Dr. Mina Bizic (Postdoctoral Researcher in Aquatic Microbial Ecology (DFG Eigene Stelle); Leibniz Institute for Freshwater Ecology and Inland Fisheries, Berlin)
Abstract:
In the last decade we have been witnessing an increasing frequency and duration of cyanobacterial blooms across many aquatic environments globally. While cyanobacterial blooms have numerous negative effects on their surrounding such as toxin release or anoxia upon bloom breakdown, there are those who attribute the phenomenon also positive effects. These lie in the potentially increased transport of fixed CO2 to the sediments of marine and freshwater environment. Downward fluxes of particulate organic matter (POM) represent the major process for sequestering and storage of atmospheric CO2 in aquatic sediments with model projections based on the ratio between carbon export and remineralization. Generally, microbial dynamics on POM is determined using closed vessels exerting a strong bias towards heterotrophy. A new flow-through rolling tank was developed for long term studies to continuously maintain POM at near in-situ conditions. Using this new device, we learn that our understanding of microbial activity on particles may be flawed and as a result more carbon may be transported to the sediment.
Nevertheless, in a recent study focusing on the role of Cyanobacteria in the “methane paradox” we revealed that these are releasing CH4, a more potent greenhouse gas than CO2, as a byproduct of photosynthesis. This comes in addition to our knowledge that cyanobacteria produce CH4 by demethylation of methylphosphonates and DMSP. Together, all these studies suggest that cyanobacteria are widespread, omnipotent methanogens.
The balance between CO2 sequestration and CH4 emission with respect to global warming effects is unknown and difficult to estimate for now. Nevertheless, given that CH4 is estimated to be 25-75 times more potent than CO2 as greenhouse gas over a century, the fixed CO2 released as CH4 by the cyanobacteria can be 25-75 lower than the sequestered CO2 for the balance to be tilted toward an overall warming effect of cyanobacterial blooms.
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