Research On Bioavailability Of Phosphorus In Surficial Sediments From Inflow Rivers Of Lake Taihu

Taihu drainage basin is one of the most important developed areas in China. With rapid industrial and agricultural development and being short of environment protection and measures of preventing the pollution in those areas, the water quality of rivers and Lake Taihu has become increasingly worse, especially the eutrophication of water body, which directly influences persistence of economic and social development. In this dissertation, the samples of surface sediments were collected in rivers that located around North, Middle and South of Lake Taihu. Then, nutrient elements and phosphorus species was determined, and the characters of rivers and lake were compared to discuss their differences and causes.The contents of main nutrient elements in sediments were detected and calculated in the beginning of this dissertation. The characteristics of nutriments were analyzed in region, river flow and pollution source. The results was as follows: TP,TN and TOM of sediments in Wuxi, Yingxing rivers were higher than in Changxing and Huzhou, and their contents in sediments were similar to the regional distribution. It was considered to be due to the different environmental condition and the industrial and agricultural structure. The rivers entering into Lake Taihu mostly have been polluted by organic nitrogen, Zhuhugang River and Caoqiao River showed more organic carbon, Yingcungang River was a less polluted river in this area. TP were higher in sediments of rivers whose main pollution source was the urban sewage, because materials contained phosphorus were used in daily life.Viewing from phosphorus species analysis, the distribution of chief bioavailable forms and species were in according with that of nutriments. Algal available phosphorus, NaHCO₃ extracted P, and Fe-P in North and Middle were higher than South, Algal available phosphorus took a smallest proportion to TP in sediments of rivers in Huzhou, the percentage of Fe-P from Middle and Ca-P in sediments from North were higher, this result is largely related to the source of pollution. During the rivers flowing into the lake, Fe-P and bioavailable phosphorus in most samples decrease at certain extent, except a sample from South because of its geographical circumstance. It was showed that Fe-P, bioavaliable phosphorus and TP had high coefficients in South and North area, acid extracted organic phosphorus was also closely associated with the bioavaliable phosphorus. The high coefficients between Fe-P and Fe, Ca-P and Ca in North suggest the relationship between metals and phosphorus fractions.Comparing with the contents of sediments in lake, the residual phosphorus in eutrophic rivers and Fe-P in mesotrophic rivers were higher, and algal available phosphorus accounted for a larger proportion to TP in rivers. The correlative coefficients between BAP and TP were different in sediments from rivers, resulting from the unstable factors in different sections. The BAP and TP in Middle did not show a good relation, resultingly the diversity of pollution source. Availability of total dissolved phosphorus released by sediments in rivers is smaller than in the lake.Generally, Algal available phosphorus and Fe-P play an important part in the river and eutrophication. Of the same trophic level for sediments, the probability of algal blooms in lake is bigger. Sediments in lake are liable to release in acid condition, while they are in alkaline condition in rivers.This research can be better to assess and evaluate cause of trophication in rivers and lakes, would show the important significance in taking appropriate measure to control and prevention of eutrophication in Lake Taihu.