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| Titel |
Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake |
| VerfasserIn |
E. Nixdorf, B. Boehrer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 11 ; Nr. 19, no. 11 (2015-11-09), S.4505-4515 |
| Datensatznummer |
250120847
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| Publikation (Nr.) |
 copernicus.org/hess-19-4505-2015.pdf |
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| Zusammenfassung |
| 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. |
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