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Abstract

Lakes are important aquatic ecosystems that are extensively influenced by seasonal variations. In this study we investigate the seasonal dynamics and trends of three environmental variables, water temperature, conductivity and dissolved oxygen (DO), in Lake Louise, a sinkhole lake located in southern Georgia. These variables were measured in-situ along a depth profile from January 27, 2024 to January 17, 2025. We also accessed archived data from field campaigns in 2003, 2004, and 2017 in order to test whether a recent increase in the number of hurricanes impacting the region, five since August, 2017, may have significantly altered the seasonal dynamics of the lake. Seasonal differences and trends were investigated using Dunn’s test of multiple comparisons and the Modified Mann-Kendall test, respectively. The study also quantified phytoplankton in the lake using imaging flow cytometry. Our results highlight the highly responsive nature of the lake’s surface waters to seasonal variation and environmental impacts while conditions in the hypolimnion (deeper layers) were relatively stable and differentially anoxic over the study period; only conductivity showed an increasing trend in the hypolimnion as thermal stratification stabilized. Pairwise comparisons of seasons showed a mix of significant and non-significant differences in water temperature, conductivity, and dissolved oxygen levels within the period of study. The Modified Mann-Kendall test results for water temperature indicated a non-significant increasing trend from 2004 to 2024, although in 2003, the increase was significant. Conductivity exhibited a significant increasing trend for the period of study in both 2017 and 2024. Meanwhile, oxygen levels demonstrated significant decreasing trends in 2004 and 2024, with non-significant decreasing trends observed in 2003 and 2017. Importantly, the large number of cyanobacteria observed following Hurricane Irma in 2017 was drastically reduced in 2024; this reduction may be related to the timing of Hurricane Helene in 2024.

Acknowledgements

Sincere thanks to Valdosta State University for providing the space and equipment used for conducting this research.

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