PLANT - GROUNDWATER INTERACTIONS AT THE LAND-WATER INTERFACE OF STREAMS, LAKES, AND WETLANDS

The land-water interface of streams, lakes, and wetlands is a critical habitat where flowing groundwaters interact with the plant root zone before discharging into associated surface waters. In a series of studies conducted across New York State from 1998 through 2003, we have been quantifying groundwater flow rates and flow paths, chemistry of pore waters within the root zone under different flow conditions, and controls by plant evapotranspiration (ET) on groundwater flow. Groundwater flow rates have been quantified using replicated seepage meters along lake shorelines in a 207km2 mesotrophic lake and in five oligotrophic ponds, and using a network of shallow and deep piezometers in a 200 ha riparian cattail wetland along the shoreline of Lake Ontario. Concentrations and loadings of phosphorus and selected elements have been monitored using pore water samplers and wells located within the root zone at each site. We also developed and monitored a set of eight in situ, groundwater-connected lysimeters to quantify ET rates. These lysimeters were monitored throughout the summer, 2003 at the cattail wetland in conjunction with the piezometer network to determine the relationship between ET and groundwater flow. The integration of these studies indicates that there are strong interactions between flowing groundwater, the sediment, and plants at the land-water interface of lakes, streamsides, and wetlands. Groundwater flow rates, and particularly the shift from high to low flow rates, influences the availability of different chemical species within the pore waters bathing the plant roots. Plant ET appears to influence groundwater processes at several spatial scales, depending on soil hydraulic conductivity properties: causing a diurnal vertical fluctuation in the water table surface, causing a mound and depression water table surface across the wetland, and strongly impacting the total hydrologic budget during the growing season. These findings have important implications for watershed management, particularly given increasing development pressures and variability in climate conditions, both of which influence groundwater quantity and quality.