Seasonal and spatial trends in manganese solubility in an alluvial aquifer.
The hydrogeochemistry of river water and groundwater in a hydraulic configuration where river water infiltrates into an alluvial aquifer was monitored monthly over a 14-month period. Trends could be seen for temperature, pH, and dissolved O 2 and Mn. Wells located within 15 m of the river show a significant seasonal variation in dissolved Mn. A threshold temperature of 10 o C seems to be necessary in order to trigger and maintain Mn solubility (miaobiologically mediated reactions). Farther from the river, where the temperature is relatively constant, there is little seasonal variation in dissolved Mn. Some of the boreholes contain little Mn (0.5 μmol L -1 ) while in others the Mn concentration is very high (up to 25 μmol L -1 )