Characteristics of bioavailable phosphorus in sediment and potential environmental risks in Poyang Lake: The largest freshwater lake in China

摘要

Distinguishing sediment phosphorus (P) species and bioavailability is conducive to recognizing the effects of hydrological variation and contamination loading. We examined the P fractions and bioavailability in four sediment cores (N4, C1, R1 and R2) to determine the long-term effects of hydrological variation and contamination loading in Poyang Lake from 1972-2012. The results showed that the total phosphorus (TP) concentrations occurred in the following order, N4 C1 R2 R1, with the highest increment in R2. Bioavailable phosphorus (BAP) accounted for 80-98% of TP, including substantial fractions of iron/aluminum-bound P (Fe/Al-P, 39%) and organic phosphorus (P-o, 40%). Acute hydrological variability reduced the concentrations of BAP and TP from the 1990s to 2000s (trough at 2002), owing to the input of coarser particles and weak absorption during catastrophic flooding (cores N4, C1). Subsequently, water level fluctuation induced by Three Gorges Dam (TGD) contributed to Fe/Al-P and most proportion of P-o remained and accumulated in the uppermost layer. Additionally, TP and BAP, especially Fe/Al-P and P-o, performed positively and were correlated with P fluvial contamination loading at the river confluences (cores R1, R2). The sediment Fe/Al-P ratio abruptly increased after 2000, originating from continuous intensification of industrial and domestic effluents. Nonlabile P-o (humic acid P-o, Hum-P-o and Residual P-o, Res-P-o) accounted for 57% of P-o and continuously increased since 1970; these substances originated from P fertilizer usage and livestock excretion. Moreover, to quantify hydrological variation, the increments of BAP were assessed at 2034.89 tons, accounting for 10% of the external P. The BAP burial flux was estimated at 251.66 x 10(-2) t.km(-2).y(-1) in R2, and fluvial contamination loading was highest. In brief, this study emphasized how hydrological variability and anthropogenic contamination loading affect the BAP in sediment, and highlighted the Fe/Al-P and P-o are the valuable objects for avoiding lake eutrophication.