Summary
The Gypsum Hill (GH) springs on Axel Heiberg Island in the Canadian high Arctic are host to chemolithoautotrophic, sulfur‐oxidizing streamers that flourish in the high Arctic winter in water ...temperatures from −1.3 to 7°C with ~8% salinity in a high Arctic winter environment with air temperatures commonly less than −40°C and an average annual air temperature of −15°C. Metagenome sequencing and binning of streamer samples produced a 96% complete Thiomicrorhabdus sp. metagenome‐assembled genome representing a possible new species or subspecies. This is the most cold‐ and salt‐extreme source environment for a Thiomicrorhabdus genome yet described. Metaproteomic and metatranscriptomic analysis attributed nearly all gene expression in the streamers to the Thiomicrorhabdus sp. and suggested that it is active in CO2 fixation and oxidation of sulfide to elemental sulfur. In situ geochemical and isotopic analyses of the fractionation of multiple sulfur isotopes determined the biogeochemical transformation of sulfur from its source in Carboniferous evaporites to biotic processes occurring in the sediment and streamers. These complementary molecular tools provided a functional link between the geochemical substrates and the collective traits and activity that define the microbial community's interactions within a unique polar saline habitat where Thiomicrorhabdus‐dominated streamers form and flourish.
Summary
Hot springs integrate hydrologic and geologic processes that vary over short‐ and long‐term time scales. However, the influence of temporal hydrologic and geologic change on hot spring ...biodiversity is unknown. Here, we coordinated near‐weekly, cross‐seasonal (~140 days) geochemical and microbial community analyses of three widely studied hot springs with local precipitation data in Yellowstone National Park. One spring (‘HFS’) exhibited statistically significant, coupled microbial and geochemical variation across seasons that was associated with recent precipitation patterns. Two other spring communities, ‘CP’ and ‘DS’, exhibited minimal to no variation across seasons. Variability in the seasonal response of springs is attributed to differences in the timing and extent of aquifer recharge with oxidized near‐surface water from precipitation. This influx of oxidized water is associated with changes in community composition, and in particular, the abundances of aerobic sulfide‐/sulfur‐oxidizers that can acidify waters. During sampling, a new spring formed after a period of heavy precipitation and its successional dynamics were also influenced by surface water recharge. Collectively, these results indicate that changes in short‐term hydrology associated with precipitation can impact hot spring geochemistry and microbial biodiversity. These results point to potential susceptibility of certain hot springs and their biodiversity to sustained, longer‐term hydrologic changes.
Karst groundwater resources in the Zagros Mountains are vital for supplying different demands in the region which need sustainable management and protection. Quantitative and qualitative ...characterization of karst aquifers in this region was understudied due to a lack of site-specific logging data and speleological investigations. In this study, state-of-the-art statistical methods developed to characterize karst aquifer based on analyses of the spring recession hydrograph and spring water quality are presented. These methods include Mangin’s method for the classification of karst aquifers, relationships of precipitation and discharge data, groundwater quality index (GQI), hydrochemical diagrams (Piper, Durov, and Gibbs), and calcite and dolomite saturation indices, Chloro-Alkaline indices (CAI), and 10 bivariate plots of hydrochemistry of spring waters. 42 major karst springs mainly located in folded part of the Zagros region (western Iran) are selected for application of the reviewed methods. Results indicated that the saturated zone exerts almost the main control over the discharge of 76% of the studied springs. The base-flow contributes between 80.0 and 100% of total water storage in the study aquifers. 78.5% of the studied aquifers have a high karstification degree. An insignificant lag time is observed between the precipitation on the karst basin and spring discharge. The hydrochemical diagrams show that the waters are dominated by HCO
3
and Ca and the majority of the waters are alkaline, originating from carbonate rocks–water interaction through the ion exchange process. Moreover, the water sources of the studied springs are young and feed through precipitation (during the rainy season) and drainage from the upper karst setting (during the dry season). Such repeatable methods adopted in this study can provide crucial information for the karst aquifers, especially those suffering from scarcity of aquifer hydrodynamic data.
Over 180 springs emerge in the Panamint Range near Death Valley National Park, CA, yet, these springs have received very little hydrogeological attention despite their cultural, historical, and ...ecological importance. Here, we address the following questions: (1) which rock units support groundwater flow to springs in the Panamint Range, (2) what are the geochemical kinetics of these aquifers, and (3) and what are the residence times of these springs? All springs are at least partly supported by recharge in and flow through dolomitic units, namely, the Noonday Dolomite, Kingston Peak Formation, and Johnnie Formation. Thus, the geochemical composition of springs can largely be explained by dedolomitization: the dissolution of dolomite and gypsum with concurrent precipitation of calcite. However, interactions with hydrothermal deposits have likely influenced the geochemical composition of Thorndike Spring, Uppermost Spring, Hanaupah Canyon springs, and Trail Canyon springs. Faults are important controls on spring emergence. Seventeen of twenty‐one sampled springs emerge at faults (13 emerge at low‐angle detachment faults). On the eastern side of the Panamint Range, springs emerge where low‐angle faults intersect nearly vertical Late Proterozoic, Cambrian, and Ordovician sedimentary units. These geologic units are not present on the western side of the Panamint Range. Instead, springs on the west side emerge where low‐angle faults intersect Cenozoic breccias and fanglomerates. Mean residence times of springs range from 33 (±30) to 1,829 (±613) years. A total of 11 springs have relatively short mean residence times less than 500 years, whereas seven springs have mean residence times greater than 1,000 years. We infer that the Panamint Range springs are extremely vulnerable to climate change due to their dependence on local recharge, disconnection from regional groundwater flow (Death Valley Regional Flow System ‐ DVRFS), and relatively short mean residence times as compared with springs that are supported by the DVRFS (e.g., springs in Ash Meadows National Wildlife Refuge). In fact, four springs were not flowing during this campaign, yet they were flowing in the 1990s and 2000s.
The Panamint Range, located partially within Death Valley National Park, is geologically complex and the location, discharge, and geochemical composition of its springs are closely coupled to the geology. Panamint Range springs are extremely vulnerable to the effects of climate change due to their disconnection from the regional groundwater flow system, dependence on local recharge, and relatively young mean residence times. In fact, several springs which were flowing in 2004 and 2005 were dry during this study in 2017.
Challenged by rapidly changing climate in combination with an increase in anthropogenic pressures, karst groundwater resources in the Old Town of Lijiang (OTLJ), SW China, are diminishing. Higher ...frequency and longer duration of dried-up periods have been observed at the Heilongtan Park (HP) Springs in recent years. Thus, there is an urgent need for an artificial recharge scheme, aimed at replenishing groundwater in the aquifer and increasing the outflow of the springs to ensure effective water resources management. Evaluation of the scheme feasibility, prior to its implementation, is important. In this study, tracer tests were conducted between the recharge area and receiving springs in order to gain insight into the transport mechanisms of karst groundwater and the structural characteristics of the aquifer. Multiple underground flow paths, exhibiting high conductivity between the recharge area and HP Springs, were revealed by the interpretation of tracer breakthrough curves. Three springs considered as the leakages of the scheme were identified. Moreover, the outflow of springs at HP and OTLJ were predicted to be increased by the artificially recharged water after 9.2 and 12.5 days, respectively. Quantitative analysis of tracer recoveries demonstrates that the springs to be recharged and the springs considered as leakages, respectively, share 45 and 55% of the increased outflow. The feasibility of the scheme has been confirmed by the tracer tests. This report provides references for the evaluation of artificial groundwater recharge and protection strategies, particularly in large and poorly investigated karst spring fields.
A hydrogeological conceptual model of the source, circulation pathways and temporal variation of a low-enthalpy thermal spring in a fractured limestone setting is derived from a multidisciplinary ...approach. St. Gorman’s Well is a thermal spring in east-central Ireland with a complex and variable temperature profile (maximum of 21.8 °C). Geophysical data from a three-dimensional(3D)audio-magnetotelluric(AMT) survey are combined with time-lapse hydrogeological data and information from a previously published hydrochemical analysis to investigate the operation of this intriguing hydrothermal system. Hydrochemical analysis and time-lapse measurements suggest that the thermal waters flow within the fractured limestones of the Carboniferous Dublin Basin at all times but display variability in discharge and temperature. The 3D electrical resistivity model of the subsurface revealed two prominent structures: (1) a NW-aligned faulted contact between two limestone lithologies; and (2) a dissolutionally enhanced, N-aligned, fault of probable Cenozoic age. The intersection of these two structures, which has allowed for karstification of the limestone bedrock, has created conduits facilitating the operation of relatively deep hydrothermal circulation (likely estimated depths between 240 and 1,000 m) within the limestone succession of the Dublin Basin. The results of this study support a hypothesis that the maximum temperature and simultaneous increased discharge observed at St. Gorman’s Well each winter is the result of rapid infiltration, heating and recirculation of meteoric waters within a structurally controlled hydrothermal circulation system.
Thermal springs provide natural laboratories to test the responses of biological communities to various stressors. To date, little is known about how water temperature and chemistry influence the ...microalgal assemblages in these ecosystems, especially in the circum-Mediterranean area. In this study, we assessed the environmental drivers of benthic diatom assemblages collected from different substrates in 8 thermo-mineral springs of Sardinia, Italy, with a focus on temperature and conductivity. A total of 205 diatom species (67 genera) were found, of which 12 (8 genera) were centric and 193 (59 genera) were pennate. Composition of diatom assemblages was associated with temperature, pH, conductivity, bicarbonates (HCO3−), and sulfates (SO42−). Multivariate analyses also confirmed differences in species composition, richness, diversity, and evenness of diatom assemblages from groups of springs distinguished by temperature and conductivity gradients. We found higher species richness, diversity, and evenness in hyperthermal (water temperature = 52.7−71.5°C) and medium-mineral springs (conductivity = 590−1193 µS/cm). Our results indicate that thermal springs are not always inhospitable environments for diatoms. Springs with high water temperatures hosted rich and diverse diatom assemblages, likely thanks to their ecotonal nature and a combination of multiple local factors.
The Mangka saline hot springs, in the Simao Basin in southwest China, are unique in having relatively large discharge (>10 L/s) from the red beds (relatively poor permeability) and travertine ...deposition from Cl-Na type hot water with high content of total dissolved solids (10 g/L). The stable hydrogen and oxygen isotopes indicate that the Mangka spring waters are meteoric in origin and the average altitude of the recharge area is estimated as 1,750 m above sea level. The high temperature of the spring water is derived from geothermal heating. The estimated geothermal reservoir temperature range is 86–91 °C and the circulation depths of the spring waters are 2,318–2,454 m. Incongruent dissolution of salt-bearing formations contributes to the mineralization of the Mangka saline hot springs, including dissolution of halite, gypsum, carbonate and sylvite. Some suitable hydrochemical factors provide beneficial conditions for travertine deposition such as a higher CO
2
partial pressure of 10
–1.94
–10
–0.9
, γCa/γHCO
3
(the milliequivalent ratio of Ca and HCO
3
) ranging from 5.76 to 6.67, and saturation indices for both calcite and aragonite over or equal to zero. There is also a favorable hydrodynamic condition for the spring water flowing down steep slopes and forming fast-flowing shallow channels with a relatively large surface area. The formation of the Mangka saline hot springs is summarized as follows: the groundwater receives recharge of infiltration from precipitation, undergoes deep circulation in the salt-bearing strata, receives heat from the geothermal heat flow, and ascends to the land surface along the permeable fault.
Definition of karst spring catchment or basin area and boundaries belongs to one of the greatest problems of karst hydrology and hydrogeology, not adequately solved until now. This paper tries to ...address main problems in defining this crucial parameter. The theoretical aspect of this issue is discussed in the first two chapters. We have presented the example of the catchment area and boundaries definition for the karst spring Žrnovnica catchment in Dinaric karst. Topographic catchment area of the Žrnovnica Spring is 8.4 km². The significant discrepancy in size of the hydrological–hydrogeological and topographical catchment is very common characteristic for the springs located in the karst areas. In the case of the Žrnovnica Spring, the hydrogeological catchment is at least seven times larger than topographic. Two following simple hydrological methods are used in order to calculate its hydrologic–hydrogeologic catchment: (1) the relationship between mean annual discharges and annual rainfall falling on the catchment, and (2) the Turc method. It is estimated that hydrogeologic catchment area of the Žrnovnica karst spring is much larger and very probably ranges between 60 and 80 km². These values represent first rough assessment, which should be confirmed by more detailed interdisciplinary investigations. According to the performed tracing tests, it seems that the catchment spreads on the north-east from the topographic catchment and that the Žrnovnica Spring karst aquifer is fed by groundwater overflow from the neighbouring more abundant karts spring Jadro.
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