Mechanism and Evolution of Soil Organic Carbon Coupling with Rocky Desertification in South China Karst

To study the spatial distribution characteristics of soil organic carbon (SOC) coupled with rocky desertification, 1212 soil samples from 152 soil profiles were sampled from different karst landforms, including karst low hills/virgin forest (KLH) in Libo County, a karst peak-cluster depression (KPCD) in Xingyi County, a karst canyon (KC) in Guanling County, a karst plateau basin (KPB) in Puding County and a karst trough valley (KTV) in Yinjiang County. The spatial distribution characteristics of the responses of SOC, SOC density (SOCD), rocky desertification and soil bulk density (SBD) to different influencing factors were analyzed. The relationships among SOC, SOCD, rocky desertification and SBD were analyzed using Pearson correlation analysis. The SOC storage capacity was characterized by using SOCD, and then the SOC storage capacity in different evolution stages of karst landforms was assessed. The SOC contents of KLH, KPCD, KC, KPB and KTV ranged from 6.16 to 38.20 g·kg−1, 7.42 to 27.08 g·kg−1, 6.28 to 35.17 g·kg−1, 4.62 to 23.79 g·kg−1 and 5.24 to 37.85 g·kg−1, respectively, and their average SOCD values (0–100 cm) were 7.37, 10.79, 7.06, 8.51 and 7.84 kg·m−2, respectively. The karst landforms as ordered by SOC storage capacity were KPCD > KPB > KLH > KTV > KC. The SOC content was negatively correlated with the SBD; light rocky desertification may lead to SOC accumulation. The rocky desertification degree and SBD were closely associated with slope position and gradient. Rocky desertification first increased, then decreased from mountain foot to summit, and increased with increasing slope gradient. However, the SBD decreased from mountain foot to summit and with increasing slope gradient. The SOC contents on the northern aspect of the mountains were generally higher than the other aspects. In summary, rock outcrops controlled the SOC contents in the studied regions. The slope position, gradient and aspect influenced the composition and distribution of vegetation, which influenced the evolution of rocky desertification. Therefore, these factors indirectly affected the SOC content. Additionally, the SOCD decreased with increasing rocky desertification. During the different evolution stages of karst landforms, the SOC storage capacity first decreases, then increases.

Geomorphology of the Mirador-Calakmul Karst Basin: A GIS-based approach to hydrogeologic mapping

This paper classifies the karst landscapes of the Petén Plateau and defines the Mirador-Calakmul Karst Basin by illustrating the distribution of its karst hydrologic features. Archaeological and spatial research of the Mirador-Calakmul area of Guatemala and Mexico has shown it to be a karst basin with geopolitical implications. Current research characterizes the karst landscapes of the Petén Plateau, maps the distribution of karst hydrologic features, and delineates the basin in geomorphological terms. To further this aim, multiple forms of remote sensing data including orthophotographs, a satellite Digital Elevation Model, satellite multispectral images, and Light Detection and Ranging (LiDAR) data have been integrated to interpret the karst features in the study area. Outcrop study and thin section analysis of the upper Buena Vista Formation document that the dominant lithologies are a shallow water algal boundstone interbedded with terrestrial caliche. Karst landforms have been mapped over the Petén Plateau and we identify five karst landscapes, the largest of which is a fluviokarst landscape dominated by karst valleys. We further map karst hydrologic features including seasonal swamps, dolines, intermittent lakes, intermittent streams, solution-enhanced fractures, and springs all of which are characteristic of drainage basins. Boundaries of the karst basin are mapped from multiple lines of evidence including distribution of the karst valleys, a line of springs along the western boundary of the fluviokarst landscape, and a surface drainage analysis. We capture and classify hydrologic data points and develop a regional groundwater map that indicates subsurface flow from east to west within the basin. A drainage map illustrates the extensive system of karst valleys, boundaries, and inferred groundwater flow paths of the Mirador-Calakmul Karst Basin. It was within this geomorphological setting that the ancient Maya developed an extensive civilization during the Middle and Late Preclassic periods (1000 BCE-150 CE).

Options for managed aquifer recharge of karst aquifer of Vis island (Croatia)

<p>Vis, a small remote island in the Adriatic Sea, inhabited since the time of ancient Greeks and Romans, exhibits a unique historical and natural environment. With an area of 89.7 km<sup>2</sup>, the island is mostly composed of karstified carbonate rocks and belongs to Dinaric karst region, locus typicus for karst landforms. Its distance from the mainland is around 50 km from the city of Split, 147 km from the Italian coastline and 18 km from neighbouring Hvar island. The climate on the island is Mediterranean with dry and hot summer and mild, rainy and humid winter (Csa). Vis island, due to its remote location, is not connected to the mainland by submarine water pipeline so it has autonomous water supply due to favourable geological and hydrological conditions which enabled the formation of excellent karst aquifers. The majority of water is abstracted from drilled wells in the central part of the island (Korita extraction site), around 40 l/s, while additional quantities are obtained from coastal spring of Pizdica. Although predominantly of good quality, existing groundwater quantities on Vis are extremely vulnerable to the effects of climate change, namely increase in temperature, quantitative and temporal variability in precipitation trends as well as seawater intrusion. Moreover, Vis island is an attractive location for summer bathing tourism which causes the highest pressure on drinking water resources precisely during the hydrological minimum. An idea to apply artificial recharge of karst aquifer on Vis emerged during the 1970s, however, only on the theoretical level.</p><p>Through the scope of the DEEPWATER-CE project, funded by Interreg Central Europe Programme, the aim is to develop implementation frame for managed aquifer recharge (MAR) solutions. Simplified, MAR is a process by which excess surface water is directed into the ground — either by spreading on the surface, by using recharge wells, or by altering natural conditions to increase infiltration to replenish an aquifer (DILLON et al., 2019). Globally, various designs of MAR schemes have successfully been implemented in unconsolidated aquifers, but there is little experience with artificially recharging karst aquifers (ROLF, 2017). A particular challenge for the technical implementation and operation of MAR is posed by strong hydraulic anisotropy and heterogeneity of karst aquifers and by their high vulnerability to contamination (XANKE, 2017). To investigate whether a MAR operation is feasible and suitable for karst aquifer on Vis, a detailed field and laboratory investigations were carried out. Field investigations included in-situ measurements of physicochemical parameters on water samples from springs and boreholes, groundwater monitoring (conductivity, temperature and water levels), geophysical methods (ERT, magnetotellurics, and seismic refraction) and structural measurements. Laboratory analyses included measurements of stabile water isotopes, and principal cations and anions. Hence, by conducting extensive investigations, coupled with historical data and previous research, a foundation for implementing efficient and sustainable management of karst aquifer through MAR on Vis island will be provided. </p>

Origin of the low-medium temperature hot springs around Nanjing, China

The exploration of the origin of hot spring is the basis of its development and utilization. There are many low-medium temperature hot springs in Nanjing and its surrounding karst landform areas, such as the Tangshan, Tangquan, Lunshan, and Xiangquan hot springs. This article discusses the origin characters of the Lunshan hot spring with geological condition analysis, hydrogeochemical data, and isotope data. The results show that the hot water is SO4–Ca type in Lunshan area, and the cation content of SO4 is high, which are related to the deep hydrogeological conditions of the circulation in the limestone. Carbonate and anhydrite dissolutions occur in the groundwater circulation process, and they also dominate the water–rock interaction processes in the geothermal reservoir of Lunshan. The hot water rising channels are deeply affected by the NW and SN faults. Schematic diagrams of the conceptual model of the geothermal water circulation in Lunshan are plotted. The origin of Tangshan, Tangquan, and Xiangquan hot springs are similar to the Lunshan hot spring. In general, the geothermal water in karst landforms around Nanjing mainly runs through the carbonate rock area and is exposed near the core of the anticlinal structure of karst strata, forming SO4–Ca/SO4–Ca–Mg type hot spring with the water temperature less than 60°C. The characters of the hot springs around Nanjing are similar, which are helpful for the further research, development, and management of the geothermal water resources in this region.

Fusion of Remote Sensing and Applied Geophysics for Sinkholes Identification in Tabular Middle Atlas of Morocco (the Causse of El Hajeb): Impact on the Protection of Water Resource

The Causse of El Hajeb belongs to the Tabular Middle Atlas (TMA), in which thousands of karst landforms have been identified. Among them, collapse dolines and dissolution sinkholes have been highlighted as a source of environmental risks and geo-hazards. In particular, such sinkholes have been linked to the degradation of water quality in water springs located in the junction of the TMA and Saïss basin. Furthermore, the developments of collapse dolines in agricultural and inhabited areas enhance the risk of life loss, injury, and property damage. Here, the lack of research on newly formed cavities has exacerbated the situation. The limited studies using remote sensing or geophysical methods to determine the degree of karstification and vulnerability of this environment fail to provide the spatial extent and depth location of individual karst cavities. In order to contribute to the effort of sinkhole risk reduction in TMA, we employed remote sensing and geophysical surveys to integrate electrical resistivity tomography (ERT) and self-potential (SP) for subsurface characterization of four sinkholes identified in the Causse of El Hajeb. The results revealed the existence of sinkholes, both visible and non-accessible at the surface, in carbonate rocks. The sinkholes exhibited distinct morphologies, with depths reaching 35 m. Topography, geographic coordinates and land cover information extracted on remote sensing data demonstrated that these cavities were developed in depressions in which agricultural activities are regularly performed. The fusion of these methods benefits from remote sensing in geophysical surveys, particularly in acquisition, georeferencing, processing and interpretation of geophysical data. Furthermore, our proposed method allows identification of the protection perimeter required to minimize the risks posed by sinkholes.