Impact of Landscape Feature and Feature Placement on Agricultural Non-Point-Source-Pollution Control

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Management of agricultural non-point-source pollution in watersheds requires an integrated approach involving implementation of on-field and off-field management practices. An off-field management practice that is widely used to control sediment and water-borne pollutants from entering surface waters is vegetated buffer (or filter) strips. When situated between a potential pollutant source and a surface water body that receives runoff, vegetated buffer strips have been shown to be very effective in removing substantial amounts of sediment and nutrients (primarily nitrogen and phosphorus) from the runoff. However, the effectiveness of vegetated buffer strips depends not only on their hydrologic and hydraulic characteristics but also on their physical characteristics (e.g., width and placement within the agricultural landscape). This paper examines the influence of width and placement of vegetated buffer strips on sediment yield in an agricultural watershed. The AGNPS hydrologic/water-quality model was linked with ARC/INFO geographic information system to predict sediment yield in the Bluegrass watershed in southern Iowa. The linked modeling system was also used to assess the impact of various buffer strip implementation strategies (width and placement along segments of the perennial stream) on sediment yield. When compared with the baseline condition, consisting of current land use/land management and no buffer strip, the vegetated buffer strip implementation strategies were effective in reducing sediment yield. For example, a buffer strip 30 m wide with a very dense alfalfa/smooth bromegrass stand reduced sediment yield by about 30% compared to the baseline condition. Furthermore, when the vegetated buffer strips were implemented along certain segments of the perennial stream within the watershed, disproportionate reductions in sediment yield were obtained.