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Lake Kivu pp 13-29 | Cite as

Stratification, Mixing and Transport Processes in Lake Kivu

Chapter
Part of the Aquatic Ecology Series book series (AQEC, volume 5)

Abstract

This chapter summarizes the knowledge on mixing and transport processes in Lake Kivu. Seasonal mixing, which varies in intensity from year to year, influences the top ∼65 m. Below, the lake is permanently stratified, with density increasing stepwise from ∼998 kg m−3 at the surface to ∼1,002 kg m−3 at the maximum depth of 485 m. The permanently stratified deep water is divided into two distinctly different zones by a main gradient layer. This gradient is maintained by a strong inflow of relatively fresh and cool water entering at ∼250 m depth which is the most important of several subaquatic springs affecting the density stratification. The springs drive a slow upwelling of the whole water column with a depth-dependent rate of 0.15–0.9 m year−1. This upwelling is the main driver of internal nutrient recycling and upward transport of dissolved gases. Diffusive transport in the deep water is dominated by double-diffusive convection, which manifests in a spectacular staircase of more than 300 steps and mixed layers. Double diffusion allows heat to be removed from the deep zone faster than dissolved substances, supporting the stable stratification and the accumulation of nutrients and gases over hundreds of years. The stratification in the lake seems to be near steady-state conditions, except for a warming trend of ∼0.01°C year−1.

Keywords

Diffusive Transport Deep Zone Vertical Transport Temperate Lake Density Stratification 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

Fieldwork was supported by the Swiss National Science Foundation (SNSF) under grant 200021–122183 (Lake Kivu – turbulence and double diffusion in permanent stratification) and by SNSF and the Swiss Agency for Development and Cooperation under grant IZ70Z0_123923 (Lake Kivu: Learning from the past for managing its future).

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Copyright information

© Springer Science+Business Media B.V. 2012

Authors and Affiliations

  1. 1.Eawag: Swiss Federal Institute of Aquatic Science and TechnologyKastanienbaumSwitzerland
  2. 2.ETH Zurich, Institute of Biogeochemistry and Pollutant DynamicsZurichSwitzerland

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