Budapest, the capital of Hungary, is famous for its abundant thermal waters. The monitoring network of the thermal karst waters of Budapest consists of 27 sampling locations, from which data for six ...geochemical parameters and temperature were available for the period 1960–2010. Based on this data, the optimal grouping for the sampling locations was sought using combined cluster and discriminant analysis. Furthermore, the homogeneity of the obtained groups, as well as temporal changes in the overall monitoring system were investigated. The seven groups found are in accordance with the previously established hydrogeological conditions, i.e. the grouping can be considered as optimal. The results obtained using combined cluster and discriminant analysis on the geochemical and temperature database of Budapest have important practical implications, since the thermal waters are an intensely used resource. Any artificial intervention will influence locations belonging to the same group, and therefore the optimal grouping of sampling locations will help in the planning of further activities. This case study might serve as an example in other settings where multiple measurements at multiple sampling locations from a monitoring network are available.
•Geochemical and temperature data of the thermal karst waters of Budapest were analysed.•Combined cluster and discriminant analysis (CCDA) can find the optimal grouping of data.•Seven main groups and smaller homogeneous sub-groups were identified.•CCDA can be applied to the investigation of temporal changes.•Considerable temporal changes were shown to have occurred over the decades.
Zhijin coal-mining district, located in Midwestern Guizhou Province, has been extensively exploited for several decades. The discharge of acid mine drainage (AMD) has constituted a serious threat to ...local water environmental quality, which greatly affected the normal use of local people. The Permian limestone aquifer is the essential potable water supply for local people, which covered under the widely distributed coal seams. To investigate the origin of the water, the evolutionary processes, and the sources of dissolved sulfate in the karst waters, the mine water, surface water, and groundwater near the coal mines were sampled for stable isotopes (H, O, and S) and conventional hydrochemical analysis. The results of hydrochemistry and isotopic composition indicate that the regional surface water and partial karst groundwater are obviously affected by coal-mining activities, which is mainly manifested in the increase of water solute concentration and the change of hydrochemical types. The isotopic composition of δ
2
H
H2O
and δ
18
O
H2O
indicates that the major recharge source of surface water and the groundwater is atmospheric precipitation and that it is influenced obviously by evaporation in the recharge process. The surface water is mainly controlled by the oxidation of pyrite, as well as the dissolution of carbonate rocks, whereas that of natural karst waters is influenced by the dissolution of carbonate rocks. The resulting δ
34
S
SO4
values suggest that the dissolved sulfate source in the surface water is mainly pyrite oxidation but atmospheric precipitation for the karst groundwater. Given the similar chemistry and isotopic composition between surface water and partial groundwater, it is reasonable to assume that most of the dissolved sulfate source in part of the groundwater was derived through the oxidation of pyrite in the coal. Furthermore, the contamination of the surface water and partial groundwater from the coal seam has occurred distinctly in the catchment, which is enriched in SO
4
2−
and is mostly depleted δ
34
S in sulfate.
•A paired catchment study was used to assess karst hydrogeochemistry of two streams.•Chemistry of streams with and without acid mine drainage (AMD) was very different.•The observation was supported ...by PHREEQC modeling of equilibrium conditions.•Ionic fluxes of AMD-impacted water were higher than that of non-AMD-impacted water.•The higher ionic fluxes were predominantly controlled by the oxidation of pyrite.
A paired catchment study was used to assess hydrochemical characteristics of streams in AMD (acid mine drainage)-impacted and non-AMD-impacted catchments in a karstic region, SW China. The catchments shared similar geology, slope, aspect, area and climate, but different land use since one encompassed mining activities. As a result, hydrogeochemical characteristics of the AMD-impacted water were dominantly controlled by oxidation of pyrite, while that of non-AMD-impacted were influenced by water–rock reactions. It is also coincident with the source of δ34SSO4 in both waters. Upstream, unit ion fluxes of the AMD-impacted catchment for Ca, Mg, H, Fe and SO4 were 17g/(m2yr), 2g/(m2yr), 0.0002g/(m2yr), 17g/(m2yr) and 136g/(m2yr), respectively, while unit ion fluxes of the non-AMD-impacted catchment were much lower than that of the AMD-impacted catchment. Along the flow, fluxes of H, Ca, Mg, Fe and SO4 decreased in the AMD-impacted water, but increased in the non-AMD-impacted water. The observation was coincident with variations of ion concentrations in both waters along the flow, supported by PHREEQC modeling of minerals such as goethite, jarosite(ss), melanterite, scorodite, calcite, and dolomite. It suggests that the transport of constituents of interest (except for Ca and Mg) is dramatically different in these catchments. Results provide important information on karst system response to AMD, together with the baseline data to understand the degree and type of impairment.
Karst water resources, which are critical for the support of human societies and ecological systems in many regions worldwide, are extremely sensitive to mining activities. Identification and ...quantification of stable isotope (δ2HH2O andδ18OH2O) composition for all sources is essential if we are to fully understand the dynamics of these unique systems and propose successful remediation strategies. For these purposes, a stable isotope study was undertaken in two similar watersheds, one impacted by acid mine drainage, and the other not. It was found that the majority of δ2HH2O and δ18OH2O values of acid mine drainage (AMD), AMD-impacted and Main channel mix waters plotted above the local meteoric water line (LMWL), while the non-AMD-impacted water was below the LMWL. The AMD and AMD-impacted water had a similar composition ofδ18OH2O and heavierδ2HH2O than that of the other waters as a result of pyrite oxidation and Fe hydrolysis. The non-AMD-impacted and spring waters were the background waters in the study area. The composition ofδ2HH2O and δ18OH2O for the former was influenced by the re-evaporation and water–rock interaction, and that for the latter was controlled by re-condensation. Along the water flow, the Main channel mix water is recharged by AMD-impacted, non-AMD-impacted and spring waters. The composition ofδ2HH2O andδ18OH2O for the Main channel mix water was coincident with the characteristics of water mixing, supported by three-component mixing modeling of upstream spring, non-AMD-impacted and AMD-impacted waters. The composition of δ2HH2O and δ18OH2O for the Main channel mix water was mainly affected by the AMD-impacted water. These results help elucidate the impact of AMD on δ2HH2O and δ18OH2O compositions for karst waters and demonstrate the utility for impact assessments and remediation planning in these unique systems.
•Elucidating δ18OH2O and δ2HH2O dynamics benefits remediation strategies.•Isotopic compositions with and without acid mine drainage were very different.•Isotopic variability was affected by pyrite oxidation and Fe hydrolysis.•The observation was supported by three-component mixing modeling.•Results present models for isotopic fractionation of mine drainage in karst settings.
Karst ecosystems are considered as priority environments for the protection of biodiversity on a global scale. This study provides a first comparative analysis of epilithic diatom flora from karst ...springs in two Mediterranean geographic areas (Spain and Italy) with contrasting characteristics (islands vs mainland). We investigated twenty-three springs with different anthropogenic impact levels once in the winter season between 2007 and 2017 (N = 23). A total of 176 diatom taxa (56 genera) were found of which 101 (44 genera) were observed in single sites. A general good biotic integrity was revealed by structural indices (species richness, diversity and evenness). However, crenophilous species were generally present and abundant in less impacted springs. Comparing islands and mainland, significant differences were found in species composition and diversity (H’) based on multivariate analyses (global R = 0.610; p = 0.001) and t-test (t = 2.304; p = 0.031). Discharge and Cl− were the most significant variables in determining diatom assemblages. Our results confirm the role of springs as multiple ecotones and refuges for rare species and suggest that the geographic insularity may be an important factor in maintaining diatom biodiversity.
In Sardinia, Italy, karst springs are strategic water resources and potential hotspots of biodiversity; however, they are understudied, and their communities remain largely unknown. This study was ...conducted at Sa Vena spring (Su Gologone system) to characterize the diatom communities, to describe their relationships with environmental variables, and to evaluate the impact of an extreme flash flood. High species richness, diversity, and evenness were found both in epiphytic and epilithic assemblages. Statistical analyses showed significant differences between assemblages from the 2 substrates and in assemblages from the same substrate. Differences seem due to the stronger impact of seasonal water level variations and flash flood on macrophytes than on cobbles. Further, epilithic assemblages showed more stable behavior over time, both on an annual (higher resistence) and a multiannual (higher resilience) scale. Alkalinity (p = 0.002) and dissolved oxygen (p = 0.004) explained a significant amount of variance in epiphytic and epilithic assemblages, respectively, according to RDA analyses; however BOD
5
, negatively correlated with dissolved oxygen, can be the most probable driver of epilithic diatoms. The results suggest the importance of the proper management and preservation of this biotope, both for the high biodiversity and potential vulnerability to climate change.
The difference in dissolved inorganic carbon (DIC) utilization and calcium carbonate precipitation by
Oocystis solitaria Wittr
grown in closed systems of karst water and non-karst water was ...investigated by using a free pH-drift experiment. It was found that the HCO
3
−
as carbon resource of
Oocystis solitaria Wittr
photosynthesis was catalyzed by carbonic anhydrase to CO
2
at low CO
2
concentration. The DIC utilization and induced calcium carbonate precipitation by
Oocystis solitaria Wittr
were much higher (4.6 and 10-fold, respectively) in karst water than in non-karst water. In karst waters, 42.6% of decreased calcium ions were precipitated as calcium carbonate; in non-karst waters, 8.9% were precipitated via physiochemical effect and the remaining were utilized by
Oocystis solitaria Wittr
for its growth. These findings clearly show the greater importance of karst water environment in DIC fertilization effect on the growth of
Oocystis solitaria Wittr
due to its higher concentrations of DIC, which is significant to the karst process-related carbon sink.
The Little River, an ephemeral stream that drains a watershed of approximately 88 km2 in northern Florida, disappears into a series of sinkholes along the Cody Scarp and flows directly into the ...carbonate Upper Floridan aquifer, the source of water supply in northern Florida. The changes in the geochemistry of ground water caused by a major recharge pulse from the sinking stream were investigated using chemical and isotopic tracers and mass-balance modeling techniques. Nine monitoring wells were installed open to the uppermost part of the aquifer in areas near the sinks where numerous subterranean karst solution features were identified using ground penetrating radar. During high-flow conditions in the Little River, the chemistry of water in some of the monitoring wells changed, reflecting the mixing of river water with ground water. Rapid recharge of river water into some parts of the aquifer during high-flow conditions was indicated by enriched values of delta (18)O and delta deuterium (-1.67 to -3.17 per mil and -9.2 to -15.6 per mil, respectively), elevated concentrations of tannic acid, higher (more radiogenic) (87)Sr/(86)Sr ratios, and lower concentrations of (222)Rn, silica, and alkalinity compared to low-flow conditions. The proportion of river water that mixed with ground water ranged from 0.10 to 0.67 based on binary mixing models using the tracers (18)O, deuterium, tannic acid, silica, (222)Rn, and (87)Sr/(86)Sr. On the basis of mass-balance modeling during steady-state flow conditions, the dominant processes controlling carbon cycling in ground water are the dissolution of calcite and dolomite in aquifer material, and aerobic degradation of organic matter.
Objective Karstic spring water is an important source of water supply for the karst areas of northern China. To rationally evaluate and scientifically exploit karstic water resources, it is important ...to identify the recharge, runoff and discharge conditions of spring water and to clearly depict the boundary of the spring area. Methods Targeting the issues of ambiguous border and unknown replenishment situations of the Gudui-Nanliang spring groups, this paper investigated and analysed the karst hydrogeological conditions of the spring area and the distribution characteristics of δD, δ18O and 87Sr/86Sr isotopes in the karstic water. The water-rock interactions and the hydraulic connection along the recharge-runoff path of karstic water were systematically examined by using isotope technique. Results The results show relatively large range of δ18O values in the karstic water. This is mainly attributed to the impacts of altitude effect, isotopic shift of oxygen in hot water, evaporation-induced enrichment and mix
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