Uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere has acidified the ocean and threatened the health of marine organisms and their ecosystems. In coastal waters, acidification is often enhanced by CO₂ and acids produced under high rates of biological respiration. However, less is known about buffering processes that counter coastal acidification in eutrophic and seasonally hypoxic water bodies, such as the Chesapeake Bay. Here, we use carbonate chemistry, mineralogical analyses and geochemical modelling to demonstrate the occurrence of a bay-wide pH-buffering mechanism resulting from spatially decoupled calcium carbonate mineral cycling. In summer, high rates of photosynthesis by dense submerged aquatic vegetation at the head of the bay and in shallow, nearshore areas generate high pH, an elevated carbonate mineral saturation state and net alkalinity uptake. Calcium carbonate particles produced under these conditions are subsequently transported downstream into corrosive subsurface waters, where their dissolution buffers pH decreases caused by aerobic respiration and anthropogenic CO₂. Because this pH-buffering mechanism would be strengthened by further nutrient load reductions and associated submerged aquatic vegetation recovery, our findings suggest that the reduction of nutrient inputs into coastal waters will not only reduce eutrophication and hypoxia, but also alleviate the severity of coastal ocean acidification.

大气中人为吸收的二氧化碳（CO ₂）使海洋酸化，并威胁到海洋生物及其生态系统的健康。在沿海水域，CO ₂通常会增强酸化以及在高生物呼吸速率下产生的酸。但是，对于在富营养和季节性缺氧的水域（例如切萨皮克湾）中抵抗沿海酸化的缓冲过程知之甚少。在这里，我们使用碳酸盐化学，矿物学分析和地球化学模型来证明由于空间解耦的碳酸钙矿物循环而导致的海湾范围pH缓冲机制的发生。在夏季，海湾顶部和浅水，近岸地区密集的淹没水生植物的高光合作用产生高pH值，碳酸盐矿物饱和状态升高和净碱度吸收。在这些条件下产生的碳酸钙颗粒随后被下游输送到腐蚀性地下水体中，₂。因为通过进一步减少养分负荷和相关的淹没水生植被恢复将加强这种pH缓冲机制，所以我们的发现表明减少养分输入沿海水域不仅会减少富营养化和缺氧，而且还会减轻沿海海洋酸化的严重性。