Assessing the Role of pH in Determining Water Column Nitrification Rates in a Coastal System |
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Authors: | Robinson W Fulweiler Hollie E Emery Elise M Heiss Veronica M Berounsky |
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Institution: | (1) Earth Sciences Department, Boston University, Boston, MA 02215, USA;(2) Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA |
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Abstract: | Ocean acidification is predicted to impact the nitrogen cycle in a variety of ways. Specifically, manipulations of water column
pH have shown that nitrification, the microbial conversion of ammonium to nitrate, is inhibited at low pH. A decrease in nitrification
may impact phytoplankton composition and production, denitrification, and the production of nitrous oxide. We compiled an
existing unique data set of concurrent water column nitrification rates and water column pH values from a temperate New England
estuary (Narragansett Bay, RI, USA). Contrary to the current hypothesis, we found that nitrification rates were highest at
low pH and significantly (P = 0.0031) lower at high water column pH. In this study, pH varied up to 0.85 units, 20% more than the maximum predicted ocean
pH decrease of 0.7 units. These results highlight that nitrifying organisms in coastal systems tolerate a wide range of pH
values. Moreover, the degree of negative correlation with pH may depend on site-specific environmental conditions. Combined,
these findings indicate that the current hypothesis of the negative impacts of ocean acidification on nitrification, at least
for the coastal ocean, might need reevaluation. |
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