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Sulfuric acid caves are widespread worldwide. In Central Italy, the Fiume-Vento karstic complex represents the most important active hypogenic cave system hosting several interconnected lakes where groundwater moves towards sulfidic springs emerging along the Sentino Stream. Stratification and dilution phenomena between freshwater and sulfidic water occur in many underground lakes, even if they remain still open if these processes are driven by stream-aquifer interaction or dripping water. The speleological knowledge coupled with geochemical surveys can help study groundwater circulation in the karst system’s inner and outer portions. The geochemical analyses on water samples taken along the Sentino Stream, inside the caves (dripping and lakes water) and in sulfidic springs allow establishing the origin of the dilution water in the dripping water. However, stream-aquifer interactions cannot be excluded during flood events. Using the tracer masse balance method (chloride and sodium ions), the discharge of the sulfidic springs ranges between 65 and 11 L/s. The results presented in this study may help understand groundwater circulation and dilution phenomena in other karst systems characterised by sulfuric acid speleogenesis type.

Microbial lipids in stalagmites are increasingly used to reconstruct the paleoclimate change, necessitating the investigations on microbial communities in dripping waters. A pilot molecular survey was conducted on bacterial communities of dripping waters at two sites (1D and 3D) in Heshang Cave of Hubei Province in central China for a period of 2008 to 2013. The samples were subjected to genome DNA extraction, 16S rRNA gene amplification, clone library construction and phylogenetic analysis to explore the seasonal variation of bacterial communities and their association with environmental factors including regional air temperature, precipitation, cave temperature, pH, conductivity and dripping rate of the water samples. Seasonal variations were clearly observed in components and diversities of bacterial communities at both sites. Bacterial community was dominated by Gammaproteobacteria in autumn and winter, whereas Betaproteobacteria became dominant in samples collected in summer and spring. Among the environmental factors investigated, regional air temperature was found to have a strong impact on bacterial communities indicated by cluster and redundancy analysis. Moreover the bacterial biodiversity was observed to increase with the temperature rising. Bacteria identified in dripping water were either oligotrophs or able to acquire nutrients from minerals under oligotrophic conditions. They may also be able to induce calcite precipitation in cave systems. Our data shed light on the potential of microbes used as a tool for the reconstruction of paleo-temperature as well as on the ecological functions of bacterial communities in oligotrophic caves. [ABSTRACT FROM AUTHOR]

The peregrine earthworm Dendrodrilus rubidus tenuis was regularly sampled in a percolating water drip originating in a habitat inaccessible to humans in the Huda luknja pri Doliču cave, Slovenia. The reconstruction of this habitat includes both a larger passage with bat colonies supplying wet bat guano sediments, on which the earthworms feed, and narrow channels, which drain water from this passage into the sampling drip. Fresh guano is deposited in autumn shortly before the earthworms become inactive. Then, it is exploited by moulds and additionally depleted by water washing out the nutrients before the earthworms reactivate in spring. Thus, this is a rather poor food resource for the earthworms. Despite this, and apart from their short size and delayed maturation, no other disturbance or damage was found caused by malnutrition, which was confirmed in individuals submitted to starvation in captivity. We suggest that Dd. r. tenuis, which shows neither disturbance from nor adaptation to living in a subterranean environment, can subsist there because of its euryoecious character. Nevertheless, in temperate climates, this is rather a harsh habitat for this earthworm. [ABSTRACT FROM AUTHOR]