Department of Geosciences, Florida Atlantic University, Boca Raton, FL 2

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1 Multi-scale characterization of biogenic gas dynamics in peat soils using hydrogeophysical methods: implications for biogenic gas distribution and carbon fluxes in the Everglades Xavier Comas 1, Lee Slater 2, Andrew Reeve 3, Paul Glaser 4, Jay Nolan 2, Andrew Parsekian 2 and Anastasija Cabolova 1 1 Department of Geosciences, Florida Atlantic University, Boca Raton, FL 2 Department of Earth & Environmental Sciences, Rutgers University, Newark, NJ 3 Department of Earth Sciences, University of Maine, Orono, ME 4 Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN

2 Outline I. Introduction Peatlands and gas ebullition II. The ground penetrating radar (GPR) method III. Applications in peatlands Spatial variability in biogenic gas distribution Temporal variability in gas fluxes both at the field and laboratory scale Caribou Bog, Maine IV. Future directions WCA-1, Florida

3 I. Introduction Caribou Bog, Maine

4 Peatlands Represent about 35-50% of total terrestrial C yet only cover 3% of Earth s land Considered net source of CH 4 (net sink of CO 2 ) Biogenic methane production methanogenesis Uncertainties in spatial and temporal distribution Uncertain response to global warming and/or restoration efforts (i.e. change in water table elevation, water chemistry, etc) Open pools in a northern peatland in Maine (central unit, Caribou Bog)

5 Current models for gas accumulation in peatlands Deep vs shallow accumulations Carbon Cycling in Northern Peatlands; AGU Geophysical Monograph Series, Volume 184, 299 pp.

6 Biogenic gas release from peatlands Mechanisms: Diffusion Transport through vascular plants Ebullition Whalen, 2005 Controls: Soil T Chemical composition (organic matter quality) Plant community structure Water table elevation (redox boundary) Atmospheric Pressure

7 Ebullition fluxes from peatlands Episodic ebullition events can release large volumes of gas over a short time scale (35 g CH 4 /m 2 in a matter of minutes or hours (Glaser et al. 2004) Spatiotemporal variation? Source: Waddington, 2007, Fall American Geophysical Union Meeting

8 II. The Ground Penetrating Radar (GPR) method

9 Principles Physical property measured: relative dielectric permittivity (ε r ) velocity of a pulse of electromagnetic (EM) waves travels from a Tx to a Rx antenna any contrast in ε r (e.g. changes in water content) will return a reflection on the GPR record Very sensitive to changes in water content and thus gas content

10 GPR measurements v = c / ε r(b) c: speed of light in free space, 3x10 8 m/s Slater and Comas, 2009 Complex Refractive Index model (CRIM): ε α r(b) = θε r α + 1 n ε ( ) ( ) ( w ) r( s) r( a ) α Gas content ε r(w) ; ε r(a) ; ε r(s) : relative dielectric permittivity of water (81), biogenic gas (1), and peat matrix; n : porosity, θ : volumetric soil water content and α : factor accounting for orientation of the electrical field + n θ ε α

11 GPR surveying techniques Comas and Slater, 2009

12 III. Applications in peatlands Caribou Bog, Maine

13 Comas and Slater, 2009 a) Spatial distribution: imaging of wood layers/peat stratigraphy Caribou Bog, ME GPR common offsets (confirmed through coring) reveal presence of wood layers Wood layers may act as confining layers preventing gas loss and enhancing accumulation (Glaser et al, 2004)

14 b) Spatial distribution: 1D/2D biogenic gas distribution Caribou Bog, ME BoreholeGPR : zero offset (ZOP) + tomography Comas et al, 2005, Comas and Slater, 2009

15 Parsekian et al, In preparation Surface GPR: CMPs Glacial Lake Agassiz Peatlands, MN

16 c) Temporal distribution: time-lapse measurements at the field scale Comas et al, 2008

17 d) Temporal distribution: time-lapse measurements in the laboratory High frequency GPR Gas dynamics comparison: northern vs. Everglades peat (WCA-2A) Comas and Slater, 2007; Cabolova and Comas, in preparation

18 WCA-1: Loxahatchee Nat l Wildlife Refuge Cabolova and Comas, in preparation

19 IV. Future directions

20 Further lab experimentation: - Sphagnum from different locations - other sites in the Everglades Effects of changes in water table, temperature, salinity Site D:Oregon

21 Field scale measurements: WCA-1, Florida

22 Thanks to: National Science Foundation: Grants No ; No ; No ENP Fellowship Initiative Harry Jol (Wisconsin-Eau Claire); Craig Ulrich, Isaiah Utne; Dimitrios Ntarlagiannis; Mike O Brien; Zach Tyczka; Nathan Stevens; Greg Mount; Diego Quiros; Tyler Beck; Dale Gawlik Caribou Bog, Maine Glacial Lake Agassiz Peatlands, Minnesota