Hydrological modeling in the karst area,Rižana spring catchment,Slovenia

Karst aquifers are known for their heterogeneity and irregular complex flow patterns which make them more difficult to model and demand specific modeling approaches. This paper presents one such approach which is based on a conceptual model. The model was applied in a karst area of the catchment of Rižana spring (200 km2). It is based on the MIKE SHE code and incorporates the main hydrological processes and geological features of the karst aquifer (diffuse and concentrated infiltration, allogenic recharge, quick and slow groundwater flow, shifting groundwater divides and groundwater outflow from the catchment area). Modeling of evapotranspiration and flow in the upper part of the unsaturated zone is more detailed. For the modeling of groundwater flow in the karst aquifer, a conceptual model was applied which uses drainage function for the simulation of groundwater flow through large conduits (karst channels and large fissures). The model was calibrated and validated against the observed Rižana spring discharge which represents a measured response of the aquifer. The results of validation show that the model is able to adequately simulate temporal evolution of the spring discharge, measured by Nash–Sutcliffe coefficient (0.82) as well as overall water balance.     

Aqueous geochemistry of rare-earth elements in karst lakes, southwestern China

Due to the unique chemical properties that are similar but still progressively change, the rare earth elements （REEs） are useful tracers of various geochemical processes in the lithosphere and hydrosphere. However, despite many studies of REE geochemistry in the ocean, the aqueous geochemistry of REEs in lake waters has been poorly documented. In the present study, two special karst lakes are chosen as case studies to investigate the distributions of dissolved REEs in lake water. Although the two lakes, Hongfeng and Aha, are both alkaline and have high pH from 7.9 to 8.7 and high carbonate concentrations, the Aha Lake has been more severely affected by acidic mining drainage with high Fe, Mn and SO42 concentrations. In the present study, the concentrations of dissolved rare-earth elements in lake waters were determined by inductively coupled plasma mass spectrometry. The result shows that the concentrations of dissolved REEs in the studied alkaline karst lakes, as compared to the concentrations of REEs in seawater, are much lower than the other investigated terrestrial surface waters in previous studies. The key factor controlling dissolved REE distributions is pH value which is negatively correlated with REE concentrations. Due to high concentration of carbonate ion and alkaline character of water chemistry, the shale （PAAS） normalized patterns of dissolved REEs show marked HREE enrichment in all water samples. This is primarily the result of the preferential formation of stronger carbonate complexes with the HREEs. In alkaline or intermediate waters, REE-carbonate complexes are the dominant and typical species, which account for about more than 90% of the total dissolved REEs.     

Boron isotopic geochemistry of karst groundwater in Guiyang City, China

Boron has two stable isotopes （^10B and ^11B） with relative abundances of about 20% and 80%, respectively. Boron isotopic ratios in natural materials show a huge range of variations, from -70‰ to ＋60‰, when expressed with the classical δ^11B notation. Most of these isotopic variations occur at the surface of the Earth. Hence, boron isotopic composition can be used as a sensitive tracer in geochemical study, for instance, to identify the different sources of contamination and factors controlling the salinity of groundwater. During the last decade, boron isotopes have been used to discriminate between the influences of seawater intrusion and anthropogenic discharge. But few of those researches can precisely identify the different sources of contamination. We measured the boron concentrations and boron isotopic ratios of groundwater samples collected in Guiyang City, as well as the major ions. The results indicate that the major ion composition of the groundwater in the investigated area is mainly controlled by the interactions between water and the dominant rock i.e. carbonates. All the water compositions are characterized by high concentrations of Ca^2＋, Mg^2＋, HCO3^-, SO4^2-, and NO3^-, which are the dominant contaminants. Both dissolved boron concentrations and isotopic ratios show large variations among the ground waters, from 2 μg/L to 90 μg/L and from -6‰ to ＋26‰, respectively. The boron concentrations and isotopic ratios indicate that the river across the studied city has been seriously contaminated by urban discharge. Boron concentrations of fiver water samples varied from 20 μg/L to 140 μg/L, with an average δ^11B value of ＋2.0‰. Using boron isotopic compositions and different geochemical indices allowed us to clearly identify and distinguish the two major sources of contamination, agricultural activity and urban wastewater. Both of the two sources are characterized by high boron concentrations but their boron isotopic compositions significantly differ.     

Review: The Yucat��n Peninsula karst aquifer, Mexico

The Yucatán Peninsula karst aquifer is one of the most extensive and spectacular karst aquifer systems on the planet. This transboundary aquifer system extends over an area of approximately 165,000? km² in México, Guatemala and Belize. The Triassic to Holocene Yucatán limestone platform is located in the vicinity of the North American/Caribbean plate boundary and has been reshaped by a series of tectonic events over its long geologic history. At the end of the Cretaceous period, the Yucatán Peninsula was hit by a large asteroid, which formed the Chicxulub impact crater. The Yucatán Peninsula karst aquifer hosts large amounts of groundwater resources which maintain highly diverse groundwater-dependent ecosystems. Large parts of the aquifer are affected by seawater intrusion. Anthropogenic pollution of the aquifer has been increasing over the past few decades, owing to relentless economic development and population growth on the Peninsula. This review summarizes the state of knowledge on the Yucatán Peninsula karst aquifer and outlines the main challenges for hydrologic research and practical groundwater-resources management on the Peninsula.     

River–groundwater connectivity in a karst system,Wellington, New South Wales,Australia

The characterization of river–aquifer connectivity in karst environments is difficult due to the presence of conduits and caves. This work demonstrates how geophysical imaging combined with hydrogeological data can improve the conceptualization of surface-water and groundwater interactions in karst terrains. The objective of this study is to understand the association between the Bell River and karst-alluvial aquifer at Wellington, Australia. River and groundwater levels were continuously monitored, and electrical resistivity imaging and water quality surveys conducted. Two-dimensional resistivity imaging mapped the transition between the alluvium and karst. This is important for highlighting the proximity of the saturated alluvial sediments to the water-filled caves and conduits. In the unsaturated zone the resistivity imaging differentiated between air- and sediment-filled karst features, and in the saturated zone it mapped the location of possible water- and sediment-filled caves. Groundwater levels are dynamic and respond quickly to changes in the river stage, implying that there is a strong hydraulic connection, and that the river is losing and recharging the adjacent aquifer. Groundwater extractions (1,370 ML, megalitres, annually) from the alluvial aquifer can cause the groundwater level to fall by as much as 1.5 m in a year. However, when the Bell River flows after significant rainfall in the upper catchment, river-leakage rapidly recharges the alluvial and karst aquifers. This work demonstrates that in complex hydrogeological settings, the combined use of geophysical imaging, hydrograph analysis and geochemical measurements provide insights on the local karst hydrology and groundwater processes, which will enable better water-resource and karst management.     

Wavelet analysis of Fuenmayor karst spring,San Julián de Banzo,Huesca, Spain

Fuenmayor spring has been monitored continuously for identification purposes to study the behavior of a karst groundwater system. This paper initially deals with linear methods employing system engineering techniques for the analysis and identification of a hydrological system, considered as a black box model, which disregards information on the internal structure of the aquifer. Under a linear time invariant hypothesis, the application of the simple correlation of spectral analysis and parametric identification of transfer function generated some interesting results in the monitored spring. These tools have historically been successful in studying a large number of karst springs and continue to be practical approximations in initial attempts to obtain a draft model. Because of the nonlinear and nonstationary nature of karst, more effective systemic techniques are required to cover certain aspects of analysis that the linear system cannot reveal adequately. This paper presents interesting results using Fuenmayor spring data, collected over almost 10 years, to show the ability of wavelet techniques in the identification of a karst spring system.     

Geochemical characterization of a karst polje – an example from Sinjsko polje, Croatia

 The poljes of the Adriatic Coast are rather special features whose like is not found anywhere else in the world. The delineation of this unique landform feature by its geochemical characteristics has been attempted by using examples from Sinjsko polje, which represents a typical karst polje in the Adriatic Coast, or the area of the Dinaric Karst. Factor analysis was performed on 96 samples collected in a regular grid of 1×1 km which covered the entire area of the Sinjsko polje valley. Another factor analysis was performed in a regular grid of 5×5 km that comprised 41 samples in the karstic environment. In this manner two factor models were created and closely inspected for possible differences due to the peculiar properties arising from two geochemically different environments. Within the polje itself it was possible to evaluate three factors, while four factors were identified to be significant for the explanation of the geochemical structure of data assessed in the regular 5×5-km grid. This grid includes the area of Sinjsko polje and its wider neighborhood. The Ba/Sr index reveals striking differences in drainage patterns between the polje itself and the surrounding area. Received: 3 May 1996 · Accepted: 25 June 1997     

Hydrogeochemistry of karst underground waters at shallow depth in Guiyang City, Guizhou Province

The aim of this study is to shed light on the hydrogeochemical characteristics of karst underground waters at shallow depth in Guiyang City, Guizhou Province with an emphasis on the geochemistry of major elements. Guiyang City bears abundant underground waters and it is also an important representative of the karst areas throughout the world. Ca^2 and Mg^2 are the dominant cations, accounting for 81% -99.7% of the total, and HCO3^- and SO4^2- are the dominant anions. Weathering of limestones and dolostones is the most important factor controlling the hydrogeochemistry of underground waters, and weathering of sulfate and evaporite rocks is less important. Moreover, the precipitation and human activities also have a definite influence on the hydrogeoehemistry of underground waters in the region studied.     

Using the dual isotopes approach to identify the nitrate sources of karst groundwater, Guiyang, Southwest China.

18O values can provide significant δ15N and δ information to understand variation of nitrate sources of groundwater. Groundwater samples were collected during summer and winter in the karstic city, 18O-NO3-·δ15N-NO3- at Guiyang, southwest China and an…     

Contrasting definitions for the term ‘karst aquifer’

It is generally considered that karst aquifers have distinctly different properties from other bedrock aquifers. A search of the literature found five definitions that have been proposed to differentiate karst aquifers from non-karstic aquifers. The five definitions are based upon the presence of solution channel networks, hydraulic conductivities >10^?6 m/s, karst landscapes, channels with turbulent flow, and caves. The percentage of unconfined carbonate aquifers that would classify as ‘karst’ ranges from <1 to >50%.     

Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—1, methodological considerations

Comparison of a database of interpreted sinkholes made using airborne laser swath mapping (ALSM) with databases of sinkholes made from interpretation of aerial photographs reveals substantial disagreement. The discrepancies involve the location, number, areas, and circularity of interpreted sinkholes. Methodological factors that contribute to the discrepancies include blockage of ALSM laser returns in thick vegetation, multi-path reflections, and misrepresentation of the true extent of sinkholes. Comparison of two ALSM-derived databases made (1) independently from versus (2) in combination with earlier air photo analysis in undeveloped regions had the following result: one-fourth of the sinkholes interpreted by using the composite method were missed by the independent analysis, and one-third of the sinkholes that were interpreted from the independent analysis were not interpreted as sinkholes using the composite method. Subjective interpretation leads to a high level of uncertainty such that the results of the remote sensing studies are suspect, if not invalid.     

Hydrogeochemical characterization and evolution of a regional karst aquifer in the Cuatrociénegas area,Mexico

The Cuatrociénegas area is useful for the investigation of the effect of groundwater extraction in the Chihuahuan freshwater xeric ecoregion. It has been investigated at this time using a selection of geochemical indicators (major, minor and trace elements) and δ³⁴S data, to characterize the origin of groundwater, the main geochemical processes and the mineral/groundwater interactions controlling the baseline geochemistry. The area is composed of limestones of Mesozoic age, with a composite thickness of about 500 m, overlaid by basin fill (poorly consolidated young sediments). Substantial water extraction and modification of natural discharges from the area along the last century have produced a detrimental impact on ecosystem structure and function. Water–rock interactions, mixing and evaporative processes dominate the baseline groundwater quality. Natural recharge is HCO₃–Ca type in equilibrium with calcite, low salinity (TDS?<?500 mg/L), Cl^? lower than 11 mg/L and average Li⁺ concentration of 0.005 mg/L. Along the groundwater flow systems, δ³⁴S evidence and mass transfer calculations indicate that Cretaceous gypsum dissolution and dedolomitization reactions adjust water composition to the SO₄–Ca type. The increase of water–rock interaction is reflected by Cl^? values increase (average 68 mg/L), TDS up to about 1500 mg/L and an average Li⁺ concentration of 0.063 mg/L. Calculations with chemical geothermometers indicate that temperature at depth could be at maximum of 15–20 °C higher than field-measured temperature for pozas. After groundwater is discharged to the surface, chemical evolution continues; water evaporation, CO₂ degassing and precipitation of minerals such as gypsum, calcite and kaolinite represent the final processes and reactions controlling water chemical composition.     

PaPRIKa: a method for estimating karst resource and source vulnerability��application to the Ouysse karst system (southwest France)

The intrinsic vulnerability mapping method, PaPRIKa, is proposed as a common basis for karst groundwater protection in France. PaPRIKa is a specialized method for studying karst aquifers, derived from updating the RISKE and EPIK methods. Both the structure and functioning of karst aquifers are considered in order to develop a resource and source-vulnerability mapping method. PaPRIKa means Protection of aquifers from the assessment of four criteria: P for protection (considering the most protective aspects among parameters related to soil cover, unsaturated zone and epikarst behavior), R for rock type, I for infiltration and Ka for karstification degree. The Ouysse karst system, located in the Causses area in southwest France, is one of the nine pilot sites where this method was tested and standardized. The specificities of the Ouysse system such as the size of the catchment area, the spatial variability of the karst network development, the thick infiltration zone and the system??s dual character (both karst and non-karst areas), have provided a valuable field of application. The vulnerability of the resource was assessed for the entire catchment area, while source-orientated cartography was attempted for the catchment areas of the three different capture works used for drinking water.     

Climatic and geologic controls on the piezometry of the Querença-Silves karst aquifer,Algarve (Portugal)

Karst aquifers in semi-arid regions, like Querença-Silves (Portugal), are particularly vulnerable to climate variability. For the first time in this region, the temporal structure of a groundwater-level time series (1985–2010) was explored using the continuous wavelet transform. The investigation focused on a set of four piezometers, two at each side of the S. Marcos-Quarteira fault, to demonstrate how each of the two sectors of the aquifer respond to climate-induced patterns. Singular spectral analysis applied to an extended set of piezometers enabled identification of several quasi-periodic modes of variability, with periods of 6.5, 4.3, 3.2 and 2.6 years, which can be explained by low-frequency climate patterns. The geologic forcing accounts for ~15 % of the differential variability between the eastern and western sectors of the aquifer. The western sector displays spatially homogenous piezometric variations, large memory effects and low-pass filtering characteristics, which are consistent with relatively large and uniform values of water storage capacity and transmissivity properties. In this sector, the 6.5-year mode of variability accounts for ~70 % of the total variance of the groundwater levels. The eastern sector shows larger spatial and temporal heterogeneity, is more reactive to short-term variations, and is less influenced by the low-frequency components related to climate patterns.     

Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—2. Accuracy statistics

We apply the logic of clinical epidemiological studies to quantify the accuracy of mapping sinkholes by ALSM in the 750 km² Pinellas County. By such studies, a new diagnostic procedure is tested by comparing the diagnoses in a clinical trial to diagnoses on the same patients from a more reliable, but more elaborate and expensive procedure (“gold standard” in epidemiological context). A relatively undeveloped, 65 km² focus area where we have aerial photographs that are effectively contemporaneous with the ALSM flights serves as the “clinical trial”. The xy-locations in the focus area are the “patients” in the trial. The “diagnostic test” for having “sinkhole disease” is inclusion in a database of sinkhole polygons delimited by ALSM contours (“ALSM-alone”), as detailed in Part 1. The standard of comparison (“gold standard” would be an overstatement in the absence of geophysical testing) is inclusion in a database of sinkhole outlines derived by best judgment of conjunctive interpretation of ALSM and aerial photography. GIS intersections that indicate the sensitivity and specificity of the test (ALSM-alone) are 43 and 98.3%, respectively, and, in the focus area where the prevalence of “sinkhole disease” is 4.7%, the positive and negative predictive values are 55.5 and 97.2%, respectively. Over much of the rest of the county, where only the test can be applied, the prevalence of sinkholes is sufficiently small that it cannot be determined to be any different from zero given the paucity of interpreted sinkholes (positive diagnoses) and the low specificity of the test method. The conclusion, therefore, is that contemporaneous aerial photography is essential to compile an ALSM-derived database that aims to state that the given xy-points lay inside or outside of topographic depressions in the covered karst of west-central Florida.     

Carbonate weathering and connate seawater influencing karst groundwaters in the Gevas–Gurpinar–Güzelsu basins,Turkey

There are 59 springs at the Gevas–Gurp?nar–Güzelsu basins, 38 of these springs emerge from the fractured karst aquifers (recrystallized limestone and travertine) and 21 emerge from the Yuksekova ophiolites, K?rkgeçit formation and alluvium. The groundwater samples collected from 38 out of the total of 59 springs, two streams, one lake and 12 wells were analyzed physico-chemically in the year 2002. EC and TDS values of groundwater increased from the marble (high altitude) to the ophiolites and alluvium (toward Lake Van) as a result of carbonate dissolution and connate seawater. Five chemical types of groundwater are identified: Ca–Mg–HCO₃, Mg–Ca–HCO₃, Mg–Na–HCO₃, Na–Ca–HCO₃ and Mg–Ca–Na–HCO₃. The calculations and hydrochemical interpretations show that the high concentrations of Ca²⁺, Mg²⁺ and HCO₃ ^? as predominant ions in the waters are mainly attributed to carbonate rocks and high pCO₂ in soil. Most of the karst springs are oversaturated in calcite, aragonite and dolomite and undersaturated in gypsum, halite and anhydrite. The water–rock interaction processes that singly or in combination influence the chemical composition of each water type include dissolution of carbonate (calcite and dolomite), calcite precipitation, cation exchange and freshening of connate seawater. These processes contribute considerably to the concentration of major ions in the groundwater. Stable isotope contents of the groundwater suggest mainly direct integrative recharge.     

Space–time distribution of ancient and active alluvial karst subsidence: examples from the central Ebro Basin,Spain

Space and time variations of alluvial karst subsidence in the central Ebro Basin are analysed in trenches (paleodolines), aerial photographs (historical dolines) and field surveys (present-day active dolines). The measured subsidence rates, as well as a comparison between densities of paleodolines computed in randomly selected scan-lines and density of active dolines computed in maps, suggest that present-day subsidence in favourable areas is more intense than that of Pleistocene times. According to diachronic maps drawn from (a) different aerial photographs taken after 1946 and (b) field surveys on deformations in urbanized areas, subsidence behaved as a nearly steady process while the whole area was used for agriculture. In contrast, rapid changes (through periods of several tens of years) have occurred in urbanized areas, in which dolines expand their boundaries through small marginal collapses, shifting sharply their sinking centres to neighbouring sites. These rapid changes do not have an equivalent in observed paleodolines.     

Analysis of soil biogeochemical characteristics in the process of karst rocky desertification

The sampling method of karst soil is always the one used for non-karst area. However, if the samples can represent the plot, it still needs further investigation due to high degree of spatial variability of karst soil. The study results of soil from the Maolan karst virgin forest in Guizhou Province elucidated that only the surface area-weighted samples could represent plot soils in the karst ecosystem. The remediation of karst rocky desertification has currently become a national issue, but soil degradation research on rocky desertification genesis types and processes is still insufficient. Soil physical, chemical, biological characteristics and enzymes activities from plots of different rocky desertification genesis types and grades in the Cha＇eryan catchment in the Huajiang Gorge area, Guizhou, were studied. The results showed that woodcutting and land reclamation influenced soil biogeochemical characteristics, and the influence of different disturbing ways was huge. The author suggested a soil degradation index system which could illustrate the rocky desertification genesis type and extent. The degraded modes of woodcutting and reclamation sequence were different, both had no synchronism with rocky desertification grades divided by current landscape index. Only soil of serious grade degraded evidently in wood cutting sequence. On the contrary, soils of slight, medium and serious grades degraded evidently in the reclamation sequence.