Project Title: Quantifying Coastal Ocean Acidification Impacts on Estuarine Nitrogen Removal
Principal Investigator(s): Robinson Fulweiler
Affiliations: Boston University
Summary: Ocean acidification in estuarine systems is expected to influence the biogeochemical cycling of nitrogen, a nutrient necessary for life. In estuarine systems, sediment denitrification is a natural microbial process that removes excess nitrogen and helps decrease the negative impacts of eutrophication. Evidence shows that sediment microbial communities that play a role in regulating denitrification are correlated with pH. For example, as pH decreases, the denitrification efficiency also decreases. This incomplete denitrification can lead to an increased production of nitrous oxide, a potent greenhouse gas that is 300 times more powerful that carbon dioxide. Yet, the impact of pH on marine sediment communities in general, and denitrifies in particular, has largely gone unexplored. In this study we will assess the impact of coastal acidification on sediment denitrification.
To address this topic we will (1) characterize the potentially active sediment microbial community under different pH regimes. (2) Couple the rates of denitrification to the key functional genes of the denitrifying community. (3) Experimentally alter the water column pH to test coastal acidification impacts on sediment denitrification processes and the active microbial community.
Oxygen metabolism and pH in coastal ecosystems: Eddy Covariance Hydrogen ion and Oxygen Exchange System (ECHOES)
Project Title: Oxygen metabolism and pH in coastal ecosystems: Eddy Covariance Hydrogen ion and Oxygen Exchange System (ECHOES)
Principal Investigator(s): Long, M.H., Charette, M.A., Martin, W.R., & McCorkle, D.C.
Abstract: An aquatic eddy covariance (EC) system was developed to measure the exchange of oxygen (O2) and hydrogen ions (H+) across the sediment‐water interface. The system uses O2 optodes and a newly developed micro‐flow cell H+ ion selective field effect transistor; these sensors displayed sufficient precision and rapid enough response times to measure concentration changes associated with turbulent exchange. Discrete samples of total alkalinity and dissolved inorganic carbon were used to determine the background carbonate chemistry of the water column and relate the O2 and H+ fluxes to benthic processes. The ECHOES system was deployed in a eutrophic estuary (Waquoit Bay), and revealed that the benthos was a sink for acidity during the day and a source of acidity during the night, with H+ and O2 fluxes of ± 0.0001 and ± 10 mmol m−2 h−1, respectively. H+ and O2 fluxes were also determined using benthic flux chambers, for comparison with the EC rates. Chamber fluxes determined in 0.25 h intervals co‐varied with EC fluxes but were ∼ 4 times lower in magnitude. Read full text…Limnology and Oceanography: Methods, 13(8), 438-450. http://onlinelibrary.wiley.com/doi/10.1002/lom3.10038/full