Climate warming experiments: Design of a mesocosm heating system

Research into the impacts of climate change on lakes requires novel experimental methods that enable realistic tests of the effects of increased water temperatures on communities. This article describes the design of a heating system that has been used in situ to study the effects of an increase in lake surface temperatures on littoral communities. Water within four 700-L enclosures was heated using a propane-fuelled heat exchange system. Hot water was circulated through a network of heat exchange pipes nested in the bottom of enclosures and temperature within the enclosures was controlled electronically by regulating water flow through a series of valves. The system performed well, with temperatures within warmed enclosures paralleling diurnal fluctuations within control enclosures. The average temperature difference between warm and control enclosures of 4.5 degrees C was close to our target temperature difference of 5 degrees C. Strengths of the experimental system are discussed and potential improvements, including improved heat retention and a design adjustment to facilitate repair in the event of lightning damage are noted. The system is adaptable to larger and smaller volumes, different temperature regimes, and can be adapted for use in pelagic systems.