Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California
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Abstract
Coupled measurements of nitrate (NO3−), nitrogen (N), and oxygen (O) isotopic composition (δ15NNO3 and δ18ONO3) were made in surface waters of Monterey Bay to investigate multiple N cycling processes occurring within surface waters. Profiles collected throughout the year at three sites exhibit a wide range of values, suggesting simultaneous and variable influence of both phytoplankton NO3− assimilation and nitrification within the euphotic zone. Specifically, increases in δ18ONO3 were consistently greater than those in δ15NNO3. A coupled isotope steady state box model was used to estimate the amount of NO3− supplied by nitrification in surface waters relative to that supplied from deeper water. The model highlights the importance of the branching reaction during ammonium (NH4+) consumption, in which NH4+ either serves as a substrate for regenerated production or for nitrification. Our observations indicate that a previously unrecognized proportion of nitrate‐based productivity, on average 15 to 27%, is supported by nitrification in surface waters and should not be considered new production. This work also highlights the need for a better understanding of isotope effects of NH4+ oxidation, NH4+ assimilation, and NO3− assimilation in marine environments.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California |
| Series title | Global Biogeochemical Cycles |
| DOI | 10.1029/2006GB002723 |
| Volume | 21 |
| Issue | 2 |
| Year Published | 2007 |
| Language | English |
| Publisher | AGU |
| Contributing office(s) | California Water Science Center, Toxic Substances Hydrology Program |
| Description | 13 p. |
| Country | United States |
| State | California |
| Other Geospatial | Monterey Bay |
| Google Analytic Metrics | Metrics page |