Eutrophication Heterogeneously Enhances Organic Matter and Phosphorus Exchanges among Dissolved, Particulate, and Sedimentary Phases in a Large Shallow Lake

Dissolved, particulate, and sedimentary phases are essential substrates in lake systems. However, few studies have explicitly examined their interactions in response to eutrophication. Here, we characterized organic matter (OM) and phosphorus (P) pools in these subsystems of Lake Taihu and analyzed their variations with a gradient from mesotrophic to hypertrophic states. We employed a "3-subsystem" conceptual model with statistical algorithms to estimate the interactions. Concentrations of dissolved and particulate OM and P increased with eutrophication, while only the surface OM and P pools in sediments exhibited variability with the trophic state. Protein- and humic-like substances in the dissolved and particulate OM pools became more prominent at higher trophic states. High mobile P and low inert P were observed in the suspended particles and surface sediments of eutrophic regions. As the trophic state increased, interactions between dissolved and particulate subsystems and between particulate and sedimentary subsystems strengthened, whereas few changes occurred in the interaction between dissolved and sedimentary subsystems. This suggests that particle release and sediment resuspension are more significant pathways for internal nutrient loading in eutrophic regions. These findings provide a comprehensive understanding of how eutrophication affects lake subsystems and their interactions, offering potential ecological restoration references for eutrophic shallow lakes.