Collaborative Research: Quantifying Geologic and Temporal Controls on Water and Chemical Exchange between Groundwater and Surface Water in Coastal Estuarine Systems

合作研究：量化沿海河口系统地下水和地表水之间的水和化学交换的时间和地质控制H。Michael、J.Bratton、D.Krantz、L.Konikow和A.S.安德斯河口生态系统正日益受到过度营养负荷的威胁。地下水是一种重要的营养盐来源，但地下水排泄的时空异质性给排泄前营养盐的通量和转化的量化带来了挑战。在特拉华州印度洋海湾典型的河口进行多学科的调查，将有助于加深对物理和化学过程相互作用的了解，这对于评价地下水排放在沿岸水氮负荷中的作用至关重要。研究的主要目标是表征地质非均质性和时变水力强迫对含水层和沿海表层水之间流体和氮通量的控制。我们假设：(1)淡水和咸水的混合，在瞬变强迫和地质非均质性的驱动下，增强了淡水来源的硝酸盐在排放前的反硝化作用；(2)在水力强迫和弥散引起的地下密度梯度的驱动下，盐分交换通量将沉积有机质腐烂产生的铵输送到沿海水域。该项目将包括在得克萨斯州印度河湾及其周围进行的数值模拟、水文和地球化学监测以及地球物理调查。将在多个空间和时间尺度上开发可变密度数值模型，以量化通量、评估系统控制、合成数据和指导数据收集。地下水流量、水力梯度和盐度的直接测量将在潮汐到年度循环中获得。将使用连续电阻率剖面绘制复杂的地下盐度分布图，并将沿着流动路径进行高分辨率地球化学采样，以确定溶质的来源和去向，并量化反硝化作用。分析将包括氮的物种和同位素，惰性气体，以计算过剩的氮气，以及盐湖补给区沉积物中的有机物作为氨的来源。地质特征，如古河道，将使用线性调频地震测量成像，水文地质特性将被部分地由模型的数据需求所引导。这项拟议的工作将产生教育影响，其结果将为管理人员提供洞察，以调节氮负荷以改善沿海生态系统健康。该项目将与沿盐度梯度的碳-矿物相互作用调查协调进行，该盐度梯度建议作为特拉华州和宾夕法尼亚州克里斯蒂纳河流域临界区观测站的一部分。

Collaborative Research: Quantifying Temporal and Geologic Controls on Water and Chemical Exchange between Groundwater and Surface Water in Coastal Estuarine SystemsH. Michael, J. Bratton, D. Krantz, L. Konikow, and A.S. AndresEstuarine ecosystems are increasingly threatened by excess nutrient loading. Groundwater is an important nutrient source, but the spatial and temporal heterogeneity of groundwater discharge makes quantifying fluxes and transformations of nutrient species prior to discharge challenging. A multi-disciplinary investigation in the well characterized and representative estuary of Indian River Bay in Delaware will improve understanding of the interaction of physical and chemical processes critical to evaluation of the role of groundwater discharge in nitrogen loading to coastal waters.The primary goal of the research is to characterize the controls of geologic heterogeneity and temporally-variable hydraulic forcing on fluid and nitrogen fluxes between aquifers and coastal surface waters. We hypothesize that: (1) mixing between fresh and saline water, driven by transient forcing and geologic heterogeneity, enhances denitrification of freshwater-derived nitrate before discharge, and (2) saline exchange flux, driven by hydraulic forcing and dispersion-induced subsurface density gradients, transports ammonium derived from decay of sedimentary organic matter into coastal waters. The project will include numerical modeling, hydrologic and geochemical monitoring, and geophysical investigations conducted within and surrounding Indian River Bay, DE. Variable-density numerical models will be developed over multiple spatial and temporal scales to quantify fluxes, evaluate system controls, synthesize data, and guide data collection. Direct measurements of groundwater discharge, hydraulic gradients, and salinities will be obtained over tidal to annual cycles. The complex subsurface salinity distribution will be mapped using continuous resistivity profiling, and high-resolution geochemical sampling will be conducted along flowpaths to determine both source and fate of solutes and to quantify denitrification. Analyses will include nitrogen species and isotopes, noble gases to enable calculations of excess N2, and organic matter in saline recharge zone sediments as a source of ammonium. Geologic features such as paleochannels will be imaged using CHIRP seismic surveys, and hydrogeologic properties will be characterized, guided in part by the data needs of the models. The proposed work will have educational impacts, and results will provide insight to managers who regulate nitrogen loading to improve coastal ecosystem health. The project will be carried out in coordination with investigations of carbon-mineral interactions along a salinity gradient proposed as part of a Critical Zone Observatory in the Christina River Basin of Delaware and Pennsylvania.