Spatial and seasonal variations of particulate phosphorus (PP) in a large shallow, eutrophic Lake Taihu with different ecotypes (including a phytoplankton-dominated zone, lake center zone, estuary zone and macrophyte-dominated zone) were investigated. The results showed that particulate organic phosphorus (POP) was the dominant form of PP (>88.0%). The concentration of POP showed higher levels in the bloom-sensitive northwestern zone (phytoplankton-dominated zone and estuary zone) during warm seasons, phytoplankton blooms and input of exogenous particulate matter were the main sources of POP in the lake water. Based on ³¹P nuclear magnetic resonance (³¹P NMR) analysis, orthophosphate (Ortho-P) was the dominant molecular species of PP and positively correlated with soluble reactive phosphorus (SRP) (p < 0.01). This suggested that the release of Ortho-P from suspended particulate matter (SPM) was the main source of SRP in the lake water. Pyrophosphate (Pyro-P), which is regarded as a highly labile species of P compounds, represented a large fraction of PP, and its significant positive correlations with chlorophyll a (Chl a), indicated that the concentration of Pyro-P could be used as an important indicator for the degree of eutrophication of Lake Taihu. These results proved that PP in lake water was a significant factor supporting lake eutrophication and must be controlled.

Organic matter was increased due to the input of plant litter, resulting in changes in the physicochemical properties and enhancement of greenhouse gas (GHG) emissions in water bodies. There are few reports on effects of decomposition of aquatic plants on GHGs emissions. This study investigated the effects of the degradation of two aquatic plants, Potamogeton crispus and Typha orientalis Presl, upon release of CO₂ and CH₄ at the sediment–water interface. During early decomposition, the release of CO₂ and CH₄ at the sediment–water interface was increased by the degradation of the two aquatic plants, and release flux of CO₂ and CH₄ were increased rapidly at first and then decreased. Due to the differences in properties of C, lignin, cellulose and other components of the plants, the Potamogeton crispus group obtained higher abundance of genes relevant to CO₂ and CH₄ metabolism, which leads to the increase of CO₂ and CH₄ emissions compared with that of the Typha orientalis Presl. In addition, dissolved oxygen and pH were decreased due to the decomposition of organic matter in the plant residues at the sediment–water interface, resulting in growth of anaerobic microorganisms. The increase of the relative abundance of anaerobic microorganisms promoted the decomposition of organic matter in the sediment and the enhancement of cell respiration, promoting the release of CH₄ and CO₂ during the decomposition of aquatic plants.