Reconstructing a 300-year history of phosphorus cycle in west Chaohu Lake, China

Anthropogenic activities could significantly increase nutrients loading, especially phosphorus (P), into aquatic systems, leading to eutrophication and disturbance of ecosystems. Detailed investigation of P cycling and its controlling factors in modern lakes could help understand mechanisms behind eutrophication, thus provide suggestions for future environmental management. Here, we investigate evolution history of P and iron (Fe) cycling over the last ∼300 years in west Chaohu Lake, a typical eutrophic lake in East China. The combination of ²¹⁰Pb-¹³⁷Cs dating and elemental analysis demonstrates drastic escalation of P input and organic carbon burial since 1960s, coincided with the rapid growth of human population near this region. P phase partitioning data indicate that Fe-bound P (P_Fe) is the predominant P pool of sediments in Chaohu Lake, which also regulates the evolving trend of reactive P (P_reac). Moreover, the highest fraction of P_Fe is consistent with observations via P K-edge X-ray absorption near edge structure (P XANES). In addition, Fe speciation results show a principal contribution of Fe (hydr)oxides (Fe_ox) and negligible presence of pyrite, suggesting a generally oxygenated depositional environment, where P could be preferentially sequestrated in sediments in association with Fe oxide minerals. Relatively high molar organic carbon/organic P (C_org/P_org) but low C_org/P_reac ratios also support limited recycling of P_reac in west Chaohu Lake. This study reveals that human activities play an important role in leading to the eutrophication of Chaohu Lake. Future environmental management could utilize the coupling of P and Fe oxides to remove P from water column.