Biotic agents of tufa formation in сarbon dioxide enriched hard-water springs of Mizhhirya basin and adjacent territories

The main groups of biote and their functional role in the calcareous tufa formation at the hard-water springs enriched by carbon dioxide of the Mizhhirya basin and adjacent territories were investigated. It has been studied that in the formation of calcareous tufa of all surveyed locations, representatives of micro-, bryo and phytobiota play an important role, and therefore, the studied sedimentary rock are mainly biogenic in their origin. Microbiota agents, mainly cyanobacteria of the order Oscillatoriales, play a leading role in the initial acts of calcareous tufa accumulation (stage I). These bacteriogenic initial forms, which can be defined as initial thromboids, are represented by small- or medium-grained, ocher-yellow aggregates of a spherical shape, with a diameter of 0.5-2 mm, which actively accumulate at the springs exits. These congestions (mesoclots) are growing and compacting over time and forming weakly cemented thrombolites, which are a cluster of separate aggregates together with particles of sand, silt, rocks, plant remains, etc. The next post-pioneer stage (II) is marked by the appearance of specialized amphibious Bryophytes vegetation of the Pellion endiviifoliae alliance and pioneer caliciophilic vegetation of the Grimmaldion fragrantis alliance. In the formation of calcareous tufa deposits of the next stage (III), the leading role is played by the Bryophytes vegetation of the Pellion endiviifoliae alliance. Their mineralized turfs are modeling light, fragile and porous bryolithes of an ocher-brown color. Bryolithes usually contain seasonal layers richly encrusted with leaves of trees, which growing near the spring. Base on the specificity and ecological value of the biotic (calcicolous Bryobiota) and abiotic, primarily geological (calcareous iron tufa) component, the hard-water tufagenic springs of Mizhhirya Verkhovyna can be considered significant natural monuments of Transcarpathia region. However, regardless of the nature protection status of most hard-water iron springs (they are hydrological monuments of nature of local importance), they often suffer from human’s improvement, illegal water extraction, high recreational load etc. Thus, they need applicating of conservation measures and nature protection management planning.