Distribution of organic phosphorus species in sediment profiles of shallow lakes and its effect on photo-release of phosphate during sediment resuspension

Abstract

In this work, the distribution of organic phosphorus (P_o) species in sediment profiles of five shallow lakes was analyzed and its effect on the photo-release of dissolved phosphate (P_i) was investigated during sediment resuspension under simulated sunlight irradiation. The results show that P_o was highly enriched in the surface sediment and gradually decreased as sediment depths increased: 33.10 ± 2.55-96.71 ± 7.60 mg/kg, 33.55 ± 2.34-142.86 ± 5.73 mg/kg, 57.50 ± 3.46-149.68 ± 7.67 mg/kg, 55.18 ± 4.67-168.73 ± 8.31 mg/kg, 98.75 ± 7.56-275.74 ± 10.70 mg/kg for Lake Hou, Lake Tuan, Lake Tangling, Lake Guozheng and Lake Miao, respectively. The photo-release amount of dissolved P_i in the resuspension composed of surface sediments was also higher than that of deep sediment during sediment resuspension under the simulated sunlight irradiation for 9 h. The potential reasons for these results are: (1) difference in morphology and composition of sediments at different depths: the mean particle size of sediment decreased first and then increased as sediment depths increased; (2) difference in composition of P_o species with depths in the sediment profiles: more photolytic P_o species existed in surface sediments confirmed by sequential extraction and ³¹P NMR analysis; and (3) more OH production in the resuspension composed of surface sediment under simulated sunlight irradiation, which directly influence the photo-release of dissolved P_i from photodegradation of organic phosphorus. All of these results indicate that the distribution of organic phosphorus species in the sediment profiles plays an important role in P cycle and its photodegradation during sediment resuspension may be one of the potential pathways for phosphate supplement in shallow lakes.