Sedimentary phosphorus form distribution and cycling in the littoral subzones of a eutrophic lake

Algae which bloom in open water and accumulate in the littoral zones may affect the biogeochemical cycle of phosphorus in eutrophic lakes. To determine such effects, a part of the lakeshore with little allochthonous nutrient input in Taihu Lake, China was selected for this field study. Distinct differences in sedimentary P forms were found among the different littoral subzones. The surface sedimentary total phosphorus (TP) content was 655 mg/kg in the eulittoral subzone and 631 to 641 mg/kg in the infralittoral subzone. Both were much higher than that in the profundal zone (410 mg/kg). Calcium-bound P (Ca-P) was significantly correlated to exchangeable P (Ex-P), and they both had the highest contents in the infralittoral subzone and the lowest in the profundal zone. The aluminum- and iron-bound P (Al-P, Fe-P) contents decreased from land to water along the ecotone section. Lower Fe/P ratios and higher Al-P/Fe-P ratios appeared in the infralittoral subzone, as compared with the profundal zone. This suggested that the accumulated algae could lead to a great deposit of P in the littoral zones. However, the active sedimentary P form transformation in the littoral zones would also result in a partial release of the accumulated P to the overlying water.