Modelling seasonal variations in nitrate and sulphate concentrations in a vulnerable alluvial aquifer

The Eisden–Meeswijk region in Belgium has been affected by mining subsidence due to the deep coal mining activities. Groundwater levels in the alluvial plain of the Meuse River are maintained below the ground surface by drainage installations and municipal well fields. A correlation between the water level in the Meuse River and the variation in nitrate and sulphate concentrations in the aquifer has been observed. A transient groundwater model is developed for the period May 1998–May 2002 and advective transport simulations have been carried out using this model. During dry periods, the major groundwater flow is directed towards the Meuse River, thereby feeding the river. During wet periods, however, groundwater flows in the opposite direction. Due to these variations in groundwater flow direction and to the extraction of groundwater, zones of higher solute concentration exist of which the position and extension vary both spatially and temporally.     

Aeolian dune‐field development in a water table‐controlled system: Skeiđarársandur,Southern Iceland

Aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on Skei?arársandur, Southern Iceland. The largest aeolian dune complex on the sandur covers an area of 80 km² and is characterized by four distinct landform types: (i) spatially isolated aeolian dunes; (ii) extensive areas of damp and wet (flooded) interdune flat with small fluvial channels; (iii) small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small, predominantly damp, interdune corridors; and (iv) larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain. The morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune, interdune and fluvial processes that operate coevally on the sandur surface. The geometry, scale, orientation and facies composition of sets of strata in the cores of the aeolian dunes, and their relationship to adjoining interdune strata, have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation, construction, pattern of migration, style of accumulation and nature of preservation. Seasonal and longer‐term flooding‐induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds. Most of the dunes are currently undergoing active construction and migration and, although sediment availability is limited because of the high water table, substantial aeolian transport must occur, especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture. Bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing. Despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century, sediment compaction‐induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long‐term preservation. Wet, dry and stabilizing aeolian system types all co‐exist on Skei?arársandur and the dunes are variously undergoing coeval construction, accumulation, bypass, stabilization and destruction as a result of interactions between localized factors.     

Large-scale interannual variation of the summer monsoon over India and its empirical prediction

Large-scale interannual variability of the northern summer southwest monsoon over India is studied by examining its variation in the dry area during the period 1871–1984. On the mean summer monsoon rainfall (June to September total) chart the 800 mm isohyet divides the country into two nearly equal halves, named as dry area (monsoon rainfall less than 800 mm) and wet area (monsoon rainfall greater than 800 mm). The dry area/wet area shows large variations from one year to another, and is considered as an index for assessing the large-scale performance of the Indian summer monsoon. Statistical and fluctuation characteristics of the summer monsoon dry area (SMDA) are reported. To identify possible causes of variation in the Indian summer monsoon, the correlation between the summer monsoon dry area and eleven regional/global circulation parameters is examined. The northern hemisphere surface air temperature, zonal/hemispheric/global surface air and upper air temperatures, Southern Oscillation, Quasi-biennial oscillation of the equatorial lower stratosphere, April 500-mb ridge along 75°E over India, the Indian surface air temperature and the Bombay sea level pressure showed significant correlation. A new predictor parameter that is preceding year mean monsoon rainfall of a few selected stations over India has been suggested in the present study. The stations have been selected by applying the objective technique ‘selecting a subset of few gauges whose mean monsoon rainfall of the preceding year has shown the highest correlation coefficient (CC) with the SMDA’. Bankura (Gangetic West Bengal), Cuddalore (Tamil Nadu) and Anupgarh (West Rajasthan) entered the selection showing a CC of 0.724. Using a dependent sample of 1951–1980 a predictive model (multiple CC = 0.745) has also been developed for the SMDA with preceding year mean monsoon rainfall of the three selected stations and the sea level pressure tendency at Darwin from Jan–Feb to Mar–May as independent parameters.     

An empirical probabilistic approach for constraining the uncertainty of long-term solute transport predictions in fractured rock using in situ tracer experiments

Although radionuclide tracer tests have been carried out for over 30  years, the role of tracer tests in radioactive waste repository performance assessment (PA) has been questioned due to the differences between the time scales for tracer tests and PA. The possibility of using in situ tracer tests to constrain PA time scale (over 10,000  years) solute transport has been demonstrated using a systematic “microstructural model” approach to define advective and retentive materials. A series of simulations were conducted of the “TRUE-1” sorbing solute transport experiments in a well-characterized block of fractured granite. These experiments were then used to constrain the uncertainty of long-term transport on the same pathways, using a gradient several orders of magnitude smaller. The comparison of uncertainty of this long-term transport, with and without this conditioning step, provided a measure of the ability of tracer tests to reduce PA time-scale uncertainty. Although this approach for quantifying uncertainty reduction is somewhat empirical, it does indicate the potential usefulness of tracer experiments in reducing the uncertainty of the key PA time-scale transport parameters such as the flow wetted surface, provided that immobile zone properties such as sorption (Kd), porosity and diffusivity are available.     

Surface Water Metabolism Potential in Groundwater-Fed Coastal Waters of Hawaii Island,USA

Submarine groundwater discharge (SGD) has become increasingly recognized as an important source of freshwater and nutrients to coastal waters worldwide. Although groundwater nutrients have been found to cause algal blooms in many temperate coastal waters, little is known about the biological response to these nutrients in the tropics. On the leeward coast of Hawaii Island, SGD is the dominant freshwater and nutrient source to coastal waters. Kiholo Bay, HI and Kaloko-Honokohau National Historical Park, HI are two nearshore regions with well-documented SGD with high nutrient concentrations; however, little is known about how biological processes within the surface waters respond to these inputs. This study examined how potential gross primary production (pGPP), respiration (RESP), and potential metabolism (pMET) within surface waters differed inside and outside of groundwater plumes at these two sites and between wet and dry seasons. pGPP and RESP were both significantly higher within groundwater plumes, suggesting that SGD stimulated these biological processes; however, RESP responded to a much greater extent than pGPP, resulting in heterotrophic surface waters. RESP also varied seasonally, with greater rates during the dry season compared to the wet one; pGPP did not vary seasonally. Autotrophic conditions were found within groundwater plumes at Kiholo Bay, while heterotrophic conditions were found within them at Kaloko-Honokohau and were greater during the dry season. Overall, our results show that coastal biological processes respond to SGD and that their responses vary over short spatial and temporal scales.     

The effect of impoundments on the structure and function of fish fauna in a highly regulated dry tropics estuary

Ross River flows through the Townsville/Thuringowa urban area in north Queensland, Australia, which has a dry tropical climate characterized by high inter-annual rainfall variation. Unregulated rivers in the Ross catchment basin deliver freshwater flows to their estuaries during both strong and weak wet seasons. The construction of a series of dams and weirs on Ross River means the wet-dry cycle is accentuated, leading to constant marine salinities throughout the estuary becoming the norm, with a lack of freshwater flow for five or more years at a time. The fish fauna of Ross River estuary was sampled in the post wet and dry seasons during an extremely dry climatic period (1994) and extremely wet climatic period (2000) using a small mesh (6 mm) pocket seine net. The fish fauna seemed to reflect seasonal differences. Catches from 1994 (dry period) were comprised entirely of 88 marine and euryhaline species, while the 69 species captured in 2000 (wet period) included 13 freshwater species. However, the freshwater species in the upper estuary were individuals washed over the weir, rather than part of a functional faunal gradient. During 1994 faunal composition was related more to site identity than to the position of the site along an upstream gradient. In contrast, during 2000 there were clear upstream faunal gradients with compositions in upstream sites heavily influenced by freshwater species, and marine and euryhaline species dominating downstream sites. Patterns of species dominance also varied between years. In contrast, trophic composition showed consistent shifts in both years, from high proportions of herbivores, carnivores and benthoplanktivores in May towards high proportions of benthivores in August. Not only do faunal composition, seasonal faunal change and ecological connectivity seem to be impaired, but ecological processes in the estuary that rely on seasonal freshwater flows are likely to be unable to operate normally in most years. The extreme seasonality in Ross River may serve as a model for many of the changes that will be experienced in dry tropics estuaries under global climate change scenarios of more extreme seasonality.     

Using field analogue soil column experiments to quantify radon-222 gas migration and transport through soils and bedrock of Halifax,Nova Scotia,Canada

Radon gas is a human health hazard; long-term exposure to high radon concentrations through inhalation is the second leading cause of lung cancer. Nova Scotia has been previously identified as a potential high risk region because of the geology. As such, the gas transport through Halifax’s fine grained leucomonzogranite (FGL) unit of the South Mountain Batholith needed to be quantified to further remediation efforts. Using controlled laboratory experiments, four different soil columns were created using the Halifax Regional Municipality’s (HRM) highest producing field tills and bedrock. Permeability, diffusivity, radon-222 gas concentrations, and gas transit time/speed were measured in both dry tills (field moisture) and wet tills (simulated rain event moisture). Columns with HRM till displayed the highest radon concentrations, and were less permeable with additional moisture. Radon diffusivity calculated from CO₂ was 7.52 × 10^?8 m² (dry), and 3.37 × 10^?8 m² (wet); diffusivity calculated from ²²²Rn was 7.30 × 10^?7 m² (dry), and 6.47 × 10^?7 m² (wet). The average FGL transit time in a 60 cm column was 3.57 days (dry), and 3.82 days (wet). Locally this study presents two different methods for diffusivity calculations, for a unit lacking previous diffusivity information. The radon gas concentrations and transport speeds quantified the transport mechanisms within the till. Globally, the correlation between soil moisture, and radon/permeability values was established using these results. The link between diffusivity and permeability was also confirmed using field tills. Implications were made for building foundations, as well as the depth and type of material necessary to reduce radon gas from reaching the surface.     

Assessing changes in the rainfall regime in Nigeria between 1961 and 2004

The study assessed changes in the rainfall regime in Nigeria between 1961 and 2004 in terms of (a) absolute seasonality—the length of dry and wet season; (b) relative seasonality—rainfall contrast during the year; (c) number of rainfall maxima and minima; and (d) timing of rainfall maxima and minima. Trends in the mean monthly surface locations of the Inter-tropical Discontinuity (ITD) were also examined as a prominent factor of the rainfall regime. Changes in the regime were examined over four time slices: 1961–1971, 1972–1982, 1983–1993 and 1994–2004. The results show that, in the area of single rainfall maximum regime, the length of the wet season has increased from 4 months (in 1961–1971) to 5 months (since 1972–1982). The rainfall relative seasonality has consistently been ‘most rain in 3 months or less’. The rainfall maxima still indicate single rainfall maximum but shift in the peak from August to July. Rainfall during the months of June to September appears to have witnessed declining trends over the first three time slices. The last time slice however indicates trends towards a wetter condition. For the area of double maxima rainfall regime, the length of the wet season has consistently been 8 months. The rainfall relative seasonality has consistently been ‘rather seasonal with a short drier season’. The rainfall maxima and minima still indicate double rainfall maxima with August as the month of the minimum but shift in the primary peak from July to September. The northward latitudinal distance of the surface location of the ITD from the equator indicates significant upward trends during the months of May to September only and for a period of 1983–2000. The trend results of the ITD appears to account for most of the observed changes in the rainfall regime in Nigeria.     

Controls on permafrost thaw in a coupled groundwater-flow and heat-transport system: Iqaluit Airport,Nunavut, Canada

Numerical simulations of groundwater flow and heat transport are used to provide insight into the interaction between shallow groundwater flow and thermal dynamics related to permafrost thaw and thaw settlement at the Iqaluit Airport taxiway, Nunavut, Canada. A conceptual model is first developed for the site and a corresponding two-dimensional numerical model is calibrated to the observed ground temperatures. Future climate-warming impacts on the thermal regime and flow system are then simulated based on climate scenarios proposed by the Intergovernmental Panel on Climate Change (IPCC). Under climate warming, surface snow cover is identified as the leading factor affecting permafrost degradation, including its role in increasing the sensitivity of permafrost degradation to changes in various hydrogeological factors. In this case, advective heat transport plays a relatively minor, but non-negligible, role compared to conductive heat transport, due to the significant extent of low-permeability soil close to surface. Conductive heat transport, which is strongly affected by the surface snow layer, controls the release of unfrozen water and the depth of the active layer as well as the magnitude of thaw settlement and frost heave. Under the warmest climate-warming scenario with an average annual temperature increase of 3.23 °C for the period of 2011–2100, the simulations suggest that the maximum depth of the active layer will increase from 2 m in 2012 to 8.8 m in 2100 and, over the same time period, thaw settlement along the airport taxiway will increase from 0.11 m to at least 0.17 m.

     

Soil heat flux and day time surface energy balance closure at astronomical observatory,Thiruvananthapuram, south Kerala

Soil heat flux is an important input component of surface energy balance. Estimates of soil heat flux were made in the year 2008 using soil temperature data at Astronomical Observatory, Thiruvananthapuram, south Kerala. Hourly values of soil heat flux from 00 to 24 LST are presented for selected days typical of the winter, pre-monsoon, SW monsoon and NE monsoon seasons. The diurnal variation is characterized by a cross-over from negative to positive values at 0700 h, occurrence of maximum around noon and return to negative values in the late evening. The energy storage term for the soil layer 0–0.05 m is calculated and the ground heat flux G ^? is estimated in all seasons. Daytime surface energy balance at the surface on wet and dry seasons is investigated. The average Bowen’s ratio during the wet and dry seasons were 0.541 and 0.515, respectively indicating that considerable evaporation takes place at the surface. The separate energy balance components were examined and the mean surface energy balance closure was found to be 0.742 and 0.795 for wet and dry seasons, respectively. When a new method that accounts for both soil thermal conduction and soil thermal convection was adopted to calculate the surface heat flux, the energy balance closure was found to be improved. Thus on the land surface under study, the soil vertical water movement is significant.     

The transport of heat and matter by fluids during metamorphism

Non-dimensional solutions to the equations for the combined advective and diffusive one-dimensional transport of heat and solute in a layer are derived for fixed temperature/concentration on the boundaries and initial conditions of a linear gradient across the layer or a step function at the lower boundary. The solutions allow distinction of regimes in which advective or diffusive transport of either heat or solute predominate as a function of fluid flux, time and a length scale. The much lower diffusive coefficients for solute than heat results in a significant range of length scales and fluid flux rates characterised by advection of matter and diffusion of heat. The advective velocity of a component is a function of its fluid:rock partition coefficient. The most rapidly transported tracers which partition largely into the fluid phase, such as He, will travel orders of magnitude faster than heat or compatible solutes such as oxygen. Geochemical profiles in boundary layer regions where both advective and diffusive transport are significant are shown to be particularly informative as to properties of the rocks related to fluid flow such as porosity, permeability, time scales and fluid flux rates. The importance of advection can be directly estimated from the asymmetry of the geochemical profiles across individual layers.     

The impact of hydrological conditions on salinisation and nitrate concentration in the coastal Velez River aquifer (southern Spain)

This study reports the impact of hydrological conditions on salinisation and nitrate concentrations of a coastal aquifer located at the Mediterranean Sea, southern Spain. Eighty-two samples of ground- and surface water taken during two extreme hydrological events between 1994 and 1996 at 25 different wells were evaluated with regard to hydrochemistry, focusing on nitrate concentrations and salinisation, which constitute the main hazard of this aquifer. Furthermore, hydrochemical data were analysed by principal component analysis (PCA). Additionally, in 2007 13 ground- and surface water samples taken at 12 different locations were analysed for stable isotopes of D/¹⁸O, and one sample was analysed for ¹⁵N. Since 1993 until present saltwater intrusion was observed only during dry hydrological conditions in 1994; it showed an irregular salinisation pattern probably related to locally elevated hydraulic conductivities. Nitrate concentrations increase significantly during wet hydrologic conditions owing to uptake of nitrate by rising groundwater. Stable isotopes of groundwater reveal an Atlantic origin of the precipitation that recharges the aquifer and a minor amount of groundwater recharge by the water coming from the La Viñuela reservoir, which is used for irrigation over the aquifer. ¹⁵N isotopes point to a considerable input of nitrates derived from organic fertilisers.     

A comparative study on nitrogen-concentration dynamics in surface water in a heterogeneous landscape

With point-source pollution controlled effectively, nonpoint-source pollution, especially that resulting from agricultural land, has become the main factor affecting surface water. Much attention has been focused on the impact of fertilizer and pesticide application, wastewater irrigation, and land management on pollutant transport. However, landscape pattern also plays an important role in pollutant transport and detention. Landscape types may be classified into two parts: "source" and "sink" landscapes, based on their functions in pollutant transport and detention. As a major contributor to eutrophication of waterbodies, nitrogen loss with runoff has received particular attention when studying nonpoint-source pollution. In this study, four watersheds in the upper parts of the Yuqiao Reservoir Basin, Zuihua, Hebei Province, China, were chosen in order to study the relationship between landscape pattern and nitrogen-concentration dynamics. The results indicate that (1) nitrogen concentration in surface water within different seasons in the rainfall-normal year is higher than that in the rainfall-deficit year and (2) the variation of nitrogen concentration within different seasons in the rainfall-deficit year is smaller compared with that in the rainfall-normal year in which two types of seasonal variation on nitrogen concentration are presented. The first variation occurs when nitrogen concentration is lowest in the dry season, and rises rapidly from the dry season to rainy season and then declines quickly from the rainy season to mean-flow season. This mainly occurs in those areas where most "source" landscapes are close to the monitored waterbody. The second variation occurs when nitrogen concentration is low in the dry season, increases rapidly in the rainy season but does not reach its peak value until the mean flow season. The second variation occurs in those areas where "source" landscape types are spread over the whole watershed. There is no clear relationship between watershed shape, relative importance of landscape types, and nitrogen concentration; however, the spatial distribution of "source" and "sink" landscape types in the watershed has a strong impact on the nitrogen concentration in surface water.     

Shallow groundwater temperature in the Turin area (NW Italy): vertical distribution and anthropogenic effects

This study investigated the thermal regime of shallow groundwater in the Turin area (NW Italy), where the large energy demand has motivated a new interest for renewable sources, such as the use of ground-source heat pumps for domestic heating and cooling. The vertical variability of the groundwater temperature between the ground surface and 10–20 m was detected: deeper temperatures were higher than shallow temperatures in spring, while a decrease with depth occurred in autumn. These variations are connected with the heating and cooling cycles of the ground surface due to the seasonal temperature oscillation. Variations below the seasonal oscillation are likely to be connected with the presence of advective heat transport due to the groundwater flow, according to the hydraulic features of a shallow aquifer. Temperature values mostly ranged between 12 and 14 °C in rural areas, while the values were between 14 and 16 °C below the Turin city. This groundwater warming is attributed to a widespread urban heat island phenomenon linked to warmer land surface temperatures in Turin city. Sparse warm outliers are connected with point heat sources and site-specific conditions of land and subsurface use, which may cause the aquifer temperature to rise. A relatively stable temperature below the seasonal fluctuation zone combined with high productivity and legislated limits for deeper groundwater use represent favourable conditions for a large-scale diffusion of groundwater heat pumps within the shallow aquifer. Moreover, this heat surplus should be regarded as a resource for future geothermal installations.     

Stratigraphic evolution of an aeolian erg margin system: the Permian Cedar Mesa Sandstone, SE Utah, USA

The Permian Cedar Mesa Sandstone of south‐east Utah is a predominantly aeolian succession that exhibits a complex spatial variation in sedimentary architecture which, in terms of palaeogeographic setting, reflects a transition from a dry erg centre, through a water table‐controlled aeolian‐dominated erg margin, to an outer erg margin subject to periodic fluvial incursion. The erg margin succession represents a wet aeolian system, accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport. Variation in the level of the water table relative to the depositional surface determined the nature of interdune sedimentary processes, and a range of dry, damp and wet (flooded) interdune elements is recognized. Variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre, locally interconnected damp and/or wet interdune ponds in the aeolian‐dominated erg margin and fully interconnected, fluvially flooded interdune corridors in the outer erg margin. Relationships between aeolian dune and interdune units indicate that dry, damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration. Temporal variation in the rates of water‐table rise and bedform migration determined the angle of climb of the erg margin succession, such that accumulation rates increased during periods of rapidly rising water table, whereas sediment bypassing (zero angle of climb) occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table. During these periods in the outer erg margin, the expansion of fluvially flooded interdunes in front of non‐climbing but migrating dunes resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass (flood) supersurfaces. A spectrum of genetic depositional models is envisaged that accounts for the complex spatial and temporal evolution of the Cedar Mesa erg margin succession.     

Geology and hydrothermal resources in the northern Lake Abaya area (Ethiopia)

The northern Lake Abaya area located in the southern part of the Main Ethiopian Rift (MER) evidently contains an advective hydrothermal system. Regional extensional tectonics and subsidence that began in Late Miocene was followed by rift margin rhyolitic volcanism which produced extensive ignimbrite succession and rift shoulder trachytic volcanism in Pliocene. The extensional axis of the MER became the locus of volcanic activity in the Quaternary with bimodal basalt – rhyolitic volcanic products in the rift floor. Shallow crustal magma chambers feeding the axial volcanic complexes provide heat for the hydrothermal system which reside in Tertiary volcanic succession and is capped by lacustrine and volcanoclastic graben infill sediments. Duguna Fango rhyolitic volcanic complex which has extruded as much volume of volcanic products as all the other felsic centers put together is the most important heat source for the hydrothermal system and related manifestations. The closed drainage basin centered at Lake Abaya with adjacent plateau receiving over 1500 mm annual precipitation maintains a stable recharge for the prevailing hydrothermal system. Regional ground water flow direction is to the southwest following Bilate River which is the major river draining into the lake flowing parallel to the major NNE-SSW structural pattern of MER.Analyses of remote sensing data provided some insight into how the structural fabric had a control on the distribution of the groups of hydrothermal manifestations identified as hydrothermal fields. Thermal infrared image showed distinct thermal signature over the rift floor where hydrothermal fields are situated as compared to the plateau and areas covered by the cap-rock. A hydrothermal field around Duguna Fango volcanic complex has volcanological favorable setting despite lower inferred reservoir equilibrium geothermometer temperatures on the thermal springs. About 30 km to the south two other hydrothermal fields are located at a latitudinal distance of less than 15 km between each other. The near boiling point spring #6 of Northwest Abaya discharge mature water with highest geothermal fluid – host rock equilibrium geothermometer temperatures which together with a nearby fumarolic activity may be explained as an outflow. Across Chewkare graben the Bolcho and northeast Abaya hydrothermal fields located between Bilate and Gidabo rivers geochemically appear to be from a different high-enthalpy geothermal reservoir probably related to the cluster of felsic volcanic centers such as Chericho, Kilisa, Donga and Werencha. The high temperature springs indicate the existence of at least two geochemically distinct hydrothermal reservoirs in the study area. It remains to be proven weather an up-flow of an advective hydrothermal system centered to the north around Duguna Fango have long distance concealed out flows to the south on the northern shores of Lake Abaya which is the hydrologic depocenter.     

Stratigraphic evolution and preservation of aeolian dune and damp/wet interdune strata: an example from the Triassic Helsby Sandstone Formation, Cheshire Basin, UK

Abstract New and previously published models of wet aeolian system evolution form a spectrum of types that may be explained in terms of aeolian dune dynamics, rate of water table rise and/or periodicity of interdune flooding. This is illustrated with an example from the Mid‐Triassic (Anisian) Helsby Sandstone Formation, Cheshire, UK. Lenses of damp and wet interdune strata exhibit an intertonguing, transitional relationship with the toe‐sets of overlying aeolian dune units. This signifies dune migration that was contemporaneous with water table‐controlled accumulation in adjacent interdunes. Downwind changes in the geometry and facies of the interdune units indicate periodic expansion and contraction of the interdunes in response to changes in the elevation of the groundwater table and episodic flooding, during which accumulation of dune strata continued relatively uninterrupted. This contrasts with other models for accumulation in wet aeolian systems where interdune flooding is associated with a cessation in aeolian bedform climbing and the formation of a bypass or erosional supersurface. Architectural panels document the detailed stratigraphy in orientations both parallel and perpendicular to aeolian transport direction, enabling a quantitative three‐dimensional reconstruction of genetically related aeolian dune and interdune elements. Sets of aeolian dune strata are composed of grainflow and translatent wind‐ripple strata and are divided by a hierarchy of bounding surfaces originating from oblique migration of superimposed dunes over slipfaceless, sinuous‐crested parent bedforms, together with lee‐slope reactivation under non‐equilibrium flow conditions. Silty‐mudstone and sandstone interdune units are characterized by wind ripple‐, wavy‐ and subaqueous wave ripple‐laminae, desiccation cracks, mud flakes, raindrop imprints, load casts, flutes, intraformational rip‐up clasts and vertebrate and invertebrate footprint impressions and trackways. These units result from accumulation on a substrate that varied from dry‐ through damp‐ to wet‐surface conditions. Interdune ponds were flooded by either fluvial incursions or rises in groundwater table and were periodically subject to gradual desiccation and reflooding. Red silty‐mudstone beds of subaqueous origin pass laterally into horizontally laminated wind‐ripple beds indicating a progressive transition from wet‐ through damp‐ to dry‐surface conditions within a single interdune.     

Geochemistry of surface waters in the vicinity of open pit mines at the Cay Cham deposit, Thai Nguyen province, northern Vietnam

This study provides an assessment of the environmental impact of open pit mining operations at the Cay Cham titanomagnetite-ilmenite deposit (northern Vietnam). The results of surface water sampling indicate the formation of acid mine drainage and contamination of adjacent areas by heavy metals (Cu, Zn, Ni, and Mn). The acid mine drainage is produced by oxidation leaching of sulfide minerals associated with primary mineralization owing to the low neutralization potential of the natural waters in the humid environment of tropical rainforest. The study showed that alternating dry and wet seasons typical of this climatic region promote the generation of stored acidity leading to a sharp decrease in pH of drainage water during the wet season and result in the negative impacts of this mine on both flowing and stagnant surface waters.     

Atmospheric sources and soil filtering of PAH content in karst seepage waters

The analysis of PAHs (polycyclic aromatic hydrocarbons) in karst environments has provided an assessment of the vulnerability of karst water and the study of PAH records in stalagmites. The major source of PAHs has generally been considered to be the soil. In this study, we report the quantification of PAHs in the ecosystem compartments of a mountain karst system over a snow-melting period and the spring to summer dry period. PAH profiles in karst seepage waters were consistently similar to those in wet deposits, following the change in PAH profiles between winter and summer periods. However, PAH signatures of atmospheric wet deposits were modulated by a loss of the high molecular weight PAHs, which appear to accumulate in soils. A PAH mass balance was calculated during a summer storm event. This mass balance suggests that dry deposits and canopy throughfall could account for the PAH abundance in karst seepage waters. This study demonstrates the ability of organic hydrophobic compounds to be directly transferred from the atmosphere or canopy into seepage waters, giving new emphasis to the study of PAHs recorded in stalagmites.     

Advective transport from a penny-shaped crack in a porous medium and an associated uniqueness theorem

This paper examines the problem of the advective transport of a contaminant from sources in the shape of either a penny-shaped crack or an elongated needle-shaped cavity located in a porous medium of infinite extent. The advective transport is induced by Darcy flow in the porous medium, where the internal boundary is maintained at a constant potential. The paper presents an approximate analytical solution to this problem, which is deduced from a formulation that models a cavity in the shape of either an oblate or a prolate spheroid. The results also represent one of the few spatially three-dimensional exact analytical solutions for the, albeit linear, hyperbolic problem governing the contaminant transport problem. The paper also presents a canonical proof of uniqueness for advective contaminant transport problems associated with media of infinite extent. Copyright © 2004 John Wiley & Sons, Ltd.