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**Bedrock, soil, and lichen geochemistry from Isle Royale National Park,
Michigan**

***By* Laurel G. Woodruff^1^, William F. Cannon^2^, Connie L.
Dicken****^2^, James P. Bennett^3^, and Suzanne W. Nicholson^2^**

**Open-File Report 03-276**

**2003**

This report is preliminary and has not been reviewed for conformity with
U.S. Geological Survey editorial standards. Any use of trade, firm, or
product names is for descriptive purposes only and does not imply
endorsement by the U.S. Government.

**\
**

**U.S. DEPARTMENT OF THE INTERIOR**

**U.S. GEOLOGICAL SURVEY**

^1^ U.S. Geological Survey, 2280 Woodale Drive, Mounds View, MN 55112

^2^ U.S. Geological Survey, MS 954, Reston, VA 20192

^3^ U.S. Geological Survey, 6006 Schroeder Road, Madison, WI 53711

**Introduction**

Isle Royale National Park, Michigan, is a large island in northeastern
Lake Superior that became a national park in 1940 and was designated as
a wilderness area in 1976. The relative isolation of Isle Royale (Figure
1), 25 kilometers out in Lake Superior from the Canadian mainland, its
generally harsh climate, and its status as a wilderness national park
have minimized human influence on the geochemical evolution of its
landscape.

USGS sampling on Isle Royale began in 1996 as part of a larger project
on the geology of the Midcontinent rift in the Lake Superior region and
continued through 2000. Sampling began with collecting bedrock samples
to characterize the geochemistry of the volcanic rocks that make up the
much of the island, as well as samples representative of the minor
native copper mineralization found on the island. Preliminary results
from the bedrock study indicated, among other findings, that basaltic
bedrock on the island had no detectable mercury, but that there was an
association between native copper mineralization and trace amounts of
mercury (Cannon and Woodruff, 1999). This finding and the recognition by
the National Park Service that 6 of 32 inland lakes on Isle Royale have
mercury levels in game fish that exceed State of Michigan acceptable
levels for human consumption (Kallemeyn, 2000) resulted in renewed
sampling on the island focused more on environmental issues.

To evaluate atmospheric inputs of mercury and other elements to soil
geochemistry, regionally distributed samples of both soils and lichens
were collected as paired samples across the entire island. At each soil
sample site, three epiphytic (grows in trees) lichen species, *Evernia
mesomorpha, Hypogymnia plysodes,* and *Parmelia sucata*, were always
collected. At some sites *Cladina rangiferina*, a lichen that grows on
bare bedrock and soil surfaces, was also collected. The occurrence of
*Cladina rangiferina* on the island is somewhat limited, and so this
lichen species was not collected at all sites.

A high density of soil samples was collected within three individual
watersheds (Sargent Lake, Lake Wagejo, and Lake Richie) for a localized
study that evaluated the terrestrial distribution of mercury and other
elements of environmental concern. These lakes were chosen using data
from Kallemeyn (2000) that showed that Sargent Lake and Lake Wagejo have
high mercury in fish, whereas Lake Richie, which is similar in size to
Sargent Lake, does not. As part of this study on the terrestrial
contribution of mercury to lakes, long cores of lake sediments were
recovered from Sargent Lake and Lake Richie using a modified Livingston
piston sampler.

For an ancillary study that evolved from the study on the distribution
of mercury in certain watersheds, some soil samples were collected to
evaluate the impact of forest fire on soil geochemistry, deliberately
sampling within and outside areas on the island that burned in severe
forest fires in 1936. To complete bedrock sampling on the island, rock
samples from the Copper Harbor Formation, a sedimentary unit that occurs
on the southeastern part of the island were collected in 1999.

This report presents all the geochemical data from samples collected by
the USGS during this period (Figures 1 and 2). A number of reports
presenting data interpretation are in preparation.

**Bedrock Geology**

The geologic evolution of Isle Royale began about 1,100 million years
ago when huge volumes of flood basalts of the Midcontinent rift erupted
near the center of what is now Lake Superior and spread laterally across
the Lake Superior region. The bedrock of Isle Royale is a series of
stacked tholeiitic basalt flows with minor andesite and rhyolite that
correlate with volcanic rocks in Michigan and Wisconsin designated as
the Portage Lake Volcanics (Huber, 1973a; 1973c). Time breaks between
flows are sometimes marked by accumulation of interflow sedimentary
units, either sandstones or conglomerates, but commonly flows erupted
one onto another. Because basalt erupted subaerially, flow tops
typically were highly vesicular or rubbley with abundant open space.
With the end of volcanism, fluids generated within the volcanic pile by
low temperature burial metamorphism filled vesicles, open spaces, and
fractures with secondary minerals, typically low-temperature zeolites,
prehnite, calcite, or datolite, as well as native copper (Huber, 1973a).

Minor native copper mineralization, similar in style and timing to the
more impressive mineralization found in contemporaneous rocks on the
Keweenaw Peninsula of Michigan, developed locally in some permeable
layers and fractures. A number of the copper deposits were mined during
the later 1800's, but production on Isle Royale was never extensive and
mining activity died out in the 1890s (Rakestraw, 1965). The two largest
areas of mining activity are the Island Mine, where copper was extracted
from a conglomerate layer, and the Minong Mine where copper is found in
fractures and openings in a rhyolite unit overlying the Minong basalt
flow and within the brecciated basalt flow top. Copper mining at the
Minong Mine included establishment of a small stamp mill where
mineralized rock was pulverized prior to removal of native copper. Waste
material from the stamp mill was dumped as stamp sands into the drainage
between Chickenbone Lake and McCargoe Cove.

Sandstones and conglomerates of the Copper Harbor Formation make up the
highlands of the southeast section of Isle Royale (Wolff and Huber,
1973). These rocks conformably overlie the volcanic section and
represent sediment influx into a subsiding basin that formed following
the end of major volcanism. A regional compressional event, estimated to
have occurred sometime from 1,080 to 1,040 million years ago (Cannon,
1994), reversed movement along the Isle Royale fault, a major
rift-bounding fault just north of the island. This reversed motion along
the Isle Royale fault, as well as many of the other major rift-bounding
faults in the Lake Superior region, uplifted the volcanic section of
Isle Royale and tilted the strata to the southeast so that the flows and
sediments on the island now dip to the southeast into Lake Superior at
angles between 5 and 30 degrees. No rocks younger than the Copper Harbor
Formation are found on Isle Royale, nor is there evidence of geologic
activity on the island following uplift and tilting until Pleistocene
glaciers moved through the region.

**GLACIAL Geology**

Early glacial history on Isle Royale was erased by the final advance and
retreat of ice out of the Lake Superior area during a glacial surge
known as the Marquette readvance, which culminated at about 10,025 yr
B.P (Clayton, 1983; Lewis and Anderson, 1989). When this final ice sheet
began to waste out of the Superior basin, an apparent still-stand of the
ice margin on Isle Royale resulted in development of several recessional
moraines and deposition of a thick till across the southern third of the
island (Huber, 1973b). Rapid ice retreat following the stand-still and
continued submergence under early glacial lakes has left only a thin
veneer of glacio-fluvial deposits on the northern two-thirds of the
island (Huber, 1973b). Glacial striations in bedrock show that ice
directions in the northern part of the island were northeast-southwest,
along the strike of the basalt flows. Across the southern part of the
island striations and other indicators of ice movement (e.g., drumlins)
trend more east-west, oblique to the strike of the flows (Huber, 1973b).

The land surface of Isle Royale emerged sporadically from changing
glacial lakes as differing outlets and spillways for the Lake Superior
basin released and held back meltwater. With emergence of the island
from ice and water, shoreline beaches, now high above current lake
levels, were deposited and inland lakes became successively isolated
from larger post-glacial lakes. Lake Minong (9500 B.P.) occupied the
Lake Superior region as soon as ice moved out. Digital reconstructions
show that much of the northern and eastern coastline of Isle Royale
remained submerged during Minong time (McRae and others, 1998). This
stage also marks a time of major drainage of glacial Lake Agassiz into
the Lake Superior basin through outlets in the Nipigon basin and Thunder
Bay areas (Clayton, 1983; Teller and Thorleifson, 1983), bringing large
quantities of gray clay into the lake in the area of Isle Royale.
Following the Minong stage, lake levels fell during the succeeding
Houghton low stand, during which all of Isle Royale and surrounding land
would have been above water. Water levels again rose during the
Nipissing transgression (5,500-4,700 yr B.P.), inundating much of the
Isle Royale coastline and forming large beach ridges below the Minong
shoreline, but well above the present shoreline. The present day level
of Lake Superior stabilized around 2,200 yr B.P.

**regional landscape**

Ice plucking and scraping from multiple glacial advances exploited the
differential erodibility of vesicular basalt flow top versus massive
flow interior and sandstone versus conglomerate, removing most erodible
rock. The resulting geomorphic pattern is a series of long, eroded
valleys and resistant bedrock ridges that run the length of the island
and control the topography. Bedrock is exposed or very near the surface
in the northern part of the island where glacial deposits are thin, but
may be covered by thick till in the southern area of the island, which
creates a more subdued land surface. Bedrock ridges typically are bare
or have minimal vegetation cover, whereas valleys between ridges are
filled with lakes, streams and wetlands. In the northern part of the
island, soils on uplands developed directly on bedrock or on thin
glacial cover. These soils are typically thin, sandy or loamy, and
boulders are common. In the southern part of the island, upland soils
formed on thicker till or other glacial deposits and are better
developed than in areas of thin glacial cover.

The forest on Isle Royale is at the southern boreal/northern hardwoods
border. Forest species on Isle Royale have been influenced by drainage
characteristics, topography, moose browsing, and fire history (Cole and
others, 1997). Today much of the island, including the northern part and
coastlines, is characterized by boreal trees such as white and black
spruce, white cedar, aspen, balsam fir, and white pine. The thick
glacial cover in the southern part of the island supports a northern
hardwood forest, with species such as red maple, sugar maple, red oak,
and yellow birch. In low wet areas black spruce is the dominant species.

The current forest species over much of the southern and central parts
of the island have been strongly influenced by major forest fires in
1936. By the summer of 1936, three drought years had created extreme
fire hazards across much of the Upper Midwest. In midsummer of that
year, fires broke out in the southern end of Isle Royale and spread
north. The fires burned out of control for weeks, eventually covering
more than 105 km^2^. In many places, the fires burned so hot that entire
stands of trees were killed leaving bare rock exposed. Much of the
pre-fire deciduous forest in the burn area was replaced by stands of
white birch and aspen (Hansen and others, 1973, Cole and others, 1997).

**Lichens**

Lichens are ideal for studying atmospheric inputs because they lack
roots (hence have no sources of elements from the soil), lack a cuticle
(hence they absorb elements from the atmosphere), and some species are
able to sequester toxic elements and render them non-toxic. There are
many species of lichens at Isle Royale (Wetmore, 1985), and several have
been used previously for atmospheric deposition studies. *Hypogymnia
physodes* and *Evernia mesomorpha* were collected at eighteen localities
in the Isle Royale National Park between 1983 and 1992 (Bennett, 1995).
In his report, Bennett found temporal and geographical patterns of
element concentration in lichens on the island. Common air pollutants,
such as Zn, Pb, Se and S, were higher in lichen tissue compared to their
concentration in the Earth's crust. Heavy metal elements associated with
atmospheric deposition increased over the nine-year study period to a
greater extent than non-metallic elements. Geographic distributions of
anthropogenic elements were elevated around known local pollution
sources and some elements did reach toxic levels in lichens (Bennett,
1995).

**mETHODS OF STUDY**

**Sample Collection**

Geochemical sample media include bedrock, mineralized rock, lake
sediments, different soil horizons and four species of lichens (Figures
1 and 2). Because of restrictions on sampling within a wilderness park,
rock samples were collected from mine dumps or loose blocks obviously
fallen from outcrop. All rock samples were trimmed in the field to
remove weathered material, and further trimmed and hand selected during
preparation to minimize contribution from weathered or altered surfaces.
Samples of native copper mineralized rock typically were composite chip
samples collected from mine dumps. Descriptions recorded in the field
are included in the data files.

Reconnaissance soil sample sites typically were from upland areas.
Within the Sargent Lake and Lake Richie watersheds both upland and
lowlands (but not wetland) sites were sampled. Soil samples were
collected from soil pits dug with a shovel and extended with a hand
auger. Sample pits were completed to the C-horizon or to a depth
dictated by the presence of impenetrable rock. From each pit, soil from
different horizons was collected so that each sample site has multiple
geochemical analyses, each representing a different soil layer. All
samples were stored in perforated polyethylene bags (Hubco Tyvek^®^).
During the first year of soil sampling, which concentrated within the
Sargent Lake and Lake Wagejo watersheds, material from the O-horizon was
not collected.

The O-horizon is the organic matter that lies on top of a mineral soil.
The organic layer is divided into Oi (forest litter), Oe (forest duff)
and Oa (humus) horizons. Forest litter is not decomposed, and contains
identifiable dead plant material. Forest duff is partially decomposed
organic material that may underlie the litter layer. Humus is completely
decomposed, non-identifiable organic material. At each soil sample site,
with the exceptions noted above, Oe-horizon material was collected, if
available. Field descriptions discriminate between forest litter that is
not decomposed and more decomposed forest duff, but do not attempt to
distinguish duff from humus. Samples from Oe-horizons typically were
grab samples collected from the soil plug removed from the sample pit.
Litter material, when collected, was composited from material in the
area of the sample site. The nature of the original material (e.g.,
needles versus leaves) was noted, as were the dominant tree species.

The upper mineral soils typically were classified as A-horizon,
indicating some accumulation of organic carbon, and were distinguished
from underlying soil horizons by changes in color. A-horizon soils were
collected from most sample sites, with material composited from the
entire thickness of the horizon. At some sites, a very thin A-horizon
overlay an E-horizon, a zone of eluviation, easily distinguished by its
light, buff or gray color. A limited number of E-horizon samples were
also collected when little or no A-horizon soil was present.

Subsoil samples typically were composed of weathered parent material,
which, on Isle Royale, is either bedrock or glacial deposits on bedrock.
The depth of collection for C-horizon soil samples in areas of thin
glacial cover typically was constrained by the depth to bedrock, with
samples collected immediately above the bedrock surface. In areas of
thick glacial cover, collection depths usually were 60 -- 80 cm, which
typically was the depth to parent glacial material. In a few cases,
multiple samples were collected when obvious changes in color or texture
were noted.

Lichen samples were collected by hand from trees in the immediate
vicinity of soil sample sites and from bedrock, if available. The three
epiphytic lichen species collected, *Evernia mesomorpha, Hypogymnia
plysodes,* and *Parmelia sucata*, are easy to identify in the field and
do not require chemical tests for identification. Each lichen species
was picked separately and cleaned as well as possible in the field.
Epiphytic lichens were collected without gloves only from evergreen
species, with one exception in a hardwood maple forest where no
evergreen trees were present. At a site, all three species were
collected from multiple individuals of a single tree species (e.g.,
white spruce or balsam fir), but the single tree species varied from
site to site, depending on availability. The result of this sampling
method is collection of multiple thalli representing an aggregate sample
from several trees in an area. Picking extended from near ground level
to as high as could be reached when standing on the ground,
approximately 1.5 -- 2 meters. Lichens picked from dead or downed trees
may have originally been higher in the air prior to tree mortality and
are so noted. *Cladina rangiferina* was collected from bedrock surfaces
by hand. Only fresh, apparently healthy lichen were picked in the field.
At each site, about 20 grams of lichen was stored in perforated
polyethylene bags (Hubco Tyvek^®^). Samples were air dried to ambient
moisture levels prior to shipping to the USGS National Wildlife Health
Center in Madison, Wisconsin for analysis.

Lake sediment samples from Sargent Lake and Lake Richie were collected
using a modified Livingston piston sampler (Wright, 1967). To obtain the
cores, researchers from the USGS flew to Isle Royale in the winter of
1999 in a U.S. Forest Service Beaver seaplane, landing on the ice of
each lake. Lake sediment core was obtained through the ice from near the
deepest part of each lake, using lake bathymetry maps as guides. The
coordinates for the site on Sargent Lake are: latitude 48.0820;
longitude 88.6548. The coordinates for the site on Lake Richie are:
latitude 48.0420; longitude 88.6930. Care was taken to sample from areas
away from shore and where the lake bottom was relatively flat. At each
lake the coring procedures were similar. After augering a hole through
the ice, the depth of the water was measured with a Vexilar^®^ portable
sounder. Core was recovered through 11 meters of water in Sargent Lake
and 9.75 meters of water in Lake Richie. To obtain the first core from
an undisturbed bottom, the piston core apparatus was lowered to the
sediment/water interface (using 2 meter extension drive rods) and then
advanced the depth of the 1 meter core barrel. Prior to removing the
piston corer, a sleeve of 15 cm (diameter) PVC was assembled and lowered
through the hole in the ice around the drive rods and piston corer to
act as a casing and guide for successive cores. The casing was pushed
about 30 cm into the lake bottom to provide a firm anchor. With the
casing in place, the piston corer was removed, and the 1 meter core
extracted. Each core was immediately wrapped in plastic and aluminum
foil and stored in a core box. The piston corer was then reintroduced
into the original hole through the casing, and advanced another length
of the core barrel (1 meter). The procedure was repeated until 5 meters
of core were collected from Sargent Lake and 6 meters of core were
collected from Lake Richie. Visual inspection of the cores as they were
removed suggested little or no slumping in the borehole, although some
compaction in the core was apparent. The length of available drive rods
limited the length of core recovery at Sargent Lake, but at Lake Richie
coring ended when advancement of the core barrel through compacted
sediment was no longer possible. Both sets of long cores were split
lengthwise immediately following fieldwork, and one half was preserved
and the other half was further split for geochemical analysis.

**Sample Preparation**

All rock, mineral soil and lake sediment samples were shipped to the
USGS analytical laboratories in Denver, CO for sample preparation.
Methods for sample preparation for analysis are described here and in
more detail in Taggert (2002). Lichen and O-horizon samples were shipped
to the USGS National Wildlife Health Center in Madison, Wisconsin for
sample preparation and analysis.

***Rocks***

Rocks were crushed to 0.5 cm fragments in a jaw crusher and fed into a
ceramic plate pulverizer where fragments were reduced to approximately
minus 100-mesh. Each pulverized sample was split, with a portion
submitted for geochemical analysis and a portion archived. Clean quartz
rock and sand were crushed and pulverized between samples to minimize
cross-contamination.

## Soils

Soil samples were air-dried and disaggregated in a soil grinder, if
necessary. Samples were then sieved to \<63 micrometers prior to
analysis. Samples were not ground.

***Lake sediment samples***

The top meter of core from each lake was composited in 5 cm intervals.
Samples from the remaining cores from each lake were collected in 2 cm
intervals every 10 cm. Splits were placed in trace-element-free
cardboard cans and dried overnight in a 50^o^ C oven. Prior to analysis,
samples were completely pulverized in a shatter-box.

***Lichens and O-horizon samples***

Upon arrival in Madison, Wisconsin, lichens and O-horizon organic
material were extracted from the bags. Lichen samples were manually
cleaned of debris, bark, and other foreign matter. Handling of tissue
was with bare hands, which were washed between samples. Hand contact
with tissues was only a few seconds for each thallus. Two to four grams
of cleaned samples were placed in clear plastic bags and labeled for
chemical analyses. Both lichen and O-horizon samples were ground to a
powder in a stainless steel Wiley ED-5 mill using a 2 mm screen. After
grinding the samples were placed in plastic vials and either stored in a
desiccator or re-dried just prior to weighing for analysis.

**Analytical Techniques**

A large number of chemical elements were determined, using a variety of
quantitative analytical techniques. The USGS contract analytical
laboratory, XRAL Laboratories, Don Mills, Ontario, Canada, did all
mineral soil, lake sediment, and some rock analyses. Other rock analyses
were done in-house at the USGS analytical laboratories in Denver,
Colorado. Quality assurance/quality control (QA/QC) concerns were
addressed through the use of internal reference standards and analytical
duplicates for all samples processed by the USGS. Standard procedures
require that QA/QC samples comprise about 10 percent of the total number
of samples analyzed. Reference standards were interspersed with each
batch of samples submitted for analysis. Values for the reference
standards were checked to assure that reported values are within +/-20
percent of the accepted standard values. Analytical duplicates were
included with each batch of samples. Duplicate analyses were checked to
assure that the relative percent difference between duplicates was no
greater than 20% for individual elements.

Each of the techniques used by either XRAL or the USGS is described in
detail in Taggert (2002). USGS analysts who provided laboratory
assistance with organic samples are Paul Briggs, Zoe Brown, and Monique
Adams. Joe Taggert and Roy Knight assisted with analyses of rock
samples.

Lichen and O-horizon samples were analyzed at the Soil and Plant
Analysis Laboratory, University of Wisconsin, Madison, Wisconsin. Ling
Zhang provided analytical assistance.

**Summary of XRAL and USGS Techniques**

## Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES)

Forty major, minor, and trace elements were determined in rocks and
mineral soils by inductively coupled plasma-atomic emission
spectrometry. Each sample was digested using a mixture of hydrochloric,
nitric, perchloric, and hydrofluoric acids at low temperature. The
digested sample was aspirated into the ICP-AES. Analyzed elements and
lower detection limits are given in Table 1. In the mineral soil
analyses a number of elements are consistently below the detection
limits given in Table 1 and are not included in the data tables
accompanying this report. These elements are Ag, As, Au, Be, Cd, Eu, Ho,
Mo, Nd, Sn, Ta, Th, U, and Yb. Ga was excluded because the relative
percent difference between duplicates consistently was above 20%.

***Wave-Length Dispersive X-Ray Diffraction (WDXRF)***

Ten major elements were determined in rocks by wavelength dispersive
X-ray fluorescence spectrometry. The sample is first ignited, then fused
with lithium tetraborate and the resultant glass disc is introduced into
a wavelength dispersive X-ray spectrometer. The disc is irradiated with
X-rays from an X-ray tube. X-ray photons emitted by the elements in the
sample are counted and concentrations determined using previously
prepared calibration standards. In addition to 10 major elements, the
method provides a gravimetric loss-on-ignition. Detection limits are
given in Table 2.

***Instrumental Neutron Activation by Long Count (INAA**)*

Some trace elements in rocks were analyzed using instrumental neutron
activation analysis. INAA selectively measures radioactive nuclide
activity produced by nuclear reactions on naturally occurring isotopes.
The activity of the indicator radionuclide produced during irradiation
is directly proportional to the amount of the element in the sample. The
analytical determination is made by comparing the induced activity in
the sample with well-characterized standards activated under identical
conditions of neutron flux. The activities of the samples and standards
are measured using gamma-ray spectroscopy. Gamma-ray radiation emitted
by a radionuclide is converted to an electrical signal by a
semiconductor detector. A multichannel analyzer analyzes the electrical
signal. Semiconductor detectors, such as high-purity and lithium-drifted
germanium detectors, are used to exploit their high resolution. Spectra
produced are analyzed by software that locates and identifies peaks, and
calculates the area of each peak.

***Atomic Absorption Spectrophotometry (AAS)***

Samples were digested using a multi-acid procedure in an open Teflon
vessel. At the end of the digestion period, arsenic and selenium are
reduced to oxidation states, +3 and +4, respectively. Sodium borohydride
is added to the solution resulting in rapid formation of the hydrides.
The gaseous hydrides are stripped from the analytical stream and
transported with inert gas to the atomizer (a heated quartz furnace) of
the atomic absorption spectrophotometer. For selenium, the quartz
furnace is heated by an air-acetylene flame to 2000°C; and the arsenic
furnace is electrically heated to 900°C. Concentrations of the elements
are determined using calibration standards in solutions of similar
matrix. The lower detection limit for arsenic is 0.6 ppm. The lower
detection limit for selenium is 0.2 ppm.

***Automated Carbon Analyzer (ACA)***

Total carbon was determined using an automated carbon analyzer. A
weighed sample (approximately 0.20 g) is combusted in an oxygen
atmosphere at 1350°C to oxidize carbon (C) to carbon dioxide (CO~2~).
Moisture and dust are removed and a solid-state infrared detector
measures the carbon dioxide gas. The lower reporting limit is 0.05.

***Columetric Titration (CT)***

Samples were analyzed for carbonate carbon by coulometric titration. The
sample is treated with hot 2 *N* perchloric acid and the evolved CO~2~
is passed into a cell containing a solution of monoethanolamine. The
CO~2~, quantitatively absorbed by the monoethanolamine, is
coulometrically titrated using platinum and silver/potassium iodide
electrodes. The lower reporting limit is 0.01%.

***Automated Sulfur Analyzer (ASA)***

Total sulfur was determined using an automated sulfur analyzer.
Approximately 0.25 g sample is weighed and mixed with 1 g vanadium
pentoxide flux. The sample is combusted in an oxygen atmosphere at
1350°C where the sulfur oxidizes to sulfur dioxide. Moisture and dust
are removed and the sulfur dioxide gas is then measured by a solid-state
infrared detector. The lower reporting limit for sulfur is 0.05%.

***Continuous Flow-Cold Vapor Atomic Absorption Spectrometry (CV-AAS)***

For mercury analyses, samples were digested with nitric acid and sodium
dichromate in a disposable test tube. After digestion, samples are
diluted with water to 12 mL. Samples are then mixed with air and a
sodium chloride-hydroxylamine hydrochloride-sulfuric acid solution and
Hg (II) is reduced to Hg° with stannous chloride in a continuous flow
manifold. The mercury vapor is separated and measured using
continuous-flow cold vapor-atomic absorption spectrometry. The lower
detection limit for mercury is 0.02 ppm

**Summary of University of Wisconsin Analytical Techniques**

Lichen and O-horizon samples were analyzed at the Soil and Plant
Analysis Laboratory, University of Wisconsin, Madison, Wisconsin.
Analytical duplicate samples comprised about 10 percent of the total
number of samples submitted.

For analyses of As, Cd, Co, Cr, Ni, Pb, Se, Ti and V, samples were
digested in a heated nitric/perchloric acid mixture, diluted, and
measured by inductively coupled plasma-mass spectroscopy (ICP-MS). For
analyses of P, K, Ca, Mg, S, Zn, Mn, B, Cu, Fe, Na, and Al, samples were
also digested in a heated nitric/perchloric acid mixture, diluted, and
measured by inductively coupled plasma-optical emission spectroscopy
(ICP-OES). Details on these methods, including detection limits, are
described in: Department of Soil Science, University of
Wisconsin-Extension-Madison, 1987, Wisconsin Procedures for Soil
Testing, Plant Analysis and Feed & Forage Analysis, No. 6, Soil
Fertility Series, 64 p. For mercury analyses, similar methods were used,
but the nitric/perchloric acid used for digestion was heated to 130^o^C.
Ash content for all samples was measured using a standard method
described in: Standard Methods for the Examination of Water and
Wastewater 15th Edition, 1980, p. 97.

# Mercury Analyses in Lichens and O-horizon soils

The 142 lichen samples collected from Isle Royale in 1999 were analyzed
by the methods described above. When the data were received, the
analyst, Ling Zhang, commented that the mercury recovery for the 1999
samples was not complete because during hot-acid digestion mercury is
easily lost. To correct this problem, Zhang developed a new, more
efficient technique for mercury analysis that minimized loss. This new
technique was used to analyze the same lichen species collected on Isle
Royale in 2000. However, inspection of the mercury data from the two
years revealed that the mean of the 2000 samples was significantly
higher in mercury than the mean for the 1999 lichen samples, suggesting
that the 1999 mercury lichen data were suspect. There was not sufficient
quantity of sample after analyses to reanalyze the lichen collected in
1999 by the new, high-mercury recovery method.

The O-horizon samples were also analyzed for mercury at the University
of Wisconsin-Madison Soils and Plant Analysis Laboratory in both years
by the two different methods. In addition, splits of all O-horizon
samples were analyzed by the USGS by cold vapor AAS. Both the University
of Wisconsin and the USGS mercury data are given in the file of
O-horizon samples. The USGS mercury data for the O-horizon are
considered to be high-mercury recovery data and are the preferred values
in this data set.

A comparison of the mercury O-horizon data analyzed in 1999 and 2000
shows fair correlation between samples analyzed at the University of
Wisconsin and samples analyzed at the USGS for 2000 samples (r = 0.823),
but a very poor correlation for 1999 samples (r = 0.233) (Figure 3). It
was hoped that it would be possible to recalculate the 1999 low recovery
lichen mercury data using a calibration factor determined from the
O-horizon mercury analyses. However, the lack of a systematic correction
for the 1999 mercury results makes it impossible to reconcile the 1999
lichen mercury data using the O-horizon data from the two years (Figure
3). Therefore, no mercury data are reported for 1999 lichen samples.

![](media/image2.jpeg){width="3.952777777777778in"
height="2.9993055555555554in"}

Figure 3. Correlation between University of Wisconsin and USGS analyses
for Hg in O-horizon samples.

**dESCRIPTION OF DATA FILES**

The analytical data files are provided as nine separate Microsoft Excel
2000.xls files. The samples are organized into media type with
individual files for O-, A-, and C- horizon soils, bedrock samples,
mineralized rock, and lichens. These files are:

1)  **Volcanic_bedrock.xls** Analyses of basalt, andesite and rhyolite

2)  **Sedimentary_bedrock.xls** Analyses of sandstone and conglomerate
    matrix collected from the Copper Harbor Formation

> 3\) **Mineralized_rock.xls** Analyses of rocks, sediment, and stamp
> sands with minor native copper mineralization collected from
> mineralized veins and mine dumps
>
> 4\) **O_horizon.xls** Analyses of organic O-horizon organic material.
> All elements except mercury have been converted from a measured
> ash-weight basis to a dry-weight basis. Mercury values, measured on
> unashed samples, are not corrected for ash content.
>
> 5\) **A_horizon.xls** Analyses of A-horizon and E-horizon mineral
> soils.

6\) **C_horizon.xls** Analyses of C-horizon mineral soils.

### 7) Lichen.xls Analyses of four lichen species (where available).

> 8\) **Sargent_Lake_core.xls** Analyses of sediment lake core collected
> from Sargent Lake
>
> 9\) **Lake_Richie_core.xls** Analyses of sediment lake core collected
> from Lake Richie

### Common Data Fields

In all data tables the following abbreviations are used: n.a. = not
analyzed; n.c. = not collected; b.d. = below analytical detection limit;
n.r. = not reported; dup. = duplicate sample.

***Field_No./Sample Site***

Field numbers are given for all bedrock, mineralized rock, and lake
sediment samples. A and B designations for mineralized rock samples are
separate samples of composited chips collected from mine dumps and are
not duplicates. The field number for the lake sediments is an identifier
for the portion of the core that was sampled. Mineral soil, organic
material, and lichen samples are designated with the sample site number
(shown in Figures 1 and 2). Identical sites numbers among the files
indicates that the samples were collected from the same site.

***Coordinates***

Latitude and longitude for sample site locations are given in the data
tables as decimal degrees. The coordinates were determined by GPS during
sample collection. The datum was 1927 CONUS and the spheroid was Clarke
1866. The coordinates for the two lake cores are not included in the
data files, but are given in this text.

***Year Collected***

Gives the year that each sample was collected. Samples were collected in
May, 1998, September, 1999, and May, 2000. The lake cores were collected
in February, 1999.

***Geochemical Analyses***

All geochemical data are given in the following format. Field
identifiers consist of three lines. The first line gives the chemical
element symbol and unit of measurement. The second line is an
abbreviated code for the analytical technique used for the element in
that particular column. Reporting units are weight percent (wt. %),
parts per million (ppm), and parts per billion (ppb). The analytical
methods codes are:

**AAS** atomic absorption spectrophotometry

**ACA** automated carbon analyzer

**ASA** automated sulfur analyzer

**CT** columetric titration

**CV-AAS** cold-vapor atomic absorption spectrophotometry for mercury

**ICP-AES** inductively coupled plasma-atomic emission spectroscopy

**ICP-MS** inductively coupled plasma-mass spectroscopy

**ICP-OES** inductively coupled plasma-optical emission spectroscopy

**INNA** instrumental neutron activation

**WDXRF** wave-length dispersive X-ray fluorescence

The third line lists the laboratory (XRAL, USGS, UWI) where the analyses
were done. An exception is the lichen data which do not have a location
line as all analyses were completed at the University of Wisconsin.

**Unique Data Fields**

Individual data files have several unique fields.

**Volcanic_bedrock.xls**

> ***Rock Description*** rock type and the named flow, after Huber
> (1973a)
>
> **Mineralized_rock.xls**
>
> ***Mineralized Rock Source*** location of the mine dump, waste rock
> pile, or area where each sample was collected
>
> **Sedimentary_bedrock.xls**
>
> ***Rock Description*** rock type

**A_horizon.xls**

***Estimated horizon thickness*** estimated thickness of soil horizon
(in cm)

**C_Horizon.xls**

***Estimated collection depth*** depth at which the sample was collected
(in cm)

**Lichens.xls**

***Epiphytic lichen comments*** tree species from which lichens were
collected

**Sargent_Lake \_core**

> ***Sample Description*** core number (increasing with depth) and
> distance from the bottom of the individual cores to the sample area

***Estimated depth to the top of*** distance (in cm) from the sample
area to the

> ***water/sediment interface*** estimated water/sediment interface\
> **Lake Richie \_core**
>
> ***Sample Description*** core number (increasing with depth) and
> distance from the bottom of the individual cores to the sample area

***Estimated depth to the top of*** distance (in cm) from the sample
area to the

> ***water/sediment interface*** estimated water/sediment interface

**acknowledgments**

This work could not have been accomplished without the assistance of a
number of people. Cheerful field work and shovel-carrying over the
four-year period was provided by Rob Barber-DeLach, USGS, Doug Ottke,
USGS, Michele McCray, USGS, and Shana Pimley, USGS. Klaus Schulz, USGS,
Susanne Schmidt, University of Basel, Switzerland, provided assistance
with bedrock sampling. Cliff Wetmore, University of Minnesota, educated
geologists about the intricacies of lichen identification, in addition
to picking lichens one season. The National Park Service staff on Isle
Royale, especially Jack Oelfke and Mark Romanski, provided both the
logistical and practical assistance that made this work possible.

**rEFERENCES**

Bennett, J.P. 1995. Abnormal chemical element concentrations in lichens
of Isle Royale National Park: Environmental and Experimental Botany, v.
35, p. 259-277.

Cannon, W.F., 1994, Closing of the Midcontinent rift\-- A far-field
effect of Grenvillian compression: Geology v. 22, 155-158.

Cannon, W.F. and Woodruff, L.G., 1999, Mercury distribution in bedrock,
native copper ore, and soils-Isle Royale National Park, Michigan: 45^th^
Annual Meeting of the Institute on Lake Superior Geology, v. 45, p.
12-13.

Cole, K. L., Flakne, R.L, Engstrom, D.R. and Harlow, D.E., 1997. Three
hundred years of vegetation change and fire history on Isle Royale,
Michigan: Bulletin of the Ecological Society of America, v. 78, p.70.

Clayton, L., 1983, Chronology of Lake Agassiz drainage to Lake Superior:
Geological Society of Canada Special Paper 26, p. 291-307.

Hansen, H. L.; Krefting, L. W. and Kurmis, V. 1973, The forest of Isle
Royale in relation to fire history and wildlife. Technical Bulletin 294;
Forestry Series 13. Minneapolis, MN: University of Minnesota,
Agricultural Experiment Station, 44 p.

Huber, N.K., 1973a, The Portage Lake Volcanics (middle Keweenawan) on
Isle Royale, Michigan: U.S. Geological Survey Professional Paper 754-B.
32 p.

Huber, N.K., 1973b, Glacial and postglacial geologic history of Isle
Royale National Park, Michigan: U.S. Geological Survey Professional
Paper 754-A. 15 p.

Huber, N.K., 1973c, Geologic map of Isle Royale National Park, Keweenaw
County, Michigan: U.S. Geological Survey Miscellaneous Investigations
Map I-796, scale 1:62,500.

Kallemeyn, L.W., 2000, A comparison of fish communities from 32 inland
lakes in Isle Royale National Park, 1929 and 1995-1997: U.S. Geological
Survey Biological Science Report 2000-0004. 65 p.

Lewis, C.F.M. and Anderson, T.W., 1989, Oscillations of levels and cool
phases of the Laurentian Great Lakes caused by inflows from glacial
Lakes Agissez and Barlow-Ojibway: Journal of Paleolimnology, v. 2, p.
99-149.

McRae, M.E., Cannon, W.F. and Woodruff, L.G., 1998, Post-glacial
shorelines of Isle Royale -- where are they now?: 44^th^ Annual Meeting
of the Institute on Lake Superior Geology, v. 44, p. 86-87.

Rakestraw, L., 1965, Historic mining on Isle Royale: Isle Royale Natural
History Association, Houghton, Michigan, 20 p.

Taggert, J.E., Jr., 2002, Analytical methods for chemical analysis of
geologic and other materials, U.S. Geological Survey: U.S. Geological
Survey Open-File Report 02-0223.

Teller, J.T. and Thorleifson, L.H., 1983, The Lake Agassiz -- Lake
Superior connection: Geological Society of Canada Special Paper 26, p.
261-290.

Wetmore, C.M., 1985, Lichens and air quality in Isle Royale National
Park: Final Report, National Park Service Contract XC0001-22-0034 and
USDI-PX6000-7-0731, 40 p.

Wolff, R.G. and Huber, N.K., 1973, The Copper Harbor Conglomerate
(middle Keweenawan) on Isle Royale, Michigan, and its regional
implications: U.S. Geological Survey Professional Paper 754-B. 15 p.

Wright, H.E., Jr., 1967, A square-rod piston sampler for lake sediments:
Journal of Sedimentary Petrology, v. 37, p. 975-976.

Table 1. Lower detection limits for 40-element ICP-AES method.

+-------------------------+--------------------------------------------+
| **Element**             | #### Lower detection limit                 |
+-------------------------+--------------------------------------------+
| Aluminum, Al            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Calcium, Ca             | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Iron, Fe                | 0.02 %                                     |
+-------------------------+--------------------------------------------+
| Potassium, K            | 0.01 %                                     |
+-------------------------+--------------------------------------------+
| Magnesium, Mg           | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Sodium, Na              | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Phosphorous, P          | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Titanium, Ti            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Silver, Ag              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Arsenic, As             | 10 ppm                                     |
+-------------------------+--------------------------------------------+
| Gold, Au                | 8 ppm                                      |
+-------------------------+--------------------------------------------+
| Barium, Ba              | 1 ppm                                      |
+-------------------------+--------------------------------------------+
| Beryllium, Be           | 1 ppm                                      |
+-------------------------+--------------------------------------------+
| Bismuth, Bi             | 10 ppm                                     |
+-------------------------+--------------------------------------------+
| Cadmium, Cd             | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Cerium, Ce              | 5 ppm                                      |
+-------------------------+--------------------------------------------+
| Cobalt, Co              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Chromium, Cr            | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Copper, Cu              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Europium, Eu            | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Gallium, Ga             | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Holmium, Ho             | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Lanthanum, La           | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Lithium, Li             | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Manganese, Mn           | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Molybdenum, Mo          | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Niobium, Nb             | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Neodymium, Nd           | 9 ppm                                      |
+-------------------------+--------------------------------------------+
| Nickel, Ni              | 3 ppm                                      |
+-------------------------+--------------------------------------------+
| Lead, Pb                | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Scandium, Sc            | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Tin, Sn                 | 5 ppm                                      |
+-------------------------+--------------------------------------------+
| Strontium, Sr           | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Tantalum, Ta            | 40 ppm                                     |
+-------------------------+--------------------------------------------+
| Thorium, Th             | 6 ppm                                      |
+-------------------------+--------------------------------------------+
| Uranium, U              | 100 ppm                                    |
+-------------------------+--------------------------------------------+
| Vanadium, V             | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Yttrium, Y              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Ytterbium, Yb           | 1 ppm                                      |
+-------------------------+--------------------------------------------+
| Zinc, Zn                | 2 ppm                                      |
+-------------------------+--------------------------------------------+

Table 2. Lower detection limits for major elements analyzed by
wavelength dispersive X-ray fluorescence.

  ----------------------- ----------------------- -----------------------
  **Element (%)**         **Lower limit of        **Lower limit of
                          detection**             determination**

  SiO~2~                  0.04                    0.07

  Al~2~O~3~               0.04                    0.07

  Fe~2~O~3~               0.01                    0.02

  MgO                     0.03                    0.05

  CaO                     0.003                   0.005

  Na~2~O                  0.06                    0.1

  K~2~O                   0.006                   0.01

  TiO~2~                  0.003                   0.005

  P~2~O~5~                0.006                   0.01

  MnO                     0.001                   0.002
  ----------------------- ----------------------- -----------------------

Table 3. Lower detection limits for element determinations by INAA long
count.

+-------------------------+--------------------------------------------+
| **Element**             | #### Lower detection limit (in ppm)        |
+-------------------------+--------------------------------------------+
| Potassium, K            | > 100                                      |
+-------------------------+--------------------------------------------+
| Barium, Ba              | > 100                                      |
+-------------------------+--------------------------------------------+
| Iron, Fe                | > 10                                       |
+-------------------------+--------------------------------------------+
| Nickel, Ni              | > 10                                       |
+-------------------------+--------------------------------------------+
| Strontium, Sr           | > 10                                       |
+-------------------------+--------------------------------------------+
| Zircon, Zr              | > 10                                       |
+-------------------------+--------------------------------------------+
| Sodium, Na              | > 1                                        |
+-------------------------+--------------------------------------------+
| Zinc, Zn                | > 1                                        |
+-------------------------+--------------------------------------------+
| Chromium, Cr            | > 0.50                                     |
+-------------------------+--------------------------------------------+
| Neodymium, Nd           | > 0.50                                     |
+-------------------------+--------------------------------------------+
| Rubidium, Rb            | > 0.50                                     |
+-------------------------+--------------------------------------------+
| Arsenic, As             | > 0.10                                     |
+-------------------------+--------------------------------------------+
| Cobalt, Co              | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Cesium, Cs              | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Holmium, Ho             | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Antimony, Sb            | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Samarium, Sm            | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Thorium, Th             | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Uranium, U              | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Ytterbium, Yb           | > 0.05                                     |
+-------------------------+--------------------------------------------+
| Europium, Eu            | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Hafnium, Hf             | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Lanthanum, La           | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Lutetium, Lu            | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Scandium, Sc            | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Tantalum, Ta            | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Terbium, Tb             | > 0.01                                     |
+-------------------------+--------------------------------------------+
| Gold, Au                | > 0.0005                                   |
+-------------------------+--------------------------------------------+