Investigation into the Dynamic Coupling Mechanisms of Labile Phosphorus, Iron, and Sulfur in Lakeside Wetland Sediments

The release of phosphorus (P) from littoral wetland sediments drives eutrophication, with iron (Fe) and sulfur (S) cycles playing key regulatory roles. This study investigated the Tongyang River corridor wetland (Lake Chaohu) in China to elucidate P–Fe–S coupling mechanisms. High-resolution two-dimensional (2D) Diffusive Gradients in Thin-Films (DGT), P-fractionation, and microbial sequencing were employed during wet and dry periods. Results indicated significant total phosphorus (TP) spatial heterogeneity and seasonal available phosphorus (AP) variation. A robust spatial co-variance between DGT-Fe and DGT-P (r > 0.95) reinforces the iron-redox paradigm. However, 2D mapping revealed discretized sub-millimeter “hotspots,” demonstrating that iron (oxyhydr)oxide reductive dissolution is governed by micro-scale niches rather than uniform processes. Microbial analysis further identified summer diversity and Chloroflexi enrichment as primary biological drivers of P mobilization. Specifically, hydrological fluctuations dictate the iron-redox cycle, with wet-period microbial activation serving as the engine for internal P release. These findings suggest that regulating sediment redox conditions across hydrological stages is essential for mitigating wetland eutrophication.