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ZOOMIX Report Summary

Project ID: 630917
Funded under: FP7-PEOPLE
Country: United Kingdom

Periodic Report Summary 1 - ZOOMIX (Zooplankton Generated Mixing in Stratified Lakes)

Bio-turbulence or bio-mixing refers to the contribution of living organisms towards the mixing of waters in oceans and lakes. Our project focuses the attention on the stirring generated by Daphnia spp. in a small lake. This very common zooplankton species is engaged in a vertical migration (DVM) at sunset, with many organisms crossing the thermocline despite the density stratification. During the ascension they may create hydrodynamic disturbances in the lake interior where the stratification usually suppresses the vertical diffusion. While turbulence and mixing from DVM have been studied in the ocean, only theoretical and laboratory experiments have been conducted using typical lake species. Thus far a clear picture has not emerged of the role of biomixing in lakes, thus the objectives of this project were:

1. Conduct the first ever measurements of turbulence in the thermocline induced by zooplankton in a lake environment;
2. Quantify the efficiency of mixing generated by zooplankton;
3. Determine the importance of this mechanism by comparison with turbulence generated by internal waves.

During the first period of this grant, we made the first direct measurements of turbulence through migrating zooplankton in a lake, which show a two order of magnitude increase in dissipation during the migration. The magnitude of the turbulence observed is on par with that from internal wave driven turbulence, but the net contribution to mixing can only be determined through further investigation of mixing efficiency (the objective for the second half of the project). These results have been disseminated through poster presentations at five international conferences thus far, and are being prepared for submission to a journal. The equipment and resources provided by this grant have also allowed the PI to expand their research agenda on biophysical interactions in stratified lakes (with two new PhD student starting soon) and develop a complementary research stream related to the water quality impacts of destratifying reservoirs by artificial mixing.

Reported by

United Kingdom


Life Sciences
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