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 l ake and the seepage fluxes through the lake bottom were measured, as w ell as was the groundwater chemistry. With a 100-fold difference in di scharge from the lake, the seepage rates through the lake bottom diffe red by only 15%, indicating that macropores provided a major part of t he inflow during high-flow events. Two larger macropores had flow rate s between 0.3 and 0.7 L s(-1), corresponding to velocities of 1-3 m mi n(-1). The flow rates of four smaller macropores were recorded to only 0.02-0.1 x 10(-4) L s(-1). One of the larger macropores had water wit h high concentration of alkalinity, Ca and Si in dry periods, whereas during wet periods dissolved organic carbon was elevated and pH was de pressed. This is a indication of different source areas depending on t he rainfall rate. As the alkalinity/chloride ratios were lower in the macropores than in the peat water, acid groundwater seemed to find a s hortcut directly into the lake.