Coastal Karst Aquifer Research Articles

Long distance seawater intrusion through a karst conduit network in the Woodville Karst Plain, Florida.

Five periods of increased electrical conductivity have been found in the karst conduits supplying one of the largest first magnitude springs in Florida with water. Numerous well-developed conduit networks are distributed in the Woodville Karst Plain (WKP), Florida and connected to the Gulf of Mexico. A composite analysis of precipitation and electrical conductivity data provides strong evidence that the increases in conductivity are directly tied to seawater intrusion moving inland and traveling 11 miles against the prevailing regional hydraulic gradient from from Spring Creek Spring Complex (SCSC), a group of submarine springs at the Gulf Coast. A geochemical analysis of samples from the spring vent rules out anthropogenic contamination and upwelling regional recharge from the deep aquifer as sources of the rising conductivity. The interpretation is supported by the conceptual model established by prior researchers working to characterize the study area. This paper documents the first and longest case of seawater intrusion in the WKP, and also indicates significant possibility of seawater contamination through subsurface conduit networks in a coastal karst aquifer.

Insights into saline intrusion and freshwater resources in coastal karstic aquifers using a lumped Rainfall–Discharge–Salinity model (the Port-Miou brackish spring, SE France)

The aim of this study was to develop a conceptual model of saline intrusion within coastal karst aquifers by analyzing Rainfall–Discharge–Salinity data and to assess freshwater resources using a lumped modeling approach. In a first step, we analyzed 4 years of data (rainfall, discharge and salinity times series) of the Port-Miou brackish submarine spring in South France (400 km2). A conceptual model of the aquifer was then designed to differentiate a deep brackish reservoir and a shallower fresh one. Salinity variations at the spring are assumed to be controlled mainly by dilution originating from the fresh water in the shallower reservoir. In a second step, a lumped modeling approach was developed based on the conceptual model to simulate discharge as well as salinity over time. We proposed a reservoir-model to take into account slow and fast components in the shallower part of the aquifer and a saline intrusion in the deeper one. This Rainfall–Discharge–Salinity model was calibrated and validated for two periods of 1.5 years at a daily time step and was also tested to reproduce a multi-annual evolution of the available discharge and salinity time series. Good simulation results were obtained to reproduce water and mass budgets as well as discharge and salinity dynamics during several hydrological cycles. The simultaneous modeling of hydrodynamics and quality data showed the robustness of the model in addition to its easy implementation. Our results led us to propose a new type of seawater mixing mechanism for brackish springs: the dilution type, in addition to the well-known Ventury suction and Head balance types. The application of the lumped model on the Port-Miou brackish spring validated the hydrogeological processes deduced from experimental data, given an initial quantification of the freshwater resources available in such complex brackish karstic aquifers.

Improved regional groundwater flow modeling using drainage features: a case study of the central northern karst aquifer system of Puerto Rico (USA).

In northern Puerto Rico (USA), subsurface conduit networks with unknown characteristics, and surface features such as springs, rivers, lagoons and wetlands, drain the coastal karst aquifers. In this study, drain lines connecting sinkholes and springs are used to improve the developed regional model by simulating the drainage effects of conduit networks. Implemented in an equivalent porous media (EPM) approach, the model with drains is able to roughly reproduce the spring discharge hydrographs in response to rainfall. Hydraulic conductivities are found to be scale dependent and significantly increase with higher test radius, indicating scale dependency of the EPM approach. Similar to other karst regions in the world, hydraulic gradients are steeper where the transmissivity is lower approaching the coastline. This study enhances current understanding of the complex flow patterns in karst aquifers and suggests that using a drainage feature improves modeling results where available data on conduit characteristics are minimal.

Monitoring and Management of Karstic Coastal Groundwater in a Changing Environment (Southern Italy): A Review of a Regional Experience

The population concentration in coastal areas and the increase of groundwater discharge in combination with the peculiarities of karstic coastal aquifers constitute a huge worldwide problem, which is particularly relevant for coastal aquifers of the Mediterranean basin. This paper offers a review of scientific activities realized to pursue the optimal utilization of Apulian coastal groundwater. Apulia, with a coastline extending for over 800 km, is the Italian region with the largest coastal karst aquifers. Apulian aquifers have suffered both in terms of water quality and quantity. Some regional regulations were implemented from the 1970s with the purpose of controlling the number of wells, well locations, and well discharge. The practical effects of these management criteria, the temporal and spatial trend of recharge, groundwater quality, and seawater intrusion effects are discussed based on long-term monitoring. The efficacy of existing management tools and the development of predictive scenarios to identify the best way to reconcile irrigation and demands for high-quality drinking water have been pursued in a selected area. The Salento peninsula was selected as the Apulian aquifer portion exposed to the highest risk of quality degradation due to seawater intrusion. The capability of large-scale numerical models in groundwater management was tested, particularly for achieving forecast scenarios to evaluate the impacts of climate change on groundwater resources. The results show qualitative and quantitative groundwater trends from 1930 to 2060 and emphasize the substantial decrease of the piezometric level and a serious worsening of groundwater salinization due to seawater intrusion.

Numerical study of groundwater flow cycling controlled by seawater/freshwater interaction in a coastal karst aquifer through conduit network using CFPv2

In this study, a groundwater flow cycling in a karst springshed and an interaction between two springs, Spring Creek Springs and Wakulla Springs, through a subground conduit network are numerically simulated using CFPv2, the latest research version of MODFLOW-CFP (Conduit Flow Process). The Spring Creek Springs and Wakulla Springs, located in a marine estuary and 11 miles inland, respectively, are two major groundwater discharge spots in the Woodville Karst Plain (WKP), North Florida, USA. A three-phase conceptual model of groundwater flow cycling between the two springs and surface water recharge from a major surface creek (Lost Creek) was proposed in various rainfall conditions. A high permeable subground karst conduit network connecting the two springs was found by tracer tests and cave diving. Flow rate of discharge, salinity, sea level and tide height at Spring Creek Springs could significantly affect groundwater discharge and water stage at Wakulla Springs simultaneously.Based on the conceptual model, a numerical hybrid discrete-continuum groundwater flow model is developed using CFPv2 and calibrated by field measurements. Non-laminar flows in conduits and flow exchange between conduits and porous medium are implemented in the hybrid coupling numerical model. Time-variable salinity and equivalent freshwater head boundary conditions at the submarine spring as well as changing recharges have significant impacts on seawater/freshwater interaction and springs’ discharges. The developed numerical model is used to simulate the dynamic hydrological process and quantitatively represent the three-phase conceptual model from June 2007 to June 2010. Simulated results of two springs’ discharges match reasonably well to measurements with correlation coefficients 0.891 and 0.866 at Spring Creeks Springs and Wakulla Springs, respectively. The impacts of sea level rise on regional groundwater flow field and relationship between the inland springs and submarine springs are evaluated as well in this study.

Regional response of the coastal aquifer to Hurricane Ingrid and sedimentation flux in the Yax Chen cave system (Ox Bel Ha) Yucatan, Mexico

Abstract Coastal karst aquifers are an important source of potable water which can be affected by external forcing on various temporal and spatial scales (e.g. sea-level) but there is a lack of long-term data to understand their response. Sediment cores and their proxy records have been used in lakes and oceans to assess past environmental change, but haven't been extensively applied to anchialine caves where there is less known about the physical, biological and chemical processes affecting sedimentation. Over fifty sediment traps were placed in Yax Chen which is part of the Ox Bel Ha cave system near Tulum, Mexico and four water level sensors were placed in two additional cave systems (Ponderosa, Sac Actun) for comparative water table fluctuations. Data collected over the past three years (2011–2013) captured seasonal and spatial sediment flux including the effect of an intense rainfall associated with Hurricane Ingrid (September 18, 2013). The data indicates that sediment deposition was controlled by cenote size and the presence of mangrove. Areas upstream of Cenote Gemini had negligible sediment accumulation as there were few cenotes and the terrain is dominated by lowland tropical forest, while areas downstream from Cenote Gemini were dominated by mangrove forests and larger cenotes which resulted in higher sediment accumulation rates (0.014 vs. 0.22 mg/cm 2 /day). Bi-annual sedimentation rates in 2013–2014 were higher in the months after the rainy season (0.2 vs. 0.5 mg/cm 2 /day) indicating that cenote productivity was likely controlling sedimentation. Mangrove areas with their peat accumulations occlude the porous karst causing funneling of nutrient rich rainwater into the sunlit cenotes enhancing primary productivity and sedimentation in downstream areas. Hurricane Ingrid had little effect on the yearly sediment rate even though water table fluctuations were high (0.7 m) compared to the yearly values (0.3 m). This likely is due to water bypassing the cenotes with little residence time to enhance productivity and sedimentation in downstream areas.

Reactive-transport modelling of gypsum dissolution in a coastal karst aquifer in Puglia, southern Italy

The gypsum coastal aquifer of Lesina Marina (Puglia, southern Italy) has been affected by sinkhole formation in recent decades. Previous studies based on geomorphologic and hydrogeological data ascribed the onset of collapse phenomena to the erosion of material that fills palaeo-cavities (suffosion sinkholes). The change in the hydrodynamic conditions of groundwater induced by the excavation of a canal within the evaporite formation nearly 100 years ago was identified as the major factor in triggering the erosion, while the contribution of gypsum dissolution was considered negligible. A combined reactive-transport/density-dependent flow model was applied to the gypsum aquifer to evaluate whether gypsum dissolution rate is a dominant or insignificant factor in recent sinkhole formation under current hydrodynamic conditions. The conceptual model was first defined with a set of assumptions based on field and laboratory data along a two-dimensional transect of the aquifer, and then a density-dependent, tide-influenced flow model was set up and solved using the numerical code SEAWAT. Finally, the resulting transient flow field was used by the reactive multicomponent transport model PHT3D to estimate the gypsum dissolution rate. The validation tests show that the model accurately represents the real system, and the multi-disciplinary approach provides consistent information about the causes and evolution time of dissolution processes. The modelled porosity development rate is too low to represent a significant contribution to the recent sinkhole formation in the Lesina Marina area, although it justifies cavity formation and cavity position over geological time.

Influence of submarine groundwater discharge on seawater properties in Rovanjska-Modrič karst region (Croatia)

Coastal karst aquifers are dynamic hydrogeological systems with substantial hydrological, geomorphological and ecological impacts on the marine and coastal karst ecosystems, mostly induced by the submarine groundwater discharge (SGD). This paper presents complex hydrogeological settings of the Rovanjska-Modric coastal karst region on the eastern Adriatic coast characterized by: (1) high temporal and spatial variations in seawater properties; (2) significantly reshaped coastal bottom morphology, and (3) plethora of associated biocenoses from fresh water, brackish, marine and cave assemblages. With the aim of resolving spatiotemporal interconnections of SGD and marine environment changes, we conducted field prospection and seasonal measurements of different water properties on- and off-shore. Obtained results pointed to: (1) the composite recharge system consisting of numerous sinking rivers in the distant hinterland (with different climate settings) and local precipitation input; (2) specific discharge settings highly governed by a complicated karst conduits network, the hydrological situation in the hinterland and local meteorological conditions, i.e. one system that permanently feeds coastal and probably submarine springs, while the other operates periodically; (3) disturbed winter isothermy and three-layered summer stratification of the seawater column, and (4) slightly changed trophic settings. All of that is the consequence of extreme heterogeneity of the coastal karst aquifer, characteristic for the eastern Adriatic coast.

Origin of groundwater salinity and hydrogeochemical processes in a confined coastal karst aquifer: A cause of the Mandalia Bay (southeastern Aegean Sea coasts)

There are numerous springs and wells within the context of this research about the part of northern and northeastern in The Mandalia Bay which has an important role regarding tourism and agriculture in Turkey’s Southeastern Aegean coasts. There are an important springs in this basin, as the high discharge with values Ekinambari springs for 5385 l/s, Savrankoy springs for 4215 l/s, Avsar springs for the 1000 l/s, Sucikti springs (Karacahisar) to 400 l/s. The change of the total annual flow observations compatible with each other, an increase was observed in springs of Ekinambari, Savrankoy and Sucikti. The springs group of Ekinambari, is located from the sea about 10 km away in the alluvium. These springs were at the foot of the hill at various points at 46 m altitude, different flow rates and temperatures, allochthonous limestone flows from the broken system. The springs in the investigation area, which was measured in the high current values, of Savrankoy and Ekinambari springs monthly average current value of resources are examined, the difference between the current value is less than by months. In this spring waters of high salinity values (0,5 to 36,2‰) was determined. In this study were questioned as origin of ground water salinity from deep aquifer formations or from current sea water? In the case of salinity, in spring waters have occurred on deep towards the karstic levels of limestones from sea water is saturation. Examined the water was fed by a high level, the transition period is short and in aquifer in contact with shallow circulating water for a short time is. They could say that mixing different amounts of surface water were also. Given these results, the most important spring waters for the region (Savrankoy, Ekinambarı, etc.,) of ground water movement in karstic system pressure and decreasing/increasing rate of interventions performed in the presence of a seawater can be mentioned.

Electrical resistivity tomography (ERT) of a coastal carbonate aquifer (Port-Miou, SE France)

As part of a larger regional research program “KarstEAU”, the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry.

The possible negative consequences of underground dam and reservoir construction and operation in coastal karst areas: an example of the hydro-electric power plant (HEPP) Ombla near Dubrovnik (Croatia)

Abstract. The Ombla Spring represents a typical abundant coastal karst spring located in the vicinity of the town of Dubrovnik (Croatia). Its outlet is at an altitude of 2.5 m above sea level (m a.s.l.) and the water from it immediately flows into the Adriatic Sea. The minimum and maximum measured discharges are 3.96 m3 s−1 and 117 m3 s−1, respectively. The Trebišnjica River traverses through its catchment. The mean annual discharge, after the canalization of over 60 km of its watercourse with spray concrete (in the time span 1981–2011), is 24.05 m3 s−1. Before massive civil engineering work which took place during 1968–1980, the mean annual discharge was 28.35 m3 s−1. There is a project for construction of the hydro-electric power plant (HEPP) Ombla, which will exclusively use groundwater from the Ombla Spring karst aquifer. The underground dam will be constructed about 200 m behind the existing karst spring outflow in the karst massif, by injecting a grout curtain. The top of the grout curtain is planned to be at an altitude of 130 m a.s.l. This karst system is complex, sensitive, vulnerable and ecologically extremely valuable. The grout curtain, as well as the HEPP Ombla development, could lead to extremely dangerous technical and environmental consequences. In this paper some probable, negative consequences of the HEPP Ombla construction and development are explained. The HEPP Ombla could result in many large and hard-to-predict negative consequences which are specific for this particular HEPP, for example (1) severe spring discharge change; (2) unpredictable regional groundwater redistribution; (3) threatening of endemic fauna; (4) induced seismicity; (5) induced sinkholes; (6) occurrence of landslides; (7) conflict regarding internationally shared karst aquifers; (8) intensification of karst flash floods; (9) sea water intrusion in coastal karst aquifer; etc.

Origin of groundwater salinity (current seawater vs. saline deep water) in a coastal karst aquifer based on Sr and Cl isotopes. Case study of the La Clape massif (southern France)

In this study a typical coastal karst aquifer, developed in lower Cretaceous limestones, on the western Mediterranean seashore (La Clape massif, southern France) was investigated. A combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer. Water samples were collected between 2009 and 2011. Three groundwater groups (A, B and C) were identified based on the hydrogeological setting and on the Cl− concentrations. Average and maximum Cl− concentrations in the recharge waters were calculated (ClRef. and ClRef.Max) to be 0.51 and 2.85mmol/L, respectively). Group A includes spring waters with Cl− concentrations that are within the same order of magnitude as the ClRef concentration. Group B includes groundwater with Cl− concentrations that range between the ClRef and ClRef.Max concentrations. Group C includes brackish groundwater with Cl− concentrations that are significantly greater than the ClRef.Max concentration. Overall, the chemistry of the La Clape groundwater evolves from dominantly Ca–HCO3 to NaCl type. On binary diagrams of the major ions vs. Cl, most of the La Clape waters plot along mixing lines. The mixing end-members include spring waters and a saline component (current seawater or fossil saline water). Based on the Br/Clmolar ratio, the hypothesis of halite dissolution from Triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater.Groundwaters display 87Sr/86Sr ratios intermediate between those of the limestone aquifer matrix and current Mediterranean seawater. On a Sr mixing diagram, most of the La Clape waters plot on a mixing line. The end-members include the La Clape spring waters and saline waters, which are similar to the deep geothermal waters that were identified at the nearby Balaruc site. The 36Cl/Cl ratios of a few groundwater samples from group C are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix. Finally, PHREEQC modelling was run based on calcite dissolution in an open system prior to mixing with the Balaruc type saline waters. Modelled data are consistent with the observed data that were obtained from the group C groundwater. Based on several tracers (i.e. concentrations and isotopic compositions of Cl and Sr), calculated ratios of deep saline water in the mixture are coherent and range from 3% to 16% and 0% to 3% for groundwater of groups C and B, respectively.With regard to the La Clape karst aquifer, the extension of a lithospheric fault in the study area may favour the rise of deep saline water. Such rises occur at the nearby geothermal Balaruc site along another lithospheric fault. At the regional scale, several coastal karst aquifers are located along the Gulf of Lion and occur in Mezosoic limestones of similar ages. The 87Sr/86Sr ratios of these aquifers tend toward values of 0.708557, which suggests a general mixing process of shallow karst waters with deep saline fossil waters. The occurrence of these fossil saline waters may be related to the introduction of seawater during and after the Flandrian transgression, when the highly karstified massifs invaded by seawater, formed islands and peninsulas along the Mediterranean coast.

Origin of Salinity in a Coastal Karst System: La Clape Massif, SE France

Recent increases in groundwater salinity, exceeding the guidelines for irrigation, prompted this investigation on the origin of mineralisation in the La Clape karst aquifer (SE France). The La Clape massif (Aude) is a typical Jurassic and Cretaceous carbonate aquifer that was deeply karstified during the Messinian crisis. The massif is affected by the vicinity of the Cevennes lithospheric fault, and numerous normal faults related to the Oligocene distension event. Potential sources of salinity are seawater intrusion, upward migration of deep saline waters, as well as dissolution of Triassic evaporites. A contribution from halite can be ruled out on the basis of the measured Br/Cl ratios that are similar to that of seawater and deep saline waters. Sr concentrations suggest mixing with an end member slightly more enriched in Sr than current seawater. Ranging from 0.707852 to 0.708875, 87Sr/86Sr ratios of groundwaters are lower than that of modern Mediterranean seawater (0.709163), and higher than that of the carbonate matrix, ranging from 0.707276 to 0.707477. Those ratios tend towards that of deep saline groundwaters observed at the nearby site of Balaruc. 36Cl/Cl ratios measured on a few samples agree with a mixing hypothesis of superficial karst waters with deep saline water at secular equilibrium with the carbonate matrix. Including dissolution of carbonate and mixing with a saline end member, PHREEQ C modelling confirms that Balaruc-type waters are a likely end member. Calculated parts of mixing range from 0 to 16% of deep saline water. This suggests that seawater intrusion in the karst system is prevented by thick off-shore sedimentary deposits. The deeply faulted and karstified La Clape system is likely to favor the upward movement of deep saline waters. At the regional scale, saline groundwaters of three coastal karst aquifers located along the Gulf of Lion show 87Sr/86Sr ratios tending towards a Sr isotopic ratio of 0.70847. This may suggest a similar origin for the observed salinities in these coastal karst systems, by upward movement of deep saline waters.

Water supply spring zone Novljanska Žrnovnica (Croatia) – new quantities of drinking water in the conditions of salt water intrusion

This paper presents an approach for solving the problem of exploitation of freshwater in the coastal karst aquifer during summer dry periods in the conditions of potential salt water intrusion. The approach is presented on the example of spring zone Novljanska Žrnovnica, situated in the northern part of Croatian Adriatic coastal region. The spring zone is used for water supply (about 250 l/s) of an important tourist area of Crikvenica and Novi Vinodolski. After unsuccessful attempts of physical separation of freshwater system from the sea influence, by construction of grout curtain, hydrogeological studies have focused on the possibility of groundwater capturing in the hinterland of discharge zone, outside of the zone of periodical salinity. The final research results with the exploitation well in the spring hinterland can serve as a model for research and exploitation of drinking water in natural conditions of unstable freshwater-saltwater interface in similar natural conditions.

Effects of drought and subtidal sea-level variability on salt intrusion in a coastal karst aquifer

In many coastal regions, groundwater is the main water source for humans. However, because of population growth and sea-level rise, many coastal aquifers increasingly suffer from salt intrusion, especially in karstic areas where the high permeability and porosity of the rock favours salt penetration. We collected field data from a Mexican karst system to show that sea-level variability at low frequencies (subtidal) may induce salt penetration further inland and generate larger oscillations than those observed at tidal frequencies. Measurements of conductivity and pressure from inland wells (5 and 10 km) and from substantial (~1 m3 s–1) submarine groundwater discharge (SGD) at ~2-m depth entering a shallow ocean were analysed. We found that sea and piezometric levels co-oscillated at subtidal frequencies, with a correlation of 0.6 and a differential lag. Conductivity of the SGD resembled that of the aquifer. Intense droughts driven by the 2009 ‘El Niño’ event markedly increased the conductivity of the aquifer and its discharge. Our findings indicated that coastal land use and the consequences of climate change (i.e. sea-level rise and the alteration of rain patterns) on the Yucatan Penisula threaten water availability.

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.

Contaminants in the coastal karst aquifer system along the Caribbean coast of the Yucatan Peninsula, Mexico

Intensive land development as a result of the rapidly growing tourism industry in the “Riviera Maya” region of the Yucatan Peninsula, Mexico may result in contamination of groundwater resources that eventually discharge into Caribbean coastal ecosystems. We deployed two types of passive sampling devices into groundwater flowing through cave systems below two communities to evaluate concentrations of contaminants and to indicate the possible sources. Pharmaceuticals and personal care products accumulated in the samplers could only have originated from domestic sewage. PAHs indicated contamination by runoff from highways and other impermeable surfaces and chlorophenoxy herbicides accumulated in samplers deployed near a golf course indicated that pesticide applications to turf are a source of contamination. Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health, thus damaging the tourism-based economy of the region.

Understanding the hydrological functioning of a shallow lake system within a coastal karstic aquifer in Wales, UK

Summary Bosherston Lakes in west Wales are an internationally important set of linked freshwater lowland lakes which were created by damming tidal creeks in the 18th and 19th centuries. The lakes have an average water depth of 1–3 m, and receive surface water inflows but have an uncertain interaction with the underlying karstic Carboniferous Limestone. This paper describes the application of the Soil Water Assessment Tool (SWAT) to improve the understanding of the hydrological functioning of the lake system. The temporally variable and limited observational data were used within a two-step calibration process. The simulated surface water inflows and groundwater levels were calibrated, followed by the lake volumes (Nash–Sutcliffe (NS) coefficient ranging from 0.67 to 0.74). Finally the simulated lake volumes were validated (NS ranging from 0.56 to 0.74) and the simulated lake outflows demonstrated to be plausible. Simulations reveal that three of the four linked water bodies lose significant water to the underlying aquifer. The simulated water balance demonstrates that the catchment outputs are dominated by evapotranspiration, surface outflow from the lake system to the sea and coastal groundwater discharge, with abstraction and lake evaporation being of lesser importance. The coastal groundwater discharge originates from both leakage from the lakes and previously unrecognised larger scale groundwater flow paths in the limestone aquifer. The study has provided an improved basis for the future hydrological management of the catchment and lakes and has demonstrated the wider utility of SWAT in simulating karstic systems.

Hydromechanism and Desalination of Coastal Karst Aquifers: Theory and Case

Brackish water of coastal karst aquifers is useless. Desalination methods are: interception method to capture fresh water in karst massif, isolation and rise-spring-level methods to prevent sea water inflow and reduced pumping of fresh water in dry periods. Four typical cases explain these methods.

Functioning of a coastal karstic system with a submarine outlet, in southern Spain

A conceptual model of the functioning of a complex coastal karst aquifer in southern Spain is presented. The system has well developed conduits below sea level and is connected to the Mediterranean Sea. It discharges through two conduits 12 m below sea level, 20 km apart. The Moraig conduit is the main outlet; the discharge to the sea is brackish. The Toix conduit only discharges to the sea during heavy floods and lets in seawater the rest of the time. During the 1999–2000 hydrological year, both conduits were monitored by flowmeters and electrical conductivity-temperature probes. On the basis of the collected data, the hydrological relationship between the functioning of the system and the sea was characterised. The conceptual model assumes the existence of a huge reservoir called an “aquifer reservoir” which is supplied by (1) freshwater from rainfall and (2) seawater flowing into the Toix conduit. In addition, during heavy rainfall events, fast infiltration brings considerable amounts of freshwater into the Moraig conduit. This is typical of a “by-pass” mechanism. Salinity and flow rates were simulated with the use of a rainfall-discharge and a rainfall-salinity model. The simulation of flow and salinity time series can be used for water management purposes.