Soil erosion and losses of nitrogen and phosphorus by using ¹³⁷Cs tracer in the areas around Miyun reservoir

Soil erosion，losses of N and P and the relations between them in Miyun reservoir neighborhood were researched by using ¹³⁷Cs tracer. The results showed that: the distribution of ¹³⁷Cs in the surface soils (0～20 cm) basically accorded with the changes of topography and physiognomy. The contents of ¹³⁷Cs on the top of hillside were lower than those in the middle and low hillside. But the distribution of ¹³⁷Cs contents was contrary on a flat slope in the mountaintop or on a sharp slope in the lowland. Based on the data of the researches, it proved that the region belongs to the slight and medium degree of erosion mainly, but erosion in some regions' conditions was serious. Different landscapes and land use patterns affected the distributions of N and P in soil greatly. The contents of the organic matter, total N, hydrolyzed N were higher in the soil than those under bush. These indications in the woodland took the second place, which accorded with the distribution of ¹³⁷Cs contents in the region. The contents of total and available P in the farmland were the highest in soil under different land utilizations, which proved that the irrational humanity activities increased the soil erosion degree and losses of N and P seriously. The N and P contents in the upper reaches of reservoir areas were lower than those in the reservoir neighborhood wholly. The mathematic models were simulated among ¹³⁷Cs (²¹⁰Pb) contents and the total N, total P, hydrolyzed N, available P of each sampling region respectively, which were described by cubic curve. The mathematic model can predict and forecast the change trends of the total P, available N and contents of P in each sampling region, simplify procedures of chemical analysis and extend application of nuclear tracer technique.