THE INFLUENCE OF LANDSCAPE POSITION ON LAKES IN NORTHERN WISCONSIN

1. Using data from the North Temperate Lakes Long-Term Ecological Rese arch site in northern Wisconsin, we present a series of examples illus trating how landscape setting can influence the static and dynamic asp ects of many physical, chemical and biological properties of lakes. 2. One important landscape attribute is the hydrologic position of a lak e within the regional flow regime. Lake position determines the relati ve importance of groundwater and precipitation input to a lake, with l akes high in the landscape receiving a greater proportion of their inp ut waters from precipitation than lakes lower in the landscape. Landsc ape position is strongly correlated with the concentration of base cat ions such as calcium and magnesium. 3. Landscape position also influen ces how lakes respond to drought conditions. Lakes high in the landsca pe responded to a 4-year drought with decreases in calcium mass, where as lakes low in the landscape increased in mass of calcium. During ext ended dry conditions, these differential responses of lakes suggest th at lakes already low in calcium (i.e. in a high position in the flow s ystem) will have further reductions in calcium concentrations. These r eductions could decrease the number of lakes offering suitable habitat for organisms such as crayfish and snails whose distributions are lim ited by calcium. 4. Landscape position also affects silica concentrati ons in lakes, with lakes low in the landscape having silica concentrat ions up to three orders of magnitude greater than lakes high in the la ndscape. Differences in silica concentration affect robustness of fres hwater sponge spicules which can potentially alter some aspects of the dynamics of littoral zone food webs. 5. Landscape position can influe nce the vertical distribution of primary production. Concentrations of dissolved organic carbon are affected by landscape setting and can in fluence vertical light penetration, thus affecting the depth at which primary production can occur. 6. Lake area and fish species richness a re correlated with landscape position: larger, species-rich lakes are low in the landscape, whereas smaller lakes with fewer species tend to be high in the landscape. 7. By taking a landscape-scale view, in add ition to the more usual lake-specific view, it is possible to reach a more robust understanding of lake dynamics and avoid some of the probl ems associated with extrapolating from single lake results.