Recent Atmospheric Deposition and its Effects on Sandstone Cliffs in Bohemian Switzerland National Park, Czech Republic

Abstract

The protected area "Bohemian Switzerland National Park" with its characteristic sandstone landscape was influenced by the long-term air pollution and acidic deposition within the area known as Black Triangle (located where Germany, Poland, and the Czech Republic meet, is one of the Europe's most polluted areas). The local Upper Cretaceous sandstone is subhorizontally stratified, fine-to coarse-grained, quartz dominated, with low content of clay minerals. One of the significant negative effects of the intensive acidic deposition on sandstone outcrops has been identified as chemical (salt) weathering, i.e., a process when the porous sandstone rock is except of chemical influence attacked also by force of crystallization of growing salts crystals. Anions NO 3 − together with SO 4 2− and cation NH 4 + were the most abundant solutes in bulk precipitation samples. Current (2002 to 2009) bulk deposition fluxes of SO 4 2− determined at three sites directly in the National Park indicate decline from 23 to 16 kg −1 ha −1 year −1 . Infiltration of bulk precipitation solutes into the sandstone mediates the weathering processes. Natural outflow of sandstone pore-water (sandstone percolates) can be sampled only during certain days of year when the sandstone becomes saturated with water and percolates drip out on small number of sites from roofs of overhangs. Under usual conditions percolation water evaporates at the sandstone surface producing salt efflorescences-the typical example is Pravčická brána Arch locality. The average pH of the dripping sandstone percolates was 3.76. Concentration of SO 4 2− and Al in sandstone percolates reached up to 46 and 10 mg L −1 . The concentration of Al in percolates has been 160-fold greater the one in the precipitation samples suggesting the sandstone as a source. The water O and H isotopic composition of percolates has been virtually identical to precipitation samples, indicating thus relatively short residence time of the solutions within the sandstone pore-spaces. Evaporation experiments with bulk precipitation and percolate samples proved possible origin of some Ca in bulk precipitation and the sandstone rock as the source of Al and possibly of K for the salt efflorescence identified on Rock Arch body.

Comparison of the city maps’ content of western, eastern and central European cities

“…The local hydrodynamic regime (rapid changes in rock massif saturation with percolate solutions, infiltration and accumulation areas), which is of crucial importance to the correct assessment of the intensity and distribution of salt efflorescence and the associated processes of the chemical weathering of the rock body (Zvelebil et al 2002;Vařilová et al 2011aVařilová et al , 2011b, was identified by using the non-standard method of DEMP. Commonly used methods to identify moisture distribution, like resistivity tomography profiling (ERT) (e.g.…”

“…Here the sandstone percolates sub-vertically infiltrates along several secondary inhomogeneities into the interior of the rock massif. Distribution of moisture within the PBRA is generally influenced by the existence of sub-vertical fissures and micro fissures that serve as preferential pathways of gravitational infiltration of rainfall and melting water under a gradual weakening of the surroundings (Young et al 2009;Vařilová et al 2011a).…”

“…Reaching a height of 16 m and length of 26.5 m, the formation represents a mature form of sandstone arches and a natural monument of European significance (Vařilová and Belisová 2010). Due to its geometry and exposure it is currently threatened not only by the stress posed by its own weight but also by extreme microclimatic factors, which act not only in the form of dynamic effects of volumetric changes but also as a driving force of physical and chemical weathering (see Vařilová et al 2011aVařilová et al , 2011bNavrátil et al 2013). The geological and tectonic patterns of the rock body together with the effects of the microclimate are fully manifested in a gradual degradation of the sandstone material and a deterioration of physico-mechanical parameters of the rock.…”

Present Climate Change as a Threat to Geoheritage: The Wildfire in Bohemian Switzerland National Park and Its Use in Place-Based Learning

“…The cement holding the rock together consists of iron oxyhydroxide and clay minerals, primarily kaolinite. Typically, the rock's surface is covered by a newly formed amorphous SiO2 crust resulting from secondary silicification [10,[21][22][23][24]. The natural processes of bedrock erosion and accumulation of sediments as a continuation of the geological development are still active in the BSNP.…”

“…Frequent extreme weather brings natural disasters such as droughts and wildfires. We anchor our text in articles about the past decade's drought and fires in Czechia [14][15][16]20] and texts characterizing the BSNP and regional geology [9,10,[21][22][23][24]. Several articles described geological (geographical) fieldwork and its specifics [25,26] and teaching about climate change [27][28][29].…”