Salinization of stream water and groundwater at daily to decadal scales in a temperate climate

Elevated salt concentrations in streams draining developed watersheds are well documented, but the effects of hydrologic variability and the role of groundwater in surface water salinization are poorly understood. To characterize these effects, we use long-term data (12-19 yr) and high-frequency specific conductance (SPC) data collected from 13 streams across New Hampshire, USA. Concentration-discharge (C-Q) relationships for chloride (Cl-) derived from high-frequency SPC showed distinct seasonal variability. Diluting behavior was common, but flushing behavior occurred in autumn and winter, suggesting that both groundwater and surface runoff contribute salts to streams. Long-term data show that although extreme flood events initially reduced salt concentrations in groundwater and rural streams, concentrations recovered to preflood conditions in about a decade. Chronic Cl- exceedances occurred in urban streams during all seasons. This research suggests that variation in stream flow, extreme events and application of deicing agents play a role in freshwater salinization.