U.S. Geological Survey Bulletin 2191

Chapter 4-Biogeochemical and Biochemical Pathway Investigations of Cadmium in Subarctic Ecosystems Using a Cadmium Accumulator Species (willow)

By L.P. Gough, R.F. Sanzolone, J.G. Crock, A.L. Foster, P.J. Lamothe, C.M. Ager, and C.A. Gent

BACKGROUND
This study focuses on a portion of the
Fortymile River and Goodpaster River
watersheds (fig. 1) in the Eagle and Big
Delta 1:250,000-scale quadrangles, respectively.
The study area comprising
these two watersheds lies within the Interior
Highlands Ecoregion of Alaska
(Gallant and others, 1995) and is a
patchwork of State, Federal, private, and
Alaska Native lands. The resource management
of the region is complex because
of the diverse land ownership and
the many land-use options. In 1980, the
Fortymile River and its major tributaries
were designated a Wild and Scenic Corridor
by the Alaska National Interest
Lands Conservation Act (ANILCA).
Jurisdiction of the land bordering the
river continues to resides with the U.S.
Bureau of Land Management. The
Alaska Department of Natural Resources
has jurisdiction over the management
of the recreation uses of the
rivers (rafting, canoeing, and fishing)
and mining. The U.S. Environmental
Protection Agency monitors mining discharges
into these watersheds as required
by the National Pollutant
Discharge Elimination System (NPDES)
of the Clean Water Act. Finally, both
sport and subsistence hunting are important
in the region and are managed by
Federal and State agencies.
Placer gold was first discovered in the
Fortymile Mining District in 1886 and
has been mined there ever since. Yeend
(1996) summarizes the mining history of
the gold placers of the Fortymile River
region and provides details of the Tertiary
and Quaternary deposits that support
those placers. Within the past 3 or 4 years there has been a dramatic increase in exploration and claim-staking activity in this region of Alaska (Swainbank and
others, 2000). This renewed interest is due mainly to the discovery of highly
Au-mineralized quartz bodies, several hundred meters below the surface, on the
Pogo property in the Goodpaster River watershed (fig. 1; Smith and others,
1999). It is this discovery, and the likelihood
of additional ones, that is a major driver for the regional environmental geochemical studies currently being conducted within the U.S. Geological Survey Mineral Resources Program.

ECOSYSTEM PROCESSES AND LANDSCAPE SETTING

A conceptual framework for this work
is taken from the state-factor model as
detailed by Van Cleve and others (1991;
see fig. 2). This approach assumes that
the processes by which energy, nutrients,
and trace elements flow through the ecosystems
of the region are controlled by
five "exogenous" conditions (statefactors):
regional climate, biota (microbes,
plants, and animals), topography,
soil parent material, and time. Ideally, in
order to study ecosystem perturbations
(either natural or human-caused), only
one of these state-factors should be varied
while the other four are kept as constant
as possible. Unfortunately, these
factors may or may not be independent
of each other and may be difficult to
isolate (for example, time); however, as
Van Cleve and others (1991) explain,
subarctic boreal forest ecosystems are
both extreme (cold, dry climate) and
simple (low number and diversity of
biotic species) compared to ecosystems
in more temperate regions. By directing
our work over geologic terrain that is
well defined in areal extent, structure,
and chemistry we hope to control the
parent-material factor while keeping the
other factors relatively constant. Understanding
the parent-material factor, in
turn, is important for understanding the
ecosystem processes affecting the regional
soils. Further, by understanding
the physical and chemical characteristics
of the soils we hope to better define the
trace-element reservoirs and their
geoavailability and bioavailability.

Terrain, Vegetation, and Hydrology
The Interior Highlands Ecoregion
(also known as the Yukon-Tanana Upland)
is characterized by vegetated,
rounded, low mountains with scattered,
sparsely vegetated to barren high peaks
(up to a maximum elevation of about
2,200 m). The vegetation of the region
is classified by Viereck and Little
(1972) as closed spruce-hardwood forest
containing tall to moderately tall
white and black spruce (Picea glauca
and P. mariana, respectively), paper
birch (Betula papyrifera), aspen
(Populus tremuloides), and balsam
poplar (Populus balsamifera). Fires are
common, due mainly to lightning strikes,
and most of the study area shows evidence
of past fire disturbance. The area
has a continental climate, and the
weather station at the village of Eagle
(70 km north of the study area) records
the following average annual weather
values for the period 1949-2000: precipitation,
302 mm (12 in.); minimum mean
annual temperature, -10.9oC (12.7oF);
maximum mean annual temperature, 2.1oC
(36oF); snowfall, 142 cm (55.3 in.).
The Fortymile and Goodpaster Rivers
drain mostly subarctic boreal forest, tundra,
and muskeg having discontinuous
permafrost. Even soils not underlain by
permafrost are commonly frozen to various
depths for much of the growing season.
Over the year, discharge by the
Fortymile River and its tributaries is
highly variable (Kostohrys and others,
1999) because of (1) a rapid spring
ice-break-up period (April-June), (2)
runoff from storm events (the frozen
nature of the terrain accentuates the runoff
potential), (3) summer dry periods,
and (4) freeze-up (October-November). Maximum flow on the mainstem of the
river in May can exceed 340 m3 s-1 (1 m3 s-1
= 35.31 ft3s-1), and base flow during
January, February, and March is <1 m3 s-1.
There is usually some flow on the
mainstem in midwinter from groundwater
sources. Breakup usually occurs
in late April. The rivers and streams of
this region are dark ("black-water")
because of dissolved organic matter.
The water is, however, low in conductivity
(~90-220 µS cm-1), has pH values
that are commonly above 7.3, and
has turbidity values that seldom exceed
2 ntu (Crock and others, 1999,
2000; Wanty and others, 2000).
Geology
Bedrock and associated surficial deposits
control the primary minerals and
chemical elements that are available for
weathering and that ultimately enter hydrologic
and biologic systems. Therefore,
understanding the geologic
framework of the area is important to
assessing the geoavailability and
bioavailability of metals in the area.
In a complementary project, new geologic
maps have been compiled of both
watersheds (Day and others, 2000; see
fig. 3). These build on the previous geologic
mapping of Foster (1976), Foster
and others (1994), and Dusel-Bacon and
others (1995). This new effort was conducted
to address two specific needs: (1)
the structural characterization of regional
lithologic units that underlie the
study area; and (2) the definition of any
possible mineralized and (or) altered
zones that might occur in the study area.
This detail of information is critical to
the assessment of both the subsurface
hydrologic flow patterns and the chemistry
of surface and subsurface water,
soils, and vegetation.
In general, the bedrock of the region
is composed of metamorphosed
supracrustal rocks intruded by various
types of granitoids and ultramafic rocks.
The supracrustal rocks are biotite schist,
biotite-amphibole schist, quartzite,
marble, sulfide-rich biotite schist, and
pelite. The protoliths for these supracrustal
rocks are, respectively, graywacke, mafic
volcanic and compositionally equivalent
intrusive rocks, quartz-rich sandstone,
limestone, sulfide-rich siliciclastic sediments,
and pelitic sediments. Late metamorphic
sulfide-bearing quartz veins cut
all of the supracrustal rocks. The supracrustal
rocks are interpreted to have
been originally deposited on a continental
margin and (or) distal to an island-arc
complex in a back-arc basin.
Intruding the metamorphic supracrustal
rocks are three main granitoid
suites. The Steele Creek Dome
Tonalite (Day and others, 2000) is a
composite body of foliated biotite-hornblende
tonalitic orthogneiss containing
country-rock rafts of paragneiss. Two
mica+garnet-bearing leucogranite bodies
locally invade the supracrustal rocks.
In addition to the geologic studies
already published on the Fortymile River
watershed (Day and others, 2000;
Gamble and others, 2001), we are completing
a detailed geologic map of a portion
of the Goodpaster watershed that
surrounds the Pogo property. These efforts
are being conducted in cooperation
with the Alaska State Department of
Natural Resources, Teck Cominco, Ltd.,
and WGM Exploration, Inc.

Soils

An understanding of soil genesis
and composition is critical to the interpretation
of the geochemical data. We
are particularly interested in understanding
the mobility of metals and
their uptake by plants within a welldefined
geologic/pedologic context.
Soils at the study sites are classified as
Cryaquepts (Inceptisols) having variable
amounts of undecomposed (fresh) anddecomposed organic matter in the A
horizon. Van Cleve and others (1983)
estimate that about 78 percent of the
land area of Alaska is occupied by
Inceptisols. More than 70 percent of
sites examined in this study thus far
have been near saturation, and permafrost
was commonly encountered 15 to
50 cm below the surface. Most sites
have silty-loam to fine-sandy-loam A
soil horizons with abundant root penetration.
The A horizon is usually less
than 10 cm thick and light brown in
color. Several of the sites have ash/
charcoal layers (usually less than 2 cm
thick) within the A horizon, indicating
past fire disturbance. The B horizon is
usually about as thick as the A horizon,
lighter in color, and contains
moderate root volume. The deepest
soils (C soil horizons) commonly extend
to depths greater than 20 to 40 cm
and consist of fine- to coarse-sandtextured
material with small blocks of
angular bedrock and few roots. Because
of the low temperatures, these
soils experience limited chemical and
biological weathering; therefore, the
clay content and cation exchange capacity
are low. Nevertheless, slow organic
matter decomposition and
nitrification does produce slightly acid
soil conditions in the mature forest
ecosystem (Gough and others, 2001).
The presence of silt (micaceous glacial
loess) in the upper horizons is ubiquitous,
and we are finding that it has an
important influence on overall soil
chemistry. Foster and others (1979) state
that in the Big Delta 1:63360 quadrangle,
silt and sand from the Tanana
River flood plain to the south dominate
the composition and texture of soils
within about 50 km of the river. Siltloam-
textured soils are common in interior
Alaska and are derived from loess
laid down during the Holocene (Daniel
Muhs, oral commun., 2000) and during
the last glacial maximum (Van Cleve
and others, 1983).
CADMIUM PATHWAYS, BIOAVAILABILITY, AND RESEARCH ISSUES
Although both reconnaissance and
detailed studies on the distribution of
Cd in stream sediments and lithologic
units have been conducted throughout
Alaska , there have been no studies on
the bioavailability of Cd and its biological
transport mechanisms. This
section describes the U.S. Geological
Survey Mineral Resources Program's
present and planned research that attempts
to fill this gap.
Distribution, Concentration, And Speciation Of Cadmium
Biogeochemical investigations will
be conducted on the pathways that
control Cd transport and uptake by
vegetation. The occurrence of Cd in
eolian-dominated subarctic soils developed
over major rock units will be examined,
as well as its relative
bioaccumulation in willow. The
bioaccumulation of Cd by willow (Salix
spp.) has been recognized for some time
(Gough and others, 1991); however, it
was Shacklette (1972) that presented
some of the earliest data for Cd in willow
and compared these data with other
deciduous tree species. The connection
of high levels of Cd in willow to adverse
animal health, under natural (geogenic)
conditions, has only recently been demonstrated
(Larison and others, 2000).
We now have Cd data (fig. 4) for three
soil horizons and for the leaf and twig
material of Salix glauca L. (grayleaf
willow) collected at sites within defined
rock units of both watersheds. Gough
and others (2001) present regional
geochemical baselines for Cd and As in
plants and soils. These values present a
"snapshot" for the material sampled during
this Fortymile River watershed study.
In general, the soil Cd concentrations areslightly higher (two to three times) in
our study area when compared to values
from material collected elsewhere in
Alaska (Gough and others, 1988),
whereas Cd concentrations in plant material
are similar (Gough and others,
1991). All geochemical data for the
Fortymile River watershed available to
date are published in Crock and others
(1999, 2000) and include data from rock,
bottom sediment, water, soil, and vegetation
samples.
New studies that will be initiated in
2002 have three major objectives: (1)
define the cycling of Cd and its bioaccumulation
in willow and compare
concentrations in willow to those in different
rock types and soil horizons in
mineralized and non-mineralized areas;
(2) define the transient (and permanent)
reservoirs for Cd (using soils and vegetation)
and the probable transfer processes
between these reservoirs; and (3)
with the assistance of an Alaska state
veterinary toxicologist assess the relative
importance of Cd concentrations in willow
to the health of browsing animals
(moose and ptarmigan). The importance
of willow to moose is demonstrated by
feeding studies that have developed the
following order of browse preference:
willow >> aspen > birch > alder > cottonwood
(K. Hundertmark, Alaska Department
of Fish and Game, oral
commun., 2001).
Processes That Mobilize And
Redistribute Cadmium
Cadmium in soils within the study
area is derived from the weathering of
loess and of the primary
metasedimentary and metavolcanic
bedrock. In these soils, Cd is commonly
adsorbed by various clay minerals
and by calcium and magnesium
carbonates. Cadmium does not form
highly stable complexes with organic
matter. In addition, in these cold boreal
forest soils, where microbial decomposition
rates are low, the Cd that
is tied up in organic matter probably
remains immobile for some time. Cadmium
can form many compounds of
low solubility by precipitation as carbonates,
hydroxides, and phosphates.
This process is less important, however,
in the moderately low pH, generally
low-carbonate soils of the study
area. Cadmium is readily leached from
soils at pH values below about 5.0,
especially if the soils have a sandy
texture. Soils so far examined in the
Fortymile watershed range in pH from
4.8 to 6.2. The oxic, slightly acidic
soils of the region may permit a large
amount of Cd to be absorbed and
translocated by plants. Zinc has close
geochemical similarities with Cd and
competes for exchange sites in soil.
However, these soils are not particularly
high in Zn, and therefore Zn
probably has a minimal adverse influence
on Cd bioavailability.
Cadmium Impacts On Biota And Processes That Influence Its Bioavailability
In general, Cd is considered a heavy
metal of major environmental concern
because of its high mobility and the
small concentration at which it can adversely
affect plant (Das and others,
1997; Hale and others, 2001) and animal
(Larison and others, 2000) metabolism.
In addition, there is growing concern
over the increase in environmental Cd
(mainly from industrial emissions) and
its adverse impact on soil biological activity
(Kabata-Pendias, 2001). Cadmium
is a nonessential heavy metal and a powerful
enzyme inhibitor. In a recent study
of white-tailed ptarmigan in Colorado,
Larison and others (2000) found that a
diet of willow buds, with mean Cd concentrations
as low as 2.1 ppm (dry
weight basis), resulted in renal tubulardamage and increased chick mortality.
In addition, these authors hypothesized
that Cd poisoning may be more widespread
than previously suspected
among other willow-feeding herbivores
(for example, hare, beaver, and
moose) in areas with high Cd in
browse species.
A major unknown in this project is
whether the levels of Cd in the accumulator
willow species in our study
area have a measurable impact on the
health of browsing animals. We are,
however, recording Cd concentrations
comparable to those in Colorado that
have been shown to be detrimental to
animal health. This fact has aroused
the interest of both game managers
and public health workers in Alaska. In
a recent study by the Alaska State Department
of Health and Social Services,
soil, sediment, fish, and berries
from the Red Dog Mine area in northwest
Alaska were examined for unusually
high heavy metal levels (State of
Alaska, 2001). This study did not find
metal levels in these foods to be excessive.
In addition, the State wishes to
know the level of Cd in moose muscle,
liver, and kidney tissue, because these
are consumed by subsistence hunters
in rural Alaska (tissue samples may be
available for analysis from the State's
archive and through cooperation with
native hunters). Very high levels of Cd
in moose liver and kidney tissue have
recently been reported as a concern for
human consumption in Vermont (K.
Hundertmark, Alaska Department of
Fish and Game, oral commun., 2001).
In addition to the U.S. Bureau of
Land Management (with which the
U.S. Geological Survey has a Memorandum
of Understanding in place),
initial activities of the project will concentrate
on arranging formal working
agreements with the Alaska Department
of Fish and Game (ADF&G),
Alaska Native groups, and industry.
ADF&G has a major project examining
the accumulation of trace elements
in important subsistence fish species.
In preliminary discussions, ADF&G
has expressed an interest in our involvement
in a companion study that would
focus on the cycling of trace elements in
regional terrestrial ecosystems.
Initial discussions with the U.S.
Geological Survey's Biological Resources
Discipline revealed that they
currently have no personnel in the
northwest with a specific interest in
the general field of trace-element toxicity
and epidemiology.

Major Knowledge Gaps And Needed New Research Directions
From a review of the literature, the
actual biochemical form (speciation) of
Cd in willow tissue has not been defined.
We plan to use X-ray absorption
spectroscopy (XAS, Stanford University
Synchrotron) and gas chromatography
mass spectrometry to define the mode of
occurrence of Cd within willow tissue
(possibly phytochelatins and related peptides
as well as metalothionines). In addition,
we need a better understanding of
the form of Cd in the soil. Investigations
using X-ray diffraction will help define
the mineralogy of both the loess and
bedrock parent materials of the soils
(primary and secondary mineral reservoirs).
Sequential extractants will be
used to define loosely vs. strongly
adsorbed Cd in soil. Specifically, we will
define the Cd reservoir that is readily
dissolved with distilled water, Cd
adsorbed onto organic matter, Cd
coprecipitated with metal oxides, and Cd
coprecipitated with crystalline iron
(oxyhydroxides). We have yet to define
the exact soil extractants to be used.
The Alaska Department of Fish and
Game has expressed an interest in examining
the possible impact of elevated Cd,
Pb, and Zn levels in willow shrubs on the health of willow ptarmigan in northwest
Alaska (P. Weber-Scannell, oral
commun., 2001). We are currently developing
a cooperative effort with several
State agencies to examine the health of
these birds in areas of high soil Cd, such
as near the sedimentary exhalative Zn-
Pb-Ag mineralized terrain surrounding
the Red Dog deposit (fig. 1).
REFERENCES
Crock, J.G., Gough, L.P., Wanty, R.B.,
Day, W.C., Wang, B., Gamble, B.M.,
Henning, M., Brown, Z.A., and Meier,
A.L., 1999, Regional geochemical results
from the analyses of rock, water,
soil, stream sediment, and vegetation
samples-Fortymile River Watershed,
east-central, Alaska: U.S. Geological
Survey Open-File Report 99-33, 82 p.
Crock, J.G., Gough, L.P., Wanty, R.B.,
Day, W.C., Wang, B., Gamble, B.M.,
Henning, M., Brown, Z.A., and Meier,
A.L., 2000, Regional geochemical results
from the analyses of rock, water,
soil, stream sediment, and vegetation
samples-Fortymile River Watershed,
east-central, Alaska, 1998 sampling:
U.S. Geological Survey Open-File Report
00-511, 157 p.
Das, P., Samantaray, S., and Rout, G.R.,
1997, Studies on cadmium toxicity in
plants-a review: Environmental Pollution,
v. 98, p. 29-36.
Day, W.C., Gamble, B.M., Henning, M.W.,
and Smith, B.D., 2000, Geologic setting
of the Fortymile River Area-
polyphase deformational history
within part of the eastern Yukon-
Tanana Uplands of Alaska, in Kelley,
K.D., and Gough, L.P., eds., Geologic
Studies in Alaska by the U.S. Geological
Survey, 1998: U.S. Geological Survey
Professional Paper 1615, p. 65-82.
Dusel-Bacon, C., Hansen, V.L., and Scala,
J.A., 1995, High-pressure amphibolite
facies dynamic metamorphism and the
Mesozoic tectonic evolution of an ancient
continental margin, east central
Alaska: Journal of Metamorphic Geology,
v. 13, p. 9-24.
Foster, H.L., 1976, Geologic map of the
Eagle quadrangle, Alaska: U.S. Geological
Survey Miscellaneous Investigations
Series Map I-922, scale
1:250,000.
Foster, H.L., Albert, N.R.D., Griscom, A.,
Hessin, T.D., Menzie, W.D., Turner,
D.L., and Wilson, F.H., 1979, The
Alaskan Mineral Resource Assessment
Program, background information to
accompany folio of geologic and mineral
resource maps of the Big Delta
Quadrangle, Alaska: U.S. Geological
Survey Circular 783, 19 p.
Foster, H.L., Keith, T.E.C., and Menzie,
W.D., 1994, Geology of the Yukon-
Tanana area of east-central Alaska, in
Plafker, G., and Berg, H.C., eds., 1994,
The Geology of Alaska: Boulder,
Colorado, The Geological Society of
America, p. 205-240.
Gallant, A.L., Binnian, E.F., Omernik,
J.M., and Shasby, M.B., 1995,
Ecoregions of Alaska: U.S. Geological
Survey Professional Paper 1567, 73 p.
Gamble, B.M., Day, W.C., and Henning,
M.W., 2001, Geochemistry of lithologic
units, Fortymile River watershed
study area, east-central Alaska, in
Gough, L.P., and Wilson, F.H., eds.,
Geologic Studies in Alaska by the U.S.
Geological Survey, 1999: U.S. Geological
Survey Professional Paper
1633, p. 127-134.
Gough, L.P., Severson, R.C., and
Shacklette, H.T., 1988, Element concentrations
in soils and other surficial
materials of Alaska: U.S. Geological
Survey Professional Paper 1458, 53 p.
Gough, L.P., Severson, R.C., Harms,
T.F., Papp, C.S.E., and Shacklette,
H.T., 1991, Biogeochemistry of selected
plant materials, Alaska: U.S.
Geological Survey Open-File Report
91-292, 30 p.
Gough, L.P., Crock, J.G., Day, W.C., and
Vohden, J., 2001, Biogeochemistry of
arsenic and cadmium, Fortymile River
watershed, east-central Alaska, in,
Gough, L.P. and Wilson, F.H., Geologic
Studies in Alaska by the U.S.
Geological Survey, 1999: U.S. Geological
Survey Professional Paper
1633, p. 109-126.
Hale, B., Berkelaar, E., Dhan, D., Black,
W., and Johnson, D., 2001, Plants as
modifiers of cadmium bioavailability:
Geoscience Canada, v. 28, p. 55-58.
Kabata-Pendias, A., 2001, Trace elements
in soils and plants: Boca Raton,
Florida, CRC Press, 3rd Edition, 413 p.
Kostohrys, J., Sterin, B.B.G., and
Hammond, T., 1999, Water resources
of the Fortymile National Wild and
Scenic River, Alaska: Bureau of Land
Management, BLM-Alaska Open File
Report 75, 64 p.
Larison, J.R., Likens, G.E., Fitzpatrick,
J.W., and Crock, J.G., 2000, Cadmium
toxicity among wildlife in the Colorado
Rocky Mountains: Nature, v. 406,
p. 181-183.
Shacklette, H.T., 1972, Cadmium in
plants: U.S. Geological Survey Bulletin
1314-G, 28 p.
Smith, M., Thompson, J.F.H., Bressler, J.,
Layer, P., Mortensen, J.K., Abe, I., and
Takaoka, H., 1999, Geology of the
Liese Zone, Pogo property, east-central
Alaska: Society of Economic Geologists
Newletter, no. 38, p. 11-21.
State of Alaska, Department of Health and
Social Services, 2001, Public health
evaluation of exposure of Kivalina and
Noatak residents to heavy metals from
Red Dog Mine: Juneau, Alaska, Department
of Health and Human Services,
24 p.
Swainbank, R.C., Szumigala, D.J.,
Henning, M.W., and Pillifant, F.M.,
2000, Alaska's Mineral Industry-
1999: Alaska Department of Natural
Resources, Division of Geological And
Geophysical Surveys Special Report
54, 73 p.
Van Cleve, K., Dyrness, C.T., Viereck,
L.A., Fox, J., Chapin, F.S., III, and
Oechel, W., 1983, Taiga ecosystems in
interior Alaska: BioScience, v. 33, p.
39-44.
Van Cleve, K., Chapin, F.S., Dyrness, C.T.,
and Viereck, L.A., 1991, Element cycling
in taiga forests-state-factor control:
BioScience, v. 41, p. 78-88.
Viereck, L.A., and Little, E.L., 1972,
Alaska trees and shrubs: U.S. Department
of Agriculture, Forest Service,
Agricultural Handbook 410, 265 p.
Wanty, R.B., Wang, B., Vohden, J., Briggs,
P.H., and Meier, A.L., 2000, Regional
baseline geochemistry and environmental
effects of gold-placer mining
operations on the Fortymile River,
eastern Alaska, in Kelley, K.D., and
Gough, L.P., eds., Geologic Studies in
Alaska by the U.S. Geological Survey,
1998: U.S. Geological Survey Professional
Paper 1615, p. 101-110.
Yeend, W., 1996, Gold placers of the historical
Fortymile River region, Alaska:
U.S. Geological Survey Bulletin 2125,
75 p.