Relation entre facteurs hydrogéologiques, conditions d’oxydo-réduction de nappe et distribution temporelle et spatiale des nitrates, Centre-Est, de la San Joaquin Valley, Californie, USA Relaciones de factores hidrogeológicas, condiciones de oxidación-reducción del agua subterránea, y distribuciones espacial y temporal de nitrato, Valle Centro-Oriental de San Joaquín, California, EEUU 美国加州东区中部 San Joaquin河谷水文地质条件、地下水氧化还原条件与硝酸盐时空分布的关系 Relações dos factores hidrogeológicos, das condições redução-oxidação das águas subterrâneas e das distribuições espacial e temporal da variável nitrato na área Centro-Este do Vale de SanJoaquin, Califórnia, EUA | Relations of hydrogeologic factors, groundwater reduction-oxidation conditions, and temporal and spatial distributions of nitrate, Central-Eastside San Joaquin Valley, California, USA
2011
Landon, M. K. | Green, Christopher T. | Belitz, Kenneth | Singleton, Michael J. | Esser, Bradley K.
In a 2,700-km2 area in the eastern San Joaquin Valley, California (USA), data from multiple sources were used to determine interrelations among hydrogeologic factors, reduction-oxidation (redox) conditions, and temporal and spatial distributions of nitrate (NO3), a widely detected groundwater contaminant. Groundwater is predominantly modern, or mixtures of modern water, with detectable NO3 and oxic redox conditions, but some zones have anoxic or mixed redox conditions. Anoxic conditions were associated with long residence times that occurred near the valley trough and in areas of historical groundwater discharge with shallow depth to water. Anoxic conditions also were associated with interactions of shallow, modern groundwater with soils. NO3 concentrations were significantly lower in anoxic than oxic or mixed redox groundwater, primarily because residence times of anoxic waters exceed the duration of increased pumping and fertilizer use associated with modern agriculture. Effects of redox reactions on NO3 concentrations were relatively minor. Dissolved N2 gas data indicated that denitrification has eliminated >5 mg/L NO3–N in about 10% of 39 wells. Increasing NO3 concentrations over time were slightly less prevalent in anoxic than oxic or mixed redox groundwater. Spatial and temporal trends of NO3 are primarily controlled by water and NO3 fluxes of modern land use.
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