Study On Impacts Of Agricultural Non-point Source On Microbial Community In Riparian Zone

With the improvement of agricultural intensive management and the rapid developmentof large-scale farming, have increased the application of fertilizers, pesticides and otheragricultural products in agriculture, at the same time, utilization method is not so reasonablethat lead to the problem of non-point pollution of agriculture becoming more and more severe.It not only caused eutrophication of water, but also has a significant impact on vegetation,groundwater, soil and microorganism in riparian zone.Since the mid-1980s, with the change of global climate, the loss of biodiversity and theproblem of sustainable development bringing up, especially the loss of riparian zone, thedecline of biodiversity in rivers and lakes and the problem of agricultural non-point sourcepollution, that give increasing prominence to the research of the riparian zone. Riparian zoneis an important ecological ecotone between land and water, its function of prevention andcontrol of agricultural non-point source pollution, conservation of soil and water as well asamelioration of soil play an important role in controlling the eutrophication of the water,protecting water sources, sustaining biological diversity and functional integrity of ecosystem.This thesis takes the riparian zone of Longmenkou reservoir as an example, and takes thenutrients such as nitrogen and phosphorus in agricultural runoff as the main agriculturalnon-point source pollutants, adopting field investigation and indoor analysis methods, theimpact of continuous input of nitrogen and phosphorus on microbial community in riparianzone, and it has a great significance to the development of microbial resources and protectionof riparian zone.The experiments carry out three-months and set up three sampling areas with differentvegetation type and concentration of nitrogen and phosphorus to conduct comparative tests.The experiments using laboratory methods to study the number of temporal and spatialdistribution characteristics nitrogen and phosphorus content, nitrifying bacteria andnitrification rate, and by using correlation analysis and regression analysis method to predictethe relationship and development trend between the number of nitrifying bacteria andagricultural non-point source pollutants. The study results show that: (1) The distribution characteristics of the nitrogen in riparian zone1) Vertical distribution characteristics of nitrogen in riparian zone: With increase of soildepth, the content of nitrogen is decreased significantly. The nitrogen content of0-10cm ofthe surface soils is obviously higher than that of the lower soil, and it is no obvious verticalvariation of20cm below the nitrogen content of soil; the monthly alternatives of0-10cm ofthe surface soils is more obvious.2) Horizontal distribution characteristics of nitrogen in soil: The nitrogen content in theareas of agricultural non-point source pollution is significantly higher than that in farm-freearea. The nitrogen content in survey region is higher, according to the classification standardof nutrientin second national soil survey; it is in serious grade of2.(2) The distribution characteristics of the phosphorus in riparian zone1) Vertical distribution characteristics of phosphorus: In the studied area, the content ofTP in farm-free area has no obvious monthly and vertical variations; but the areas of affectingby agricultural non-point source pollution, the TP content is significantly reduced withincreasing soil depth, the TP content of0-10cm of the surface soils is obviously higher thanthat of the lower soil and vertical distribution of the seasonal variation of total phosphoruscontent is more significant, relatively speaking, the TP content is slightly higher in August,the lowest in September.2) Horizontal distribution characteristics of nitrogen in soilThe TP content of surface soil in agricultural non-point source pollution area is higherthan that in farm-free area. The TP content of whole region is higher than the national averageTP in soil (500mg/kg). Except for the A, there has the little fluctuation with monthlychanges of TP in riparian zone.(3) Potential ecological risk index method is adopted to assess the ecological risk ofriparian zoneThe potential ecological risks of TN and TP are at Grade Ⅱ; the result indicated thatorganic nitrogen pollution of surface soil is mild and it is at the clean level in the riparian zoneof Longmenkou reservoir.(4)The distribution characteristics and affecting factors of the nitrification rate and thenumbers of nitrifying bacteria in surface soil of riparian zone1) The characteristics of average value of nitrification rate in surface soil are mainlyembodied in: August> July> September, however, there is no significant difference between July and August; the horizontal distribution characteristics of nitrification rate and thenumbers of nitrifying bacteria in surface soil are A> O>W.2) In the vertical direction, with increase of soil depth, the numbers of nitrifyingbacteria are decreased significantly. The numbers of nitrifying bacteria of the surface soil arethe largest, and the numbers of nitrifying bacteria are decreased significantly of20cm belowthe soil, and the vertical change is not obvious.The research shows that: the factors that have a significant impact on the nitrificationrate and the numbers of nitrifying bacteria in surface soil of riparian zone are agriculturalnon-point source pollutants, such as NH4+-N,TN, TP, etc.(5)We have divided region into the area of agricultural non-point source pollution andthe area of none polluted depending on the demands of research. The study showed that thecorrelation between nutrients and nitrifying bacteria in the area of agricultural non-pointsource pollution is higher than that in area of none polluted.