Nutrient Attenuation In Agricultural Surface Runoff By Riparian Buffer Strips

Water pollution control and treatment will be an long-term and important task in China. Nowadays, the controls of point sources have brought noticeable achievements. But the large-volume, rapid changes and other characteristics make the non-point source pollution hard to deal with. Researches and practices abroad indicate that the riparian buffer strips is an effective way in filtering sediment, reducing non-point source pollution from agricultural land to streams, improving water quality and enhancing habitat.Based on "Study in Practical Technology of Suzhou Creek Comprehensive Rehabilitation Project Stage III", we carried out the studies in "Riparian Buffer Strips- Agricultural Non-Point Source Pollution Control Technology in Upper Stream of Suzhou Creek". First, chose the five common greenswards in Shanghai, set up a small laboratory test pilot; the buffer strips in laboratory, and analyzed the effect of each buffer strip. Second, on the basis of the results from the small test in the laboratory, we built the riparian buffer strips for agriculture non-point source control experiments in a large scale, analysis the impacts of different vegetation riparian buffer zone. The main conclusions are as follows:(1) With the different initial concentration of SS, the riparian buffer strip with Cynodon dactylon have a prominent impact on SS removing, whose average removal rate is 68.87%, Trifolium repens ,Festuca Arundinacea and Dichondra repens also have high reduced rates of SS concentration in the runoff, they are 65.59%, 63.37% and 60.09% respectively. Lolium perenne riparian buffer strips only get 52.51%, which is the lowest removal efficiency. There is not impact on reduction in the SS concentration by the vacant buffer strip. Clearly, there is some relation between the removal of SS in the runoff and the growth of lawns.(2) When the initial concentration of TN is between 7.01 to 30.40 mg / L, Trifolium repens buffer strip got the best effect in TN removing, the average removal rate was 24.76 percent. The average removal rate of Cynodon dactylon and Festuca Arundinacea rate were 24.22% and 20.08% respectively, Lolium perenne id the less effective one for the reduction of TN, which is only 9.15%. Compared with the vacant strip, the buffer strips with lawn enhanced the higher reduce ratio for TN in the runoff remarkably.(3) The study showed that the riparian vegetation system has obvious efficiency for the control of agricultural TP pollution. Trifolium repens has 25.60% average reduce ratio for TP, followed by Cynodon dactylon and Dichondra repens, whose ratio are 21.24% and 17.97% respectively. Because Lolium perenne got into the dormant in summer, it only had a little impact on the cutting down the nutrients in farmland runoff. Therefore, its removal ratio is the minimum of the five buffer strips, which is only 11.25%. Obviously, the growths of the vegetation in the buffer strips have certain effect on TN removal in runoff.(4) Researches showed that there isn't any relationship between the load of pollutants and the removal ratios.Because of their high efficiency for the control of agricultural pollution in small pilot test, Cynodon dactylon, Festuca Arundinacea and Trifolium Repens, they were chosen to plant in the large-scale experiments. Further analyzed their impact on the reducing of the agricultural runoff, mainly obtained following conclusions:(1)When the SS concentration range in the runoffs is from 223 to 942 mg/L, the order of nutrient attenuation in agricultural surface runoff by different vegetation riparian buffer strips is Cynodon dactylon> Trifolium repens> Lolium perenne, with the average reducing ratio 89.38%, 86.05% and 85.53% respectively. The blank strip had a certain effect on the removal, but unstable. (2) In different buffer strips, the TN concentration and the SS concentration has a close linear relationship. With the distance increasing, the cumulative removal ratio of runoff TN increased. The order of the contribution to the TN attenuation is: Cynodon dactylon > Trifolium repens > Lolium perenne, in which, Cynodon dactylon got the maximum value of 16.68%. The trend of the TN decrease in the blank strips is wavy.(3) In different sward buffer strips, these is a significant linear relationship between SS and TP concentration in the runoff, but no any rule can be found in the blank strip. Different terminal buffer zone effluent removal order of TP is: Trifolium repens > Cynodon dactylon > Festuca Arundinacea, which were 18.31%, 16.62%, 14.44%.(4) In the buffer strips with Cynodon dactylon, the effects on the removal of SS concentration did not differ significantly, which is different from Trifolium repens and Festuca Arundinacea. We can see that, season replacement, climate change will have corresponding changes in growth conditions, thereby, it will have a further impact on the SS and nutrients attenuation in agricultural surface runoff by different riparian buffer strips.