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Lake stratification controls the cycling of dissolved matter within thewater body. This is of particular interest in the case of meromictic lakes,where permanent density stratification of the deep water limits verticaltransport, and a chemically different (reducing) milieu can be established. As aconsequence, the geochemical setting and the mixing regime of a lake canstabilize each other mutually. We attempt a quantitative approach to thecontribution of chemical reactions sustaining the density stratification. Asan example, we chose the prominent case of iron meromixis inWaldsee near Doebern, a small lake that originated from near-surfaceunderground mining of lignite. From a data set covering 4 years ofmonthly measured electrical conductivity profiles, we calculated summedconductivity as a quantitative variable reflecting the amount ofelectro-active substances in the entire lake. Seasonal variations followedthe changing of the chemocline height. Coinciding changes of electricalconductivities in the monimolimnion indicated that a considerable share ofsubstances, precipitated by the advancing oxygenated epilimnion,re-dissolved in the remaining anoxic deep waters and contributedconsiderably to the density stratification. In addition, we designed a labexperiment, in which we removed iron compounds and organic material frommonimolimnetic waters by introducing air bubbles. Precipitates could beidentified by visual inspection. Eventually, the remaining solutes in theaerated water layer looked similar to mixolimnetic Waldsee water. Due to itsreduced concentration of solutes, this water became less dense and remainedfloating on nearly unchanged monimolimnetic water. In conclusion, ironmeromixis as seen in Waldsee did not require two different sources ofincoming waters, but the inflow of iron-rich deep groundwater and theaeration through the lake surface were fully sufficient for the formation ofiron meromixis

Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake