Economic and ecological impacts riverine nutrient inputs in Bohai rim coastal zone, China

Nutrient enrichment in coastal ecosystems not only degrades water quality but also imposes substantial economic burdens on regional fisheries, tourism, and coastal infrastructure. This study investigates the riverine nutrient inputs and seasonal eutrophication dynamics in the Bohai Rim coastal zone, one of China's most industrially active and economically vital regions. Field observations and secondary datasets from 2022 to 2023 were analyzed for dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), chlorophyll-a, and dissolved oxygen across river mouths and adjacent coastal waters during wet (July) and dry (January) seasons. Results reveal that DIN concentrations consistently exceeded China's Class III seawater standard, with nitrogen loads dominated by agricultural runoff and industrial effluents. Seasonal eutrophication patterns were strongly linked to economic activity: peak nitrogen fluxes in the dry season coincided with higher energy consumption and fertilizer demand. Dissolved oxygen levels frequently dropped below 4 mg L^-1 near the Haihe and Liaohe river estuaries, indicating localized hypoxia risk. Econometric estimation suggests that a 10 % reduction in DIN load could yield annual welfare benefits of approximately 1.8 billion CNY, mainly through restored fishery productivity and reduced water treatment costs. Findings emphasize that nutrient management is not merely an ecological issue but an economic imperative-particularly under China's "Beautiful Bay" and "Dual Carbon" policy frameworks. Strengthened river basin governance, nitrogen-use efficiency improvements, and green agricultural transitions are recommended to align coastal water quality protection with sustainable economic development.