Ecological environmental characterization and relationship exploration between riverine input and coastal waters of Dalian, China

Abstract

Anthropogenic pressure and climate change have severely impacted coastal ecosystems. Coastal environmental issues have become a major concern worldwide. The ecological stability of coastal waters requires the establishment of a scientific and systematic conservation program. This paper explores the relationships between riverine inputs and the nutrient structure of the coastal waters of Dalian. It also analyzes the anthropogenic activities from the watershed on riverine systems, utilizing the data collected in Dalian between 2021 and 2023. The results showed that the Bohai Sea part of Dalian coastal had the highest average DIN in spring at 0.114 mg·L⁻¹ and highest PO₄-P in autumn at 0.008 mg·L⁻¹, while the Yellow Sea part had the highest average DIN in spring at 0.095 mg·L⁻¹ and highest PO₄-P in autumn at 0.005 mg·L⁻¹ in 2023. In the two sea areas, significant phosphorus limitation was observed, with a notable proportion of over 74 % of monitoring stations recording the DIN/DIP exceeding 16 across the entire coastal water in autumn. The coastal waters of Dalian are heavily influenced by rivers in different seasons. There are higher concentrations of nutrients and more severe phosphorus limitation in estuaries and bays, which respond well to high nitrogen-to-phosphorus ratio nutrient flux inputs from rivers. The nutrient structure of coastal waters is also influenced by physical and biogeochemical processes and current transport. The nutrients from the rivers in the watershed are closely related to anthropogenic activities, and agriculture is an important source. The contribution of nutrient inputs from rivers in different watersheds varies significantly, with the Fuzhou River and Biliu River having the largest input fluxes of TN and TP, amounting to 145.18 and 2.10 t/month and 246.36 and 4.42 t/month in 2023, respectively. It is recommended to adhere to the “land-sea cooperation” and organically integrate the development of watershed nutrient reduction policies with the stabilization of the marine ecosystem.