The consequences of increased groundwater abstraction for groundwater dependent closed-basin lakes in glacial terrain

摘要

According to the European Union Water Framework Directive groundwater and surface-water resources have to be managed in an integrated way. The utilisation of groundwater resources must not harm surface-water ecosystems that are directly dependent on groundwater. The study evaluates the effects of increased groundwater abstraction (a) on a regional scale to groundwater and lake levels in a lake district, and (b) on a local scale to the seepage patterns in one example lake. After a 51 % increase in the pumping rates from an unconfined aquifer the water levels of three closed-basin lakes near the intake fell 0.3-0.7 m in 1 year, but did not change in the two lakes further from the intake. Ground-water levels in the aquifer dropped up to 0.8 m near the intake, but did not change further from the wells. Seepage measurements at the bottom of one lake showed that before the increased abstraction outseepage occurred in its northern side, after the increased abstraction the outseepage area had widened towards its western side. The results confirm that the groundwater level drop and the consequent lake-level drop were caused by the increased abstraction rate. The outcomes of the rare opportunity to analyse lake/groundwater interactions both before and after increased human intervention provide a cautionary example of what may happen to and in groundwater-dependent lakes if the groundwater/surface-water interactions are not fully clarified before the intervention in potentially similar cases around the world.