Particle-Associated Biogeochemical Processes in Fayetteville Green Lake, a High Sulfur, Permanently Anoxic Lake

Ashley Brooke Cohen1, Felix Weber2, Evan Lo3 and Gordon T Taylor2, (1)Stony Brook University, Stony Brook, NY, United States, (2)Stony Brook University, School of Marine and Atmospheric Sciences, Stony Brook, NY, United States, (3)Stony Brook University, Stony Brook, United States
Abstract:
In low O2 environments, communities of autotrophs are organized along redox gradients by the vertical succession of available terminal electron acceptors used to derive energy and the tolerance of their carbon fixation enzymes to O2. Their carbon fixation pathways fractionate carbon to differing extents while simultaneously fractionating their terminal electron acceptors. Within these redox zones, they are further partitioned into particle-associated (PA) and free-living (FL) assemblages. So, there should be a predictable relationship along redox gradients and among PA and FL particulate matter between δ13CPOC, stable isotope measurements relevant to the terminal electron acceptors (e.g., δ15N, δ34S), genes that encode for carbon fixation enzymes and for those that mediate transformations of terminal electron acceptors.

There have been many projects that have studied the geochemistry of size-fractionated particulate matter and PA versus FL microbiology, but few have studied both in parallel. Here I present δ13CPOC, δ15N and the molecular biology data of particulate matter operationally defined as PA (> 2.7 μ)and FL (0.2 – 2.7 μ) from Fayetteville Green Lake, NY- a meromictic lake with similar concentrations of dissolved inorganic carbon and sulfate to marine anoxic basins.

PA δ13CPOC ranged from -27 to -43 with a minimum at 20.5m (upper monimolimnion). FL δ13CPOC reached a minimum of -41 at the lower redoxcline boundary, followed by a positive excursion to -34 in the upper monimolimnion. The greatest difference between PA and FL δ13CPOC occurred in the upper monimolimnion, where δ15N reached a minimum of -6, consistent with complete denitrification. These features coincided with the maximum concentration of RuBisCO-II, which was predominantly PA. This was unexpected, as carbon fixation via RuBisCO-II results in δ13CPOC between 9 and -13. The most abundant OTUs at these depths were Sulfuricurvum kujiense, a sulfur-oxidizing denitrifier, Desulfobulbaceaand purple sulfur bacteria (PSB). TheDesulfobulbaceaare known ectosymbionts of the PSB, and both are typically particle-associated. Sulfuricurvum kujiensefixes carbon through the reverse citric acid (rTCA) cycle and is common in free-living assemblages.