The characteristic and environmental pollution records of phosphorus species in different trophic regions of Taihu Lake, China

Total organic carbon (TOC), Total nitrogen (TN) and the phosphorus species concentrations of sediment cores taken from Zhushan Bay, Meiliang Bay, and East Taihu Lake regions in Taihu Lake, a large shallow lake in China, were determined. Experimental results showed a conspicuous eutrophication trend in the northern area of Taihu Lake. Inorganic P was found to be the main phosphorus form. Fe-bound P accounted for the largest proportion of Inorganic P in Meiliang Bay, an alga-type lake region. In East Taihu Lake, a macrophytic lake region, Ca-bound P was found in higher proportions than in other lake regions, with Organic P present in similarly large proportions. With respect to Taihu Lake sediment cores, the date at approximately 20 cm layer depth was roughly identified as 1950s, while upper 5 cm layers corresponded to the turn of the century. The drastic increase in phosphorus species concentration except for Ca-bound P was indicative of the large quantities of effluent discharge into Zhushan Bay owing to the increased industrial and agricultural production from the 1950s onwards. TN, Inorganic P, Organic P, and total phosphorus (TP) concentrations increased by over 2, 2.5, 2 and 2.5-fold, respectively, over the past five decades. A large proportion of Organic P accounted for TP, and high C/N ratios indicated that East Taihu Lake can be properly classified as an oligotrophic lake.