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SHORT TERM EFFECTS OF HURRICANE IRMA ON THE PHYTOPLANKTON OF LAKE LOUISE, GEORGIA**

Abstract

Natural disturbances such as fires and severe storms can have profound impacts on the hydrology and ecology of inland waters, potentially altering structure and function of the ecosystem for extended periods of time. Studies of the initial impacts are, however, uncommon. Here we report on the short-term impacts of Hurricane Irma in the structure of the phytoplankton assemblage in Lake Louise, a small blackwater lake in southern Georgia. Irma hit the region on September 11, 2017, with tropical storm force winds. This corresponded to a period during which we were conducting routine weekly monitoring of environmental conditions in the lake. Parameters monitored included temperature, dissolved oxygen, conductivity, and light profiles from to surface to a depth of 6 meters. 2-liter water samples were also collected from the surface and at depths of 1, 2, 3, 4, and 5 meters. 250-500 milliliter subsamples of these were filtered and extracted for chlorophyll analysis. 50 milliliter subsamples were fixed with Lugol’s iodine for analysis using imaging flow cytometry. The immediate impact of the storm on the physical parameters of the lake can be seen in an abrupt rise in the water temperature at a depth of four meters from 17.7o C to 19.6o C, as well as changes in the conductivity profile. These changes were accompanied by an increase in the overall abundance of phytoplankton in the upper meter of the lake, and a decrease in the abundance of phytoplankton deeper in the water column, changes still evident four weeks after the passage of the storm. We are currently applying visual filters to the images obtained from flow cytometry to determine the exact changes to the composition of the phytoplankton at each depth in order to assess the potential impacts of these changes on the trophic structure of the lake. The results should provide insight into the role of short term environmental disturbances in the development of aquatic systems.

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