PARENT SESSION
Oral Session #100: Landscape Ecology.
Presiding: T. Crist
Friday, August 9. 9:00 AM to 12:00 PM. Gila Meeting Room, TCC.
Patterns of soil P: Concentrations and variability across an urbanizing agricultural watershed .
Bennett, Elena*,1,2, Carpenter, Stephen1, 1 University of Wisconsin-Madison, Madison, WI2 embenne1@facstaff.wisc.edu
ABSTRACT- Eutrophication is a critical problem for freshwater resources. Phosphorus (P) runoff from upland soils is a leading cause of freshwater eutrophication. Advancing our understanding of upland soil P will improve long-term lake management. P is accumulating in the soils of many watersheds, thus increasing the potential for eutrophication; however, we have little understanding of the spatial pattern of that accumulation. Here, I examine several methods for understanding the spatial pattern of P accumulation in Dane County, Wisconsin. I test the usefulness of urban-rural gradients as a predictor of soil P, and find that while the relationships are significant (p<0.0001), they do not explain much variation (r 2 = 0.06) due to high variability in soil P values. Furthermore, soil P concentration variability itself varies across scales and land use types. Given the high level of variability in soil P concentrations across the county, I use a new statistical technique called bagging (short for Bootstrap AGGregatING) that incorporates additional information about variance into the predictions. Bagging significantly improved soil P prediction accuracy (root mean squared error decreased 9 percent and r2 =0.29) and increased understanding of where patterns in P concentrations might be expected across Dane County.
KEY WORDS: phosphorus, variability, spatial pattern, nonpoint pollution