Coastal sediments are major contributors to global carbon (C) mineralization and nutrient cycling and are tightly linked to processes in the pelagic environment. In this study, we aimed to investigate the regulating potential of quantity and quality of planktonic organic matter (OM) deposition on benthic metabolism, with a particular focus on nitrogen (N) cycling processes. We simulated inputs of spring (C : N 10.9) and summer (C : N 5.6) plankton communities in high and low quantities to sediment cores, and followed oxygen consumption, nutrient fluxes as well as nitrate reduction rates, that is, denitrification and dissimilatory nitrate reduction to ammonium for 10 d. Our results demonstrate the primary importance of OM quality in determining the fate of organic N once it settles to the sediment surface. Settling of N-rich summer plankton material resulted in a ∼ twofold lower denitrification efficiency (40–56%) compared to N-poor spring plankton (88–115%). This indicates that N-rich plankton deposition favors recycling of inorganic nutrients to the water column over N-loss via denitrification. OM quantity was positively related to mineralization activity, but this neither directly affected N fluxes nor denitrification activity, highlighting the complex interplay between the OM quantity and quality in regulating N cycling. In light of these new findings, we support the use of simple qualitative indicators such as C : N ratio of OM to investigate how future changes in benthic-pelagic coupling might influence N budgets at the sediment–water interface.

中文翻译：

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沉降有机物数量和质量对底栖氮循环的影响

沿海沉积物是全球碳（C）矿化和养分循环的主要因素，并且与远洋环境中的过程紧密相关。在这项研究中，我们旨在研究浮游有机质（OM）沉积对底栖生物代谢的调节潜力，特别关注氮（N）循环过程。我们模拟了春季和春季（C：N 10.9）和夏季（C：N 5.6）浮游生物群落对沉积物核心的高，低输入，并跟踪了耗氧量，养分通量以及硝酸盐还原率，即反硝化和异化作用硝酸盐还原成铵10 d。我们的结果表明，OM质量对于确定有机N沉淀到沉积物表面的命运至关重要。与低氮春季浮游生物（88-115％）相比，富含氮的夏季浮游生物的沉降导致反硝化效率降低了约两倍（40-56％）。这表明富氮浮游生物的沉积比通过反硝化的氮损失有利于将无机养分循环到水柱中。OM量与矿化活性呈正相关，但这既不直接影响氮通量，也不反硝化活性，突显了OM量与质量之间在调节氮循环方面的复杂相互作用。根据这些新发现，我们支持使用简单的定性指标（例如OM的C：N比）来调查底栖-上浮耦合的未来变化如何影响沉积物-水界面的N预算。