As a kind of clean energy, geothermal energy has attracted the attention of scholars all over the world in recent years. Previous geochemical exploration methods for geothermal resources are limited to the analysis of individual geochemical indices. Moreover, previous studies of microorganisms in geothermal fields mostly focus on hot spring outcrops, lacking ecological studies of geothermal resources in complex terrains. This study investigated the soil geochemistry and microbial diversity of the Bantang Hot Spring geothermal field in Chaohu, Anhui Province. Geochemical indices such as head-space gas, soil gas, acid-hydrolyzed hydrocarbons, and altered carbonate were detected in this study. Combined with the microbial high-throughput sequencing technology, this study analyzed the composition and spatial-temporal distribution of the microbial population above the geothermal fields in uplifted mountains and the relationship between these bioinformatics characteristics and the geochemical indices. The results indicate that the acid-hydrolyzed hydrocarbons on the surface of the geothermal field showed a maximum methane concentration of 43.7 μL/kg in the area between faults F2 and F3, adequately reflecting the fault location of the geothermal field.Bacillaceae, Hydrogenophilaceae, and Thermodesulfovibrionaceae in the geothermal field and the background area showed large relative abundance differences, which were 0.178%, 0.108%, and 0.060%, respectively. This result indicates that they are sensitive to geothermal resources and correspond well to geochemical indices above the known geothermal field. This study preliminarily investigated the diversity of geothermal microorganisms in the geothermal field and analyzed the corresponding relationships between microbial distribution characteristics and geochemical indexes, providing technical support for the microbiological exploration of geothermal resources.

This study aims to explore the feasibility of the carbon dioxide (CO₂) and sulfur dioxide (SO₂) gas geochemical survey method for mineral exploration in forested areas. Based on the newly designed gas rapid analysis instrument, this study conducted an experimental investigation of the method in the forested Jiapigou gold concentration area, Jilin Province. The results show that significant CO₂ and SO₂ anomalies were observed above the concealed ore bodies and structures. In the forested area, the CO₂ and SO₂ gas geochemical survey method reflected the fault structures and effectively indicated the deep concealed gold deposit. This method holds critical significance for the breakthrough of prospecting technology in China's covered areas.

Geothermal resources are significant clean energy and tourism mineral resources. The Rucheng Basin, a carbonate basin in the southeastern mountainous area of Hunan Province, possesses favorable conditions for the formation of convective geothermal energy. However, the basin is enclosed on three sides by the giant Zhuguangshan rock mass, and its basement is subjected to the intrusion and destruction by the rock mass, resulting in severely deformed formations, crisscrossing faults, and significantly different eastern and western structures. The understanding of the basin's water- and heat-conducting pathways and deep reservoir structures remains elusive, thus restricting the investigation of the basin's geothermal potential. Hence, this study probed the basin's deep structures through gravity survey and audio magnetotellurics (AMT), obtaining the following insights: (1) The Rucheng Basin has developed into a bidirectional ramp structure due to east-west differentiation. The synclinorium in the east experienced compression and clockwise rotation due to the emplacement of the Yanshanian rock mass, rocks were fragmented in the core zone, and strike-slip fracture zones were found at the boundary. The faults have vertical cutting depths exceeding 4 km, widths ranging from 300~600 m, and dip angles between 80°~90°. (2) The basin's basement anticlinal axis hosts several NWW-directed concealed rock masses, with diameters from 3~4 km and buried depths from 0.5~1.5 km. Hot springs reside in the fracture zones crossing the boundaries of the concealed rock masses. (3) The basin boasts favorable conditions for the formation of convective geothermal energy. Folds, fault zones, and concealed rock masses match each other to form a unified spatial combination of heat-controlling elements, manifesting heat accumulation characterized by east-west recharge and intermediate discharge. With more thriving deep geothermal reservoirs in the east, the basin has high potential for geothermal resources.

The Fengtai ore concentration area is an important producing area of plumbum-zinc and gold ores in the middle of the Qinling orogenic belt. It hosts many large to super-large deposits, such as Qiandongshan-Dongtangzi, Bafangshan-Erlihe, Baguamiao, and Shuangwang deposits. With the exploitation proceeding, the reserves of these deposits have decreased significantly, and the ore prospecting in these deposits has shifted from the surface to the deep part. However, the geophysical fields in the deposits are yet to be ascertained, severely restricting research on the metallogenic regularity of the deposits and the ore prospecting and exploration in the peripheral zones. Based on the latest 1∶50,000 aeromagnetic and airborne radioactivity survey data, as well as gravity data, this study investigated the multi-source geophysical fields on the scales of the region, the ore concentration area, and deposits, aiming to summarize the distribution patterns of geophysical anomalies of different scales and provide evidence for research on metallogenic regularity and prospecting prediction. The results show that the Fengtai and the Xicheng ore concentration areas, with similar magnetic structures, are separated by the zone with strong magnetic anomalies caused by the crystalline basement of the Huicheng Basin. The first vertical derivative of gravity reveals that the Fengtai and Xicheng ore concentration areas have density structures similar to the Huicheng Basin. It can be inferred that the shallow part is a unified basin and that a large prospecting space exists between the two ore concentration areas. Many NW-trending linear magnetic anomaly zones occur in the Fengtai ore concentration area. Their locations are highly consistent with those of fault structures, and they were offset by NE-trending structures due to late transformation. The second vertical derivative of gravity reveals that many intermediate-acid intrusive stocks or veins have developed in the deep part of the Fengtai ore concentration area. Structural boundaries can be effectively identified based on the first vertical derivative, X-directional derivative, and wavelet transform of aeromagnetic data. Furthermore, ore bodies are mostly distributed in the NW direction along the tectonic belt. All these will play an important role in guiding ore prospecting and exploration in the Fengtai ore concentration area.

Despite abundant geothermal reserves of the Tangyu geothermal field in Meixian County, Shaanxi Province, long-term exploitation has decreased the water temperatures and yields of its existing geothermal wells year by year. Hence, there is an urgent need to explore new potential geothermal resources in the geothermal field. Since the known geothermal wells in the geothermal field are significantly controlled by faults, investigating the deep fault propagation holds critical significance for exploring the geothermal field’s potential geothermal resources. Due to the method limitations and the topographic influence, identifying thermal control faults through conventional geological route investigation or large-scale engineering is not applicable to the geothermal field. Therefore, a new technical method combining the penetrating soil radon measurement and the controlled source audio magnetotelluric (CSAMT) method was employed in this study to find concealed faults and delineate potential geothermal areas. Based on the measured surface soil radon concentration anomaly data and the subsurface electrical structure model derived from the CSAMT data inversion, this study inferred six new concealed faults on the basis of corroborating the known faults, predicted two potential geothermal areas, and built a conceptual model for the Tangyu geothermal field. As revealed by the results, the soil radon concentrations at concealed faults are much higher than the regional background value, and the concealed faults are located in the low-resistivity fracture zones as indicated by the apparent resistivity results based on CSAMT data inversion. Besides, the two potential geothermal areas spread from 450~750 m and 850~1 150 m on the profile, respectively, at depths of approximately 250~300 m. This study concludes that the geothermal field resides in a low-resistivity region with soil radon anomalies three times the regional background value. The results of this study provide a reference for the subsequent sustainable production and utilization of potential geothermal resources in the region.

The Eerguna block with metallogenic geological conditions is an important metallogenic area in Heilongjiang Province. Globally, China boasts the richest resource of antimony. However, the high mining intensity in recent years imposes huge challenges to this resource advantage of China. In this context, it is necessary to ascertain the geochemical characteristics of antimony in the Eerguna block. Based on the data of the 1∶250 000 stream sediment survey in the Eerguna block, this study explored the geochemical parameters of antimony in different tectonic units and the regional geochemical anomalies of this block. The results show that the study area has median and average concentrations of antimony of 0.33×10^-6 and 0.55×10^-6, respectively. The Mohe foreland basin is rich in antimony, with median and average concentrations of antimony higher than those of the study area. Furthermore, zones with high and extremely high antimony concentrations in the study area are distributed primarily in the Mohe foreland basin. Based on the 85% cumulative percentage, this study determined 66 geochemical anomalies of antimony, among which two reach the scale of geochemical provinces. Furthermore, this study identified significant geochemical anomalies of antimony in the discovered gold, antimony, and plumbum deposits or ore occurrences (mineralization points). Based on the spatial distributions of geochemical anomalies and metallogenic geological conditions of antimony, arsenic, and gold, this study delineated three metallogenic prospect areas of antimony: the Beijicun-Sanlianshan metallogenic prospect area, the Wangsushan-Daling metallogenic prospect area, and the Baikalushan-Huzhong metallogenic prospect area. In addition, the geochemical anomalies and metallogenic prospect areas for antimony, arsenic, and gold provide important areas for searching for sulfide deposits such as gold, antimony, and plumbum ones in the study area.

This study proposed a fracture prediction method based on unsupervised clustering of fracture sensitivity attributes to accurately characterize the distribution of fractures with different attitudes in tight sandstones of the Upper Triassic Xujiahe formation in the Yuanba area, northeastern Sichuan. First, the sensitivity of fractures was extracted and selected based on the optimized post-stack seismic data. Then, the convolutional neural network, a deep learning algorithm, was used to learn global massive fault and fracture databases of various types, obtaining the intensities, dip angles, and azimuths of fractures. In combination with high-precision-guided curvature attributes, an unsupervised clustering algorithm based on the Bayesian probability model was used to predict the intensities of fractures with different dip angles through dimensionality reduction using principal component analysis (PCA). The prediction results are highly consistent with both the fracture interpretation results from imaging logs and the geological results. The results of this study show that the third member of the Xujiahe Formation has more developed fractures than the second member. Fractures in the third member include both the fault-induced fractures distributed near the faults in the southeast flank of the Jiulongshan anticline and the fold-induced fractures in the areas with large formation flexures. By contrast, only fault-induced fractures near the faults occur in the second member.

The performance of ray-based tomography inversion is affected by many factors,such as initial model error and low-velocity interlayer.The conventional tomography method based on first-arrival wave travel time,which constrains or smooths models,destroys the relative relationship between model parameters and rays and affects the inversion stability.By testing the performance of first-arrival wave travel time-based tomography inversion under different initial models,this study proposed a first-arrival wave travel time-based tomography inversion method with surface wave information as constraints.The process of this method is as follows:(1)Given that surface waves feature high energy and frequency dispersion in seismic data,the surface-wave frequency dispersion curves are obtained through the multi-channel analysis of surface waves;(2)Using the damped least squares method,the shallow-surface shear wave (S-wave) velocities are determined through inversion;(3)With the S-wave velocity structure as the constraint,the initial compressional wave (P-wave) model is established,and accordingly,the first-arrival wave travel time-based tomography inversion that considers regularization is achieved.This method improves the accuracy and stability of shallow structure inversion by fully utilizing the surface wave information in seismic data to counteract the inherent defects of tomography inversion.The effectiveness of this method has been verified using actual data.

The transient electromagnetic method (TEM) commonly uses the all-time apparent resistivity parameter for interpretation, which involves complex formulas and time-consuming iterative processes. Based on the characteristics of TEM data, this study employed the artificial neural network (ANN) for TEM pseudo-resistivity imaging. First, this study designed a multi-hidden-layer BP neural network and calculated a response amplitude through TEM analysis. The response amplitude, as the mapping parameter of pseudo resistivity, was used for network training. Then new data outside the training set were used to test the trained network. A homogeneous half-space and one-dimensional layered model was built to verify the correctness and adaptability of the neural network. The imaging of the three-dimensional geoelectric model was performed. As revealed by the results, the pseudo resistivity calculated based on the neural network can reflect the target anomalies of the geoelectric model, with highly accurate network imaging results. Finally, the measured data were processed using the neural network algorithm, further indicating that the neural network-based imaging can serve as a basis for data interpretation. This study verified the feasibility of the ANN in TEM imaging, thus providing a new approach for TEM imaging.

It is difficult to explore the overlapping double-layer waterlogged goafs using the transient electromagnetic method. The reason is that upper waterlogged goafs will hinder the propagation of the electromagnetic field, thus prolonging the observation of the lower waterlogged goafs and reducing the signal-to-noise ratio. Besides, the burial depths and layer spacings of double-layer waterlogged goafs affect the signal-to-noise ratio and the observation time of transient electromagnetic signals. By building a double-layer waterlogged goaf model based on the Majiayan coal mine in Shanxi, this study analyzed the electromagnetic field propagation under layer spacings of 25 m, 50 m, 75 m, and 100 m,and calculated the observation time of waterlogged goafs with different layer spacings. Furthermore, it quantitatively characterized the differences between induced voltages in the double-layer waterlogged goafs with different layer spacings using root mean square errors. Additionally, this study proposed the identification criteria for explorable lower waterlogged goafs based on the record errors and noise levels during the observation. The results of physical simulation experiments are as follows: The differences between the induced voltages of double-layered waterlogged goafs with different layer spacings occur mainly in the late stage; the differences between induced voltages gradually decrease as the layer spacing and the burial depth of upper waterlogged goafs increases; the difference between induced voltages is close to the noise level when the layer spacing is greater than 75 m. The actual detection of the double layer waterlogged goaf with a spacing of 75 meters was conducted in Majiayan Coal Mine, and the results showed that the lower waterlogged goaf was not effectively identified.Therefore, It is difficult to effectively explore the lower waterlogged goafs when the layer spacing is greater than 75 m.

To avoid aggregate interference on the detection target in concrete quality detection by Rayleigh waves, the abnormal signals from the aggregate and the target should be distinguished for high detection reliability. Hence, this study explored the propagation characteristics of Rayleigh waves in aggregate concrete. By building the mesostructural random aggregate models and employing the high-order staggered-grid finite difference scheme, this study examined the effects of the randomness, shape, size, and content of aggregate on the Rayleigh wave field and dispersion curves, thus obtaining the Rayleigh wave scattering, energy attenuation, distortion, and dispersion curve characteristics under different aggregate parameters. Based on the forward modeling data of different aggregate concrete models, this study quantitatively analyzed the sizes and influence ranges of aggregate-induced anomalies of the Rayleigh wave field and dispersion curves. The results are as follows. The randomness and content of aggregate could affect the energy attenuation of direct Rayleigh waves. The Rayleigh wave field was slightly influenced by the aggregate shape but significantly impacted by the aggregate size. When the aggregate size exceeded half of the dominant wavelength, Rayleigh waves would produce strong scattering, distorting its waveforms. In contrast, these aggregate parameters caused no anomalies in the dispersion curves. Therefore, data analysis using dispersion curves can avoid aggregate interference on the target in concrete quality detection by Rayleigh waves.

The grounded-source transient electromagnetic (TEM) method, which enjoys the advantages of high topographic adaptability and large exploration depths, is suitable for deep resource exploration in mountainous areas. However, the TEM responses can be distorted due to topographic effects, causing great difficulties in data interpretation. This study investigated the influence patterns and correction method of topographic effects based on the three-dimensional unstructured time-domain finite element method. First, this study conducted the fine-scale description of mountains using unstructured tetrahedral grids, calculated the response of various topographic models, and analyzed the influence patterns of topographic effects. Then, it proposed a correction method for topographic effects based on the principle of the linear superposition principle of electromagnetic fields, established a geoelectric model of mountains according to the actual elevation data, and calculated the model responses through three-dimensional forward modeling. Subsequently, this study determined the topographic responses by subtracting the flat Earth model responses from the mountain model responses and then obtained the corrected TEM responses by removing the topographic responses from the total responses. The results are as follows: (1) The influence of mountains on the TEM responses is concentrated in the early stage and weakens gradually with time; (2) The topographic effects are concentrated near mountains, and their intensity depends on the distance of survey points from mountain peaks; (3) The influencing range and response amplitude of mountains are proportional to the mountain scale. In other words, a larger mountain scale corresponds to a larger influencing range and higher response amplitude; (4) Mountains with relatively high resistivity show more intense topographic influence. As shown by multiple models with simple and regular topographic anomalies, the corrected TEM responses, which match well with the responses from direct forward modeling, can effectively eliminate topographic effects to a certain extent. The research on the influence and correction method of topographic effects can be used as a reference for the processing and interpretation of TEM data of areas with complex terrain.

Velocity is a key parameter determining the migration imaging resolution of ground penetrating radars (GPR).The method combining minimum image entropy and migration usually estimates the medium velocity by calculating the entropy curves using the overall migration profile as a fixed window.Therefore,such a method is not applicable to non-uniformly distributed media.Moreover,for this method,a too-high or too-low test velocity will make the convergence position of hyperbolic diffracted waves go beyond the fixed window,thus reducing the estimation accuracy.This study proposed a minimum entropy method based on a velocity-controlled moving window,in which the calculation window in the migration profile is accurately controlled by the test velocity.Then,this method was combined with inverse time migration to estimate the optimal migration velocity.By automatically adjusting the position of the calculation window using the trial velocity,this method keeps the convergence position of hyperbolic diffracted waves at the center of the calculation window.In this manner,stable and accurate entropy curves can be obtained.By comparing the calculation results with those of the minimum entropy method based on a fixed window,this study verified the correctness and effectiveness of the minimum entropy method based on a velocity-controlled moving window for a typical hyperbolic diffracted wave.As revealed by numerical experiments and the tests of measured data,compared with the minimum entropy method based on a fixed window,the minimum entropy method based on a velocity-controlled moving window can keep the convergence position of hyperbolic diffracted waves accurately at the center of the calculation window,yielding more stable entropy curves,lower computational complexity,higher estimation accuracy of the migration velocity,and better imaging performance of reverse time migration.

The strong seismic reflection separation method based on the matching pursuit algorithm has yielded encouraging results in practical applications.However,this method faces some challenges in the selection of key parameters and has been scarcely investigated.This study thoroughly investigated the optimization of frequency parameters in the method thereof and established a technical process.First,this study analyzed the spatial variations in the frequency of seismic waves from the perspective of seismic wave propagation and attenuation and proposed a matching pursuit algorithm under the constraints of frequency.Then,this study designed corresponding geological models,conducted frequency optimization tests,and separated the strong seismic reflections using the matching pursuit algorithm under the constraints of the seismic wave frequency of the overlying strata.The test results verify the accuracy and effectiveness of the strong reflection separation method.Finally,the strong reflection separation method was applied to the fracture-vug carbonate reservoirs in the Tarim Basin.The great application effects indicate that the separation method can separate strong reflection events more reasonably and effectively,making the characteristics of underlying small-sized fractures and vugs more significant.This study further optimizes the strong reflection separation method based on matching pursuit and improves the adaptability and application performance of seismic data,thus laying a better foundation for further promotion and application of this method.

Given large data volumes and low post-processing efficiency of full matrix capture-total focusing imaging,this study proposed a planar array-total focusing method(PATFM) for the imaging of planar array data.First,the wave front time of the downgoing planar array was calculated using the eikonal equation based on the characteristics of both the total focusing imaging algorithm and the planar array wave field.Then,the total focusing imaging formula was improved using the upgoing and downgoing ultrasonic propagation time based on the delay superposition principle.Finally,focusing imaging was performed on a wide range of imaging points below the planar array aiming at the derived directivity and diffusion correction coefficient of the planar array.Through Field II simulation,the PATFM was compared with three imaging methods,including phase-controlled scanning imaging,full matrix capture-based total focusing imaging,and plane wave capture-based total focusing imaging.The results show that the PATFM can be used for large-range focusing imaging of single planar array data,greatly improving the computational efficiency while obtaining corresponding accuracy.Therefore,this study provides a feasible technical means for 3D imaging of array acoustic waves.

During the flight exploration of the time-domain airborne electromagnetic system, signals are influenced by the artificial noise from high-voltage transmission lines. Consequently, the responses acquired contain power frequency interference information and thus fail to truly reflect the distribution of subsurface media. Hence, this study conducted research on the removal of power frequency interference. This study proposed a comb filter that can directly process data in the time domain, shortening the time of time-frequency and frequency-time transform, avoiding the cumbersome transform steps, and reducing the risk of possible transform errors. The key to utilizing the comb filter is to suppress the power frequency signal and its k^th harmonic by means of an ideal stopband for the suppression of power frequency interference. This study developed IIR and FIR comb filters and compared their removal effects on power frequency interference with that of a single notch filter. This study aims to offer a power frequency interference removal method for the processing of time-domain airborne electromagnetic data.

Seismic data acquired from mature industrial areas frequently contain a large amount of local strong noise with high amplitude due to the continuous operation of production equipment.However,such local strong noise can be hardly suppressed using conventional denoising methods.This study integrated dilated convolution(DC) and U-Net into a DC-UNet network for suppressing local strong noise.For the circular DC blocks at the front end of the DC-Unet network,a circularly expanded DC kernel was used to extract the features of strong noise at different scales,with the receptive field being expanded.Meanwhile,an encoder was used at the back end of the network to extract the features of strong noise and restore the details of strong noise.Subsequently,the DC-UNet network was employed to perform a nonlinear mapping from noisy data to noise.On this basis,strong noise was suppressed by subtracting the learned strong noise from the noisy data.As indicated by the experimental results of synthetic and real data obtained from the training using the PyTorch framework in the GPU environment,the DC-UNet network can effectively suppress the local strong noise and improve the signal-to-noise ratio compared with DnCNN,U-Net,and PCA-UNet networks.

Ground-penetrating radar (GPR) data are often contaminated by random noise in the actual engineering inspection.The noise in data will reduce the signal-to-noise ratio and resolution of the data,adversely affecting the subsequent inversion and interpretation.Accordingly,this study proposed neural network-based denoising for GPR data.First,a multi-layer neural network model was constructed to integrate the data corrupted by white Gaussian noise into the noise-free data.Then,the corrupted data and their corresponding noise patches were built as training data.The weights of neurons in every layer of the model e updated using a back-propagation algorithm to minimize the model training loss.Finally,the two synthetic data and the measured radar data were input to the trained model,and the model's output was calculated using the noise characteristic weights acquired from the training.Compared with the curvelet transform,the numerical simulation test results verify the effectiveness and robustness of the method proposed in this study.Moreover,the proposed method can suppress the noise more thoroughly in areas with complex structures and weak amplitudes,and show effective signals more clearly.

Gravity survey is an important part of geodetic mapping and geophysical exploration. Different gravity specifications adopt different methods to calculate the zero drift rates in two-way reciprocal observations (i,j,j',i'). The repeated measurements of point j are subjected to static drift in the geological survey specification. By contrast, the zero drift rate is calculated through regression analysis in the petroleum specification. Different processing methods for the repeated measurement interval of point j yield significantly different zero drift rates based on the two specifications. Through theoretical formula analysis and comparison of measured data, this study analyzed the influence of g'_j- g_j {}_{} and t'_j-t_j in the repeated measurements of point j on the calculation of the zero drift rate. By comparing with the regression analysis, this study illustrated the importance of static drift in reducing the uncertainties caused by instrument performance and measurement environment. Moreover, this study proposed the applicable conditions of the two specifications.

In the one-dimensional (1D) forward modeling of transient electromagnetic (TEM) responses based on spectral methods, multiple calculation steps significantly influence the calculation accuracy of TEM responses. To improve the efficiency of 1D forward modeling, the common practice is to directly calculate the frequency-domain electromagnetic responses of dozens of frequency points and then obtain the responses of hundreds of frequency points through cubic spline interpolation. Although the numerical results calculated using the cubic spline interpolation function can meet the requirements of most forward modeling scenarios, their accuracy can be further improved. This study introduced high-order B-spline interpolation into the 1D forward modeling of TEM responses to replace the conventional cubic spline interpolation and verified the accuracy of the method based on magnetic dipole sources and circle-shaped loop sources. The results show that the TEM responses of several geoelectric models calculated based on high-order B-spline interpolation exhibit higher accuracy than those calculated using conventional cubic spline interpolation.

This study aims to ascertain the heavy metal pollution of groundwater in a typical chemical industry park in northwestern Shandong. According to the investigation and evaluation requirements for groundwater environments in chemical industry parks, this study collected 10 groundwater samples to analyze the concentrations and spatial distributions of eight heavy metals, namely Fe, Cu, Zn, Al, Cd and Pb. Furthermore, it conducted the health risk assessment of groundwater for different populations. The results indicate that: (1) except Mn and Al, all heavy metals in the groundwater of the chemical industry park showed concentrations lower than the class III water quality standard stated in the Standard for Groundwater Quality (GB/T 14848—2017), with a comprehensive pollution index ranging from 0.37 to 0.78. The monitoring points for heavy metal elements are all pollution-free; (2) the overall spatial distributions of heavy metals are roughly consistent with the distribution areas of key enterprises in the chemical industry park. This consistency indicates that external factors such as the production activities of enterprises affect the spatial distributions of heavy metals in groundwater; (3) the health risks are lower for children than for adults and lower via skin contact than via drinking. The non-carcinogenic risks under different exposure routes are acceptable for different populations. Carcinogens As and Cd have slight carcinogenic risks for adults. Local authorities should strengthen the supervision of the production activities of enterprises and thoroughly inspect enterprises with suspected pollution. Only in this way can we effectively control and then gradually reduce the risks to human health caused by groundwater pollution.

Investigating the concentrations of natural radionuclides in soils is basic for soil pollution prevention and control. First, this study determined the background values and anomaly thresholds of radionuclides ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K in soils in Guangdong Province using the geographic information system (GIS) and three methods, namely conventional statistics, exploratory data analysis (EDA), and median absolute deviation (MAD). Then, this study assessed the radioactivity levels of the soil environment using four indices: the γ radiation dose rate, the equivalent radium specific activity, the external exposure index, and the annual effective dose rate. Finally, this study assessed the health risks of the soil radioactivity using the geoaccumulation index method, the single factor index method, and the Nemerow composite index method. The results indicate that: (1) Radionuclides ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K in soils of Guangdong Province have average concentrations of 79.4, 102.95, 74.59, and 541.25 (Bq·kg^-1·dry), respectively; (2) The four radionuclides have background values of 34.27、46.75、32.87 and 271.79 (Bq·kg^-1·dry), and the anomaly values of 111.35、141.805、105.12、946.26 (Bq·kg^-1·dry); (3) The radioactivity level indices for soil environment, namely D, Ra_eq, Hex, and AEDR, show averages of 121.44 ± 67.08 nGy/h, 263.48 ± 147.72 Bq/kg, 0.08~2.3, and 148.93 ± 82.26 μSv/a, respectively; (4) The radionuclide geoaccumulation index suggests clean soils, the single factor index indicates slight pollution, and the Nemerow composite index of 0.22~5.52 (average: 1.74 ± 0.97) indicates mild pollution. These three indices, which suggest roughly consistent results for the health risk assessment of radionuclides in soils, can serve as a supplement to the health risk assessment method for soil radioactivity.

This study aims to ascertain the distribution patterns and influencing factors of fluorine in irrigation water and soils in the Gaomi area, Shandong Province, China. Through systematic sampling and testing, this study obtained data including the pH and fluoride concentration of irrigation water and the pH, organic matter, and fluorine concentration of soils. Based on these data, this study plotted the geochemical contour maps for statistical, correlation, and difference analyses. Furthermore, this study explored the influencing factors. The results are as follows: (1) The irrigation water in the study area has a fluoride concentration of 1.89 mg/L on average, which shows strong spatial variability. Zones with high fluoride concentrations in irrigation water are distributed in the northern low-flat alluvial plain, with the number of samples with fluoride concentrations greater than 2 mg/L accounting for 63.16%. There is a significant positive correlation between the fluoride concentration in the irrigation water and the pH (P < 0.01); (2) The soils have a fluoride concentration of 455×10^-6 on average, which shows an inhomogeneous spatial distribution. Zones with high or excess fluorine concentrations are distributed in the northern part of the study area. The fluorine concentrations of soils show significant positive correlations with the pH and organic matter of soils and the fluoride concentration of irrigation water (P < 0.01); (3) The fluoride concentrations in the irrigation water and soils are high in the distribution area of lime concretion black soil. The results of this study reveal the background characteristics and influencing factors of fluoride in the irrigation water and soils of the Gaomi area, providing a geochemical basis for the precise prevention and control of endemic fluorosis.

Establishing the selenium threshold for soils in selenium-rich wheat producing areas in Shaanxi Province is closely related to the lean, fine-scale, and accurate production of natural selenium-rich wheat. Moreover, it can improve the utilization efficiency of selenium-rich land, thus promoting the development of selenium-rich industry in this province. This study determined the selenium threshold of soils in selenium-rich wheat producing areas in Shaanxi at 0.27×10^-6 based on the 1∶250 000 land quality geochemical survey data, the selenium concentration data of 544 sets of soil samples and corresponding wheat seed samples collected in Shaanxi in recent years, the lower limit of geochemical anomalies of selenium in topsoil in the Guanzhong area, and the wheat-soil function. The empirical study showed that the validation set formed via random sampling yielded a selenium accumulation rate of 83.78%, while the third-party inspection yielded a selenium accumulation rate of 87.14%. The wheat produced from selenium-rich land delineated based on the selenium threshold 0.27×10^-6 satisfies the recommended nutrient intake of selenium (60 μg/d) stipulated by the Chinese Nutrition Society. Furthermore, the area of the selenium-rich land is about 1 500 km² (2 250 000 mu), increasing by 640 km² (960 000 mu) compared with that of land delineated based on a selenium threshold of 0.3×10^-6. Therefore, determining selenium-rich soil threshold by crop species can greatly improve the utilization efficiency of selenium-rich land, thus promoting the development of the selenium-rich industry. This study provides a scientific basis for setting selenium enrichment criteria for soils in Shaanxi Province.

To ascertain the pollution characteristics and source of sediments in the upper reaches of the Hanjiang River, this study collected sediment samples at 17 sampling sites in the study area. Based on these samples, this study determined the concentrations of organochlorine compounds (α-666;β-666;γ-666;δ-666;4,4'-DDE;4,4'-DDD;2,4'-DDT; and 4,4'-DDT) and heavy metals (V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb) in the sediments. Then, it assessed the heavy metal pollution using the geoaccumulation and potential ecological risk indices. Furthermore, through redundancy analysis and multivariate statistical analysis, this study explored the sources of heavy metals and the relationships between the physicochemical properties of the sediments and heavy metals concentrations. The results indicate that: (1) The organochlorine compounds in the sediments at all sampling sites show low concentrations, without affecting the ecological environment. However, attention should be paid to the pollution caused by organochlorine compounds; (2) All the heavy metals from the sampling sites show non-pollution or mild pollution, except for Cd, which caused slightly strong pollution; (3) As revealed by the analysis of potential ecological risks, heavy metals generally show extremely high potential risks. Cd, which causes the most serious environmental pollution at the sampling sites, serves as the main factor influencing the environmental and ecological risks in the study area; (4) The redundancy analysis shows that there is no significant relationship between the physicochemical properties of sediments and the concentrations of heavy metals in the study area; (5) As revealed by the multivariate statistical analysis, Cd and Pb may be related to the application of agricultural materials (e.g., chemical fertilizers and pesticides) and the discharge of waste gas, wastewater, and industrial residue, indicating anthropogenic sources; the concentrations of V, Cr, Mn, Co, Ni, Cu, Zn, and As are related to the natural weathering of rocks mainly and to industrial wastewater and agricultural activities partially, indicating dominant natural sources. The comprehensive study shows that the potential ecological hazards caused by heavy metals (dominated by Cd) in the sediments should be treated seriously.

Targeting the selenium resource in soils of Luoyang City, Henan Province, this study analyzed the distribution of total selenium concentration under different geological settings, soil types, land use types, acidity and alkalinity, and organic matter. Furthermore, it determined the bioavailability and speciation distribution of selenium in the soils. The results indicate that: (1) The soils in Luoyang City have total selenium concentrations of (0.03~5.67)×10^-6, with an average of 0.30×10^-6, and the area of soils with moderate and rich selenium accounts for 94.73%; (2) The average selenium concentration is the highest in soils of the Jixian Yunmengshan formation and the lowest in soils of the Cambrian Xinji Formation; (3) The average total selenium concentration is the highest in lime concretion black soil and the lowest in paddy soil; (4) Regarding land use types, the average total selenium concentration is relatively high in soils of paddy land and woodland; (5) Soils with high acidity and high organic matter concentrations are favorable for selenium enrichment; (6) In terms of soil types, the average concentration of bioavailable selenium is the highest in fluvo-aquic soils and the lowest in red clays; (7) The average concentration of bioavailable selenium is higher in alkaline soils than in neutral and acidic soils; (8) Selenium in soils primarily occurs in residue, strong organic bound, and humic acidic bound forms, with the highest average concentration of bioavailable selenium occurring in alkaline soils and red clays. The selenium resource in the soils in Luoyang City has high utilization potential, and it is feasible to conduct targeted development and planning of the selenium-rich industry according to the distribution of total selenium concentration in the study area.

With the rapid development of urban infrastructure,the demand for urban geological work is increasing,and urban geological surveys become particularly important.Urban geophysical exploration has different exploration purposes and working environments from conventional geophysical exploration.Accordingly,compared with conventional geophysical exploration methods,the geophysical exploration methods for urban geological surveys face the challenges of many interference factors,limited construction sites and time,and high requirements for exploration accuracy.The opposing-coils transient electromagnetic(OCTEM) method enjoys a strong anti-interference ability,convenient and efficient construction,and high resolution.Therefore,this study employed the OCTEM method to investigate the test profile in the urban geological survey and evaluation of Haidong City.This test profile was subjected to numerous interference sources since it crossed 11 highways and railways and passed through factories,schools,logistics parks,villages,living quarters,and rivers.Consequently,the OCTEM results agree well with the results of single-point resistivity sounding and drilling results.Therefore,the OCTEM method proposed in this study is effective for urban geological surveys.