Multi-scale characterization of biogenic gas dynamics in peat soils using hydrogeophysicalmethods: implications for biogenic gas distribution and carbon fluxes in the Everglades

Xavier Comas1, Lee Slater2, Andrew Reeve3, Paul Glaser4, Jay Nolan2, Andrew Parsekian2 and Anastasija Cabolova1

1 Department of Geosciences, Florida Atlantic University, Boca Raton, FL2 Department of Earth & Environmental Sciences, Rutgers University, Newark, NJ3 Department of Earth Sciences, University of Maine, Orono, ME4 Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN

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

IV. Future directions

Caribou Bog, Maine

WCA-1, Florida

I. Introduction

Caribou Bog, Maine

Represent about 35-50% of total terrestrial C yet only cover 3% of Earth’s land

Considered net source of CH4 (net sink of CO2)

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)

Peatlands

Open pools in a northern peatland in Maine (central unit, Caribou Bog)

Current models for gas accumulation in peatlands

Deep vs shallow accumulations Carbon Cycling in Northern Peatlands; AGU Geophysical Monograph Series, Volume 184, 299 pp.

Biogenic gas release from peatlands

Mechanisms: Diffusion Transport through

vascular plants Ebullition

Controls: Soil T Chemical composition

(organic matter quality)

Whalen, 2005

Plant community structure Water table elevation (redox boundary) Atmospheric Pressure

Ebullition fluxes from peatlands

Source: Waddington, 2007, Fall American Geophysical Union Meeting

Spatiotemporal variation?

Episodic ebullition events can release large volumes of gas over a short time scale (35 g CH4/m2 in a matter of minutes or hours (Glaser et al. 2004)

II. The Ground Penetrating Radar

(GPR) method

Physical property measured: relative dielectric permittivity (εr)

velocity of a pulse of electromagnetic (EM) waves travels from a Tx to a Rx antenna

any contrast in εr (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

Principles

r(b)ε / c v =

( ) ( ) ( ) ( ) ( )α

arα

srα

wrα

r(b) εθnεn1θεε −+−+=

GPR measurements

c: speed of light in free space, 3x108 m/s

Complex Refractive Index model (CRIM): εr(w); εr(a); εr(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

Gas contentSlater and Comas , 2009

Comas and Slater, 2009

GPR surveying techniques

III. Applications in peatlands

Caribou Bog, Maine

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)

Comas and Slater, 2009

Caribou Bog, ME

a) Spatial distribution: imaging of wood layers/peat stratigraphy

BoreholeGPR : zero offset (ZOP) +tomography

Comas et al, 2005, Comas and Slater, 2009

Caribou Bog, ME

b) Spatial distribution: 1D/2D biogenic gas distribution

Parsekian et al, In preparation

Glacial Lake Agassiz Peatlands, MN

Surface GPR: CMPs

Comas et al, 2008

c) Temporal distribution: time-lapse measurements at the field scale

Comas and Slater, 2007; Cabolova and Comas, in preparation

High frequency GPR

Gas dynamics comparison: northern vs. Everglades peat (WCA-2A)

d) Temporal distribution: time-lapse measurements in the laboratory

Cabolova and Comas, in preparation

WCA-1: Loxahatchee Nat’l Wildlife Refuge

IV. Future directions

Further lab experimentation: - Sphagnum from different

locations- other sites in the Everglades

Effects of changes in water table, temperature, salinity…

Site D:Oregon

Field scale measurements:

WCA-1, Florida

National Science Foundation: Grants No. 0242353; No. 0510370; No. 0609534

ENP Fellowship Initiative Harry Jol (Wisconsin-Eau

Claire); Craig Ulrich, Isaiah Utne; DimitriosNtarlagiannis; Mike O’Brien; Zach Tyczka; Nathan Stevens; Greg Mount; Diego Quiros; Tyler Beck; Dale Gawlik

Thanks to:

Caribou Bog, Maine

Glacial Lake Agassiz Peatlands, Minnesota