Distribution And Species Of Dissolved Phosphorus In Lake Taihu

Dissolved phosphorus (DP), as an important part of phosphorus cycle, has been paid more attention to its importance in phosphorus biogeochemical cycle and leading to eutrophication. DP can be divided into dissolved inorganic phosphorus (SRP) and dissolved organic phosphorus (DOP) in terms of chemical composition or into reduced phosphorus (lower+5valence) and orthophosphate (+5valence) in terms of its oxidation state.These dissolved inorganic phosphorus can readily be uptaken by algae or phytoplankton. In certain conditions, dissolved organic phosphorus also can be translated partly into dissolved inorganic phosphorus, then be utilized by living organisms, which could accelerate the eutrophication. The transform of different phosphorus types may change the bioavailability of phosphorus in eutrophic lake. Since reduced P, such as phosphine (PH3), hypophosphite (H2PO2-,+1) and phosphite (H2PO3-and HPO32-,+3) has been detected in various environments. The existence of reduced P and its effect on the phosphorus cycle and eutrophication has been considered during recent researches.In this thesis, the spatial and temporal variation characteristics of dissolved phosphorus and its correlation with chlorophyll a (Chl a) was studied during the whole year of2010in Lake Taihu. The main factors affecting Chl a were discussed simultaneous. In addition, a preliminary study on reduced phosphorus and organic phosphorus was carried out to assess the differences in determining the dissolved phosphorus in water environment with conventional colorimetric method and ICP-AES method. Meanwhile the existence of dissolved organic phosphorus in the water of Lake Taihu was assessed. The main results are as follows:1. The content of phosphorus fractions (total phosphorus (TP), total dissolved phosphorus (TSP), dissolved reactive phosphorus (SRP)) in coastal N1site is higher than in N2site away the bank in Lake Taihu water, while no obvious difference could be found between the bottom water and the surface water. From the whole area analysis, the content of phosphorus fractions of north area (N) of is obviously higher than southern area (S) in Lake Taihu and N5site is highest. The correlation analysis shows that:TSP is positive correlated with TP (r=0.437**, n=192). SRP is also positive correlated with TSP (r=0.657**, n=191). Also, daily variation analysis shows that:change of TP and Chl a of N1site and N2site is obvious. The correlation analysis bewteen different phosphorus fractions and Chl a showed that:TP, TSP, SRP and temperature are significantly positive correlated with Chl a with the correlation coefficient of0.333**,0.313**,0.284**(p<0.01, n=184), respectively.2. The content of TSP from the sediment interstitial water is higher in site N1than in site N2. The change of the TSP from sediment interstitial water at site N1and site N3in depth as follows:the TSP of N1site from sediment with surface layer(0.050mg·L-1)> the TSP of interlayer (0.047mg·L-1)> the TSP of bottom (0.040mg·L-1), the TSP of point N3from sediment with surface layer (0.038mg·L-1)> the TSP of interlayer (0.037mg·L-1)> the TSP of bottom (0.028mg·L-1).3. The determination of the R2of standard curve for the phosphate, hypophosphite orthophosphate and the mixture of all the three P species by ICP-AES is0.999、0.993、0.999and0.984respectively, and the recovery rate is81.0%、81.4%.92.3%and102.9%respectively.4. The differences of TSP and SRP determined by by ICP and colorimetric method are as follows:TSP(ICP method)=TSP(colorimetric method)> SRP(ICP method)> SRP(colorimetric method), the recovery rates obtained by ICP method of glyphosate, phytic acid and the mixture of the two are97.1±3.8、88.8±2.4and92.9±3.1respectively. The removals of C18column are higher than99%、96%and96%respectively. The dissolved organic phorphorus (DOP) concentration is estimated by the difference before and after filtration with C18column. The DOP in Taihu water accounts for8.30%～74.9%of dissolved phosphorus.