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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 as pertaining to the categories of peat and karst geophysics 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 and Figure 2 shows two examples of GPR common offset transects in the Everglades (FL) and West Kalimantan (Indonesia). 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 dynamics (mainly methane and carbon dioxide) in peat soils. Figure 3 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 4 shows a time-lapse dataset collected in the Everglades depicting the variability in GPR estimated gas content within the peat column over a 5 month period. Other methods such as gas traps, time-lapse cameras and surface deformation sensors were also used. The dataset depicts 3 gas releasing events and their associated fluxes as expressed in mL gas m2 day-1. Further details about this dataset can be found in Comas and Wright, 2014. Surveying sites for monitoring temporal changes in gas dynamics have been deployed in several locations in Maine (currently not active) and in Florida, mainly in the Everglades where a total of 5 surveying sites in WCA-1, WCA-2 and WCA-3 are currently being monitored. Two additional sites are currently in preparation.

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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.

 

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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.

 

CorsMaine
Figure 3: 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.
 
 
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Figure 4: Estimated GPR volumetric gas content (%), gas flux inferred from gas traps (syringe flux) and time-lapse cameras and surface deformation for a site in WCA-3 in the Everglades. The dataset depicts three gas releasing events (event 1, 2 and 3) associated with a) decreases in GPR gas content; b) increases in camera and syringe fluxes; and c) overall decreases in surface deformation. See Comas and Wright, 2014 for further details.
 
 

 

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. Two 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; and 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).

 

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Figure 5: Peat sample monoliths in the laboratory. Setup also shows gas traps and time-lapse cameras for estimating biogenic gas fluxes
 

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2)  Karst Geophysics :

Both laboratory and field-based studies that explore the use of hydrogeophysical methods in karst environments are also currently undergoing in the Environmental Geophysics Lab. Field-based studies include the imaging of dissolution features and certain karst environments such as tufa mounds. Figure 6 shows a survey collected in Basturs (Spain) using a 50 MHz RTA antenna over a tufa mound and depicts depths of penetration up to 30 meters. Figure 7 exemplifies some laboratory work to estimate porosity from Miami limestone samples. See Mount and Comas, 2014 for further information

 

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Figure 6: GPR common offset transect collected in a tufa mound in Basturs (Spain). Survey was collected using 50 MHz RTA antennas, with depths of penetration exceeding 30 m in places. Manuscript in preparation.
 
 
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Figure 7: a) sample of Miami limestone approximately 0.25 x 0.25 x 1.2 m; b) 2D plot of estimated porosity from GPR measurements. Dataset shows porosity estimates exceeding 10 % variability. Modified from Mount and Comas, 2014.

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Table 1: summary of current ongoing projects in the Environmental Geophysics Lab 

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Environmental Geophysics Lab
Department of Geosciences; Florida Atlantic University
3200 College Ave, Davie West bldg. DW - 339
Davie, Florida 33314

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