Analysis of the thermohydrochemical stability of Lake Meirama

Abstract

[Abstract] Meirama Lake is a system resulting from the forced flooding of a large brown lignite mine. Through the exhaustive monitoring of a wide variety of physical, chemical and biological parameters, it is possible to describe the main characteristics of this lake after eight years of flooding. This work focuses on the study of the thermal structure and stability of the lake during filling and in the post-filling stage. In the lake, of meromictic character, thermal and chemical homogenization processes are identified. In the first year of flooding, the lake was fully mixing and thermally and chemically homogeneous. In the following years, it became meromictic and mixing processes affected only the uppermost 30 m. The stability calculations of the lake support the homogenization processes in that volume, in which the contribution of energy by the wind could play a prominent role. The deeper volume of the lake, separated by a halocline resulting from the entry of denser waters in the first months of the flood, would be stable, except for external contributions of energy, according to the values obtained for the Brunt-Väisäla frequency. Once full, the lake presents a stable structure as demonstrated by the profiles of the different physical parameters obtained and the calculated indices.