Farmed calcite δ13C at Ascunsă Cave, Romania, and its relation with CO2 outgassing and drip rate

When calcite precipitates in caves, its carbon stable isotope signature can be modified by the CO2 outgassing gradient between drip water and cave atmosphere. This effect is modulated by water residence time in the cave, from its emergence in the cave until the deposition of calcite. Moreover, CO2 solubility, calcite precipitation rate, and isotopic fractionation are controlled by temperature. Here, we present up to date results of an ongoing monitoring study at Ascunsă Cave (Romania), exploring the relationship between farmed calcite δ13C, drip rate, and CO2 outgassing. In addition to measuring CO2 concentration in cave air, we also measured the CO2 concentration in the headspace of a water-air equilibrator that collects drip water without exposing it to cave atmosphere, preventing outgassing. δ13C from calcite farmed at two neighboring stalagmites with different drip rates was also measured. Although caves have generally stable temperatures, we show here that temperature inside Ascunsă and Isverna caves has risen by more than 2°C over the course of a year, bearing important implications for stable isotopic fractionation equations and CO2 dynamics. Our results show that δ13C of farmed calcite has a strong relationship with drip rate at the slow dripping site, but no correlation at the faster dripping site. These two sites are also different when δ13C is compared to the outgassing gradient. At the slower drip site, δ13C and the outgassing gradient are directly correlated, whereas at the faster drip site their correlation is inverse. Our study brings new light onto speleothem δ13C behavior in general, and at Ascunsă Cave in particular, which is crucial for understanding the paleoclimate information captured by speleothems from this cave or elsewhere

Farmed calcite δ13C at Ascunsă cave, Romania, and its relation with CO2 outgassing and drip rate

When calcite precipitates in caves, its carbon stable isotope signature can be modified by the CO2 outgassing gradient between drip water and cave atmosphere. This effect is modulated by the water residence time in the cave, from its emergence in the cave until the deposition of calcite. Moreover, CO2 solubility, calcite precipitation rate, and isotopic fractionation are controlled by temperature. Here, we present up to date results of an ongoing monitoring study at Ascunsă Cave (Romania), exploring the relationship between farmed calcite δ13C, drip rate, and CO2 outgassing. In addition to measuring CO2 concentration in cave air, we also measured the CO2 concentration in the headspace of a water-air equilibrator that collects drip water without exposing it to cave atmosphere, preventing outgassing. δ13C from calcite farmed at two neighboring stalagmites with different drip rates was also measured. Although caves have generally stable temperatures, we show here that temperature inside Ascunsă and Isverna caves has risen by more than 2°C over the course of a year, bearing important implications for stable isotopic fractionation equations and CO2 dynamics. Our results show that δ13C of farmed calcite has a strong relationship with drip rate at the slow dripping site, but no correlation at the faster dripping site. These two sites are also different when δ13C is compared to the outgassing gradient. At the slower drip site, δ13C and the outgassing gradient are directly correlated, whereas at the faster drip site their correlation is inverse. Our study brings new light onto speleothem δ13C behavior in general, and at Ascunsă Cave in particular, which is crucial for understanding the paleoclimate information captured by speleothems from this cave or elsewhere.Lorsque la calcite précipite dans les grottes, la signature isotopique en carbone peut être modifiée par le gradient de dégazage du CO2 entre l’eau de ruissellement et l’atmosphère de la grotte. Cet effet est modulé par le temps de séjour de l’eau dans la grotte, depuis son émergence dans la grotte jusqu’au dépôt de la calcite. De plus, la solubilité du CO2, le taux de précipitation de la calcite et le fractionnement isotopique sont contrôlés par la température. Dans cette étude, nous présentons des résultats actualisés d’une étude de suivi en cours dans la grotte d’Ascunsă (Roumanie), qui explore la relation entre les valeurs de δ13C de calcite déposée, le taux d’écoulement goutte-à-goutte et le dégazage du CO2. En plus de la mesure de la concentration de CO2 de l’air de la grotte, nous avons également mesuré la concentration de CO2 dans la partie supérieure d’un équilibreur eau-air qui collecte les gouttes d’eau sans les exposer à l’atmosphère de la grotte, empêchant ainsi le dégazage. Les valeurs modernes de δ13C de la calcite dans deux stalagmites voisines avec des débits d’écoulement goutte-à-goutte différents ont également été mesurées. Bien que les grottes aient des températures généralement stables, nous montrons ici que la température à l’intérieur des grottes d’Ascunsă et d’Isverna a augmenté de plus de 2°C en un an, ce qui a des implications importantes pour les équations de fractionnement d’isotopes stables et sur la dynamique du CO2. Nos résultats montrent que les valeurs de δ13C de la calcite et du taux d’écoulement goutte-à-goutte ne sont corrélées que dans le site ayant un débit goutte-à-goutte faible. Ces deux sites diffèrent également lorsque l’on compare les valeurs de δ13C avec le gradient de dégazage. À débit d’écoulement goutte-à-goutte lent, les valeurs de δ13C et le gradient de dégazage sont directement corrélés, alors que lorsqu’il est rapide, ces deux valeurs sont anti-corrélées. Notre étude apporte donc un nouvel éclairage sur le comportement des valeurs de δ13C des spéléothèmes en général, et dans les grottes d’Ascunsă en particulier, ce qui est crucial afin de comprendre les informations paléoclimatiques enregistrées par les spéléothèmes de ces grottes et d’autres

Metal Contents and Pollution Indices Assessment of Surface Water, Soil, and Sediment from the Arieș River Basin Mining Area, Romania

The current study was conducted to assess the level and spatial distribution of metal pollution in surface water, soil, and sediment samples from the Arieș River basin, located in central Romania, an area impacted by various mining and industrial operations. Several pollution indices, spatial distributions, cluster analyses, principal component analyses, and heat maps were applied for evaluating the contamination level with Ni, Cu, Zn, Cd, Pb, Mn, As, and Hg in the area. Based on the results of the Heavy-Metal Pollution Index and of the Heavy-Metal Evaluation Index of the surface-water samples, the middle part of the Arieș River basin, near and downstream of the gold mine impoundment, was characterized by high pollution levels. The metal concentration was higher near the tailing impoundment, with increased levels of Cu, Ni, Zn, and Pb in the soil samples and As, Cd, Pb, Na, K, Ca, Mn, and Al in the sediment samples. Ca (23.7–219 mg/L), Mg (2.55–18.30 mg/L), K (0.64–14.70 mg/L), Al (0.06–22.80 mg/L), and Mn (0.03–22.40 mg/L) had the most remarkable spatial variation among the surface-water samples, while various metal contents fluctuated strongly among the sampling locations. Al varied from 743 to 19.8 mg/kg, Fe from 529 to 11.4 mg/kg, Ca from 2316 to 11.8 mg/kg, and Mg from 967 to 2547 mg/kg in the soil samples, and Al varied from 3106 to 8022 mg/kg, Fe from 314 to 5982 mg/kg, Ca from 1367 to 8308 mg/kg, and Mg from 412 to 1913 mg/kg in the sediment samples. The Potential Ecological Risk Index values for soil and sediments were in the orders Cu > Ni > Pb > Hg > Cr > As > Mn > Zn > Cd and As > Cu > Cr > Cd > Pb > Ni > Hg > Mn > Zn, respectively, and the highest values were found around the gold mine impoundment

Metal Contents and Pollution Indices Assessment of Surface Water, Soil, and Sediment from the Arieș River Basin Mining Area, Romania

The current study was conducted to assess the level and spatial distribution of metal pollution in surface water, soil, and sediment samples from the Arieș River basin, located in central Romania, an area impacted by various mining and industrial operations. Several pollution indices, spatial distributions, cluster analyses, principal component analyses, and heat maps were applied for evaluating the contamination level with Ni, Cu, Zn, Cd, Pb, Mn, As, and Hg in the area. Based on the results of the Heavy-Metal Pollution Index and of the Heavy-Metal Evaluation Index of the surface-water samples, the middle part of the Arieș River basin, near and downstream of the gold mine impoundment, was characterized by high pollution levels. The metal concentration was higher near the tailing impoundment, with increased levels of Cu, Ni, Zn, and Pb in the soil samples and As, Cd, Pb, Na, K, Ca, Mn, and Al in the sediment samples. Ca (23.7–219 mg/L), Mg (2.55–18.30 mg/L), K (0.64–14.70 mg/L), Al (0.06–22.80 mg/L), and Mn (0.03–22.40 mg/L) had the most remarkable spatial variation among the surface-water samples, while various metal contents fluctuated strongly among the sampling locations. Al varied from 743 to 19.8 mg/kg, Fe from 529 to 11.4 mg/kg, Ca from 2316 to 11.8 mg/kg, and Mg from 967 to 2547 mg/kg in the soil samples, and Al varied from 3106 to 8022 mg/kg, Fe from 314 to 5982 mg/kg, Ca from 1367 to 8308 mg/kg, and Mg from 412 to 1913 mg/kg in the sediment samples. The Potential Ecological Risk Index values for soil and sediments were in the orders Cu > Ni > Pb > Hg > Cr > As > Mn > Zn > Cd and As > Cu > Cr > Cd > Pb > Ni > Hg > Mn > Zn, respectively, and the highest values were found around the gold mine impoundment

Potential Environmental Drivers of Fossil Bones Degradation—A Metabarcoding Approach in Two Carpathian Caves

Studies on fossil bone microbial communities are scarce; even fewer studies were performed in cave deposits. For our research, sediments and fossil bones were sampled, and the whole community 16S rRNA gene-based metabarcoding analyses were performed on samples from Muierilor and Ursilor caves, some of Romania’s most important archaeological and paleontological sites. Most of the identified taxa belong to Bacteria, with Proteobacteria, Acidobacteriota, Bacteroidota, and Actinobacteriota amongst the most abundant phyla in bone samples from both caves. The sediment samples presented similar composition, with Proteobacteria and Acidobacteriota being the most abundant phyla. The inferred bacteriomes indicated the presence of environment-specific bacteria, typical bone colonizers, and bacteria found in soils and decomposing human remains or archaeological profiles as well as phosphate-solubilizing and organotrophic bacteria. Diversity indices indicated a higher diversity in bone samples from Muierilor Cave than in Ursilor Cave samples and sediment samples from both caves. Environmental conditions, especially air relative humidity, were also considered in explaining the bacteriome diversity in different cave settings. These findings help to understand fossil bones’ deposition and degradation in various environmental conditions. Furthermore, this is the first attempt to relate microenvironments and bacteria to preserving fossil bones from caves.</p

Monitoring Human Impact in Show Caves. A Study of Four Romanian Caves

(1) Background: Show caves are unique natural attractions and touristic traffic can trigger their degradation within a short time. There are no universal solutions to counter the effects of the touristic impact upon the cave environment and both protection protocols and management plans have to be established on a case-by-case basis. (2) Methods: The study includes four show caves from the Romanian Carpathians, where monitoring of the number of visitors, paralleled by the monitoring of the main physicochemical parameters of the air and water (CO2, temperature, humidity, drip rate, conductivity, and pH) was implemented. (3) Results and Conclusions: The results of the study have: established a set of basic principles to be enforced by the management of show caves and issued a set of preventive measures and instructions to be followed by the personnel and stakeholders of the caves

Testing Different Membrane Filters for 16S rRNA Gene-Based Metabarcoding in Karstic Springs

Introduction: Karstic springs are used worldwide by rural communities as sources of fresh water for humans and livestock. In Romania, one-third of the population has no direct access to a public water supply. The present study is part of a country-wide project to develop simple, quick and cheap methods for seasonal environmental and microbiological monitoring of karstic springs used as drinking water by rural populations. Critical steps for monitoring workflow consist of evaluating water quality and selecting suitable membrane filters to efficiently capture environmental DNA for further microbial diversity estimation using 16S rRNA gene-based metabarcoding. Methods: Several commercial membrane filters of different compositions and pore sizes were tested on the water sampled from three karstic springs in Romania, followed by water chemistry and whole community 16S rRNA gene-based metabarcoding analysis. Results: We found that different types of applied membrane filters provide varying recovery in diversity and abundance of both overall and pathogenic bacteria. Conclusions: The result of the experiment with different filters shows that mixed cellulose ester, cellulose acetate, and nitrate membranes of 0.20 and 0.22 &micro;m are the best for amplicon-based metabarcoding monitoring of karst springs

Last deglaciation flooding events in the Southern Carpathians as revealed by the study of cave deposits from Muierilor Cave, Romania

Caves often hold valuable palaeoclimate archives including speleothems, fossil remains, and clastic sediments that complement each other. This paper presents a multi-archive interdisciplinary study of an extensive deposit of fossil mammals from the scientific reserve in the Muierilor Cave, Southern Carpathians, Romania. We present two new palaeontological excavations that indicate a high abundance and diversity of MIS 3–2 fossil mammals (carnivores, omnivores and herbivores) synchronous with the early modern humans known from this cave. Using geochronological and sedimentological methods, we present a general reconstruction of the cave evolution between ~120 kyr B.P. and the Holocene. The study is based on a combination of geochronological tools including OSL dating of sediments, U/Th dating of speleothems, and radiocarbon dating of fossil remains, with a total of 54 ages. Based on U/Th dating of speleothems from stratigraphically-relevant positions, we show that the MIS 3 assemblage of fossil mammals were massively reworked and deposited during the post-LGM deglaciation, slightly earlier than previously known for the Southern Carpathians. On the other hand, several young radiocarbon ages of cave bear samples suggest that the Southern Carpathians might have been functioning as a glacial refuge for this species as late as ~22 kyr B.P. •High diversity of MIS 3–2 fauna was recorded in two excavations in Muierilor Cave.•We documented one of the last cave bear population in Eurasia.•Geochronological methods helped to determine key-stages during the last 120 kyr.•The fossil assemblage has been most probably reworked during the last deglaciation.•The deglaciation took place ~2 kyr earlier than for the northern slopes of the region