Karst Aquifer System Research Articles

Modeling the groundwater recharge in karst aquifers by using a reservoir model

The estimation of the groundwater recharge in a karstic system becomes an important challenge due to the great hydrodynamic variability in both time and space. This paper proposes a two reservoir conceptual model to simulate inflow into both the conduit system and the fissure network system based on the analysis of the spring hydrograph. The structure of the model and the governing equations are proposed on the basis of the physical considerations, with the assumption that flow at the outlet of the reservoirs obeys a linear threshold function. The model is applied on the Houzhai karstic underground river basin where it successfully reflects the temporal recharge distribution. The simulated accumulation recharge is 34.29 mm, which is reasonable in relation to the actual rainfall of 92.8 mm. The variations of water volume in two reservoirs represent the storage and transform characteristics of the karst aquifer system. However, this model is particularly well suited to simulate the recharge event after intensive rainfall.

Ostracod Assemblages in the Frasassi Caves and Adjacent Sulfidic Spring and Sentino River in the Northeastern Apennines of Italy

Rich, diverse assemblages comprising a total (live + dead) of twenty-one ostracod species belonging to fifteen genera were recovered from phreatic waters of the hypogenic Frasassi Cave system and the adjacent Frasassi sulfidic spring and Sentino River in the Marche region of the northeastern Apennines of Italy. Specimens were recovered from ten sites, eight of which were in the phreatic waters of the cave system and sampled at different times of the year over a period of five years. Approximately 6900 specimens were recovered, the vast majority of which were disarticulated valves; live ostracods were also collected. The most abundant species in the sulfidic spring and Sentino River were Prionocypris zenkeri, Herpetocypris chevreuxi, and Cypridopsis vidua, while the phreatic waters of the cave system were dominated by two putatively new stygobitic species of Mixtacandona and Pseudolimnocythere and a species that was also abundant in the sulfidic spring, Fabaeformiscandona ex gr. F. fabaeformis. Pseudocandona ex gr. P. eremita, likely another new stygobitic species, is recorded for the first time in Italy. The relatively high diversity of the ostracod assemblages at Frasassi could be attributed to the heterogeneity of groundwater and associated habitats or to niche partitioning promoted by the creation of a chemoautotrophic ecosystem based on sulfur-oxidizing bacteria. Other possible factors are the geologic age and hydrologic conditions of the cave and karst aquifer system that possibly originated in the early– middle Pleistocene when topographic uplift and incision enabled deep sulfidic waters to reach the local carbonate aquifer. Flooding or active migration would have introduced the invertebrates that now inhabit the Frasassi Cave system.

Geochemical and stable isotopic variability within two rivers rising under the same mountain, but belonging to two distant watersheds

Complementary geochemical and stable isotope investigations of the Gorski Kotar karst aquifer system in western Croatia were obtained for the first time, to answer the question whether both studied rivers drain the same aquifer system or not. The two main rivers, the Kupa and the Rječina, rise under the same mountain range, but belong to two different watersheds (Black Sea and Adriatic Sea). The karst aquifer of Gorski Kotar is a potentially important source of drinking water for two neighboring countries, Croatia and Slovenia (Central and South Europe), and is strongly influenced by both Mediterranean and continental weather conditions. It is a part of the Dinaric karst, which is “locus typicus” for karst worldwide and one of the most typical karst areas in the world.To answer the main question of our research, baseline data were thoroughly collected comprising stable isotopes, concentration of dissolved and total trace metals in water, and multi-elemental analyses of river sediments, together with other physical-chemical parameters (pH, dissolved oxygen, electric conductivity and temperature). Total dissolved solid (TDS) was not measured but estimated as (EC) 0.67. Such multi-technique approach was applied for the first time in the Dinaric karst systems.Multi-elemental analysis of fine sediment fraction (<63μm) of eight samples was performed by ICP-MS. Elemental composition of sediments is quite different in the two studied river valleys, which indicates different origin of their waters. Also, concentrations of selected metals were compared with existing sediment quality criteria and anthropogenic influence is evaluated and discussed.Analytical results of major ions determined in three springs (Kupa spring, Rječina spring, Zvir spring in the City of Rijeka) were used to construct a Piper diagram, which showed that they are of a Ca–Na–HCO3–Cl type. The highest concentration of Mg is present in the Kupa spring, while the highest concentrations of Na and Cl are present in the Zvir spring. Groundwaters are underlain by limestone, less by dolomite and are under a maritime influence. There is a big difference with the main groundwater types reported in North Africa, i.e. in the south Mediterranean Sea, where two main groundwater types are Na–Cl and Ca–SO4–Cl.Concentrations of total and dissolved fractions of trace metals in surface water samples were determined by voltammetry and compared to the European Water Framework Directive values. Concentrations of total Pb and Zn are significantly higher in the water of the Kupa spring than the Rječina spring, suggesting that the karst water bodies of the two springs are not of the same origin.In addition, stable isotope composition (deuterium and oxygen-18) was determined in the spring waters sampled during low and high water conditions. Due to the significant difference in oxygen isotope-ratios it was concluded that the karst reservoir for the Kupa and Rječina springs is not identical.The results obtained from the combination of physical–chemical, geochemical (water and sediment) and isotope multi-technique analyses pointed out that even though the springs of the Kupa and Rječina rivers originate from the same mountain range, they do not drain the same karst aquifer.

Sources and migration path of chemical compositions in a karst groundwater system during rainfall events

Physical and chemical dynamics at Jiangjia Spring (JJS), the outlet of the Qingmuguan karst groundwater system in Chongqing, were monitored in situ during rainfall events to acquire a series of high-resolution data. Principal component analysis (PCA) was employed to identify the sources of chemical compositions in the karst groundwater. The coefficients of variations (CVs) of the physical and chemical data of JJS were utilized to interpret the migration path of the chemical compositions. The results showed that water-rock interactions, agricultural activities, and soil erosion were the main sources of the groundwater chemical compositions. Ions of potassium, sodium, nitrate, chloride and phosphate from agricultural activities together with ions of calcium, magnesium, strontium and bicarbonate derived from carbonate dissolution appear to be stored and regulated by the karst unsaturated zone in features such as fissures, pores and solution cracks. The concentrations of the ions remained relatively stable and they showed low CVs owing to their migration by diffuse flow to recharge the underground river. In contrast, concentrations of ions such as total iron, total manganese and aluminum from soil erosion were unstable and showed high CVs owing to their migration by overland flow to recharge the underground river directly via sinkholes. During heavy rainfall events, the nutrients from agricultural activities and sediment from soil erosion could quickly impair the aquatic ecosystem and pose serious threats to water quality. Therefore, it is necessary to reinforce management of the ecological system for better control of the influx of mass nutrients into the karst aquifer system.

Preferential Groundwater Flow Pathways and Hydroperiod Alterations Indicated by Georectified Lineaments and Sinkholes at Proposed Karst Nuclear Power Plant and Mine Sites

Sustainable development of any type that utilizes water or involves excavations in karst aquifer systems, such as the regional Floridan aquifer system (FAS), requires knowledge of preferential groundwater flow pathways that can extend adverse impacts beyond the development site and alter natural hydroperiods. Such pathways include fractures and other types of karst conduits that are associated with modern and relict sinkholes. Developments, including power plants and mines, that have not accounted for these features have caused induced recharge, altered hydroperiods and saltwater intrusion in the FAS, resulting in destruction of wetlands and adverse impacts to other surface waters, wildlife habitat and threatened and endangered species. This study analyzed indicators of preferential groundwater flow by considering surface expressions of underlying geological conditions (lineaments and modern sinkholes) in the FAS, which coincide with the United States southeastern coastal plain. Lineament mapping by Vernon (1951) and the Florida Department of Transportation (FDOT, 1973), incorporating analog mapping techniques and hardcopy prints of satellite imagery, preceded extensive urbanization, groundwater extractions, and mining in the region. All of these alterations limit the ability to identify fractures using lineaments by reducing groundwater discharges and vegetation indicative of those discharges. In this study, established methods for georectification, including control-point identification and spatial matching of scanned maps and remotely sensed images, were applied to these previously mapped lineaments. These results were applied to the environmentally sensitive karst study area of Citrus and Levy Counties, Florida in the southern extent of the FAS. Geospatial analyses of lineament distribution and modern sinkhole locations from the state database showed a dense network of lineaments with associated sinkholes throughout the study area and seven surrounding counties, including the proposed sites for a nuclear power plant and two mines in Levy County. Proposed excavations and water use for construction and operation of the power plant and mines would result in irreversible adverse environmental impacts on extensive depressional wetlands beyond the surface-footprint impact of these developments via these preferential flow pathways that were not evaluated during the review process.

Studying the Flow Dynamics of a Karst Aquifer System with an Equivalent Porous Medium Model

The modeling of groundwater flow in karst aquifers is a challenge due to the extreme heterogeneity of its hydraulic parameters and the duality in their discharge behavior, that is, rapid response of highly conductive karst conduits and delayed drainage of the low-permeability fractured matrix after recharge events. There are a number of different modeling approaches for the simulation of the karst groundwater dynamics, applicable to different aquifer as well as modeling problem types, ranging from continuum models to double continuum models to discrete and hybrid models. This study presents the application of an equivalent porous model approach (EPM, single continuum model) to construct a steady-state numerical flow model for an important karst aquifer, that is, the Western Mountain Aquifer Basin (WMAB), shared by Israel and the West-Bank, using MODFLOW2000. The WMAB was used as a catchment since it is a well-constrained catchment with well-defined recharge and discharge components and therefore allows a control on the modeling approach, a very rare opportunity for karst aquifer modeling. The model demonstrates the applicability of equivalent porous medium models for the simulation of karst systems, despite their large contrast in hydraulic conductivities. As long as the simulated saturated volume is large enough to average out the local influence of karst conduits and as long as transport velocities are not an issue, EPM models excellently simulate the observed head distribution. The model serves as a starting basis that will be used as a reference for developing a long-term dynamic model for the WMAB, starting from the pre-development period (i.e., 1940s) up to date.

Review: Groundwater flow and transport modeling of karst aquifers, with particular reference to the North Coast Limestone aquifer system of Puerto Rico

Karst systems have a high degree of heterogeneity and anisotropy, which makes them behave very differently from other aquifers. Slow seepage through the rock matrix and fast flow through conduits and fractures result in a high variation in spring response to precipitation events. Contaminant storage occurs in the rock matrix and epikarst, but contaminant transport occurs mostly along preferential pathways that are typically inaccessible locations, which makes modeling of karst systems challenging. Computer models for understanding and predicting hydraulics and contaminant transport in aquifers make assumptions about the distribution and hydraulic properties of geologic features that may not always apply to karst aquifers. This paper reviews the basic concepts, mathematical descriptions, and modeling approaches for karst systems. The North Coast Limestone aquifer system of Puerto Rico (USA) is introduced as a case study to illustrate and discuss the application of groundwater models in karst aquifer systems to evaluate aquifer contamination.

Palaeogeographic records in sediments of karst caves in Ukrainian Carpathians

Karst caves in the Ukrainian Carpathians are not numerous due to the limited extent of karst rocks in the region. Most known caves are concentrated in the Uhlja karst district, associated with the Marmarosh Klippen Zone. The known cavities are relics/fragments of ancient, probably Pre-Quaternary, hypogenic karst aquifer systems, partly destroyed and partly modified by infiltration and condensation water during Pleistocene. Clastic cave deposits in few caves were examined. The palaeontological records in these sediments are represented mainly by Vertebrate faunal remains: Ursus spelaeus, U . arctos, Panthera leo cf. spelaea, Martes martes , Meles meles , Vulpes vulpes , Felis silvestris , Rangifer tarandus , Bison priscus, Ochotona sp . Well stratified fine clastic sediments are quite rare, as well as the speleothems available for radioisotope examination

Distribution and speciation of trace elements in iron and manganese oxide cave deposits

Fe and Mn oxide minerals control the distribution and speciation of heavy metals and trace elements in soils and aquatic systems through chemical mechanisms involving adsorption, incorporation, and electron transfer. The Pautler Cave System in Southwest Illinois, an analog to other temperate carbonate-hosted karst systems, contains Fe and Mn oxide minerals that form in multiple depositional environments and have high concentrations of associated trace elements. Synchrotron-based micro-scanning X-ray fluorescence (μ-SXRF) shows unique spatial distributions of Fe, Mn, and trace elements in mineral samples. Profile maps of Mn oxide cave stream pebble coatings show Fe- and As-rich laminations, indicating dynamic redox conditions in the cave stream. μ-SXRF maps demonstrate that Ni, Cu, and Zn correlate primarily with Mn whereas As correlates with both Mn and Fe; As is more enriched in the Fe phase. Zn is concentrated in the periphery of Mn oxide stream pebble coatings, and may be an indication of recent anthropogenic surface activity. X-ray absorption fine structure spectroscopy measurements reveal that As(V) occurs as surface complexes on Mn and Fe oxides whereas Zn(II) associated with Mn oxides is adsorbed to the basal planes of phyllomanganates in a tetrahedral coordination. Co(III) and Se(IV) are also observed to be associated with Mn oxides. The observation of Fe, Mn, and trace element banding in Mn oxide cave stream pebble coatings suggests that these materials are sensitive to and document aqueous redox conditions, similar to ferromanganese nodules in soils and in marine and freshwater sediments. Furthermore, speciation and distribution measurements indicate that these minerals scavenge trace elements and limit the transport of micronutrients and contaminants in karst aquifer systems while also potentially recording changes in anthropogenic surface activity and land-use.

Advancement in Research of Hydrological Processes Simulation for Karst Region and Future Challenges

Hydrological processes simulation is an effective way for water resources evaluation and can provide scientific basis for sustainable utilization of water resources and ecological environment restoration. Compared with traditional watershed hydrological processes, hydrological processes in karst region have their unique in runoff generation and concentration stage because of the complexity and multiplicity of karst aquifer system. This paper reviews the two stages of hydrological processes simulation method in karst region: 1. systematic simulation model stage; 2. process based mechanism model stage. By analyzing the characteristics and limitation of two kinds of models, the tendency of future karst hydrological processes simulation method in two aspects are discussed: 1. quasi physically based model balancing physical senses and data richness; 2. scale adaptable model based on macro-scale applicable equations.

Karstification beneath the Birs weir in Basel/Switzerland: A 3D modeling approach

We present a three-dimensional model describing the evolution of a gypsum karst aquifer along the Birs river near Basel in Switzerland. Here, a small dam-site was built in 1890 to generate hydro-electric power. After subsidence of a nearby highway, geophysical and geological field studies have been carried out and a detailed hydrogeological model has been developed. These observations identified a karstified weathered zone as the reason for the subsidence. To prevent any further damage, remedial construction measures have been carried out. We employ our numerical model KARSTAQUIFER, which simulates the temporal evolution of a karst system by dissolution, increasing the porosity in the aquifer. We used results from geological and geophysical investigations as a priori information for implementing the initial boundary conditions into our three-dimensional numerical model. Our model accounts for topography, precipitation and geology and especially for the anisotropy of the local bedrock. It can successfully reproduce the weathered zone in its current horizontal and vertical extent. We cm also simulate the possible evolution of the aquifer following a remedial construction phase. Therefore, taken together with the geophysical and geological observations and the groundwater model, our three-dimensional karst aquifer evolution model enhances the understanding of the development of this heterogeneous karst aquifer system. (C) 2012 Elsevier B.V. All rights reserved. Hydrogeologie der Nordwestschweiz, Grundwasser

Major Ion Chemistry in a Coastal Karstic Groundwater Resource Located in Western Ireland

The extent of seawater intrusion in a coastal karstic aquifer system along the southern shore of Galway Bay, western Ireland, was investigated using spatial and temporal variations in major ion chemistry and nutrient levels. The background water was Ca- and bicarbonate-rich with variable concentrations of Mg. In general, higher Mg concentrations were detected in the Gort lowlands region compared with sites in the Burren, likely due to contact with dolomite layers. Nitrate concentrations ranged from 1.3mg/L to 78.5mg/L as NO3, and dissolved organic carbon concentrations ranged from 0.6mg/L to 4.9mg/L, suggesting that anthropogenic contamination due to surface activities occurs at some locations in the study area. Based on salinity values, on Na and Cl concentrations and on Cl/Br mass ratios, five of the 24 operational wells sampled were in a saltwater-influenced zone. Three of these wells contained <0.5% seawater, and the extent of saltwater influence was dependent on seasonal conditions. Water levels were monitored in six unused wells, and at four of these locations groundwater levels responded to the tidal variations in Galway Bay. During the study period, seawater intrusion and/or tidal influence on groundwater levels was found to occur within 5km of the coastline. The inland extent of seawater intrusion on the karst system is dependent on the hydrologic conditions at the time of measurement. The results provide a baseline dataset from which the influence of climatic and environmental changes on the aquifer system can be assessed in the future.

Geospatial Analysis of Depressional Wetlands near Peace River Watershed Phosphate Mines, Florida, USA

Mining throughout the Floridan aquifer system alters groundwater conditions. Determination of magnitude and extent of groundwater alterations in this regional karst aquifer system is difficult due to preferential flow paths, blasting, and widespread aquifer withdrawals and injections. Additionally, hydrologic models do not reveal subsurface impacts to the biotic environment, such as destruction of vegetative buffers, which are essential habitat for endangered and threatened species and other wildlife, and degradation from invasive species responding to hydroperiod disruptions. Our case study uses remote sensing and a geographic information system (GIS) to evaluate near-infrared (NIR) data for natural herbaceous depressional (wet prairie) wetlands in a central Florida phosphate mining area. These wetlands characteristically are dominated by graminoids, which have lower NIR reflectance and consequent digital numbers (DNs) in remotely sensed imagery than invasive species associated with hydroperiod alterations. Maximum aquifer withdrawals of 76,457 m 3 /d were permitted in November 1977 and remain active for study-area mines, which are surrounded primarily by un-irrigated pasture. Digital color infrared aerial imagery acquired in winter 2003–04 (1-m ground resolution) was used to extract NIR values within depressional wetlands. Digital historic (mid-1950s) U.S. Geological Survey topographic quadrangle maps (1:24,000 scale) were selected to delineate baseline wetland boundaries using ESRI ArcGIS 9.2. The study area included 567 of these wetlands, totaling 1,367 hectares. High mean NIR values (≥100 DN) consistent with hydroperiod-altered wetlands dominated by invasive plant species characterized 284 wetlands (50 and 60 percent total number and area, respectively), including some >5 km from study-area mines. Only 108 wetlands (20 and 10 percent total number and area, respectively) had low mean NIR values (≤80 DN) indicative of natural wet prairies without invasive species. Shallow ditches were not a statistically significant factor influencing NIR signatures in these wetlands. The spatial distribution of wetlands with high NIR DNs was inconsistent with conical groundwater drawdown predicted by groundwater models but suggests more linear fluid movement via subsurface preferential NW-SE flow paths.

Microbial Characteristics of a Submerged Karst Cave System in Northern Florida

Karst aquifer systems contain submerged caves that act as conduits for subterranean water flow and are subject to rapid surface recharge at points such as sink holes and submerging streams. We examined the microbial communities in six conduits of the Northern Florida Wakulla Springs cave system and in several hydrologically connected surface sinks. Culturable bacteria were assessed using both oligotrophic and copiotrophic media, and specific media for Enterococcus and Escherichia coli. Culture independent methods included using 16S rRNA PCR amplified DNA for T-RFLP analysis and development of clone libraries for sequencing. Pronounced seasonality was found in all microbiological parameters suggesting responsiveness to surface conditions from recharge of the groundwater despite near constant groundwater temperature. Other differences may reflect the character of the drainage areas feeding different conduits and flow rates and flow reversals that affected residence time in cave conduits. In a region of groundwater flow divide, elevated numbers of a plate counts, flocculent material, and a sulfide smell were reflected in T-RFLP pattern differences. Sequence data from five selected sampling locations revealed the presence of Enterobacter and Klebsiella sequences in surface waters, but not in conduits. One conduit contained a high percentage of sequences with close homology to the archaeal species Thermococcalles archaeon. Other cave-specific sequences were found that do not match previously characterized bacteria. Overall, the data suggest both temporal and spatial differences in the microbial communities within the extensive cave system conduits feeding the spring vent, reflecting both drainage area influences and undocumented subterranean microbial diversity.

Karst Interest Group 2011

The United States Geological Survey (USGS) Karst Interest Group (KIG) held its fifth triennial meeting at the University of Arkansas in Fayetteville, Arkansas, during April 26–29, 2011. After an interesting keynote presentation by Art Palmer on paleokarst of the USA, oral and poster presentations were given during 2-day sessions on a variety of topics, including karst in coastal zones, geochemistry and contaminant transport in karst systems, karst mapping and GIS, karst program updates, Ozarks plateau karst, karst aquifer systems, karst modeling, karst hydraulics, and geophysical methods in karst. There were 123 people registered for the meeting from government agencies, universities, state, and local agencies. Goals of the USGS KIG are to encourage and support interdisciplinary collaboration and technology transfer among scientists working in karst areas. The KIG encourages cooperative studies between the different disciplines of the USGS and other Department of Interior agencies and university researchers or research institutes. Previous KIG meetings were held in St. Petersburg, Florida (2001), Shepherdstown, West Virginia (2002), Rapid City, South Dakota (2005), and Bowling Green, Kentucky (2008). The next meeting is scheduled for 2014 in Carlsbad, New Mexico. For the 2011 meeting, field trips were organized on the geology and karst landscapes of the Buffalo National River and other karst features in northern Arkansas and southern Missouri. A good time was had by all, despite the recordbreaking rainfall and flooding prior to and during the first 2 days of the meeting. Proceedings from the 2011 KIG meeting have been published in the U.S. Geological Survey Scientific Investigations Report 2011-5031, which is available on-line at: http://pubs.usgs.gov/sir/2011/5031/. For additional information about KIG, please visit the KIG website at: http://water.usgs.gov/ogw/karst/kig/ or contact Eve Kuniansky (elkunian@usgs.gov) (770-409-7716).

Recharge rate estimation in the Mountain karst aquifer system of Figeh spring, Syria

Figeh watershed spring is one of the important groundwater aquifer, which is considered a major source for drinking waters of Damascus city and countryside. The origin identification and recharge estimates of groundwater are significant components of sustainable groundwater development in this Mountain karst aquifer of Figeh spring. During the period 2001–2009, monthly groundwater and precipitation samples were taken and the isotopic compositions of δ18O, δ2H, and chloride contents were analyzed to identify groundwater origins and to estimate recharge rates. The δ18O, δ2H of the groundwater show that the groundwater recharge is of meteoric origin. The chloride mass balance (CMB) method was used to quantify recharge rates of groundwater in the Mountain karst aquifer of Figeh spring. The recharge rate varies from 192 to 826 mm/year, which corresponds to 43 and 67% of the total annual rainfall. Recharge rates estimated by CMB were compared with values obtained from other methods and were found to be in good agreement. This study can be used to develop effective programs for groundwater management and development.

Contributions of C3/C4 organic materials and carbonate rock to dissolved inorganic carbon in a karst groundwater system on Miyakojima Island, southwestern Japan

Summary Groundwater δ 13 C values and chemical compositions were employed to quantitatively evaluate the controlling processes and sources of dissolved inorganic carbon in a karst aquifer system on Miyakojima Island (MI), southwestern Japan. Most MI groundwater is Ca–HCO 3 type water, but some Na–Cl, Ca–Cl, or Na–HCO 3 type groundwaters occur, formed mainly by seawater intrusion and partly by cation exchange reactions. Calculations using the WATEQ4F and PHREEQC programs revealed that all MI groundwater, not just the Ca–HCO 3 type, was strongly influenced by calcite dissolution in a karst aquifer system open with respect to soil CO 2 , initially derived from organic materials with mainly around 10–50 matm as pCO 2 , and that most groundwater was saturated with respect to calcite. Moreover, oxidation of ammonium sulfate (applied as fertilizer) added H + to the MI groundwater, resulting in surplus calcite dissolution. These processes sufficiently explained contents of alkalinity, DIC, and Ca 2+ in the groundwater, and were evaluated by model calculation using the PHREEQC program with measured groundwater δ 13 C and pH values. The results showed that the average mass fractions of dissolved inorganic carbon (DIC) initially from calcite dissolution and C3 and C4 organic materials in the groundwater were 46.4%, 18.5%, and 35.1%, respectively. The model results regarding the origins of DIC in the groundwater agreed fairly well with land use distributions on MI, in particular, with the spatial distribution of forest and sugarcane fields, and gave us some constrains of groundwater recharge areas and flowpaths.

Temperature-driven meltwater production and hydrochemical variations at a glaciated alpine karst aquifer: implication for the atmospheric CO2 sink under global warming

About two hydrological years of continuous data of discharge, temperature, electrical conductivity and pH have been recorded at the Glarey spring in the Tsanfleuron glaciated karst area in the Swiss Alps, to understand how glaciated karst aquifer systems respond hydrochemically to diurnal and seasonal recharge variations, and how calcite dissolution by glacial meltwater contributes to the atmospheric CO2 sink. A thermodynamic model was used to link the continuous data to monthly water quality data allowing the calculation of CO2 partial pressures and calcite saturation indexes. The results show diurnal and seasonal hydrochemical variations controlled chiefly by air temperature, the latter influencing karst aquifer recharge by ice and snowmelt. Karst process-related atmospheric CO2 sinks were more than four times higher in the melting season than those in the freezing season. This finding has implication for understanding the atmospheric CO2 sink in glaciated carbonate rock terrains: the carbon sink will increase with increasing runoff caused by global warming, i.e., carbonate weathering provides a negative feedback for anthropogenic CO2 release. However, this is a transient regulation effect that is most efficient when glacial meltwater production is highest, which in turn depends on the future climatic evolution.

Sustainable yield of a karst aquifer system: a case study of Jinan springs in northern China

Based on the long-term monitoring data of rainfall, groundwater levels, groundwater abstraction, spring flow rates and groundwater quality, an assessment has been undertaken of the sustainable yield of a karst aquifer system in Shandong Province, northern China, to maintain perennial outflow of the karst springs while meeting water demands. One of the fundamental indicators for sustainable yield of groundwater is identified as maximum allowable water-level drawdown. A regional three-dimensional finite-difference numerical model has been developed to optimize the schemes associated with well fields and their locations and sustainable yields, in the Jinan spring catchment and its adjacent karst groundwater catchments, with the aim of maintaining the water level higher than the allowable lowest water level of 27.5 m above sea level. Furthermore, measures necessary to move towards sustainable use of the karst groundwater are outlined, drawing on contingency plans of water-source replacement and artificial recharge, dual water supply (based in water quality), use of the spring waters themselves, and groundwater quality protection.

Identification of a karst system’s intrinsic hydrodynamic parameters: upscaling from single springs to the whole aquifer

For water management purposes, information about an entire aquifer system is generally more important than information about a specific spring. Since a karstic aquifer system might drain to several outlets, conclusions derived from a single spring can be misleading for characterization and modeling. In this study we apply a conceptual model to an Alpine dolomite karst system in Austria. The particular challenge was that several small springs with strongly varying hydrological behavior and diffuse flow into surrounding streams drain this system. Instead of applying the model to a single spring, it was calibrated simultaneously to several observations within the system aiming to identify the karst system’s intrinsic hydrodynamic parameters. Parameter identification is supported by modeling the transport of water isotopes (δ18O). The parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty. The results show that it is possible to identify system intrinsic parameters. But the sensitivity analysis revealed that some are hardly identifiable. Only by considering uncertainty reasonable predictions can be provided for the whole system. Including isotopic information increases the sensitivity of some intrinsic parameters, but it goes along with a sensitivity decrease for others. However, a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling routines.