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When underground flows in a karst region are derived not only from autogenic, but also from allogenic recharge, natural chemical tracers can be used for distinguishing between these two contributing inputs. And since allogenic recharge prevalently originates in weathering of silicate rocks, the most appropriate natural tracers are those which are more abundant in such formations than in carbonate ones. Moreover, the tracers must not interact with the limestone or dolomite rocks hosting the underground flow-paths. The karst setting addressed by the present study includes a sinking stream, a cave intercepting the sunken streamflow, and three karst springs, two perennial, and one temporary. The objective of the present study was to assess, for the concerned setting, the capability of four natural tracers, SiO2, Ba, Rb and U, of tracking the specific contributions of allogenic and autogenic inputs along underground karst flow-paths. Those chemical constituents were noticed to comply with the specified requirements for natural tracers, as their maximum concentrations were recorded in the swallet flow, and gradually declined toward the cave stream, then further to the temporary spring. The latter was thus proven to act as an overflow of a currently inaccessible underground course, which is supplied by the cave stream, but whose final outlet is not yet identified. Alternatively, the perennial springs resulted to be proxies of two chemically distinct autogenic inputs: one supplementing the groundwater flow between the swallet and the cave stream, and the other contributing to the flow between the cave stream and the temporary karst spring. It is worth mentioning that so far, the four indicated natural chemical tracers have been only sporadically utilized in karst aquifers with allogenic recharge.

Endemic and rare species as bioindicators of habitat vulnerability were used to develop protection and management plans for biotope prioritization (mainly islands habitats, lava tubes or groundwaters). Due to their narrow distribution, the endemic species (species confined to a restricted geographic area) are more susceptible to ecological disequilibrium and habitat loss than the widespread ones. Consequently, endemics become endangered in the context of ecological disturbance caused by anthropogenic pressure, making them suitable candidates to assess environmental preservation needs. Taking into consideration that most of the stygobitic and troglobitic species are endemic and confined to specific karst areas, based on their association and frequency we propose an endemicity index (EI) adapted to the fragmented nature of the cave habitat. We used a double ranking methodology: (1) ranking the endemic species according to their frequencies in caves, and (2) ranking the caves according to their EI computed for a geographic area. Further, by mapping the caves based on their related EI, we identified the hotspots of vulnerable karst areas. The EI has been developed using as case study of 380 caves from Romania, known up to now to be inhabited by a total of 278 endemic stygobitic and troglobitic species and subspecies. In our study area, 35 out of 380 caves with endemic species, narrowly distributed to karst areas of the Carpathian massifs and Dobrogea, had a considerable high EI. The EI proves to be highly sensitive to unique taxa (endemics recorded in only one cave) and also to other endemic taxa - recorded in more than one cave. However, all the endemites are confined to a specific geographic area (in this case of study - the Carpathians and Dobrogea karst area). EI provides a reliable criterion to rank caves using the contribution of endemic species in order to assess cave and karst vulnerability and prioritize them for environment protection management.

The authors provide the centralized data about the Romanian caves with endemic fauna, based on all reliable bibliographic sources (as quoted in text and cited in the chapter references) and based on their research activity. The complete list of the Romanian caves with endemic cave-dwelling arthropod species identified up to the subspecies level is presented.

Spatial distribution analyses of fossil bones are often used in cave taphonomy for i) assessing directly the size of a given fossil population and ii) indirectly, for palaeo-environmental reconstructions. Urşilor Cave from northwestern Romania hosts one of the richest MIS 3 cave bear bone assemblages of Europe, and as the nature of the bone deposition was not settled yet, the study of the size of cave bear population and the distribution of the skeletal element was needed

The authors provide a list of 213 caves and of the species of Oniscidea known to inhabit them, presenting their altitudinal distribution across major physical-geographic units of Romania

The karst geosystems functioning frequently implies very quick mass and energy transfers, which make them highly sensitive to any natural or anthropogenic disturbance. Therefore, the groundwater resources, threatened by agricultural and industrial pollution, should be carefully exploited, taking into account the intrinsic vulnerability of the region

The Mehedinţi Plateau represents an area highly marked by the intensity of the karst processes and by the diversity of the exokarst and endokarst features. The analyzed area includes two parallel limestone bars, developed on the Carpathian structures direction (NNE-SSW). In addition to the results obtained following the EPIK method protocol, we bring forward data concerning the water quality, performing hydrogeochemical analyses on water samples collected from the main sources in the region

A major socio-economic and scientific issue is represented by karst hydrostructures vulnerability mapping, which qualitatively and quantitatively highlights their exposure degree. Two research trends have been developed, one taking into account the environment features exclusively – the aquifer and protective cover type, permeability, aquifer depth, recharge rate, etc. (intrinsic vulnerability), the other focused on the types and quantities of pollutants (specific vulnerability)