Project Description
Study Site
The Trout Lake (TL) WEBB site is in the Northern Highland
area of north-central Wisconsin. The site includes five open lakes and two bog
lakes. It is also the site of the NSF-sponsored North
Temperate Lakes Long-Term Ecological Research (NTL/LTER) project,
which has been ongoing since 1980 under the direction of the Center for Limnology,
University of Wisconsin-Madison. The WEBB hydrologic and biogeochemical research
in the LTER lake watersheds complements the ecological research conducted at
the NTL/LTER, which is focused on in-lake processes.
More than 3,000 kettle lakes, formed at the end of the
last continental glaciation about 10,000 years ago, are concentrated in the Northern
Highland area of north-central Wisconsin. In this sparsely populated area, many
lakes have totally forested watersheds and no private frontage.
Geologic features of the area are dominated by a sandy
outwash plain consisting of 30 to 50 meters of unconsolidated sand and coarser
till overlying Precambrian igneous bedrock. The predominant soils are thin forest
soils with high organic content in the uppermost horizon. The site is representative
of the glacial lake districts common to the upper Midwest and Canada, but certain
individual characteristics distinguish it from other nearby lake areas. Among
the most important of these characteristics is glacial drift that is virtually
carbonate free; as a result, the ground-water chemistry is almost entirely controlled
by silicate hydrolysis.
Most of the lakes in the Northern Highland area are
seepage lakes--they have no surface-water inlets or outlets. Water budgets are
thus dominated by direct precipitation, ground-water flow, and evapotranspiration.
The seven study lakes, four of which are seepage lakes, are all in the same ground-water-flow
system. Lakes in topographic highs, such as the two bog lakes and Crystal Lake,
receive little ground-water flow and no streamflow and have water with low ionic
concentrations (10 to 20 microSiemens per centimeter, mS/cm). Lakes in topographic
lows such as Trout Lake, are dominated by ground-water and stream inputs and
have water with higher ionic concentrations (70 to 90 mS/cm). Although linked
by a common ground-water-flow system and similar climate, the lakes represent
a broad range of size, morphometry, habitat, thermal features, chemistry, biological
productivity, and species composition.
Overall Objectives: The following are the long-term
objectives of the TL-WEBB project:
- Describe processes controlling water and solute fluxes
in the TL watersheds.
- Examine interactions among those processes and their
relations to climatic variables.
- Improve the capability to predict changes in water and
solute fluxes for a range of spatial and temporal scales.
The WEBB study is initially focusing on three areas of research that will provide
information on water and solute flux (1) rainfall, streamflow, and recharge,
(2) groundwater/surface water interaction and (3) carbon fluxes within the watershed.
Data from these studies will serve as a framework for future research on hydrologic,
chemical, and biological responses to changing environmental conditions.
Rainfall, Streamflow, and Recharge Processes
Objectives
- Investigate the processes controlling streamflow generation
in response to rainfall for low-relief hydrologic settings.
- Investigate the processes that lead to ground-water
recharge in the TL basin.
- Develop appropriate predictive capabilities for the
identified streamflow-generation and ground-water-recharge processes.
- Investigate the implications of increases in spatial
and temporal scale on the predictive capabilities.
Approach
- Use stable isotopes of water (oxygen-18 and deuterium)
to identify streamflow-generation mechanisms by examining the isotopic evolution
of water as in moves through the hydrologic system. Three detailed hillslope
sites along Allequash Creek are instrumented with nested piezometers, lysimeters
and bulk rainfall and throughfall collectors.
Groundwater/Surface Water Interactions
Objectives
- Determine the water and solute yields for the Trout
Lake Basin and determine the relative importance of streamflow to the water and
solute budgets for Trout Lake.
- Identify the geochemical processes that control the
flux of major chemical species (such as nitrogen and sulfur species) at the aquifer-lake
and aquifer-stream interfaces, and the temporal and spatial variability of these
processes.
Approach
- Streams tributary to Trout Lake are sampled periodically
to allow the computation of solute fluxes from streams into and out of Trout
Lake.The samples are analyzed for nutrients and major ions. The importance of
surface-water sources to the complete hydrologic and chemical budget of Trout
Lake is being determined from the estimated surface-water fluxes and the existing
NTL/LTER data base.
- Processes that control the mass flux of chemical species
across the stream interface are being identified by means of fine-scale sampling
(that is, less than 1 centimeter, cm). The samples are collected at various times
of the year at two locations along Allequash Creek. Samples are also collected
periodically from a detailed transect along Allequash Creek to determine larger-scale
variations.
Carbon Flux Processes
Objectives
- Identify the processes that control the flux of major
carbon species (such as dissolved inorganic carbon, dissolved organic carbon,
carbon dioxide and methane) within the Allequash Creek watershed, and the temporal
and spatial variability of these processes.
Approach
- Carbon fluxes are being estimated through periodoc
sampling of various system components (see carbon flux schematic for details),
and measured directly for soil effux using soil chambers. A variety of land cover
and slope/aspect combinations are being sampled to help pinpoint the spatial
variability.
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U.S. Department of the Interior |
U.S. Geological Survey