Impact Factors And Nitrogen Removal Efficiency Of Denitrification From Natural Ditch In The Hilly Area Of Sichuan Central

With the exacerbation of the agricultural non-point source pollution, the eutrophication of downstream lakes and rivers is getting more and more serious. Natural ditches connected farmland drainage with the river can cut down the agricultural non-point source pollution. Denitrification is the most effective mechanisms to treat nitrogen pollution in water body, but lack of related research. This study aims to research the rate of the natural ditch sediment denitrification, the factors and the contribution of denitrification in Sichuan hilly basin by using the modified method of amended acetylene inhibition technique, which will provide a creative method to protect the agricultural water environment in upstream of Yangtze River. The main conclusions as following:（1）The high content of carbon and nitrogen in the water and sediment of natural ditch changed with seasons. The concentration of ammonium nitrogen and nitrogen is high in the winter and low in the summer; the concentration of nitrate nitrogen is high in spring and summer and low in winter. The concentration of DOC is high in spring and low in summer.the content of sediment inorganic carbon and nitrogen is high in spring and low in summer and autumn; the content of organic carbon and nitrogen is high in spring and no significant difference in other seasons. The ditch water and the content of the sediment nitrogen show the significant difference in drying-wetting area.（2） The natural ditch have a significant seasonal variations. The high denitrification rate shows in the period of season exchange. Different ditch plants have a significant effect on the denitrification. Cana’s ability of denitrification of is most stable,acorus calamus is strongest but fluctuates wildly. The ability of denitrification of fishscale bamboo and thalia dealbata is controlled by the temperature obviously. The denitrification rate in different wet partition has significant difference. In the intermittent flooding area, the rate is high, then the second is in perennial flooding area and in drying-wetting alternating area the rate is the lowest.（3）The main factors which influence the rate of denitrification are plants, temperature, salinity, DO, TOC and NO₃^-_N. Some vegetation have indirect effect on the denitrification rate through affecting other ditch environmental factors. The Ditch environment factor affecting denitrification rate among temperature, Ec, TDS, water body NO₃^-_N, TN, sediment NO₃^-_N, TN and TOC is significant positive correlation. And the temperature, NO₃^-_N concentration and the wet process is the key factor to affect denitrification rate. In a short, ditch environmental factors affecting denitrifying process presents the complex and changeable characteristics.（4）The average of removal of ditch nitrogen loading is 49.1 kg?ha-1?d-1, and the average of contribution rate of removal nitrogen load is 28.87%. The ability of denitrogenation in wet partition is: the perennial flooding area> perennial flooding area> drying-wetting alternating area. The contribution of denitrification rate and denitrogenation of fishscale bamboo is almost the same and it has the denitrogenation effect. The thalia dealbata’s ability of denitrification and the contribution of denitrogenation is low. Cana’s ability of denitrification of is most stable, the contribution of denitrogenation is high. Acorus calamus’ s average ability of denitrification is highest but not stable, it also fluctuates wildly. The denitrification and denitrogenation rate in different wet partition is between 1.88⁸4.99%, and the vegetation region contributes more than the non-vegetation region.