Chapter 6 Karst

Karst vegetation coverage detection using UAV multispectral vegetation indices and machine learning algorithm

BACKGROUND

Karst vegetation is of great significance for ecological restoration in karst areas. Vegetation Indices (VIs) are mainly related to plant yield which is helpful to understand the status of ecological restoration in karst areas. Recently, karst vegetation surveys have gradually shifted from field surveys to remote sensing-based methods. Coupled with the machine learning methods, the Unmanned Aerial Vehicle (UAV) multispectral remote sensing data can effectively improve the detection accuracy of vegetation and extract the important spectrum features.

RESULTS

In this study, UAV multispectral image data at flight altitudes of 100 m, 200 m, and 400 m were collected to be applied for vegetation detection in a karst area. The resulting ground resolutions of the 100 m, 200 m, and 400 m data are 5.29, 10.58, and 21.16 cm/pixel, respectively. Four machine learning models, including Random Forest (RF), Support Vector Machine (SVM), Gradient Boosting Machine (GBM), and Deep Learning (DL), were compared to test the performance of vegetation coverage detection. 5 spectral values (Red, Green, Blue, NIR, Red edge) and 16 VIs were selected to perform variable importance analysis on the best detection models. The results show that the best model for each flight altitude has the highest accuracy in detecting its training data (over 90%), and the GBM model constructed based on all data at all flight altitudes yields the best detection performance covering all data, with an overall accuracy of 95.66%. The variables that were significantly correlated and not correlated with the best model were the Modified Soil Adjusted Vegetation Index (MSAVI) and the Modified Anthocyanin Content Index (MACI), respectively. Finally, the best model was used to invert the complete UAV images at different flight altitudes.

CONCLUSIONS

In general, the GBM_all model constructed based on UAV imaging with all flight altitudes was feasible to accurately detect karst vegetation coverage. The prediction models constructed based on data from different flight altitudes had a certain similarity in the distribution of vegetation index importance. Combined with the method of visual interpretation, the karst green vegetation predicted by the best model was in good agreement with the ground truth, and other land types including hay, rock, and soil were well predicted. This study provided a methodological reference for the detection of karst vegetation coverage in eastern China.

Preliminary Study on the Distribution, Source, and Ecological Risk of Typical Microplastics in Karst Groundwater in Guizhou Province, China

Karst groundwater is one of the important drinking water sources in karst areas, and it has an important role in maintaining the regional ecosystem and human health. The study of microplastics (MPs) in karst groundwater has rarely been reported, and the occurrence and migration behavior of MPs under the unique environmental conditions of karst is unclear. This study selected cave groundwater and common MPs in karst areas to explore the occurrence characteristics of MPs in groundwater to clarify the factors affecting the distribution and migration of MPs. The results showed that the abundance of MPs in karst groundwater was between 2.33 and 9.50 items·L^-1, with an average abundance of 4.50 items·L^-1. The microplastic size, type, color, and chemical composition were primarily 1~5 mm, film and fiber, color and transparent, and PS and PE, respectively. The risk characterization ratio (RCR) index results indicated that 80% of the samples were at a low ecological risk level, whereas 60% of the sampling points after concentrated rainfall in June were a medium ecological risk. The study showed that rainfall events significantly changed the abundance and migration of MPs in karst groundwater. The Pearson analysis showed a positive correlation between microplastic distribution and suspended particles (SP), total organic carbon (TOC), and water velocity (WV) in water. The study indicated that strong soil erosion in karst areas may also be one of the main sources of MPs in karst groundwater, and that karst groundwater microplastic pollution is an environmental problem that should not be ignored.

Dissolution-After-Precipitation (DAP): a simple microfluidic approach for studying carbonate rock dissolution and multiphase reactive transport mechanisms

We propose a simple microfluidic approach: Dissolution-After-Precipitation (DAP), to investigate regimes of carbonate rock dissolution and multiphase reactive transport. In this method, a carbonate porous medium is created in a glass microchannel via calcium carbonate precipitation, after which an acid is injected into the channel to dissolve the precipitated porous medium. Utilizing the DAP method, for the first time we realized all five classical single-phase carbonate rock dissolution regimes (uniform, compact, conical, wormhole, ramified wormholes) in a microfluidic chip. The results are validated against the established theoretical dissolution diagram, which shows good agreement. Detailed analysis of these single-phase dissolutions suggests that the heterogeneity of the porous medium may significantly impact how the dissolution patterns evolve over time. Furthermore, DAP is utilized to investigate multiphase dissolution. As examples we tested the cases of an oleic phase (tetradecane) and a gaseous phase (CO₂). Results show that the presence of a nonaqueous phase in pore spaces induces the formation of wormholes despite weak advection, and these wormholes ultimately become pathways for nonaqueous phase transport. However, the transport of tetradecane in the wormhole is very slow, causing acid breakthrough into neighboring regions. This mechanism enhances lateral connectivity between wormholes and may lead to a wormhole network. In contrast, CO₂ moves rapidly and continuously seeks to enter a widening wormhole from a narrower wormhole or the porous regions, generating phenomena such as ganglia redistribution and counterflow (flow of gas opposite to acid flow). Extensive independent experiments are conducted to verify the reproducibility of the observed phenomena/mechanisms and further analyze them. Real-time monitoring of fluid pressure drop during dissolution is implemented to complement microscopy image analysis. Our method can be implemented repeatedly on the same chip, which offers a convenient and inexpensive option to study pore-scale reactive transport mechanisms.

A Multiscale Framework for Sustainable Management of Tufa-Forming Watercourses: A Case Study of National Park “Krka”, Croatia

Tufa sedimentary systems are sensitive fluvial landscapes subject to various external disturbances. Tufa landscape degradation reflected in negative hydrological changes and a decrease in the intensity of the tufa formation process have been detected in National Park Krka (Croatia). The main causes were recognized in the uncontrolled spread of invasive vegetation (Ailanthus altissima) and increased anthropogenic influence. Therefore, the Park administration launched the project, Management and Maintenance of Macro-Vegetation at Skradinski Buk (SB)—Development of a Multicriteria Model for Sustainable Management. The methodological framework was divided into three scales of research. The macro-scale research comprised a set of activities aimed at selecting the most suitable test surface within a wider area of the Skradinski Buk (SB) waterfall. The meso-scale research involved mapping the reference and final state of the vegetation and hydrological network after the removal of invasive vegetation and mitigation of negative anthropogenic impact. At the micro-scale, a monitoring system was established to track the quality of the tufa sedimentary system. Special emphasis was placed on the measurement of tufa formation dynamics (TFD) on limestone plates using a new methodological approach based on structure from motion (SfM) photogrammetry. Implementation of the proposed multiscale framework resulted in reactivation of tufa-forming watercourses, prevention of invasive vegetation regeneration and achievement of sustainable conditions for the tufa formation process. In reactivated watercourses, the average tufa growth rate was 4.267 mm a−1 (n = 18). Potential users of this framework include local authorities and administrators of protected areas.

Evidence of thermophilisation and elevation-dependent warming during the Last Interglacial in the Italian Alps

Thermophilisation is the response of plants communities in mountainous areas to increasing temperatures, causing an upward migration of warm-adapted (thermophilic) species and consequently, the timberline. This greening, associated with warming, causes enhanced evapotranspiration that leads to intensification of the hydrological cycle, which is recorded by hydroclimate-sensitive archives, such as stalagmites and flowstones formed in caves. Understanding how hydroclimate manifests at high altitudes is important for predicting future water resources of many regions of Europe that rely on glaciers and snow accumulation. Using proxy data from three coeval speleothems (stalagmites and flowstone) from the Italian Alps, we reconstructed both the ecosystem and hydrological setting during the Last Interglacial (LIG); a warm period that may provide an analogue to a near-future climate scenario. Our speleothem proxy data, including calcite fabrics and the stable isotopes of calcite and fluid inclusions, indicate a +4.3 ± 1.6 °C temperature anomaly at ~2000 m a.s.l. for the peak LIG, with respect to present-day values (1961–1990). This anomaly is significantly higher than any low-altitude reconstructions for the LIG in Europe, implying elevation-dependent warming during the LIG. The enhanced warming at high altitudes must be accounted for when considering future climate adaption strategies in sensitive mountainous regions.

A Test of the Biogenicity Criteria Established for Microfossils and Stromatolites on Quaternary Tufa and Speleothem Materials Formed in the "Twilight Zone" at Caerwys, UK

The ability to distinguish the features of a chemical sedimentary rock that can only be attributed to biology is a challenge relevant to both geobiology and astrobiology. This study aimed to test criteria for recognizing petrographically the biogenicity of microbially influenced fabrics and fossil microbes in complex Quaternary stalactitic carbonate rocks from Caerwys, UK. We found that the presence of carbonaceous microfossils, fabrics produced by the calcification of microbial filaments, and the asymmetrical development of tufa fabrics due to the more rapid growth of microbially influenced laminations could be recognized as biogenic features. Petrographic evidence also indicates that the development of "speleothem-like" laminae was related to episodes of growth interrupted by intervals of nondeposition and erosion. The lack of any biogenic characteristics in these laminae is consistent with their development as a result of variation in the physicochemical parameters that drive calcite precipitation from meteoric waters in such environmental settings.

The Neanderthal in the karst: First dating, morphometric, and paleogenetic data on the fossil skeleton from Altamura (Italy)

In 1993, a fossil hominin skeleton was discovered in the karst caves of Lamalunga, near Altamura, in southern Italy. Despite the fact that this specimen represents one of the most extraordinary hominin specimens ever found in Europe, for the last two decades our knowledge of it has been based purely on the documented on-site observations. Recently, the retrieval from the cave of a fragment of bone (part of the right scapula) allowed the first dating of the individual, the quantitative analysis of a diagnostic morphological feature, and a preliminary paleogenetic characterization of this hominin skeleton from Altamura. Overall, the results concur in indicating that it belongs to the hypodigm of Homo neanderthalensis, with some phenetic peculiarities that appear consistent with a chronology ranging from 172 ± 15 ka to 130.1 ± 1.9 ka. Thus, the skeleton from Altamura represents the most ancient Neanderthal from which endogenous DNA has ever been extracted.

Carbonate build-ups in lacustrine, hydrothermal and fluvial settings: comparing depositional geometry, fabric types and geochemical signature

Carbonate build-ups in lakes, hydrothermal and fluvial settings are characterized by distinctive geometry, spatial distribution, fabrics and geochemical signature but also by some comparable features. Lake margin bioherms form continuous belts for hundreds of metres to kilometres, subparallel to shorelines. Sublacustrine spring mounds are spaced at hundreds of metres to kilometres and aligned along faults. Hydrothermal travertine mounds and aprons with planar clinoforms or terraced slopes are controlled by faults, thermal water discharge and substrate topography. Fluvial tufa barrages, cascades and terraced slopes are controlled by climate, vegetation and substrate gradient. The wide spectrum of carbonate microfabrics ranges from clotted peloidal micrite and laminated boundstone to crystalline dendrite cementstone. Non-marine carbonate microfabrics cannot be linked to specific depositional environments, and are not deterministic proxies for the interpretation of build-up architecture. Microfabric associations can be indicative, but not exclusive, of specific depositional environments and geometry. Stable isotope geochemistry is a useful tool to distinguish between hydrothermal, karstic freshwater and evaporative lake carbonates. Carbonate precipitation results from a continuum of abiotic and biologically influenced/induced processes in settings where carbonate supersaturation is largely driven by physico-chemical mechanisms and microbial biofilms, even if acting as passive low-energy surface sites for nucleation, are widely present.

A framework for the extraction and interpretation of organic molecules in speleothem carbonate

RATIONALE

The organic content of speleothem calcite is a well-recognized component of their chemical composition. To date, the techniques for interpretation of this material include UV fluorescence, FTIR spectroscopy and biomarker analysis using gas chromatography/mass spectroscopy (GC/MS). However, investigation of the minute concentrations of molecules in speleothems demands careful sampling and laboratory controls.

METHODS

To be certain extracted molecules were encapsulated at the time of speleothem growth and do not represent contamination, we submitted three pieces of speleothem calcite to a rigorous extraction procedure. Based on sequential digestion and analysis by GC/MS, we measured concentration profiles of individual compounds with increasing distance from sample surfaces.

RESULTS

Declining concentrations toward interior extracts identified cholesterol, phthalates, and n-alkanes as surface contaminants. In contrast, iodo organic compounds had homogeneous concentration profiles and were also significantly above laboratory background levels, consistent with an indigenous origin. However, further laboratory testing demonstrated that iodo organics were produced by the reaction of iodine derived from the speleothem with solvent additives and other impurities of the extraction procedure. Sitosterol and some fatty acids demonstrated distributions which were probably indigenous to the speleothem archive, thus recording environmental conditions commensurate with time of growth.

CONCLUSIONS

We do not aim to provide an environmental interpretation of extracted molecules, but highlight the caution necessary before doing so. We ultimately establish a framework for differentiating between organic constituents that are introduced to the speleothems during storage, handling and as artifacts of extraction, and those encapsulated in situ at the time of growth.

Definition of the Anthropocene: a view from the underworld

Annually laminated stalagmites from natural caves and limestone mines capture a number of significant environmental and climatic signals during the anthropogenically disturbed era. The effects of forest clearance, or development of agricultural or industrial practices, can be marked by changes in soil or hydrological responses leading to shifts in both chemical (e.g. carbon and oxygen isotope ratios or trace elements) and physical (e.g. fabric, thickness of laminae) signals. However, these signals are diachronous because of the spatial heterogeneity of human societies. Twentieth-century changes in atmospheric composition are known from speleothems at several sites and demonstrate pollution disturbance of the sulphur cycle and the signal provided by the 1950s rise in radiocarbon caused by atmospheric nuclear tests. This latter is a global signal and hence a strong candidate to define the start of the Anthropocene, although other considerations, including comparison with instrumental archives, would favour an earlier timing. An attractive option is the climate amelioration marking the end of the Little Ice Age in the mid-nineteenth century, which is marked in Alpine and other Northern Hemisphere areas. Examples are illustrated from the Grotta di Ernesto cave to illustrate the appearance of a putative mid-nineteenth-century boundary.