Ephemeral Research Articles

An assessment of the freshwater natural capital in KwaZulu-Natal for conservation planning

Freshwater conservation planning, while lagging behind terrestrial conservation planning, is beginning to be implemented in a complementary manner to the latter. Ezemvelo KZN Wildlife is currently preparing an aquatic conservation plan for the freshwater systems of KwaZulu-Natal. The development of a freshwater conservation plan requires an initial understanding of the broad characteristics of the resource and associated biodiversity. Within KwaZulu-Natal, which is water-rich relative to the remaining provinces in South Africa, there are approximately 585 000 ha of mapped freshwater wetlands, 17% of which fall within protected areas. At the 1:500 000 scale, there are in excess of 18 400 km of perennial and ephemeral rivers mapped, and just over 1 000 km (5.6%) of these fall within existing formal protected areas. The river systems feed into 79 estuaries covering a mapped area of over 30 600 ha, of which 41% amounting to almost 12 400 ha are found largely within protected areas, although this does not reflect the actual number protected. These freshwater resources provide over 28% of South Africa's total average MAR. Protection of this resource requires the protection of freshwater biodiversity, and the processes which maintain these ecosystems. Currently the greatest threats to this resource are river regulation and land transformation.

Modeling Riparian Restoration Impacts on the Hydrologic Cycle at the Babacomari Ranch, SE Arizona, USA

This paper describes coupling field experiments with surface and groundwater modeling to investigate rangelands of SE Arizona, USA using erosion-control structures to augment shallow and deep aquifer recharge. We collected field data to describe the physical and hydrological properties before and after gabions (caged riprap) were installed in an ephemeral channel. The modular finite-difference flow model is applied to simulate the amount of increase needed to raise groundwater levels. We used the average increase in infiltration measured in the field and projected on site, assuming all infiltration becomes recharge, to estimate how many gabions would be needed to increase recharge in the larger watershed. A watershed model was then applied and calibrated with discharge and 3D terrain measurements, to simulate flow volumes. Findings were coupled to extrapolate simulations and quantify long-term impacts of riparian restoration. Projected scenarios demonstrate how erosion-control structures could impact all components of the annual water budget. Results support the potential of watershed-wide gabion installation to increase total aquifer recharge, with models portraying increased subsurface connectivity and accentuated lateral flow contributions.

The role of water and mass balances in treatment assessment of a flooded natural wetland receiving wastewater effluent (Frank Lake, Alberta, Canada)

Constructed, and to a lesser extent, natural wetlands are increasingly used to treat treated wastewater effluent from small municipalities and industries. Wetland treatment efficiency evaluation typically involves comparison of solute inflow and outflow concentrations, or estimation of the export of nutrients per unit wetland area. A more holistic approach, which evaluated water and solute mass balances, in addition to seasonal changes in water quality, yielded an improved understanding of where nutrient storage occurred, long-term wetland treatment capabilities, and downstream water quality impacts of a flooded natural wetland receiving wastewater. The lowest solute concentrations in the flooded wetland were observed soon after ephemeral creek flow in the spring, increasing concentrations over the summer attributed to evaporation, and the highest concentrations under winter ice. Chloride accumulation in shoreline sediments was attributed to transpiration pumping, and high salt and phosphorus accumulation in lake and shoreline sediments were a long-term concern at Frank Lake. Limited historic data suggested water quality impacts on the receiving watershed, the Little Bow River, were significant, with about 80, 230, and 20 times increased mass fluxes for chloride, total phosphorus, and total nitrogen, respectively. The flooded wetland, Frank Lake, is not a sustainable approach to wastewater effluent treatment in its current form.

Limited influence of landscape on the genetic structure of three small mammals in a heterogeneous arid environment

AbstractAimThe complexity and biologically challenging nature of arid landscapes can generate high inter‐ and intra‐species diversity, although these biomes remain poorly studied. We investigated whether prominent geomorphic features in an Australian arid landscape had similar influences on patterns of intra‐specific genetic diversity of three small mammals with different distribution and life history traits. Specifically, we tested (a) whether mountain ranges harbour high diversity and act as refugia, (b) the extent to which ephemeral river systems pose barriers to gene flow or (c) whether environmental differences explain genetic structure in these species.LocationThe topographically complex Pilbara bioregion of the Australian arid zone.TaxaTwo rodents, the Western pebble‐mound mouse, Pseudomys chapmani and the Sandy inland mouse, Pseudomys hermannsburgensis and a dasyurid, Ningaui timealeyi.MethodsWe used maximum parsimony networks of mitochondrial haplotypes and spatially‐explicit Bayesian clustering analysis of microsatellite genotypes to identify historical and contemporary genetic structure in each species. Based on measures of individual diversity and genetic distance, we distinguished ‘hotspots’ and ‘coldspots’ (>1.5 standard deviations from the mean) of genetic diversity and genetic connectivity and assessed their concordance with landscape features. The influence of environmental dissimilarity on observed genetic differentiation was evaluated using generalized dissimilarity modelling.ResultsPatterns of genetic diversity and connectivity were complex, with few consistent patterns across species. Both microsatellite and mitochondrial diversity were high across species, with limited spatial genetic structure. Rivers had the most influence on genetic patterns but were not consistently identified as barriers. Environmental dissimilarity amongst sampling sites had low explanatory power.Main ConclusionsLimited genetic structure in each of the three species suggests that the structurally complex Pilbara landscape remains relatively permeable to species with high dispersal capacity. Additionally, population responses to boom‐bust cycles in arid environments are likely to obscure spatial genetic patterns.

Identification of hydrological controls on dust emissions from Xilingol Grassland of Inner Mongolia, China

In view of various impacts on biosphere and possible cross-regional environmental problems, dust attracts global concerns. We employed multiple spatial resolution satellite images to identify dust sources and the relevantly hydrological land covers. We used true-colour composite images of MODIS to obtain the preliminary information on dust emissions and then distinguished the land covers of dust sources in Landsat images of Xilingol Grassland. The study found that hydrologically associated land covers, such as ephemeral lakes, bajadas, ephemeral river beds, dry lakes and their margins, dominated dust emission areas. Factors responsible for aeolian dusts are from both natural and human aspects. Besides abnormal weather phenomena, factors contributed to dust emissions include ecological and water balance destructions caused by human activities in alkali and coal exploitations and water pumping from rivers or lakes for agriculture and industry. This study will help grassland manager combat land desertification and control dust emission in the future.

Digital soil mapping based site-specific nutrient management in a sugarcane field in Burdekin

In the highly productive Burdekin valley, the soil is heterogeneous. To optimise productivity, for irrigated crops such as sugarcane, essential nutrients such as calcium (Ca) and magnesium (Mg) need to be applied. To assist sugarcane farmers, nutrient management guidelines for these mineral elements have been recommended (i.e. Six-Easy-Steps) based on the exchangeable (Exch.) Ca and Mg. However, these are applied using ‘one size fits all’ approach, which lead to fertiliser use inefficiencies, given the alluvial nature of the landscape; where sandy soil characterises the ephemeral creeks (Chromosols) and clay soil types (Sodosols and Vertosols) of the plains. Herein we used and compared regression kriging (RK) and linear mixed models (LMM) to create digital soil maps (DSM). We also compared the efficacy of various proximal sensed γ-ray spectrometry and EM data. Using measures of bias (mean error - ME) and precision (root mean squared error - RMSE) of predictions, as well as the Lin's concordance, we determine which model and data was most useful using a leave-one-out cross-validation. The results for Exch. Ca showed that while RK approach had a strong concordance (0.81), unbiased (0.01) and precise (0.06), the LMM outperformed RK, given the better concordance (0.87) and bias (0.00). The MSPE of the final LMM DSM (0.01) was also smaller compared to the RK DSM (0.0123). Moreover, both DSM was superior to the traditional Soil Order map (0.0171). The results for Exch. Mg were equivalent. We also conclude, that while good concordance was achieved using either γ-ray (Lin's = 0.79) or EM (0.83) for Exch. Ca, using both proximal sensors was optimal. The results showed that pedometric approach can be used to generate a DSM of Exch. Ca and Mg in a sugarcane field. In terms of soil use and management, the infertile sandy textured soil associated with the prior stream channels and characterised by small Exch. Ca (<0.2 cmol(+)/kg) and Mg (<0.5 cmol(+)/kg), require large fertiliser rates of lime (3 t/ha) and magnesium sulphate (150 kg/ha), respectively. Conversely, variable amounts of fertiliser rates of lime (2.5 and 2 t/ha) and magnesium sulphate (125, 100 and 75 kg/ha), were required for the clayier soil types associated with the Sodosols (2Dyb) and Vertosols (2Uge).

Tips for the childhood immunisation OSCE

The effectiveness of check dams on channel morphology of managed torrents is rarely assessed. Therefore, there is a need for studies that focus on the impacts of existing engineering check dams on the planoaltimetric characteristics of the torrent, particularly in Mediterranean areas, where the hydrological regime of ephemeral channels is dynamically unsteady. The quantitative evaluation of the effects of the check dams on channel morphology after many years (i.e., at least four or five decades) helps introduce innovations to the usual analysis of check dam efficacy which have often been limited to qualitative observations for only a few years after installation. As a contribution to make up these shortcomings, this paper investigates the geomorphologic asset of a torrent in southern Italy containing 10 check dams (installed in the 1950s to 1960s) and analyzes the dynamics of the scouring and sedimentation processes upstream and downstream of selected check dams after 8 rainfall events; moreover, the capability of the model by Castillo (2007) to predict scouring/sedimentation in proximity to these check dams is assessed. Sediment stored upstream of each check dam (where lower channel gradients and wider channel sections formed very long and wide sedimentary wedges) is more than one order of magnitude higher compared to scouring downstream. The morphological analysis revealed that the check dams installed in the headwater reach play a function of bed stabilization (due to the longitudinal slope reduction) and flood lamination (because of the wider channel section) rather than a role of sediment collectors as their sediment storage capacity has already been completed. Scouring/sedimentation dynamics depend mainly on the channel slope and width in proximity to the check dams rather than on structure height. Finally, Castillo9s model showed an acceptable performance in predicting scouring/sedimentation in the channel bed close to check dams after the monitored rainfall events, the model efficiency being satisfactory and the differences between the mean observed and simulated values low. This investigation improves the understanding about morphological effects of check dams in Mediterranean torrents based on field observations and quantitative analysis.

Diagenetic Environment of Sandstones from the Ermaying Formation (Middle Triassic), North-eastern Margin of the Ordos Basin, China: Implications for the Erosion Vulnerability of the Pi Sandstone

A hard layer of calcite cemented sandstones overlaid weakly consolidated mudstones occur in the Middle Triassic, Ermaying Formation in the eastern margin of the Ordos Basin, China, were examined to reveal the diagenetic environment of Pi sandstone. The Pi sandstone refers to a type of terrigenous clastic rock assemblage composed mainly of sandstone, siltstone and mudstone with red and white color, which is characterized by exposing or being covered with sand or loess, vulnerable to weathering and erosion, distributed in the contiguous area of Shaanxi province, Inner Mongolia autonomous region and Shanxi province in China, and formed during Late Paleozoic–Mesozoic. The “Pi” comes from the folk name (pishuang) of arsenic in Chinese, the appellation of the “Pi sandstone” means that it is harmful to soil and water conservation. The Pi sandstone samples were collected from a sheet-like sandstones deposited in ephemeral river. Petrographic observation show that the samples studied carry a semi-arid climate signal, are cemented by mictrie (microcrystalline calcite), sparry (coarse-crystalline) calcite as well as quartz overgrowths. The δ13C and δ18O values of calcite in the studied are –6.2 to – 3.8 ‰ PDB and from–10.2 to –8.9‰ PDB, respectively. The evidence from petrography and stable isotopes suggests that the cementation of the sandstone mainly occurred in the vadose - phreatic environment.

Architectural and facies characterization of the Aptian fluvial Barbalha Formation, Araripe Basin, NE Brazil

Abstract The Aptian Barbalha Formation records the beginning of the post-rift stage of the Araripe Basin. It consists predominantly of sandstones and mudstones interbedded with thin layers of bituminous black shales and conglomerates. The depositional and architectural features of the alluvial succession of the Barbalha Formation were characterized by detailed study and descriptions of the selected outcrops and analysis of well core data. In this study, two main depositional sequences were identified. The lower depositional sequence is more than 100 m thick and comprises a vertical facies succession composed of amalgamated, multistorey, braided fluvial channel sandstone bodies overlain by a widespread lacustrine black shale up to 10 m thick. The lacustrine black shales–carbonate mixed interval is known as the Batateira Beds and constitutes a regionally important stratigraphic correlation marker in the basin. This interval records the establishment of a large lake that experienced severe water-level fluctuations and anoxic events. The upper depositional sequence is 60–95 m thick, and mainly consists of thin, yellowish, medium- to fine-grained sandstones and variegated shales. The upper sequence rests unconformably on the lacustrine black shales of the Batateira Beds. Thin and discontinuous conglomerate beds at the base of the upper sequence laterally grade into coarse-grained sandstones. These coarse-grained sandstones are overlain by interbedded sandstones and mudstones organized in fluvial cycles. The upper and lower sequences of the Barbalha Formation are separated by an erosive unconformity, traceable throughout the study area, formed during a period of stratigraphic base-level lowering. This surface marks a change in the lower sequence from a dominantly fluvial depositional style, with amalgamated multistorey braided fluvial channel sand bodies, to a lacustrine system in the top to an eminently fluvial sedimentation, which in the basal section comprises amalgamated, multistorey, braided fluvial channel sand bodies, and in the superior section the amalgamated fluvial channels are overlain by floodplain and overbank sandstone bodies with fixed fluvial channel deposits, interpreted as a suspended-load-dominated fluvial system in the upper sequence. This change in the depositional style is accompanied by a reduction in grain size and a change in the fluvial regime, suggesting that the drainage system was restructured due to tectonic movements in the basin and climatic variations. In addition to the restructuring of the drainage basin, the characteristics of the discharge of the river system have changed, probably because of the more humid climatic conditions that dominated during the deposition of the upper sequence. The fluvial deposition in the lower sequence is associated with more ephemeral river systems, while the facies architecture of the upper sequence is associated with perennial systems and is suggestive of a suspended-load-dominated fluvial system. This fluvial system is capped by lacustrine deposits of the Crato Formation. The upper sequence grades upwards into the Crato Formation. The boundary between these two units is delineated by the presence of greenish calciferous shales that are covered by lacustrine laminated limestones and shales of Neoaptian age. Palaeocurrent readings from the fluvial deposits of both sequences display a consistent palaeoflow to the SE. Sedimentological and palaeontological evidence indicates a tectonic control on sedimentation and humid to subhumid climate conditions.

Comparison of detrital mineral compositions between stream sediments of the Yangtze River (Changjiang) and the Yellow River (Huanghe) and their provenance implication

ABSTRACT A comparative comparative study on the detrital mineral composition of stream sediments of the Yangtze River (Changjiang) and Yellow River (Huanghe) shows that, light minerals of the Yangtze River basin were mainly quartz, feldspar, and detritus, the compositional characteristics of light minerals differed among tributaries, the main stream had a generally higher maturity index than tributaries; heavy mineral content tended to decrease progressively from the upper stream to lower stream of the Yangtze River, the primary assemblage was magnetite-hornblende-augite-garnet-epidote, and diagnostic minerals of different river basins were capable of indicating the nature and distribution of the source rock. Detrital mineral assemblages in sediments of tributaries and the main stream of the Yellow River were basically similar, Primary heavy mineral assemblage was opaque mineral-garnet-epidote-carbonate mineral and alteration mineral. Variations in the contents of garnet, opaque mineral, and hornblende mainly reflected the degree of sedimentary differentiation in suspended sediment and the hydrodynamic intensity of a drainage system. The heavy mineral differentiation index F revealed sedimentary differentiation of diagnostic detrital mineral composition due to changes in regional hydrodynamic intensity and can serve as an indicator for studying the dynamic sedimentary environment of a single-provenance river and the degree of sedimentary differentiation of its detrital minerals. Changes in detrital mineral content of the Yellow River was not completely controlled by provenance but reflected gravity sorting of the detrital mineral due to variations in the ephemeral river hydrodynamic intensity and sedimentary environment, however the index changing of Yangtze River were mainly influenced by the complex sediment sources. Therefore caution must be exercised in using the detrital mineral composition of marginal sea to determine the contribution of the Yangtze River and Yellow River. © 2019 China Geology Editorial Office.

Mid to late Holocene fluvio-marine record from the ephemeral rivers of northern Alluvial Plains of Gujarat, western India

Mid to late Holocene fluvio-marine record from the ephemeral rivers of northern Alluvial Plains of Gujarat, western India

Ostracod faunas from the Dalazi and Tongfosi formations (Yanji Basin, northeast China): Biostratigraphic, palaeogeographic and palaeoecological implications

This work provides a detailed taxonomic study of ostracod species from the Dalazi and Tongfosi formations of the Yanji Basin (Jilin Province, NE China). Fourteen species including one new species belonging to nine genera have been recovered: Scabriculocypris tonfosiensis, Scabriculocypris yanbianensis, Cypridea concinaformis, Mongolocypris yanjiensis, Mongolianella kyranbeki sp. nov., Lycopterocypris infantilis, Lycopterocypris sp., Yumenella toorojensis, Candona spp., Cyprois sp., Vlakomia ustinovskii and Vlakomia jilinensis. With the recovery of well-preserved specimens, the sieve pore, ontogeny and sexual dimorphism of Vlakomia jilinensis and Vlakomia ustinovskii are recognized for the first time. The ostracod biostratigraphic correlations suggest that the age of the Tongfosi Formation is Albian and may extend upwards into the Upper Cretaceous, and the Dalazi Formation is not older than the Albian, probably of early Late Cretaceous age. The ostracod faunas of the Tongfosi and Dalazi formations show affinities to faunas of Eastern Mongolia and South Korea, providing evidence of potential faunal exchanges between Northeastern China, Eastern Mongolia and South Korea during the Albian to early Late Cretaceous time. On the basis of their ostracod faunas, the Tongfosi and Dalazi formations represent a shallow-littoral lacustrine depositional environment that potentially included small ephemeral water bodies.

Genetic units and facies architecture of a Lower Cretaceous fluvial-aeolian succession, São Sebastião Formation, Jatobá Basin, Brazil

The Lower Cretaceous São Sebastião Formation of Jatobá Basin consists of continental strata accumulated in an arid environment dominated by aeolian deposits. The best outcrops are located in the county of Ibimirim, in the Pernambuco State. Through the description of several stratigraphic sections, three aeolian and two fluvial facies associations characterize this formation. The aeolian facies represent (a) aeolian crescentic dunes, (b) aeolian sand sheets, and (c) blowouts; the fluvial facies record (d) sheet floods and (e) channelized ephemeral rivers. These facies associations are organized into three genetic units that are bounded by supersurfaces. The unit 1 is formed by the intercalation of sheet flood, aeolian dry sand sheets, and aeolian dunes facies associations, often with soft sediment structures. The cross-bedded strata ascribed to aeolian dunes become larger and more frequent towards the top of the unit, as the soft sediment deformation structures become scarcer. The Unit 2 comprises aeolian sand sheets facies scoured by fluvial channels, with erosive concave bases, and by blowouts, which are subsequently filled by aeolian dunes deposits. Unit 3 consists of cross-bedded strata related to medium-to-large, either simple or compound aeolian dunes (draas). Supersurfaces bound the genetic units recording depositional gaps, thus defining different episodes of accumulation.

Pseudo soil in hyper-arid ephemeral stream channel beds: Geo-ecological implications of the fluvio-pedogenic unit (FPU)

The type of stratum in dryland ephemeral channel beds (wadis) determines its hydrological characteristics, which impact vegetation productivity. The objective of this study was to assess some key properties of a cemented, fine-grained bed stratum, previously characterized as a fluvio-pedogenic unit (FPU), as well as those of the overlying non-cohesive gravel bed stratum, known as a fluvially active unit (FAU). While the latter is an outcome of regular fluvial processes of recurring scour and fill, the former is characterized by horizonation, calcium carbonate deposition, oxidation, and accumulation of fine-grained material, defining it more as a soil or pseudo soil than as a sediment. The study was conducted in the hyper-arid southern Negev and Arava Valley of Israel, where the FAU and the underlying FPU were investigated, focusing on geo-ecological functioning. The results revealed considerable differences between the two types of strata. The contents of hygroscopic moisture, total organic carbon, and calcium carbonate were fourfold, 57%, and 36% greater, respectively, in the FPU than these in the FAU. Above all, the fine particle contents, including the clay and silt fractions, were almost eightfold and almost sixfold greater, respectively, for the FPU than those for the FAU, characterizing the former as loamy fine sand and the latter as fine sand. Altogether, these properties determine the stratum's field capacity and permanent wilting point, which were 73% and 50% greater, respectively, in the FPU than those in the FAU. In turn, the last two properties determine the available water capacity, which was almost twofold greater under the FPU than that under the FAU. Considering the (i) FPU's mean thickness of 0.6 m; (ii) FPU's horizonation into A, B, and C horizons; and (iii) a 70–90% decrease in available water capacity between FPU's A and B horizons, as well as between its B and C horizons, then the total available water capacity throughout this stratum's thickness is 20–87% greater under the FPU than that under the FAU. In addition, the FPU's cemented nature seems to provide a safe stratum that remains stable during floods, sustaining the establishment and growth of deep-rooted perennial vegetation. It is concluded that the FUP's properties have positive implications for vegetation growth and survival under the harsh climatic conditions across the region.

Geomorphic hazards in south‐west Saudi Arabia: The human–environmental nexus

Despite limited attention to geomorphic hazards in Saudi Arabia, the mountainous region in the south‐west portion of the Kingdom has experienced a series of devastating debris flows, landslides, rockfalls, and debris floods during the past several decades. While undisturbed hillslopes are relatively stable, many rock slides, rockfalls and landslides are associated with cut and fill slopes of mountain roads and other disturbances in this steep terrain. These human‐induced geomorphic hazards act synergistically to exacerbate downslope and downstream disasters, such as debris flows and debris floods. The progressive sediment loading in low‐gradient channels (wadis) together with large convective rainfall events, have caused episodic evacuation of these ephemeral channels. As such, hydrogeomorphic linkages between hillslope and channel mass wasting processes may be temporally separated as wadis accumulate sediment, posing challenges for prediction of the timing of damaging debris flows. Furthermore, there is little appreciation of the extent to which human‐related disturbances (e.g., mountain roads, construction sites, overgrazing) contribute to these downstream disasters or the vulnerability of passengers, residents, or herders to these anthropogenically induced hazards. Such knowledge and information is needed to develop effective hazard mitigation and real‐time warning systems for this and similar dry mountain regions that experience episodic storms. Here we demonstrate the need for improved road location, construction practices, and land management in this steep terrain as well as better appreciation of the hillslope and in‐channel hazard nexus to reduce downstream impacts of geomorphic disasters.

Quantifying CO2 Leak Rates in Aquatic Environments

The Daylesford region of Victoria (Australia), is a region of natural CO2 seepage. Small bubble streams of CO2 are released into ephemeral river beds proximal to mineral springs that contain high dissolved CO2 content. We study four sites of CO2 degassing to (i) establish the characteristics of CO2 seepage caused by transport to surface of CO2-rich water, (ii) provide an estimate of CO2 flux in the region, and (iii) investigate seasonal effects on CO2 seepage. We observe that bubbling behavior varies considerably between sites, including the number and distribution of bubbling points, and bubble stream the continuity. Total CO2 seep rates at each site were low (< 20 kg/d) but varied substantially between different sites. There were no obvious indicators of total emission rate; the bubble density or other characteristics at the highest emission seep were not remarkably different to the smaller seeps. We find that the total CO2 emission varies inconsistently with season, with some seep rates increasing and other decreasing in the dry season when water levels are lower. We find there are challenges in quantifying the total gas leakage at sites of highly localized and intermittent degassing. Our work has implications for detecting and quantifying leaks from engineered CO2 storage sites which emerge in aqueous environments, which could be these are marine or terrestrial (lakes or rivers).

Use of U-isotopes in exploring groundwater flow and inter-aquifer leakage in the south-western margin of the Great Artesian Basin and Arckaringa Basin, central Australia

The distribution of uranium isotopes (238U and 234U) in groundwaters of the south-western margin of the Great Artesian Basin (GAB), Australia, and underlying Arckaringa Basin were examined using groundwater samples and a sequential extraction of aquifer sediments. Rock weathering, the geochemical environment and α-recoil of daughter products control the 238U and 234U isotope distributions giving rise to large spatial variations. Generally, the shallowest aquifer (J aquifer) contains groundwater with higher 238U activity concentrations and 234U/238U activity ratios close to secular equilibrium. However, the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238U activity concentrations. Other locations in the J aquifer that receive little or no recharge contain higher 238U activity concentrations because uranium from localised uranium-rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution. The geochemical conditions of the deeper aquifers generally result in lower 238U activity concentrations in the groundwater accompanied by higher 234U/238U activity ratios. The sequential extraction of aquifer sediments showed that α-recoil of 234U from the solid mineral phases into the groundwater, rather than dissolution of, or exchange with the groundwater accessible minerals in the aquifer, caused enrichment of groundwater 234U/238U activity ratios in the Boorthanna Formation. Decay of 238U in uranium-rich coatings on J aquifer sediments caused resistant phase 234U/238U activity ratio enrichment. The groundwater 234U/238U activity ratio is dependent on groundwater residence time or flow rate, depending on the flow path trajectory. Thus, uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers; however, spatial heterogeneity, and the lack of clear regional correlations, made it difficult to identify recharge and inter-aquifer leakage.

Isotopic characteristics and paleoclimate implications of the extreme precipitation event of March 2015 in northern Chile

Prior to the 24-26 March 2015 extreme precipitation event that impacted northern Chile, the scenarios for Pleistocene and Holocene wetter paleoclimate intervals in the hyperarid core of the Atacama Desert had been attributed to eastern or southwestern moisture sources. The March 2015 precipitation event offered the first modern opportunity to evaluate a major regional precipitation event relative to those hypothetical paleoclimate scenarios. It was the first opportunity to determine the 18O and 2H composition of a major precipitation event that might eventually be preserved in geological materials. The driver for the March 2015 event was a synoptic-scale weather system, a cutoff cold upper-level low system that traversed the Pacific Ocean at a time of unusually warm temperatures of Pacific surface water. Ground-based precipitation data, stable isotopes in precipitation and river samples, NCEP/NCAR reanalysis atmospheric data and air mass tracking are utilized to connect the Earth surface processes to atmospheric conditions. The δ18O and δ2H of the precipitation and ephemeral rivers were significantly heavier than the rain, snow and ephemeral rivers fed by more frequent but less voluminous precipitation events registered prior to March 2015. Consistent with the atmospheric analyses, the rain isotopic compositions are typical of a water vapor whose source was at more equatorial latitudes of the Pacific and which moved southward. The late March 2015 system was an unforeseen scenario even for El Niño Pacific ocean conditions. Furthermore, the late summer season warmth led to greater potential for erosion and sediment transport than typical of more common moderate precipitation scenarios which usually include widely distributed snow. A comparison of the March 2015 scenario to the spatial distribution of wetter paleoclimate intervals leads to the hypothesis that the March 2015 scenario likely better fits some parts of the paleoclimate record of the continental interior hyperarid Atacama Desert than do the eastern or southwestern moisture source paleoclimate scenarios deduced previously.

Dynamics of metals bound to suspended sediments in floods and on channel banks of the ephemeral Wadi Sekher, northern Negev desert, Israel

This study examines the variation in the concentration of eight heavy metals (Cu, Ni, Pb, Cd, Cr, Co, V, Sc) bound on suspended sediments during flow events and those deposited in channel banks. The study was undertaken in Wadi Sekher, an ephemeral flash-flood channel draining the Neot Hovav industrial chemical complex in the semi-arid northern Negev, Israel, at sites varying with bank height and distance from the industrial complex.Metal concentrations were found to be higher in the initial flow and recession than during peak flow. Bound metal concentrations were mainly affected by suspended sediment composition and concentrations. During peak flow the suspended sediment concentration rises and quartz sand is a major constituent. This leads to a decrease in bound metal concentrations, as the larger particles have a weaker affinity to binding. In six sediment samples, taken during the first 15 min of two floods, the bound metal concentrations changed similarly. These changes are suggested to represent variations in the source and cannot be attributed to dilution or binding effects.Six banks were sampled along Wadi Sekher, from the Neot Hovav hydrometric reach downstream to the confluence of Wadi Sekher and Wadi Beer-Sheva, at specified heights, following a bank-full flood. In every cross-section, a significant difference (p < 0.01) was seen in Cu, Cd, Co, V and Sc concentrations with bank height, with highest concentrations at bank-bed intersection. Downstream variations in bound metal concentrations along Wadi Sekher were statistically (p > 0.05) undifferentiated, indicating that the industrial area is not a source point for these metals, and that a constant input exists into the channel from tributaries along the channel.Due to the difficulty in sampling flash floods in ephemeral channels, existing data are not abundant, and our understanding of these environments is therefore limited. This study improves knowledge of interrelated variations in bound metal concentrations in fluvial deposits, in suspended sediment and in water during flash floods.

A participatory design approach for modernization of spate irrigation systems

Spate Irrigation represents the main source of livelihood for rural population of many communities living in arid and semi-arid areas of the world. The area of Raya Valley (Ethiopia), is one such example that is used here to analyse the importance of participatory approach in making this irrigation technique sustainable, effective and durable. Spate irrigation development projects realised in Raya Valley during the last twenty years led to a partial failure, due to the low involvement of local farmers who have experience of the local environment and who have been practising the techniques from centuries. This paper describes the implementation of a participatory methodology, based on the integration of Participatory Rural Appraisal and Participatory Design, for the design of effective improvements in a traditional spate irrigation system in Raya Valley. Water is harvested from seasonal floods of wadis (ephemeral rivers) using diversion bunds made by local materials or concrete. Farmers’ participation allowed to defining gabions as a suitable solution and to realise a technical design of improved structures. The design of an improved diversion structure and a gabion wall against bank erosion was completed. The structures resulted in line with operation and maintenance strategy and with traditional spate irrigation management. New insights from local farmers knowledge, to be considered for future spate irrigation development projects, are analysed and presented.