Abstract
AbstractLong‐term patterns of dissolved oxygen (DO) in estuarine and coastal waters remain poorly understood. Here we summarized DO concentrations and analyzed the crucial drivers of hypoxia in northwestern and southern Hong Kong and Mirs Bay over the past three decades. Deoxygenation was weak in the bottom water in northwestern Hong Kong, although DO was consistently undersaturated, whereas the annual minimum DO in the bottom water exhibited a significant decrease in southern Hong Kong (−0.06 ± 0.01 mg L−1 yr−1) and Mirs Bay (−0.10 ± 0.02 mg L−1 yr−1). Seasonal hypoxia in the bottom water was accompanied by supersaturated DO and high Chl‐a in surface waters of southern Hong Kong, indicating a crucial role of local extensive productivity in the oxygen depletion of the bottom water. The rapid deoxygenation was also attributed to the water stratification preventing oxygen replenishment in southern Hong Kong and the predeoxygenation of bottom water retained in Mirs Bay. The dissolved inorganic nitrogen concentrations have increased from 1 to 3 mg N L−1, which increased the primary productivity contributing to the decrease in water DO over the past three decades. Therefore, these results suggest that biological oxygen consumption and seasonal stratification are mainly driving the formation and maintenance of hypoxia in the Pearl River Estuary and adjacent areas.
Published Version
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