, Volume 108, Issue 1–3, pp 219–232 | Cite as

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

  • Andrea R. Albertin
  • James O. Sickman
  • Agnieszka Pinowska
  • R. Jan Stevenson


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).


Florida Karst springs Isotope Nitrate Algae Denitrification 



We thank Martin Anderson, Mi Youn Ahn, Scott Fulbright, Delores Lucero, Francisco Alvarado, Mayana Anderson, Eric Jorczak, Alyson Dagang, Will Vicars, Yu Wang, Gavin Wilson, Yubao Cao and Xiaowei Gu for assistance with field surveys and laboratory analyses. We thank Russ Frydenborg and Denise Miller for their support of the project. We also thank Dr. Brian Fry for insightful comments on the study. Funding was provided by the Florida Department of Environmental Protection and the University of Florida.

Supplementary material

10533_2011_9592_MOESM1_ESM.doc (67 kb)
Supplementary material 1 (DOC 67 kb)


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Andrea R. Albertin
    • 1
    • 2
  • James O. Sickman
    • 3
  • Agnieszka Pinowska
    • 4
  • R. Jan Stevenson
    • 5
  1. 1.Soil and Water Science DepartmentUniversity of FloridaGainesvilleUSA
  2. 2.School of Forest Resources and ConservationUniversity of FloridaGainesvilleUSA
  3. 3.Department of Environmental SciencesUniversity of CaliforniaRiversideUSA
  4. 4.Advanced Fuels DivisionGeneral AtomicsSan DiegoUSA
  5. 5.Department of ZoologyMichigan State UniversityEast LansingUSA

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