Research Transportation Of Nitrogen And Phosphorus Under Vegetation Buffer Strips

Non point source pollutions, such as nitrogen and phosphorus, are the main factors contributed to the eutrophication. Many scientists have indicated that the vegetation buffer zone is an effective way to reduce non point source pollution. Vegetation buffer strips is the transition zone between the sloping land and the water at the bottom, through a series of physical, chemical and biochemical process for nitrogen, phosphorus retention and transformation. This paper focused on the vegetation buffer zone, which is a typical bay of Danjiangkou Reservoir. According to the simulating experiment in laboratory, we compared the retention effects of vegetation buffer zone with different land use types on non point source pollutions, including nitrogen and phosphorus. The main results as followed:(1) Nitrogen mineralization characteristics of typical plant species form vegetative buffer strip. An incubation method was used to identify the relationship between N mineralization and initial chemical composition of17kinds plant residues during a100days in a flood plant soil at25℃and50%water holding capacity. The plant residues had a wide range of N, cellulose, hemicelluloses, and lignin concentrations and C:N ratios. The N content of the residue was negatively associated with the contents of cellulose, hemicellulose and lignin. The content of total N was negatively related with the contents of hemicellulose (P<0.05) and lignin (P<0.01). Lignin, lignin: total N ration were positively associated with each other significantly. Net N mineralization were ranged from-1.14mg·kg-1to-3.16mg·kg-1for all treatments. Torilis scabra (Thunb.) DC. and Abutilon theophrasti Medic. showed the immobilization of nitrogen. Net N mineralization was negatively associated with the cellulose content in the initial chemical composition. The N immobilization occurred during the whole incubation period for all17kinds of plant residues. However, the immobilization were different among different plants.(2) The vertical transport of nitrate under different land uses. We studied the vertical transport rules of nitrate in soils of different land use types using simulated undisturbed soil column. There were spatial differences between the breakthrough curves (BTC) of nitrate transported vertically. BTC of five types of land use showed the same trends. The peak values of BTC decreased in the order: flood plain> abandon farmland> sesame land> orangery> conservation forest. As soil depth increased, the peak values of BTC decreased, but the total time of nitrate transported vertically increased. The peak values of BTC were affected by the content of clay. As clay content increased, the peak value of BTC decreased, and the total time of nitrate transported vertically increased. Organic matter and the total time of nitrate transported vertically were positively related to each other (p1.01).(3) The horizontal transport of nitrate under different land uses. The horizontal transport rules of nitrate were simulated using disturbed soil column of different land use types. In the horizontal transportation process of nitrate, there was a power function between the transport velocity and the distance of the tracer source. The transportation velocity decreased with the increase in distance. In the horizontal transportation process of nitrate, the concentration of nitrate in horizontal transport decreased as the soil moisture content increased and there was a power function between them. The nitrate concentration changes a little as soil water content increased from0.3cm3·cm-3to saturated. However, the nitrate concentration changes greatly when the water content was lower than0.3cm3·cm-3.(4) The soil sample was taken from water-level-fluctuating zone to examine the effect of flooding-drying condition on the isothermal adsorption of the P from the soil samples, and to compare the adsorption-desorption of phosphorus of flooded-dried soil sample with original soil sample. After the treatment of flooding-drying, amorphous iron/aluminum oxide and free iron/aluminum content increased, whereas soil acidity and available phosphorus content decreased. Flooding-drying treatment had significant influence on the adsorption properties. The adsorption capacity of P increased from263.55mg·kg-1to297.51mg·kg-1, and the EPC0increased from3.37mg·L-1to4.06mg·L-1. After flooding-drying treatment, the peak value of the desorption capacity of P increased from263.55mg·kg-1to297.51mg·kg-1, and EPC0increased from3.37mg·L-1to4.06m·-L-1, whereas the desorption capacity of P increased from222.36mg·kg-1to239.72mg·kg-1, but the desorption ratio of P was decreased from84%to81%.(5) In order to study the forms and spatial distributions of phosphorus, soil samples from0cm-5cm,5cm-15cm,15cm-25cm soil layer in different land use types in the typical Bay. The content of total phosphorus varied from314.11mg·kg-1to537.56mg·kg-1. Soil total phosphorus content decreased in the order: sesame land> orangery> rape filed> flood plain. Calcium P and residual P are the main form of P, which account for31.54%-71.76%and21.43%-58.01%of soil total P under different land uses, respectively. For all land uses, labile P averaged less then0.5%of total P, Fe-Al P concentration in this fraction averaged less then1%of the total P. For all land uses, labile P was less then0.5%of total P, whereas the concentration Fe-A1P was about1%of the total P.