Assessment of temporal and spatial variation in chemical composition of groundwater in an unconfined esker aquifer in the cold temperate climate of Northern Finland

Samples of groundwater, surface water, snow and precipitation were collected to identify potential end-members for aquifer recharge in an unconfined esker aquifer connected to nearby surface waters. Concentrations of Ca2 +, Cl−, NO3–N and SiO2 and electrical conductivity were determined in these water samples. Time series, ANOVA followed by HSD test and biplots were used to investigate temporal and spatial variations in surface water and groundwater chemistry. Examination of the spatial and temporal variations in groundwater solutes revealed that water quality was similar in perched groundwater and the main aquifer. The exception was NO3–N concentration, which increased in the perched groundwater with rising groundwater level, indicating a nitrogen source from the overlying airport. In the main aquifer, solute concentrations generally decreased during and immediately after snowmelt periods, indicating the importance of snowmelt input for groundwater quality. Groundwater solute concentrations generally decreased with declining groundwater level. During the spring melt period, the surface water level rise higher than groundwater level and the Cl− concentration in groundwater decreased showing a seasonal surface water intrusion. During the anomalously warm period in winter (T > 0 °C) the solute concentration decreased, implying that groundwater quality may be sensitive to future warming.

► The seasonal water quality in the perched groundwater and the main aquifer showed a similar fluctuation pattern.
► The solute concentrations generally decreased during and immediately after snow melt periods.
► The water levels between surface water and groundwater reversed during the spring melt period.
► Surface water infiltration into aquifer was detected by a decrease in Cl− concentration in groundwater.