Groundwater cation concentrations in the riparian zone of a forested headwater stream

Abstract

AbstractGroundwater cation concentrations in relation to hydrologic flow paths were studied in the riparian forest zone of a small headwater catchment near Toronto, Ontario. Groundwater entering the riparian zone from uplands showed significant differences in cation concentrations between slope‐foot and near‐stream locations. Mean Ca, Mg, K, and Na concentrations in shallow groundwater at the upland perimeter of the riparian forest were 65‐0, 11‐2, 0‐7, and 1‐8 mg L−1 respectively. Mean Ca, Mg, K, and Na concentrations in deep groundwater flowing upwards through glacial sands beneath the riparian zone were 52‐1, 15‐1, 1‐3, and 2‐6 mg L−1 respectively. Shallow groundwater emerged as slope‐foot springs producing surface rivulets which crossed the riparian zone to the streams. Deep groundwater flowed upward through organic soils into the rivulets and also discharged directly to the streams as bed and bank seepage. Springs had higher Ca concentrations and lower Mg, K, and Na values than rivulets entering the streams. Conversely, Mg, K, and Na concentrations were higher and Ca concentrations were lower in bank seeps in comparison to rivulets. These results suggest that differences in cation concentrations in groundwater entering the streams result from initial contrast in the chemistry of shallow and deep groundwater rather than from the effects of riparian soils and vegetation.