Application of lake marl at Lake Arendsee, NE Germany: First results of a geochemical monitoring during the restoration experiment

The application of lake marl for the in-situ restoration of eutrophic hard-water lakes with very low fresh water input has recently been carried out during a pilot study at Lake Arendsee, NE Germany. Calcite-rich lake marl taken from a natural deposit in the littoral zone was spread over the lake surface in order to co-precipitate phosphorus and cyanobacteria as well as to cover the sediment surface. The aim of this measure was to reduce the release of phosphorus from the nutrient-rich sediments into the water column under the anoxic conditions which prevail during periods of stratification. Monitoring the dispersion, transport and sedimentation of the lake marl in the water column was carried out using the in-situ multi-sensor system MINIBAT as well as by limnological studies and sediment core observations. During summer stagnation of the lake waters, suspended fine-grained calcite up to 15 μm was found at the thermocline whereas the coarser particles sedimented immediately. Following the application of the lake marl, bottom sediments were covered by a 20–120-mm calcareous layer.