The impact of fire on hydrology and suspended sediment and nutrient export in southern California chaparral watersheds

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The impact of fire on hydrology and suspended
sediment and nutrient export in southern
California chaparral watersheds
Masters Research Seminar By J. Scott Coombs
Santa Barbara Coastal Long Term Ecological
Research (SBC LTER)
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Talk Outline

• Introduction
• Methods
• Hydrology
• Suspended Sediment Export
• Nutrient Biogeochemistry
• Nutrient Export
• Summary of Results
• Acknowledgments
• Questions

February 23, 2005
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Gaviota Wildfire June 5 to 12, 2004
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Historical Fires in Study Area
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San Onofre Creek
Stream Sampling
February19, 2005
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Stream Gauging
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Changes to Hydrologic Response

• Infiltration decreases
• formation of hydrophobic soil layer
• compaction of soil
• Evapotranspiration and Interception decrease
• more rainfall is available for runoff

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Early Season Storm Hydrographs

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Mid-Winter Storm Hydrographs

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San Onofre Creek
October 26, 2004
October 19, 2004
November 15, 2004
December 28, 2004
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San Onofre Creek
January 7, 2005
January 26, 2005
February 22, 2005
February19, 2005
April 27, 2005
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Discharge Patterns

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Changes to Sediment Export

• Infiltration decreases
• Runoff and peak discharge increase
• Interception decreases due to vegetation loss

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Discharge-Suspended Sediment Trends

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Gaviota Watershed
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Sediment Deposition in Gaviota November 22,2004
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Discharge-Suspended Sediment Trends

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Sediment movement in San Onofre
Photos taken May 2005
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Discharge-Suspended Sediment Trends

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Suspended Sediment Storm Export

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Nitrogen Biogeochemistry

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Nitrogen Biogeochemistry

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Dissolved Nitrogen Response

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Nitrate Storm Export

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DON Storm Export

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Changes in Phosphate Export

• Phosphate is rapidly mineralized and deposited on
  soil surface but is not as mobile as nitrate
• Increases in phosphate concentration in runoff
  roughly correlates with peak discharge

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Phosphate Storm Export

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Summary of Results

• Hydrology
• Hydrologic response was typical for southern
  California chaparral during early season storms
  but differences decreased as the season
  progressed with above average rainfall.
• Suspended Sediment
• 10-fold increase in suspended sediment export
• Nutrients
• 30 times increase in ammonium export
• 5.5 times increase in nitrate export
• 2.8 times increase in DON export
• 2 times increase in phosphate export

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Acknowledgements

• Special thanks to
• My advisors John Melack, Arturo Keller, and
  Jordan Clark.
• Frank Setaro and Allen Doyle for their assistance
  in sample processing and analysis.
• Tim Robinson and Al Leydecker for their advice
  and solace.
• My family and friends for their support and
  encouragement.
• My wife, Maria, for her love and understanding of
  my absence on all those rainy nights.

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Questions?