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Projects

Current research in the Environmental Geophysics Lab in the Department of Geosciences at FAU includes a wide variety of projects focused on the use of near-surface hydrogeophysical methods for environmental applications both at the field and laboratory scale. A full summary of specific projects including funding is shown in the table at the end of this page ( Table 1 ), however a few examples are shown below: 

 

1) Peatlands Geophysics :

1a) Field Scale: current projects include both discrete and time-lapse measurements using electromagnetic (EM) methods such as ground penetrating radar (GPR) and terrain conductivity. Discrete measurements are focused on estimating carbon stocks at high spatial resolution. For example, Figure 1, Figure 2, and Figure 3 shows examples of GPR common offset transects in the Everglades (FL), West Kalimantan (Indonesia); and the Ecuadorian Andes (Ecuador). The images allows determining thickness variability of the peat column with a lateral resolution of 15-20 cm (confirmed with direct sampling). Such approach would be unfeasible using traditional methods such as direct coring. Similar datasets have been collected in a wide variety of boreal and tropical peatland systems worldwide, including Maine, Minnesota, Oregon and Florida in the US, or in several international locations such as Indonesia, Ecuador, Spain and the UK.

Time-lapse and discrete measurements at the field scale are also focused on better understanding the spatial and temporal variability of biogenic gas release and production (mainly methane and carbon dioxide) in peat soils. Figure 4 shows two sets of tomographic images from borehole GPR surveys collected in two peatlands: a) Cors Fochno (UK) and b) Caribou Bog (Maine). The images show the estimated distribution of gas content within the peat column, and reveal marked differences related to how gas accumulates in different peatland system (see Comas et al, 2013 for further details on this specific survey). Figure 5 shows a time-lapse dataset collected at several sites in the Everglades depicting the variability in GPR estimated gas content,flux release, and inferred gas produciton within the peat column over a 4 month period. Other methods such as gas traps, time-lapse cameras and surface deformation sensors were also used. The dataset depicts rates of flux release inferred from GPR and gas traps expressed in g CH4 m2 day-1. Further details about this dataset can be found in Wright and Comas, 2015. Surveying sites for monitoring temporal changes in gas dynamics have been deployed in several locations in Maine and in Florida, mainly in the Everglades with active sites in WCA-1, WCA-2 and WCA-3 being monitored.

 CO everglades

Figure 1: GPR common offset from WCA-2 in the Everglades (manuscript in preparation). The reflection record allows characterizing the peat-clay interface at cm lateral resolution. Note also the detail as related to peat microtopography.

 

figure 5b

Figure 2: GPR common offset from West Kalimantan, Indonesia (from Comas et al, 2015). The reflection record shows the ability to characterize thickness of the peat column at cm vertical resolution. Presence of diffraction hyperbolas within the peat column (white arrows) associated with the presence of wood fragments.

 



Figure 3: (a) Image of Site 1 in the Ecuadorian Andes showing the location of core S1 (from Comas et al, 2017). (b) GPR common offset (CO) profile showing distribution of GPR reflectors chosen (R1–R7). Most reflectors coincide with ash and pumice layers. (c) Core data showing C content distribution with depth and correspondence to GPR reflectors (R1–R7). An average C content for each layer (1–7) in between reflectors is shown next to core image. This value is used to estimate total C content in between reflectors once volume of peat for each portion along the peat column is determined.

 

CorsMaine

Figure 4: Inverted tomographic images from borehole GPR surveys showing 2D distribution of estimated gas contents in (a) Cors Fochno (UK) and (b) Caribou Bog (Maine, USA). From Comas et al, 2013. Areas of increased gas content in Caribou Bog are associated with the presence of wood layers (confirmed through coring) acting as gas traps that are absent in Cors Fochno.
 
 
 
Figure 5: (a) Stacked bar graph for four sites in the Everglades (WCA-2 and WCA-3) (from Wright and Comas, 2015), showing all terms necessary for estimation of production rates, including flux to the gas trap, change in gas content as estimated by GPR, which is shown as positives or negative values, consumption [Le Mer and Roger, 2001], and diffusion [Blodau, 2002]. The zero line is darkened. (b) Estimated production values for each site.
 
 

 

1b) Laboratory Scale: similar time-lapse measurements using EM methods for investigating the temporal and spatial variability in gas dynamics and rapid gas releasing events (i.e. ebullition) as described above are also being monitored in the laboratory. The lab currently holds peat monoliths (Figure 5) from several loc ations including Maine, Minnesota, Oregon and Florida, and intends to expands to peat samples from other locations around the world including Indonesia, Ecuador and Spain. Several lines of research are intended for the near future: 1) to establish a comparison of gas dynamics from peat soils from a wide variety of latitudes (from boreal to tropical) treated under the same conditions; 2) to induce changes in temperature (by using temperature controlled environmental chambers) and explore how warmer temperatures may alter current gas dynamics (i.e. climate change scenario); 3) to better constrain temporal releases by collecting continuous GPR measurements using an autonomous rail system (Figure 5); and 4) to better constrain spatial distribution of gases and upward migration by measuring gas distribution along a 1m long monolith from the Everglades representing the entire peat column under field conditions (from surface to mineral soil contact) (Figure 5).