Identifying sources of groundwater nitrate contamination in a large alluvial groundwater basin with highly diversified intensive agricultural production.

摘要: Groundwater quality is a concern in alluvial aquifers underlying agricultural areas worldwide. Nitrate from land applied fertilizers or animal waste can leach to groundwater and contaminate drinking water resources. The San Joaquin Valley, California, an example of landscape with large diversity field, vegetable, tree, nut, citrus crops, but also confined feeding operations (CAFOs, here mostly dairies) that generate, store, apply amounts liquid manure. As other such regions around the world, rural population Valley relies almost exclusively on shallow domestic wells (≤150 m deep), which many have been affected by nitrate. Variability soil type, depth contribute variability nitrate occurrence across aquifer system. role these factors controlling contamination levels examined. Two hundred were sampled two sub-regions Stanislaus Merced (Stan/Mer) Tulare Kings (Tul/Kings) Counties. Forty six percent well samples Tul/Kings 42% Stan/Mer exceeded MCL for (10mg/L NO3-N). For statistical analysis contamination, 78 crop landuse types considered grouping them into ten categories (CAFO, citrus, deciduous fruits nuts, field forage, native, pasture, truck urban, vineyards). Vadose zone thickness, construction information, proximity dairies, dominant near considered. In area, elevated most strongly correlate combination very (≤21 m) table presence either CAFO derived applications fruit nut crops (synthetic fertilizer applications). County, data indicate are associated orchards when located table. County had relatively few exceedances wells, probably due deeper County.