Evaluating the structure characteristics of epikarst at a typical peak cluster depression in Guizhou plateau area using ground penetrating radar attributes

Epikarst, defined as the “skin” of karst environment, is widely developed in southwest China, largely as a result of the subtropical monsoon climate. Typical SW China karst accommodates a dual hydrogeological structure, with surface and subsurface hydrological systems. The epikarst ecosystem of karst environments plays a key role in biogeochemical cycling and energy and material storage and transport. Due to low rates of soil-formation derived from carbonate rock weathering, the soil layer is shallow and scattered, presenting interlocked features within carbonate rock. Research on epikarst structure is primarily based on section field survey with semi-quantitative characterization, often lacking a fully quantitative description of soil-rock structural characteristics. We utilized ground penetrating radar (GPR) attributes to interpret the structure of epikarst at a peak cluster depression in the Guizhou karst plateau. Two typical types of epikarst slope profiles and one peak cluster depression in Maguan Town, Puding County were selected for study. We used MALA GPR equipment with 500 MHz and 50 MHz antennas to acquire data. GPR data was processed conventionally and then average energy attributes, average amplitude attributes and coherence attributes were extracted to interpret the structure of the two epikarst profiles and the soil depth of the depression. The results show that: (i) energy and coherence attributes can highlight the soil-rock structure of the epikarst profiles with relative ease; (ii) compared to the original returned image, the energy attributes visualise the soil and rock medium more effectively; and (iii) the coherence attributes can identify the reflection interface between complete bedrock and bedrock containing fissure and grikes (epikarst). In addition, using the 50 MHz antenna we were able to determine the soil depth in depression with coherence attributes indicating a depth of 3.6 m, very close to the real depth (3.58 m) measured by our auger verification work. GPR attributes provide evidence that the epikarst has developed a large number of fissures filled with soil or other materials, but that the bedrock under the epikarst has few fractures. GPR attributes are therefore helpful for increasing our confidence of studying the structure of slope epikarst structure and depression soil depth

Seismic Signatures and Site Characterization of an Intermittent Stream in Dry and Flood Conditions: An Implication for Soil Losses and Landslide Triggering

The seasonal soil losses and frequent shallow landslides in the Cerrado region of Brazil have high destructive potential with social, economic, and climatic implications. As fluvial systems substantially drive such environmental threats; therefore, it is essential to conduct geological site characterization and continuously monitor the seasonal erosive potentials of the rivers and streams. However, in such unstable and sensitive conditions, traditional intrusive investigation approaches may not be safe; therefore, the geophysical investigation might offer a good alternative. For the present study, a geophysical approach (particularly the seismic method) was adopted to examine the seismic footprints and GPR site characterization of a seasonal stream in the Rua do Matto, Brasilia, Brazil. The monitoring was conducted (at a safe distance) on the intermittent stream over several durations of dry (no rain) and rainy (flood) conditions. After pre-processing the raw data, the power spectral density (PSDs) was computed as a function of several variables (wind speed), time-frequency spectrograms, ambient noise displacement root mean square (RMS), the single station horizontal-to-vertical spectral ratio (HVSR) curves. In addition, change-point analysis was used for comparing the ambient noise with wind speed (both were well correlated). The GPR amplitude and waveform variation features were attributed to the subsurface material and the presence of boulders in the floodplain as well as regions (low coherence value) susceptible to erosion (weak spots). The river flows were evident on the mean probabilistic PSD values, spectrograms, HVSR curves and different patterns of RMS displacements (at selective ranges of frequency). The multi-peaks emerged on the HVSR curve are further analyzed for changes in amplitude, width and troughs possibly related to river activities and soil moisture due to rain. The approach provides the basis for non-destructive monitoring tools enabling the detection of 'seismic signatures' and weak spots of the fluvial channels for improving their environmental management

A generalized GPR application potential zonation in the karst catchment of SW China

The epikarst together with its soil stocks (subcutaneous structure), resulted from the dissolution and weathering of soft rocks, are crucial to the fact that they may contribute to the canopy growth and can significantly influence the ecological restoration and organic carbon sequestration. For the delineation of these ecological significant karst features, ground penetrating radar (GPR) seemed to be a promising technique because of its noninvasive, cost-prohibited and lesser labor-intensive operations. However, the landscape heterogeneity, connection between surface morphology and underground environments and high vegetative endemism making karst as a complicated environment for any geophysical application. Same is the case with the GPR applicability in SW Chinese catchment as it is affected by numerous features such as epikarst slope, peak-cluster depression, tree trunks and roots, precipitation and moisture contents as well as proximity to high voltage power lines. Considering these factors, the present study analyzes the GPR data acquired at the sites representing each of these aforementioned features. The analysis includes calculation of GPR attributes as average energy, coherence and total energy together with the forward calculations wherever required. Tilt signals from surrounding hills mix with the tilt signals from subsurface inclined interfaces in a GPR image. The information of soil-rock distribution above epikarst in the slope is difficult to obtain completely for GPR. The interpretation of epikarst bottom boundary faces two possibilities considering the affects of moisture. The affects of tree trunks and roots and strong electromagnetic fields of high voltages lines make the GPR data interpretation about subsurface soil-rock structure high difficult. The soil moisture greater than ~ 30% makes GPR inapplicability. These site-specific findings are used for the generalized GPR application potential zonation in the typical SW Chinese catchment (the central Guizhou plateau). The findings of the present study may prove as a reconnaissance and an application paradigm for the future GPR utilities in complex karst characterization especially, in SW China as well as the areas having similar karstic conditions

A catchment scale GPR application potential zonation. Case study from SW China

The epikarst together with its soil stocks (subcutaneous structure) are crucial to the fact that they may contribute to the canopy growth and can significantly influence the ecological restoration and organic carbon sequestration. Geophysical techniques especially, the ground penetrating radar (GPR) are advantageous for such investigations. However, the complicated karst environment due to numerous influencing factors (i.e., the forest, epikarst slope, peak-cluster depression, soil humidity,high voltage power lines) can significantly influence the exploration with GPR. In the past, such applications were limited to local scales without considering the aforementioned factors together. Hence, the present study analyses the influences of these factors on the performance and reliability of GPR results considering the central Guizhou plateau of south-west China as a case study. These site-specific findings are summarized into a GPR application potential zonation map at the catchment scale. The zones were rated as low, moderate and high potential degree regions, each reflecting results reliability which can be considered as a cost-effective feasibility reference for the future GPR applications in complex karst terrain characterization, as well as the areas having similar karstic conditions

Strong Blue Emissive Supramolecular Self-Assembly System Based on Naphthalimide Derivatives and Its Ability of Detection and Removal of 2,4,6-Trinitrophenol

Two simple and novel gelators (<b>G-P</b> with pyridine and <b>G-B</b> with benzene) with different C-4 substitution groups on naphthalimide derivatives have been designed and characterized. Two gelators could form organogels in some solvents or mixed solvents. The self-assembly processes of <b>G-P</b> in a mixed solvent of acetonitrile/H₂O (1/1, v/v) and <b>G-B</b> in acetonitrile were studied by means of electron microscopy and spectroscopy. The organogel of <b>G-P</b> in the mixed solvent of acetonitrile/H₂O (1/1, v/v) formed an intertwined fiber network, and its emission spectrum had an obvious blue shift compared with that of solution. By contrast, the organogel of <b>G-B</b> in acetonitrile formed a straight fiber, and its emission had an obvious red shift compared with that of solution. <b>G-P</b> and <b>G-B</b> were employed in detecting nitroaromatic compounds because of their electron-rich property. <b>G-P</b> is more sensitive and selective toward 2,4,6-trinitrophenol (<b>TNP</b>) compared with <b>G-B</b>. The sensing mechanisms were investigated by ¹H NMR spectroscopic experiments and theoretical calculations. From these experimental results, it is proposed that electron transfer occurs from the electron-rich <b>G-P</b> molecule to the electron-deficient <b>TNP</b> because of the possibility of complex formation between <b>G-P</b> and <b>TNP</b>. The <b>G-P</b> molecule could detect <b>TNP</b> in water, organic solvent media, as well as using test strips. It is worth mentioning that the organogel <b>G-P</b> can not only detect <b>TNP</b> but also remove <b>TNP</b> from the solution into the organogel system