Data from: Habitat context influences nitrogen removal by restored oyster reefs

1. Like many ecosystem functions in marine and terrestrial environments, nutrient processing varies dramatically over small spatial scales, making efforts to apply findings within and across ecosystems challenging. In estuaries, information on the influence of habitat context on sediment nutrient cycling is lacking even though this is an important estuarine function with high societal value. 2. We collected triplicate intact sediment cores from restored oyster reefs located in different habitat contexts (adjacent to salt marshes, seagrass beds, and mudflats), as well as salt marshes, seagrass beds, and mudflats without reefs (controls). Sediment denitrification and fluxes of dissolved inorganic nitrogen were measured under ambient and experimentally elevated water column nitrate levels. 3. Under ambient nitrate, oyster reefs enhanced sediment denitrification by 18–275% over the controls, with highest rates of denitrification in the mudflat context. With experimentally elevated nitrate, the rate of denitrification was higher for oyster reefs compared to the controls in all contexts. This suggests that oyster reefs prime sediments to denitrify nitrate pulses by providing a labile carbon source for denitrifying bacteria. 4. There was a weak positive relationship between oyster density and denitrification under ambient nitrate concentrations and a positive relationship with denitrification that became negative beyond ~2400 individuals m−2 with elevated nitrate concentrations. The effect of the oyster reef on sediment denitrification was most pronounced in the mudflat context, due to the absence of other structured habitats and higher oyster density, compared to the other two habitat contexts investigated. 5. The consistency of denitrification efficiency across the habitats and lack of difference between habitats with reefs and those without (controls) suggests oyster-mediated denitrification is an effective sink for nitrogen in coastal systems. 6. Synthesis and applications. Our study indicates that oyster-mediated denitrification is dependent on the habitat context of the oyster reef, and variation in oyster density and the relative functional redundancy of oyster reefs where other structured habitats exist (e.g. seagrass and salt marshes) may explain this pattern. Efforts to model and predict ecosystem services provided through oyster reef restoration such as the removal of anthropogenically-derived nitrogen should incorporate how habitat context influences ecosystem functions.1. 与海洋及陆地环境中的多数生态系统功能类似，养分周转过程在微小空间尺度上存在显著差异，这使得在生态系统内部及跨生态系统应用研究成果的工作极具挑战性。在河口生态系统中，尽管栖息地背景（habitat context）对沉积物营养循环的影响是一项兼具高社会价值的重要河口生态功能，但目前相关研究信息仍较为匮乏。 2. 我们从不同栖息地背景下的修复型牡蛎礁（oyster reefs）中采集了三份重复的完整沉积物柱状样（sediment cores），这些牡蛎礁分别毗邻盐沼（salt marshes）、海草床（seagrass beds）与潮滩（mudflats）；同时设置无牡蛎礁的盐沼、海草床及潮滩作为对照（controls）。在原位环境与实验性升高的水柱硝酸盐（water column nitrate）浓度条件下，我们分别测定了沉积物反硝化作用（denitrification）速率与溶解态无机氮（dissolved inorganic nitrogen）的通量。 3. 在原位硝酸盐浓度条件下，牡蛎礁可使沉积物反硝化作用速率较对照样地提升18%~275%，其中潮滩背景下的反硝化速率最高。在实验性升高硝酸盐浓度的条件下，所有栖息地背景中的牡蛎礁沉积物反硝化速率均显著高于对应对照样地。本研究结果表明，牡蛎礁可为反硝化细菌提供易变碳源（labile carbon source），从而触发沉积物对硝酸盐脉冲的反硝化过程。 4. 在原位硝酸盐浓度条件下，牡蛎密度与反硝化速率之间存在弱正相关关系；而在升高的硝酸盐浓度条件下，二者的正相关关系会在牡蛎密度超过约2400 个·米⁻²时转为负相关。相较于本次研究涉及的另外两种栖息地背景，潮滩背景下无其他结构化生境且牡蛎密度更高，因此牡蛎礁对沉积物反硝化的促进效应在此处最为显著。 5. 不同生境下的反硝化效率保持一致，且有牡蛎礁的生境与无牡蛎礁的对照生境之间并无显著差异，这表明牡蛎介导的反硝化作用是海岸系统中一种有效的氮汇。 6. 总结与应用：本研究表明，牡蛎介导的反硝化作用依赖于牡蛎礁所处的栖息地背景；而牡蛎密度的变化，以及存在其他结构化生境（如海草床与盐沼）时牡蛎礁的相对功能冗余性，或可解释上述观测规律。若要通过建模预测牡蛎礁修复所提供的生态系统服务（ecosystem services），如移除人为来源氮（anthropogenically-derived nitrogen），则需将栖息地背景对生态系统功能的影响纳入考量。