A Research On The Ditches’ Interception Effect On The Migration Of Agricultural Runoff Nitrogen And Phosphorus

In this paper, the typical adricultural area in northern Changsha County township has been taken as the research object. First, via field sampling to analyze how the rural decentralized breeding and domestic sewage influence the surrounding soil and water environmen, and the output risk of agricultural runoff nitrogen and phosphorus; Besides, by monitoring the ecological demonstration ditch water’s quality that the agricultural runoff has polluted to analyze the ecological ditches’ functions to the migration of agricultural runoff nitrogen and phosphorus, as well as the features of seasonal changes; At last, combining with the simulative tests outdoors and indoors to analyze the feasibility of the biomass materials as carbon source applied in the ditch.Here are the results as follows.The results of survey on decentralized breeding areas’soil and water environment pollution’s status quo show that:(1) Due to the long-term influence of waste water from pigs,85%of the surface water samples’ ammonium nitrogen weighs more than the V-class standard, taking the total nitrogen and total phosphorus to count, and more than90%of that is the inferior V-class water quality; Groundwater is mainly polluted by nitrate nitrogen,80%of the samples’ nitrate nitrogen content is more than the limit of drinking water---10mg/L.(2) In the soil from0to20cm, organic matter and total nitrogen content in paddy soil is more than the national secondary standard, total phosphorus content in vegetable soil is above the national primary standard. Compared with the second soil census data, total nitrogen and organic matter content in paddy soil from0to20cm has increased by5.46%and7.96%respectively. Total nitrogen, total phosphorus and organic matter content in the vegetable garden soil have increased by39.09%,93.94%and39.09%respectively.(3) In the study area the nitrogen in the soil mainly focuses on the insoluble organic nitrogen.The result of ecological ditches’ interception on nitrogen and phosphorus in demonstration area shows that: (1) Ecological ditches’total interception to ammonium nitrogen, nitrate nitrogen and total nitrogen all over the year reaches the amount of38070.8,35095.5, and110341.1g. From the input amount of inorganic nitrogen, the input amount of nitrate nitrogen is more than that of ammonium nitrogen, but for the ammonium nitrogen interception whose rate was85.8%, which is greater than that of nitrate nitrogen obviously.(2)Ecological ditches’total interception to phosphate and total phosphorus all over the year reaches the amount of7113.7g and18511.1g.(3) Ecological ditches have quite better in May and September, with the worst effect in December. From September to December the ability of removing nitrogen load takes on a decreasing tendency. Meanwhile, the ability to remove phosphorus load achieves the best in June and the worst in December, and the ability of removing total phosphorus is significantly greater than that of phosphate.Results of simulative tests outside show that:(1) Take straw as the carbon source in the simulated ditches, the removing rate of nitrate nitrogen and ammonium nitrogen is higher than that of sawdust and activated carbon, including a rate over90%on nitrate nitrogen removal.(2)When the hydraulic load is9m3per day, dosage of straw and ammonium nitrogen removal rate takes on extremely significant positive correlation (P<0.01).Results of simulative tests indoor show that:With straw as the carbon sources in the anaerobic environment, removal of nitrate nitrogen is mainly converted into N2O and ammonium nitrogen.When it comes to a comprehensive analysis of the result of the existence form of nitrogen in the aquaculture wastewater, features of ecological ditches on the intercepting to nitrogen, simulative tests outdoor and indoor, it can be indicated that with the help of exogenous carbon source getting into ecological ditches, it has an effective effect on removing nitrogen and phosphorus in the agricultural non-point source pollution and proves great feasibility. The results this paper can provide technical support for developing trench denitrification reinforcement technology and at the same time provide a theoretical basis for popularizing and applying ecological ditches on the control of rural non-point source pollution.