Water Pathways and Chemistry at the Groundwater/Surface Water Interface to Lake Skjervatjern, Norway

Macropore flow at the groundwater/surface water interface to a humic lake and the seepage fluxes through the lake bottom were measured, as well as was the groundwater chemistry. With a 100‐fold difference in discharge from the lake, the seepage rates through the lake bottom differed by only 15%, indicating that macropores provided a major part of the inflow during high‐flow events. Two larger macropores had flow rates between 0.3 and 0.7 L s −1 , corresponding to velocities of 1–3 m min −1 . The flow rates of four smaller macropores were recorded to only 0.02–0.1 × 10 −4 L s −1 . One of the larger macropores had water with high concentration of alkalinity, Ca and Si in dry periods, whereas during wet periods dissolved organic carbon was elevated and p H was depressed. This is a indication of different source areas depending on the rainfall rate. As the alkalinity/chloride ratios were lower in the macropores than in the peat water, acid groundwater seemed to find a shortcut directly into the lake.