Sandy beaches are places of active organic matter mineralization due to water renewal providing organic matter and electron acceptors in the porous and permeable sands. Recycled biogenic compounds are efficiently transferred to the coastal marine environment via wave and tidal-driven advective flows. The biogeochemical processes in beach aquifers were mainly studied in semi enclosed systems with low tidal amplitude, and with a connection to continental aquifers contributing to solute fluxes to the coast from terrestrial groundwater. We present here the study of a pocket beach isolated from terrestrial aquifers with a high tidal amplitude and a medium energy wave regime. In situ measurements, cross-shore profiles and vertical sampling were conducted during several tidal cycles in spring and autumn. Cross-shore transects, obtained at low tide from holes that represent a mixture of the upper 20 cm of the water saturated zone, showed concentration gradients of redox and recycled compounds. Increase in pCO₂, dissolved phosphate and ammonium concentrations downslope revealed that more products from organic matter mineralization accumulated in the lower beach. The related increase in total alkalinity downslope indicated that the part of anaerobic processes in organic matter oxidation was higher in the lower beach. Concentration and δ¹³C of dissolved inorganic carbon in pore waters suggested that the carbon mineralized in pore waters came from marine plant debris that were mixed with the sand. Continuous probe records of dissolved oxygen saturation and vertical profiles revealed a tidally-driven dynamics of pore water in the first centimetres of the lower beach aquifer. Ventilation of pore waters corresponded to wave pumping and swash-induced infiltration of seawater in the upper 10–20 cm of sediment. Nutrients and reduced compounds produced through organic matter mineralization remained stored in pore water below the layer disturbed by wave. The flux of these components to seawater is possible when this interface is eroded, for example when wave energy increases after a less energetic period. The low extension of the studied aquifer, typical of pocket beaches, limits the connection with continental groundwater. Both tidally-driven and wave-driven recirculation of seawater allows pocket beaches to be efficient bioreactors for marine organic matter mineralization. As such, they provide the coastal environment with recycled nutrients, and not new nutrients.

沙滩是活跃的有机物矿化的地方，这是由于水的更新会在多孔和可渗透的沙子中提供有机物和电子受体。回收的生物化合物通过波浪和潮汐驱动的对流有效地转移到沿海海洋环境中。滩面含水层的生物地球化学过程主要在低潮汐半封闭系统中进行研究，并且与大陆含水层有关，从而促使溶质从陆地地下水流向海岸。我们在这里介绍从潮汐振幅高和能量波中等的陆地含水层中分离出来的小袋海滩的研究。在春季和秋季的几个潮汐周期中，进行了现场测量，跨岸剖面和垂直采样。跨岸样带，在退潮时从代表水饱和区上部20 cm的孔的孔隙中获得的氧化还原和再循环化合物的浓度梯度显示。增加pCO_{如图2所示}，溶解的磷酸盐和铵盐浓度向下倾斜表明，更多的有机物矿化产物积聚在较低的海滩中。总碱度下降的相关增加表明，下部海滩中有机物氧化过程中的厌氧过程部分较高。浓度和δ ¹³孔隙水中溶解的无机碳的C值表明，孔隙水中矿化的碳来自与沙子混合的海洋植物碎屑。连续的溶解氧饱和度和垂直剖面的探针记录显示，潮汐驱动的滩下含水层第一厘米的孔隙水动力学。孔隙水的通风对应于波浪泵送和冲刷诱导的10-20 cm沉积物上部的海水​​渗透。通过有机物矿化产生的营养物质和还原性化合物仍然存储在受波扰动的层下方的孔隙水中。当界面被侵蚀时，例如当波能在较低的能量周期后增加时，这些成分可能流入海水。研究的含水层的延伸度低，典型的是袋装海滩，限制了与大陆地下水的连接。潮汐驱动和波浪驱动的海水再循环都使口袋海滩成为海洋有机物矿化的有效生物反应器。因此，它们为沿海环境提供了可循环利用的营养素，而不是新的营养素。