The Phosphorus Forms In Surface Sediments And Their Relation To The Eutrophication Of Urban Lakes In Guangdong Province, South China

Eutrophication of urban lakes is becoming a major water pollution problem with consequence of development of social economy and urbanization. The internal release of phosphorus from sediment plays an important role in maintaining eutrophic status in urban lakes. The knowledge of internal loading, phosphorus forms, and potential release and bio-availability of different phosphorus species will therefore be of significance for further study of mechanisms of eutrophication. In this study, the phosphorus fractionation and bio-availability in the surface sediments of thirteen urban lakes in Guangdong Province, South China were investigated by sequential chemical extraction method of Psenner with slightly modifications by Huper. Moreover, the relation between phosphorus forms and internal release of phosphorus and lake eutrophication were discussed.The results showed that among the thirteen urban lakes in Guangdong Pronvince, South China, 61.67% of the lakes were meso-eutrophic, 16.67% eutrohic, 13.89% hyper-eutrophic. Trohic status of Panlong tianhu Lake and Liuhuahu Lake were worst. Water content (WC) and loss on ignition (LOI) in surface sediments were 72.12%, 12.38%, respectively. Total sedimentary phosphorus ranged from 386.21 mg/kg to 4365.17 mg/kg. The concentration of different phosphorus forms followed the order: metal oxide bound P (NaOH-P) >Organic P (Org-P)> calcium bound P (HCl-P) >iron associated P (BD-P)>loosely sorbed P (NH₄Cl-P). The total sedimentary phosphorus consisted mainly of NaOH-P, Org-P and HCl-P. The bio-available phosphorus contents were ranging from 132.82 mg/kg to 2821.87 mg/kg. The potential phosphorus release from sediments to the overlying water and the availability of phosphorus for algal uptake in sediments of urban lakes are high.The transformation of phosphorus forms in lake sediments has been recognized as a critical factor for controlling the release of sedimentary phosphorus. The total sedimentary phosphorus was highly correlated to phosphorus forms in the surface sediments of urban lakes in Guangdong Province. The higher bio-availabile phosphorus content was exhibited in sediment where the higher total sedimentary phosphorus was also found. NH₄Cl-P in the sediments was significantly correlated to BD-P while NaOH-P was correlated to Org-P. The higher NH₄Cl-P and BD-P contents appeared in the sediments of hyper-eutrophic and meco-eutrophic lakes while the lower NH₄Cl-P and BD-P contents were found in oligotrophic lakes. The concentration of loosely sorbed P was significantly correlated to total dissolved phosphorus and soluble reactive phosphorus in water body and the Chla was positively correlated to NH₄Cl-P and BD-P, which indicated NH₄Cl-P and BD-P played an important role in lake eutrphication precess. After the transformation of phosphorus forms, sedimentary phosphorus was release from interstitial water to overlaying water with the form of NH₄Cl-P which could be used by phytoplantonic algae in lakes.