Hydrochemical and water source variations across a floodplain mire,Insh Marshes,Scotland

Groundwater heads and chemical composition were measured at approximately two week intervals during the summer of 1993 along a 1 km transect across the Insh Marshes floodplain mire in Inverness-shire, Scotland. Groundwater heads were generally higher near the valley side slope, with lower pH values and greater dissolved organic carbon, A1 and C1 concentrations. In the centre of the transect, upward groundwater heads were identified and pH, conductivity and concentrations of base cations were much greater. Near the River Spey, pH and base cation concentrations decreased and A1 and C1 concentrations increased. Deep groundwater followed a similar spatial trend but was generally more base-rich than shallow groundwater. These variations reflect the influence of three major water sources with different chemical signatures. Runoff from the valley side slope increased dissolved organic carbon and A1 in the shallow groundwater, the upward flow of groundwater increased the pH and Ca concentration and inundation near the river decreased the base status and increased C1 and A1.