Eutrophication leads to production and accumulation of recalcitrant dissolved organic matter in an urban-agricultural wetland

Urban Farm DB summary

A two-year monthly investigation of water quality and dissolved organic matter (DOM) optical properties (absorbance and fluorescence) in a eutrophic, urban-agricultural wetland. Dissolved organic carbon (DOC) increased from spring to summer in both years and correlated significantly with trophic level index (TLI), total nitrogen, COD, and chlorophyll a, indicating that eutrophication added to the organic carbon pool through both sewage inputs and algal production. Loss of protein-like component C3, together with a significant negative correlation between microbial humic-like component C2 and dissolved oxygen, suggested that microbial deoxygenation converted bio-labile DOM into recalcitrant DOM (RDOM) during summer. In winter, lower temperatures limited microbial transformation, and continuous sewage inputs increased protein-like C3, while RDOM removal via particle adsorption-sedimentation and photodegradation exceeded its accumulation. Machine learning analysis found microbial transformation explained 39.1-41.2% of variation in humic-like components, more than terrestrial inputs, sewage sources, and algal production combined (2.1-31.6%), identifying microbial transformation as the dominant driver of wetland RDOM formation. Eutrophication is stated to have negative effects on wetland ecosystems, though the study also notes that, if sewage and algae are effectively managed, the same process could enhance carbon sequestration.