Distribution and characteristics of glaciokarst on the island of Gotland, Baltic Sea - its role on groundwater recharge and sensitive wetland ecosystems

Abstract

 Glaciokarst is widespread in the Silurian carbonate bedrock on the Island of Gotland. Grikes and limestone pavements are the most common karst features. Although, less well documented, caves and subsurface channels also contribute to the complex hydrogeology in the bedrock. The karst is interpreted to have been formed, primarily, before the Pleistocene when the landscape was covered with acidic organic soils. Glacial erosion and postglacial karstification have also played significant roles in sculpturing the epikarst morphology we see today. The study presents quantitative and qualitative characterization of karst within several pilot areas on the island of Gotland. High resolution aerial photographs were acquired over the pilot areas using a drone. These images were then analysed in GIS-software to provide a statistical evaluation of length, width, and relative area with karst. As well as providing a statistical understanding of the occurrence and geometry of karst, the results also help to clarify the impact of karst on the sensitive and limited groundwater resources on Gotland. Since a large part of the carbonate bedrock surface is barren or covered by thin quaternary deposits the epikarst provides important pathways for the percolation of meteoric water and recharge to the groundwater. It also locally provides guided pathways for surface runoff. Furthermore, the study demonstrates that the presence of karst often is in conjunction with sensitive ecosystems such as temporary wetlands. Extensive development of grikes and limestone pavements also provide conditions for periodically hanging aquifers, which not only promotes groundwater recharge but also the formation of unique habitats for a variety of often threatened ecosystems. This study, which includes both biologists and earth scientists highlights the importance of the identification of catchment areas and mapping of karst. It also emphasises that investigations into the hydrogeology (including aspects such as groundwater recharge, surface runoff and subsurface transport pathways) is essential for a better understanding of wetland dynamics and their protection. The presence of karst and spreading of contaminations in the ground is also discussed. The work summarizes early results from a collaboration between authorities working with Natura 2000 karst habitats and geological classification and mapping of karst.