Title: Forecasting rates of sediment nutrient and metal fluxes under coastal acidification for improved estuarine water quality
Principal Investigator/contact information: Claudia I. Mazur (she/her) Ph.D. Candidate, Fulweiler Lab NOAA Margaret A. Davidson Fellow Earth & Environment, Boston University Email: email@example.com Lab Website: fulweilerlab.com
Abstract: Coastal acidification refers to the reduction in pH of coastal waters. Unlike the open ocean, coastal acidification is driven by excess nitrogen (N). This N fuels primary productivity and the subsequent decomposition of this organic matter lowers estuarine pH. In fact, estuaries experience pH shifts of ≥ 0.5 daily. Thus, estuaries are natural laboratories in which to study how acidification alters fundamental ecosystem processes such as nutrient filtration and cycling. The purpose of this research is to determine the impact of coastal acidification on sediment N, phosphorus (P), and iron (Fe) cycling. To address this issue, I will experimentally manipulate pH in the overlying water column of sediment cores collected from Waquoit Bay, MA. Using continuous flow through incubations, I will quantify rates of sediment denitrification (microbial removal of N to di-nitrogen gas), N, P and Fe fluxes. I will use these findings and data from the WBNERR System-Wide Monitoring Program to develop a model that will predict the impact of low pH conditions on these fluxes and future water quality in Waquoit Bay. This study will be a crucial link to understanding how coastal acidification alters total ecosystem productivity, biogeochemical cycling and water quality.
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.
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