A mardel (tiny pond) is a small hollow mould, which is at least temporarily filled with water. It is a typical form connected to dissolution of gypsum lenses or limestones from a marly subsoil. In places where the gypsum or limestone lenses were dissolved, the surface lowered. Mardels are a valuable archive of the history of land use, soil erosion and climate change and are found on all marly substrates with only slightly inclined topography. They provide rare habitats for special animals, such as amphibians. Differences in interests between nature conservation and geological or archaeological activity can be a source of conflict. If due care is not taken, valuable archives of natural or cultural history may be destroyed in an effort to enhance the ecological value of a site.