Hobart

Seminar Abstract

Thursday 6 August 2009, 2.00pm (Tas time)
CSIRO Auditorium, Hobart

Klaus D Jöhnk
Institute of Freshwater Ecology and Inland Fisheries
Germany

Climate - turbulence - phytoplankton dynamics

Lake characteristics are to a large extent determined by regional climatic conditions. Changes in climate patterns like increasing air temperature or decreasing cloudiness will lead to a shift in lake characteristics thus changing the physical basis for live in the aquatic system. Here we look at three different aspects of aquatic systems influenced by variations in climate.

Time scales: The appearance of some nuisance cyanobacteria species in lakes of temperate regions is believed to be a consequence of global warming. Using a dynamic model for nostocale cyanobacteria allows the prediction of their seasonal development over decades. This tool is used to extract time-scales of development under different temperature scenarios and subject to extreme events.

Stratification and mixis: Here we have a deeper look into the effects of climate on lake stratification and the development of Microcystis populations. For an artificially mixed deep lake in Amsterdam, The Netherlands, a coupled hydrodynamic-competition model was used to predict the seasonal development of Microcystis blooms under extreme events. We then checked for the impact of different physical parameters (turbulent mixing, water temperature, cloudiness) on plankton development. Here it can be seen that the combined effect of changes in all three parameters will non-additively boost Microcystis blooms due to higher water temperatures, more stable stratification, and higher irradiance.

Global change in lake characteristics: Using numerical simulations with a k-epsilon turbulence model the seasonal hydrodynamics of lakes on a global scale, Europe, are simulated. To account for hydrodynamic differences due to lake morphometry and trophic state, we use several model lakes differing in depth and absorption, respectively. The model lakes are forced by meteorological data given as gridded fields over Europe for current climate condition as well as for future climate scenarios. This results in several tens of thousands simulations of lake temperature and turbulent diffusivity profiles, from which we extract cardinal events and values such as the onset of stratification, thermocline depth or ice cover duration. Our simulations provide predictions for differences in lake hydrodynamics and ecology across the latitudinal, longitudinal and altitudinal gradients.

About the speaker: Klaus Johnk is a research scientist at the Institute of Freshwater Ecology and Inland Fisheries, Germany. He is a geophysicist/environmental physicist by training, originally working on fluid motion in the Earth's outer core and avalanche dynamics. 15 years ago he changed focus to lake hydrodynamics coupled to biogeochemical processes. His interest is in the interactions between climate and aquatic systems from a modelling perspective. He has worked on transport processes in Lake Constance, Germany, double-diffusive mixing in post-mining lakes of Lusatia, Germany, artificial mixing to prevent Microcystis blooms in Lake Nieuwe Meer, The Netherlands, and recently on the spread of originally tropical cyanobacteria to lakes of Northern Germany. Basis of these research themes are one-dimensional coupled biogeochemical-hydrodynamic models. In the last years another topic gained his attention, nonlinear analysis of ecohydrological time-series.

Further details on work and publications are available at: http://www.igb-berlin.de/~k.joehnk/

Seminar recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 8/12/09