Abstract
Total dissolved solids (TDS) concentrations throughout the San Joaquin Valley, California (SJV) have increased over the last 100 years. The SJV is the southern two-thirds of the Central Valley of California, and has experienced massive growth in agriculture and urban development over this time. This growth has altered the volume and chemistry of groundwater recharge in the SJV through irrigation practices, and has created stratified and concentrated subsurface waters. Correlations between agricultural land-use and altered water chemistry consistent with repeated irrigation and flow through shallow sediments, as well as increased evapoconcentration were observed. Bicarbonate concentrations as a component of TDS composition have risen dramatically throughout the Eastern SJV as a result of these irrigation and land-use practices. Agricultural application of nitrate fertilizers and gypsum has increased nitrate, sulfate and calcium concentrations in SJV groundwater. The results of this study clearly show the long term impact of irrigation and land use practices on the quality and viability of the groundwater resource in the San Joaquin Valley.