GEOCHEMICAL AND PLANKTONIC DYNAMICS IN THE LAKE MAUMELLE RESERVOIR (ARKANSAS) DRINKING WATER SOURCE

Lake Maumelle reservoir is Central Arkansas’s main water supply, primarily servicing the residents of Little Rock, AR. Maintaining a high standard of water quality is important to the over 400,000 residents of this area whom rely on this oligotrophic/mesotrophic waterbody for drinking water. Additionally, Lake Maumelle is a scenic attraction for recreational boating and bass fishing. Lake Maumelle watershed is densely forested and mostly within the Ouachita National Forest. Past research has focused primarily on watershed management with land use/land cover modeling and quarterly water sampling of the 13.91mi² reservoir. For this investigation, water samples were collected vertically throughout the water column, horizontally throughout the lake following reservoir zonation, and within the littoral zone over a 7-month timespan in order to determine the geochemical and planktonic changes in the water body. Parameters collected vertically for water quality profiles are temperature, dissolved oxygen, electric conductivity, salinity, and pH. Cation and anion concentrations in the water samples were determined using ion chromatography, and trace element concentrations were determined using ICPMS. Planktonic abundances were determined using an inverted microscope and a 10ml counting chamber. Varying water quality parameters have been compared with planktonic abundance and location to determine response to change. Low electrical conductivity readings and high water clarity are consistent with the lake’s oligotrophic/mesotrophic state index classification. During the June 2017 sampling, parameters varied throughout the water column (temperature decreased 4 degrees Celsius and dissolved oxygen decreased from 98% to 30% from surface to bottom depths), revealing that the reservoir was becoming thermally and geochemically stratified (increased Fe and Mn). Collected plankton samples revealed the presence of copepod, daphnia, bosmina, and dinoflagellate algae throughout the water body, while Utricularia gibba was present in the littoral zone. The results will be compared to previous sampling events and used to compare geochemistry and plankton in the lake through time.