Impact of agricultural activity and geologic controls on groundwater quality of the alluvial aquifer of the Guadalquivir River (province of Jaen, Spain):: a case study

The alluvial aquifer of the Alto Guadalquivir River is one of the most important shallow aquifers in Jaen, Spain. It is located in the central-eastern part of the province, and its groundwater resources are used mainly for crop irrigation in an agriculture-dominated area. Hydrochemical and water-quality data obtained through a 2-year sampling (2004-2006) and analysis program indicate that nitrate pollution is a serious problem affecting groundwater due to the use of nitrogen (N)-fertilizers in agriculture. During the study, 231 water samples were collected from wells and springs to determine water chemistry and the extent of nitrate pollution. The concentration of nitrate in groundwater ranged from 1.25 to 320.88 mg/l. Considerable seasonal fluctuations in groundwater quality were observed as a consequence of agricultural practices and other factors such as annual rainfall distribution and the Guadalquivir River flow regime. The chemical composition of the water is not only influenced by agricultural practices, but also by interaction with the alluvial sediments. The dissolution of evaporites accounts for part of the Na+, K+, Cl-, SO42-, Mg2+, and Ca2+, but other processes, such as calcite precipitation and dedolomitization, also contribute to groundwater chemistry.