Karst

New geochemical data on dissolved major and minor constituents in 276 groundwater samples from Etna aquifers reveal the main processes responsible for their geochemical evolution and mineralisation. This topic is of particular interest in the light of the progressive depletion of water resources and groundwater quality in the area. Multivariate statistical analysis reveal 3 sources of solutes: (a) the leaching of the host basalt, driven by the dissolution of magma-derived CO2; (b) mixing processes with saline brines rising from the sedimentary basement below Etna; (c) contamination from agricultural and urban wastewaters. The last process, highlighted by increased concentrations of SO4, NO3, Ca, F and PO4, is more pronounced on the lower slopes of the volcanic edifice, associated with areas of high population and intensive agriculture. However, this study demonstrates that natural processes (a) and (b) are also very effective in producing highly mineralised waters, which in turn results in many constituents (B, V, Mg) exceeding maximum admissible concentrations for drinking water.

Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending to a cave-forming zone from below in leaky confined conditions, where deeper groundwaters in regional or intermediate flow systems interact with shallower and more local groundwater flow systems. This is in contrast to more familiar epigenic speleogenesis which is dominated by shallow groundwater systems receiving recharge from the overlying or immediately adjacent surface.Hypogenic caves are identified in various geological and tectonic settings, formed by different dissolutional mechanisms operating in various lithologies. Despite these variations, resultant caves demonstrate a remarkable similarity in patterns and meso-morphology, which strongly suggests that the hydrogeologic settings were broadly identical in their formation. Hypogenic caves commonly demonstrate a characteristic suite of cave morphologies resulting from rising flow across the cave-forming zone with distinct buoyancy-dissolution components. In addition to hydrogeological criteria (hydrostratigraphic position, recharge–discharge configuration and flow pattern viewed from the perspective of the evolution of a regional groundwater flow system), morphogenetic analysis is the primary tool in identifying hypogenic caves.Cave patterns resulting from ascending transverse speleogenesis are strongly guided by the permeability structure in a cave formation. They are also influenced by the discordance of permeability structure in the adjacent beds and by the overall hydrostratigraphic arrangement. Three-dimensional mazes with multiple storeys, or complex 3-D cave systems are most common, although single isolated chambers, passages or crude clusters of a few intersecting passages may occur where fracturing is scarce and laterally discontinuous. Large rising shafts and collapse sinkholes over large voids, associated with deep hydrothermal systems, are also known.Hypogenic caves include many of the largest, by integrated length and by volume, documented caves in the world. More importantly, hypogenic speleogenesis is much more widespread than it was previously presumed. Growing recognition of hypogenic speleogenesis and improved understanding of its peculiar characteristics has an immense importance to both karst science and applied fields as it promises to answer many questions about karst porosity (especially as deep-seated settings are concerned) which remained poorly addressed within the traditional epigenetic karst paradigm.

In many places throughout the world, drinking water is frequently contaminated by turbidity. Such turbidity, however, as representative of particle transport, can be used as to trace certain features of particle transport properties. In order to investigate the relation between particle and dissolved species transport and hydrodynamics in karst systems, correlation and spectral analyses were performed on time series of rainfall (input signal), and water level, specific conductance, and turbidity (output signals) at a karst spring system in the chalk aquifer of the lower Seine valley, France. This system is composed of a spring connected to a sinkhole on the chalk plateau where a small creek enters the subsurface. The autocorrelation functions for water level and turbidity showed a short memory effect, demonstrating the short duration of the influence of flood events on these two parameters, whereas specific conductance (representing less-mineralized storm-derived water) had a much longer memory effect. These results were interpreted as reflecting the rapid reactivity of the spring to rain events, with storage of water in the fissured chalk explaining the longer memory effect for specific conductance than for particles. Energy spectra computed by fast Fourier transform of autocorrelation functions showed a strong structure in the output signals, whereas the input signal (rainfall) was random, thus allowing assessment and comparison of system behaviour regarding dissolved and solid transport, as well as hydraulics. Cross-correlation functions (which allow an assessment of impulse response functions) confirmed the low inertia of the system for water level and turbidity and the much higher inertia for specific conductance. In addition to the main peak, two secondary peaks in the cross-correlation functions suggest the existence of additional flowpaths that might involve the contribution of other point-source recharge and/or delayed infiltration through the clayey surficial formation and solution pipes, which could act as epikarst. Analysis using continuous wavelet spectra allowed a better investigation of the rainfall signal structure and highlighted a strong relationship between turbidity and rainfall, which could not be deduced from the energy spectra. Specific spectral components in water level were isolated and a time-domain reconstruction using inverse wavelet transform allowed separation of quick-flow and slow-flow components.

Abstract: Channel water balance analysis based on streamflow loss coupled with traced groundwater
basins allow refinement of upland autogenic recharge values comparable to those derived from more
precise site-scaled measurements. Based on total discharge and calculated flow loss in major stream
channels, the channel contributions to recharge on the Barton Springs Segment of the Edwards (Balcones
Fault Zone) Aquifer are: Onion Creek (32.6%), Barton Creek (less than 10.5%), Slaughter Creek (7.2%),
Bear Creek (6.2%), Blanco River (6%), Little Bear Creek (3.4%), and Williamson Creek (1%). Major stream
channels contributed from 56% to 67% of total groundwater recharge to the groundwater system, 17%
of which was stream autogenic recharge, while upland autogenic recharge and other smaller sources
contributed the remaining 33% to 44%. As a percent of precipitation over the Edwards Aquifer outcrop
source area, autogenic recharge (upland and tributary recharge in the major stream channels) was 22% to
28%, compared with a recharge value of 28% of precipitation from climate tower water balances in Central
Texas. Prior to delineation of groundwater basins using injected tracers, older channel water balance
studies determined that upland autogenic recharge was only 15% of the total groundwater recharge (about
1% of precipitation). This study suggests that the channel water balance approach, based on gauged
streamflow and spring discharge, is more accurate when one incorporates groundwater basins delineated
by groundwater tracing, especially in karst aquifers. Refinement of an appropriate catchment area for the
calculation of autogenic recharge also significantly affected the results of a precipitation water balance.

The late Holocene environmental history of two karstic uplands in the Burren, western Ireland is reconstructed. The palaeoecological investigations focus on species-rich, upland plant communities of high biogeographic interest that include Sesleria-dominated grasslands and heath communities with Dryas octopetala, Arctostaphylos uva-ursi and Empetrum nigrum. Short monoliths taken from shallow peats were pollen analytically investigated. Particular attention was paid to non-pollen palynomorphs, and especially coprophilous fungal spores as indicators of environmental change and pastoral activity at local level. The exposed north-west Burren uplands carried Pinus sylvestris-dominated woodland during the mid and late Bronze Age. The demise of pine on these uplands at ca. 600 B.C. is ascribed to human impact. Evidence is presented for increased pastoral activity in the uplands from early medieval times (ca. sixth century A.D.) onwards. Farming, involving intensive grazing of the uplands, attained greatest intensity during the late 18th and early 19th century, and resulted in more or less total clearance of Corylus scrub which, prior to that, was common in both the upland and lowland Burren. The potential of non-pollen palynomorphs and especially the coprophilous fungal spore record for elucidating traditional Burren farming practices, including winterage (a type of transhumance), is highlighted.

Not only the nutritional status and biological activity but also the soil ecological functioning or soil health has been impacted profoundly by land degradation in the karst area of southwest China where the karst ecosystems are generally considered as extremely vulnerable to land degradation under intensified land-use changes. The objectives of this study are to elucidate the changes in overall soil quality by a holistic approach of soil nutritional, biological activity, and soil health indicators in the karst area as impacted by intense cultivation and vegetation degradation. Topsoil samples were collected on selected eco-tesserae in a sequence of land degradation in a karst area of southwest Guizhou in 2004. The soil nutrient pools of organic carbon (Corg), extractable extracellular carbon (Cext), total soil nitrogen (Nt), alkali-hydrolyzable nitrogen (Nah), total phosphorus (Pt), available phosphorus (Pa) were analyzed by wet soil chemistry. The soil biological properties were studied by means of measurements of microbial biomass carbon (both by fumigation–extraction, FE-Cmic, and by calculation from substrate-incubation respiration, SIR-Cmic) of respiration [respiration without addition of substrates, basal respiration (BR), and potential respiration (PR) with substrate-incubation] and of soil enzyme activities (invertase, urease, and alkaline phosphatase). Soil health status was assessed by simple indices of Cmic/Corg and BR/Cmic in conjunction with bacterial community structures determined by polymerase chain reaction and denaturing gradient gel electrophoresis. While the nutritional pool parameters, such as Corg and Cext, described basically the changes in soil life-supporting capacity with cultivation interference and vegetation declined, those parameters of biological activity such as FE-Cmic, SIR, and SIR-Cmic as well as bacterial community structures measured by molecular method evidenced well the changes in soil functioning for ecosystem health with the land degradation.

A step from resource to source vulnerability mapping is presented, based on the European COST Action 620 approach for karst groundwater protection. Guidelines on vulnerability assessment of the horizontal groundwater flow path within the karst saturated zone (K factor) are proposed. By integrating this into the previously existing COP method for intrinsic resource vulnerability mapping, adequate source protection can be assessed. The proposed “Karst saturated zone (K) factor” assessment considers groundwater travel time (t subfactor), connection and contribution to the source (r subfactor) and active conduit or fissured network (n subfactor). The extended COP method was applied in two carbonate aquifers in southern Spain with different geological, hydrogeological and climate settings. The results are coherent with previous research results of the studied areas. Moreover, they are consistent with the occasional groundwater contamination detected in one of the springs. On the other hand, an absence of contamination, despite high risk, justifies the lower degrees of vulnerability assigned to the sources surveyed. The source vulnerability maps obtained can thus be used as a basis for the delineation of protection zones.

In a karst system, the characterization of transport properties is based on the comparison of natural tracers observed at the inlet (a swallow hole on the karst plateau) and the outlets of the system (a spring and a well). At Norville, northwest France, electrical conductivity (EC) and turbidity (T) were used as natural tracers for characterizing dissolved elements (surface water geochemistry) and particulate matter transport, respectively. Two methods were used for this study: (1) a comparison of the relations between EC, T and spring discharge (Q) by means of normalized EC–T–Q curves, and (2) a principal component analysis (PCA) including water geochemistry data in addition to EC, T and Q. Three different characteristic flood events have been chosen for the analyses. EC–T–Q curves highlighted the direct transfer, resuspension and deposition of particles during their transport in the karst network. Transport from the swallow hole to both the spring and the well appeared to be dominated by karst-conduit flow. On the other hand, PCA results showed a diffuse source of contamination of groundwaters by nitrate and a point-source contamination of groundwaters by streaming/runoff surface waters with high turbidity and phosphate concentration infiltrated at the swallow hole. Dans un système karstique, la caractérisation des propriétés de transport est basée sur la comparaison des traceurs naturels observés à l’entrée (une dépression sur le plateau karstique) et à la sortie du système (une source et un puits). A Norville, Nord-Ouest de la France, la conductivité électrique (EC) et la turbidité (T) ont été utilisées comme traceurs naturels pour caractériser les éléments dissous (géochimie des eaux de surface) et le transport des particules en suspension, respectivement. Deux méthodes ont été utilisées dans cette étude: (1) une comparaison des relations entre EC, T et le débit de la source (Q) au moyen de courbes EC–T–Q normalisées, et (2) une analyse en composante principale (ACP) incluant les données géochimiques de l’eau en complément de EC, T et Q. Trois différents évènements de crues caractéristiques ont été choisis pour les analyses. Les courbes EC–T–Q ont mis en évidence le transfert direct, la remise en suspension et le dépôt des particules durant leur transport dans le réseau karstique. Le transport de la dépression vers la source et le puits apparaît comme dominé par l’écoulement en conduit karstique. D’un autre côté, les résultats de l’ACP ont montré une source diffuse de la contamination des eaux souterraines par les nitrates et une contamination ponctuelle des eaux souterraines par des eaux de surface de ruissellement et de cours d’eau présentant une turbidité et une concentration en phosphate élevées, infiltrées dans la dépression. En un sistema kárstico, la caracterización de las propiedades de transporte se basa en la comparación de trazadores naturales observados en la entrada (una sima somera en una superficie kástica) y la salida del sistema (un manantial y un pozo). En Norville, al Noroeste de Francia, la conductividad eléctrica (EC) y la turbidez (T) se usaron como trazadores naturales para caracterizar los elementos disueltos (geoquímica de aguas superficiales) y transporte de material particulado, respectivamente. Para este estudio, fueron utilizados dos métodos: (1) una comparación entre las relaciones de EC, T y descarga del manantial (Q) mediante curvas normalizadas EC–T–Q, y (2) un análisis de componentes principales (PCA) que incluye datos geoquímicos además de EC, T y Q. Para el análisis, se seleccionaron tres eventos de flujo característicos. Las curvas EC–T–Q pusieron de manifiesto la transferencia directa, resuspensión y sedimentación de las partículas durante su transporte en el sistema kárstico. El transporte desde la sima somera al manantial y al pozo parece estar dominado por el flujo por los conductos kársticos. Por otro lado, los resultados de PCA muestran una fuente difusa de contaminación de aguas subterráneas por nitratos y una contaminación puntual de aguas subterráneas por aguas superficiales con alta turbidez y concentraciones de fosfatos infiltradas en la sima somera.