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：量化沿海河口系统中水和地下水与地表水之间化学交换的地质和时间控制

• 批准号: 0910756
• 负责人: Holly Michael
• 金额: $ 45万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0910756&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantifying; Geologic; Temporal

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.

合作研究：量化沿海河口系统中水和地下水与地表水之间的化学交换的时间和地质控制H。迈克尔、J. 布拉顿、D. Krantz、L. Konikow 和 A.S.安德烈斯河口生态系统日益受到营养过剩的威胁。地下水是重要的营养源，但地下水排放的空间和时间异质性使得在排放前量化营养物质种类的通量和转化具有挑战性。在特拉华州印第安河湾特征明确且具有代表性的河口进行的多学科调查将增进对物理和化学过程相互作用的理解，这对于评估地下水排放在沿海水域氮负荷中的作用至关重要。研究的目的是表征地质异质性和随时间变化的水力强迫对含水层和沿海地表水之间的流体和氮通量的控制。我们假设：（1）在瞬态强迫和地质异质性的驱动下，淡水和咸水之间的混合增强了淡水来源的硝酸盐在排放前的反硝化，以及（2）在水力强迫和分散引起的地下密度的驱动下，盐水交换通量梯度，将沉积有机物腐烂产生的铵输送到沿海水域。该项目将包括在特拉华州印第安河湾及其周边地区进行的数值模拟、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变密度数值模型，以量化通量、评估系统控制、合成数据并指导数据收集。地下水流量、水力梯度和盐度的直接测量将通过潮汐到年周期获得。将使用连续电阻率剖面来绘制复杂的地下盐度分布图，并将沿流路进行高分辨率地球化学采样，以确定溶质的来源和归宿，并量化反硝化作用。分析将包括氮物种和同位素、稀有气体（用于计算过量的 N2）以及盐水补给区沉积物中作为铵来源的有机物。将使用 CHIRP 地震勘测对古河道等地质特征进行成像，并在部分模型数据需求的指导下对水文地质特性进行表征。拟议的工作将产生教育影响，其结果将为调节氮负荷以改善沿海生态系统健康的管理者提供见解。该项目将与作为特拉华州和宾夕法尼亚州克里斯蒂娜河流域关键区域观测站的一部分的盐度梯度碳矿物相互作用调查相协调进行。