Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

Water quality and fish habitat models were developed and applied to investigate impacts of future climate change in aquatic systems, mainly lakes in this study. Long-term daily water temperature and dissolved oxygen (DO) profiles and ice/snow covers on lakes were simulated for 27 types of small lakes (surface area up to 10 km²) at 209 geographic locations in the contiguous USA under past (1961–1979) and projected 2 × CO₂ climate conditions using a process-oriented, dynamic, one-dimensional, year-round lake water quality model (MINLAKE96). The projected climate scenario was based on the output from the second generation general circulation model (GCM 2.0) for a doubling of atmospheric CO₂ (2 × CO₂). The 2 × CO₂ climate scenario is projected to increase lake surface temperatures by up to 5.2°C when GCM 2.0 projects an increase of mean annual air temperature up to 6.7°C. Summer stratification in lakes is projected to last up to 66 days longer, and this leads to a longer period of anoxic hypolimnetic conditions that will result in various negative environmental and ecological impacts on lakes. Projected climate warming has a strong impact on ecological conditions in ice-covered lakes, i.e., shorter ice cover period (up to 90 days) and reductions in snow and ice thickness were projected. Winterkill of fish in shallow, eutrophic and mesotrophic, ice-covered lakes is projected to disappear under a 2 × CO₂ climate scenario. Climate warming is also projected to reduce the number of geographic locations in the contiguous USA where lakes have suitable cold- and cool-water fish habitat, by up to 45% and 30%, respectively. Warm-water fish habitat is projected to extend in lakes over the entire contiguous USA, and this is a positive impact of climate warming. A recent study to identify potential refuge lakes important for sustaining cisco habitat under climate warming scenarios is summarized.