15 Tracer Tests in the Hydrological Cycle

Tuesday, 15 March 2022
1:30 PM - 5:30 PM
Online

TRACING SOURCES AND FATE OF NITRATE USING ENVIRONMENTAL TRACERS AND NUMERICAL MODELS IN KARST WATERSHEDS AND SPRINGS, CENTRAL TEXAS

Paper number: 15-9
Program: Theme Sessions
Time: 3:50 PM – 4:10 PM

Authors

  • Yongli Gao Presenting Author
    University of Texas at San Antonio, San Antonio, TX
  • Timothy Sullivan
    University of Texas at San Antonio, San Antonio, TX
  • Xianglei Li
    University of Minnesota, Minneapolis, MN
  • Lin Ma
    The University of Texas at El Paso, El Paso, TX

Abstract

Assessing the fate and transport of contaminants in karst aquifer is challenging because it is not possible to identify the location and geologic characteristics of all karst features within an aquifer. Soil & Water Assessment Tool (SWAT) models were developed to identify the predominant source of nitrate entering surface waters in karst watersheds in central Texas. The analysis of watershed nitrogen inputs identified livestock, atmospheric deposition, wildlife, and fertilizer use as primary sources of nitrogen. The SWAT model showed that the largest contributors to nitrate stream yield were atmospheric deposition, livestock, and a Wastewater Treatment Plant (WWTP). A contaminant transport model was developed using CFPv2, an experimental version of the Conduit Flow Process (CFP) module of MODFLOW, in conjunction with the Three-Dimensional Underground Mine Transport Model (UMT3D). Nitrate concentration and aquifer recharge estimated from the SWAT model were used as input to the CFPv2 and UMT3D models. The hydrologic calibration of the CFPv2 model demonstrated that it outperformed a previously developed Equivalent Porous Medium (EPM) model for the Edwards Aquifer. The UMT3D model was successfully calibrated for nitrate concentrations and the results obtained were consistent with the assessment of nitrate sources from the SWAT model. Preliminary results of multiple radiogenic and stable isotopes on surface water and groundwater demonstrated that multi-isotope tracers can be used to characterize residence time and sources of nitrate in several streams and springs in central Texas.

Geological Society of America Abstracts with Programs. Vol. 54, No. 1

doi: 10.1130/abs/2022SC-374392

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.