LONG TERM ECOLOGICAL RESEARCH (LTER):
An area in the hardwood forests of northern Wisconsin has been the
focus of ecological research since 1981. Supported by the National Science
foundations's Long-Term Ecological Research Program Wisconsin's site supports
a highly interdisciplinary team of researchers from the University of Wisconsin
addressing questions related to the controls of long-term variation in
natural systems, distinguishing between natural and human induced changes
in the environment, improving our understanding of the interactions among
physical, chemical and biological processes in the landscape. The national
program now supports comparable research programs at 17 sites within
the continental U.S., Puerto Rico, and Antarctica. As one of the initial
sites funded in 1981 the North Temperate Lakes LTER site is run through
the Center for
Limnology on the Madison campus.~ An interdisciplinary team made up
of faculty and graduate student members from the Center for Limnology,
Zoology, Botany, Geology, Atmospheric and Oceanic Sciences, Water Chemistry,
and Rural Sociology. Over 10 students from the geology department have
completed Ph.D. or Masters theses related to work on the LTER site and
include: Galen Kenoyer, Emeka Okwueze, David Krabbenhoft, Jeff Ackerman,
Susannah Michaels, and Kangjoo Kim.
The geology department's role in the LTER program at Wisconsin has focussed largely on lake/water interaction, relating changes in the local groundwater system to long-term changes in a seven lake area just north of Minocqua, Wisconsin in Vilas County. Located in a mixed deciduous-hardwood forest the area is rich with lakes and wetlands (approximately one per square mile). Glacial in origin the lakes are formed as kettles in remmanants of the stagnated ice sheet that covered much of the continent during the last ice-age approximately 10,000 years ago. A large number of lakes in the area have no surface water connection to adjoining lakes and are intimately linked with the local groundwater. Hydrologically groundwater storage is the dominant water mass with thick glacial drift and outwash deposits generally greater than 30-50 meters and most lakes with mean depths of less than 10 meters. Quantification of the mass interaction between lakes is therefore crucial to understanding the physical and chemical responses of lakes to short and long-term climate change.
Solute budgets of the lakes in the region are controlled by silicate weathering and biogeochemical cycling. Isotopic techniques are being used to constrain the water budgets of lakes, and identify plumes of lake water within the groundwater system. Mass balance techniques allow us to quantify the mineralogical controls on the groundwater geochemistry.
MASS BALANCE STUDIES: Closely related to the LTER lake/groundwater studies my colleague, Blair Jones (Reston, VA) and I have been using mass balance tools to help better understand the quantitative mineralogical control on the chemistry of surface and groundwaters in the U.S. Current work underway focusses on several type examples of waters dominated by silicate mineral weathering and includes Loch Vale, CO, Vekol Valley, AZ, Catoctin Mt., MD, Sierran Spring Waters, CA, Inyo Mts, CA, and the Trout Lake region, WI. A spreadsheet approach allows us to quickly evalulate quantitative mineral control on water compositional changes, providing a powerful analytical tool to explore various mineral reactions and to better understand the importance of chemical variations within mineral series such as plagioclase, amphobole, biotite, and the clay minerals. An example plot of the Sierran Spring waters studied by Garrels and Mackenzie shows the mineral mass transfers for the reactant and product phases as a function of plagioclase composition. Garrels and Mackenzie reported the plagioclase compositions to be close to An-38. From the plot showing the evolution of deeper spring waters (their perennial springs) it is clear that weathering of plagioclase alone will not explain the higher Ca/Na ratios of the spring waters, and that an additional calcium bearing phase is needed to explain results. Garrels and Mackenzie proposed calcite as the needed mineral, generally considered reasonable based on results of Mast, et. al. from rocks in a similar geologic setting in Loch Vale, Colorado.
COLORADO RIVER TAILWATER STUDIES: In
the Spring of 1997 a team of investigators from several agencies withing
the Department of Interior, cooperating state agencies from Arizona and
Utah, and investigators from numerous universities took part in an "experimental
flood" designed to evaluate the effect of controlled flooding on
a number of aspects of the lower Colorado River between Lake Powell and
Lake Mead. Included among these were studies to evaluate the effect of
floods on beach habitats (especially with regard to sand budgets), effects
on endangered and introduced fish species, water quality, disturbance of
the food base for a variety of aquatic organisms, and the quality of tourist
related river rafting.
During sabbatical leave with the USGS in 1995-96 I began collaborative investigations with G.R. "Dick" Marzolf on temporal dynamics related to biologic processes in the Colorado River in a stretch of river from the Glen Canyon Dam to Less Ferry, 15 miles downstream. Studies were initiated by Marzolf the previous year that provided a base of data from which our experiment during the flood was conducted.~ Studies of primary production related P-CO2, pH, dissolved oxygen, and dissolved inorganic/organic carbon were made during low flows immediately before and after the flood to assess the effect of the flood on the removal of benthic algae (primarily Cladophora).