Citation:

Rogers, Johne, J. Lisa, R. Devereux, AND D. Morton. Biogeochemistry of three small Eutrophic Lakes Differentially Influenced by Marine Waters from Bayou Chico Bay, Pensacola, Florida. American Society for Microbiology Microbe 2017, New Orleans, LA, June 01 - 05, 2017.

Impact/Purpose:

This study was undertaken to better understand the relationship between N, S, Fe and C cycling in lakes where the oxycline (OC) develops within 4 to 6 meters of the surface. These lakes provide a unique environment for investigation of nutrient cycling over a range of environmental conditions.

Description:

Biogeochemical models predict microbial mediated pathways but generally do not account for microorganisms. This study was undertaken to better understand relationships among microbial communities and N, S, Fe and C cycling in three lakes. Jackson Lakes formed from abandoned sand pits within the Bayou Chico Watershed in NW FL, USA. The three adjacent eutrophic lakes (SW, SE, and NE) are 12.0, 8.5, and 9.0 m deep, each with an oxycline 4 to 6 m below the surface. The NE lake is fully freshwater, whereas salinity below the oxycline in the SE and SW lakes are 2.4 and 4.5. Water column chemical profiles were obtained for O2, NH4+, NO3-/NO2=, dissolved Fe2+, SO4-, H2S, and CH4. The dominant biogeochemical pathways in the lakes were inferred by comparison of the chemical profiles. NH4+ levels above the oxycline ranged from 150 µM near the bottom of the NE and SW lakes and 820 µM in the SE lake. NO3- and NO2= levels were negligible below the oxycline, however, NO3- levels were 44 µM (SE lake), 100 uM (NE), and 8.5 uM (SE lake) above the oxycline, coinciding with supersaturated O2 surface waters. NO2= levels spiked 50 fold over surface levels at the oxycline for the SE lake (3.5 µM) and the NE lake (4 µM) but decreased from the surface to the oxycline in the SW lake. Maximum SO4- levels below the oxycline ranged from 0.25 mM (NE lake) to 1.8 mM (SE) and 3.0 mM (SW). Bottom water H2S levels peaked at > 164 uM (SW and SE lakes) but remained low at 8.0 uM in the NE lake. In contrast, Fe2+ concentrations were high (105 uM) near the bottom in the NE lake, and low (21 uM or less) in the SE and SW lakes. CH4 levels in the SE lake were 2.0 mM at the oxycline and increased with depth to near saturating 18.0 mM levels near the bottom. Despite high SO4- and H2S concentrations, similar CH4 profiles were observed for the SW and NE lakes. The lakes demonstrated zones of NO3-, Fe2+, and SO4- (when present) reduction and methanogenesis. Two lakes (SE and SE) were clearly sulfidic whereas the third (NE) was methanic. Ongoing work entails DNA and RNA isolation from synoptic samples to investigate microbial communities in relation to C, N, Fe, and S cycling in these biogeochemically different lakes. As reduction in uncertainty of ecosystem models is important for guiding environmental decisions, the overall goal of this research is to evaluate microbial communities and genes alongside biogeochemical models to obtain more realistic bases for balancing biogeochemical reactions.

Record Details: