Conservation concept for a river ecosystem (River Spree, Germany) impacted by flow abstraction in a large post-mining area

In the Lusatia region of northeastern Germany, dewatering for mining activities has resulted in an 8-km3 deficit in the groundwater balance. In order to refill aquifers and empty lignite pits, water will be abstracted for several decades from the River Spree which drains this region. This affects the ecological integrity of a 230 km river section including the floodplain in several aspects. Ecological consequences are shown for fishes, the aquatic invertebrate fauna, the retention of suspended matter, and oxygen concentrations. Therefore, an ecologically based minimum discharge has to be instituted. Current concepts on the assessment of minimum flow requirements in streams are reviewed. A multiple compartment method (MCM) for the assessment of flow requirements in extended river sections is suggested. Using the MCM, it can be shown that the minimum discharge that is required to preserve the river ecosystem is largely influenced by ambient channel morphology and nutrient concentration. This means that the ecological impacts of water abstraction could be abated by measures of morphological restoration of the river as well as of nutrient input restriction. Also, instream minimum flow requirements would be reduced, so that more river water could be abstracted, and the restoration of the water balance in the post-mining area in Lusatia accelerated.