Comparison of GPR signals over simulated clandestine graves with domestic pigs (Sus Scrofa domesticus) and human remains.

Studies assessing the use of ground-penetrating radar (GPR) for locating unmarked human graves commonly use pigs as proxies, with recent concerns about the adequacy of pigs as substitutes for humans. Also, there is little agreement on how to identify and describe GPR signals associated with graves. Hence, this project's aim is to compare GPR signals acquired over simulated clandestine graves with pig and human remains. We established human, pig, and control graves at the REST[ES] human decomposition facility in May 2022 and monitored the graves over 17 months using a 250 MHz antenna GPR system. Our results showed the presence of perturbed and V-shaped reflectors, diffraction hyperbolas, and reflectors with amplitude loss at depth between 0.6 and 0.75 m in the radargram for graves with human and pig remains. We corroborate recent studies which concluded that the use of proxies is a viable alternative to human cadavers. The observed radar signatures were classified into five key patterns, which are characteristic of similar data collected with 250 MHz above graves reported in the literature. These classes are: V-shaped dipping reflections from grave walls (class A), small hyperbolic reflections superimposed onto a near-linear reflector (class B), hyperbolic reflections from remains within the grave (class C), new high-amplitude reflection patterns (class D) and significant loss or interruption of reflections (class E). Our proposed classification can help streamline future investigations where the goal is to interpret burials within large GPR datasets and provide language to communicate these results to the broader scientific community.

Short-Term Groundwater Level Fluctuations Drive Subsurface Redox Variability.

As global change processes modify the extent and functions of terrestrial-aquatic interfaces, the variability of critical and dynamic transitional zones between wetlands and uplands increases. However, it is still unclear how fluctuating water levels at these dynamic boundaries alter groundwater biogeochemical cycling. Here, we used high-temporal resolution data along gradients from wetlands to uplands and during fluctuating water levels at freshwater coastal areas to capture spatiotemporal patterns of groundwater redox potential (Eh). We observed that topography influences groundwater Eh that is higher in uplands than in wetlands; however, the high variability within TAI zones challenged the establishment of distinct redox zonation. Declining water levels generally decreased Eh, but most locations exhibited significant Eh variability, which is associated with rare instances of short-term water level fluctuations, introducing oxygen. The Eh-oxygen relationship showed distinct hysteresis patterns, reflecting redox poising capacity at higher Eh, maintaining more oxidizing states longer than the dissolved oxygen presence. Surprisingly, we observed more frequent oxidizing states in transitional areas and wetlands than in uplands. We infer that occasional oxygen entering specific wetland-upland boundaries acts as critical biogeochemical control points. High-resolution data can capture such rare yet significant biogeochemical instances, supporting redox-informed models and advancing the predictability of climate change feedback.

Using geophysics to guide the selection of suitable sites for establishing sustainable earthen fishponds in the Niger-Delta region of Nigeria.

Water retention in earthen fishponds throughout a fish farming cycle is challenging due to climate-induced water loss via evapotranspiration, seepages, and lowering of the groundwater table. These processes depend on the soil hydrostratigraphic condition and constitute a major challenge for fish farmers in the Niger-Delta region of Nigeria, where seasonal variations cause groundwater levels to fluctuate. This study assesses the use of non-invasive geophysical methods, including electrical resistivity and induced polarization, to guide the selection of sites with appropriate hydrostratigraphic conditions for establishing earthen fishponds. We combined measurements of electrical resistivity and chargeability distributions to assess the subsurface of two earthen fishpond sites at Ugono-Abraka and Agbarha-Otor areas in the Niger-Delta region of Nigeria. Electrical soundings were acquired at ten locations, while two-dimensional electrical resistivity and Induced polarization were acquired across five transects using Schlumberger and dipole-dipole electrode configurations. The field data were inverted using IP2win, and Diprowin software. The geophysical models were combined with lithological data from soil cores to characterize the subsurface stratigraphy, while measured clay contents were used to estimate infiltration coefficients relying on established petrophysical relationships. The delineated subsurface properties at Ugono-Abraka and Agbarha-Otor show higher variations than assumed by practitioners. The complementary results of low resistivity (20-140 Ωm) and high chargeability (10-50 msec) revealed areas with clay-rich sediments. Soil samples confirmed higher clay contents of up to 10% at Ugono-Abraka and low values of 2% at Agbarha-Otor. Estimated infiltration coefficients are lower at the Ugono-Abraka site (1.6 m/day) compared to Agbarha-Otor (8.4 m/day). This implies variable water loss in the earthen fishponds; hence, we recommend characterizing these variations using non-invasive geophysical methods before establishing medium to large-scale earthen fishponds in the area.

A review of the occurrence, distribution, and impact of bitumen seeps on soil and groundwater in parts of southwestern Nigeria.

The impact of bitumen components on soil and groundwater resources is of environmental importance. Contaminants' influx into the environment from bitumen components through anthropogenic activities such as exploration, mining, transportation, and usage of bitumen in all its forms have been reported globally. However, gaps exist in the geogenic occurrence of bitumen in the shallow subsurface such as in southwest Nigeria, contaminating the soil and groundwater resources. This review presents in situ bitumen seeps as a source of geogenic soil and groundwater contaminants in southwestern Nigeria. We conducted a systematic review of literatures based on defined selection criteria. We derived information on the state of knowledge about bitumen seep occurrences and distribution in southwestern Nigeria. Also, the processes that exacerbate bitumen contaminants' influx into soil and groundwater were enunciated. At the same time, case examples highlighted areas for possible in situ bitumen contamination studies in Nigeria. The results of this review showed that a multidisciplinary approach has been employed to assess and monitor the contaminants resulting from the various activities involving the exploitation and application of bitumen in Nigeria. These studies emphasize bitumen contaminants as emanating from anthropogenic sources. The results also suggested that bitumen studies have been mainly exploratory to improve the understanding of the economic potential of the hydrocarbon reserve. Also, recent advances in bitumen contaminants studies accounted for the heterogeneous nature of the bitumen. This allows for the optimized categorization of the mechanism and processes undergone by the different bitumen components when released as environmental contaminants. However, a knowledge gap exists in characterizing and understanding the effects of in situ bitumen seeps as a geogenic source of soil and groundwater contamination. This review identifies the possibility of geogenic soil and groundwater contamination by in situ bitumen seeps in the coastal plain sand of the Dahomey basin in southwestern Nigeria. The impact of the bitumen contaminants on the environment was discussed, while methods for accessing the occurrence and distribution of the bitumen contaminants were highlighted.

Self-potential time series reveal emergent behavior in soil organic matter dynamics.

The active cycling of carbon between soil organic matter and the atmosphere is of critical importance to global climate change. An extensive body of research exists documenting the capricious nature of soil organic matter (SOM) dynamics, which is symptomatic of an intricate network of interactions between diverse groups of heterotrophic microorganisms, complex organic substrates, and highly variable local environmental conditions. These attributes are consistent with elements of complex system theory and the temporal evolution of otherwise unpredictable patterns of behavior that emerge from long range dependency on initial conditions. Here we show that vertical depth profile of self-potential (SP) time series measurements responds in a quantitative manner to variations in soil moisture, SOM concentrations, and relative rates of microbial activity. Application of detrended fluctuation analysis (DFA) of self potential time series data is shown additionally to reveal the presence of long-range dependence and emergence of anomalous electrochemical diffusion behavior, both of which diminish with depth as SOM specific energy densities decline.

Geophysical imaging of buried human remains in simulated mass and single graves: Experiment design and results from pre-burial to six months after burial.

In this study, we present an experiment design and assess the capability of multiple geophysical techniques to image buried human remains in mass and individual graves using human cadavers willingly donated for scientific research. The study is part of a novel, interdisciplinary mass grave experiment established in May 2021 which consists of a mass grave with 6 human remains, 3 individual graves and 2 empty control graves dug to the same size as the mass grave and individual graves. Prior to establishing the graves, we conducted background measurements of electrical resistivity tomography (ERT), electromagnetics (EM), and ground penetrating radar (GPR) while soil profiles were analyzed in situ after excavating the graves. All graves were also instrumented with soil sensors for monitoring temporal changes in soil moisture, temperature, and electrical conductivity in situ. Measurements of ERT, EM and GPR were repeated 3, 37, 71 and 185 days after burial with further repeated measurements planned for another twelve months. ERT results show an initial increase in resistivity in all graves including the control graves at 3 days after burial and a continuous decrease thereafter in the mass and individual graves with the strongest decrease in the mass grave. Conductivity distribution from the EM shows a similar trend to the ERT with an initial decrease in the first 3 days after burial. Distortion in linear reflectors, presence of small hyperbolas and isolated strong amplitude reflectors in the GPR profiles across the graves is associated with known locations of the graves. These initial results validate the capability of geoelectrical methods in detecting anomalies associated with disturbed ground and human decay while GPR though show some success is limited by the geology of the site.

Gradient magnetometer dataset and MATLAB numerical code for simulating buried firearms at a controlled field site.

Magnetic survey using multiple magnetometers to obtain gradiometric data can be used as a non-destructive method to search for buried firearms. We present magnetic dataset collected above a set of weapons buried at 0.6 m, 1.2 m, and 1.8 m depths. We provide three datafiles: two datafiles were collected on a coarse grid (1 m by 0.5 m) before and after burial of the weapons, and a third one collected on a fine grid (0.25 m by 0.1 m) after the burial of the weapons which concentrates on the area of buried firearms. We used a Gem Systems GSM-19GW Overhauser gradiometer consisting of two sensors with a relative vertical separation of 55 cm. Data acquisition was done via non-automated point measurements within a gridded measurement domain with data collection locations managed using measurement tape. Each field campaign resulted in about 3,000 data points. In addition, we developed a set of MATLAB scripts to model the magnetic anomalies (total field and gradient) for buried firearms, this set is also included here. The data and modeling scripts relate to a research article published in Forensic Science International (Deng et al., Suitability of magnetometry to detect clandestine buried firearms from a controlled field site and numerical modeling [1]). The dataset may be helpful for testing new algorithms for weapons detection while the numerical codes can be modified and applied for simulating magnetic anomalies resulting from similar buried objects with potential application in the sub-disciplines of forensic and archaeological geophysics.

Suitability of magnetometry to detect clandestine buried firearms from a controlled field site and numerical modeling.

The detection of buried firearms remains a critical issue in law enforcement. We assess the suitability of magnetic gradiometers to detect buried rifles and handguns at multiple depths using numerical modeling and field investigations. Our simulation is based on a simple approach to characterize handguns and rifles as long magnetic dipoles with the firearm characterized by its magnetization, length, centre, azimuth and plunge which allows us to calculate their total magnetic field and gradient anomalies. We compare these synthetic data to field gradiometer data collected with a Gem Systems GSM-19GW Overhauser magnetometer at a field site near Toronto, Canada, where six firearms are buried. Our field magnetometer consists of two sensors with a relative vertical sepration of 0.55 m. We measure the largest anomaly (+/-20 nT) for a rifle at 0.6 m depth, and the smallest anomaly (+/-2 nT) for a handgun buried at 1.8 m depth. The measured anomalies spatially coincide with the locations of weapons while dipole anomalies align along the orientation of the firearms. Our modeling results show that vertically buried weapons produce significantly stronger anomalies than horizontal ones, and even slight tilts enhance the anomalies. We recommend a 0.25 m grid spacing to search for weapons using magnetometry. Our study shows that a range of firearms buried up to 1.8 m can be detected, suggesting that gradient magnetometers are useful tools in forensic weapon searches.

Tracer tomography: design concepts and field experiments using heat as a tracer.

Numerical and laboratory studies have provided evidence that combining hydraulic tomography with tomographic tracer tests could improve the estimation of hydraulic conductivity compared with using hydraulic data alone. Field demonstrations, however, have been lacking so far, which we attribute to experimental difficulties. In this study, we present a conceptual design and experimental applications of tracer tomography at the field scale using heat as a tracer. In our experimental design, we improve active heat tracer testing by minimizing possible effects of heat losses, buoyancy, viscosity, and changing boundary conditions. We also utilize a cost-effective approach of measuring temperature changes in situ at high resolution. We apply the presented method to the 8 m thick heterogeneous, sandy gravel, alluvial aquifer at the Lauswiesen Hydrogeological Research Site in Tübingen, Germany. Results of our tomographic heat-tracer experiments are in line with earlier work on characterizing the aquifer at the test site. We demonstrate from the experimental perspective that tracer tomography is applicable and suitable at the field scale using heat as a tracer. The experimental results also demonstrate the potential of heat-tracer tomography as a cost-effective means for characterizing aquifer heterogeneity.