Evaluation of the fate of wastewater effluent organic matter in receiving water: Effect of sequential photochemical and biological processes

High potential in synergizing the reduction of dissolved organic carbon concentration and carbon dioxide emissions for submerged-vegetation-covered river networks

Various technologies and projects have been explored and developed for the synergetic control of environmental pollution and carbon emissions in aquatic ecosystems. Planting submerged vegetation in shallow waters was also expected to achieve this purpose. However, the magnitude and mechanism of carbon dioxide (CO2) emission affected by submerged vegetation is not clear enough in complex aquatic ecosystems. This study investigated the influences of submerged plants on CO2 emission, ecosystem metabolism features, and microbial community traits based on observations in river networks on the Changjiang River Delta. The results showed that CO2 emission from planted waters accounted for 73% of unplanted waters. Meanwhile, planted waters had higher dissolved organic carbon removal capacity in overlying water and higher potential of carbon sequestration in sediment at the same time. These distinctions between the two habitats were attributed to (1) improved CO2 and bicarbonate consumption in water columns via enhancing photosynthesis and (2) inhibited CO2 production by reconstructing the benthic microbial community. Additional eco-advantages were found in planted sediments, such as a high potential of methane oxidation and xenobiotics biodegradation and a low risk of becoming black and odorous. In brief, submerged vegetation is beneficial in promoting pollution removal and carbon retention synchronously. This study advances our understanding of the feedback between aquatic metabolism and CO2 emission.