Details zur Publikation

Kategorie Textpublikation
Referenztyp Zeitschriften
DOI 10.5194/hess-19-4505-2015
Titel (primär) Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake
Autor Nixdorf, E.; Boehrer, B.
Quelle Hydrology and Earth System Sciences
Erscheinungsjahr 2015
Department SEEFO; ENVINF
Band/Volume 19
Heft 11
Seite von 4505
Seite bis 4515
Sprache englisch
UFZ Querschnittsthemen RU5;
Abstract Lake stratification controls the cycling of dissolved matter within the water body. This is of particular interest in the case of meromictic lakes, where permanent density stratification of the deep water limits vertical transport, and a chemically different (reducing) milieu can be established. As a consequence, the geochemical setting and the mixing regime of a lake can stabilize each other mutually. We attempt a quantitative approach to the contribution of chemical reactions sustaining the density stratification. As an example, we chose the prominent case of iron meromixis in Waldsee near Doebern, a small lake that originated from near-surface underground mining of lignite. From a data set covering 4 years of monthly measured electrical conductivity profiles, we calculated summed conductivity as a quantitative variable reflecting the amount of electro-active substances in the entire lake. Seasonal variations followed the changing of the chemocline height. Coinciding changes of electrical conductivities in the monimolimnion indicated that a considerable share of substances, precipitated by the advancing oxygenated epilimnion, re-dissolved in the remaining anoxic deep waters and contributed considerably to the density stratification. In addition, we designed a lab experiment, in which we removed iron compounds and organic material from monimolimnetic waters by introducing air bubbles. Precipitates could be identified by visual inspection. Eventually, the remaining solutes in the aerated water layer looked similar to mixolimnetic Waldsee water. Due to its reduced concentration of solutes, this water became less dense and remained floating on nearly unchanged monimolimnetic water. In conclusion, iron meromixis as seen in Waldsee did not require two different sources of incoming waters, but the inflow of iron-rich deep groundwater and the aeration through the lake surface were fully sufficient for the formation of iron meromixis.
dauerhafte UFZ-Verlinkung
Nixdorf, E., Boehrer, B. (2015):
Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake
Hydrol. Earth Syst. Sci. 19 (11), 4505 - 4515 10.5194/hess-19-4505-2015