Future Projections of Water Temperature and Thermal Stratification in Connecticut Reservoirs and Possible Implications for Cyanobacteria – an online presentation on March 23, 2021 given by Cristina Mullin of the Oak Ridge Institute for Science and Education, Environmental Protection Agency.
This study seeks to understand how climate warming may increase water temperature, stratification, and the occurrence of cyanobacteria blooms in Connecticut lakes. Past relationships between air temperature, water temperature, stratification, and cyanobacteria prevalence are quantified in six Connecticut, U.S.A., reservoirs. High‐risk cyanobacteria blooms, defined as those exceeding 70,000 cells ml−1, historically occurred in three of the study reservoirs and are correlated with the occurrence of high surface water temperatures, cool bottom water temperatures, and high total Relative Thermal Resistance to Mixing (RTRM). Lake‐specific empirical models were developed and used to project historical (1971–2000) and future (mid‐century, 2041–2070) water temperature and thermal stratification in the study lakes. Projections are driven with downscaled air temperature projections from three general circulation models (i.e., HadGEM2‐CC365, CCSM4, and GFDL‐ESM2M) under Representative Concentration Pathway 8.5. Results suggest that small reservoirs in Connecticut are warming faster than global lakes on average. We anticipate that surface, average, and bottom water temperatures will continue increase by 0.44°C, 0.30°C, and 0.16°C per decade, with the most substantial increases in both temperature and stratification expected from July–September. Days with extreme hot surface water temperatures (above 77°F) are expected to increase by approximately 48 ± 8 days a year by mid‐century (2041–2070), compared to the historical reference period (1971–2000). Moreover, stratification is likely to begin 2–4 weeks earlier and last 2–4 weeks longer by mid‐century. These shifts may favor increased dominance of certain cyanobacteria species that tend to grow best in these extreme conditions, especially in reservoirs where cyanobacteria blooms are already a concern.