Study On Control Of Agricultural Non-point Source Pollutants By Riparian Vegetated Filter Strips

Water pollution has become a major problem for both developed and developing in recent decades. The contribution from agricultural non-point source pollution(ANSP) has become a major cause of water quality degradation in China. Riparian vegetated filter strips (RVFS), a zone of transition between aquatic ecosystems and terrestrial, can be effectively intercept ANSP into water bodies, and reduce the risk of pollution of water bodies. Liaohe River Basin located in northern China, the water quality is polluted by ANSP. Riparian vegetation has been damaged due to irrational activity by local people, RVFS’performance are deteriorating. It is an effective approach that recovering and building RVFS to reduce ANPS pollution load. But first it is important to choose more suitable riparian vegetation, and to understand the mechanism of conversion about ANPS. Three types of artificial RVFS demonstration area was built in the wild through screening plants in the laboratory, namely with sweet clover, sweet clover mixed with sweet clover/Chinese Wingnut and weeds (control), two consecutive years of field monitoring experiment was carried out by field plot test methods to examine the effects of RVFS in reducing ANSP and mechanisms and characteristics of RVFS in retaining ANSP in term of vegetation types, width, seasonal changes, soil enzyme activities and microbial community. The resulting conclusions are as follows:The mechanisms of RVFS in retaining ANSP include:intercepting surface runoff, vegetation, increased soil penetration, absorption and adsorption pollutants, microbial degradation and so on.(1) Overall, the capability of RVFS in retaining ANSP are followed by sweet clover/Chinese Wingnut> sweet clover> weeds. Sweet clover is appropriate to RVFS as herbaceous vegetation. Various types of RVFS can reduce effectively surface runoff, suspended particulate matter concentration and quality, nitrogen and phosphorus, but they have no significant effect on the concentration of nitrogen and phosphorus runoff of nitrogen and phosphorus concentration in the soil solution resistance control effect are different according to the type of RVFS and different forms of nitrogen and phosphorus.(2) The width of RVFS is an important factor to affect the ability to reduce ANSP. The wider of RVFS, the more obvious these effect on ANSP,5m wide RVFS can significantly reduce rainfall runoff, quality, and quality of suspended particulate matter in rainfall runoff of nitrogen, the ability of tree/grass filter is strongest, and retention efficiency is the range of42%-99%. The retention efficiency of sweet clover for ammonia nitrogen is low.9m wide RVFS can significantly reduce the quality of rainfall runoff phosphorus. The effect of tree/grass filter is better than the other filter in reducting ANPS. It is may be due to the larger band grass biomass, phosphorus accumulation ability of the reasons, and infiltration may be another major contaminant removal mechanism.(3) Seasonal changes significantly affect the effect of RVFS in reducting ANPS. The effect of RVFS on resistance of rainfall runoff is significantly greater than that of snowmelt runoff. Only the width of the riparian buffer exceeds a certain value, the resistance of snowmelt runoff pollutants was obvious, and snowmelt runoff pollutants content is higher, its resistance control effect is less obvious. Freeze-thaw effect can increase the content of soluble phosphate of buffer system, therefore, snowmelt runoff of this area can increase the risk of snowmelt runoff water soluble phosphorus pollution.(4) The plants in the riparian buffer zone can contribute to the resistance control agricultural non-point source pollution. Melilotus and Pterocarya have a strong ability of adsorption and accumulation for nitrogen and phosphorus. Taking a harvest for melilotus in July, the mount of nitrogen removed by the above-ground part can be in the range of15.2123.66g m-2, and the phosphorus in the range of0.72-1.02g m-2.(5) The distributions of soil microbial community of Melilotus and Pterocarya riparian buffers tend to be diverse, belonging to the type of bacteria. The characteristics of distributions can be regarded as one indicator for evaluating the riparian buffer resistance control non-point source pollution of nitrogen and phosphorus ability. The relationship between Soil urease activity and riparian buffer system and nitrogen resistance control has shown obvious correlation, and the tie between soil phosphatase activity and soil resistance control for phosphorus removal effect has a good correlation.