Synergy of algal particle deposition and bioturbation amplifies the internal phosphorus loading

Increasing algal blooms in lakes promote algal particle aggregation, deposition, and decomposition, driving hypoxia across the sediment-water interface (SWI). This hypoxic environment favors pollution-tolerant benthic organisms, such as Limnodrilus hoffmeisteri. Massively settled algal particles are often disturbed and transported by these benthic organisms, potentially influencing environmental conditions and phosphorus (P) exchange across the SWI. Our study investigates the synergistic effects of algal particle decomposition and bioturbation on internal P loading. The results demonstrate that the burrowing of L. hoffmeisteri during its active phase enhances sediment oxygenation, while sustained algal decomposition exacerbates hypoxia. Ultimately, the anaerobic state across the SWI is synergistically enhanced during algal degradation and benthic faunal decay. Redox-sensitive P (Fe-P) dissolution remains the primary pathway for P release across the SWI. Additionally, the decomposition of organic P (Org-P) over longer timescales and its enrichment in the subsurface sediment also present significant potential for P release. The organic matter derived from algal particle deposition drives P cycling processes, affecting the Fe-S-P cycle by facilitating sulfate reduction processes on the one hand. On the other hand, bioturbation accelerate the mineralization rate of Org-P, promoting P release across the SWI. Our findings suggest that effective management of P in eutrophic lakes should consider bioturbation, particularly in littoral areas with dense algal accumulation.