Gas dynamics

Peat soils are known to be a significant emitter of atmospheric greenhouse gasses.
However, the spatial and temporal variability in production and release of greenhouse
gases (such as methane) in peat soils remains uncertain, particularly for low-latitude
peatlands like the Florida Everglades, as the majority of studies on gas dynamics in
peatlands focus on northern peatlands. The purpose of the work outlined here is focused
on understanding the spatial and temporal variability in biogenic gas dynamics (i.e.
production and release of methane and carbon dioxide) by implementing various
experiments in the Florida Everglades at different scales of measurement, using noninvasive
hydrogeophysical methods. Non-invasive methods include ground-penetrating
radar (GPR), gas traps, time-lapse cameras, and hydrostatic pressure head measurements,
that were constrained with direct measurements on soil cores like porosity, and gas
composition using gas chromatography. By utilizing the measurements of in-situ gas
volumes, we are able to estimate gas production using a mass balance approach, explore
spatial and temporal variabilities of gas dynamics, and better constrain gas ebullition models. A better understanding of the spatial and temporal variability in gas production
and release in peat soils from the Everglades has implications regarding the role of
subtropical wetlands in the global carbon cycle, and can help providing better production
and flux estimates to help global climate researchers improve their predictions and
models for climate change.

Peatlands act as carbon sinks while representing major sources of biogenic gases
such as methane (CH4) and carbon dioxide (CO2), two potent greenhouse gases. Gas
production and release in these peats soils are also influenced by overall warm
temperatures and water table fluctuations due to the naturally shallow water table in the
Florida Everglades. Releases of biogenic gases from Florida Everglades peat soils are not
well understood and the temporal distribution and dynamics are uncertain. The general
objective of this work was geared towards a methodological approach which aimed to
examine the feasibility of capacitance moisture probes to investigate biogenic gas
dynamics in various Florida Everglades peat soils at high temporal resolution. This work
has implications for establishing capacitance moisture probes as a method to monitor gas
dynamics in peat soils at high temporal resolution and better understanding patterns of
gas build-up and release from peat soils in the Everglades.

Peat soils are known to be a significant source of atmospheric greenhouse gasses. However, the releases of methane and carbon dioxide gasses from peat soils are currently not well understood, particularly since the timing of the releases are poorly constrained. Furthermore, most research work performed on peatlands has been focused on temperate to sub-arctic peatlands, while recent works have suggested that gas production rates from low-latitude peat soils are higher than those from colder climates. The purpose of the work proposed here is to introduce an autonomous Ground Penetrating Radar (GPR) method for investigating the timing of gas releases from peat soils at the lab scale utilizing samples originating from Maine and the Florida Everglades, and at the field scale in a Maine peatland. Geophysical data are supported by direct gas flux measurements using the flux chamber method enhanced by timelapse photography, and terrestrial LiDAR (TLS) monitoring surface deformation.

Peatlands cover a total area of approximately 3 million square kilometers and are one of the largest natural sources of atmospheric methane (CH4) and carbon dioxide (CO2). Most traditional methods used to estimate biogenic gas dynamics are invasive and provide little or no information about lateral distribution of gas. In contrast, Ground Penetrating Radar (GPR) is an emerging technique for non-invasive investigation of gas dynamics in peat soils. This thesis establishes a direct comparison between gas dynamics (i.e. build-up and release) of four different types of peat soil using GPR. Peat soil blocks were collected at peatlands with contrasting latitudes, including the Everglades, Maine and Minnesota. A unique two-antenna GPR setup was used to monitor biogenic gas buildup and ebullition events over a period of 4.5 months, constraining GPR data with surface deformation measurements and direct CH4 and CO2 concentration measurements. The effect of atmospheric pressure was also investigated. This study has implications for better understanding global gas dynamics and carbon cycling in peat soils and its role in climate change.