Construction and application of coastal ecosystem model coupling multiple human activities

Human activities have led to the discharge of pollutants into near- shore ecosystems worldwide, resulting in frequent ecological disasters and environmental issues such as red tides, hypoxia, and acidification (Wang et al., 2021; Keys et al., 2017), significantly impacting marine resources and environments. Among them, the excessive nitrogen and phosphorus inputs from anthropogenic sources represent a critical global environmental challenge (Duhamel et al., 2021; Pe et al., 2013), profoundly disrupting marine biogeochemical cycles and ecosystem stability.
In China, rivers dominate the transport of nitrogen and phosphorus to the ocean, followed by mariculture and atmospheric deposition (Gaoet al., 2020; Wang et al., 2021). During the 20th century, riverine fluxes of nitrogen and phosphorus to coastal zones increased by 90 % and 75 %, respectively, driven by intensified human activities (Beusen et al., 2016), significantly altering coastal biogeochemical cycles and ecosystem health (Sinha et al., 2017). Globally, human activities have also reshaped the fluxes and composition of nutrients delivered via at- mospheric deposition (Myriokefalitakis et al., 2020), with nitrogen fluxes increasing by 400 % since the pre-industrial era (Shi and Herbert, 2016), while phosphorus fluxes rose by 5-15 % (Mahowald et al., 2008). Mariculture has further exacerbated nutrient loading, contributing to eutrophication and nutrient imbalances in Chinese nearshore waters (Wu et al., 2020). Additionally, large-scale reclamation has reduced the nutrient buffering capacity of coastal waters and altered hydrodynamic

conditions (Sengupta et al., 2023). Concurrently, global climate change may amplify regional eutrophication through changes in coastal circu- lation and water temperature (Seidel et al., 2021). Nevertheless, human activities remain the dominant driver of environmental change in coastal zones.
In summary, the long-term coexistence of multiple human activities has led to excessive nutrient discharges, exerting nonlinear and cumu- lative impacts on nearshore ecosystems. These impacts are not attrib- utable to single activities but rather to their synergistic interactions, which remain poorly understood. Historically, research has predomi- nantly focused on individual human activities, limiting insights into the driving mechanisms of nearshore environmental changes and hindering the development of sustainable marine management strategies.
To address these gaps, this study focuses on the Bohai Sea, a region heavily influenced by human activities. A biological-physical model integrating ROMS (Regional Ocean Modeling System) and CoSiNE (Carbon, Silicate, and Nitrogen Ecosystem) model is developed to simulate the impacts of runoff discharge, atmospheric deposition, mariculture, and reclamation on nearshore ecosystem. Scenario simu- lations are conducted to quantify the contribution rates of these human activities by orthogonal experiment. This approach provides critical insights into the mechanisms driving nearshore ecosystem changes and supports the development of adaptive management strategies for coastal environments.