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The hemispheric impact of industrial emissions upon atmospheric sulphur loading is reflected in the sulphur depositional history recorded in cores from ice sheets. However, these do not reveal regional variations. Recently deposited speleothems are used here as archives of regional sulphur depositional history at two locations within the United Kingdom and Ireland. d34S-SO4 and d18O-SO4 present within speleothem carbonate are measured for the first time as part of a dual isotope approach to decode the speleothem sulphur record. The largely refractory nature of d34S-SO4 under oxidising conditions enables source provenance of atmospheric SO2, whereas the complex cycles of isotopic exchange and fractionation during incorporation of oxygen into sulphate molecules enable d18O-SO4 signatures to yield insights into ambient environmental conditions and biogeochemical cycling in the ecosystem above the cave. d34S-SO4 values extracted from speleothem carbonate formed within
Browns Folly Mine, UK, range from +3.5 to +5.5& and d18O-SO4 +10.3 to +13.7&. Both signatures lie within the range expected from sulphate deposition in industrial locations and reflect the transfer of sulphate into speleothem calcite with little fractionation. However, d18O-SO4 signatures at Crag Cave, western Ireland, are isotopically heavier than expected and approach isotopic equilibrium with d18O-H2O under reducing conditions. Dual isotope analysis of d34S-SO4 and d18O-SO4 optimises
the correct identification of sulphur sources and biogeochemical cycling prior to incorporation into the speleothem record. At carefully selected cave sites where drip water flowpaths into the cave remain oxic, speleothems hold the potential to retain records of atmospheric sulphur loading at the local and regional scale.
Information about sources of recharge, distributions of flow paths, and the extent of water–rock reactions in karst aquifers commonly result from monitoring spring chemistry and discharge. To investigate the relationship between spring characteristics and the complexities of karst aquifers, we couple variations in surface- and groundwater chemistry to physical conditions including river stage, precipitation, and evapotranspiration (ET) within a sink-rise system through a 6-km portion of the Upper Floridan aquifer (UFA) in north-central Florida. Principal component analysis (PCA) of time series major-element compositions suggests that at least three sources of water affect spring discharge, including allogenic recharge into a swallet, diffuse recharge through a thin vadose zone, and water upwelling from deep within the aquifer. The deep-water source exerts the strongest influence on water chemistry by providing a majority of Na+, Mg2+, K+, Cl, and SO2 4 to the system. Anomalously high temperature at one of several monitoring wells reflects vertical flow of about 1 m/year. Mass-balance calculations suggest diffuse recharge and deep-water upwelling can provide up to 50% of the spring discharge; however, their contributions depend on head gradients between the conduit and surrounding aquifer matrix, which are influenced
by variations in precipitation, ET, and river stage. Our results indicate that upwelling from deep flow paths may provide significant contributions of water to spring discharge, and that monitoring only springs limits interpretations of karst systems by masking critical components of the aquifer, such as water sources and flow paths. These results also suggest the matrix in eogenetic aquifers is a major pathway for flow even in a system dominated by conduits.
Assessing water quality in aquifers has become increasingly important as water demand and pollution concerns rise. In the Yucatan Peninsula, sinkholes, locally known as cenotes, are karst formations that intercept the water table. Cenotes are distributed across the peninsula, but are particularly dense and aligned along a semicircular formation called the Ring of Cenotes. This area exhibits particular hydrogeological properties because it concentrates, channels, and discharges fresh water toward the coasts. In this study, we identify spatial and temporal variations in chemical and physical variables at twenty-two cenotes to identify groups that share similar characteristics. Water samples from each cenotes were taken at three depths (0.5, 5.5, and 10.5 m) and during three seasons (dry, rainy, and cold-fronts season). Field measurements of pH, temperature, electrical conductivity, and dissolved oxygen were taken, and the concentrations of major ions (K+, Na+, Mg2+, Ca2+, HCO{ 3 , SO2{ 4 , Cl2 and NO{ 3 ) were quantified. Identifying regions of the cenotes were done by applying multivariate statistical techniques (PCA, PERMANOVA, CAP). The chemical variables revealed spatial trends among the cenotes. We identified three main regions. Region 1 is associated with sea-water encroachment and high levels of sulfate that travel through preferential groundwater flowpaths from evaporites in the southern Yucatan Peninsula; Region 2 is a recharge zone, and Region 3 is characterized by sea water encroachment and by the high chemical and physical variability associated with groundwater flow from the east.
An updated conceptual circulation model for the Caldas da Rainha and Quinta das Janelas thermomineralwaters was developed. These thermomineral waters (T _ 33 _C) are related to a huge syncline ascribed tothe regional flow paths. Two diapiric structures were responsible for the uplift and subsequent folding ofregional Jurassic carbonate rocks. Environmental isotopic (d2H and d18O) data indicates that the mainrecharge area of the thermomineral system is linked to the Jurassic limestones (Candeeiros Mountains,E border of the syncline). The thermomineral waters belong to the Cl–Na sulphurous-type, with a totalmineralization of about 3000 mg/L. The thermomineral aquifer system seems to be ‘‘isolated’’ fromanthropogenic contamination, which is typical for the local shallow groundwater systems, due to theexistence of impermeable layers composed of a series of loamy and detritic rocks of the Upper Jurassic.The presence of 3H in some thermomineral borehole waters, not accompanied by an increase in SO2_4 andNO_3 , could be ascribed to different underground flow paths and different mean residence time. Thed34S(SO4) and d18O(SO4) values of dissolved sulphate of groundwaters of the Caldas da Rainha Spas indicatethat the sulphate is the result of water–rock interaction with evaporitic rocks (e.g. gypsum and anhydrite)ascribed to the regional synclinal structure.
The Ankarana is a limestone plateau in the northern part of Madagascar, where a cave system, more than 120 km long, has been explored. The plateau is bordered by volcanoes and is cut across by several canyons. An analysis of surface landforms and caves suggests that the karst genesis was probably initiated by volcanism beneath an impervious cover. Volcanic bulging and magma intrusions may have favored a basalt-limestone assimilation process and metamorphism. The ascent of deep volcanic fluids (CO2 and SO2) from magma degassing and from limestone metamorphism, may explain the speleogenesis. Once denuded, the karst evolved classically, but the selective erosion of metamorphosed rocks (more likely to be weathered than pure limestone), resulted in the creation of unusual landforms such as canyons and large circular basins.