PARENT SESSION
Poster Session #23: Fish, Lakes, Streams, and Wetlands.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Spatial patterns in the nutrient status of Wisconsin lakes: interactions between landscape position and catchment disturbance.

Webster, Katherine^1,2, Emmons, Edward¹, Knight, Susan^1,3, Riera, Joan³, ^{1 2 3}

ABSTRACT- Lake nutrient status reflects hydrogeologic setting, internal cycling, and catchment land use. We propose that consideration of landscape position, the location of a lake along a hydrologic flowpath, adds significant explanatory power. To test this, we sampled 120 Wisconsin lakes (>40 ha in area) divided among three ecoregions with contrasting land use: forest; mixed agriculture/forest; and mixed agriculture/urban. Within each ecoregion we sampled isolated seepage, headwater, and lowland lakes to represent high to low landscape position. To account for internal nutrient cycling, we included deeper stratified lakes and shallow lakes within each hydrologic class. Across ecoregions, average chlorophyll, total phosphorus (TP), and total nitrogen (TN) concentrations increased with the intensity of agriculture and urbanization. Dissolved organic carbon (DOC) and color, however, showed the highest values and ranges in the forested basin. Accounting for ecoregion and landscape position, deeper lakes had lower TP, chlorophyll, and TN compared to shallow lakes, but had lower color and DOC only in the forested ecoregion. After accounting for lake depth, patterns related to landscape position were strongest in the forested ecoregion, weak in the mixed agriculture/forest ecoregion, and generally absent in the agriculture/urban ecoregion. In the forested ecoregion TP, chlorophyll, DOC, and color increased with landscape position. These results suggest that lake nutrient status is related to landscape position, but that this relationship can be obscured by human alteration of catchments by agriculture and urbanization.

KEY WORDS: lake, nutrients, landuse, landscape position