobsen, 1988; Elderfield and others, 1990; Sholkovitz, 1992). Filtering through 

progressively smaller pore-size filters resulted in progressively more LREE depletion in the filtrate (Elderfield, 1990; 

Sholkovitz, 1992, 1995; Ingri, 2000). In general, REEs in river 

water appear to fractionate between the colloidal and dissolved 

phases to produce an LREE-enriched colloidal phase and an 

LREE-depleted dissolved phase, with total REE concentrations dominated by the colloidal fraction. The colloidal fraction may be composed of organic matter, Fe oxyhydroxides, 

and (or) organically stabilized Al or Fe oxide (Ingri, 2000). 

When the total REE concentration is plotted against the Fe+Al 

contents, a linear relation is obtained (fig. 10), as if Fe+Al 

contents indicate the colloid concentration remaining in the 

filtrate. Furthermore, these waters are supersaturated with 

respect to amorphous Fe oxy hydroxides, and the Fe is most 

likely present as an oxyhydroxide or an organically stabilized 

Fe-containing colloid (Langmuir, 1997; Ingri, 2000). Therefore, Fe+Al contents are used here as a proxy measure for 

colloidal matter.

The four creeks (Steele, Mariner, Bow, and Polly) with 

the highest REE and colloid concentrations drain the Steele 

Creek Dome orthogneiss. Differences in the REE concentrations of 1997 and 1998 samples can be explained by higher 

colloid concentrations in the 1998 samples relative to those 

collected in 1997. In 1998, the total REE and colloid concentrations of the South Fork were about twice those of the 

North Fork. Downstream concentrations on the main stem 

of the Fortymile River fell linearly between these two values 

(Y=Q.005+0.532, /?2=0.984; fig. 10). The differences in colloid 

concentrations appear to explain the difference in total REE 

concentrations between the North and South Forks and within 

the main stem of the river.

Colloid concentration also appears to influence Ce* 

values (fig. 11). Consistent with the effects of colloidal matter 

on the Ce anomaly observed by other workers (Ingri, 2000), 

the most pronounced negative Ce anomalies were observed in 

samples with the lowest colloid concentrations. In contrast, pH 

did not affect either REE concentrations or Ce anomaly (fig. 

10). Neither colloid concentration nor pH appeared to influence the Eu/Eu* or (La/Yb)n ratio (fig. 12). No relation was 

noted between Fe or Fe+Al content and total REE concentrations in stream sediment.
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry 13

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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb 

EXPLANATION

—•—1997 samples

---••-- 1998 samples

1,000

100

10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb 

EXPLANATION

• — 1997 samples ••*••• 1998 samples

Figure 7. Rare-earth-element (REE) concentrations in water samples collected from 

small tributaries in the Fortymile River Basin (fig. 3), normalized to chondrite (A) and the 

North American Shale Composite (NASC) (B).
14 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

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—•*••• 97 North Fork

—•——98 North Fork

—±—— 98 South Fork

—•—— 98 Main stem above 

^ Polly Creek

—•—— 98 Main stem below 

Moose Creek

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

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• 97 North Fork 

98 North Fork 

98 South Fork 

98 Main stem above 

Polly Creek 

98 Main stem below 

Moose Creek

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

Figure 8. Rare-earth-element (REE) concentrations in water samples collected from the North Fork, 

South Fork, and main stem of the Fortymile River normalized to chondrite (A) and the North American 

Shale Composite (NASC) (B).
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry 15

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Figure 9. Rare-earth-element (REE) concentrations in stream-sediment samples from the Fortymile River Basin, eastern Alaska (figs. 1,3), normalized to chondrite (A) and the North American Shale Composite (NASC) (B).
16 Selected Geochemical and Biogeochemical Studies of the Forty mile River Watershed, Alaska

LJJ 16 l-

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1998 main stem below 

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H 1998 main stem above 

Polly Creek

• 1998 North Fork "

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• 1997 North Fork

i i i i

^0 100 200 300 400 5C i—

500 1000 1500 2000 Fe + Al CONTENT, IN MICROGRAMS PER LITER

Fe + Al CONTENT, IN MICROGRAMS PER LITER

Figure 10. Total rare-earth-element (REE) concentration versus Fe+AI content in water samples from small tributaries (A) and the 

Fortymile River (B), eastern Alaska (figs. 1,3).

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.0 6.5 7.0 7.5 8.0 8.5 9.0

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Figure 11. Sensitivity of Ce anomaly (Ce*) to colloidal matter (Fe+AI content) and pH in 

water samples collected from the Fortymile River Basin, eastern Alaska (figs. 1,3). NASC, 

North American Shale Composite.
Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry 17

o

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* * *

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Figure 12. Sensitivity of Eu anomaly (Eu/Eu*) and (La/Yb)n ratio to colloidal matter (Fe+AI content) and pH in water samples collected 

from the Fortymile River Basin, eastern Alaska (figs. 1,3). NASC, North American Shale Composite.

Summary

The waters of the Fortymile River and its tributaries are 

classified primarily as Ca2+ and Mg2+-HCO3~ to mixed Ca2+ and 

Mg2+-HCO^" and SO42~type. Trace-element concentrations are 

generally low except for Cu content, which commonly exceeds 

aquatic-life standards for both short (CMC) and indefinite 

(CCC) exposure. Trace-element concentrations of regulatory 

concern were detectable in stream-sediment samples, but only 

the Cr content appears to be elevated relative to the Canadian 

standards for stream sediment. Development in the basin is 

limited, and the elevated Cr content most likely represents a 

natural signature that reflects the presence of metavolcanic 

rocks. The extent to which the Cr content may or may not 

affect aquatic biota is uncertain because no information is 

available on the Cr bioavailability in this aquatic system. Such 

bioavailability partly depends on the elemental form.

Total REE concentrations in water samples from the 

Fortymile River Basin range from <0.61 to 15 |ig/L and are 

generally higher than those reported by workers elsewhere. The 

strong association observed between total REE concentrations 

and Fe+AI content may point to the influence of colloid concentrations on chemical transport. Other workers have reported 

decreases in both Ce* value and (La/Yb)M ratio with decreasing colloid concentration, indicating Ce depletion and LREE 

enrichment in the colloidal matter (Elderfield, 1990; Sholkocitz, 

1992, 1995; Ingri, 2000). Consistent with these results, a more 

negative Ce* anomaly was correlated with decreasing colloid

concentration; however, no effect was observed on (La/Yb)n 

ratio. The absence of an observed association between (La/Yb)n 

ratio and colloid concentration may indicate the dominance of 

colloidal matter to such an extent that the LREE-depleted dissolved component in the aquatic system was not observed.

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18 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

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Geochemical Processes and Geologic Framework Influencing Surface-Water and Sediment Chemistry 19

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Chapter 2

Biogeochemistry, Stable-lsotopic Composition, and 

Feeding Habits of Arctic Grayling (Thymallus arcticus) 

in the Lower Fortymile River, Eastern Alaska

By Larry P. Gough, James G. Crock, Robert R. Seal, Bronwen Wang, and Phyllis Weber-Scannell 1

Contents

Abstract..........................................................................................................21

Introduction...................................................................................................22

Methods.........................................................................................................24

Field .....................................................................................................24

Laboratory............................................................................................25

Data Analysis.......................................................................................25

Results ..........................................................................................................27

Fish Organic Chemistry ......................................................................27

Biogeochemical-Baseline Estimations.................................27

Mercury......................................................................................28

Other Inorganic Elements........................................................30

Downstream Biogeochemical Comparisons..................................30

Quantitative Intersite Comparisons .................................................30

Stable-lsotopic Signatures of Grayling Muscle Tissue................34

Composition of Grayling Stomach Contents...................................38

Summary and Conclusions..........................................................................40

Acknowledgments........................................................................................41

References Cited ..........................................................................................41

Abstract

We report on the inorganic chemistry of Arctic grayling, an ecologically important resident freshwater sport 

and subsistence fish in the Fortymile Mining District of the 

Interior Highlands Ecoregion in eastern Alaska. Placer gold 

has been mined in the study area for more than a century and 

mineral exploration activity is currently being renewed there. 

We report functional biogeochemical baseline values and (or) 

ranges for 38 elemental concentrations in muscle (fillet) tissue, 

liver tissue, and stomach contents from 34 fish caught at 11 

sampling sites within the watershed. Included in these data are 

geometric means for total Hg contents of 0.069 and 0.062 ppm

'Alaska Department of Fish and Game.

in muscle and liver tissue, respectively. These levels are more 

than an order of magnitude below the Food and Drug Administration's permissible value for methylmercury in fish fillets.

This study does not attempt to correlate fish age (weight) 

with tissue chemistry (we sampled only sexually mature fish); 

however, biogeochemical variation in association with fish age 

nevertheless occurs. For example, we found a positive correlation (r^O.41) between the total Hg content in muscle tissue 

and fish weight.

Because we are most interested in the relation between 

elemental concentrations in fish tissue and regional geochemistry (as influenced by the geochemistry of lithologic 

units), we normalized tissue elemental concentrations to fish 

weight. In general, we noted little variation in the normalized 

elemental concentrations in muscle tissue among samples at 

each of the 11 fish-sampling sites. No definitive link could 

be attributed between biogeochemical patterns and regional 

lithology. Differences among fish-sampling sites (as determined by an unpaired t test), however, were important for 

a few major nutrient elements (Ca, K, Mg, Na, P) and trace 

elements (Cr, Cs, Hg, Se). Stomach-content chemistry, also 

normalized to fish weight, varied widely (relative to liver or 

muscle tissue) and generally reflected sediment chemistry—a 

component of the ingested material. The N-isotopic compositions of fillet samples are homogeneous (815N=7.6-9.7 

permil), reflecting a restricted, low trophic (primary predator) position for the grayling. C- and S-isotopic compositions (813C, 834S values) of fillet samples range from -33.1 

to -25.8 permil and from -8.4 to 8.2 permil, respectively, 

suggesting heterogeneity of food sources (both aquatic and 

terrestrial).

Stomach-content material was examined for the occurrence and frequency of macroinvertebrates and their chemical composition in three fish. Results showed considerable 

diversity, with 9 to 15 invertebrate taxa of which both aquatic 

and terrestrial forms were represented.
22 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Introduction

Arctic grayling (Thymallus arcticus) is an ecologically 

important, nonanadromous3 (resident) salmonid fish that 

inhabits streams in the subarctic and Arctic regions of North 

America and Europe (Reynolds, 1997). Although several studies have examined the effect of mining on grayling habitat and 

physiologic health (for example, Reynolds and others, 1989), 

few data are available on the major- and trace-element content 

in grayling tissue or on the possible link between regional 

geochemical signatures (as defined by lithologic units) and 

fish chemistry. Farrell and others (2000) analyzed individual 

scales from grayling collected in eastern Alaska and correlated 

their metallic-ion contents with those in muscle tissue; they 

did not, however, relate metallic-ion contents to geochemistry. 

Gray and others (1996,2000) reported on the relation between 

the Hg content (both inorganic and organic forms) in grayling 

and the geochemistry of surface water and stream sediment 

in a region of Hg mineralization and abandoned Hg mines 

in southwestern Alaska. The Alaska Department of Fish and 

Game and the U.S. Fish and Wildlife Service have more than 

10 years of data (both published and unpublished) on traceelement contents in surface water, sediment, and grayling (and 

other fish species) from various sites in interior Alaska (Snyder-Conn and others, 1992; Mueller and others, 1996).

This study focuses on the chemistry of Arctic grayling collected within the Fortymile River in eastern Alaska 

(fig. 1), whose basin has been mined for placer gold since the 

late 1880's. Recently, mineral-exploration activity has been 

renewed in the study area; however, lode-deposit mining is not 

currently being conducted in the basin.

Understanding the relation between fish chemistry and 

the geochemistry of surface water, stream sediment, and local 

lithologic units is essential for establishing baseline biogeochemical values for this and other aquatic organisms in areas 

that are both mineralized and nonmineralized. Stable-isotopic 

analyses (for the elements N, C, and S) of muscle tissue 

have been used extensively to help explain the trophic level 

that most closely characterizes the feeding habits of the fish 

(DeNiro and Epstein, 1978, 1981; Minagawa and Wada, 1984; 

Peterson and Fry, 1987; Hobson, 1999). Questions that can 

be addressed with stable-isotopic data on fish tissue (coupled 

with diet information determined from stomach-content 

analysis) include definition of the mixture of vegetative versus 

invertebrate material in the diet (trophic or feeding level within 

the food web), definition of aquatic versus terrestrial sources 

of the invertebrates, and definition of the sources of trace elements that may be bioavailable in the diet. All of these questions are important because they assist in explaining possible 

relations between the trace-element contents in fish muscle 

tissue and the underlying geology.

The life history and physiological ecology of grayling in 

North America have been extensively studied (for example,

'Nonanadromous fish are those that do not possess a sea run as part of their 

life history.

West and others, 1992; Deegan and others, 1997; Reynolds, 

1997). Grayling inhabit clearwater streams, where, during 

the short high-latitude summer, they aggressively feed on 

both aquatic and terrestrial (accidental intruder) macroinvertebrates. Of particular interest to our study is the "residence 

time" within which fish might be expected to inhabit a given 

reach of the river during the feeding period, to determine how 

much the geochemistry of a given section of the river might 

influence fish chemistry. Data suggest that the trace-element 

chemistry of resident fish is influenced more by diet than by 

the water column (Hershey and others, 1997). During the long 

high-latitude winter, grayling commonly migrate to areas of 

deep water, springs, or pipelike channels in aufeis where the 

water does not freeze completely. West and others (1992) 

reported that the migration distance between summer feeding areas and ice-free winter residence sites can exceed 100 

km but commonly ranges from 25 to 75 km. Although no 

studies have been conducted on the specific migratory habits 

of grayling in the Fortymile River (fig. 1), most grayling are 

speculated to migrate downstream to large pools, or even as 

far as the Yukon River, as much as 100 km from the farthest 

upstream fish-sampling site in this study. Kostohrys and others 

(1999) reported base flow for the main stem of the Fortymile 

River during January, February, and March (1990-95) to be 

generally <1 m3/s. In contrast, maximum flow during spring 

breakup in May can exceed 340 m3/s. On April 2, 1998, we 

measured the flow on the North Fork of the Fortymile River 

100 m above its confluence with the South Fork to be 0.59 to 

0.76 m3/s, indicating that fish along the main stem of the river 

probably migrate some distance because free-flowing water 

would not normally be available for oxygenation of overwintering, deep-water sites.

Buzby and Deegan (2000) reported that grayling studied along a stretch of the Kuparuk River north of the Brooks 

Range displayed remarkable interyear fidelity to summer 

feeding sites—that is, more than half the fish were recaptured 

within 300 m of the site where they had been captured in 

previous years. They attributed this behavior to adaptation that 

selects for fish returning to productive drift-feeding sites in 

the river where little time is available during the short summer feeding period for the exploration of alternative feeding 

locations. Furthermore, Reynolds (1997) reported that grayling 

appear to be remarkably faithful to overwintering sites as well, 

and so, for our study, we consider it reasonable to assume that 

the fish we sampled have been feeding along that particular 

section of the river in past years. Therefore, geochemical signatures for the fish-sampling sites, as defined by the geochemistry of surface water, stream sediment, and local lithologic 

units, probably influence the chemistry of fish tissue.

The purposes of this study were to (1) establish biogeochemical-baseline data for the muscle and liver tissues 

of Arctic grayling along the lower reaches of the Fortymile 

River within the Fortymile Mining District, (2) establish 

biogeochemical-baseline data for fish-forage organisms as 

measured on whole-gut content, and (3) analyze the biogeochemical elemental and stable-isotopic patterns related to
§3 Fish sampling site 

(numbers keyed to Table 1)

INTRUSIVE ROCKS

Monzodiorite-diorite 

suite

Leucogranite

Steele Creek 

Dome tonalite

SUPRACRUSTAL ROCKS

Metavolcanic rocks

Metasedimentary 

rocks-contains the 

marble (ma) and 

biotite schist (bs) unitsSulfide-rich biotite schist

Contact, 

approximate

Contact, uncertain

Koyukuk Nationa^ 

Wildlife 

Refuge

— 64°25'

— 64°20'

— 64° 15'— 64°10'

142°00' 14TOO'

1 2 3 f^—5MILES 

012345 KILOMETERS

ro5'

ca

CDo o

CD

3

ooo

ca

a:B)

.

n

Figure 1. Fortymile River study area, eastern Alaska, showing locations of fish-sampling sites (numbers keyed to table 1) and local lithologic units of Day and others (2000). 

Arctic grayling from Koyukuk National Wildlife Refuge (inset) were used for comparison with those collected from the Fortymile River.
24 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

regional geochemistry—that is, in relation to surface water, 

stream sediment, and local lithologic units. This study presents 

muscle-tissue and stomach-content data for 38 major and trace 

elements in 34 fish collected from 11 sampling sites in the 

watershed. In addition, we present N-, C-, and S-isotopic data 

for muscle samples. These data are the first to be reported for 

Arctic grayling in this region of Alaska.

Methods 

Field

Fish were collected by using rod and lure on September 

10-12, 2000. Three fish, each of approximately the same 

weight and length, were collected at each of 10 sampling 

sites along an 80-km stretch of the North Fork, South Fork, 

and main stem of the Fortymile River (fig. 1; table 1). Site 

localities are identified by geographic coordinates and by the 

name of the tributary nearest to where the fish were collected 

(table 1). In addition to these collections, four fish were collected from O'Brien Creek, about 13 km north of its confluence with the main stem. Thus, a total of 34 fish make up the 

sample population for this study (table 2).

Lithologic units that dominate the study area are mapped 

in figure 1 and listed in table 1. Seven fish-sampling sites fell

within the metavolcanic rocks (unit mv), 3 within the metasedimentary rocks (unit ms), and 1 within the intrusive leucogranite (unit g). A detailed discussion of the regional geology, 

soils, and biogeochemistry of the lower Fortymile River is 

presented in companion studies (see chap. 1; Day and others, 

2000; Gough and others, 2001).

Fish were dissected in the field, and muscle (fillet), liver, 

and stomach contents were harvested. A stainless-steel blade 

was used in the dissection; the blade was wiped clean with 

disposable tissue and rinsed, using distilled water, before each 

organ dissection. Because of the small volume of material, 

the livers from the fish collected at each site were composited, as were the stomach contents. Samples were individually placed in plastic bags, double-sealed, and frozen. A total 

of 11 samples each of liver tissue and stomach contents and 

34 samples of muscle tissue were thus obtained. Samples 

were kept frozen and shipped to the U.S. Geological Survey 

laboratories in Denver, Colo. Owing to insufficient material, 

stomach contents were not identified in the 2000 material 

that was used for chemical analysis. A resampling of three 

of the fish-sampling sites was conducted in 2001 within the 

same timeframe as for the 2000 sampling, and the stomach 

contents from three fish were examined (but not chemically 

analyzed). We assume that the stomach contents sampled 12 

months later in 2001 are similar in invertebrate composition 

and proportion.

Table 1. Locations and description of fish-sampling sites in the Fortymile River study area, 

eastern Alaska.

[See figure 1 for locations and local geology. Units: g, leucogranite; ms, metasedimentary rocks; mv, 

metavolcanic rocks]

Site

1

2

3

4

5

6

7

8

9

10

11

Description

North Fork, 0. 1 km upstream of

confluence with Wilson Creek, near

right bank.

South Fork, 0.75 km upstream of

confluence with the North Fork,

near left bank.

Main stem, 0.75 km downstream of

confluence with the South and North

Forks, near left bank.

Main stem, 0.5 km downstream of

confluence with Polly Creek, near

right bank.

Main stem, 1.5 km below the Taylor

Highway Bridge, near left bank (noname creek).

Main stem, 0.5 km below confluence

with Flat Creek, near left bank.

Main stem, 0. 1 km below confluence

with Steele Creek, near right bank.

Main stem, 1.5 km below confluence

with Canyon Creek, near right bank.

Main stem, 0. 1 km below confluence

with Smith Creek, near right bank.

Main stem, 0. 1 km below confluence

with Moose Creek, near right bank.

O'Brien Creek, at confluence with

Alder Creek

Lat°N.

64.2722

64.2381

64.2422

64.3086

64.2937

64.2929

64.2767

64.2633

64.2683

64.2999

64.4053

Long ° W.

141.9045

141.7567

141.7406

141.4292

141.3757

141.3191

141.2857

141.1443

141.0804

141.0262

141.4050

Unit

mv

mv

mv

mv

mv

mv

mv

ms

g

ms

ms
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 25

Table 2. Summary statistics for weight and total length of Arctic 

grayling collected from the Fortymile River, eastern Alaska.

[See figure 1 for locations. Distances are measured from confluence of the North 

and South Forks that forms the main stem of the Fortymile River. Negative values, upstream (on the North Fork); positive values, downstream (on main stem)]

Sample

Wilson Creek- 1

Wilson Creek-2

Wilson Creek-3

Arithmetic mean —

Standard deviation -

South Fork-1

South Fork-2

South Fork-3

Arithmetic mean —

Standard deviation —

North Fork-1

North Fork-2

North Fork-3

Arithmetic mean ----

Standard deviation -

Polly Creek-1

Polly Creek-2

Polly Creek-3

Arithmetic mean —

Standard deviation -

No-name creek- 1

No-name creek-2

No-name creek-3

Arithmetic mean —

Standard deviation --

Flat Creek-1

Flat Creek-2

Flat Creek-3

Arithmetic mean —

Standard deviation --

Steele Creek-1

Steele Creek-2

Steele Creek-3

Arithmetic mean — -

Standard deviation -

Canyon Creek- 1

Canyon Creek-2

Canyon Creek-3

Arithmetic mean —

Standard deviation -

Smith Creek- 1

Smith Creek-2

Smith Creek-3

Arithmetic mean —

Standard deviation -

Moose Creek-1

Moose Creek-2

Moose Creek-3

Arithmetic mean —

Standard deviation -

O'Brien Creek-1

O'Brien Creek-2

O'Brien Creek-3

O'Brien Creek-4

Arithmetic mean —

Standard deviation -

Sex

F

M

M

.................

-—-"———

M

M

F

M

M

M

.................

M

F

M

.................

M

M

M

F

F

M

M

M

M ———————

.................

F

M

M

.................

.................

M

M

F

.................

M

F

F

.................

M

M

F

F ———————

.................

Wet 

weight 

(kg)

0.47

.19

.14

.27

.18

.42

.24

.39

.35

.10

.39

.42

.46

.42

.04

.34

.44

.38

.39

.05

.16

.34

.19

.23

.10

.32

.14

.18

.21

.09

.52

.18

.22

.31

.19

.31

.20

.23

.25

.06

.38

.42

.29

.36

.07

.36

.38

.32

.35

.03

.34

.48

.34

.35

.38

.07

Length Distance 

(cm) (km)

330 -15

292 -15

260 -15

294

35

356

305

356

339

29

3

3

3

356 .3

357 .:J

362 .3

358

3.2

356 27

357 27

343 27

351

7.8

273 31

342 31

279 31

299

38

318 35

241 35

267 35

275

39

394 41

267 41

304 41

322

65

318 50

279 50

292 50

296

20

356 58

343 58

318 58

339

19

356 64

349 64

311 64

339

24

318

368

330

330

337

22

1

1

Laboratory

In the laboratory, fish tissue was thawed, washed thoroughly in deionized water, and digested in ultrapure HNO3 and 

30 volume percent H2O2 (CEM Corp., 1994). All elemental 

analyses (except Hg) were performed by using inductively 

coupled plasma mass spectrometry on the acid-digested material; Hg analyses were performed on a separate aliquot of the 

digested material (which was redigested with HNO3/Na2Cr2O7), 

using cold-vapor atomic-absorption spectroscopy (Kennedy 

and Crock, 1987). For quality-control purposes, standard reference materials, analytical duplicates, and matrix spike samples 

were analyzed by the same analytical methods (Taggart, 2002).

Stable-isotopic analyses (N, C, S) were made by using a 

Thermofinnigan Delta Plus mass spectrometer, coupled with 

a Carlo Erba NC2500 Elemental Analyzer. Sample sizes for 

N- and C-isotopic analyses were approximately 0.5 mg, and for 

S-isotopic analyses approximately 5.0 mg. N-, C-, and S-isotopic compositions were measured on N2 , CO2, and SO2 gas, 

respectively. Data are reported in 5-notation relative to the references of air for N, Vienna Pee Dee belemnite (VPDB) for C, and 

Vienna Canyon Diablo troilite (VCDT) for S. The 5-notation for 

the 15N/14N, 13C/12C, and "S/^S ratios of a substance is defined as

515N, 513C, or 534S =

n _ D

R

x 1,000,

reference

'Upstream on O'Brien Creek, 13 km from its confluence with the main 

stem of the Fortymile River.

where the 5 value is in parts per thousand, or permil, and R is 

the ratio of interest ( 15N/UN, 13C/12C, or 34S/32S). The N- and 

C-isotopic compositions were calibrated relative to a scale 

based on two samples of glutamic acid selected for use as 

laboratory reference materials: one with 515N=-4.6 permil and 

513C=32.5 permil, and the other with 515N=49.3 permil and 

513C=-26.2 permil, whose compositions, in turn, are based 

on a scale defined by the international reference materials 

NBS-19 (513C=1.95 permil), LSVEC (513C=-46.48 permil), 

IAEA-N1 (515N=0.4 permil), and USGS-32 (515N=180 permil). S-isotopic compositions were measured on SO2 gas on a 

scale defined by the reference materials NBS-123 (534S=17.09 

permil) and Maine Light (534S=-30.7 permil). The analytical 

uncertainties (la) are ±0.3 permil for N isotopes, ±0.2 permil 

for C isotopes, and ±0.3 permil for S isotopes.

Fish stomachs, whose contents were used for macroinvertebrate identification, were removed from the fish, frozen, and 

sent to the Alaska Department of Fish and Game laboratories. 

There, the material was thawed, and the contents were removed 

from both the anterior and posterior parts of the stomach and 

preserved separately in 70-volume-percent ethanol.

Data Analysis

The Arctic grayling in our study ranged in weight from 

0.21 to 0.42 kg (wet weight) and in total length from 275 to 

358 mm (estimated fork length, 250-330 mm, based on the 

total-length versus fork-length regression of Grabacki, 1981)
26 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

(table 2). We did not determine the age of any of the fish collected in this study. Studies that correlate Arctic grayling age 

and length appear to be specific to a given drainage up to an 

age of about 5-7 years (Merritt, 1989). After age 5-7 (depending on the population), the correlation between age and length 

is less certain. Hughes (1999) reported Arctic grayling from 

the Goodpaster River, interior Alaska, with a size range to that 

of our fish (229-298 mm long), to be 4-6 years old, whereas 

Merritt reported Arctic grayling from the Seward Peninsula in 

this same size range to be 3-7 years old.

All the fish in our study were sexually mature, and 32 

percent were female. For the purposes of this study, both 

sexes were combined in the calculations of summary statistics 

(table 2). The major- and trace-element analyses of fish muscle 

and liver tissue and stomach contents (wet-weight basis) are 

summarized in tables 3 through 5. Multiplying these data by 4 

results in a close estimate of the concentrations converted to a 

dry-weight basis (Chen and others, 2001). Typical frequency 

diagrams of the elemental concentrations represented by Mg 

and Hg in muscle tissue are plotted in figure 2. Because logtransformed data generally displayed more normal distributions (as measured by skewness and kurtosis), we subsequently used the transformed data for all statistical analyses.

Most statistical analyses depend on the use of uncensored data (values above the lower limit of detection [LLD]). 

In samples where the censored data (values below the LLD)

for a particular element in a particular tissue did not exceed

33 percent, we followed the convention of Miesch (1976) 

and substituted a value of 0.7xLLD. For example, 12 of the

34 measured Cu contents in muscle tissue were censored 

(table 3). Whenever Cu is included in a statistical test, a value 

of 0.35 ppm (0.7x0.5 ppm) is substituted for the censored data.

Fish sampling for this study focused on older, sexually 

mature individuals. Fish weights, therefore, varied only by 

about a factor or 2 or less (table 2). Nevertheless, the variation 

in fish chemistry that is associated with differences in fish 

size (weight) is a concern because the main emphasis in this 

study is on the relation of fish chemistry to regional lithology. 

Using fish weight as a proxy for age, we have assigned but 

one "age" class in the interpretation of the chemical data and 

normalized the elemental concentrations to fish weight. This 

transformation decreased the data variance associated with 

differences in fish weight (age).

Macroinvertebrates were counted in samples of material from both the anterior and posterior parts of the stomach; 

contents of the intestine were generally too digested to identify. The relative numbers of invertebrates in each fish were 

counted. We also determined the total number of identified taxa 

(generally at the genus level), the relative proportion of aquatic 

to terrestrial organisms, and the proportions of EPT (Ephemeroptera-Plecoptera-Trichoptera combined) taxa, Chironomidae, 

and dominant taxa (an indication of selective feeding).

0

160 180 200 220 240

Mg content, in parts per million

260 2.22 2.26 2.3 2.34

Log Mg content

2.38 2.42

0.02 0.04 0.06 0.08 0.1 0.12 0.140.16

Hg content, in parts per million

-1.7-1.6-1.5-1.4-1.3-1.2-1.1 -1 -0.9-0.8-0.7

Log Hg content

Figure 2. Bar charts of typical arithmetic (left plot) and logarithmic (right plot) frequency distributions (n=34) 

of elemental concentrations of Mg (A) and Hg (6) in muscle tissue of Arctic grayling collected from the Fortymile River, eastern Alaska (fig. 1).
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 27

Table 3. Summary statistics for elemental concentrations in muscle tissue of Arctic grayling collected from the 

Fortymile River, eastern Alaska, in comparison with grayling from Koyukuk National Wildlife Refuge.

[See figure 1 for locations. All Fortymile concentration data reported in parts per million wet weight, all Koyukuk concentration data 

reported in parts per million dry weight (Phyllis Weber-Scannell, unpub. data, 1999). LLD, lower limit of detection; analytical-detection ratio, ratio of number of uncensored (above LLD) analytical values to total number of analyses. Dashes, not calculated because of 

the presence of censored (below LLD) analytical values; n.d., not determined or available. Data from Crock and others (2003)]

Element

Ag—————

A1 ________

Ac ________ .

Ba——— ---

Ro

Ri

Pa

Cd— — — —

pe ______

Co——— ——

Cr — — — —

ps _____

Cu— — — ~

Fe _____

Ga— — ------

Hg (total)-—

La 

Li— — — — -

Mg~--~

Mn — — — -

Mo

Na— — — —

Nb— —— -

Ni — — — ...

Pb -------.—-

p.... ..........

Rb ———————

CU

Q r ________

Qe ________

Sr— — — — -

T^t

Ti ——— - ——

Tl— ... — — -

U — — .... ...

V — — .— —

Zn --—--—-

LLD 

(ppm)

0.02 

8 

.1 

.5 

.001 

.005 

20 

.003 

.5 

.1 

.2 

.003 

.5 

50 

.006 

.004 

20 

.3 

.2 

.3 

.2 

.1 

6 

2 

1 

.2 

8 

.01 

.02 

.3 

.2 

.05 

.03 

40 

.003 

.02 

.4 

5

Analytical- Geometric 

detection mean 

ratio (ppm)

0:34

0:34

0:34

0:34 —

4:34 —

0:34

33-34

5:34

0:34

0:34 —

34:34 .4 

34:34 .019 

22-34

0:34

34:34 .02 

34:34 .069 

34:34 3,750 

0:34 0'34

34:34 210 

12-22

0:34

34:34 220 

0:34

0:34

0-^4.

34:34

34:34 4.1 

0:34

0:34

33:34

15:19

0:34 0:34 --

^1 -^4.

0:34

0:34

2-34

.£. JTObserved range (ppm)

Geometric ———————————————————— 

deviation Fortymile 

(»=34)

<0.02^0.02

^Q _ ^Q

<1-<0.1 

<.5^0.5

<.001-0.001

<. 005^0.005

^•^c\D 98ft

<.003-1.2 

<5^0.5

<. 1^0.1

1.09 .3-0.5 

2.05 .004-0.016 

<5 1.3

<50-^50 

1.32 .01-0.03 

1.62 .021-0.15 

1.07 3,240-4,110 

<.3^0.3 ^ 0— ff\ *)

1.08 175 254

s *) *) 8

<.1-<0.1 1.15 182 344

<2^2 

<!-<!

<.2-<0.2

^o — ^.o 1.44 2.2 9.9

<. 02^0.02

<.3^0.3

*^.£ i .j

<.05-5.9

<.03^0.03

^tV/ ^•sTV/

<.003-0.009

<.02-^0.02

^.H ^sV.H

v. j U

Koyukuk 

(w=8)

<0.4-^:0.4 

< 1.9-2.9 

<.5^0.5 

<. 1-0.65 

<. 1^0.1 

n.d. 

n.d. 

<.5^0.5 

n.d. 

n.d. 

<.3^0.3 

n.d. 

1.6-2.7 

21-40 

n.d. 

.22-0.66 

n.d. 

n.d. 

n.d. 

1,000-1,200

1110

<.30-0.33 

n.d. 

n.d. 

<1.0-<1.0 

<3.0-^3.0 

n.d. 

n.d. 

<3. 0-^3.0 

n.d. 

1523

<1.5-4.7 

n.d. 

n.d. 

<11^11 

n.d. 

<.3^0.3 

11-16

Results

Fish Inorganic Chemistry

Biogeochemical-Baseline Estimations

The geometric mean (GM value) and geometric deviation (GD value) for 38 elemental concentrations in muscle 

tissue, liver tissue, and stomach contents are listed in tables 

3,4, and 5, respectively, along with the LLD, the analyticaldetection ratio (that is, the ratio of the number of uncensored 

data to the total number of analyses), and the observed range 

for each element. We did not calculate the GM and GD values

for elements with censored data; however, we do report the 

observed ranges for these elements. The GM and GD values 

and observed ranges can be used together to estimate biogeochemical baselines for grayling in the lower reaches of the 

Fortymile River. A more precise determination of biogeochemical baseline should await additional sampling of fish 

from second- and third-order streams within the watershed, as 

well as at other times within the life history of grayling.

The wet-weight base element ranges for the muscle and 

liver tissues of grayling collected from the Fortymile River 

area (fig. 1) are compared, in tables 3 and 4, with similar 

material (dry-weight basis) collected in Koyukuk National 

Wildlife Refuge, western Alaska (Mueller and others, 1996).
28 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Table 4. Summary statistics for elemental concentrations in liver tissue of Arctic grayling collected from 

the Fortymile River, eastern Alaska, in comparison with grayling from Koyukuk National Wildlife Refuge.

[See figure 1 for locations. All Fortymile concentration data reported in parts per million wet weight, all Koyukuk concentration data reported in parts per million dry weight (Phyllis Weber-Scannell, unpub. data, 1999). LLD, lower limit of detection; 

analytical-detection ratio, ratio of number of uncensored (above LLD) analytical values to total number of analyses. Dashes, 

not calculated because of the presence of censored (below LLD) analytical values; n.d., not determined or available. Data 

from Crock and others (2003)]

Element

Ag—— ——

Al __

Ac _

Ba— - — -----

rj~

r>:

Pa

r~*\

re ____

Co—————

Cr ..

PC ________

Cu TM«TM-—

pe ______

Qa ..........

Hg (total)--

La ............

T j _________

Mg—— — ~ 

Mn — —— —

Mo

Na— —— —

\JK ............

Mi ..........

pk ____

p ....

Rb. ...........

Sb — — — ...

cOV c_____ ««»«»•

^C "•""«•"•—"—«

cr ______

Th — — — --

Tl—— ------

u

V ——--—

Zn --------

LLD

(ppm)

0.02 

8 

.1 

.5 

.001 

.005 

20 

.003 

.5 

.1 

.2 

.003 

.5 

50 

.006 

.004 

20 

.3 

.2 

.3 

.2 

.1 

6 

2 

1 

.2 

8 

.01 

.02 

.3 

.2 

.05 

.03 

40 

.003 

.02 

.4 

5

Analyticaldetection 

ratio

0:11 

0:11 

9:11 

0:11 

5:11 

6:11 

5:11 

11:11 

0:11 

11:11 

11:11 

11:11 

11:11 

4:11 

11:11 

11:11 

11:11 

0:11 

0:11 

11:11 

11:11 

6:11 

11:11 

0:11 

0:11 

0:11 

11:11 

11:11 

0:11 

0:11 

0:11 

0:11 

0:11 

0:11 

0:11 

0:11 

0:11 

0:11

Geometric 

mean 

(ppm)

.27

.19

.4 

.015

1.7

.02 

.062 

2,600

130 

1.5

640

2,350 

5.6

.67

— -

Geometric 

deviation

1.85

1.36 

1.20 

1.83 

1.32

.0 

1.53 

1.12

1.16

1.2

1.2

1.13 

1.24

1.73

—

Observed range (ppm)

Fortymile 

(n=ll)

<0.02^0.02 

<8^8 

<. 1-0.2 

<5^0.5 

<.001-0.001 

<005-0.01 

<20-55 

.09-0.63 

<0.5^0.5 

.13-0.35 

.3-0.6 

.006-0.030 

1.0-2.6 

<50-70 

.02-0.02 

.031-0.10 

2,100-3,240 

<.3^0.3 

<2^0.2 

100-160 

1.1-1.9 

<. 1-0.4 

470-830 

<2^2 

<1^;1 

<.2^0.2 

1,800-2,800 

4.4-9.5 

<.02-^0.02 

<3^0.3 

.2-1.5 

<.05-5.9 

<.03^0.03 

<40-<40 

<003-0.009 

<.02-^0.02 

<.4-<0.4 

<5-6

Koyukuk 

(«=8)

<0.4-<0.4 21 37

n.d. 

<. 1-0.29 

<. 1^0.1 

n.d. 

n.d.

<.l 1.1 

n.d. 

n.d. 

<.7-0.85 

n.d. 

7.8-27 

270-320 

n.d. 

.2-0.9 

n.d. 

n.d. 

n.d. 

630-700 

7.4-11 

<.4-0.84 

n.d. 

n.d. 

<1.0^:1.0 

<3. 0^:3.0 

n.d. 

n.d. 

<3. 0^:3.0 

n.d. 

n.d. 

<1.5^1.5 

n.d. 

n.d. 

<15^15 

n.d. 

.7 1.9

87-94

Like the Fortymile River area, Koyukuk National Wildlife 

Refuge is generally unmineralized (Mueller and others, 1996) 

but, unlike the Fortymile River area, is topographically flat and 

dominated by Quaternary glacial and glaciolacustrine deposits 

(Snyder-Conn and others, 1992). To compare our wet-weightbasis data with the Koyukuk dry-weight-basis data, a factor of 

4 needs to be applied to the Koyukuk data (Chen and others, 

2001). Nevertheless, with a few notable exceptions (for those 

elements with similar LLDs), the chemistries of fish muscle 

and liver tissue in these two areas appear to be nearly identical. Because few data on grayling chemistry are available, this 

comparison should serve as an initial benchmark for future 

assessments.

Mercury

The biogeochemical cycling and bioaccumulation of Hg 

in diverse ecosystems has received increasing attention since 

the 1990s (for example, Lindberg and others, 2000). Only 

a few studies, however, have been done on the Hg content 

in Arctic grayling (Gray and others, 1996, 2000; Duffy and 

others, 1999), reporting total Hg content and methylmercury 

(MeHg) concentrations in the muscle and liver tissues of fish 

collected in the Kuskokwim River watershed of southwestern Alaska—an area known for its Hg mineralization. MeHg 

accounted for 90-100 percent of the total Hg content in 

muscle material in these studies. The Hg content in the muscle
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 29

Table 5. Summary statistics for elemental concentrations in the stomach contents of Arctic 

grayling collected from the Fortymile River, eastern Alaska.

[See figure 1 for locations. All concentrations in parts per million wet weight. LLD, lower limit of detection; 

analytical-detection ratio, ratio of number of uncensored (above LLD) analytical values to total number of 

analyses. Dashes, not calculated because of the presence of censored (below LLD) analytical values. Data from 

Crock and others (2003)]

Element

Ag———— ——

A1 __________

Ac __________

Ba —— --------

Be ————— n;

PO V^d. _______________ TMTMTMTMTMTMTMTM««TM

PH V-/U _______ —— —— —— ———— -

pn _______

rv

rv _______

p., V_-U _______ MMMMMMM ——

Fe _______

Qa ___________

Hg (total)—— ~

T o ___________

Li—— — — ——

Mg — — —— — 

Mn —— ——— -

Mo —— — — -

•NJo ___________

Nb—— —— ——

•NJj _____ _ _

pb ___________ 

p _____________

DK IV LJ ___________ M —— MM —— MM

Cp ......

Cp Ljt1 ___________ TMTM«TMTMTMTMTMTM"TM

Sr—— —— —— -

T"U

Ti— —— —— —

Tl——— — ——

U — — — ——

V —————

Zn ——————

LLD 

(ppm)

0.02 

8 

.1 

.5 

.001 

.005 

20 

.003 

.5 

.1 

.2 

.003 

.5 

50 

.006 

.004 

20 

.3 

.2 

.3 

.2 

.1 

6 

2 

1 

.2 

8 

.01 

.02 

.3 

.2 

.05 

.03 

40 

.003 

.02 

.4 

5

Analyticaldetection 

ratio

0:11 

0:11 

10:11 

11:11 

11:11 

5:11 

11:11 

11:11 

3:11 

6:11 

11:11 

11:11 

11:11 

11:11 

11:11 

11:11 

11:11 

3:11 

2:11 

11:11 

11:11 

11:11 

11:11 

0:11 

0:11 

0:11 

11:11 

11:11 

0:11 

0:11 

11:11 

11:11 

0:11 

0:11 

9:11 

8:11 

5:11 

11:11

Geometric 

mean 

(Ppm)

2.1 

.004

140 

.13

.72 

.02 

5.6 

170 

.04 

.0097 

760

90 

9.5 

.19 

260

1,780 

1.3

1.3 

1.6

12

Geometric 

deviation

1.86 

2.21

1.92 

1.68

1.79 

1.84 

1.47 

2.41 

1.9 

1.31 

1.3

1.77 

1.99 

1.4 

1.36

1.31 

1.28

1.31 

1.97

1.36

Observed 

range 

(ppm)

<0.02-<0.02 

<8-<8 

< 1-0.6 

.84-5.2 

.003-0.01 

<005-0.01 

59-510 

.06-0.29 

<.5-1.0 

< 1-0.37 

431

.008-0.06 

2.4-9.1 

50-710 

.02-0.1 

.0063-0.014 

430-1,110 

<.3-0.5 

<.2-0.4 

33-350

2.0-19 

.1-0.29 

120-370 

<2-<2 

<!-<! 

<2-<0.2 

1,100-2,600 

.9-1.8 

<02-<0.02 

<3-<0.3 

.8-1.9 

.6-5.1 

<.03-<0.03 

<40-<40 

<003-0.005 

<02-0.27 

<.4-0.4

7 e 99

tissue of fish collected at "background" sites (at some distance 

from old Hg mining and refining areas) ranged from less than 

0.02 to 0.20 ppm (Gray and others, 1996) (unless specifically 

stated, these and all subsequent values for fish-tissue material 

are on a wet-weight basis). In contrast, the Hg content in the 

muscle tissue of fish from mineralized areas (and areas downstream of mining activities) ranged from 0.07 to 0.42 ppm. 

Duffy and others (1999) reported a range of 0.079 to 0.16 ppm 

total Hg in grayling muscle tissue from the delta region of this 

watershed. We report observed ranges of 0.021 to 0.15 ppm 

total Hg in muscle tissue (GM=0.069 ppm; table 4) and 0.031 

to 0.10 ppm total Hg in liver tissue (GM=0.062; table 5). Total 

Hg content in the muscle tissue of grayling from the Fortymile 

River is therefore somewhat less than what was defined as 

"background" by Gray and others (2000) but nearly identical

to that reported by Duffy and others (1999) for the delta region 

of the Yukon-Kuskokwim River watershed.

The Fortymile River watershed is not a mineralized area 

particularly rich in Hg. Gamble and others (2001) reported 

a maximum of 0.16 ppm Hg in major local lithologic units, 

mostly from quartz vein material. The Hg content in most rock 

samples was below the LLD of 0.02 ppm. Total Hg content in 

stream-sediment samples for the Fortymile River study area 

(fig. 1) ranged from less than 0.02 to 0.30 ppm, with a GM 

value of 0.05 ppm, in comparison with a background value of 

1.0 ppm reported by Gray and others (2000) in the Kuskokwim River watershed. In addition, integrated surface-water 

samples from both tributary and Fortymile River main-stem 

sites were below the LLD of 0.005 ppb (except Steele Creek, 

which had 0.014 ppb Hg).
30 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

The relation between fish weight (a proxy in this study 

for age) and total Hg content in muscle tissue is plotted as 

a simple regression in figure 4. These data, which conform 

to those in the general fish literature, indicate that grayling 

continue to accumulate Hg in their tissue over time (Hudson 

and others, 1994), even in a watershed determined to have low 

levels of bioavailable Hg. We note that the highest total Hg 

content measured in our data is nearly an order of magnitude 

below the Food and Drug Administration (FDA)'s action level 

(in seafood used for human consumption) of 1.0 ppm MeHg 

(U.S. Environmental Protection Agency, 2000).

Finally, the Hg level in stomach-content material is 

listed in table 5. The GM value is approximately 0.01±0.004 

ppm, lower than the range of 0.02 to 0.3 ppm we report for 

stream sediment from the Fortymile River watershed (but 

within the experimental variation of the stream-sediment 

data) or for various lithologic units. Hg-speciation studies are 

required to ascertain how much of the Hg content of fish tissue comes from ingested sediment, invertebrates, or the water 

column.

Other Inorganic Elements

In addition to Hg, the contents of other inorganic elements in muscle and liver tissue are listed in tables 3 and 4, 

respectively. An assessment of the relative importance to this 

watershed of these elemental concentrations in fish tissue is 

beyond the scope of this study. However, the Se content of 

muscle tissue versus fish weight (age) is plotted in figure 4. 

Though weak, this negative trend is intriguing because of 

reports that Se may physiologically inhibit the bioaccumulation of Hg in fish tissue (Paulsson and Lundbergh, 1991; Chen 

and others, 2001).

Downstream Biogeochemical Comparisons

Statistical analysis of the GM values of elemental 

concentrations in stream-sediment samples indicates that, of 

the 11 fish-sampling sites, Wilson Creek, South Fork, Moose 

Creek, and O'Brien Creek appear to differ geochemically the 

most (Crock and others, 1999, 2000). The locations of these 

four fish-sampling sites within the study area are shown in 

figure 3D. The Wilson Creek and South Fork fish-sampling 

sites are within the metavolcanic rocks (unit mv, fig. 1), 

whereas the Moose Creek and O'Brien Creek fish-sampling 

sites are within the metasedimentary rocks (unit ms, fig. 

1). Unit mv, fine- to medium-grained, dark-green to black 

amphibolite gneiss of tholeiitic and calc-alkaline affinity, consists chiefly of metabasalt (Day and others, 2000). Many of 

the minerals that make up these rocks are fairly easily weathered but not especially trace element rich. Unit ms, however, 

is a relatively easily weathered biotite schist composed of dispersed to massive (60 m thick at one site) sulfide-rich zones 

(Gamble and others, 2001). Unit ms is more trace element 

rich than unit mv (Crock and others, 2000). We hypothesize,

therefore, that fish chemistry may vary regionally, reflecting 

the local lithologic geochemistry.

The relative differences in normalized elemental concentrations among the four fish-sampling sites for liver tissue, 

muscle tissue, and stomach contents are plotted in figures 3A, 

3fl, and 3C, respectively (see tables 3-5). These results show 

that liver tissue is the most nearly uniform among the four 

fish-sampling sites for most elements. Hg, Mo, and Se have 

the widest observed ranges with no particular site showing 

consistently the highest or lowest normalized values. Elemental concentrations in muscle tissue appear to vary somewhat 

more. Of the two tissues, liver shows far more elemental 

concentrations above the LLDs, and these normalized values 

generally exceed those measured in muscle tissue (with the 

notable exception of Hg, which is similar between the two 

tissues). As is the trend in our data, most metals tend to be 

concentrated in the liver (and kidneys) as opposed to muscle 

tissue (Sorensen, 1991).

Stomach contents are of particular interest because they 

show the greatest intersite variation and because most of the 

normalized values are larger than those measured in liver 

or muscle. This result is not surprising because the ingested 

material contains a considerable amount of sediment. The 

reason why some elements have normalized values that are 

actually smaller than those measured in liver or muscle tissue 

(for example, Hg and Se) is that the concentration of these 

elements in the quartz-rich sediment is low and the mass of the 

sediment in the stomach content material "dilutes" the overall 

concentration of the trace elements.

Quantitative Intersite Comparisons

We used a t test to quantitatively assess the difference in 

fish muscle-tissue chemistry between sampling sites along the 

Fortymile River. Liver tissue and stomach contents were not 

quantitatively compared because the material collected from 

individual fish at each of the 11 sampling sites was combined 

before analysis to give, effectively, only one sample per site. 

The results of t tests for the elements without censored data 

(Cr, Cs, Hg, K, Mg, Na, P, Rb) and for the three elements with 

censored data (Ca, Cu, Se) are listed in table 6; the t test was 

not performed on the remaining elements with censored data. 

For Ca, Cu, and Se, a value of 0.7xLLD was substituted for 

the censored data as follows: Ca (1 value of 14 ppm), Cu (12 

values of 0.35 ppm), and Se (1 value of 0.14 ppm) (table 3). 

The t test compared the variation in data among six samples 

(three from each fish-sampling site, except for O'Brien Creek, 

where four samples were used). Thus, the comparisons utilized 

four degrees of freedom among sites using six samples, and 

five degrees of freedom among sites using seven samples. 

Only those elements showing significant intersite differences 

(that is, where p<0.05) are listed in table 6.

For discussion purposes, the 11 elements listed in table 

6 are grouped as major-nutrient elements (Ca, K, Mg, Na, P), 

heavy metals or metalloids (Cr, Cu, Hg, Se), and alkali metals
Tl 33 CO 

<a < o 

C CD 

CONCENTRATION ELEMENTAL NORMALIZED 

O -• 

o o 

o o 

o o 

•£-

n ~r

I ![<P 

Ci . CD CD ci x 

3- 3 

•

o' 3 o a QJ -*• 

to =: ~n 

—— ON 

i is 

E. E" CD 

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CD to — 

-d^ o CD 

w

o. 3 > 

CD "5. oT 

3 cf 

«

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o

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3- I* Q) 

-

> CD' -i -j o 1 -

c±. O 

CD -*• l*

Q.

o 

3

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3 -i 

"S. c± 

• — Crt' 

m CD" 

IJI r+ 

° to' 

H- to «t

CD C~l 

'Aj)s;uj3i|3oaBojg -a|qe)$ 'u pue !.£
32 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

(Cs, Rb), of which the normalized total Cu and Rb contents in 

fish muscle tissue showed no intersite differences.

For heavy metals or metalloids, the normalized total 

Cr, Hg, and Se contents differed significantly among five, 

five, and three fish-sampling sites, respectively (table 6). For 

example, differences in Se content were noted between fish 

collected on the South Fork and Canyon Creek, on the South 

Fork and O'Brien Creek, and on Canyon Creek and O'Brien 

Creek. These curious differences indicate that the variance in 

the normalized data (always less than an order of magnitude) 

for Hg, Cr, and Se may be systematic across the landscape and 

probably not due simply to randomness.

One explanation for the observed systematic differences 

in fish-muscle-tissue chemistry could be differences in the 

geochemistry of the feeding sites for these fish. A scatterplot 

of the normalized data for Hg, Cr, and Se does not support 

the supposition that differences in the geochemistry of local 

lithologic units are necessarily reflected in differences in fish 

chemistry. Of course, progressing downstream toward the sites 

dominated by unit ms, the stream sediment represents more 

and more of an integration of the geochemistry of the watershed in general.

A couple of interesting exceptions to the observation 

above are the Cr and Se data. The Cr and Se contents in the 

muscle tissue of fish collected from O'Brien Creek differ 

significantly from those of fish collected from Canyon Creek 

(table 6). Figure 5 shows that the Cr and Se data for these two 

fish-sampling sites certainly do appear as two distinct populations. (The / test for Hg between these two fish-sampling sites 

yielded an important, yet insignificant, p value of 0.08.) These 

two fish-sampling sites are within the same area of metasediQ)

X

Q

LU

01

O

0.45

0.4

0.35

0.3

0.25

0.2

0.15

0.1

.005

0

©

(34

-IIms

©•

• 

t

ms

-20-10 0 10 20 30 40 50 60 70

WAJ

CO

in

00

0.6 

0.5 

0.4 

0.3 

0.2 

0.1

=J o

r =0.41

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 

TOTAL Hg CONTENT, IN PARTS PER MILLION

0.6

0.5 

0.4 

0.3 

0.2

0.1 

0

r =-0.11

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 

TOTAL Se CONTENT, IN PARTS PER MILLION

Figure 4. Simple regression of fish weight versus total Hg 

and Se content in muscle tissue of Arctic grayling collected 

from the Fortymile River, eastern Alaska (fig. 1).

IQ

LU

01 

O

IQ) 

CO

Q

LU 

N

. 

01

O

4 - 

3 -

2.5 -

2 -

1.5 -

1 -

0.5 -

1

•

1 ""'.••

^ •

. « f.

J

9

•

ms

9

I « I

ms *

-20-10 0 10 20 30 40 50 60 70

u -

9 -

8

-

7 ~

6 -

5 -

4 -

3 - 

2 - 

1 -

•

mv •

• •

' I •"'

• 1 «

0

•

• 

ms

9

• 

•

•

it-

• 1

«

ms 

„

-20-10 0 10 20 30 40 50 60 70 

DISTANCE, IN KILOMETERS

Figure 5. Scatterplots of Hg, Cr, and Se contents (normalized to 

fish weight) in muscle tissue of Arctic grayling collected from 11 

fish-sampling sites on the Fortymile River, eastern Alaska (numbers, fig. 1; table 1). Distance is measured from confluence of 

the North and South Forks. See figure 1 for local lithologic units.
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 33

Table 6. Unpaired f-test results of a comparison of the elemental concentrations (normalized to fish weight) in the muscle tissue of 

Arctic grayling collected at 11 fish-sampling sites on the Fortymile River, eastern Alaska.

[See figure 1 for locations. Values in lower left, number of degrees of freedom used in calculations; values in parentheses in upper right, resultant p values. If 

/><0.05, sites are significantly different for that element at the 95-percent-confidence level. Only elements with concentrations >66 percent of uncensored (above 

lower limit of detection) analytical values were included in calculations]

•1

^^^^H Wilson 

^^^^^^H Creek

^^^^B

Wilson 

Creek

North

Fork 

of the 

Fortymile

River

South

Fork

of the 

Fortymile

River

Polly 

Creek

No-name 

creek

Flat

Creek

Steele 

Creek

Canyon 

Creek

Smith 

Creek

Moose 

Creek

O'Brien 

Creek

1

4

4

4

4

4

4

4

4

4

5

North

Fork 

of the 

Fortymile

River

- *,

\

\

4

4

4

4

4

4

4

4

5

South

Fork 

of the 

Fortymile

River

Polly 

Creek

Na (0.03)

^^•H

^^

4

4

4

4

4

4

4

5

4

4

4

4

4

4

5

No-name 

creek

Hg(0.05) 

P(0.03)

P(0.05)

4

4

4

4

4

5

Flat 

Creek

Cr (0.04)

Hg (0.04)

m

4

4

4

4

5

Steele 

Creek

Cs(<0.01)

Cs(<0.01)

4

4

4

5

Canyon 

Creek

Cr (0.03)

K (0.04) 

Mg (0.03) 

Na (0.04)

P (0.04)

Se (0.05)

Cr (0.05) 

Cs(O.Ol) 

Hg (0.02)

Hg (0.03)

4

4

5

Smith 

Creek

Ca

Hg (0.03)

Ca (0.03)

4

5

Moose 

Creek

Ca(O.Ol) 

Mg (0.04)

Ca (0.04) 

K (0.05)

Ca (0.03)

•

5

O'Brien 

Creek

Se (0.03)

Mg (0.04) 

P (0.03)

Cr(0.03)

Cr (0.03)

K (0.04) 

Mg (0.03)

Se (0.05)
34 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

mentary rocks. The normalized data among fish at a particular 

fish-sampling site are remarkably similar. (The data show 

only slight variation.) For example, figure 5 shows only slight 

variations in the Hg, Cr, and Se data for fish-sampling sites 2, 

3, 10, and 11 (fig. 1).

The normalized data for fish stomach contents are plotted 

in figure 6. Just as with the muscle-tissue data, no relation to 

lithology is noted in these plots of the normalized data for Hg, 

Cr, and Se. Because of the presence of stream sediment in the 

ingested material, we anticipated that the stomach-content 

chemistry might correlate with the stream-sediment chemistry. At 8 of the 11 fish-sampling sites where we collected

O 

O

en

I

0.40

0.35-

0.30-

0.25

0.20

0.15

0.10-

0.05-

n

"

I !

I 1

1 1

mv i

'9

,'8 ' l]0

sj ®-,(^: ~ ^ O

"^T (-) \ B $J -* ms ' ms

- - ^j n i n

V ^ ni n T

5 v v wT V '-1| H ,,

, — , —— , —— , ——————————— i ———————————————— / 1 —

-u.^o

0.40

0 35

-0.30

0.25

0.20

0.15

0.10

0.05

_n

-20-10 0 10 20 30 40 50 60 70

1-

LU

1-

2

O 

O

O

Q

LU

ISI

_J

<

0

2

3-

2.5-

2

1.5-

1-

0.5

n

^ V D j ;

, i mv ' ' !

H V Q

V D TD V,

n !

ms ms

/MO

150

100

50

-20-10 0 10 20 30 40 50 60 70

I- •z.

LU

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U

<u

LO

Q

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ISI

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^

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•z.

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V V V V

_

1

w

ms

,

9 v v

^

ms

- , , , it—

-20-10 0 10 20 30 40 50 60 70 

DISTANCE, IN KILOMETERS

Figure 6. Scatterplots of Hg, Cr, and Se contents (normalized 

to fish weight) in stomach contents of Arctic grayling (inverted 

triangles) and of Hg and Cr contents in stream sediment (squares) 

at 11 fish-sampling sites on the Fortymile River, eastern Alaska 

(numbers, fig. 1; table 1). Distance is measured from confluence of 

the North and South Forks. See figure 1 for local lithologic units.

samples of both materials (Crock and others, 2000), correlations between the Hg and Cr contents in stomach contents 

and stream sediment are negative (r=-QAQ and -0.17, respectively). A comparison for Se is not made because we have no 

Se data for the stream-sediment samples (fig. 6). In addition, 

the normalized data for metals or metalloids in stomach 

contents correlate poorly with those in muscle tissue (r=-0.05,

-0.17, and 0.48 for Hg, Cr, and Se, respectively), indicating 

either that the material is not in the gut long enough for element release and absorption, or that the total concentration of 

the elements in the gut is not indicative of their bioavailability

Stable-lsotopic Signatures of Grayling Muscle 

Tissue

We use stable-isotopic analysis to help explain (1) the 

trophic level that most closely characterizes the feeding habits 

of grayling, and (2) the possible relation between metallic-ion 

contents in fish tissue and the underlying geology. This type 

of approach has been used successfully to trace the flow of 

N, C, and S through both aquatic and terrestrial ecosystems 

(Kline and others, 1997; Hobson, 1999). In this study, we first 

interpret the stable-isotopic data for fish tissue in terms of 

food source, then we relate those data to the possible influence 

of the local geologic geochemical signature. For example, if 

the isotopic signatures indicate that the diet is characteristic 

of aquatic food sources, then watershed-scale geochemical processes may be most important, and the relation to 

geology would be less important; whereas if the isotopic 

signatures indicate that the diet is characteristic of terrestrial 

food sources, then we might expect a closer local (geologic) 

geochemical link (signature).

The stable-isotopic ratios of N and C have received 

widespread application in food-web and ecosystem studies 

(DeNiro and Epstein, 1978, 1981; Minagawa and Wada, 1984; 

Peterson and Fry, 1987; Hobson, 1999). The stable-isotopic 

ratios of S have found more limited application but have been 

demonstrated to be useful for distinguishing trophic-level relations and migratory habits offish (Hesslein and others, 1991; 

Doucett and others, 1999). Thus, stable isotopes offer potentially important insights into the processes of bioaccumulation 

of metals and other constituents in Arctic grayling from the 

Fortymile River area.

Stable-isotopic data from muscle tissue for grayling from 

the Fortymile River are plotted in figure 7 and listed in table 7. 

The N-isotopic data from our study show only limited variation: the 815N values for all samples average 8.7±0.5 permil 

(la) and range from 7.6 to 9.7 permil. The C-isotopic data 

vary more widely: the 813C values for all samples average

-29.0±1.7 permil (la) and range from -33.1 to -25.8 permil. 

The S-isotopic data vary most widely: the 834S values for all 

samples average 1.7±4.0 permil (la) and range from -8.4 to 

8.2 permil.

N isotopes have been shown to be accurate monitors 

of trophic level and food sources in food webs. In general,
Biogeochemistry. Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 35

PERMIL CD in oc

Z 

~ 8.5 

UJ

3 8.0

Z 7.5 

in

•0 7.0

6.5

6.0 

-3

10.0 

8.0

=J 6.0

a! 4.0 

UJ

°- 2.0

ul °-°

3 -2.0

> -4.0 

tt>

3 -6.0

10

-8.0

-10.0 

-35

10.0 

^ 9.5

o:

UJ 9.0 

QL

— 8.5 

LU 

3 8.0

>

Z 7'5 

in

iO 7.0

6.5 

6.0

A *• 

• *

•+•

A *

D +

5.0 -30.0 -25.0

5 13C VALUE, IN PERMIL

s

A .* ^ °

X 

A * .

^ 0» • 0

* ' *

D

.! • *

*

.0 -30.0 -25.0

513C VALUE, IN PERMIL

C & °

x * 0

* . ^ *

A 

" + . *

X A

* D

EXPLANATION

• O'Brien Creek 

n Canyon Creek 

o North Fork River 

o Flat Creek

• Moose Creek 

A Polly Creek 

x Smith Creek 

A South Fork River 

x Steele Creek 

+ No-name creek

• Wilson Creek

0.00 0.05 0.10 0.15 0.20

TOTAL Hg CONTENT, IN PARTS PER MILLION

Figure 7. Plots of 8'5N versus 813C values, S^S versus 813C values, and 8' 5 N value versus total Hg content 

in muscle tissue of Arctic grayling collected from 11 fish-sampling sites on the Fortymile River, eastern 

Alaska (fig. 1).
36 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Table 7. Summary of N-, C-, and S-isotopic data for Arctic grayling collected from the Fortymile River, eastern Alaska.

[See figure 1 for locations. All values in permil]

Sample

Wilson Creek-1 

Wilson Creek-2 

Wilson Creek-3

South Fork-1 

South Fork-2 

South Fork-3

North Fork-1 

North Fork-2 

North Fork-3

Polly Creek-1 

Polly Creek-2 

Polly Creek-3

Standard deviation ——————

No-name creek-1 

No-name creek-2 

No-name creek-3

Flat Creek-1 

Flat Creek-2 

Flat Creek-3 

Arithmetic mean --—-—-—----

Steele Creek-1 

Steele Creek-2 

Steele Creek-3

Canyon Creek-1 

Canyon Creek-2 

Canyon Creek-3

Smith Creek-1 

Smith Creek-2 

Smith Creek-3

Moose Creek-1 

Moose Creek-2 

Moose Creek-3

O'Brien Creek-1 

O'Brien Creek-2 

O'Brien Creek-3 

O'Brien Creek-4

515N

8.2 

8.6

8.3

8

1

.2

8.4 

7.9 

8.9 

8.4

.5

9.4 

9.3 

9.3 

9.4

.0

9.7 

8.8 

9.0 

9.2

.5

7.7 

8.0 

8.2

8 A

.2

9.2 

8.7 

8.9 

8.9

.2

7.9 

9.2

8.9 8f

.7

8.7 

8.8 

7.6 

8.4

.6

8.9 

8.6 

8.9

8

0

.2

9.4 

8.9 

9.1 

..... 9.1

..... .3

8.3 

8.7 

9.3 

9.0

8

0

5

8

1

.5

513C

-30.1 

-31.4 

-27.4 

-29.6

2.0

-28.9 

-29.9

-30.7

TQ O

.9

-28.1 

-28.4 

-26.5

-27.7 

1.0

-26.5 

-31.7 

-29.2

-29.1 2f

-27.4 

-31.1 

-27.6

TO 7

2.1

-26.9 

-29.1 

-28.0

TO A

1.1

-28.7 

-29.5 

-29.3

-29.2 

.4

-29.2 

-28.5 

-31.5

-29.7

1.6

-25.8 

-29.0

-28.7

T7 fi

1 O

-29.8

-27.9 

-27.9

TO £

1.1

-27.9 

-33.1 

-30.1 

-30.8

-30.5

2.2

-29.0 

1.7

534S

5.5 

-.2 

.9 

2.1

3.0

6.8 

8.2 

4.1 

6.4

2.1

3.3 

6.2 

3.3 

4.3

1.7

.5 

6.1 

-3.3 

1.1

4.7

2.1 

-8.4 

-2.4

-2.9

5.3

3.3 

4.0 

1.8 

3.0

1.1

.5 

-3.8 

4.9

.5

4.4

-2.5 

-2.8 

-1.3

-2.2

2.5 

6.4 

.0 

2.9

3 2

6.7 

3.9 

3.4 

4.6

1 8

2.2 

3.0 

-6.9 

.8

-.2 

4.5

1.7

4.0

animal tissues will have a 2- to 5-permil increase in 815N value 

relative to their diets (DeNiro and Epstein, 1981; Minagawa 

and Wada, 1984; Peterson and Fry, 1987; Hesslein and others, 

1993; Hicks, 1997). Therefore, differences in 815N values 

greater than 2 to 5 permil among the tissues of individual 

fish generally reflect different trophic levels in a food web. 

Thus, the restricted range of 815N values for grayling from the 

Fortymile River, 7.6 to 9.7 permil (fig. 7A), indicates a limited 

trophic position for these fish, consistent with the dominance 

of aquatic and terrestrial flies in their guts. The low isotopic 

mean suggests that the grayling occupy a low trophic level in 

the Fortymile River watershed ecosystem. Hesslein and others 

(1991) reported that the 815N values in the lowest-trophic-level 

fish (white sucker, ninespine stickleback, juvenile northern 

pike) from the Lower Mackenzie River Basin, Northwest 

Territories, Canada, ranged from 6.3 to 9.3 permil. They 

concluded that the diets of these fish must be dominated by 

the trophic level occupied by herbivores. Hicks concluded 

that nonanadromous fish with 815N values of 5.0 to 9.4 permil 

represented the trophic level of second-level carnivores (primary predator), a result consistent with the gut contents of the 

grayling in our study.

C isotopes have been shown to reflect both food sources 

and trophic level. Animals generally show a 0.0- to 2.0-permil 

increase in 813C values of their tissues relative to their diets 

(DeNiro and Epstein, 1978; Peterson and Fry, 1987). Hesslein 

and others (1993) reported a fractionation between muscle tissue and food of 2.0 permil in their laboratory feeding study of 

broad whitefish (Coregonus nasus). Thus, the 7.3-permil range 

in 813C values for grayling from the Fortymile River cannot be 

due to differences in trophic level because the N-isotopic data 

indicate that the trophic position of the grayling is confined to 

a single, restricted level (fig. 7/4). Several studies have investigated the C-isotopic fractionation among bulk tissue and such 

organic compounds as soluble proteins, carbohydrates, and 

lipids (fats) for various animals (DeNiro and Epstein, 1978; 

Tieszen and others, 1983; Hilderbrand and others, 1996). In 

general, the C-isotopic composition of bulk tissue is indistinguishable from that of proteins and carbohydrates, although 

lipids generally have isotopic compositions 2.5 to 4.5 permil lower than those of bulk tissue. The difference in the fat 

content in grayling is not considered a likely explanation for 

the variation in C-isotopic composition because the fish are 

all similar in size and maturity. In addition, no gender-based 

differences exist in the C-isotopic compositions of fish that 

could be attributed to an increase in the reproductive caloric 

requirements of females; the 813C values in females averages -29.411.4 permil (la) and of males averages -28.911.8 

permil (la).

The most likely explanation for the variation in the Cisotopic composition of grayling is that the 813C values reflect 

primary variations in the isotopic composition of food sources 

for the fish. Hicks (1997) used N and C isotopes to elucidate 

food-web relations in forest and pasture streams in New Zealand. He concluded that the variation in C-isotopic compositions in the lowest levels of the food web reflected mixtures
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling (Thymallus arcticus) 37

of allochthonous and autochthonous C in the primary producers, on the basis of material analyzed from his study area. 

Allochthonous C is derived from terrestrial plants as leaf litter. 

Terrestrial plants dominantly utilize the C3 photo synthetic 

pathway to derive their C from atmospheric CO2 , which typically yields 8 13C values in organic matter of -29 to -26 permil 

(O'Leary, 1988). Autochthonous C is produced by aquatic 

plants, which derive most of their C from aqueous bicarbonate. 

Aquatic plant tissue can have 8 13C values ranging from -40 to 

-20 permil (Rau, 1980; France, 1995). In the absence of data 

from primary producers in the Fortymile River watershed, a 

quantitative assessment of the relative importance of autochthonous and allochthonous C is difficult because the published 

range of 813C values for algae (-40 to -20 permil) overlaps 

that for allochthonous material (-30 to -26 permil) and the 

means of autochthonous (-29±4 permil) and allochthonous 

(-28±1 permil) C are indistinguishable (France, 1995, 1996). 

Nevertheless, the range of 8 13C values, from -33.1 to -25.8 

permil, for grayling from the Fortymile River is consistent 

with mixtures of autochthonous and allochthonous C sources. 

8 I3C values outside the range -30 to -26 permil probably 

represent instream algal C sources.

S-isotopic compositions of animal tissue are primarily 

indicative of source (Hesslein and others, 1991; Doucett and 

others, 1999), because isotopic fractionations associated with 

trophic-level variations are small (that is, 0.0-1.0 permil per 

trophic level; Peterson and Fry, 1987). Hesslein and others (1993) attributed isotopic fractionations greater than 1.0 

permil in laboratory-raised broad whitefish (1.5 permil) to 

differential assimilation of food components, because no evidence exists for metabolic fractionation of S isotopes in fish. 

Because of the limited trophic fractionation of S isotopes, the 

variation in S34S values for grayling from the Fortymile River 

(-8.4 to 8.2 permil) must reflect variations in food sources. 

Doucett and others (1999) reported a similar variation in 834S 

values for brook trout in New Brunswick, Canada (1.5-14.1 

permil). Hesslein and others (1991) reported a variation in 

834S values of -8 to 3 permil for broad whitefish from the 

Lower Mackenzie River Basin, Northwest Territories, Canada. 

However, the higher S34S values reported in both of these studies were attributed to the elevated 834S value of marine sulfate 

(-21 permil), in combination with the anadromous behavior of 

broad whitefish and brook trout. For nonanadromous grayling 

from the Fortymile River, the range of 834S values must reflect 

an isotopically heterogeneous local food supply (fig. IB).

S isotopes are expected to have the closest links to the 

underlying geology of the Fortymile River watershed relative 

to N and C. Igneous rocks, siliciclastic marine sedimentary 

rocks, and marine evaporites all have reasonably well constrained ranges of isotopic compositions. The 834S values of 

igneous rocks generally range from 0 to 5 permil, those of 

siliciclastic sedimentary rocks are generally negative and average -20 permil, and those of Lower Paleozoic marine evaporites range from 16 to 33 permil (Ohmoto and Rye, 1979; Seal 

and others, 2000). Because the 834S values of grayling range 

from significantly negative (-8.4 permil) to significantly positive (8.2 permil), and because of the geologic setting of the 

study area, all three lithologic reservoirs (fig. 1; table 1) may 

be important in the Fortymile River Basin.

In a laboratory feeding study of broad whitefish (Hesslein 

and others, 1993), N-, C-, and S-isotopic changes were modeled in response to feeding with an isotopically distinct food. 

The modeling was reflective of two processes: tissue addition 

(growth) and metabolic tissue replacement. Hesslein and others, 

1993 reported that the half-time for replacement of N, C, and 

S associated with growth was on the order of a few months, 

whereas that associated with metabolic replacement was more 

than a year. Thus, for natural populations, which are slow 

growing relative to laboratory conditions, several years may be 

required to equilibrate with a new food source. Therefore, in 

slow-growing natural populations, isotopic differences among 

individuals in a group should reflect differences in food choices.

From the perspective of grayling in the Fortymile River, 

the N-, C-, and S-isotopic signatures probably reflect longerterm feeding habits because of the long turnover time for 

metabolic replacement. Thus, the N-isotopic data reflect a consistent and restricted, long-term trophic position for the fish. 

In contrast, the C- and S-isotopic signatures of the fish record 

diverse and heterogeneous food sources. For example, the four 

fish from the O'Brien Creek sampling site span 71 percent of 

the total C-isotopic range and 60 percent of the total S-isotopic 

range observed for all fish (fig. IB). Other sampling sites show 

similar wide observed ranges. Furthermore, the nonlinear 

scatter suggests that the population is feeding on a minimum 

of three distinct food components. In addition, individual fish 

are probably exhibiting a high degree of long-term selectivity in food choices, because the isotopic differences reflect 

long-term feeding habits due to the slow rates of metabolic 

replacement of muscle tissue. This conclusion is somewhat 

remarkable because of the interyear fidelity of grayling to 

summer-feeding and overwintering sites (Reynolds, 1997; 

Buzby and Deegan, 2000), which would tend to decrease the 

isotopic variation in potential food sources. Causes for the 

observed isotopic variations include differences in overwintering sites for individual fish caught at a specific sampling site, 

individual preferences in diet for aquatic or terrestrial invertebrates, and shortened isotopic turnover times.

Aquatic invertebrates dominate the stomach contents of 

grayling from Steele Creek (69 percent) and Polly Creek (66 

percent), whereas terrestrial invertebrates dominate the stomach contents of grayling from Canyon Creek (77 percent; table 

8). In addition, the grayling from the Polly Creek sampling 

site show a lower percentage of dominant taxa in their stomach content (29 percent) than do those from the Steele Creek 

sampling site (61 percent) and the Canyon Creek sampling site 

(55 percent). Thus, the stomach contents minimally show a 

short-term diversity in the food sources for grayling.

The feeding habits recorded in the isotopic signatures 

may actually represent shorter-term behavior than the multiyear periods required to equilibrate with new food sources 

through metabolic tissue replacement. Because grayling feed 

aggressively during the summer, their isotopic signatures
38 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Table 8. Summary of dominant invertebrate taxa identified in the stomach contents of three 

Arctic grayling collected at fish-sampling sites along the main stem of the Fortymile River, 

eastern Alaska.

[See figure 1 for locations. Insect orders: Diptera, Ephemeroptera, Plecoptera, and Trichoptera; insect family: 

Chironomidae. EPT, combined Ephemeroptera-Plecoptera-Trichoptera. Do., ditto]

Parameter

Total individual invertebrates counted —

Total aquatic invertebrates ——————

Total terrestrial invertebrates — — — —

Total Ephemeroptera ——————————

Percent Ephemeroptera —————————

TfYf ol Pl^pnT^t^Ti _....«

Percent Plecoptera ——————————— • Total Trichoptera ———————————— • Percent Trichoptera —————————

Total aquatic Diptera ———————————

Percent aquatic Diptera — ——— — ——

Percent EPT ———————————————

Percent Chironomidae (Diptera) — ———

Totals: 

Percent dominant taxa ——————.

Percent aquatic invertebrates — ——

Percent terrestrial invertebrates — — —

Common 

name

— Mayfly — —

do _

— Stonefly —

do- -

— Caddisfly -

Hn -

— True fly —

... do— - -

Triif* flv- —

Steele 

Creek

- - 120

o-j

37

15

7

3

. - 1

1 — 78 

65

\

1

9

69

0

61

69

31

Canyon 

Creek

109

25 

84 

9

1 

1 

0 

0 

20 

18 

4 

4 

0 

0

19

4

55 

23 

77

Polly 

Creek

172 

113 

59 

15

5 

3 

15 

9 

58 

34 

45 

26 

10 

6

47 

9

29 

66 

34

may equilibrate with local food sources if significant growth 

accompanies summer feeding. If so, then the feeding period 

recorded by the stable-isotopic composition of muscle tissue 

will probably fall between the several months inferred for 

rapid growth, and the several years inferred for metabolic 

tissue replacement. In either case, reliance on aquatic invertebrates, particularly larval forms, would be expected to have a 

homogenizing effect on the stable-isotopic signatures in grayling found in the main stem of the Fortymile River. In contrast, 

reliance on terrestrial invertebrates would be expected to cause 

a greater variation in stable-isotopic signatures because of 

local variations in geology and land cover.

The diversity in the stable-isotopic data help explain the 

weak correlation between the metallic-ion contents in fish 

tissue and the underlying geology. Stable-isotopic data can be 

interpreted in terms of the varying mixing of food sources that 

incorporate aquatic sources (which reflect watershed-scale 

geochemical signatures) and terrestrial sources (which may 

reflect a more local or geologic geochemical signature). Mixing of multiple components is unlikely to show simple correlations with local geology. Hg is documented to bioaccumulate 

in the muscle tissue of higher organisms, and N isotopes monitor trophic position. Examination of the interdependence of Hg 

content and 815N value in the grayling samples reveals a poor 

correlation and no systematic intersite variation (^=0.179; fig. 

1C), consistent with the idea that the grayling are tapping into 

varied food sources.

Composition of Grayling Stomach Contents

The stomachs and upper intestines of the three Arctic 

grayling analyzed were fully distended—that is, feeding 

success appeared to be high. Invertebrates were identified in 

material from the anterior part of the stomach and, when key 

characteristics remained, in other, more digested material from 

the posterior part of the stomach and the intestine (table 9).

We identified 109 to 172 individual invertebrates from 

each of the fish and from 9 to 15 distinct taxonomic groups 

(generally to family level, although some specimens contained 

sufficient remaining characteristics to identify to genus level; 

see Crock and others, 2003, table 8). The fish stomachs from 

the Steele and Polly Creek sampling sites contained high 

proportions (47-69 percent) of EPT taxa. In contrast, the 

proportion of EPT taxa in the Canyon Creek fish was only 19 

percent. This difference in the proportion of EPT taxa indicates that food sources vary somewhat with location on the 

river; fewer EPT taxa reflect the lower proportion of aquatic 

taxa observed in the Canyon Creek sampling-site population.

Most of the invertebrates counted in fish from the Steele 

and Polly Creek sites were well-developed aquatic Trichoptera 

larvae. Similarly, 61 percent of the total invertebrates identified in Steele Creek fish stomachs were Trichoptera (genus 

Arctopsyche). In contrast, only 29 percent of the invertebrates 

identified in the Polly Creek fish were Trichoptera (genus 

Micrasemd). The stomach contents contained many wings
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 39

Table 9. Numbers of aquatic and terrestrial invertebrate taxa identified in three Arctic grayling 

individuals collected from sampling sites on the main stem of the Fortymile River, eastern Alaska.

[Form: A, aquatic; T, terrestrial]

Order 

(common name) Family Genus

Anterior Posterior 

stomach stomach

A T A T

Lower 

intestine

A T

Male fish (406 mm long) collected at the Steele Creek confluence

Ephemeroptera 

(mayfly).

Plecoptera 

(stonefly).

Trichoptera 

(caddisfly).

Coleoptera 

(beetle).

Diptera 

(true fly).

Homoptera 

(leafhopper).

Hemiptera 

(water boatman).

Hymenoptera 

(wasp).

Arachnida 

(spider).

ae e ...

Brachycentridae ————— Brachycentrus -----

2

j

__ i __ __

2 — 3

10 CC

1 1

10 

8 

5 

1

1 

__ __ __ i

1 

8 

1

—

—

Female fish (360 mm long) collected at the Canyon Creek confluence

Ephemeroptera 

(mayfly).

Trichoptera 

(caddisfly).

Diptera 

(true fly).

Homoptera 

(leafhopper).

Hymenoptera 

(wasp).

Thysanoptera 

(thrip).

Brachycentridae ——— 

Glossosmatidae ————

- —- Brachycentrus -—- 

-—- Glossosoma —-—-

1

1 8 i o —

4

20 40

20 

1

3 

1

1 

1

—

—

Male fish (340 mm long) collected at the Polly Creek confluence

Ephemeroptera 

(mayfly).

Plecoptera 

(stonefly).

Trichoptera 

(caddisfly).

Coleoptera 

(beetle).

Diptera 

(true fly).

Hymenoptera 

fwasrA

Baetidae ———————

MvmaniHaF' - —

—- Baetis —————. 3 

2

2

0

10

5

• 10 — 15

j

. __ 3

25 

• 10 

• 15 — 20 

10

3 1

s 1

—

25

--
40 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

that appeared to be from emerging winter stoneflies (likely 

Nemouridae). These invertebrates were not counted as part 

of the sample because they could not be positively identified; 

however, we estimated about 75 to 100 wing pairs.

As stated above, the fish from the Canyon Creek sampling site contained the highest proportion of terrestrial 

insects, mostly Homoptera (18 percent of the total counted) 

and adult Chironomidae (55 percent). Only 18 percent of the 

invertebrates were Trichoptera, most of which were Brachycentridae (genus Brachycentrus).

Summary and Conclusions

1. We present quantitative information on the chemistry 

of 38 elements in the muscle tissue, liver, and stomach 

contents of Arctic grayling collected from the lower 

reaches of the Fortymile River watershed. We also 

present N-, C-, and S-isotopic data for fish muscle 

tissue. These data can be used as estimates of biogeochemical baselines for grayling in this region of Alaska.

2. Although interyear feeding-site fidelity is known to 

be high for grayling, and although differences in the 

chemistry of fish tissue can be quantitatively demonstrated between fish-sampling sites, this variation is 

not directly attributable to intersite lithologic differences, possibly because the total chemistry of stomach 

contents is an inadequate measure of element bioavailability (that proportion of the total amount present 

which is finally incorporated into fish tissue). The poor 

correlation between lithology and fish chemistry may 

also be due to the low "geoavailability" of elements 

within minerals that make up the metasedimentary and 

metavolcanic rocks—that is, the common minerals, such 

as feldspar, mica, hornblende, and so on, would not be 

easily weathered in this environment, where ground and 

surface waters are most commonly circumneutral in 

pH. Wang and others (see chap. 1) report subtle differences in the rare-earth-element signatures of waters that 

drain various lithologic units within the Fortymile River 

watershed. Streams draining the Steele Creek tonalite were found to have low major-ion concentrations, 

whereas those draining metasedimentary-rock units had 

higher Cu and Cr contents. No systematic variation in 

Hg content with lithology was observed. Finally, the 

slight variation in the geochemistry of major iithologic 

units and stream sediment, coupled with the limited 

areal extent of the lithologic units, might not result in 

enough of a geochemical imprint on the landscape to be 

reflected in fish-tissue chemistry.

3. Macalady and others (see chap. 3) found that the 

abundant dissolved natural organic matter (NOM) in 

water from the Fortymile River main stem and O'Brien 

Creek sequesters some cationic metals in solution. 

From a comparison of the binding ability of these 

NOM-rich waters with those of streams from other

parts of the globe, however, this process probably has 

a minimal role in the mobilization of metallic ions in 

these two Alaskan streams.

4. The results of a Mest comparison of the variation in 

the concentrations of 12 elements in fish muscle tissue 

collected among the 11 sampling sites showed significant differences between at least 2 sites for 10 of 

these elements. This nonrandom, possibly systematic 

pattern is a direct function of the slight variation in the 

data for fish collected at individual sites. We compare 

this "clustering" of values within samples at a given 

fish-sampling site with the greater intersite variation in 

the data. This intersite variation is not attributable to 

specific lithologic units (see above) but may be due to 

as-yet-undetermined differences in site geochemistry 

and element bioavailability.

5. Although the low Hg content in fish tissue is not 

surprising, the importance of analyzing for Hg in this 

watershed is driven by a concern over its use, since the 

1890s, in gold amalgamation by placer miners in the 

region. The evaluation of Hg contamination in Arctic 

and subarctic aquatic and terrestrial ecosystems certainly deserves closer scrutiny because of the general 

global Hg concern and a growing appreciation for the 

unique cycling of Hg between ecosystems and the 

atmosphere in Arctic regions (Schroeder and others, 

1998; Belts, 2001). Total Hg content in muscle tissue 

ranged from 0.021 to 0.15 ppm (wet-weight basis), 

with a GM value of 0.069 ppm, and in liver tissue from 

0.031 to 0.10 ppm, with a GM value of 0.062 ppm. 

The total Hg content in muscle tissue of grayling from 

the Fortymile River are nearly an order of magnitude 

below the PDA's action level of 1.0 ppm MeHg in 

fish and well below the U.S. Environmental Protection Agency's risk-based concentration of 0.14 or 0.30 

mg/kg (maximum daily consumption). In addition, 

the concentrations of other metals and metalloids in 

muscle tissue are low relative to published values for 

many diverse freshwater and marine fish.

6. The N-isotopic signatures of fish muscle tissue indicate 

a restricted trophic position for the grayling population, consistent with their stomach contents and known 

feeding habits. The C- and S-isotopic data indicate 

selectivity in feeding habits for individual fish. The 

diversity in the stable-isotopic data helps explain the 

weak correlation between metallic-ion contents in 

fish tissue and the underlying geology. Stable-isotopic 

data can be interpreted in terms of a mixing of food 

sources that incorporate aquatic sources, which reflect 

watershed-scale geochemical signatures, and terrestrial 

sources, which may reflect a more local (geologic) 

geochemical signature.

7. Stomach contents from three grayling (collected 1 year 

after, but at the same time of year as, the biogeochemical samples) showed an incredible number of invertebrate individuals and diversity of invertebrate taxa.
Biogeochemistry, Stable-lsotopic Composition, and Feeding Habits of Arctic Grayling ( Thymallus arcticus) 41

From 109 to 172 individual invertebrates were separated and cataloged from the three fish, representing 

from 9 to 15 distinct taxa. The proportion of EPT taxa 

varied with fish-sampling site on the river, indicating 

variation in either feeding habits or, more probably, 

available taxa. Fewer EPT taxa reflect a lower proportion of aquatic forms relative to terrestrial forms. These 

data indicate that the river has a diverse food web 

which is being effectively exploited by the resident 

grayling. A complete listing of invertebrate taxa identified for each of the three individual fish examined was 

given by Crock and others (2003).

Acknowledgments

We thank Larry and June Taylor of the Fortymile Mining 

District for their hospitality, good humor, and the second collection of fish stomachs. Chemical analyses were performed in 

the USGS laboratories in Denver, Colo., by Z.A. Brown, A.L. 

Meier, and P.M. Theodorakos, and isotopic analyses in the 

USGS laboratories in Reston, Va., by G.A. Wandless. Johanna 

Crock assisted with the preparation of fish samples.

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Chapter 3

Comparative Characteristics of Natural Organic Matter in 

the Fortymile River, Alaska

By Donald L Macalady,1 Kaylene Ritter,1 Aaron D. Redman, 1 and Magnus Skold 1

Contents

Abstract..........................................................................................................45

Introduction...................................................................................................45

Methods .........................................................................................................47

Water Samples....................................................................................47

Data Analysis.......................................................................................48

Results and Discussion................................................................................48

Conclusions...................................................................................................52

Acknowledgments........................................................................................52

References Cited ..........................................................................................52

Abstract

Water samples collected from Alaska's Fortymile River 

and O'Brien Creek, a major tributary, were analyzed to evaluate the potential for metallic-ion mobilization caused by natural organic matter (NOM). This factor is of concern because 

of the high NOM concentrations in these rivers and historical 

and present-day mining activities in the river-drainage areas. 

Analyses of the samples for metallic-element contents showed 

nondetectable to very low trace-element concentrations, 

especially of those elements commonly associated with basemetal-mining activities. This result diminishes any immediate 

concern about metal loads in these rivers.

We have evaluated the potential for NOM-induced metallic-ion mobilization due to future mining or other anthropogenic sources by comparing the NOM concentrations of 

water samples from these two Alaskan streams with those of 

other NOM-rich waters from various sources. In fact, the two 

Alaskan streams are unique among the samples tested because 

of their very high alkalinities and elevated Ca, Mg, Ba, and 

Sr contents, resulting from the geochemistry of the drainage 

basins, not from anthropogenic sources. Overall, comparisons of several measured properties of water samples from 

the Fortymile River and O'Brien Creek with those of other 

water samples suggest a minimal role for NOM/metallic-ion-

'Colorado School of Mines, Golden.

complex formation in the two Alaskan streams. Measurement 

of the Cu-complexation capacities for these and other NOM 

samples confirms that these Alaskan streams are characterized 

by NOM with very low metallic-ion-complexation capacities. These results clearly suggest that the NOM in these two 

Alaskan streams has only a minimal potential for metallic-ion 

mobilization.

Introduction

Natural organic matter (NOM) is abundant in the drainage of many Alaskan rivers and streams, including the 

Fortymile River and several of its tributaries. This factor 

is of special interest for the Fortymile River drainage area 

because of widespread current and historical placer gold-mining operations in the river and its riparian zones. NOM is 

known to sequester cationic metals in solution, thus increasing 

their mobility and ease of transport (Macalady and Ranville, 

1998). Recent evidence suggests that NOM can increase the 

mobility of anionic metalloids, such as arsenic (Redman and 

others, 2002). As we show below, metallic-ion concentrations 

in waters of the Fortymile River drainage are not of current 

concern. Nevertheless, it is prudent to investigate questions 

surrounding the possible role of NOM in determinations of 

metallic-ion mobility so as to set a baseline against which 

anthropogenic impacts can be compared.

NOM samples represent inherently complex mixtures of 

polyfunctional organic acids and phenols with properties that 

vary considerably, depending on the origin and pretreatment of 

the samples (MacCarthy, 2001; Macalady and Ranville, 1998). 

The phrase "humic substances" has generally been applied to 

operationally defined components of soil or solution-phase 

NOM. Humic substances have the seemingly contradictory 

properties of recalcitrance to further degradation and reactive 

lability with respect to oxidation/reduction reactions, metallicion complexation, and molecular configurations.

Humic acids, fulvic acids, humin, and hydrophilic acids 

are among the operationally defined isolates of NOM that are
46 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

commonly used to investigate the roles and functions of NOM 

in natural and polluted environments. The use of isolates has 

the advantage that a sample of fulvic acid, for example, from a 

given soil or aquatic system can be expected to have relatively 

constant chemical and physical properties over time because 

the more geochemically and biologically labile NOM components, as well as the inorganic matrix, have been removed 

during the isolation procedures. Standardized samples of 

humic and fulvic acids are commercially available through the 

International Humic Substances Society, among other sources. 

Also, as a consequence of the standardized isolation procedures (Thurman and Malcolm, 1981), samples of fulvic acid 

from various sources generally are more similar than might 

be expected for the bulk NOM samples from which the fulvic 

acids were derived (McKnight and others, 1983). Thus, much 

of the reported research involving NOM actually involves the 

use of one or more of these operationally defined fractions.

Particularly for solution-phase NOM, these defined 

fractions (humic materials) constitute only about half of the 

organic C in most aquatic systems. This fact represents one 

obvious disadvantage of using such isolates as fulvic, humic, 

or hydrophilic acids for investigating the roles and influences 

of NOM in natural systems. The suite of molecules composing the whole of an NOM sample may behave quite differently from the fulvic acid, for example, derived from the same 

aquatic system, partly because the fraction is only part of the 

whole but also because the influences of inorganic constituents 

in the aquatic system are obviated. Finally, no evidence has 

been observed to support the notion that the various defined 

fractions represent unaltered portions of the original NOM. 

Because aspects of molecular behavior related to molecular 

conformations may be critical for NOM, removal of a fraction 

from the whole may alter the behavior of both the isolate and 

the remaining fraction.

Thus, unlike fulvic acid, the organic components of 

whole, NOM-rich waters from diverse environments vary 

widely in their ability to form stable metallo-organic complexes. This variety can be reflected in the native metallic-ion 

concentrations of NOM, or in the ability of the NOM to complex additional metallic ions from solution or from material 

adsorbed onto, or precipitated with, solid-phase minerals. For 

example, when NOM-rich water samples (all adjusted to a pH 

of 6.0 and diluted to a dissolved-organic-carbon (DOC) content 

of 10 mg/L) from various sources were spiked with 3 |iM Cu, 

free (electrochemically labile, noncomplexed) Cu(II) contents 

ranged over almost two orders of magnitude (Skold, 1999). 

This Cu content, equivalent to 200 |ig/L, is not unreasonable 

for waters contaminated by mining activities (Peiffer and others, 1998). Thus, even at relatively low metallic-ion concentrations, the ability of NOM to complex metals varies significantly when the NOM source is considered—from almost all 

present in a complexed form to about 90 percent free (labile).

The (total dissolved) metallic-ion concentrations of 

NOM-rich natural waters show a comparable variety (see 

below). In this regard, the levels of "dissolved" (operationally defined) metals that are sparingly soluble in the absence

of NOM or other solution-phase complexing agents are 

particularly instructive. Fe(III) is especially useful in this 

regard because equilibrium Fe(III) contents are expected to 

be immeasurably low over the pH range relevant to natural 

waters (for example, Macalady and others, 1990). Waters rich 

in NOM are shown below to have Fe(III) contents that range 

from one sequestered Fe(III) ion per six C atoms to virtually 

Fe free. Such variations can reflect the geochemical environment from which the NOM was sampled and (or) the botanic 

and microbiologic origins of the samples.

Another NOM property of interest, with respect to the 

ability to sequester metals, is the fraction of NOM (as measured by organic C) that is adsorbed upon equilibration with the 

surfaces of such metal oxyhydroxides as hematite or gibbsite. 

Particularly for Fe and Al hydroxides, NOM is known to form 

stable surface complexes with mineral grains (McKnight and 

others, 1992). Under identical experimental conditions, the 

fractions of total organic carbon (TOC) removed for various 

NOM samples upon exposure to a model mineral, such as 

hematite, can also be used as reflections of the relative ability 

to form stable (surface) metallic-ion complexes.

The extent and importance of NOM metallic-ion complexation in a given aquatic system is a complex function of 

the composition and source of the NOM, as well as of other 

system characteristics, including basic mineralogy and inorganic water characteristics. Our study is part of a more extensive laboratory effort to develop a predictive methodology for 

assessing the relative importance of NOM and other aqueous 

constituents in various chemical and physical processes within 

aquatic systems. As a part of these investigations, we have 

quantified many characteristics of a wide variety of NOM-rich 

waters, including such standard water-quality parameters as 

alkalinity, pH, conductivity, anionic composition, and metallic-ion concentration. In addition, we determined NOM-specific characteristics, all normalized to unit C contents, such 

as carboxylate acidity (defined as acidity neutralized between 

pH 2 and 7), phenolic acidity (defined as acidity neutralized 

between pH 7 and 10), metallic-ion-complexation capacity (defined in terms of Cu(II) complexation), and aromatic 

content (defined in terms of specific ultraviolet absorbance 

[SUVA] at 254 nm). We also investigated the oxidation/ 

reduction properties of NOM.

We report here the results of investigations on waters 

from the Fortymile River and O'Brien Creek, a major tributary 

to the former, in comparison with other NOM-rich waters that 

have been part of our continuing studies. The specific hypothesis guiding our investigations of waters from the Fortymile 

River and O'Brien Creek is that the composition of the NOM 

present in these waters, along with associated inorganic 

constituents, is such that the risk of substantial metallic-ion 

mobilization by placer-mining operations in these waters is 

minimal. All of our investigations, as implied above, have been 

with "whole water" samples; we have made no effort to isolate 

NOM or to separate it into defined fractions (such as fulvic 

acids). We have measured native metallic-ion concentrations, 

but we have made no effort to remove these metals. Generally
Comparative Characteristics of Natural Organic Matter 47

speaking, all samples are near neutral and have greater-thanmillimolar DOC concentrations. Because whole waters are 

used, other components and characteristics of each sample 

must be considered in addition to NOM—in other words, 

unambiguous ascription of all observed behaviors exclusively 

to NOM is outside the scope of this study.

Methods

Water Samples

Samples of Alaska river water were collected during 

April 2001. The water sample from the Fortymile River was 

obtained on April 3 in the South Fork, approximately 200 m 

above its confluence with the North Fork (lat 64°14.483' N., 

long 141°45.143' W.; elev, 1,380 ft). The samples (8) were 

obtained through an auger-drilled hole in the ice, using a peristaltic pump, into acid-washed, 1-L-volume brown (opaque) 

Nalgene bottles. Bottles were thoroughly rinsed with river 

water before the samples were collected. At that time, the river 

was frozen completely, and no flow was detected. Thus, the 

sample probably represents a considerable freeze concentration over the river water under nonfrozen conditions. At the 

time of sampling, the water had a pH of 7.29 (measured at 

0°C), a conductivity of 720 |j,S/cm, an undetectable Fe content 

(<0.05 mg/L), and a dissolved-O content of 4 to 5 mg/L.

The water samples from O'Brien Creek were collected 

several miles upriver from its confluence with the Fortymile 

River, approximately 150 m downstream from the confluence 

of Alder Creek with O'Brien Creek (lat 64°21.035' N., long 

141°23.388' W.) and about 30 m below a pronounced circular 

upwelling in the stream that had cleared the ice at the upwelling and in a channel below. The samples (9) were obtained by 

submerging 1-L-volume brown Nalgene bottles in the flowing 

water and rinsing several times before filling. The water had 

a pH of 7.90 (measured at 0.4°C) and a conductivity of 1,795 

|j,S/cm. Samples were transported to the Colorado School of 

Mines and refrigerated at 4°C until analyzed.

We note that because the samples were not filtered and 

acidified in the field, alterations between the time of sampling 

and analysis are likely; however, no visible changes in the 

samples were observed during storage (that is, no staining was 

observed in the containers, nor were any visible precipitates 

formed). Nevertheless, the conclusions of this study are based 

on sample characteristics at the time of analysis, which may 

vary somewhat from field conditions.

The other water samples used in this study were collected 

at various times and locations (table 1). Generally, samples were 

collected at or near the surface of the relevant water body by submersing 2- to 10-L-volume, acid-washed plastic bottles beneath 

the surface, rinsing and then filling, and allowing little or no 

headspace. Several water samples (Inangahua River, Suwannee 

River, Black River) were collected by tossing a plastic bucket 

(with a rope attached) into a fast-flowing stream, retrieving the

bucket, and filling the plastic bottles from the bucket. Samples 

were not preserved or altered in any deliberate way. Depending 

on location, samples were removed to a refrigerated (4°C) site as 

quickly as possible; the interval between sampling and refrigeration ranged from several hours to 2 weeks. Samples from New 

Zealand (Inangahua, Stoney Creek) were shipped to Colorado in 

insulated containers by airfreight. Samples from the Rio Negro 

were carried as checked baggage from Brazil and left unrefrigerated for several days. Upon their arrival at the laboratory, all 

samples were stored until analysis at 4°C, generally in polyethylene bottles; some samples were stored in brown glass bottles to 

minimize the effects of oxygen and light.

Sample MW-6 is from a shallow (~1 m deep) well 

beneath a wetland near Leadville, Colo.; the wetland receives 

much of its water from two streams heavily contaminated with 

acid mine drainage (Peiffer and others, 1998). When pumped 

from the ground (using a peristaltic pump), the sample was 

anaerobic and contained about 5 mg HS~/L, 25 mg Fe(II)/L, 

and 35 mg DOC/L. After storage and before analysis, sample 

MW-6 had been oxidized (by air) to the extent that it contained no measurable sulfide or Fe(II). The Fe content of the 

filtered (0.2 or 0.45 |J,m) water did not change upon oxidation, 

although all of the Fe had been converted to Fe(III). Sample 

characteristics and locations are summarized in table 1.

The change in NOM characteristics during storage is a 

nontrivial issue for whole-water samples, which necessarily 

contain labile organic constituents that degrade over time, 

either abiotically or because of microbial activity. The extent 

to which such changes are observable and (or) important can 

be expected to vary among sample locations and over time at 

the same location. Our laboratory observations indicate that 

monthly changes in measurable characteristics range from 

barely within statistical significance to substantial. DOC contents, for example, can fluctuate by 0 to 20 percent per year for 

whole-water samples stored in dark plastic containers at 4°C. 

We are currently attempting to understand both these changes 

in DOC content and the factors affecting their magnitude. Our 

goal is to eventually develop storage protocols that minimize 

temporal variations in whole-water samples. A corollary 

series of investigations concerns the seasonal variation among 

water samples from the same locations. For the purposes of 

our investigations, all measurements reported here for a given 

water sample are on subsamples isolated at a specific time, 

with filtrations, pH and (or) ionic-strength adjustments, and 

dilutions, where necessary, made immediately before analysis.

Reagents used were "metal free" or high-purity commercial-grade chemicals, used as received. Potassium phthalate was used both for (daily) standardization of NaOH titrant 

solutions and for preparation of standards for DOC determinations. Measurement methods for most whole-water or NOMspecific characteristics are relatively standard and have been 

described elsewhere (see Skold, 1999, Redman and others, 

2002, and references therein) and so are not detailed here. 

These measurements include DOC content, pH, alkalinity, 

conductivity, carboxylate and (or) phenolic acidity, aromatic 

content (by SUVA), metals (by inductively coupled plasma
48 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska 

Table 1. Description of sites sampled for natural-organic-matter investigations.

[See text for descriptions of the Alaska river-water samples]

Sample 

identifier Location and sampling date Comment

Rio Negro ————— 

Stoney Creek ——— 

Inangahua River—— 

Black River ———— 

Suwannee River——

50 km upstream from Manaus, Amazonia,

Brazil, July 2000. 

Central Otago, South Island, New Zealand,

April 1997. 

Westland, South Island, New Zealand, April

1997. 

Upper Michigan peninsula, near Republic,

Mich., July 1999. 

At weir defining outlet of the Okeefenokee

Swamp, southern Georgia, August 1994. 

MW-6 ——————— Ground water from a shallow (1 m deep)

aquifer beneath a high-altitude wetland,

Leadville, Colo., August 1994.

Sample taken during high-water

period. 

Catchment basin is grassland,

totally devoid of trees. 

Catchment dominated by red

beech. 

River flows through Fe-rich

terrain.

Wetland is highly impacted by 

streams contaminated with 

acid mine drainage.

Table 2. Characteristics of water samples.

[Numbers in parentheses represent one standard deviation from the mean of three replicate determinations, n.a., not analyzed. Some of these data were previously reported by Redman and others (2002). DOC, dissolved organic carbon; SUVA, specific ultraviolet absorbance]

Sample 

identifier

Fortymile River ———

Inangahua River ———

Stoney Creek ————

MW-6— — — — — —

Black River —————

pH

8 n ^n i\

8

T (O "3\

— 4.8(0.3) 

— 5.5 (0.3)

— 7.2 (0.3)

... 3.4 (0.4)

--- 5.4 (0.3)

— 5.2 (0.3)

DOC 

(mg C/L)

19.9(0.3) 

16.6(0.4) 

12.8 (0.5) 

11.5(0.5) 

8.0 (2.0) 

39(5) 

31(4) 

26.5 (3.0)

Alkalinity 

(mg CaCO3/L)

203 (5) 

450 (50) 

n.a. 

n.a. 

n.a. 

n.a. 

n.a. 

n.a.

COOH 

acidity 

(uequiv/mg 

C)

9.09 (0.06) 

8.98 (0.07) 

3.69 (0.05) 

16.77 (0.05)

1.8 (n-1) 

7.15(0.06) 

25.23 (0.06) 

11.42(0.07)

Phenolic 

acidity 

(uequiv/mg C)

n.a. 

n.a. 

n.a. 

n.a. 

18.9 

4.2 

n.a. 

n.a.

SUVA 

(L/mg C 

per centimeter 

at 254 nm)

0.019 (0.002) 

.015(0.001) 

.040 (0.005) 

.043 (0.009) 

.095 (0.004) 

.035 (0.008) 

.089 (0.004) 

.045 (0.002)

atomic-emission spectroscopy [ICP-AES]), and anions (by 

ion chromatography). Unless otherwise specified, all analyses 

were on 0.45-(im-filtered samples, with filtration performed 

by using Nucleopore or similar screen filters immediately 

before analysis whenever possible. Before acidity titrations, all 

samples were thoroughly purged with He or N2 at a pH of 2 to 

eliminate any acidity due to carbonate species.

Cu-complexation capacity was determined on samples 

adjusted to a pH of 6.0 and an ionic strength of 0.05 M (as 

KNO3 ). Samples were diluted to approximately 10 mg C/L 

before titration with Cu(II) (as copper perchlorate). Reported 

fractions of complexed and free Cu are normalized to 10.0 mg 

C/L (see Skold, 1999, for details). Procedures used to investigate the (competitive) binding of NOM (and (or) As(V)) to 

Fe oxyhydroxides involved prepared hematite suspensions, as 

described by Redman and others (2002). For these measurements, samples were also adjusted to a pH of 6.0, an ionic 

strength of 0.05 M, and a DOC content of 10 mg/L.

Data Analysis

Unless otherwise indicated, the results reported below 

are mean values from at least three independent determinations. Uncertainties represent one standard deviation (la) from 

the mean. Detection limits are method or instrument specific 

except for ICP-AES, for which detection limits are operator determined at the time of analysis. The results reported 

below for water samples from elsewhere than the two Alaskan 

streams were obtained during the period 1998-2003 and were 

not necessarily obtained solely for the purposes of this study. 

Except where noted, data have not been previously published.

Results and Discussion

The comparisons of the water samples used in this study 

are listed in tables 2 and 3. Two outstanding features of the
Comparative Characteristics of Natural Organic Matter 49

Table 3. Anionic composition of water samples.

[All values in milligrams per liter (n=2). Numbers in parentheses, detection limits. BDL, below 

detection limit]

Sample 

identifier

O 'Rrien Creek 1 ____

Inangahua River — — 

Stoney Creek ——— —

MW-6 —————.—

Chloride 

(0.02)

.55

9.36

3 92

7.21

.96

7 Q<

Nitrate 

(0.03)

n.a. 

n.a. 

.14 

.028 

.44 

.015 

13.3 

BDL

Phosphate 

(0.06)

n.a. 

n.a. 

.064 

.054 

.041 

BDL 

.056 

.13

Sulfate 

(0.01)

72 

237 

.095 

1.59 

.79 

1.15 

95.25 

2.83

'As indicated by the inductively coupled plasma atomic-emission-spectroscopic values for 

sulfur, the other dominant anion in these water samples is bicarbonate; thus, if all of the alkalinity 

comes from bicarbonate, O'Brien Creek water contains 275 mg HCOj/L.

Table 4. Elemental concentrations in Alaska river waters.

[All values in milligrams per liter. Number in parentheses, uncertainties (average deviation for 

replicate analyses). All other trace metals were undetectable by inductively coupled plasma 

atomic-emission spectroscopy. BDL, below detection limit]

Element

Al

Ba —— ——

C-A

Cu — — — -

Fe— — — --

Li— ... ... -

Mg -----

Mn — — —

xi a _____

s ____

CU

Sn — — — -

Sr— — ——

Fortymile River

BDL 

.03(0.01) 

.06(0.01) 

50.0(0.5) 

.0041 (0.008) 

.015(0.001) 

1.77(0.03) 

.0060 (0.0005) 

14.48 (0.03) 

BDL 

13.37(0.06) 

24.07(0.05) 

BDL 

.30(0.01) 

.30(0.01) 

.031 (0.05)

O'Brien Creek

0.04 (0.02) 

.08(0.07) 

.06 (0.02) 

96(3) 

.0018(0.005) 

.006 (0.001) 

2.19(0.07) 

.0081 (0.0004) 

51(2) 

.059 (0.003) 

6.6 (0.4) 

79(3) 

BDL 

.11(0.01) 

.11(0.01) 

.012(0.001)

Detection 

limit

0.02 

.03 

.0005 

.04 

.0007 

.003 

.14 

.002 

.003 

.004 

.08 

.04 

.01 

.05 

.0005 

.0007

water samples from the two Alaskan streams in comparison 

with those of other NOM-rich waters are the very high alkalinity and sulfate content and the low aromatic content (by SUVA). 

Although alkalinities were not specifically determined by 

titration for many of the water samples, their pH and Ca, Mg, 

and Fe contents do not indicate substantial alkalinity, except 

in sample MW-6. The elemental compositions of the water 

samples, not listed in tables 4 and 5, are below detection limits 

in all samples.

The low SUVA values and, presumably, aromatic content 

(table 2) indicate relatively "new" NOM from sources low 

in lignin and high in carbohydrates. This result suggests that 

such nonwoody plants as mosses and lichens may dominate 

the NOM content of these waters. The moderately high COOH

acidity is also consistent with this hypothesis. Our ongoing 

investigations of NOM originating from the decay of mosses 

and lichens may confirm or refute this hypothesis about the 

origin of the NOM in the Alaska water samples.

The other outstanding feature of the elemental analyses is 

the absence of significant contents of Fe, Cu, As, Sb, and (or) 

other metals that in other locations are ordinarily associated 

with mining of precious metals. This result almost certainly 

reflects both the composition of the NOM in these samples 

and the absence of significant mineralization that facilitates 

mobility of these metallic ions. The high Ca and Mg contents, 

along with substantial Ba and Sr contents, reflect the important 

influence of sedimentary minerals in determining the behavior 

of aquatic systems. Calcite, dolomite, gypsum, and related
50 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

Table 5. Elemental concentrations in natural-water samples.

[All values in milligrams per liter. Single inductively coupled plasma atomic-emission-spectroscopic analyses with triplicate injections. Same 

detection limits as in table 4. DDL, below detection limit]

Element

A] ________

Ra

PO

Cu— — — —

Fe _____ -

Li— —— ——

Mg——— — 

Mn

Na—— ——

o _______

Si— — — — -

Zn— — ——

Rio

Negro

n 9

fi9

RTVT

.48

RTYT

.17

RTYT

RTYT

.10

RTYT

.31

91

RTYT

RTYT

Inangahua 

River

0.34

.03

RTYT

1.16

RTYT

.02

RTYf

RTYf

CO

DTYT

5 Q8

.35

RTYT

RTYf

Stoney 

Creek

RTYT

.06

no

1.48

RTYT

.19

RTYT

QTYT

.70

RTYT

3

O£.

.06

RTYT

.001

Suwannee 

River

n 98

23

.09

1.24

1 8

.51

.17

.05

.59

RTYT

4.11

.69

.03

.03

MW-6

0.48

.02

.06

21.97

.02

'ye 88

O/^

RTYT

6.34

CO

6

1 9

30.12

.02

RTYT

MW-6 

duplicate

0.491

023

.076

22.4

.017

97 81

.468

RTYT

6.49

£QQ

6.761

34.55

.064

.008

Black 

River

0.06

.07

.01

9 8

.14

.95

2.47

RTYT

.79

RTYT

9 Q8

1.13

RTYT

.07

Table 6. Cu-complexation capacity and COOH acidities of natural-organic-matter samples 

containing 10 mg C/L, showing the complexed fraction of total Cu (3.15x1fr6 M, 0.2 mg/L).

[Specific ultraviolet absorbance (SUVA) and undiluted-sample dissolved-organic-carbon (DOC) content are 

shown for comparative purposes. Uncertainties in SUVA and DOC content are listed in table 2. Bound-Cu 

fraction is determined from single-titration trials, with estimated uncertainties of ±10 percent. Note that SUVA 

and DOC values may vary slightly from those listed in table 2 because experiments were performed at different times on different samples (that is, obtained at different times from those in table 2) or subsamples]

Water source

Fortymile River — — —— —

O'Brien Creek — —— ——

Suwannee River —— —— —

Inangahua River — —— — —

Hyde County, N.C

Rio Negro ———————

Mossy Burn River, New

Zealand.

Sunset Beach State Park,

Oreg. (seep).

MW-6 (ground water) ——

Stoney Creek —— —— ——

Sutton Stream, New

Zealand.

SUVA

0.019

.015

.031

.039

.043

.045

.05

.062

.085

.095

.089

.045

DOC

(mg C/L)

19.9

16.6

44""

11.5

8.9

8.3

11.5

20.1

28.1

2.1

5.7

26.5

Bound-Cu 

fraction

0.45

.50

.691

Q£Q

.OJO

.914

.919

.902

.797

.916

.982

.822

.437

COOH 

acidity 

( equiv/mg 

C)

9.1

9

7.15

16.77

3.69

--

--

25.23

1.8

1.7

11.41

minerals must be significant in the region. The relatively high 

Sn content in these samples is probably related to these rock 

origins.

A corollary to these observations is the apparent absence 

of the influence of Fe minerals in these river catchments, suggesting that if hard-rock mining, which exposes pyrite-rich 

minerals to the atmosphere and surface waters, becomes active 

in this region, these data provide little assurance that enhanced 

mobility of toxic metals will not be a problem.

The results of Cu titrations to determine the extent to 

which NOM samples can form solution-phase Cu complexes 

are listed in table 6, along with data from several natural-water 

samples not listed in tables 1 and 2 that are included here to 

expand the data set (Skold, 1999). The Alaska water samples 

have Cu-complexation abilities that are among the lowest 

of all the samples analyzed. These samples are quite similar 

in several regards to the Black River water sample, which is 

the only other high-latitude sample in the data set. In fact,
Comparative Characteristics of Natural Organic Matter 51

the catchment vegetation in the Black River drainage basin 

is dominated by sphagnum bogs and conifer/willow species, 

similar to that in the Alaska river drainages. The Black River 

water sample shows a similarly low SUVA value, and Cu-complexation capacity has been related in general to the aromatic 

fraction of NOM (Skold, 1999). The low metallic-ion-complexation capacity of the Alaska water samples also indicates 

that this NOM is unlikely to be a causative agent for increased 

metallic-ion mobility in these aquatic systems.

The extent to which DOC and the aromatic fraction of 

DOC are removed by adsorption/surface complexation with 

Fe minerals in natural aquatic systems is indicated in table 7, 

which lists the reductions in SUVA value and TOC content 

upon equilibration with 500-mg/L suspensions of colloidal 

hematite (Redman and others, 2002). Note that the Fortymile 

River water sample showed the lowest tendency to adsorb 

to, or form surface complexes with, colloidal hematite. The 

Black River water sample shows similar DOC fractionation 

upon exposure to hematite. The data in table 7 reflect a similar 

tendency to those illustrated by the data in table 6, in that the 

mechanisms of formation for surface complexes with Fe(III) 

minerals are not expected to be dissimilar to those for the 

formation of solution-phase metallic-ion complexes.

These data, along with additional SUVA data at 280 nm, 

are illustrated in figure 1, which clearly shows the uniqueness 

of the Fortymile River water sample among the suite of NOM 

samples analyzed. The figure also highlights that removal of 

the aromatic fraction from the NOM in the Fortymile River 

water sample is significantly less than for any other represented NOM sample. This result again reflects the relatively 

low ability of South Fork NOM to form metallic-ion complexes, because the aromatic fractions are known to be among 

the most active in metallic-ion complexation (Skold, 1999).

The final data to be mentioned here concerning the 

characteristics of the Alaska water samples are from Redman and others (2002), who reported the ability of NOM-rich 

waters to alter the otherwise-complete adsorption of As(III)

Table 7. Percent removal of natural organic matter and 

aromatic portion of natural organic matter upon exposure 

to 500 mg of colloidal hematite per liter.

[All values are averages of replicate trials in a single experiment 

Variations are less than 10 percent]

Sample 

identifier

Rio Negro —————— 

Fortymile River ——— 

Black River —————

MW— f\ -—-—.———

Suwannee River ———

Inangahua River ———

Absorbance 

at 254 nm 

(pet)

36.6 

12.3 

23.5

•jo -7

25.2

30.8

DOC 

removal 

(pet)

26.4 

7.7 

7.7 

27.4

23.6

16.1

and As(V) species onto colloidal hematite. This behavior is 

registered in terms of the ability of NOM samples to liberate 

hematite-bound As(III) or As(V) into solution. The experiments involved NOM-rich waters (a suite similar to that listed 

in tables 1 and 2) diluted to 10 mg C/L and adjusted to a 

pH of 6.0, 1.0 \\M As, and 300-mg/L suspensions of colloidal hematite. NOM was shown to liberate 5 to 15 jug As/L 

from hematite onto which either As(III) or As(V) had been 

adsorbed, presumably due to competitive adsorption and (or) 

the formation of solution-phase As-NOM complexes. The 

same NOM samples, when adsorbed onto hematite, were able 

to prevent the complete adsorption of As(III) or As(V) onto 

hematite, leaving similar As contents in solution.

Contrary to other investigated properties, the ability of 

Fortymile River water to liberate hematite-bound As does not 

appear to be unique. In the absence of hematite, Fortymile 

River water shows virtually no ability to form solution-phase 

complexes with As(V)—different from all the other samples 

tested. However, Fortymile River water forms solution-phase

,_ to

w 40 ~

FRACTION OFNREMOVED, PEIN ISJ C-^ Ul Ol C5

1 

- cf

—

- - -g]- 254 nm 

---G-28enm

---Q-TOC--

: "- : f

V Hi: n::

ii

— 1 — 1_

a' ^ ^ ^ x^ ^ vJr «\^ A^ 

rv cJi xC"

^ 9^ \c^. ,e^

V <OV «T^

Figure 1. Fractionation of natural organic matter (NOM) by adsorption onto colloidal 

hematite in 0.01 M NaCI at a pH of 6.0. See table 1 for locations and descriptions of sites. 

TOC, total organic carbon.
52 Selected Geochemical and Biogeochemical Studies of the Fortymile River Watershed, Alaska

complexes with As(III) to an extent comparable to that of several other NOM samples, and so it may most closely resemble 

Black River NOM in this regard. The mechanisms of these 

As/hematite/NOM interactions are unclear and require more 

detailed investigation.

Conclusions

The NOM constituents present in the two Alaskan rivers sampled in April 2002 are unique in their extremely low 

trace-element contents and their relatively low ability to form 

metallo-organic complexes. These waters have a very high 

alkalinity and sulfate content, with concomitantly high Ca 

and Mg contents, somewhat complicating interpretation of the 

observed metallic-ion-complexation behavior and possibly 

masking the role of NOM in these processes. Nevertheless, the 

composition of these waters and their NOM is ideal insofar 

as minimizing trace-metallic-ion mobilization is concerned. 

In several aspects, as summarized above, the NOM samples 

from these waters represent end members in the spectrum of 

observed NOM behaviors.

Oxidation/reduction behavior, which is one important aspect 

of NOM that has not been investigated to any extent for the 

Alaska water samples in this study, could have important contributions to the overall influence of NOM in these waters. This behavior is the subject of continuing investigation in our laboratory.

Acknowledgments

We are grateful for the laboratory assistance by students 

Fabio Parolin, Stephanie Fevig, Valeric Strassberg, and James 

Mosby. Larry and June Taylor were gracious and helpful hosts 

during the sampling operations. Thanks to Larry Gough, Bronwen Wang, and Richard Wanty for their valuable assistance 

with logistics and operations during the sampling trip, and to 

the USGS for providing the opportunity to conduct the sampling and for supporting the overall idea of this project.

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