Effects of heated effluent on Midwestern US lakes: implications for future climate change

Abstract

Numerous simulation studies have considered the effects of impending climate change on lakes. Predictive models exist for the responses of a multitude of variables to a warmer climate, and potential effects on food webs and ecosystem functions. Although these predictions are numerous, there is a need for manipulative experiments testing for the effects of warming on actual lake systems. We used power plant lakes across the central Midwestern US as a substitute for future climate change effects. These treatment lakes receive heated effluent and are typically 2–6 °C warmer than other regional lakes. We collected data from 1997 to 2010 on a number of abiotic and biotic variables from three of these treatment lakes and six control lakes that were of similar size and location but did not have an artificial thermal regime. Phosphorus and phytoplankton concentrations were similar between treatment groups, although treatment lakes had greater phosphorus and less phytoplankton in September. No differences existed in turbidity (measured as Secchi depth transparency). Zooplankton were less abundant in treatment lakes than in control lakes throughout our sampling period (May–October), with differences in cladocerans driving this disparity. There was evidence of earlier spawning of gizzard shad (Dorosoma cepedianum) due to the warmer temperature regime, but not for bluegill (Lepomis macrochirus). Average sizes of juvenile bluegill were larger in warmed systems in July and August. Juvenile largemouth bass (Micropterus salmoides) were larger in heated systems in June, but no differences existed in July or August. Growth of adult largemouth bass was greater in systems with a warmer thermal regime. Our results provide insights into patterns that can be expected in the future, and may be used to further understand the wide-reaching implications of climate change.