Estimating methane gas production in peat soils of the Florida Everglades using hydrogeophysical methods

Abstract

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 Everglades. Ground penetrating radar (GPR) is a hydrogeophysical tool that has been successfully used in the last decade to noninvasively investigate carbon dynamics in peat soils; however, application in subtropical systems is almost non-existent. This study is based on four field sites in the Florida Everglades, where changes in gas content within the soil are monitored using time-lapse GPR measurements and gas releases are monitored using gas traps. A weekly methane gas production rate is estimated using a mass balance approach, considering gas content estimated from GPR, gas release from gas traps and incorporating rates of diffusion, and methanotrophic consumption from previous studies. Resulting production rates range between 0.02 and 0.47 g CH 4 m À2 d À1 , falling within the range reported in literature. This study shows the potential of combining GPR with gas traps to monitor gas dynamics in peat soils of the Everglades and estimate methane gas production. We also show the enhanced ability of certain peat soils to store gas when compared to others, suggesting that physical properties control biogenic gas storage in the Everglades peat soils. Better understanding biogenic methane gas dynamics in peat soils has implications regarding the role of wetlands in the global carbon cycle, particularly under a climate change scenario.

The effect of sampling effort on estimates of methane ebullition from peat

“…Although natural peat was not used directly to guide the placement of shelves, higher porosity shelf arrangements represented less decomposed peat, while shelves located in deeper parts of the profile represented peat undergoing compression and more advanced decomposition [ Boelter , ; Quinton et al ., ]. The resulting profile had porosities (Figure b) that were similar to measured values of porosity (91–98%) in shallow northern [ Beckwith and Baird , ; Warner et al ., ; Kettridge and Binley , ; Parsekian et al ., ] and subtropical [ Wright and Comas , ] peatlands.…”

A Lumped Bubble Capacitance Model Controlled by Matrix Structure to Describe Layered Biogenic Gas Bubble Storage in Shallow Subtropical Peat

“…Variations in peat stratigraphy have previously been suggested to regulate bubble storage in specific layers within different soil columns, and control the redistribution of gas bubbles (Chen & Slater, ; Kettridge & Binley, ; Wright & Comas, ). The smallest void ratio r1 at 4.9 cm depth suggests the presence of a barrier structure in the surface layer, being ascribed to the decay of poorly decomposed roots and stems of vascular plants (Figure ).…”

“…Laboratory observations were performed on a submerged peat monolith extracted from Water Conservation Area 3 (WCA-3) in the US Florida Everglades (Figure 3a). The site corresponds to one of the locations included in the study by Wright & Comas (2016), has a thickness of 0.72 m, and is characterized Water Resources Research 10.1029/2018WR022573 predominantly by Loxahatchee peat, thus dominated by water lily (Nymphaea odorata) plant species with a typical organic content of 92% (Craft & Richardson, 2008). The site is located in a slough, and is perennially inundated with an average water depth of 0.5 m.…”

Estimating Belowground Carbon Stocks in Isolated Wetlands of the Northern Everglades Watershed, Central Florida, Using Ground Penetrating Radar and Aerial Imagery

“…When compared with other studies our surface values are similar to what is reported in the literature. For example, Wright and Comas () report C content values from south Florida wetlands within water conservation areas (WCA) 2 and 3 ranging from 42.9% to 29.5% (422.91–235.18 g C kg −1 ). Wright et al () report similar values for the WCAs with values ranging from 471 to 347 g C kg −1 ; they also report values ranging from 103 to 158 g C kg −1 for Big Cypress National Preserve as well as four other areas within the state of Florida with C content values varying from 355 to 202 g C kg −1 .…”