Harmful algal blooms (HABs) have been increasing over the last 50 years due to anthropogenic nutrient enrichment and increasing temperatures. One HAB control method is the use of solar-powered mixers. In this study we investigated the timing of thermal stratification, depth of the thermocline and oxycline, and dispersion of nutrients within the water column by comparing two reservoirs in Georgia, U.S.A. over a three-year period – Lake Varner (LV), which utilizes mixers, and Hard Labor Creek Reservoir (HLCR), which does not. Our data show that the onset of thermal stratification is within ± 2 days and appears at the same depth within both reservoirs. The timing of fall turnover consistently occurred one month earlier in LV than in HLCR. Both reservoirs had similar oxygen profiles during stratification, but in LV, dissolved oxygen levels increased more quickly in autumn compared to HLCR in all years. Both reservoirs had similar nutrient concentrations throughout the years and water column. These findings suggest the thermal, oxygen, and nutrient dynamics in the reservoirs are similar, despite LV having solar-powered mixers. Any differences can be attributed to LV being a slightly smaller and shallower reservoir.


We would like to thank Oxford College of Emory University for financially supporting this research. We would also like to thank the following student researchers that helped advance this project – Camilla Kline, Julia Danko, Yaling Covey, Ayaka Smart, and Stella Rae Kinard. Essentially information about Lake Varner was provided by Bob Snipes, Assistant Water Production Manager with the Newton County Water System, and about Hard Labor Creek Reservoir by Jimmy Parker, PE, project manager for Hard Labor Creek Reservoir. This manuscript was substantially improved thanks to the help of Dr. Sarah Cadieux, Emily Kelly, and three anonymous reviewers.

Daily Average Temp (3 years).xlsx (261 kB)
Daily averaged temperature, three year dataset

Dissolvd Oxygen Data (3 years).xlsx (28 kB)
Dissolved oxygen, three year dataset