Chemocline erosion and its conservation by freshwater introduction to meromictic salt lakes

Abstract

Salinity stratification has been documented in two meromictic lakes in detail. We present seven years of field data on the salinity stratification of meromictic lakes Wallendorfer See and Rassnitzer See forming in the pits of the former lignite mine Merseburg-Ost in the Central German Mining District. Mainly from groundwater inflows, salinity stratified meromictic residual lakes had formed before freshwater was introduced intentionally over a period of two years to fill the pits more rapidly close to the final water level. From the observations, changes in the salinity stratification were interpreted in terms of deposited potential energy. Freshwater introduction (capping) was quantified in terms of potential energy. Thus the evolution of the salinity profiles was explained and their residual shapes became understandable as a consequence of the flooding procedure. Based on the quantitative estimates of energy deposited in the stratification during deep recirculation in winter, prospective statements could be made about the further evolution of the monimolimnia.