Owen Coyle, 2012, Geosciences

Using mesocosms (small simulated environments containing sediment and seawater) from Chesapeake Bay, we studied the effects of a simulated high organic material flux on the microbial communities living in the sediment. We focused on the response of the bacteria involved in classical denitrification, assessed whether the availability of organic material would favor anammox or denitrifiers, evaluated whether the sediment system could respond adequately to this unnaturally high supply of fixed nitrogen. My work to date has focused on collecting and analyzing daily water samples for various dissolved inorganic fixed nitrogen (DIN) species: ammonium, nitrate, and nitrite, as well as collecting and preparing samples for genetic and direct tracer experiments to determine the metabolic contribution of anammox and denitrifiers. While some results are still outstanding (I may revisit them on my Fall JP), using multiple box models we can draw some initial conclusions about how the microbial community responded. First, it appears that those mesocosms receiving a large influx of organic material showed higher denitrifier activity relative to anammox than did those receiving low treatments. Second, in all mesocosms, denitrifier activity appeared to lag behind anammox activity (which may be critical to the prevalence anammox bacteria given their slower growth rates relative to denitrifiers). Third, while our mesocosms were subjected to nitrogen loadings much greater than current or projected anthropogenic fluxes, microbial activity was able to acclimate relatively quickly indicating that continental shelf systems may be able to buffer future anthropogenic influxes from reaching the open ocean.