An aquatic mesocosm array to regulate spatial and temporal water temperature variability

Temporal and spatial variability in temperature are key habitat features that will determine individual, population, and community-level responses to global climate warming. Lakes and ponds exhibit thermal heterogeneity in the form of diel and seasonal fluctuations as well as vertical stratification; however, experimental studies of warming in these ecosystems have largely focused on elevated mean temperatures within thermally homogeneous settings. Thus, new tools are needed to incorporate temperature variability into aquatic mesocosm experiments. We present a design for a mesocosm array to simulate lentic environments with different magnitudes of spatial and temporal temperature variability. Each mesocosm consists of a 77-L plastic container heated by two independent band heaters, where water temperature is regulated via a programmable logic controller that receives feedback from thermocouples. We find that the controller is capable of producing high temperatures (> 35°C) and substantial thermal stratification, with low variability between replicate mesocosms. We generated a vertical temperature gradient up to 12.4°C across 54 cm of water depth and diel fluctuations up to 12.2°C in the surface layer (top 14 cm). We additionally demonstrate the utility of the mesocosm array for other common applications, including temperature ramps and real-time transformations of ambient temperature time series. The control system's ability to simultaneously regulate temporal and spatial thermal variability, while being cost-effective and requiring relatively little technical knowledge to assemble, demonstrates the utility of the array for ecological experiments that seek to investigate the impacts of climate warming on thermally variable aquatic ecosystems.