Study On Eutrophication Of Wei River And Loss Of Phosphorus From Soil To Water

In this thesis, water samples of Wei river were determined by Heckrath & Brookes methods, who regarded that phosphorus(P) could be fractioned by total phosphorus (TP), particulate phosphorus(PP), total dissolved phosphorus(TDP), dissolved organic phosphorus (DOP) and Molybdate-reactive phosphorus(MRP), prediction indexes of P loss from soil to water, which were analyzed by"change-point"and PSD methods, who regarded the relationship between CaCl2-P/water-P (extracted P with 0.01 mol·L-1 CaCl2 or H2O) and Olsen-P in soil as indexes, and P release with different pH in sediments of Wei river, studied 11 Wei river water samples collected from May, 2004 to May, 2005, of different P fractions and percentage of TP, pH and PM to relate eutrophication in Wei river, studied soil of north site of Wei river and Lou soil in Northwest A & F University experimental site, Shaanxi, studied contents of P release and effect on eutrophication. The data were analyzed to assess water body of Wei river, to find proper indexes to predict P loss from soil to water and to measure the contents of P release in sediments of Wei river. Results showed as follows: 1. The TP concentrations of weihe are 0.18~1.47 mg P kg-1, the mean is 0.63 mg P kg-1, which exceeds 0.02 mg·L-1. The percentage of PP/TP and DOP/TP are more than MRP/TP, which PP is 0.056~1.28 mg kg-1, the mean is 0.37 mg kg-1and PP/TP is 10.92%~87.34%, 0.033~0.33 mg kg-1, the mean is 0.15 mg kg-1 of DOP, 2.25%~62.64% of DOP/TP, 0.017%~0.39 mg kg-1, the mean is 0.12 mg kg-1of MRP, 3.17%~60.75% of MRP/TP. 2. There are three prediction indexes to assess P loss in Lou soil. (I) TP. If TP of the soils exceed 1.92 g·kg-1, P will leach from soil to water. (II) Phosphate saturation degree (PSD). PSD is a useful parameter to estimate fixation ability of soil of P. In the results, PSD of the soil changes from 9.7% to 41.46% where only the treatments of no fertilizer and chemical fertilizer are lower than 25%, which is regarded sensitive index of P leaching in soil. That means, except for the treatments of no fertilizer and chemical fertilizer, P in the soils of other treatments will leach to water. (III) Change-point. When contents of Olsen-P of the soils are more than 23mg·kg-1, CaCl2-P reaches a large content suddenly. This value is regarded as change-point. That means, if Olsen-P contents of the soils are lower than 23mg·kg-1, P in soil will not or will hardly leach from soil to water. On the contrary, if Olsen-P of the soils exceeds 23 mg·kg-1, P in the soils will leach from soil to water. 3. When pH of sediments of Wei river is 1, the contents of release of P reaches a peak, 566.79mg·kg –1(mean), whose value covers from 462.26 to 647.30 mg·kg –1. When pH is 6, the contents of P release are 4.10~5.59 mg·kg-1, whose mean is 5.08 mg·kg-1. That's to say, with the increasing of pH of sediments, the contents of P release decrease sharply. And if pH reaches about 7, the contents of P release will be minimized.