Geologic, geomorphic and chemical characteristics of wetlands selected for use in biocriteria development by the Montana Department of Environmental Quality

332 Pages·1995·4 MB·English

by  Shapley, Mark

C MONTANASTATELIBRARY
551-41
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1995
Appendix B
Geologic, Geomorphic and Chemical Characteristics
of Wetlands Selected for Use in Biocriteria
Development by the Montana Department of
Environmental Quality
by
Mark D. Shapley
Montana Natural Heritage Program
1515 East 6th Avenue
Helena, MT 59620
for the
Montana Department of Environmental Quality
Water Quality Division
December, 1995
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Geologic, Geomorphic and Chemical Characteristics
of Wetlands Selected for Use in Biocriteria
Developnnent by the Montana Department of
Environmental Quality
by
Mark D. Shapley
Montana Natural Heritage Program
1515 East 6th Avenue
Helena, MT 59620
for the
Montana Department of Environmental Quality
Water Quality Division
December, 1995
STATE DOCUMENTS
COLLECTION
';ay O200I
1
MONTANA STATE LIBRARY
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Appendix B.
Narrative Summaries of the Physical Setting and Chemical
Characteristics of the DEQ Wetland Characterization Sites

Alkali Lake
Climatic setting. The net annual precipitation balance for Alkali
Lake (from the MAPS database) is approximately -13 inches. This
places the site toward the less evaporative end of the climatic
spectrum for closed basin sites, but near the more evaporative
extreme for Rocky Mountain sample sites. Monthly average
precipitation for the Fortine climatic station shows relatively
even distribution throughout the year, with a moderate peak in May
and June. Annual records from the Fortine station show the 3-year
running average precipitation has been below the long-term mean
during most of the last 30 years. Annual precipitation during the
sample year of 1993 exceeded the average for the period of record
by approximately 5 inches.
Geologic setting. The Alkali Lake basin is underlain by calcareous
till and possibly other glacial sediment types of late(?) Wisconsin
age. Shorelines are composed of coarse-grained sediments in high
energy areas, marly mud in deeper water and sheltered littoral
areas. Bedrock geologic units are of the Proterozoic Belt Series,
probably including the calcareous and dolomitic Helena Formation.
Hydrologic type. Alkali Lake is a glacial depression lacking
surface drainage at current water levels. Strandlines represented
by tree kills indicate historic water levels within the past few
decades which would have allowed surface discharge. Groundwater
outflow is inferred from moderate salinity of this topographically
closed basin.
Basin characteristics. Alkali Lake has a small surface catchment
with respect to lake area and volume. The basin is linear and
shallow at both ends, with a maximum measured depth in mid-basin
of 37 feet. The cluster of lakes in the vicinity display disjunct
water quality; Thirsty Lake, nearby and at a lower elevation,
exceeds Alkali Lake in specific conductance by more than an order
of magnitude. Road construction has partially isolated the eastern
arm of the lake during high-water conditions.
Water chemistry- Alkali Lake is proportionately high in magnesium
and is almost completely depleted in calcium; low calcium
concentrations appear to be maintained by solubility controls,
evidenced by deposition of authigenic carbonate minerals. High
relative magnesium concentrations are typical of hydrologically
similar sample sites. Equilibrium calculations indicate
supersaturation with calcium and magnesium carbonate species.
In comparison to hydrologically similar sample sites, Alkali
Lake exhibits relatively low water-column concentrations of trace
elements. Total organic carbon concentrations are at the high end
for the region and for hydrologically similar sites.
Chemical history. Specific conductance measurements from 1968 were

.
approximately 25% lower than 1993 and 1994 measurements. Seasonal
measurements in 1993 and 1994 show approximately 10% difference in
salinity. Vegetation indicators show considerably higher lake
volume within the past few decades, implying significantly more
dilute water chemistry. The measured salinity range within the
lake basin was minor, amounting to approximately 5% in specific
conductance
Sediments. Sediment trace element concentrations are generally low
with respect to regionally and hydrologically similar sample sites.
Trace elements found above detection limits (arsenic, boron, copper
and zinc) occurred at concentrations below the regional mean soil
concentrations for these parameters (Shacklette and Boerngen,
1984)
.