Unraveling spatiotemporal dynamics of dissolved organic phosphorus in an urban lake using FT-ICR MS and fluorescence...

With the intensification of phosphorus (P) pollution in natural water bodies, dissolved organic phosphorus (DOP), a key fraction of P, has received increasing attention because of its migration and transformation in aquatic environments. However, urban lakes functioning both as typical lake systems and components of urban ecosystems remain insufficiently studied with respect to the spatiotemporal dynamics of their DOP. In this study, fluorescence spectroscopy combined with Fourier transform ion cyclotron resonance mass spectrometry (FT - ICR MS) was used to elucidate the spatiotemporal variations and underlying factors of DOP compositions in Tangxun Lake, Asia's largest urban lake and a typical P-polluted system. The results showed that during the wet season, DOP in the lake was mainly influenced by external inputs, with an overall mean concentration of 0.08 mg/L. The molecular composition of DOP exhibited higher degrees of unsaturation, aromaticity, and humification, particularly in the outer lake regions affected by urban stormwater runoff and fish pond effluents. In contrast, during the dry season, external inputs decreased markedly, and the overall mean DOP concentration declined to 0.06 mg/L, with domestic sewage becoming the dominant source. The molecular characteristics of DOP shifted toward more aliphatic structures; meanwhile, enhanced water residence time and hydrodynamic isolation further strengthened the relative contributions of endogenous biological production and photochemical processes to DOP in the inner lake regions. Overall, the spatiotemporal patterns of DOP demonstrate a seasonal transition from external dominance to increasing internal contributions, jointly governed by hydrological conditions, source inputs, and biogeochemical processes. The results provide molecular-level insights into the dynamics of DOP in urban lakes and may serve as a scientific reference for P pollution management in similar lake environments.