Pyro-eco-hydro-geomorphology : Implications of organic soil combustion on the hydrology and ecology of peat wetlands

Transcription

1 Pyro-eco-hydro-geomorphology : Implications of organic soil combustion on the hydrology and ecology of peat wetlands Conference on Ecological and Ecosystem Restoration New Orleans, LA, July 2014 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

2 A fire ecologist, a soil scientist, and two hydrologists walk into a cypress dome

3 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?

4 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

5 Significance of Peat Fires

6 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

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8 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

9 1. Smoldering in thick organic soil

10 1. Smoldering in thick organic soil 2. Microtopographic change basin formation V B1

11 1. Smoldering in thick organic soil 2. Microtopographic change basin formation 3. Tree bases as catalysts V B1 V B2

12 1. Smoldering in thick organic soil 2. Microtopographic change basin formation 3. Tree bases as catalysts 4. Aggregate basin volume = V B1 +V B2 + +V Bn = ΣV Bn

13 Hydrologic Implications Example: Seasonally-inundated landscape

14 Hydrologic Implications Example: Seasonally-inundated landscape

15 Hydrologic Implications Example: Seasonally-inundated landscape d i = V SW /A (steady state snap-shot ) V SW ~ Hydro (P, ET, SW in/out, GW in/out ) + Geo (slope, soil properties)

16 Hydrologic Implications Example: Seasonally-inundated landscape d postburn = d i ΣV Bn /A

17 Hydrologic Implications Example: Seasonally-inundated landscape At what point does aggregate basin volume alter landscape storage competence enough to substantially affect water level/water table depth? d postburn = d i ΣV Bn /A

18 Hydrologic Implications Ecological Effects? Example: Seasonally-inundated landscape

19 Hydrologic Implications Ecological Effects? Example: Seasonally-inundated landscape

20 + Atm. CO 2 - Fire Storage + Hydroperiod + OM Accumulation + Wildlife Habitat - +?? NPP

21 + Atm. CO Fire + Storage 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 CO 2 emissions. H3: Increased hydroperiod reduces fire likelihood. H4: Over time, OM accumulation reduces storage and hydroperiod, with fire likelihood and CO 2 emissions converging to pre-fire rates. H5: Effects at regional scale (hydrology and habitat) + Hydroperiod Wildlife Habitat + OM Accumulation - + +?? NPP

22 Testing H1 w/ Simple Model Big Cypress National Preserve (BICY) Organic-soil wetland area: 10% to >50%

23 Testing H1 w/ Simple Model

24 Testing H1 w/ Simple Model Model Inputs 1. Wetland area (%) Pre-burn 2. Initial basin depth, d b,i 3. Burn extent (%) 4. Post-burn basin depth, d b,pb 5. Soil porosity 6. Initial water level, d w,i 7. Rain events d b,i Post-burn d w,i % wetland Caveats: Steady-state, snapshot, no explicit flow between upland and wetland, etc d w,pb % wetland burned

25 Testing H1 w/ Simple Model 10% Wetland 10% wetland; d b,i = 1 m 50% burned; d b,pb = 1.4 m Porosity = 0.5 Initial water level = 0.5 m

26 Testing H1 w/ Simple Model 10% Wetland After fire, overall water table declines slightly (0.1 m), drying upland and shallow wetland areas Deep-water refugia established Depth Increases (hydroperiod?) Water Table Decline

27 Testing H1 w/ Simple Model 50% Wetland 50% wetland; d b,i = 1 m 50% burned; d b,pb = 1.4 m Porosity = 0.5 Initial water level = 0.5 m

28 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 Depth Decreases (hydroperiod?) Water Table Decline

29 Scenario: 25% extent, shallow (0.25 m) fire

30 Scenario: 50% extent, deep (0.50 m) fire

31 Scenario: 10% extent, deep (1 m) fire, drought

32 Summary of Findings

33 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

34 Next Steps Improve model Compare model predictions against field observations Incorporate soil, vegetation, ecosystem data and wildlife habitat and population studies Locate additional test landscapes Funding McLaughlin, D., D. Kaplan, and M.J. Cohen A Significant Nexus: Geographically Isolated Wetlands Influence Landscape Hydrology. Water Resources Research 203WR

35 Thank you! Questions?

36 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 Pre-Rain Post-Rain Water depth increases by 7.5 cm Pre-Rain Post-Rain Water depth increases by 7.5 cm

37 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 Pre-Rain Post-Rain Water depth increases by 7.5 cm Pre-Rain Post-Rain Water depth increases by 11.8 cm