Collaborative Research: Redox Boundaries in Shallow Groundwater: Effects of Flow Paths, Sediment Chemistry and Kinetics

地下水地球化学演化的许多信息 已经在相对较深的含水层系统中进行。 许多 影响养分循环的地球化学反应， 温室气体浓度的变化以及 然而，污染物是发生在近- 地表地下水 氧化还原边界可以是扩散的，也可以是非常尖锐的。 各种情况。 这些氧化还原边界的性质是 受沉积物化学的影响， 反应（包括细菌介导的反应）， 地下水流路径和地下水混合，或组合 这些因素。 在大多数关于硝酸盐浓度的研究中， 其他溶质参与氧化还原反应，可能的物理 和化学系统没有同时或在 确定对地下水的主要影响的足够详细资料 氧化还原反应。 我们建议使用广泛的领域 含水层理化特性监测 和水的不同物理特性的网站， 沉积物化学 嵌套式压力计和张力计将 用于监测地下水流路径，多层次采样器将 用于测定水的化学性质。 地下水年龄将是 通过测量氯氟烃的浓度来确定 (CFC的）溶解在水中。 氮和其他的测量 生物分馏同位素将被用来确定 溶质浓度的降低是否是由于生物学上的 介导的过程或由于稀释通过地下水混合。

Much of the information on the geochemical evolution of groundwater has been conducted in relatively deep aquifer systems. Many of the biogeochemical reactions that influence nutrient cycling, concentrations of greenhouse gases, and degradation of contaminants, however, are redox reactions that occur in near- surface groundwaters. Redox boundaries can be either diffuse and extremely sharp under various situations. The nature of these redox boundaries are influenced by sediment chemistry, the kinetics of the redox reaction (including mediation of the reactions by bacteria), groundwater flow paths and mixing of groundwater, or combinations of these factors. In most studies of nitrate concentrations or other solutes involved in redox reactions, the possible physical and chemical systems have not been examined simultaneously or in sufficient detail to identify major influences on groundwater oxidation-reduction reactions. We propose to use extensive field monitoring to physical and chemical characteristics of the aquifers and water at sites with different physical characteristics and sediment chemistry. Nested piezometers and tensiometers will be used to monitor groundwater flow paths, multi-level samplers will be used to determine water chemistry. Groundwater ages will be determined by measuring concentrations of chlorofluorocarbons (CFC's) dissolved in the water. Measurements of nitrogen and other biologically fractionated isotopes will be made to determine whether reductions in solute concentrations are due to biologically mediated processes or due to dilution via groundwater mixing.