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  • Nitrification in a Subterranean Estuary: An Ex Situ and In Situ Method Comparison Determines Nitrate Is Available for Discharge
Title: Nitrification in a Subterranean Estuary: An Ex Situ and In Situ Method Comparison Determines Nitrate Is Available for Discharge
Abstract Subterranean estuaries (STEs) form in the subsurface where fresh groundwater and seawater meet and mix. Subterranean estuaries support a variety of biogeochemical processes including those transforming nitrogen (N). Groundwater is often enriched with dissolved inorganic nitrogen (DIN), and transformations in the STE determine the fate of that DIN, which may be discharged to coastal waters. Nitrification oxidizes ammonium (NH4+) to nitrate, making DIN available for N removal via denitrification. We measured nitrification at an STE, in Virginia, USA using in situ and ex situ methods including conservative mixing models informed by in situ geochemical profiles, an in situ experiment with15NH4+tracer injection, and ex situ sediment slurry incubations with15NH4+tracer addition. All methods indicated nitrification in the STE, but the ex situ sediment slurries revealed higher rates than both the in situ tracr experiment and mixing model estimations. Nitrification rates ranged 55.0–183.16 μmol N m−2 d−1based on mixing models, 94.2–225 μmol N m−2 d−1in the in situ tracer experiment, and 36.6–109 μmol N m−2 d−1slurry incubations. The in situ tracer experiment revealed higher rates and spatial variation not captured by the other methods. The geochemical complexity of the STE makes it difficult to replicate in situ conditions with incubations and calculations based on chemical profiles integrate over longer timescales, therefore, in situ approaches may best quantify transformation rates. Our data suggest that STE nitrification produces NO3−, altering the DIN pool discharged to overlying water via submarine groundwater discharge.  more » « less
Award ID(s):
1737258
PAR ID:
10579805
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
Journal of Geophysical Research: Biogeosciences
Date Published:
Journal Name:
Journal of Geophysical Research: Biogeosciences
Volume:
129
Issue:
6
ISSN:
2169-8953
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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