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Watershed Export and Estuarine Ecosystem Response to Pulsed Inputs of Nitrogen to South Texas Bays

Watershed Export and Estuarine Ecosystem Response to Pulsed Inputs of Nitrogen to South Texas Bays. Jim McClelland Rae Mooney University of Texas at Austin Marine Science Institute. Sampling. San Antonio & Guadalupe Sampling base flow monthly 12/07 – 6/08

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Watershed Export and Estuarine Ecosystem Response to Pulsed Inputs of Nitrogen to South Texas Bays

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  1. Watershed Export and Estuarine Ecosystem Response to Pulsed Inputs of Nitrogen to South Texas Bays Jim McClelland Rae Mooney University of Texas at Austin Marine Science Institute

  2. Sampling • San Antonio & Guadalupe • Sampling base flow monthly 12/07 – 6/08 • • Increased base flow sampling each week 6/08 – 8/08 • • 9/08 – present, base flow sampling every 2 weeks • • Storm event sampling continuous • Mission & Aransas • Monthly and event sampling 7/07 – 11/08

  3. Analysis Mission & Aransas • All analyses ran • Nitrate, ammonium, phosphorus, DON, DOC, PON, δ15N, POC, δ13C, TSS San Antonio & Guadalupe • Summer 09 – finish analyses

  4. San Antonio, Guadalupe, Mission and Aransas River Watersheds

  5. DON: concentration-runoff relationships

  6. NO3-: concentration-runoff relationships

  7. NH4+: Concentration-runoff relationships

  8. Water discharge, 2000-2007

  9. Mission and Aransas river export, 2007 % export during July AR MR NO3- 32 40 NH4+ 57 45 DON 70 55

  10. Copano Bay Sampling Sites Copano East Copano Aransas Copano West 5 km

  11. Salinity response in Copano Bay

  12. Nitrate concentrations in Copano Bay During storm, average river nitrate conc. ~ 12 µM

  13. Ammonium concentrations in Copano Bay During storm, average river ammonium conc. ~ 3 µM

  14. DON concentrations in Copano Bay • During storm, average river DON conc. ~ 31 µM

  15. September-January Recovery Period

  16. Conclusions Characterization of water chemistry during storm events is necessary for accurate estimation of annual nitrogen export from watersheds to the coastal ocean While nitrogen concentrations in coastal waters return to pre-storm values relatively quickly after individual events, slower recovery of ammonium and DON concentrations compared to nitrate demonstrate the lasting effects of pulsed inputs through recycling Variations in the timing and magnitude of nitrogen inputs to coastal waters may fundamentally alter ecosystem structure and productivity

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