Source, variability, and transformation of nitrate in a regional karst aquifer: Edwards aquifer, central Texas


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Material Information

Title:
Source, variability, and transformation of nitrate in a regional karst aquifer: Edwards aquifer, central Texas
Series Title:
Science of The Total Environment
Creator:
Musgrove, M.
Opsahl, S.P.
Mahler, B.J.
Herrington, C.
Sample, T.L.
Banta, J.R.
Publisher:
Elsevier
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Nitrogen ( local )
Nutrients ( local )
Nitrification ( local )
Isotopes ( local )
Urbanization ( local )
Genre:
serial ( sobekcm )

Notes

Abstract:
Many karst regions are undergoing rapid population growth and expansion of urban land accompanied by increases in wastewater generation and changing patterns of nitrate (NO3−) loading to surface and groundwater. We investigate variability and sources of NO3− in a regional karst aquifer system, the Edwards aquifer of central Texas. Samples from streams recharging the aquifer, groundwater wells, and springs were collected during 2008–12 from the Barton Springs and San Antonio segments of the Edwards aquifer and analyzed for nitrogen (N) species concentrations and NO3− stable isotopes (δ15N and δ18O). These data were augmented by historical data collected from 1937 to 2007. NO3− concentrations and discharge data indicate that short-term variability (days to months) in groundwater NO3− concentrations in the Barton Springs segment is controlled by occurrence of individual storms and multi-annual wet-dry cycles, whereas the lack of short-term variability in groundwater in the San Antonio segment indicates the dominance of transport along regional flow paths. In both segments, longer-term increases (years to decades) in NO3− concentrations cannot be attributed to hydrologic conditions; rather, isotopic ratios and land-use change indicate that septic systems and land application of treated wastewater might be the source of increased loading of NO3−. These results highlight the vulnerability of karst aquifers to NO3− contamination from urban wastewater. An analysis of N-species loading in recharge and discharge for the Barton Springs segment during 2008–10 indicates an overall mass balance in total N, but recharge contains higher concentrations of organic N and lower concentrations of NO3− than does discharge, consistent with nitrification of organic N within the aquifer and consumption of dissolved oxygen. This study demonstrates that subaqueous nitrification of organic N in the aquifer, as opposed to in soils, might be a previously unrecognized source of NO3− to karst groundwater or other oxic groundwater systems.
Original Version:
Science of The Total Environment, Vol. 568 (2016-10-15).

Record Information

Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
This item is licensed with the Creative Commons Attribution Non-Commercial No Derivative License. This license allows others to download this work and share them with others as long as they mention the author and link back to the author, but they can’t change them in any way or use them commercially.
Resource Identifier:
K26-05188 ( USFLDC: LOCAL DOI )
k26.5188 ( USFLDC: LOCAL Handle )

USFLDC Membership

Aggregations:
University of South Florida
Karst Information Portal

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