Possible factors controlling the distribution of phosphorus in the sediment of Longgan Lake, middle reach of Yangtze River, China

Major elements [aluminum (Al), calcium (Ca), iron (Fe), manganese (Mn)] and phosphorus (P) as well as its fractions in the sediment of Longgan Lake, a shallow lake in the middle reach of Yangtze River, China, were investigated to assess the effect of factors such as the grain size, organic matter (OM), and redox conditions on the behavior of P. Meanwhile, the anthropogenic impact on the P accumulation during the last century was distinguished from the natural one. The grain size, redox conditions, and major elements had close relationship with inorganic P, while there was a significant correlation between organic P and OM. Different relationships between Ca-bound P and Ca in the sediment indicated the anthropogenic Ca source besides the natural one. The marked anthropogenic impact on the lake was detected since 1950 ad, while it significantly intensified since 1970 ad. This change corresponded well to the history of the reclamation, constructions of dams, and reservoirs, the utilization of phosphate fertilizers, and the utilization of lime to kill off schistosomes. The P flux was applied to distinguish the anthropogenic versus natural P accumulation. Before 1950 ad, the natural P inputs by soil erosion, runoff, and so on, were the main source of P in the sediment, while thereafter the increasing human activity in the catchment resulted in more extra P or so-called anthropogenic P accumulation.