Fingering flow in the subterranean estuary - A multiplier for the iron curtain and reactive transport processes?

海底地下水排放（SGD）是水文循环的重要组成部分，对沿海含水层向海洋的营养物、碳和金属通量有显着贡献，并且已被发现影响沿海沃茨水域和生态系统。通常的科学观点是，在地下河口，潮汐和波浪引起了一个盐水再循环单元，通常被称为上部盐水羽流（USP），覆盖在所谓的排放新鲜地下水的“管道”上。相反，我们自己最近的研究表明，不稳定性和指状流出现在受潮汐影响的近岸含水层在一定的边界条件下，干扰USP和淡水管，并大大改变SGD模式在次表面。因此，这将有重要的影响，在地下河口的反应运输过程。结合物理实验和数值模拟，该项目的目标是：（i）评估自然界中是否存在指进流以及指进流在何处存在;（ii）描述沉积物特性（例如，异质性）和边界条件（例如，季节性变化的淡水通量）对盐指流的影响，（iii）调查三维效应在多大程度上会改变目前对盐指生成的理解，（iv）提高稳定性图的预测能力;（v）研究和预测SGD过程中指进流对地球化学过程和高吸附性氢氧化铁表面的发展的潜在影响（“铁幕”）在桑迪海滩含水层和相应的溶质物质通量的海洋。

Submarine groundwater discharge (SGD) is an important component of the hydrological cycle significantly contributing to the nutrient, carbon and metal fluxes from coastal aquifers to the sea and has been found to affect coastal waters and ecosystems. It is the common scientific view that in the subterranean estuary, tides and wave set-up induce a saline recirculation cell, often referred to as the upper saline plume (USP) overlying a so-called “tube” of discharging fresh groundwater. In contrast, our own recent research suggests that instabilities and fingering flow appear in the tide-affected near-shore aquifers under certain boundary conditions, disturbing USP and freshwater tube and considerably changing the SGD pattern in the sub-surface. This would consequently have important implications on reactive transport processes in the subterranean estuary. Combining physical experiments and numerical modelling, the project objectives are to (i) assess if and where fingering flow could exist in nature, (ii) delineate the impact of sediment characteristics (e.g., heterogeneity) and boundary conditions (e.g., seasonally variable freshwater flux) on salt-fingering flow, (iii) investigate to what degree 3-dimensional effects will alter the current understanding on the generation of salt-fingering, (iv) improve the prediction capability of stability diagrams and finally (v) study and predict the potential implications of fingering flow during SGD on the biogeochemical processes and the development of highly adsorptive iron(II)hydroxide surfaces (“Iron curtain”) in sandy beach aquifers and the corresponding solute matter fluxes to the sea.