Spatial distribution of phosphorus fractions in sediment and the potential mobility of phosphorus in Dianchi Lake

Abstract

In order to understand phosphorus (P) cycling and mobility in the sediment of Dianchi Lake, the spatial distribution of P fractions in surface sediment has been investigated through sequential extraction. The relationship of P fractions with the P concentrations in the overlying water, mobile P contents, and organic matters was also analyzed to determine the potential mobility and the retention effect of P in surface sediments from Dianchi Lake. Results showed that (1) the average total amount of P in the surface sediments of Dianchi Lake was 2,050.31 ± 620.27 mg kg−1. The pollution levels in Caohai and in the south of Waihai were significantly higher than those in other parts of the lake. The P fractions were ranked as follows: HCl-P > NaOH-RP > Res-P > BD-P > NaOH-NRP > NH4Cl-P. Among these P fractions, NaOH-RP content (1,285.23 ± 1,110.51 mg kg−1) was highest in Caohai sediments, whereas HCl-P (925.64 ± 513.58 mg kg−1) was dominant in Waihai. (2) The average content of mobile P was 242.31 ± 98.11 mg kg−1 in sediments; this value accounted for 13.54 % of total extractable P. Nonetheless, this content decreased from north to south in the lake. The average immobile P content was 1,547.22 ± 593.05 mg kg−1. This value constituted 86.46 % of total extractable P. The trend of immobile P content was the opposite to that of mobile P content. (3) The P content and retention rate (66.93 %) of sediments were generally high. However, this rate was significantly lower in Caohai (13.80 %) than in Waihai (72.61 %). This result indicates that the risk of releasing the P in Caohai sediments is considerably higher than that in Waihai sediments.