NDLI: Identification of nitrogen sources and transformations within karst springs using isotope tracers of nitrogen

Content Provider	Springer Nature Link
Author	Albertin, Andrea R. Sickman, James O. Piwska, Agnieszka Stevenson, R. Jan
Copyright Year	2011
Abstract	Isotope analyses of nitrate and algae were used to gain better understanding of sources of nitrate to Florida’s karst springs and processes affecting nitrate in the Floridan aquifer at multiple scales. In wet years, δ15N and δ18O of nitrate ranged from +3 to +9‰ in headwater springs in north Florida, indicating nitrification of soil ammonium as the dominant source. With below normal rainfall, the δ15N and δ18O of nitrate were higher in almost all springs (reaching +20.2 and +15.3‰, respectively) and were negatively correlated with dissolved oxygen. In springs with values of δ15N-NO3 and δ18O-NO3 greater than +10‰, nitrate concentrations declined 40–50% in dry years and variations in the δ15N and δ18O of nitrate were consistent with the effects of denitrification. Modeling of the aquifer as a closed system yielded in situ fractionation caused by denitrification of 9 and 18‰ for Δ18O and Δ15N, respectively. We observed no strong evidence for local sources of nitrate along spring runs; concentrations declined downstream (0.42–3.3 μmol-NO3 L−1 per km) and the isotopic dynamics of algae and nitrate indicated a closed system. Correlation between the δ15N composition of nitrate and algae was observed at regional and spring-run scales, but the relationship was complicated by varying isotopic fractionation factors associated with nitrate uptake (Δ ranged from 2 to 13‰). Our study demonstrates that nitrate inputs to Florida’s springs are derived predominantly from non-point sources and that denitrification is detectable in aquifer waters with relatively long residence time (i.e., matrix flow).
Starting Page	219
Ending Page	232
Page Count	14
File Format	PDF
ISSN	01682563
Journal	Biogeochemistry
Volume Number	108
Issue Number	1-3
e-ISSN	1573515X
Language	English
Publisher	Springer Netherlands
Publisher Date	2011-03-22
Publisher Place	Dordrecht
Access Restriction	Subscribed
Subject Keyword	Florida Karst springs Isotope Nitrate Algae Denitrification Life Sciences Environmental Chemistry Biogeosciences Ecosystems
Content Type	Text
Resource Type	Article
Subject	Earth-Surface Processes Environmental Chemistry Water Science and Technology

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