Water, Energy, and Biogeochemical Budgets (WEBB): Trout Lake

Science Center Objects

USGS initiated the Water, Energy, and Biogeochemical Budgets (WEBB) program to understand the processes controlling water, energy, and biogeochemical fluxes over a range of temporal and spatial scales, and the effects of atmospheric and climatic variables. Trout Lake is one of five small, geographically and ecologically diverse watersheds representing a range of hydrologic and climatic conditions.

USGS initiated the Water, Energy, and Biogeochemical Budgets (WEBB) program to understand the processes controlling water, energy, and biogeochemical fluxes over a range of temporal and spatial scales, and the effects of atmospheric and climatic variables. Trout Lake is one of five small, geographically and ecologically diverse watersheds representing a range of hydrologic and climatic conditions.

SITE DESCRIPTION

The Trout Lake 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. 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.

 

RESEARCH AREAS

Photograph of the Middle Allequash stream site in winter, 2003
Middle Allequash stream site in winter, 2003

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.