Unique Habitat for Benthic Foraminifera in Subtidal Blue Holes on Carbonate Platforms

Dissolution of carbonate platforms, like The Bahamas, throughout Quaternary sea-level oscillations have created mature karst landscapes that can include sinkholes and off-shore blue holes. These karst features are flooded by saline oceanic waters and meteoric-influenced groundwaters, which creates unique groundwater environments and ecosystems. Little is known about the modern benthic meiofauna, like foraminifera, in these environments or how internal hydrographic characteristics of salinity, dissolved oxygen, or pH may influence benthic habitat viability. Here we compare the total benthic foraminiferal distributions in sediment-water interface samples collected from <2 m water depth on the carbonate tidal flats, and the two subtidal blue holes Freshwater River Blue Hole and Meredith’s Blue Hole, on the leeward margin of Great Abaco Island, The Bahamas. All samples are dominated by miliolid foraminifera (i.e., Quinqueloculina and Triloculina), yet notable differences emerge in the secondary taxa between these two environments that allows identification of two assemblages: a Carbonate Tidal Flats Assemblage (CTFA) vs. a Blue Hole Assemblage (BHA). The CTFA includes abundant common shallow-water lagoon foraminifera (e.g., Peneroplis, Rosalina, Rotorbis), while the BHA has higher proportions of foraminifera that are known to tolerate stressful environmental conditions of brackish and dysoxic waters elsewhere (e.g., Pseudoeponides, Cribroelphidium, Ammonia). We also observe how the hydrographic differences between subtidal blue holes can promote different benthic habitats for foraminifera, and this is observed through differences in both agglutinated and hyaline fauna. The unique hydrographic conditions in subtidal blue holes make them great laboratories for assessing the response of benthic foraminiferal communities to extreme environmental conditions (e.g., low pH, dysoxia).

Selection of Remote Sensing Images And Evapotranspiration Models On Complex Land Surfaces for a Humid Karst Catchment

Evapotranspiration (ET) is predominant variable for water management in various types of ecosystems, and ET processes in these ecosystems have been assessed through in-situ measuring and modelling methods. However, it is challenging to measure actual ET and upscale it to regional level. In addition, the accuracy of retrieved parameters from models is usually low for karst landscapes, where the underlying surface is more complex than non-karst landscapes. Due to various porosities and conduits, aquifers in karst landscapes typically show remarkable and rapid responses to precipitation events, leading to serious water stress. Therefore, there is an urgent need to quantify water fluxes to provide reliable evidence for the protection and sustainable management of karst water resources. In this study, five plots were built to observe actual ET based on Thermal Dissipation Probes (TDP), re-designed Ventilated-chamber and Micro-lysimeters in a karst catchment in southwest China. Then, three models (Penman-Monteith-Leurning, PML; Remote Sensing-Priestley and Taylor, RS-PT; and Hargreaves) were selected to upscale ET estimation to the regional level based on Landsant-8 and MODIS data. The results showed that: 1) The PML model performed better than other models (p < 0.01) with higher R2 values (0.72 for MODIS images and 0.87 for Landsat-8 images) and smaller RMSE values (1.4 mm·day-1 and 0.8 mm·day-1 for MODIS and Landsat-8 images, respectively); 2) Daily ET exhibited significant seasonal variability and different spatial distribution; 3) ET had a slightly positive correlation with DEM; however, ground temperature had a negative correlation with ET. By combining remote sensing data and upscaling it to the regional level, this study helps improve the accuracy of measured and estimated ET. It suggests that ET is strongly regulated by vegetation coverage and available energy in subtropical humid karst catchments.

Pretreatment for Tunnel Karst Cave during Excavation: A Case Study of Guangxi, China

Karst landscape is a general term for earth surfaces and underground patterns that have been formed by the dissolution of soluble rock. Karst landscapes are widely distributed throughout China—particularly in the Guangxi and Guangdong provinces. The main features of karst landscapes are typically reflected in karst caverns, sinkholes, and other geographical phenomena. During tunnel construction in karst areas, various forms of karst caverns may appear on the construction route, and they can cause hazards—such as water inrush and collapse—during tunnel construction. These hazards affect the tunnel construction process. As such, it is necessary to propose a treatment for karst caverns. In this work, a case study of the tunnels on the Hechi-Baise expressway is presented. A comprehensive pretreatment method suitable for this tunnel is proposed. On the premise of prioritizing the safety and timeline of construction, an optimized treatment scheme for the karst caverns of Hebai tunnel is followed. The optimized treatment scheme primarily includes calculation of safe thickness of tunnel face, strengthening the initial support and increasing the thickness of the second lining, increasing the reserved deformation, and grouting. The proposed scheme achieved favorable results in the treatment of a karst cavern in the Hebai tunnels.

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).

Linking Hydrogeology and Ecology in Karst Landscapes: The Response of Epigean and Obligate Groundwater Copepods (Crustacea: Copepoda)

Groundwater invertebrate communities in karst landscapes are known to vary in response to multiple environmental factors. This study aims to explore the invertebrate assemblages’ composition of an Apennine karst system in Italy mainly described by the Rio Gamberale surface stream and the Stiffe Cave. The stream sinks into the carbonate rock and predominantly feeds the saturated karst into the cave. For a minor portion, groundwater flows from the epikarst and the perched aquifer within it. The spatial distribution of the species belonging to the selected target group of the Crustacea Copepoda between the surface stream and the groundwater habitats inside the cave highlighted a different response of surface-water species and obligate groundwater dwellers to the hydrogeological traits of the karst unit. Our results suggest that fast endorheic infiltration routes promoted the drift of epigean species from the surface to groundwater via the sinking stream while most of the obligate groundwater dwellers come from the perched aquifer in the epikarst from diffuse infiltration pathways.

DESIGNING TOURISM IDENTITY COMMUNICATION IN SATUN UNESCO GLOBAL GEOPARK

Satun Geopark, located in the south of Thailand, was recently designated as UNESCO Global Geopark in 2018. The geopark is well known for its abundance and variety of Paleozoic fossils with many outstanding geological tourist sites, incl uding specular karst landscapes, stunning caves, and remarkable sea caves. To promote Satun Geopark as tourist destination, its tourism identities must be communicated to wider audiences. This will convey the unique value of local communities to draw attention to new visitors and attract existing ones for a revisit. This research conducted in-depth interviews with community leaders and surveyed on-site signage systems to find out an improvement on tourism identity communication. The design of identity mascot was proposed as a new tool to communicate its identity with visitors in various channels.

Underestimated diversity of Cnemaspis Strauch, 1887 (Sauria: Gekkonidae) on karst landscapes in Sarawak, East Malaysia, Borneo

The paraphyletic group of Old World rock gecko genus Cnemaspis, currently comprises ~180 described species from Africa and Asia. The south-east Asian clade with 63 described species, is most diverse on the Thai-Malay Peninsula, with just five species known from Borneo, an island biodiversity hotspot. Karst regions are known as centres for species endemism, and vast areas of caves and karst exist across northern Borneo. Fieldwork from 2017 to 2020 recovered additional undescribed species of Cnemaspis from areas of karst forests in western and northern Sarawak. These discoveries emphasize the importance of preserving areas of limestone karst within rainforest areas for maintaining species diversity, as well as accelerating research on documenting the biota.

Calcerous Tufa as Invaluable Geotopes Endangered by (Over-)Tourism: A Case Study in the UNESCO Global Geopark Swabian Alb, Germany

Calcerous tufa and sinter are among the most impressive natural spectacles in karst landscapes whose scientific and aesthetic value is universally recognized. Being visually often very appealing they attract numerous visitors. At the same time tufa landforms are extremely vulnerable and can be seriously damaged even by minor interference. The challenge is, therefore, to protect the calcerous tufa heritage, to communicate its values, and to enhance it with the help of adequate geotourism offers. Tufa geotopes are an essential part of the geological heritage of the UNESCO Global Geopark Swabian Alb in Southwest Germany. Unfortunately tufa landforms, especially tufa cascades, suffer serious impairments by (over-)tourism, particularly during the Corona pandemic. The article explores where best to strike the balance between valorization and protection, as well as how to ensure that growth in tourism is compatible with nature preservation, especially in the case of the extremely vulnerable tufa geotopes.