“Pyro-eco-hydro-geomorphology”: Implications of organic ... · “Pyro-eco-hydro-geomorphology”: Implications of organic soil combustion on the hydrology and ecology of peat

“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…

Thank you! Questions? dkaplan@ufl.edu

www.watershedecology.org

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