role of hydroperiod and fire on carbon dynamics of a
TRANSCRIPT
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David SumnerUS Geological SurveyCaribbean-Florida Water Science Center
Scott Graham and Ross HinkleUniversity of Central FloridaDepartment of Biology
Role of hydroperiod and fire on carbon dynamics of a subtropical peat marsh
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Blue Cypress Marsh
Blue Cypress marsh
Headwaters of St. Johns River
Thick (> 3 meters) peat soils
Underlain by clay
Active water level management
Predominantly sawgrass cover with invasive willows
Sawgrass in marsh is tall and dense compared to sawgrass in much of EvergladesTaylor Slough
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Flux station
Blue Cypress Lake
Stick Marsh
Blue Cypress marsh within headwaters of the St. Johns River
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1993 2000 2005 2010
Water management change apparent in year 1999 and thereafter
Stage variability has increased markedly – intra-year stage range has increased from average of 50 to 90 cm.
Fires in 2001, 2008, and 2014
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Why measure carbon fluxes ?1. CO2 and CH4 are important
greenhouse gases – relate fluxes to environment, landscape, and management….. carbon credits
2. Topographic loss or gain
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Why measure carbon fluxes ?
1. CO2 and CH4 are important greenhouse gases
2. Topographic loss or gain/nutrients
Organic N converts via:
Mineralization/Nitrification
Nitrate
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Mass and heat fluxes
Eddy covariance method
Net ecosystem exchange (NEE) = CCO2w = mean(CCO2’ w’)
CCO2 = vapor densityw = vertical wind speed’ = fluctuation about average
= cov (CCO2 ,w)
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LI-COR 7500 - CO2/H2O
CSI CSAT3 – uvw & Ts LI-COR 7700 – CH4
10 Hertz samplingEddyPro processing30-minute composites
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Gap-filling & partitioning NEE to Photosynthesis and Respiration (ER)
Light response curveParameters (α, NEEmax & ER) defined monthlybased on regression with daytime half-hour NEE data
α PPFD + NEEmaxNEE =
-α PPFD NEEmax+ ERd
Day
Night
ERn = Lloyd&Taylor function of Ta and water level; likewise, daily CH4 flux
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Carbon exchange strongly impacted by hydroperiod
When marsh is wet:
Heterotrophic respiration is low
therefore, net CO2 sequestration is high
but methane release enhanced
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Blue Cypress marsh – NEE
NEE = 597 65 97 284
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Blue Cypress marsh – RnOne size fits all function of temperature and water level
RE = 939 1220 1278 1020
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Blue Cypress marsh – CH4One size fits all function of temperature and water level
2010 - 33 g C/m^2
2011 – 26
2012 – 32
2013 - 44
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2,248 g DM m-2
Before March 2014 fire
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318 g DM m-2
Post March 2014 fire
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1 month
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4 months
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fire
RE
NEEday
Rapid recovery from fire
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Impact of fire on light response curves
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J F M A M J J A S O N D
ET was modestly impacted by low water levels
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Questions ?
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Long- and short hydroperiod marsh comparison
Schedlbauer et al., 2010 Blue Cypress marshAgricultural & Forest Meteorology
Sawgrass & muhly grass SawgrassCanopy height of 0.73 m 2 to 3 m – very denseHydroperiod: 4-month (2008) 9-month (2011) to 12-month (2010)Shallow (0.14 m) marl soils over limestone Deep (3.4 m) peat soils over clay
Year2010 Year2011NEP = 50 597 65R = 446 939 1,220 GEP = 496 1,537 1,285CH4 = ? 33 26All flux units are in: g C / m2 / year
Inundation suppresses productivity Inundation has little impact on productivitySubstantial canopy submergence Slight canopy submergence
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Climate change
Higher temperature increased loss of C via respiration and methane releases
Greater frequency of droughts -> increased loss of C via respiration, but lower methane releases
More fires – loss of vegetation during spring 2014 fire = 963 g C/m2 or 3.2 years
Insolation – cloud cover changes ?
Water management can mitigate climate change impacts