Wednesday, November 7, 2007 - 11:25 AM
303-8

Disproportionalities in Sediment Delivery from Critical Landscapes.

David Mulla, University of Minnesota, Dep. of Soil Water & Climate, 1991 Upper Buford Univ. of MN, St. Paul, MN 55108 and Adam Birr, Minnesota Department of Agriculture, Minnesota Department of Agriculture, 2300 Silver Creek Road, Rochester, MN 55906.

Erosion risks vary spatially across watersheds and recent research suggests that small critical areas of the landscape contribute disproportionately high amounts of sediment This study uses the Revised Universal Soil Loss Equation (RUSLE) to estimate the relative impact of small proportions of the landscape on sediment pollution of surface waters. Erosion risks were evaluated on 220 fields located within two watersheds in the south-central portion of Minnesota. Erosion risks were very low (< 4 Mg ha-1 yr-1) in 14.5% of the fields, low (4-9 Mg ha-1 yr-1) in 37.3% of the fields, medium (9-14 Mg ha-1 yr-1) in 32.7% of the fields, high (14-20 Mg ha-1 yr-1) in 10.9% of the fields and very high (>23 Mg ha-1 yr-1) in 4.5% of the fields. Based on these estimates, sediment was routed to the mouth of the watershed based on a sediment delivery ratio that depended on distance from the field to the mouth of the watershed. Results showed that small areas of the watershed contributed disproportionately high amounts of sediment to the mouth of the watershed. From a conservation practices perspective, these results suggest that it is important to identify critical landscapes on which to implement conservation practices.