Investigation of Dissolved Organic Nitrogen in Water from a Prairie Pothole in Eastern South Dakota

• Main Author: Goerdt, Jessica M.
• Format: Text
• Language: unknown
• Published: Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange 2008
• Subjects: Ice cap
• Online Access: https://openprairie.sdstate.edu/etd/5177; https://openprairie.sdstate.edu/context/etd/article/6195/viewcontent/Goerdt_Jessica_2008.pdf

The oxidation-reduction (redox) potential of wetland waters may lead to differences in the composition of organic matter formed because microbial and abiotic processes differ significantly based on the amount of oxygen available. For example, different decomposition products are formed under reducing conditions than under oxidizing conditions. XAD-8 and XAD-4 resins were used to fractionate the organic matter in prairie pothole water into hydrophobic and hydrophilic acids, bases, and neutrals. Determination of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), 13C solid-state NMR spectroscopy, and the Bradford assay were performed on the fractions. Magnetic beads whose surfaces were covered with C3 groups were used to extract protein from the whole water samples. MALDI-TOF mass spectrometry was performed on the whole water sample and the extracted magnetic beads. It was found that the pothole waters undergo rapid shifts in redox potential during the winter and summer. Extremely reducing conditions (-350 mV) were observed when the pothole was covered by and ice cap, and oxidizing conditions (+800mV) were observed during the summer when the water was shallower and better mixed due to wind. DOC and DON mass balances were constructed for a twelve-month period, and it was shown that both the DOC and DON concentrations peak during these periods of extreme redox potential. Carbo-13 solid-state DPMAS NMR spectra showed that the most of the DOC present in the fractions was aliphatic in origin. Carbohydrate and carboxyl carbon types were also prevalent, with very little aromatic carbon in any of the fractions. MALDI-TOF mass spectrometry of the organic matter in the whole water sample showed several high molecular weight peaks, as did the spectra of the organic matter isolated with the magnetic beads. However, peaks were not reproducible and more research should be done to determine the reason. The Bradford assay showed that protein is present in all six of the fractions, with acids containing over 50% ...