Biogenic gas

It is well known that biogenic gas emissions (mainly methane and carbon dioxide) vary both spatially and temporally in peatlands. While most studies have focused on northern systems, several recent studies in tropical and subtropical peatlands (like the Everglades) have revealed the presence of areas of increased gas accumulation and emissions, or hotspots, that may be related to physical and/or biogeochemical changes within the peat's matrix. However, these studies are often limited in terms of sampling volume and resolution or are based in laboratory studies that may not be totally representative of field conditions. In this study we investigate the spatial variability (both lateral and vertical) in gas accumulation and release at the field scale, over 10 m long transects at two locations in Water Conservation Area 1 of the Florida Everglades, using an array of hydrogeophysical methods. Resulting data infers the presence of hotspots with dimensions ranging from 1-2 m in width and approximately 0.5 m tall. These areas showed high variations in biogenic gas accumulation and release an order of magnitude higher than surrounding areas and occur seasonally as the highest gas releases were observed during Florida’s wet season. This study therefore has implications for better understanding the spatial and temporal variability of biogenic gas hotspots in peat soils, and how the matrix structure affects gas accumulation and release. This study shows the importance of considering the heterogenous nature of the peat's matrix when quantifying gas fluxes in the Everglades, and particularly when using methods with small sampling volumes like gas chambers.

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.