Nutrient and organic matter dynamics in a macrotidal estuary impacted by human activities, the Nanliu Estuary, southern China

Anthropogenic nutrients, mainly from agriculture but also from aquaculture, cause eutrophication. Negative effects include ecosystem degradation via oxygen depletion following organic matter decomposition. Mangrove forests are potential nutrient filters. This study investigates land-derived material inputs into coastal waters of southern China and assesses the effect of mangroves. Nanliu River and Lianzhou Bay comprise multiple human impacts. Transformations and fates of nutrients and organic matter were investigated by biogeochemical field and laboratory methods. The role of mangroves was assessed by field measurements, incubation experiments, and model calculations. Results show that land-use in river catchments dominantly contributes to eutrophication in coastal waters. This is a regional rather than local conservation issue. Natural factors do not sufficiently reduce nutrients, making improved nutrient management the only option preventing eutrophication.