Study On Nitrogen Retention In Riparian Vegetation System

With the development of economy and expansion of population,water pollution has become more serious,which has limited the economic and social development and threatened human's health.Riparian vegetation system has a good function to reduce the pollutant of surface water and ground water to enter aquatic ecosystems. The riparian systems which were full of bamboos were common secondary vegetation communities in hilly area of south China.As a result,the further study of bamboo-soil systems in riparian zone is very important to prevent environmental pollution and the eutrophication of recipient water.This study took the riparian bamboo-soil as a system,and used the creative acquisition device to collect the soil interflow by combining the analysis of N in the water and the in-situ denitrification experiments,to find out the inside main biogeochemical process and make sure the mechanism and process of pollutants retention.The main conclusions are as follows:1.The start time of through fall was latter than rainfall,but the duration time was longer and the quantity was small because of the canopy interception.The canopy interception of the second time and third time precipitation were 0.8mm and 3.8mm. Nitrogen in through fall was higher than that in rainfall.The ratio of NH₄⁺-N and NO₃^--N to rainfall were 18.8～307.2%,74.7～925%respectively。2.Most of nitrogen enter the riparian vegetation system was retained in the system.The retention efficiency of NH₄⁺-N was 98.75～99.46%,that of NO₃^--N was 85.92～99.81%.The system retained more NH₄⁺-N than NO₃^--N,the main reason may be the soil.Because the soil particles and soil colloids were negatively charged,which can absorb NH₄⁺-N strongly and lead to the exchangeable NH₄⁺-N attach on the surface of soil colloids and retain in the soil finally.But once the soil is saturated with NH₄⁺-N,NH₄⁺-N may be desorbed with the infiltration,leak into the soil,and enter the river.Since the absorption capacity limitation of soil colloids to NO₃^--N,it will leach into groundwater easily,or enter the river through runoff and erosion,pollute the water finally.3.The rate of denitrification in study site was influenced mainly by the concentration of NO₃^--N,organic matter and so on.Riparian vegetation system was high with denitrification,and NO₃^--N retention by denitrification was more than 14.57 comparing to the whole system in our study site.Denitrification was an important way to retain N.In our study,the average concentration of NH₄⁺-N in the outlet of riparian vegetation system was 12.58 mg·L^-1,which have reached the first discharge standard. The results proved that the width of riparian system was basic suitable.But under fertilization,the width was unsuitable.