Different from the existing Critical Zone Observatory sites (www.czen.org), with the Hainich Critical Zone Exploratory (Hainich CZE), we focus on integrated research on the functioning and biodiversity of the subsoil compartments of the Earth´s Critical Zone and their links and connections to the pedosphere, the biosphere, and the lower atmosphere. The compartments of interests are therefore the soils - sensu strictu, the water-unsaturated zone, and the water-saturated subsurface including used aquifers (Figure 1).
Fig. 1: Scheme of the near-surface compartments of the Earth's Critical Zone at a location of the Hainich Exploratory. The bedrock is mainly composed of triassic marine alternations of limestone and marlstone beds. (Source: Lehmann in Küsel et al. 2016, CC-BY 4.0, unmodified)
Location of the Hainich CZE, Landscape
The Hainich CZE is located in the northwestern part of the Federal State of Thuringia, central Germany. The well and monitoring plot transect (Figure 2) follows the eastern slope of the Hainich low-mountain range. Dominant land-use types of the cultural landscape are ancient woodland (Hainich National Park) in Hainich ridge areas, as well as managed forest. The eastern slopes are agriculturally impacted and used for cropland and pasture land (Figure 2). Small villages in the surrounding of the transect are Kammerforst, Flarchheim, Langula, and Oberdorla.
Autumnal Beech Forest, Hainich National Park
View over Kammerforst and the geomorphological, tectonic syncline "Mühlhausen-Langensalzaer Mulde"
Agricultural soil management
The Hainich carbonate-rock landscape, as a part of the Thuringian Basin, is situated at its western margin. The major geological units that build the eastern Hainich hillslope belong lithostratigraphically mainly to the Middle and Upper Muschelkalk subgroups (marlstones, limestones; Germanic Triassic) and to the Lower Keuper (clay-/siltstones) in the western part (Figure 2). Holocene alluvial deposits are found along little creeks and rivers. Locally, pleistocene loess deposits are found. The area is tectonically stressed with fault systems/decompaction zones striking in a north-west-south-eastern direction.
Fig. 2: Geological cross section through the Hainich CZE (Source: Totsche, Lehmann in Küsel et al. 2016, CC-BY 4.0, unmodified)
Hydrology and Hydrogeology
Hydrologically, the area is characterized by its water divide - the Hainich ridge. This important groundwater recharge area discharges to the river Werra (tributary to the Weser catchment) in the west and to Unstrut (tributary to the Elbe catchment) in the east. The carbonate-rock formations of the Upper and especially of the Middle Muschelkalk are prone to karstification. Sinkholes are a frequent indicator of the subsurface dissolution and erosion (subrosion). Some of these collapse-sink elements facilitated the rise of pressurized groundwaters of the confined aquifers and formed famous springs. The major and investigated aquifers of the area are developed in the bedrock as fissure to and karstic-fissured aquifers.
Soil types found are rendzinas, brown rendzinas, and cambisols with the lime- and marlstones as parent material; fluvisols and gleysols along the rivers; and luvisols, with cambic and stagnic properties as well as stagnosols in the loess-covered planes.