The biological carbon pump acts as part of the global carbon cycle through the photosynthetic fixation of inorganic carbon into dissolved and particulate organic carbon by phytoplankton. Previously, the biological carbon pump was attributed to large aggregates and zooplankton fecal pellets since their size and density results in faster sinking rates, efficiently exporting organic carbon to deeper depths in the ocean. However, recent studies have indicated that small cells, known as picoplankton, contribute significantly to the formation of sinking particles. The presence of exopolymeric substances (EPS), among them sticky transparent exopolymeric particles (TEP) and proteinaceous coomassie stainable particles (CSP), serve as influential factors of export flux and aggregation. The presence of heterotrophic bacteria can also affect aggregation and sinking velocity, as seen in previous studies, and is likely attributed to their EPS and TEP production. The staining and visualization of TEP and CSP allow for the qualitative determination of these types of EPS from bacteria isolated from sinking particles collected with particle interceptor traps at various depths in the Sargasso Sea. I study the presence of TEP and CSP in particle-associated bacteria. Cultures of picocyanobacteria, consisting of xenic Synechococcus and axenic Prochlorococcus, were used to establish positive and negative controls for stained isolate analysis. Marinobacter adhaerens served as a tertiary control for an axenic culture that stains positive for TEP. I chose six isolates of bacteria isolated from sinking particles to be stained and visualized to test for the secretion of TEP and CSP. Four of the isolates stained positive for both TEP and CSP, including Pseudoalteromonas sp., Erythrobacter sp., and Marinobacter sp., while one isolate, Micrococcus sp., stained positive only for TEP, and the last isolate, another Marinobacter sp., stained positive for only CSP. These results are important in understanding the role of plankton organisms in the formation of sinking particles.
The global transport and deposition of anthropogenic nitrogen (N) to downwind ecosystems are significant and continue to increase. Indeed, atmospheric deposition can be a significant source of N to many watersheds, including those in remote, unpopulated areas. Bacterial denitrification in lake sediments may ameliorate the effects of N loading by converting nitrate (NO3-) to N2 gas. Denitrification also produces nitrous oxide (N2O), a potent greenhouse gas. The ecological effects of atmospheric N inputs in terrestrial ecosystems and the pelagic zone of lakes have been well documented; however, similar research in lake sediments is lacking. This project investigates the effects N of deposition on denitrification and N2O production in lakes. Atmospheric N inputs might alter the availability of NO3- and other key resources to denitrifiers. Such altered resources could influence denitrification, N2O production, and the abundance of denitrifying bacteria in sediments. The research contrasts these responses in lakes at the ends of gradients of N deposition in Colorado and Norway. Rates of denitrification and N2O production were elevated in the sediments of lakes subject to anthropogenic N inputs. There was no evidence, however, that N deposition has altered sediment resources or the abundance of denitrifiers. Further investigation into the dynamics of nitric oxide, N2O, and N2 during denitrification found no difference between deposition regions. Regardless of atmospheric N inputs, sediments from lakes in both Norway and Colorado possess considerable capacity to remove NO3- by denitrification. Catchment-specific properties may influence the denitrifying community more strongly than the rate of atmospheric N loading. In this regard, sediments appear to be insulated from the effects of N deposition compared to the water column. Lastly, surface water N2O concentrations were greater in high-deposition lakes compared to low-deposition lakes. To understand the potential magnitude of deposition-induced N2O production, the greenhouse gas inventory methodology of Intergovernmental Panel on Climate Change was applied to available datasets. Estimated emissions from lakes are 7-371 Gg N y-1, suggesting that lakes could be an important source of N2O.