Effectiveness of Riparian Vegetated Filter Strips in Removing Agricultural Nonpoint Source Pollutants in Agricultural Runoff from the Liao River Area, China

Riparian vegetated filter strips (RVFS) can effectively intercept agricultural non-point source pollution (ANSP) into a water body and reduce the risk of water body pollution. The present study evaluates the long-term effectiveness of different types and lengths (5 m, 9 m, 13 m) of RVFS in reducing the suspended solids (SS) and nutrients from agricultural runoff. Three field experimental plots (T1-T2-T3) planted with weeds, sweet clover (Melilotus suaveolens L.) and sweet clover/Chinese wingnut (Pterocarya stenoptera C. DC.) were established adjacent to the agricultural edge from 2011 to 2018. The runoff volumes, SS, and nutrients concentrations were determined at each effective runoff event during the study periods. The results indicated that all RVFS (T1, T2, and T3) reduced the mass of the nutrients rather than the concentration in all runoff events. In the rainfall events, the pollutants were reduced significantly in the presence of RVFS. The removal efficiency of T2 and T3 amounted to 79% and 84% for SS within the first 5 m, which was significantly higher than T1(61%). The 9 m-long T3 caused a significant reduction in the mean total phosphorus (TP) and dissolved phosphorus (DP) by 84% and 82%, respectively. More than 70% of the pollutants from rainfall runoff could be controlled by a 13 m RVFS. The snow-melt events increased the risk of ANSP migrating to streams, especially for the DP. However, the Chinese wingnut strip increased the filtering capacity of the DP as compared to the other two RVFS. Results from this study confirmed that the RVFS is a very effective mitigation system to reduce the sediment and nutrient loads in the agricultural runoff.