2019 REUs presented at the CERF Conference in Mobile, AL
Diel and Size Scale Variability in the Uptake and Regeneration of Ammonium and Nitrate by a Subestuarine Plankton Population of the Chesapeake Bay, USA
Short-term ammonium and nirate dynamics in three plankton size classes were studied in a mesocosm experiment using tracer and 15N isotope dilution techniques. A single site in the Choptank River, a sub-estuary of the Chesapeake Bay, was chosen for initial whole water collection. The samples were then size-fractionated and incubated. Subsamples were extracted over 36 hours and analyzed for ambient concentrations, uptake rates, and regeneration rates of the inorganic nitrogen sources.
In each size class population, initial utilization and regeneration of ammonium, preferred over nitrate, was noted. Absence of light for photosynthesis during the night in the smaller size classes caused nitrogen cycling shifts to affect the larger populations. Nitrate preferences dominated the upper fractions near the end of the 36-hour period. Diel variation was not related to nitrogen source preferences.
Methanogenesis in Anoxic Estuarine Sediments
This study attempts to ascertain the effect of substrate addition on methanogenesis in anoxic estuarine sediments. Box cores of sediment were taken from the upper and middle Chesapeake Bay from which the top and bottom layers were collected, so that a profile of methanogenesis with changing sulfate concentration and changing or by methanogens alone ("noncompetitive"). When sulfate ion was decreased from ambient levelssalinity could be seen. The mud was slurried and assays were made of methanogenesis in the presence of added substrates that are metabolized by both methanogens and sulfate reducing bacteria ("competitive") or by methanogens alone ("noncompetitive"). When sulfate ion was decreased from ambient levels increased methane production from acetate was observed. No significant difference in methane production from methanol was noted between sulfate containing and sulfate depleted samples possible because of the high concentration of added methanol. When noncompetitive substrates were available methanogens were able to coexist with sulfate reducing bacteria in anoxic estuarine sediments. Sulfate did not inhibit methanogens from producing substantial amounts of methane from added trimethylamine dimethylamine and monomethylamine. Estuare methanogens from sulfate rich areas rapidly metabolize methylamines and appear readily able to adapt to acetate metabolism when sulfate levels decrease.
210Pb Dating of Three Sediment Cores in mid-Chesapeake Bay
The geochronological dating tool, 210Pb dating, was used to determine average sedimentation rates in three mid-bay stations. The stations (M1, M2, M3) followed a lateral transect from 27537.5 x 42404.4, to 27530.0 x 42405.0, to 27523.9 x 42406.6 respectively. Average sedimentation rates were .161 g cm-2 yr-1 for station M1 and .27 g cm-2 yr-1 for station M2. No value was obtained for station M3 due to homogenous mixing of 210Pb throughout the sediment core. Mixing most likely resulted from anthropogenic disturbances or from a slumping of sediment into a depression. Mixing later depth was ~10 cm at stations M1 and M2. Mixing was a result of current action as well as some bioturbation.