Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer
Abstract
Aquifer denitrification is among the most poorly constrained fluxes in global and
regional nitrogen budgets. The few direct measurements of denitrification in groundwaters
provide limited information about its spatial and temporal variability, particularly
at the scale of whole aquifers. Uncertainty in estimates of denitrification may also
lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby
confound the inference of N source from these data. In this study, our objectives
are to quantify the magnitude and variability of denitrification in the Upper Floridan
Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale.
Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations
for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived)
N2 is highly variable in space and inversely correlated with dissolved oxygen (O2).
Negative relationships between O2 and δ15N NO3 across a larger dataset of 113 springs,
well-constrained isotopic fractionation coefficients, and strong 15N:18O covariation
further support inferences of denitrification in this uniquely organic-matter-poor
system. Despite relatively low average rates, denitrification accounted for 32 % of
estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source
δ15N NO3 based on denitrification progression suggest that isotopically-enriched nitrate
(NO3-) in many springs of the UFA reflects groundwater denitrification rather than
urban- or animal-derived inputs. © Author(s) 2012.
Type
Journal articlePermalink
https://hdl.handle.net/10161/8359Published Version (Please cite this version)
10.5194/bg-9-1671-2012Publication Info
Heffernan, JB; Albertin, AR; Fork, ML; Katz, BG; & Cohen, MJ (2012). Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer.
Biogeosciences, 9(5). pp. 1671-1690. 10.5194/bg-9-1671-2012. Retrieved from https://hdl.handle.net/10161/8359.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Megan Fork
Teaching Assistant
Megan Fork is a current PhD candidate in Environmental Science & Policy at Duke's
Nicholas School of the Environment.
James Brendan Heffernan
Associate Professor of Ecosystem Ecology and Ecohydrology
I am interested in major changes in ecosystem structure, particularly in streams,
rivers and wetlands. My work focuses on feedbacks among ecological, physical, and
biogeochemical processes, and uses a wide range of tools and approaches. I am particularly
interested in projects that address both basic ecological theory and pressing environmental
problems. Increasingly, we are applying tools and theories developed for local ecosystems
to better understand ecological patterns and mechanisms at regi
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