Physical Controls on Coastal Hypoxia: Insights from a Novel Dual-Model Framework

Area of Science:

• * Marine science
• * Estuarine oceanography
• * Biogeochemistry

Background:

• * Coastal hypoxia is a growing environmental concern.
• * Managing hypoxia requires understanding physical and biogeochemical drivers.
• * Existing models often struggle to isolate these complex interactions.

Purpose of the Study:

• * To develop and apply a novel dual-model framework to disentangle physical and biogeochemical drivers of coastal hypoxia.
• * To quantitatively separate the influence of stratification and substance transport on hypoxia.
• * To investigate how nutrient loading variability modulates physical controls on hypoxia in the Pearl River Estuary.

Main Methods:

• * Developed a dual-model framework pairing a physical-biogeochemical model with a simplified oxygen model.
• * Utilized satellite chlorophyll climatology to prescribe fixed biogeochemical rates in the simplified model.
• * Compared model responses to identical forcing perturbations to isolate physical controls.

Main Results:

• * Physical transport amplifies stratification-driven hypoxia changes, contributing 54-70% of wind-induced hypoxic area variability.
• * Nutrient loading variability can amplify or counteract hypoxia changes depending on loading scenarios.
• * Nonpoint-source-dominated systems show amplified hypoxia responses (approx. 4-fold) compared to point-source-dominated systems.

Conclusions:

• * Physical transport and stratification interact synergistically to control coastal hypoxia.
• * Nutrient loading variability significantly modulates the physical controls on hypoxia.
• * The developed framework offers a portable and accessible methodology for hypoxia attribution and simulation.