BACTERIAL RESPONSES TO GEOCHEMICAL AND DIURNAL PROCESSES OCCURING IN LAKE MAUMELLE, ARKANSAS

Lake Maumelle is a drinking water reservoir that serves ~400,000 people in the Little Rock-North Little Rock Metropolitan area in Arkansas. Aqueous inorganic and organic chemical and biological profiles were completed at 1 meter intervals every 4 hours over a 24 hour period. The site was selected because of the potential sensitivity to diurnal changes, while remaining representative of the reservoir dynamics. Biological samples were collected for bacteria counts as well as phytoplankton, zooplankton, and bacterial populations. Geochemical parameters were combined to decipher the relationship between aqueous chemistry and the biological response as a function of time of day. We combined proxies for land plant-derived sources of organic matter with solid and solution phase total organic carbon and total biomass to construct a carbon mass balance for the lake system. Bacterial compositions and abundance may provide evidence for biological responses to water chemistry changes. Observed bimodal bacterial counts corresponded to periods (5-9 PM) of high and low dissolved oxygen, whereas morning to early afternoon data indicated a decline in populations adapted to low dissolved oxygen conditions. Preferential functionality of aerobic and anaerobic bacteria responds to diurnal events, with a bias toward heterotrophic processes becoming dominant once autotrophic bacterial activity declined. Bacterial distributions and preferences inferred from geochemical trends and confirmed via culturing may elucidate the relative significance of biological versus physical processes in the lake over a diurnal cycle.