Phosphorus cycling mechanisms in lake sediments affected by algal biomass

Algal blooms, intensified by eutrophication, pose persistent ecological challenges in aquatic systems. This study investigated the transformation of phosphorus (P) in lake surface sediments under anaerobic conditions using microcosms amended with varying amounts of Lyngbya, a cyanobacterium, to evaluate the impact of algal biomass. Phosphorus pools were monitored via sequential extraction and microbial communities were characterized through 16S rRNA gene sequencing. Results showed that higher algal biomass loadings markedly enhanced P solubilization and mineralization, leading to a significant increase in total extractable P. Sequential extraction further indicated a shift from mineral-bound P to more labile forms over time, particularly in treatments with elevated biomass loadings. Solution ³¹P NMR confirmed the dominance of orthophosphate and a decline in monoester-P, suggesting active microbial turnover of organic P. Sediment chemistry analyses revealed an increase in Fe(II) and a shift toward more reducing conditions, implying reductive dissolution of Fe minerals that may contribute to subsequent release of Fe-bound P. Microbial community analysis highlighted Firmicutes dominance after long-term sediment incubation with high algal biomass input, along with considerable enrichment of anaerobic fermenters and Fe(III) reducers within this phylum. Furthermore, predictive microbial metabolic function profiling recognized possible pathway shifts due to high biomass loading, promoting organic matter fermentation and enhancing P solubilization. Collectively, these findings underscore the role of algal detritus in reshaping sedimentary P dynamics and offer new insights into internal P cycling mechanisms that may guide eutrophication management yielding long lasting effects.