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

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
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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

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Analysis

• Mission Aransas
• All analyses ran
• Nitrate, ammonium, phosphorus, DON, DOC, PON,
  d15N, POC, d13C, TSS
• San Antonio Guadalupe
• Summer 09 finish analyses

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San Antonio, Guadalupe, Mission and Aransas River
Watersheds
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DON concentration-runoff relationships
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NO3- concentration-runoff relationships
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NH4 Concentration-runoff relationships
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Water discharge, 2000-2007
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Mission and Aransas river export, 2007
export during July AR MR NO3-
32 40 NH4 57 45 DON 70 55
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Copano Bay Sampling Sites
Copano East
Copano Aransas
Copano West
5 km
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Salinity response in Copano Bay
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Nitrate concentrations in Copano Bay
During storm, average river nitrate conc. 12 µM
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Ammonium concentrations in Copano Bay
During storm, average river ammonium conc. 3 µM
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DON concentrations in Copano Bay

• During storm, average river DON conc. 31 µM

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September-January Recovery Period
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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