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Effects of Drought and Wastewater on Nitrate Concentrations in the Barton Springs Zone

Effects of Drought and Wastewater on Nitrate Concentrations in the Barton Springs Zone. Barbara Mahler U.S. Geological Survey bjmahler@usgs.gov. Hydrologic conditions: transition from drought to wet. Nitrate concentrations in streams increased when the drought broke in Sept. 2009. Drought.

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Effects of Drought and Wastewater on Nitrate Concentrations in the Barton Springs Zone

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  1. Effects of Drought and Wastewater on Nitrate Concentrations in the Barton Springs Zone Barbara Mahler U.S. Geological Survey bjmahler@usgs.gov

  2. Hydrologic conditions: transition from drought to wet

  3. Nitrate concentrations in streams increased when the drought broke in Sept. 2009 Drought time

  4. ….and were high relative to measured streamflow Flow rate 10,000

  5. Nitrate concentrations in groundwater had contrasting responses to the break in the drought (Sept. 2009) Barton Springs Buda well Marbridge well

  6. Barton Springs: Nitrate concentrations were higher relative to historical levels 1988 to 2010 1993-2008 2008-10

  7. What’s changed? Barton Springs

  8. Septic systems permitted by year

  9. Irrigation volume permitted by year Williamson

  10. Cumulative N loading Stream Recharge • Organic N is being converted to nitrate in the aquifer • Total N is being stored (conservatively?) in the aquifer Nitrogen, in kilograms Barton Springs Nov 08 Nov 08 Jan 09 Jan 09 Mar 09 Mar 09 May 09 May 09 Jul 09 Jul 09 Sep 09 Sep 09 Nov 09 Nov 09 Jan 10 Jan 10 Mar 10 Mar 10

  11. Implications of nitrification • Organic nitrogen  NH4+ (ammonification) • NH4+ + 1.5 O2  2H + + 2H2O + NO2- • NO2- + 0.5 O2  NO3- • For every mg of ammonia oxidized to nitrate, 4.18 mg of oxygen are consumed • Nitrification lowers the pH

  12. Infiltration and discharge to surface water Partial ammonification and nitrification; recharge to groundwater Continued ammonification and nitrification of organic nitrogen

  13. Related publications • Nitrate concentrations and potential sources in the Barton Springs segment of the Edwards Aquifer and its contributing zone, Central Texas. 2011. Mahler, B.J., Musgrove, M., and Herrington, C. USGS Fact Sheet 2011-3035 http://pubs.usgs.gov/fs/2011/3035/ • Recent (2008–10) concentrations and isotopic compositions of nitrate and concentrations of wastewater compounds in the Barton Springs Zone, South-Central Texas, and their potential relation to urban development in the contributing zone. 2011. Mahler, B.J., Musgrove, M., Herrington, C., and Sample, T.L. USGS Scientific Investigations Report 2011-5018. http://pubs.usgs.gov/sir/2011/5018/ • Recent (2008–10) water quality in the Barton Springs segment of the Edwards Aquifer and its contributing zone, Central Texas, with emphasis on factors affecting nutrients and bacteria. 2011. Mahler, B.J., Musgrove, M., Wong, C.J., and Sample, T.L. USGS Scientific Investigations Report 2011-5139. http://pubs.usgs.gov/sir/2011/5139/ • bjmahler@usgs.gov; 512-927-3566

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