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Aerobic respiration in a high-energy sandy beach

机译：高能沙滩上的有氧呼吸

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Wave and tide dominated beaches are composed of medium to coarse sandy sediments depleted in organic matter. In these sediments, the availability of organic matter limits benthic heterotrophic respiration processes. This study shows that oxygen consumption linked with nutrient recycling occurs in sands and that the intensity of this process follows a seasonal pattern. Furthermore, substantial seawater exchange occurs through intertidal sandy sediments during each tide. During floods, seawater penetrates sandy sediments, filling the pore spaces with dissolved oxygen and marine organic matter. Water expelled from the sediment during ebb is depleted in oxygen and enriched in nitrate. In order to quantify the extent of respiration processes, we collected pore waters at low tide on tidal cross-shore transects on the True Vert beach (France) every two weeks over 20 months. Temperature, salinity and oxygen saturation were recorded in situ and nutrient concentrations were determined from collected samples. The seasonal monitoring showed that aerobic respiration occurred in sands. Organic matter supplied by the seawater entering the pore spaces during floods was trapped long enough to be mineralized. An efficient recycling of nutrients was thus found to occur in tidal sandy beaches. The intensity of the respiration processes varied seasonally. The strongest oxygen depletions occurred in spring, when planktonic organic matter was abundant, as well as in summer when we observed occasional denitrifica-tion. Nitrate concentration of recycled seeping seawater reached values up to 40 uM. According to our calculations, the 240-km-long Aquitanian beach recycles 3500 t of carbon and releases 600 t of N-nitrate to the adjacent coastal zone each year. Since phosphorus is readily adsorbed on particles, the N:P ratio of recycled nutrients released to the seawater was much higher than the Redfield ratio.
机译：波浪和潮汐主导的海滩是由中度至粗度的沙质沉积物组成，这些沉积物富含有机物。在这些沉积物中，有机质的可利用性限制了底栖异养呼吸过程。这项研究表明，与养分循环有关的耗氧量在沙子中发生，并且该过程的强度遵循季节性模式。此外，在每次潮汐中，大量的海水交换是通过潮间带沙质沉积物发生的。在洪水期间，海水会渗透到沙质沉积物中，并在孔隙中充满溶解氧和海洋有机物。在退潮期间从沉积物排出的水贫化了氧气，并富含硝酸盐。为了量化呼吸过程的程度，我们在20个月内每两周在True Vert海滩（法国）的潮汐跨岸样点收集低潮时的孔隙水。原位记录温度，盐度和氧饱和度，并从收集的样品中确定营养物浓度。季节性监测表明，有氧呼吸发生在沙滩上。洪水期间海水进入孔隙空间所提供的有机物被捕集的时间足以被矿化。因此发现在潮汐沙滩上有效地循环利用了养分。呼吸过程的强度随季节变化。最强的氧气消耗发生在春季，这时浮游有机质含量很高；夏天，我们观察到偶尔发生反硝化作用。循环利用的渗出海水中的硝酸盐浓度达到40uM。根据我们的计算，每年240公里长的阿基坦海滩会回收3500吨碳，并向邻近的沿海地区释放600吨硝酸盐。由于磷很容易吸附在颗粒上，因此释放到海水中的循环养分的N：P比远高于Redfield比。

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