Groundwater-Surface Water Interactions along a Lake Shore: Spatial Patterns and Temporal Dynamics

In this study the spatial and temporal variability of groundwater-surface water interactions along a lake shore is investigated by combining different experimental methods. Study area is Lake Hinnensee, situated in the lake district north of Berlin in Germany. The lake is a seepage lake with no surface inflows or outflows. To investigate the spatial patterns of groundwater surface water interactions as well as their temporal dynamics we applied a number of different techniques: snapshots of spatial patterns were determined by gridded measurements of temperature profiles in the lake sediment as well as with distributed temperature sensing (DTS), using a fiber optic cable placed at the sediment surface. The spatial resolution of measurements adequate for pattern detection was determined by comparing experimental designs at various spatial scales and resolutions. Continuous time series of water levels and temperature time series in piezometer transects at different locations along the lake shore give insight into both spatial variability and temporal dynamics of vertical hydraulic gradients and heat transport. Exfiltration rates of groundwater into the lake were estimated with 3 different approaches. The experimental methodologies were evaluated in a "cost-benefit" analysis, comparing effort with scientific benefit. The results show that groundwater exfiltration into the lake is to some extent variable in time and is highly variable in space: there is a strong gradient perpendicular to the lake shore as well as high heterogeneity along the lake shore.