“pyro-eco-hydro-geomorphology”: implications of organic ... ·...
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“Pyro-eco-hydro-geomorphology”: Implications of organic soil combustion on
the hydrology and ecology of peat wetlands
David A. Kaplan, University of Florida, Environmental Engineering Sciences Casey A. Schmidt, Desert Research Institute, Division of Hydrologic Sciences
Daniel L. McLaughlin, Virginia Tech, Forest Resources and Environmental Conservation
Adam C. Watts, Desert Research Institute, Division of Atmospheric Sciences
Conference on Ecological and Ecosystem Restoration New Orleans, LA, July 2014
A fire ecologist, a soil scientist, and two hydrologists walk into a cypress dome…
A fire ecologist, a soil scientist, and two hydrologists walk into a cypress dome…
How do ground fires and organic soil combustion affect the hydrology and ecology of peat wetlands?
Peatlands = Large Global Carbon Storage
• 2-3% of Earth land surface • 25% - 33% of global soil C • Exceeds global vegetation C • Similar to atmospheric C pool
Source: Wetlands International/Economist
Significance of Peat Fires
Significance of Peat Fires
• Peat Fires Smoldering combustion Soil consumption - Smoke, particulates - Carbon release and emissions - Management challenge
• Susceptibility to fire increasing - Some peat fires occur naturally - High latitudes: warming - Tropics: clearing for agriculture
Implications of Peat Fire Management?
• Hazards are clear • Difficult to control de facto policy of suppression • Unintended effects of prevention? • What are the ecological effects of soil-consuming fires…and their
suppression?
Photo: USFWS
1. Smoldering in thick organic soil
1. Smoldering in thick organic soil 2. Microtopographic change basin formation
VB1
1. Smoldering in thick organic soil 2. Microtopographic change basin formation 3. Tree bases as “catalysts”
VB1 VB2
1. Smoldering in thick organic soil 2. Microtopographic change basin formation 3. Tree bases as “catalysts” 4. Aggregate basin volume = VB1+VB2+…+VBn = ΣVBn
Hydrologic Implications Example: Seasonally-inundated landscape
Hydrologic Implications Example: Seasonally-inundated landscape
VSW ~ Hydro (P, ET, SWin/out, GWin/out) + Geo (slope, soil properties)
di = VSW/A (steady state “snap-shot”)
Hydrologic Implications Example: Seasonally-inundated landscape
Hydrologic Implications Example: Seasonally-inundated landscape
dpostburn = di – ΣVBn/A
Hydrologic Implications Example: Seasonally-inundated landscape
dpostburn = di – ΣVBn/A
At what point does aggregate basin volume alter landscape storage competence enough to substantially affect water level/water table depth?
Hydrologic Implications Ecological Effects? Example: Seasonally-inundated landscape
Hydrologic Implications Ecological Effects? Example: Seasonally-inundated landscape
Fire OM Accumulation
Hydro-period Storage
+
Atm. CO2 -
+
+
+
Wildlife Habitat
NPP
- + ?
+
- -
?
Fire OM Accumulation
Hydro-period Storage
+
Atm. CO2 -
+
+
+
Wildlife Habitat
NPP
- + ?
+
- -
H1: Fire increases storage and hydroperiod, increasing wetland wildlife habitat. H2: Increased hydroperiod following fire amplifies OM accumulation (via anoxic stress) relative to pre-fire rate, partially offsetting CO2 emissions. H3: Increased hydroperiod reduces fire likelihood. H4: Over time, OM accumulation reduces storage and hydroperiod, with fire likelihood and CO2 emissions converging to pre-fire rates. H5: Effects at regional scale (hydrology and habitat)
?
Testing H1 w/ Simple Model
Big Cypress National Preserve (BICY)
Organic-soil wetland area: 10% to >50%
Testing H1 w/ Simple Model
Testing H1 w/ Simple Model
Pre-burn
Post-burn
% wetland
db,i
dw,pb
% wetland burned
Model Inputs 1. Wetland area (%) 2. Initial basin depth, db,i
3. Burn extent (%) 4. Post-burn basin depth, db,pb 5. Soil porosity 6. Initial water level, dw,i 7. Rain events Caveats: Steady-state, snap-shot, no explicit flow between upland and wetland, etc…
dw,i
Testing H1 w/ Simple Model – 10% Wetland
• 10% wetland; db,i= 1 m • 50% burned; db,pb = 1.4 m • Porosity = 0.5 • Initial water level = 0.5 m
Testing H1 w/ Simple Model – 10% Wetland
Water Table Decline
Depth Increases (hydroperiod?)
• After fire, overall water table declines slightly (0.1 m), drying upland and shallow wetland areas
• Deep-water refugia established
Testing H1 w/ Simple Model – 50% Wetland
• 50% wetland; db,i= 1 m • 50% burned; db,pb = 1.4 m • Porosity = 0.5 • Initial water level = 0.5 m
Testing H1 w/ Simple Model – 50% Wetland
• After fire, overall water table declines more (0.5 m), drying upland and shallow wetland areas
• Shallow-water (0.4 m) refugia established
Water Table Decline
Depth Decreases (hydroperiod?)
Scenario: 25% extent, shallow (0.25 m) fire
Scenario: 50% extent, deep (0.50 m) fire
Scenario: 10% extent, deep (1 m) fire, drought
Summary of Findings
Summary of Findings
• Increasing area of soil combustion or depth of burn drives decrease in local water table…
• …but burned areas are deeper and likely have longer hydroperiods (particularly important during drought)
• Self-sustaining? Dry areas get drier, wet areas stay wet longer
• Exploratory model indicates potential conservation benefit of ground fires in low-relief landscapes with patchy organic soil
Next Steps
McLaughlin, D., D. Kaplan, and M.J. Cohen. 2014. A Significant Nexus: Geographically Isolated Wetlands Influence Landscape Hydrology. Water Resources Research 203WR015002.
• Improve model • Compare model
predictions against field observations
• Incorporate soil, vegetation, ecosystem data and wildlife habitat and population studies
• Locate additional test landscapes
• Funding…
Testing H1 w/ Simple Model – Rain Effects
• Simulating a single rain (P) event, P = 5 cm • 50% wetland, 50% burned, initial water level = 0.5 m
Water depth increases by 7.5 cm
Water depth increases by 7.5 cm
Pre-Rain Post-Rain
Pre-Rain Post-Rain
Testing H1 w/ Simple Model – 50% Wetland
• Simulating a single rain (P) event, P = 5 cm • 50% wetland, 50% burned, initial water level = 0.2 m
Water depth increases by 7.5 cm
Water depth increases by 11.8 cm
Pre-Rain Post-Rain
Pre-Rain Post-Rain