Abstract

Large lakes play an important role in global carbon cycling. However, deep lakes are susceptible to anoxia with the associated loss of biodiversity if overloaded with nutrients; the balance between the forces that stabilise a lake and those that mix the water column is very delicate and there are signs that global change is upsetting this delicate balance with potentially devastating effects for the endemic fauna and flora. I will illustrate the subtleties of the balance using two extreme examples, Lake Ohrid, a deep, very old European lake that is under threat from global warming because of its great depth and Lake Argyle, a very large reservoir, that has the potential of being used for aquaculture to provide about 35% of Western Australia’s fish needs and sequester about 20% of WA’s carbon emissions, providing an opportunity to mitigate global warming. The large expanses of shallow littoral waters of Lake Argyle have been shown to support very active differential heating, cooling and wind mixing, provided a very active horizontal exchange between the littoral and deep central waters, making it ideal for aquaculture.

I will review the underlying fluid dynamics of these two extreme lakes and show how a fundamental understanding of underlying fluid dynamics of lakes has allowed us to set up a real-time coupled hydrodynamic-ecological model, forced by a full high resolution meteorological model, that now serve as real-time decision support systems for lake managers.

In conclusion, I shall, very briefly, summarise some important unresolved hydrodynamic and ecological problems and put the proposal to use Lake Argyle as a carbon sequestration site and food source into the Western Australian context of making the State carbon neutral, energy and water self sufficient and with an enhanced social well-being. The same understanding may be used to install impellers in Lake Ohrid to save this lake from suffocating from lack of oxygen brought about by global warming. Together, these two examples serve to illustrate how large lakes may be harnessed as a resource for meeting the challenges of global change.