Marine ecosystems are prone to tipping points, particularly in coastal zones where dramatic changes are associated with interactions between cumulative stressors (e.g., shellfish harvesting, eutrophication and sediment inputs) and ecosystem functions. A common feature of many degraded estuaries is elevated turbidity that reduces incident light to the seafloor, resulting from multiple factors including changes in sediment loading, sea‐level rise and increased water column algal biomass. To determine whether cumulative effects of elevated turbidity may result in marked changes in the interactions between ecosystem components driving nutrient processing, we conducted a large‐scale experiment manipulating sediment nitrogen concentrations in 15 estuaries across a national‐scale gradient in incident light at the seafloor. We identified a threshold in incident light that was related to distinct changes in the ecosystem interaction networks (EIN) that drive nutrient processing. Above this threshold, network connectivity was high with clear mechanistic links to denitrification and the role of large shellfish in nitrogen processing. The EIN analyses revealed interacting stressors resulting in a decoupling of ecosystem processes in turbid estuaries with a lower capacity to denitrify and process nitrogen. This suggests that, as turbidity increases with sediment load, coastal areas can be more vulnerable to eutrophication. The identified interactions between light, nutrient processing and the abundance of large shellfish emphasizes the importance of actions that seek to manage multiple stressors and conserve or enhance shellfish abundance, rather than actions focusing on limiting a single stressor.

中文翻译：

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累积压力会降低沿海生态系统的自我调节能力。

海洋生态系统很容易达到临界点，特别是在沿海地区，这些地区的急剧变化与累积压力源（例如贝类收获，富营养化和沉积物输入）与生态系统功能之间的相互作用有关。许多退化河口的一个共同特征是浊度升高，降低了入射到海底的光，这是由多种因素导致的，包括沉积物负荷的变化，海平面上升和水柱藻类生物量的增加。为了确定浊度升高的累积效应是否会导致驱动营养物质加工的生态系统组件之间的相互作用发生显着变化，我们进行了一项大规模实验，在全国海底入射光的全国范围内，对15个河口的沉积物氮浓度进行了控制。我们确定了入射光的阈值，该阈值与驱动营养物质加工的生态系统相互作用网络（EIN）的明显变化有关。超过此阈值，网络连接性很高，并且与脱氮和大型贝类在制氮过程中的作用有着明确的机械联系。EIN分析显示，相互作用的压力因素导致浑浊的河口中生态系统过程解耦，而其反硝化和处理氮的能力较低。这表明，随着浊度随着沉积物负荷的增加而增加，沿海地区可能更容易发生富营养化。所确定的光，养分加工与大型贝类之间的相互作用强调了寻求管理多种应激源并保护或增强贝类丰富度的行动的重要性，