Assessment of the Effects of Riparian Buffer Zones on Water Quality in the Jinghe Catchment Using the AnnAGNPS and REMM Models

Direct discharge of sediments and agricultural chemicals into rivers is a major areal source for surface water pollution. This study was conducted to evaluate the impact on water quality by converting riverside crop fields to riparian buffer zones at river basin scale. The Jinghe catchment of the Weihe River basin in China, a heavily cultivated watershed in the middle reach of the Yellow River basin, was selected for this study. The Annualized Agricultural Non-Point Source Pollution Model (AnnAGNPS) was used to simulate water and sediment loadings from upland fields. These generated upland loadings then were used as inputs to run the Riparian Ecosystem Management Model (REMM) for assessing the impact of riparian buffer zones on reducing sediment concentration and nutrients in surface runoff. The whole Jinghe catchment was divided into 4290 homogeneous drainage areas by AnnAGNPS, and both models were run for each drainage area for one year. The annual output data for each drainage area were spatially integrated over the whole Jinghe catchment. Five designs of the riparian buffer with different zone numbers, zone widths and vegetation types were tested. Annual totals of water inflow, sediment yields and dissolved nitrogen in surface runoff into zones 3, 2, and 1, and those out of zone 1 for the whole Jinghe catchment were calculated, compared and analyzed for all the five designs. The analysis indicated that the sediment was reduced by 85.7% to 90.8% and the dissolved nitrogen in surface runoff was reduced by 85.4% to 91.9% over the whole catchment. Our study has provided a helpful way in using the field-scale REMM model in conjunction with the well accepted AnnAGNPS model in evaluating ecological engineering projects at river basin scale. The results of this study are anticipated useful in guiding the land use changes in the Yellow River basin in China for improving surface water quality by building riverside riparian buffer zones.