SEDIMENT AND CHEMICAL LOAD REDUCTION BY GRASS AND RIPARIAN FILTERS

Vegetated filter strips help reduce non-point source pollution from ag ricultural areas. Even though they are an accepted and highly promoted practice, little quantitative data exist on their effectiveness under field conditions. The objective of this research was to determine the amount of nutrients and sediment removed by natural and planted filte rs. This was achieved by collecting and analyzing runoff at field edge s and at various locations in vegetated buffers. Total weight of sedim ent and nutrients in runoff from North Carolina agricultural fields sh owed that the grass and riparian filter strips studied reduced runoff load by 50 to 80%. Total sediment decrease through the filters was abo ut 80% for both grass and riparian vegetation. The reduction in the ch emical load depended on the nutrient and its form. Filters reduced tot al P load by 50%, but 80% of the soluble PO4-P arriving at the field e dge frequently passed through the Biters. The filters retained 20 to 5 0% of the NH4 and approximately 50% of the total Kjeldahl N and NO3. H igh-volume Bows commonly overwhelmed both grass and riparian filters n ext to cultivated fields. Forested ephemeral channels had little veget ation and were effective sediment sinks during the dry season but were ineffective during large storm events because there was little resist ance to Bow. When possible, drainageways should be designed to hold se diment and to disperse the discharge into a riparian area.