Biogeochemical processes in sandy beach sediments of Spiekeroog Island and Majorca

波浪和潮汐主导的桑迪构成了世界海岸线的主要部分，在碳、养分和金属循环中发挥着重要作用。在涨潮时，海水渗入沉积物，同时有机物也被吸收。底栖微生物降解这种有机物质，在退潮期间，富营养水排入沿海海水，在那里，再循环的营养物质被用于初级生产。微生物降解过程导致氧化还原梯度，这对孔隙水组成有影响。海滩还可以位于新鲜地下水和海水的混合区（地下河口）。在这里，盐度梯度可能会影响沉积物-孔隙水的相互作用和新鲜的地下水流作为一个来源的陆地衍生溶质。为了了解全球海滩系统的碳，养分和金属循环的作用，因此，它是至关重要的，调查在海滩沉积物中的地球化学过程的细节，并在世界各地的几个地点。由于在这一领域的研究仍然很少，特别是与这些系统的源或汇功能的氧化还原敏感的痕量金属的重点，该项目将形成一个重要的贡献，目前的研究状态。我们计划调查地下河口的两个对比海滩系统的Spiekeroog（西北德国，中潮，silicicidal）和马略卡岛（西班牙，微潮，石灰质）的地球化学过程。本文分析了海滩孔隙沃茨中主要离子、溶解有机碳、氧、硫化氢、营养盐（N、P、C、Si）和微量金属（Mn、Fe、U、Mo、V、Re）以及Fe同位素比值。我们进一步的目的是表征沉积物的组成，这显着影响孔隙水的组成。高分辨率采样将分别沿沿着交叉海岸断面（沙丘至低水位线）进行，深度为5 m（Spiekeroog）和2 m（Majorca）。该项目的重点是确定氧化还原和盐度梯度及其对孔隙水组成的影响。水化学建模的基础上获得的数据将被应用，以促进更好地了解化学不同的地下水混合的影响。我们将能够评估源或汇功能的海滩有关重要的浮游植物营养素和氧化还原敏感的微量金属。铁同位素比值将扩展有限的铁循环在地下河口的知识，并提供一个更好的证实铁同位素签名排放孔隙沃茨从这些系统。此外，这项研究将提供一个深刻的数据基础，模拟不同的孔隙水组分从渗透性沉积物进入沿海海洋的通量率。

Wave- and tide-dominated sandy beaches comprise a major part of the Worlds coastline and play an important role in carbon, nutrient and metal cycling. During rising tide seawater penetrates into the sediment and simultaneously organic matter is incorporated. Benthic microorganisms degrade this organic matter and during ebb tide nutrient-enriched water discharges into coastal seawater where the recycled nutrients are utilized for primary production. Microbial degradation processes lead to redox gradients, which have an impact on the pore water composition. Beaches can further be located in a mixing zone of fresh groundwater and seawater (subterranean estuary). Here, salinity gradients may influence sediment-pore water interaction and fresh groundwater flow serves as a source for terrestrial-derived solutes. To understand the global role of beach systems regarding carbon, nutrient and metal cycling, it is therefore vital to investigate biogeochemical processes in beach sediments in detail and at several locations worldwide. Since there are still few studies in this field, especially with a focus on the source or sink function of these systems regarding redox sensitive trace metals, this project will form an important contribution to the present state of research. We plan to investigate biogeochemical processes in the subterranean estuaries of two contrasting beach systems on the Islands Spiekeroog (NW Germany, mesotidal, siliciclastic) and Majorca (Spain, microtidal, calcareous). We intend to analyze major ions, dissolved organic carbon, oxygen, hydrogen sulfide, nutrients (N, P, C, Si) and trace metals (Mn, Fe, U, Mo, V, Re) as well as Fe isotope ratios in beach pore waters. We further aim to characterize the sediment composition, which significantly influences the pore water composition. High resolution sampling will be conducted along cross shore transects (dune to low water line) down to 5 m (Spiekeroog) and 2 m (Majorca), respectively. This project focuses on the identification of redox and salinity gradients and their effects on the pore water composition. Hydrochemical modeling on the basis of the obtained data will be applied to contribute to a better understanding of the effects of mixing of chemically different groundwaters. We will be able to evaluate the source or sink function of beaches concerning essential phytoplankton nutrients and redox sensitive trace metals. Fe isotope ratios will extend the limited knowledge of Fe cycling in subterranean estuaries and provide a better substantiated Fe isotopic signature of discharging pore waters from these systems. Furthermore, this study will provide a profound data basis for modeling flux rates of distinct pore water constituents from permeable sediments into the coastal ocean.