Drip Water Research Articles

Transfer of environmental signals from the surface to the underground at Ascunsă Cave, Romania

Abstract. We present here the results of a 4-year environmental monitoring program at Ascunsă Cave (southwestern Romania) designed to help us understand how climate information is transferred through the karst system and archived by speleothems. The air temperature inside the cave is around 7 °C, with slight differences between the upper and lower parts of the main passage. CO2 concentrations in cave air have a seasonal signal, with summer minima and winter maxima. These might indicate the existence of an organic matter reservoir deep within the epikarst that continues to decompose over the winter, and CO2 concentrations are possibly modulated by seasonal differences in cave ventilation. The maximum values of CO2 show a rise after the summer of 2014, from around 2000 to about 3500 ppm, following a rise in surface temperature. Using two newly designed types of water–air equilibrators, we were able to determine the concentration of CO2 dissolved in drip water by measuring its concentration in the equilibrator headspace and then using Henry's law to calculate its concentration in water. This method opens the possibility of continuous data logging using infrared technology, without the need for costly and less reliable chemical determinations. The local meteoric water line (δ2H = 7.7 δ18O + 10.1), constructed using monthly aggregated rainfall samples, is similar to the global one, revealing the Atlantic as the strongly dominant vapor source. The deuterium excess values, as high as 17 ‰, indicate that precipitation has an important evaporative component, possibly given by moisture recycling over the European continent. The variability of stable isotopes in drip water is similar at all points inside the cave, suggesting that the monitored drip sites are draining a homogenous reservoir. Drip rates, as well as stable isotopes, indicate that the transfer time of water from the surface is on the order of a few days.

Analysis of Temporal and Spatial Variations in Trace Element Migration in Karst Critical Zone:An Example of Jiguan Cave, Henan

To explore the temporal and spatial variations and the process of trace element migration in the karst critical zone, continuous fixed-point monitoring and sampling analysis was applied to measure each cave system component, which includes rainfall, soils, bedrock, drip waters, and their aerial sediment. Approximately 650 experimental data were obtained from October 2009 to May 2015 in a typical karst critical zone in north China-an interactive zone of the Jiguan Cave in the west Henan Province. The variations in and the migration rules of Ca, Mg, Ba, Sr, and δ13C as well as their ratios to different components were studied. The results show that:① Soil and bedrock are the main sources of drip water. The values of Mg, Ba, and Sr are consistent with the "soil-bedrock" two end-members model and their respective proportions are 43.6:56.4, 1.01:98.09, and 47.2:52.8. ② From the spatial perspective, element migration of each component in the cave system interactive zone is interrelated. Drip water inherits the signals of the soil and bedrock and the modern sediment can continue the element information of the drip water. Elements in the soil profile cause the leaching and deposition effect and the subsoil better inherits the information of trace elements in the bedrock. ③ From the temporal perspective, the migration of elements in the cave system interactive zone is complex. Because of the leaching effect, soil and drip water show obvious seasonal discrepancies. However, under the influence of karst water migration path, the prior calcite precipitation (PCP), and extreme arid and annual precipitation type, the seasonal discrepancy in the element concentrations in drip water is smaller than in soil. The PCP effect, selective leaching, and other factors change the continuity of elements released from sediment to drip water. ④ In order to systematically and comprehensively ascertain the trace element migration in the karst critical zone and energy transformation rules, the study of cave system should be based on the research of the cave's critical zone and should consider comprehensive information ranging from the atmospheric origins to secondary sediments.

Influx and concentration of triazine pesticides in the Amaterska cave system, Moravian Karst, Czech Republic

The aim of this study was to detect three triazine pesticides and their metabolites in the drip water and the sediment of the Amaterska cave system. Diversity of the bacterial community in the sediment was also assessed, and the potential role of bacteria in degradation of these pesticides was evaluated. Triazines and their metabolites were analyzed in the soil, drip water, and sediment of the Amaterska cave system area in seven sampling sites (S1–S7) based on the above ground cover that included forest, permanent grassland, and agriculture cropland. The bacterial community in the cave sediments (S1–S6) was also analyzed using the Illumina sequencing of the V3 and V4 regions of 16S rDNA. Triazines were present in the soil and drip water in all sites below grassland and agricultural land but not under the forest area. Only atrazine metabolites were detected in the surface soil. In contrast, atrazine was detected in all cave sediments regardless of above ground cover, and this is likely due to the occasional alluvial influx. The overall prevalence of bacteria potentially capable of atrazine degradation in the cave sediment ranged from 13.4 to 64.0% of the entire bacterial community. The concentrations of atrazine in the cave sediment were 16 to 70 times higher than in those in drip water. High concentrations of atrazine in the cave sediment indicate a slow degradation rate of triazines in the cave likely due to low temperatures and absence of photolysis. The main source of atrazine in the Amaterska cave system is likely not drip water but the alluvial influx. Bacteria potentially capable of triazine degradation in the cave sediment were detected; however, their role in this process remains to be investigated.

Seasonal cave air ventilation controlling variation in cave air PCO2 and drip water geochemistry at Inazumi Cave, Oita, northeastern Kyushu, Japan

Seasonal cave air ventilation controlling variation in cave air PCO2 and drip water geochemistry at Inazumi Cave, Oita, northeastern Kyushu, Japan

Constraining the subsoil carbon source to cave-air CO2 and speleothem calcite in central Texas

Canonical models for speleothem formation and the subsurface carbon cycle invoke soil respiration as the dominant carbon source. However, evidence from some karst regions suggests that belowground CO2 originates from a deeper, older source. We therefore investigated the carbon sources to central Texas caves. Drip-water chemistry of two caves in central Texas implies equilibration with calcite at CO2 concentrations (PCO2_sat) higher than the maximum CO2 concentrations observed in overlying soils. This observation suggests that CO2 is added to waters after they percolate through the soils, which requires a subsoil carbon source. We directly evaluate the carbon isotope composition of the subsoil carbon source using δ13C measurements on cave-air CO2, which we independently demonstrate has little to no contribution from host rock carbon. We do so using the oxidative ratio, OR, defined as the number of moles of O2 consumed per mole of CO2 produced during respiration. However, additional belowground processes that affect O2 and CO2 concentrations, such as gas-water exchange and/or diffusion, may also influence the measured oxidative ratio, yielding an apparent OR (ORapparent). Cave air in Natural Bridge South Cavern has ORapparent values (1.09±0.06) indistinguishable from those expected for respiration alone (1.08±0.06). Pore space gases from soils above the cave have lower values (ORapparent=0.67±0.05) consistent with respiration and gas transport by diffusion. The simplest explanation for these observations is that cave air in NB South is influenced by respiration in open-system bedrock fractures such that neither diffusion nor exchange with water influence the composition of the cave air. The radiocarbon activities of NB South cave-air CO2 suggest the subsoil carbon source is hundreds of years old. The calculated δ13C values of the subsoil carbon source are consistent with tree-sourced carbon (perhaps decomposing root matter), the δ13C values of which have shifted during industrialization due to changes in the δ13C values and concentrations of atmospheric CO2. Seasonal variations in PCO2_sat in most of the drip waters suggest that these waters exchange with ventilated bedrock fractures in the epikarst, implying that the subsoil CO2 source contributes carbon to speleothems.

Monitoring of selected caves as a prerequisite for the speleothem-based reconstruction of the Quaternary environment in Croatia

Quaternary palaeo-environmental changes that have taken place in Croatia are likely to be recorded in speleothems – secondary carbonate deposits precipitated in caves. Confident interpretation of well dated speleothem proxy records relies on modern monitoring programs, which we provided in three regionally different caves. Parallel monitoring of the surface and cave air temperature and relative humidity, precipitation and cave drip intensity, as well as stable isotope modification of meteoric and drip water was carried out in order to estimate the most reliable stalagmites for the interpretation of Quaternary landscape history. In all three caves, Nova Grgosova (239 m a.s.l.; Tcave = 11.2 °C) in central Croatia, Lokvarka (780 m a.s.l.; Tcave = 7.5 °C) in the mountainous part of Croatia, and Modrič (32 m a.s.l.; Tcave = 16.6 °C) in coastal Croatia, we selected the parts of the caves where the ambient cave conditions appeared to be appropriate for equilibrium deposition of calcite in terms of constant air temperature (seasonal amplitudes of 0.73, 0.38 and 0.45 °C, respectively) and relative humidity (100%). Both Atlantic and Mediterranean moisture influences were detected in all three caves, but of different intensities. Cave hydrological settings governed by karst aquifer properties were resolved by the comparison of the precipitation intensities and drip site responses to the rain events, and generally, seasonal rainwater isotopic signal was almost completely attenuated, except for one drip site. Such homogenized drip water and stable cave environmental settings give confidence for calcite deposition under equilibrium conditions, especially for Modrič and Nova Grgosova caves where speleothems' inner structures also look promising for potentially quality dating results and stable isotopic profiles. The fracture-flow drip regime of selected drip sites in Lokvarka Cave, and uncompleted homogenization of the water in the epikarst might point to speleothem samples that are unsuitable for resolving multi-annual Quaternary climate changes. This view is supported by the high porosity internal structure of some Lokvarka speleothems, so further monitoring, sampling and the thorough speleothem examination is therefore necessary for adequate interpretations of palaeo-environmental changes.

THE QUALITY AND TOTAL MICROBES OF BROILER CHICKEN IN TRADITIONAL MARKETS OF DENPASAR CITY

The purpose of this study was to determine the quality and total microbes of broiler at different location in the traditional markets of Denpasar City. This study used a completely randomized design (CRD) with four treatments. The treatments used in this study, broiler chicken sold at traditional markets in East (DT), North (DU), West (DB), and South of Denpasar (DS). The data obtained from this study were analyzed by analysis of variance. If there were significant differences (P <0,05) among the treatments, then continued with Duncan's multiple range test. The variables used in this study were carcass weight, cooking loss, drip loss, water holding capacity, water content, protein, fat, ash, and total microbes. The results showed that on the average, the highest carcass weight in DB treatment was 1.482 grams, with other treatments to get results not significantly different (P>0,05). The result of this study for variable drip loss, water content, protein, fat, and ash significantly different (P<0,05), then research result for cooking loss, and water holding capacity, were not significantly different (P>0,05). The research result for total microbies broiler chicken at traditional markets in Denpasar City have a range of 1,84 x 104 to 2,62 x 104 CFU /gram. The results were still normal when compared to SNI 7388: 2009 which states that the maximum amount that the content of TPC 1x106 CFU/gram. From these results, it was concluded that there were similarities quality of broiler chicken (carcass weight, cooking loss, water holding capacity, and total microbes), however, there were differences in the quality of broiler seen from drip loss, water content, protein, fat, and ash of broiler at traditional markets in Denpasar City.

Recently forming stalagmites from the Baradla Cave and their suitability assessment for climate–proxy relationships

Determination of the long-term behavior of cave systems and their response to changing environmental conditions is essential for further paleoclimate analyses of cave-hosted carbonate deposits. For this purpose, four actively forming stalagmites were collected in the Baradla Cave where a three-year monitoring campaign was also conducted. Based on textural characteristics and radiocarbon analyses, the stalagmites are composed of annual laminae, whose counting was used to establish age–depth relationships. Fast and slowly growing stalagmites have different stable carbon and oxygen isotope compositions as well as trace element contents that could be attributed to differences in drip water migration pathways. The stable isotope compositions were compared with meteorological data of the last ∼100 years indicating that carbon isotope compositions of the stalagmites may reflect changes in precipitation amount, while oxygen isotope compositions are more related to temperature variations. The combined textural–geo...

The effect of hydrological and hydrochemical parameters on the microdistribution of aquatic fauna in drip water in the Velika Pasica Cave, Central Slovenia

AbstractWater quality and quantity significantly affects the aquatic fauna in the epikarst and conversely can also reflect the hydrological environment. Intensive, long‐term studies on hydrological and hydrochemical parameters were monitored at 4 permanent dripping sites (VP1–VP4) in the Velika Pasica Cave (Slovenian) over a period from 2006 to 2013 concurrently with aquatic fauna sampling. Multivariate methods were applied to elucidate the relationship between the environmental conditions and the resident aquatic ecosystem. Seven major aquatic taxa were collected from the drips, with Copepoda being the dominant taxa; however, the spatial distribution and composition of these species varied distinctively at the 4 study sites; the drip water from different sites had distinct hydrological and hydrochemical characteristics. The most significant parameters influencing community composition were drip water discharge volume and NO3− ion content. The results indicate that hydrology and hydrochemistry significantly influence the microdistribution of aquatic fauna within the epikarstic aquifer.

Effect of extreme precipitation events on the hydrochemistry index and stable isotope compositions of drip water in a subtropical cave, Guangxi, SW China

To study the effects of extreme precipitation events on drip water in Liangfeng Cave, hydrochemistry and stable isotope compositions of drip water and pool water samples, as well as contemporaneous precipitation samples were measured. Results show that cave temperature had marked diurnal variations, with similar trends to atmospheric temperature on season timescales. However, the amplitude of cave temperature variation was less than atmospheric temperature, related to “buffering effects” inside the cave. Drip water and pool water ionic concentrations of Ca2+, $${\text{HCO}}_{3}^{ - }$$ , and specific conductivity increased after extreme precipitation events, while values of δD, δ18O and δ13CDIC in drip water and pool water became more negative. However, samples from sites LF-9 and LF9-1 showed a longer delay to these effects, related to their longer flow paths. The δD and δ18O composition of precipitation mainly controlled the isotope values in drip water, because this mainly depends on water vapor source. However, the δ13CDIC of drip water and pool water negative excursions were likely caused by massive amounts of soil CO2 dissolved by percolating precipitation. Thus, hydrochemistry and stable isotope signals in cave drip and pool water appear to mainly reflect precipitation information during extreme precipitation events. Although at different drip sites (e.g., LF-9 and LF9-1), variable hydro-geochemical processes produce different timing and duration to changes in hydrochemistry and stable isotope signals.

The temperature variation in an epikarstic cave and its impact factors: a case from Velika Pasica Cave, Central Slovenia

In order to reveal the temperature variation mechanism of a small and relatively closed cave, the surface temperature, the cave air temperature and the drip water temperatures were monitored with high-resolution recorders for a 7-year period. The results indicated that the cave temperature is mainly affected by the external seasonal oscillations. The temperature curve of the inner cave area (with standard deviation between 0.59 and 0.87) was much smoother in comparison with that of the surface (with SD as high as 8.46). However, the cave reacted to the temperature drifts with some delay, for example, at VP3 in 2006, the internal temperature increased for additional 49 days after the surface temperature dropped colder than inside of the cave. This seasonal variation and delayed response of the internal temperature were mainly affected by conduction from the epikarst rock mass. Air convection also occurred in the cave, especially when the surface temperature dropped lower than that of the inside cave (during the winter time) and in the outer section (close to the entrance), which caused an abrupt and irregular variation of the outer section. In addition, the influence from the percolating water was ephemeral and depended on its supplementary amount and temperature difference, e.g., there were more apparent responses at VP1 and VP3 when the intensive rain fell. The percolating water temperature could be a good indicator for water flow in epikarst.

Analysis of drip water in an urban karst cave beneath the Hungarian capital (Budapest)

Our geological heritage is increasingly threatened by anthropogenic activity. This is especially true of the Pal-volgyi Cave System beneath Budapest. It is among the 150 longest and at the same time most endangered cave systems in the world. The aims of the study were (i) to set up a monitoring system in the cave, (ii) to track the daily changes in the quality and quantity of drip water, and (iii) to determine the exposure of the cave. Monitoring was conducted at two locations in a shallow area next to a fracture zone (site name: TG) and one lying in a tectonically less disturbed, geologically more homogeneous location 20 m deeper (site YC). The data obtained in respect of 13 variables were assessed using descriptive statistics, principal component- and periodicity analyses. At first glance, it was apparent that the eight water quality parameters differed in quantity between the two sites. Furthermore, using principal component analysis it was shown that in the fractured-shallow setting, anthropogenic activity (external urban pollution, e.g. de-icing, decrease of land cover etc.) is the driving process determining water quality. At the tectonically less fractured site (YC) external influences originating above ground may be added to the natural karst-forming processes. The assessment of drip intensity and electric conductivity again highlighted the differences between the sites in terms of their reaction to precipitation. With regard to diurnal periodicity, although pH and Eh indicated a mature periodic behavior at both sites (covering 56−65 % of the total observed time), at site TG electric conductivity displayed diurnal periodicity over only 21 % of the total time, compared to 56 % at YC. All results pointed towards a conclusion that at site YC daily periodicity and water quality are much more connected to natural processes, while at site TG anthropogenic external influences suppress these. Key words: cave drip water, hydrochemistry, karst, Pal-volgyi Cave System, time series analysis, urban pollution. Analiza prenikle vode v urbani kraski jami pod madžarsko prestolnico (Budimpesta) Nasa geoloska dediscina je vse bolj ogrožena zaradi clovekovih dejavnosti. To se posebej velja za jamski sistem Pal-volgyi pod Budimpesto. Sodi med 150 najdaljsih in hkrati najbolj ogroženih jamskih sistemov na svetu. Cilji raziskave so bili (i) vzpostaviti sistem spremljanja izbranih parametrov v jami, (ii) spremljati dnevne spremembe kakovosti in kolicine prenikle vode, in (iii) dolociti izpostavljenost jame onesnaženju. Raziskava je bila izvedena na dveh lokacijah v plitvem obmocju blizu razpoklinske cone (ime vzorcnega mesta: TG) in na tektonsko manj pretrti in geolosko bolj homogeni lokaciji 20 m globlje (ime vzorcnega mesta: YC). Pridobljeni podatki 13 spremenljivk so bili obdelani s pomocjo opisne statistike, analize glavnih komponent in periodicostno analizo. Na prvi pogled je bilo ocitno, da se je osem parametrov kakovosti vode kvantitativno razlikovalo med obema mestoma. Poleg tega se je s pomocjo analize glavnih komponent pokazalo, da je mesto v plitvem pretrtem obmocju pod velikim vplivom antropogenih aktivnosti (urbano onesnaženje, npr. sredstva proti zmrzovanju, zmanjsanje pokrovnih plasti, itd.), ki vplivajo na kakovost vode. Na tektonsko manj preoblikovanem mestu (YC) se zunanji vplivis povrsja mesajo z naravnimi kraskimi procesi. Ocena intenzivnosti kapljanja in elektricne prevodnosti je ponovno izpostavila razlike med vzorcnimi mesti v smislu njunega odziva na padavine. V zvezi z dnevno periodicnostjo je vzorcno mesto TG kazalo dnevno periodicnost vec kot 21 % celotnega casa, mesto YC 56 %, ceprav sta pH in Eh izkazali zrelo periodicno obnasanje (56−65 % celotnega opazovanega casa) na obeh mestih. Vsi rezultati kažejo na sklep, da je na mestu YC dnevna periodicnost in kakovost vode veliko bolj povezana z naravnimi procesi, medtem ko jih na mestu TG antropogeni zunanji vplivi zadusijo. Kljucne besede: jamska prenikla voda, hidrokemija, kras, jamski sistem Pal-volgyi, analiza casovne vrste, urbano onesnaževanje.

The Relationship between pH and Bacterial Communities in a Single Karst Ecosystem and Its Implication for Soil Acidification.

Enhanced monsoon duration and soil acidification from acid rain are expected to impact the distribution of microbial communities in surface and subsurface environments, although these impacts are poorly understood for most systems. In central China, soluble carbonate bedrock forms extensive karst landscapes. Current predictions are that the amount of monsoonal precipitation and acid rainfall in central China will increase, which is expected to lead to changes in the pH balance of karst ecosystems. To evaluate the role of pH, total organic carbon, and other geochemical parameters (e.g., Ca2+, Mg2+, NH4+, NOx, SO42-) in shaping bacterial communities within a single karst system in central China, samples were collected from the thin surface soils overlying Heshang Cave, cave sediments, and weathered cave passage rocks from the entrance, twilight, and dark zones, as well as from epikarstic drip waters inside the cave. Illumina sequencing of 16S rRNA genes and multivariate statistical analyses revealed that each tested community was distinct and the community variability was significantly correlated with pH, total organic carbon, and potassium concentrations. Specifically, surface soils were dominated by Acidobacteria, Verrucomicrobia and Planctomycetes, and diversity significantly decreased with acidic pH values. Nitrospirae, Gemmatimonadetes, Firmicutes, and Chloroflexi were unique to cave sediments, while Actinobacteria and Proteobacteria dominated weathered rocks and drip waters, respectively. The results reveal important implications regarding the effects of acidification on bacterial communities in karst areas, and on the control of pH in shaping bacterial communities throughout a karst system. Increased water flux into and through karst habitats due to monsoonal precipitation may result in deeper penetration of acidic solutions into karst and shift the bacterial communities inside the cave in the future.

Enrichment of 88Sr in continental waters due to calcium carbonate precipitation

δ88/86Sr data published over the last few years suggest that continental waters are enriched with 88Sr as compared to the rocks in their drainage basins. In an attempt to understand this phenomenon, this study established the fractionation in the 88Sr/86Sr ratio during precipitation of continental carbonates (i.e., carbonates precipitated on land from surface, pedogenic, or ground waters), and evaluated the contribution of this process to the 88Sr-enrichment in rivers. For this, stable and radiogenic Sr isotopes (88Sr, 87Sr and 86Sr) were measured in calcite samples and their precipitating waters collected in various continental environments, such as soil, cave, streams and groundwater.The results indicate that continental carbonates are 88Sr-depleted relative to their precipitating waters, placing them as one of the most 88Sr-depleted reservoirs on earth. The average difference in δ88/86Sr values between waters and solid CaCO3 (tufas or speleothems) that they precipitate is Δcarb-water=−0.218±0.014‰ (1SD). An even larger fractionation (εcarb-water=−0.285±0.02‰) was measured in groundwater with particularly high carbonate-alkalinity and high carbonate precipitation rate that depleted ∼65% of the Sr in the groundwater, resulting in substantial 88Sr-enrichment in the residual dissolved Sr (δSr88/86=0.656‰). Results also suggest that pedogenic carbonate precipitation in soil profile removes 50–85% of the Sr from the recharging soil–water, thereby increasing the δ88/86Sr value of the soil-water from ∼0.18‰ to 0.3‰–0.6‰. Similar 88Sr-enrichment was observed in drip water from a karst cave.A maximum removal flux of Sr into continental carbonates of about 20 Gmol(Sr)⋅y−1 is required to yield the reported 88Sr-enrichment in global rivers (δSr88/86=0.32‰) relative to their rock sources when using the fractionation factor derived in this study, Δcarb-water=−0.218‰, and the published δ88/86Sr composition of marine carbonates of 0.16‰. This surprisingly large flux requires that ∼40% of the originally weathered Sr should co-precipitate with continental carbonates. This calculation may suggest that CaCO3 precipitation is a significant mechanism in the continental Sr cycle. It is possible however that other mechanisms such as Sr uptake by plants or incongruent weathering of silicates, could also contribute to the riverine 88Sr-enrichment. Alternatively, the average δ88/86Sr value of marine carbonate rock sections undergoing weathering is higher than suggested in current literature. It is concluded that additional δ88/86Sr data on marine carbonate rock sections should be collected to resolve the enigma of the high value of riverine δ88/86Sr.

Geochemistry of speleothems affected by aragonite to calcite recrystallization – Potential inheritance from the precursor mineral

Formerly aragonite speleothems recrystallized to calcite result from solutions subsaturated in aragonite and supersaturated in calcite that infiltrate into the speleothem through the interconnected porosity. In most cases, the crystal replacement takes place through a thin solution film. This diagenetic process can occur under open or semi-closed geochemical conditions. Thus, secondary calcite crystals record the composition of the fluid at the time of diagenesis affected by calcite partition coefficients and fractionation factors (open system) or partly inherit the composition of the primary aragonite (semi-closed system). So, whether or not recrystallized aragonite speleothems can record reliable geochemical signals from the time of speleothem primary deposition still is an open debate. We studied a stalagmite from Eagle Cave (Spain) predominantly composed of secondary calcite that replaced aragonite, although a core of primary aragonite extending 45mm along the growth direction was preserved at the base of the sample. We obtained Mg and Sr compositional maps, paired U–Th dating and δ18O and δ13C profiles across the diagenetic front. Additionally, two parallel isotope records were obtained along the speleothem growth direction in the aragonite and calcite sectors. Our results support that recrystallization of this speleothem took place in open system conditions for δ18O, δ13C, Mg and Sr, but in semi-closed system conditions for U and Th. The recrystallization of this sample took place during one or several events, likely after the Younger Dryas as a result of climate change influencing drip water composition. Based on compositional zoned patterns, we suggest that the advance of diagenetic fronts in this speleothem had an average rate of 50±45μm/yr. Such recrystallization rate can transform any aragonite speleothem into calcite within a few centuries. We suggest that the volume of water interacting with the speleothem at the time of recrystallization is of critical importance for inheritance of different elements. The volume of solution is controlled by (1) the discharge of water passing through the sample and (2) the lapse time between aragonite dissolution and calcite precipitation. Hydrology and hydrochemistry of the interacting solution, together with the mineralogy and texture of the speleothem are the essential controls for the diagenesis of the speleothem. Recrystallization of aragonite speleothems does not follow stratigraphical levels of the sample but occurs along sites with preferential flow paths in any sector of the speleothem. In these cases the relationship between age and distance from base is not preserved. However, alternation of periods of recrystallization with periods of aragonite precipitation causing speleothem accretion can result in recrystallized speleothems with coherent distance from the base-age relationship. Thus, early diagenesis of speleothems affected by seasonal or inter-annual oscillation of drip waters supersaturated and subsaturated in aragonite may provide best-scenario conditions for dating and preservation of paleoenvironmental records along recrystallized speleothems. However, even in this scenario, the variable discharge and the diagenetic rate control the geochemical inheritance from the primary aragonite crystals.

Formation of amorphous calcium carbonate in caves and its implications for speleothem research.

Speleothem deposits are among the most valuable continental formations in paleoclimate research, as they can be dated using absolute dating methods, and they also provide valuable climate proxies. However, alteration processes such as post-depositional mineralogical transformations can significantly influence the paleoclimatic application of their geochemical data. An innovative sampling and measurement protocol combined with scanning and transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy is presented, demonstrating that carbonate precipitating from drip water in caves at ~10 °C contains amorphous calcium carbonate (ACC) that later transforms to nanocrystalline calcite. Stable oxygen isotope fractionations among calcite, ACC and water were also determined, proving that ACC is 18O-depleted (by >2.4 ± 0.8‰) relative to calcite. This, in turn, has serious consequences for speleothem-based fluid inclusion research as closed system transformation of ACC to calcite may induce a negative oxygen isotope shift in fluid inclusion water, resulting in deterioration of the original compositions. ACC formation increases the speleothems’ sensitivity to alteration as its interaction with external solutions may result in the partial loss of original proxy signals. Mineralogical analysis of freshly precipitating carbonate at the studied speleothem site is suggested in order to determine the potential influence of ACC formation.

Isotopic assessment of fog drip water contribution to vegetation during dry season in Junshan wetland, northern Dongting Lake

Stable isotopes 2H and 18O of fog drip water, lake water, soil profiles, and vegetation leaves in Junshan wetland of East Dongting Lake, China, were investigated to estimate the contribution of fog drip water to wetland vegetation. Because of its recycled terrestrial meteoric water source, fog drip water is characterized by isotopic compositions that plot above the local meteoric water line (LMWL). Lake water undergoes intense evaporation owing to its low water volume and long residence time. The isotopic compositions of soil water suggest that it is recharged by both recent rainfall and fog drip water. A binary mixing model shows that approximately 16% of unsaturated soil water originates from continuous recharge by fog drip water, reaching 31% in surface soil where the vegetation roots are mainly distributed. Inspired by the literatures on acidification of intercepted clouds and fog as the major factor in forest die-back in Europe, the findings in this study inform future investigations into the relationships between fog water deposition and wetland degradation especially in heavily industrialized foggy areas.

ENSO–cave drip water hydrochemical relationship: a 7-year dataset from south-eastern Australia

Abstract. Speleothems (cave deposits), used for palaeoenvironmental reconstructions, are deposited from cave drip water. Differentiating climate and karst processes within a drip-water signal is fundamental for the correct identification of palaeoenvironmental proxies and ultimately their interpretation within speleothem records. We investigate the potential use of trace element and stable oxygen-isotope (δ18O) variations in cave drip water as palaeorainfall proxies in an Australian alpine karst site. This paper presents the first extensive hydrochemical and δ18O dataset from Harrie Wood Cave, in the Snowy Mountains, south-eastern (SE) Australia. Using a 7-year long rainfall δ18O and drip-water Ca, Cl, Mg / Ca, Sr / Ca and δ18O datasets from three drip sites, we determined that the processes of mixing, dilution, flow path change, carbonate mineral dissolution and prior calcite precipitation (PCP) accounted for the observed variations in the drip-water geochemical composition. We identify that the three monitored drip sites are fed by fracture flow from a well-mixed epikarst storage reservoir, supplied by variable concentrations of dissolved ions from soil and bedrock dissolution. We constrained the influence of multiple processes and controls on drip-water composition in a region dominated by El Niño–Southern Oscillation (ENSO). During the El Niño and dry periods, enhanced PCP, a flow path change and dissolution due to increased soil CO2 production occurred in response to warmer than average temperatures in contrast to the La Niña phase, where dilution dominated and reduced PCP were observed. We present a conceptual model, illustrating the key processes impacting the drip-water chemistry. We identified a robust relationship between ENSO and drip-water trace element concentrations and propose that variations in speleothem Mg / Ca and Sr / Ca ratios may be interpreted to reflect palaeorainfall conditions. These findings inform palaeorainfall reconstruction from speleothems regionally and provide a basis for palaeoclimate studies globally, in regions where there is intermittent recharge variability.

Solar-forced diurnal regulation of cave drip rates via phreatophyte evapotranspiration

Abstract. We present results of a detailed study of drip rate variations at 12 drip discharge sites in Glory Hole Cave, New South Wales, Australia. Our novel time series analysis, using the wavelet synchrosqueezed transform, reveals pronounced oscillations at daily and sub-daily frequencies occurring in 8 out of the 12 monitored sites. These oscillations were not spatially or temporally homogenous, with different drip sites exhibiting such behaviour at different times of year in different parts of the cave. We test several hypotheses for the cause of the oscillations, including variations in pressure gradients between karst and cave due to cave breathing effects or atmospheric and earth tides, variations in hydraulic conductivity due to changes in viscosity of water with daily temperature oscillations, and solar-driven daily cycles of vegetative (phreatophytic) transpiration. We conclude that the only hypothesis consistent with the data and hydrologic theory is that daily oscillations are caused by solar-driven pumping by phreatophytic trees which are abundant at the site. The daily oscillations are not continuous and occur sporadically in short bursts (2–14 days) throughout the year due to non-linear modification of the solar signal via complex karst architecture. This is the first indirect observation leading to the hypothesis of tree water use in cave drip water. It has important implications for karst hydrology in regards to developing a new protocol to determine the relative importance of trends in drip rate, such as diurnal oscillations, and how these trends change over timescales of weeks to years. This information can also be used to infer karst architecture. This study demonstrates the importance of vegetation on recharge dynamics, information that will inform both process-based karst models and empirical estimation approaches. Our findings support a growing body of research exploring the impact of trees on speleothem paleoclimate proxies.

Water isotopic variability in Mallorca: a path to understanding past changes in hydroclimate

AbstractThis paper reports the first results on δ18O and δ2H analysis of precipitations, cave drip waters, and groundwaters from sites in Mallorca (Balearic Islands, western Mediterranean), a key region for paleoclimate studies. Understanding the isotopic variability and the sources of moisture in modern climate systems is required to develop speleothem isotope‐based climate reconstructions. The stable isotopic composition of precipitation was analysed in samples collected between March 2012 and March 2013. The values are in the range reported by GNIP Palma station. Based on these results, the local meteoric water line (LMWL) δ2H = 7.9 (±0.3) δ18O + 10.8 (±2.5) was derived, with slightly lower slope than Global Meteoric Water Line. The results help tracking two main sources of air masses affecting the study sites: rain events with the highest δ18O values (> −5‰) originate over the Mediterranean Sea, whereas the more depleted samples (< −8‰) are sourced in the North Atlantic region. The back trajectory analysis and deuterium excess values, ranging from 0.4 to 18.4‰, further support our findings. To assess the isotopic variation across the island, water samples from eight caves were collected. The δ18O values range between −6.9 and −1.6‰. With one exception (Artà), the isotopic composition of waters in caves located along the coast (Drac, Vallgornera, Cala Varques, Tancada, and Son Sant Martí) indicates Mediterranean‐sourced moisture masses. By contrast, the drip water δ18O values for inland caves (Campanet, ses Rates Pinyades) or developed under a thick (>50 m) limestone cap (Artà) exhibit more negative values. A well‐homogenized aquifer supplied by rainwaters of both origins is clearly indicated by groundwater δ18O values, which show to be within 2.4‰ of the unweighted arithmetic mean of −7.4‰. Although limited, the isotopic data presented here constitute the baseline for future studies using speleothem δ18O records for western Mediterranean paleoclimate reconstructions. Copyright © 2016 John Wiley & Sons, Ltd.