You are here:
Microbial Community Structure and Biogeochemistry of Three Small Eutrophic Lakes
Citation:
James, J., Johne Rogers, J. Lisa, K. Houghton, AND R. Devereux. Microbial Community Structure and Biogeochemistry of Three Small Eutrophic Lakes. ASM General Meeting, Atlanta, GA, June 07 - 11, 2018.
Impact/Purpose:
The Jackson Lakes (JL) project will investigate nitrogen, sulfur and carbon cycling pathways in Jackson Lakes. The site is in the Bayou Chico watershed and consists of three lakes. Two of the lakes, SE and SW, are hydrologically connected to Bayou Chico as evidenced by anoxic bottom water having elevated salinity and dissolved sulfide. The third lake, NE, is an artesian, spring-fed system filled with freshwater and independent of Bayou Chico and Jackson Stream. This NE lake may also become hypoxic and contribute to elevated methane production, a potent greenhouse gas. The lakes have 100 μM ammonium in bottom waters making these excellent sites near the GED to develop methods new to the division that are needed to measure nitrogen (N), sulfur (S) and carbon (C) cycles. This project will employ field and laboratory measurements that integrate geochemical and molecular microbiological approaches to monitor the changes in N cycling rates and microbial community structure.Successful completion of this effort will contribute to major advances in the capabilities of GED to investigate C, N, and S cycles and evaluate the effects of nutrients on coastal ecosystems using a novel, interdisciplinary approach. The results will be used to develop a nitrogen cycle model that incorporates C, N, and S pathways and validate the measurements by providing a genomic and nutrient data base for model calibration. The project will further the use molecular methods to characterize active nitrogen-cycling microbial communities and identify potential microbial indicators of stressed and recovered systems. Use of gene abundances in modeling microbial processes is a unique and forward thinking effort for modeling nutrient cycling, which would be useful to program and regional partners.
Description:
Background: The three Jackson Lakes within the Bayou Chico Watershed in NW FL, USA were formed at different times from abandoned sand pits. The lakes experienced inundation with marine water during Hurricane Ivan 2004 and, despite their proximity and similar physical structures, have developed different biogeochemical profiles over time. While NE lake is fully freshwater. The SE and SW lakes have freshwater above the oxycline with salinities below the oxycline ranging between 2.3 and 4.5. This study was undertaken to investigate the microbial communities of the lakes and how they are structured over the different biogeochemical conditions of the three lakes to better understand how microbial communities are shaped over redox gradients. Methods The lakes were sampled quarterly during September of 2016 through October 2017. Water column chemical profiles were obtained for salinity, O2, NH4+, NO3-/NO2-2, particulate nitrogen, total nitrogen, PO4-3, SO4-2, H2S, CO2, particulate carbon, dissolved organic carbon (DOC), N2O, particulate carbon, and CH4. Continuous dissolved oxygen and temperature sensors were deployed 14 days prior to sampling. Water was collected at ten depths, from surface to bottom, with focus around the oxycline. The water was filtered using .22 µm filters, the DNA extracted from the filters, and the V4 region of the 16S rRNA gene amplified and sequenced. The sequences were used to determine community structures for comparison with environmental data. Results The communities were more similar within a lake than between lakes with depth being a major determinant within lakes. In agreement with the chemical data, the sulfidic SW and SE lakes were more like one another than either was to the NE lake. Continuous data monitors demonstrated that these lakes are polymictic. The community structure data suggests that after a mixing event, the SW and SE lakes returned to a stratified state more rapidly than in the NE lake, where DOC concentrations were lowest. The community structures of the lakes correlated to different environmental drivers. However, as expected, the highest single correlation to community structure was with salinity. Organisms were identified as common across lakes, as well as being abundant only in a particular lake, or during single sampling events. Conclusion The putative identification of the organisms in the different depths and seasons within the lakes, along with the water column chemical profiles, provides insights into the biogeochemical cycling within the lakes.