Geometry and dynamics of the freshwater—seawater interface in a coastal aquifer in southeastern Spain

Abstract

The contact between freshwater and seawater in coastal aquifers is studied using a relatively simple model for homogeneous aquifers. However, for real aquifers it is not so simple. The desalination plant built to supply water to the city of Almería is situated over the aquifer in the southern part of the River Andarax Delta. Its design capacity is 1100 L s^?1, and it is supplied from boreholes pumping water from beneath the freshwater—seawater contact in this aquifer. Well logs kept over a period of two years have allowed us to accurately define the interface geometry of the freshwater—seawater contact. Lithological data collected from 31 boreholes have also indicated the existence of strata with low hydraulic conductivity, within others of high conductivity. During a simultaneous pumping test of six wells with 690 L s^?1 total discharge, electrical conductivity measurements showed the influx of seawater 6–10 m below sea level and a drawdown of the interface in the piezometers closest to the pumping wells.     

Series solutions for saturated–unsaturated flow in multi-layer unconfined aquifers

A semi-analytical mesh-free series solution method is presented for modeling regional steady-state subsurface saturated–unsaturated flow in 2-D geometrically complex homogenous and stratified hill-slope cross sections. Continuous solutions for pressure in the saturated and unsaturated zone are determined iteratively, as is the location of the water table surface. Mass balance is satisfied exactly over the entire domain except along boundaries and interfaces between layers, where errors are in an acceptable range. The solutions are derived and demonstrated on multiple test cases. The errors for specific cases are assessed and discussed.     

‘Overshooting’ effects due to hydrodispersive mixing of saltwater layers in aquifers

In computation of saltwater intrusion processes transient effects, wherein an elevation of salinity above a final steady state occurs, have been observed and termed as ‘overshooting’. To clear the overshooting phenomena a paradigmatic saltwater layer problem is studied. A new analytical solution for two-dimensional unsteady convective and hydrodispersive saltwater spreading in a bilayered aquifer is presented. A good agreement between analytical predictions and numerical results obtained by finite elements is exhibited. Using the analytical solution it has been found that the major factors for the existence and the development of overshooting are the initial conditions of saltwater layering and the difference of the flow velocities between the layers. The results presented in the paper can provide better insight into the mixing process of flowing saltwater layers.     

Ecological–Geochemical Conditions of Surface Water and Groundwater and Estimation of the Anthropogenic Effect in the Basin of the Ganjiang River

Water Resources - Data of studies of 2013–2019 were used to assess the current environmental-geochemical conditions of surface water and groundwater in the basin of the Ganjiang River, the...     

Spatial variations of methane distribution in marine environment and its fluxes at the water–atmosphere interface in the western Sea of Okhotsk

Data of integrated gas-geochemical studies in the 45 cruise of the R/V Akademik M.A. Lavrent’ev in July 2008 were used to study the spatial distribution of methane in the surface seawater layer, the distribution and qualitative composition of hydrocarbon gases in bottom sediments of the northwestern continental shelf, northeastern slope of Sakhalin Island, and Deryugin depression in the Sea of Okhotsk. The specific features of the methane anomalies that form in this case are considered. Tectonic faults and the distribution of oil-and-gas-bearing structures are the main factors governing the formation of hydrocarbon gas fluxes in the study area. The surface water in the entire examined area was found to be oversaturated with methane. A developed model was used to calculated methane fluxes at the water–atmosphere interface and to identify areas with maximal fluxes (up to 324 mol/(km² day).     

Charnock dynamics: a model for the velocity structure in the wave boundary layer of the air–sea interface

We present a unified model of the air–sea boundary layer, which takes account of the air–sea momentum exchange across the sea surface. The recognition of the importance of the velocity shears in the water (which comprise a frictional shear and the Stokes shear due to the wave motion) in determining the sea surface roughness is a distinctive feature of the analysis, which leads to a prediction of the Charnock constant (α) in terms of two independent parameters, namely the wave age and the ratio of the Stokes shear to the Eulerian shear in the water. This expression is used to interpret the large observational variability of the Charnock constant. The 10-m drag coefficient can also be expressed using similar reasoning, and the introduction of a relation in which the ratio of the frictional shear in the water to the frictional shear in the air decreases with the friction velocity yields predictive relations for the variation of the 10-m drag coefficient at very high wind speeds both in the open ocean and in wind–wave tanks. The physical interpretation of this relation is that the production of spray essentially returns momentum from the ocean to the atmosphere, and this process becomes progressively more important as the wind speed increases.     

Estimation of the temperature in the Earth’s interior from surface measurements of the electromagnetic field

The possibility of contactless remote estimation of the temperature in the Earth’s interior from surface magnetotelluric (MT) measurements is examined. The neuronet analysis of MT and temperature measurements in the Bishkek geodynamic research area (the Northern Tien Shan) showed that a contactless electromagnetic geothermometer can in principle be realized. An optimal method including MT measurements and treatment of available thermograms is developed. The method minimizes uncertainties of the remote temperature estimation. The use of six to eight thermograms for calibration of electromagnetic data is shown to provide a 12% relative error of prediction, and a priori geological information available for the region under study can reduce this error. Areas of practical application of a contactless electromagnetic geothermometer are outlined.     

Using growth measures in the freshwater shrimp Caridina nilotica as biomarkers of Roundup® pollution of South African freshwater systems

There has been global concern about the effect of toxic chemicals on aquatic biota due to the upsurge in contamination of aquatic ecosystems by these chemicals, which includes pesticides. Roundup® and other glyphosate-based herbicides are frequently used in the chemical control of weeds and invading alien plant species in South Africa. These bio-active chemicals ultimately get into water courses directly or indirectly through processes such as drifting, leaching, surface runoff and foliar spray of aquatic nuisance plants. However, there is no South African water quality guideline to protect indigenous freshwater non-target organisms from the toxic effects of glyphosate-based herbicides. This study evaluated the possible use of growth measures in Caridina nilotica as biomarkers of Roundup® pollution as part of developing glyphosate water quality guideline for the protection of aquatic life in South Africa. Using static-renewal methods in a 25-day growth toxicity test, 40 days post hatch shrimps were exposed to different sub-lethal Roundup® concentrations of 0.0 (control), 2.2, 2.8, 3.4, 4.3 and 5.4 mg/L. Shrimps were fed daily with TetraMin® flake food and test solutions changed every third day. Shrimp total lengths and wet weights were measured every fifth day. These data were used to determine the shrimp’s growth performance and feed utilization in terms of percent weight gain (PWG), percent length gain (PLG), specific growth rate (SGR), condition factor (CF), feed intake (FI), feed conversion ratio (FCR) and feed conversion efficiency (FCE). Moulting was observed for 14 days and the data used to determine the daily moult rate for each concentration. Results of growth performance and food utilization indices showed that growth was significantly impaired in all exposed groups compared to control (p < 0.05). Moulting frequency was also higher in all exposed groups than in control (p < 0.05). Although all the tested growth measures proved to be possible biomarkers of Roundup® pollution, moulting frequency gives a clearer indication of the sub-lethal effects of Roundup® toxicity.     

Predicting salt intrusion into freshwater aquifers resulting from CO2 injection – A study on the influence of conservative assumptions

Brine migration and saltwater intrusion into freshwater aquifers are among the hazards which may result from injecting CO₂ into deep saline formations. Comprehensive risk assessment should include estimates of the salinization of freshwater aquifers, preferably based on numerical simulation results. A crucial task is to choose an appropriate conceptual model and relevant scenarios. Overly conservative assumptions may lead to estimation of unacceptably high risks, and thus prevent the implementation of a CO₂ storage project unnecessarily. On the other hand, risk assessment should not lead to an underestimation of hazards. This study compares two conceptual model approaches for the numerical simulation of brine-migration scenarios through a vertical fault and salt intrusion into a fresh water aquifer. The first approach calculates salt discharge into freshwater using an immiscible two-phase model with constant salinity in the brine phase. The second approach takes compositional effects into account and considers salinity as a variable parameter in the water phase. A spatial model coupling is introduced to adapt the increased model complexity to the required complexity of the physics. The immiscible two-phase model is applied in the CO₂ storage reservoir and spatially coupled to a single-phase (water) two-component (water, salt) model, where salt mass fraction is a variable. A Dirichlet–Neumann technique is used for the coupling conditions at the interface of the two models. The results show that the predicted salt discharges can vary by orders of magnitude depending on the choice of the model. The implications of the results for risk assessment are discussed.     

Effect of climate changes on the maximal runoff in the Amur Basin: Estimation based on dynamic–stochastic simulation

The potentialities of dynamic–stochastic simulation are analyzed as applied to changes in the regime of summer–autumn rain-flood runoff, which is the governing phase of water regime in the Amur Basin. The scenario of climate changes was formulated in a maximally generalized form as an increase in the sum of seasonal precipitation by an amount of up to 20% of its average long-term value; therefore, all obtained estimates are to be regarded as tentative. Notwithstanding the relatively poor support by observation data, a regionally adapted hydrological model with a flood cycle model (FCM) as its core yields reliable and convincing results. The most important conclusion regards the possible disproportionate response to a climate impact, i.e., the relative increase in minimal-runoff characteristics is far in excess of the assumed increase in the total precipitation.     

Seawater–freshwater mixing and resulting calcite dissolution: an example from a coastal alluvial aquifer in eastern South Korea

Abstract

In order to evaluate groundwater quality and geochemical reactions arising from mixing between seawater and dilute groundwater, we performed a hydrochemical investigation of alluvial groundwater in a limestone-rich coastal area of eastern South Korea. Two sites were chosen for comparison: an upstream site and a downstream site. Data of major ion chemistry and ratios of oxygen–hydrogen isotopes (δ¹⁸O, δD) revealed different major sources of groundwater salinity: recharge by sea-spray-affected precipitation in the upstream site, and seawater intrusion and diffusion zone fluctuation in the downstream site. The results of geochemical modelling showed that Ca²⁺ enrichment in the downstream area is caused by calcite dissolution enhanced by the ionic strength increase, as a result of seawater–groundwater mixing under open system conditions with a constant P_CO2 value (about 10^?1.5 atm). The results show that, for coastal alluvial groundwater residing on limestone, significant hydrochemical change (especially increased hardness) due to calcite dissolution enhanced by seawater mixing should be taken into account for better groundwater management. This process can be effectively evaluated using geochemical modelling.

Editor D. Koutsoyiannis; Associate editor Y. Guttman

Citation Chae, G.-T., Yun, S.-T., Yun, S.-M., Kim, K.-H., and So, C.-S., 2012. Seawater–freshwater mixing and resulting calcite dissolution: an example from a coastal alluvial aquifer in eastern South Korea. Hydrological Sciences Journal, 57 (8),1–12.     

Estimation of Seismic Velocities from Deep Reflections in the τ-p Domain

—In deep reflection seismics the estimation of seismic velocities is hampered in most cases due to the low signal level with respect to noise. In the τ-p domain, it is possible to perform the velocity analysis even under such unfavorable signal conditions. This is achieved by making use of special properties of the transform, which enhance the signal-to-noise ratio. Further noise suppression is realized by incorporating filter procedures into the transform algorithm. The velocity analysis itself is also done in the τ-p domain by calculating and evaluating constant velocity gathers. The results can be directly used in the time domain. A mute algorithm, implemented into the τ-p velocity analysis procedure, further reduces noise. This velocity estimation method is discussed with synthetic data and applied to DEKORP data.     

Annual runoff estimation—an example of karstic aquifers in the transboundary region of Croatia and Slovenia

Abstract

An approach to the global estimation of water balance elements and their spatial distribution using GIS is presented. It is primarily related to the catchments where measured data are scarce and the spatial differentiation of the hydrological characteristics is not possible without climatological data. Emphasis is placed on estimating the water balance of transboundary karstic aquifers, where problems concerning the hydrometeorological data, catchment boundaries and determination of water balance elements in general are far more complex. The runoff estimation was done using the Turc and Langbein methods, which are the most frequently applied in this region. The years 1961–1990 were used as the reference period. Based on comparison of the results, the applicability of the methods is discussed. The approach proposed is suitable for estimation of water balance in the study area and may also be applied in a wider region.     

Monitoring of organic pollutants in coastal waters of the Gulf of Gdańsk, Southern Baltic

This paper presents an overview of changes in organic pollution of coastal waters of the Gulf of Gdańsk (Baltic Sea). Toxic pollutants including volatile organic compounds (VOC), volatile organohalogen compounds (VOX), chlorophenols, phenoxyacids, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were determined in seawater from the Gulf of Gdańsk coastal waters in the period 1996-2001. In the case of the Gulf of Gdańsk, non-conservative behaviour of VOC was observed due to random temporal and spatial of inputs along the Vistula estuary and to the dilution of VOC-enriched river water with seawater. The concentrations of VOX in seawater decreased throughout the period and the concentrations of VOX were in the range of few ng dm(-3) up to 250 ng dm(-3), similar to estuaries elsewhere. The average concentrations of chlorophenols and phenoxyacids were between 0.1 and 6.0 and 0.05 and 2.2 microg dm(-3), respectively. However, remarkably high concentrations of 2,4-dichlorophenol (6 microg dm(-3)) were obtained in samples collected from the Vistula River. Generally concentrations of PCBs did not exceed few ng dm(-3) with the exception of 1999, when all samples exhibited elevated concentrations of PCBs. In addition, higher concentrations of PCBs in the open sea compared to river waters suggested localised inputs. Due to the ability of most organic pollutants to bioaccumulate and biomagnify, especially the persistent organic pollutants, continued monitoring is of crucial importance for the health of marine life in the Gulf of Gdańsk.     

Introducing the recharge–discharge relationship to evaluate the recharge coefficient of karstic aquifers: thematic and indexing approaches

ABSTRACT

Karst aquifers and springs are important with respect to their potential for supplying drinking water in regions suffering from water scarcity in Iran. Accordingly, it is essential to determine the recharge potential of the catchment and the regions with higher obtainability potential. This study provides a road map for the Sheshpeer catchment in southern Iran. A recharge potential (RP) map was produced from which a recharge index (RI) was computed for several selected springs in the catchment. Furthermore, the unit discharge (q) – defined as the average annual discharge for a given catchment area and unit rainfall depth for each spring – was calculated. The plot of q versus RI for the springs showed a linear positive relationship between the two variables (R ² = 0.9). Applying the trend equation of this plot to the whole Sheshpeer karstic catchment reveals that its long-term recharge coefficient is 0.74.     

Groundwater travel time in the freshwater lenses of Samborombón Bay,Argentina

Abstract

The Samborombón Bay area (Argentina) is a coastal plain environment that contains groundwater resources with high salinity. In addition, there are local freshwater lenses associated with shell ridges and sand sheets in the region. In this work, the groundwater travel time in these freshwater lenses is estimated based on their geological conditions, which include hydraulic conductivity, recharge, morphology and discharge to surface freshwater or to saline groundwater. Groundwater travel times in the freshwater lenses were calculated from the equations developed by Chesnaux and Allen. The travel times estimated for the different scenarios were relatively short. The results indicate that the groundwater flow tends to be strongly dependent on the recharge conditions, with an excess of water in the water balance. The results can be applied to help design sustainable management methods to exploit this water resource system and also to assess the impact of contaminant plumes on this groundwater resource.

Citation Carol, E., Kruse, E. & Roig, A. (2010) Groundwater travel time in the freshwater lenses of Samborombón Bay, Argentina. Hydrol. Sci. J. 55(5), 754–762.     

Variations in the area of the global field of noctilucent clouds of the northern hemisphere in 2007–2012 seasons

Using daily distributions of noctilucent cloud fields obtained for 2007–2012 by the AIM satellite, we analyzed temporal changes in the area of the global field of mesospheric noctilucent clouds. These clouds have been shown to be characterized by some common features that can be approximated mathematically by simple functions reflecting the seasonal course of the temperature and humidity regime of the high-latitude mesosphere, allowing a clear physical interpretation. We discuss the specific features of changes in the cloud field area for individual seasons.     

Role of the Russell–McPherron effect in the acceleration of relativistic electrons

While it is well known that high fluxes of relativistic electrons in the Earth's radiation belts are associated with high-speed solar wind and its heightened geoeffectiveness, less known is the fact that the Russell–McPherron (R–M) effect strongly controls whether or not a given high-speed stream is geoffective. To test whether it then follows that the R–M effect also strongly controls fluxes of relativistic electrons, we perform a superposed epoch analysis across corotating interaction regions (CIR) keyed on the interfaces between slow and fast wind. A total of 394 stream interfaces were identified in the years 1994–2006. Equinoctial interfaces were separated into four classes based on the R–M effect, that is, whether the solar wind on either side of the interface was either (geo)effective (E) or ineffective (I) depending on season and the polarity of the interplanetary magnetic field (IMF). Four classes of interface identified as II, IE, EI, and EE are possible. The classes IE and EI correspond to CIRs with polarity changes indicating passage through the heliospheric current sheet. To characterize the behavior of solar wind and magnetospheric variables, we produced maps of dynamic cumulative probability distribution functions (cdfs) as a function of time over 10-day intervals centered on the interfaces. These reveal that effective high-speed streams have geomagnetic activity nearly twice as strong as ineffective streams and electron fluxes a factor of 12 higher. In addition they show that an effective low-speed stream increases the flux of relativistic electrons before the interface so that an effective to ineffective transition results in lower fluxes after the interface. We conclude that the R–M effect plays a major role in organizing and sustaining a sequence of physical processes responsible for the acceleration of relativistic electrons.