Connectivity processes and riparian vegetation of the upper Paraná River,Brazil

In fluvial systems, the relationship between a dominant variable (e.g. flood pulse) and its dependent ones (e.g. riparian vegetation) is called connectivity. This paper analyzes the connectivity elements and processes controlling riparian vegetation for a reach of the upper Paraná River (Brazil) and estimates the future changes in channel-vegetation relationship as a consequence of the managing of a large dam. The studied reach is situated 30 km downstream from the Porto Primavera Dam (construction finished in 1999). Through aerial photography (1:25,000, 1996), RGB-CBERS satellite imagery and a previous field botany survey it was possible to elaborate a map with the five major morpho-vegetation units: 1) Tree-dominated natural levee, 2) Shrubby upper floodplain, 3) Shrub-herbaceous mid floodplain, 4) Grass-herbaceous lower floodplain and 5) Shrub-herbaceous flood runoff channel units. By use of a detailed topographic survey and statistical tools each morpho-vegetation type was analyzed according to its connectivity parameters (frequency, recurrence, permanence, seasonality, potamophase, limnophase and FCQ index) in the pre- and post-dam closure periods of the historical series. Data showed that most of the morpho-vegetation units were predicted to present changes in connectivity parameters values after dam closing and the new regime could affect, in different intensity, the river ecology and particularly the riparian vegetation. The methods used in this study can be useful for dam impact studies in other South American tropical rivers.     

Lithologic and structural controls on fluvial knickzones in basalts of the Paraná Basin,Brazil

Knickzones are common features along rivers on the basaltic plateaus of the Paraná Basin. According to current conceptual models, knickpoints are formed in massive basalts that have a high density of vertical joints. Vesicular–amygdaloidal basalts and those with horizontal joints tend to form reaches of low slope due to their lower resistance to erosion. However, field surveys revealed complexities in this general relationship. The research presented here sought to verify the controls on the genesis of knickzones in this type of geological environment. We studied a 61 km-long mixed bedrock–alluvial river. The longitudinal profile of the river was surveyed on a topographic map with 5 m contour intervals. Tectonic lineaments oriented transverse to the channel and longitudinal lineaments in which the river lies were identified from maps. A detailed field survey of the lithologic characteristics of the riverbed was also performed. The results show that knickzones may form in any litho-structural zone in the flood basalts. On the other hand, low slope zones are predominantly sculpted into vesicular–amygdaloidal basalts, which are less resistant to erosion. The fracture densities of vesicular–amygdaloidal basalts are similar in low slope zones and in knickzones (4.86 and 4.93 m/m², respectively). This indicates that knickzones in this type of basalt are not caused by higher resistance to erosion. Approximately 60% of the 18 knickzones identified are associated with tectonic lineaments, irrespective of the structural characteristics of the basalts. Vesicular–amygdaloidal basalt and/or basalt with horizontal joints allow the fastest knickzone migration and aid in the formation of convexities. Knickpoints in these basalts do not migrate, but erosion in the pools advances downstream and breaks the bedrock steps, thus increasing the slope. Massive basalt with vertical joints causes slower migration, and its presence at convexities indicates local uplift. Convex segments are only formed upstream of faults.     

Early Permian post-glacial bivalve faunas of the Itararé Group,Paraná Basin,Brazil: Paleoecology and biocorrelations with South American intraplate basins

The uppermost portion of the Taciba Formation, Itararé Group, Paraná Basin, Brazil, records a succession of depositional environments tied to the demise of late Paleozoic glaciation. In the study area, Teixeira Soares county, state of Paraná, the unit is dominated by massive to laminated diamictites with inclusions of sandstones and other coarse-grained lithotypes, representing re-sedimented material in proximal areas. These are succeeded by fine to medium-grained sandstones with tabular cross-stratification and pectinid-rich shell pavements, interpreted as nearshore deposits. Above this, laminated and intensely bioturbated siltstones with closed articulated bivalve shells are recorded, probably deposited in inner shelf settings. Fine to very fine sandstones/siltstones with hummocky cross-stratification and intercalated mudstones, including infaunal in situ shells, are interpreted as stacked storm deposits, generated in distal shoreface environments. These are succeeded by fossil-poor, massive to laminated siltstones/mudstones or gray shales (=Passinho shale) that are inferred to be outer shelf deposits, generated in organic-rich, oxygen-deficient muddy bottoms. In this sedimentary succession dropstones or ice-rafted debris are missing and locally the Passinho shale marks the maximum flooding surface of the Itararé succession. These are capped by the fluvio-deltaic deposits of the Rio Bonito Formation (Sakmarian–Artinskian). Six facies-controlled, bivalve-dominated assemblages are recognized, representing faunal associations that thrived in aerobic to extreme dysaerobic bottoms along a nearshore–offshore trend. Within these assemblages, nineteen bivalve species (three of them new) were recorded and described in detail. The presence of Myonia argentinensis (Harrington), Atomodesma (Aphanaia) orbirugata (Harrington) and Heteropecten paranaensis Neves et al. suggests correlation with bivalve assemblages of the Eurydesma-bearing Bonete Formation, Pillahuincó Group, Sauce Grande-Colorado Basin (Buenos Aires Province), Argentina, indicating a possible Asselian age for this diverse post-glacial bivalve fauna. Despite that, typical members of the icehouse-style Eurydesma–Trigonotreta biota (stricto sensu) have not yet been found in the studied bivalve assemblages.     

A comparative study of aquifer systems occurring at the Paraná sedimentary basin, Brazil: U-isotopes contribution

The radioactivity due to ²³⁸U and ²³⁴U in three aquifer systems occurring within the Paraná sedimentary basin, South America, has been investigated. Uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the U-mobility coefficients between 7.6 × 10^?6 and 1.2 × 10^?3 g cm^?3. These values are also compatible with the U preference ratios relative to Na, K, Ca, Mg and SiO₂, which showed that U is never preferentially mobilized in the liquid phase during the flow occurring in cracks, fissures, fractures and faults of the igneous basaltic rocks. Experimental dissolution of diabase grains on a time-scale laboratory has demonstrated that the U dissolution appeared to be a two-stage process characterized by linear and second-order kinetics. The U dissolution rate was 8 × 10^?16 mol m^?2 s^?1 that is within the range of 4 × 10^?16–3 × 10^?14 mol m^?2 s^?1 estimated for other rock types. The ²³⁴U/²³⁸U activity ratio of dissolved U in solutions was higher than unity, a typical result expected during the water–rock interactions when preferential ²³⁴U-leach from the rock surfaces takes place. Some U-isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in São Paulo State. A modeling has been also realized considering all U-isotopes data obtained in Bauru (35 samples), Serra Geral (16 samples) and Guarani (29 samples) aquifers. The results indicated that the Bauru aquifer waters may result from the admixture of waters from Guarani (1.5 %) and Serra Geral (98.5 %) aquifers.     

A comparative study of aquifer systems occurring at the Paraná sedimentary basin, Brazil: major hydrochemical trends

This investigation was carried out within the Paraná sedimentary basin, Brazil, and involved the sampling of 80 pumped tubular wells for evaluating the hydrochemistry in three aquifer systems (Bauru, Serra Geral and Guarani) occurring in 21 localities of S?o Paulo and Mato do Grosso Sul states. The Guarani aquifer of Triassic?CJurassic age has continental dimensions and extends over some 1.2 million km² within the Paraná basin. A thick (up to 1,500?m) basaltic package of the Serra Geral Formation overlies this aquifer that is covered by Cretaceous sediments of the Bauru Group. Major hydrochemical data were obtained and compared in each aquifer system, allowing the establishment of the principal trends among the parameters analyzed. The redox potential Eh decreased according to the pH increase in the three aquifers. A consistent database has been assured from expected relationships found for typical parameters commonly evaluated in hydrogeochemical surveys. Thus, direct relationships of conductivity with ionic strength (IS) were determined and, despite bicarbonate, assumed an important role in justifying such trends; other direct significant correlations involving IS were also identified with Na⁺, Cl^?, F^? and SO₄ ^2?. Precipitation of carbonates was evidenced by opposite relations among CO₃ ^2?, Ca²⁺ and Mg²⁺ that are strongly linked to the temperature effects on Ca²⁺ and Mg²⁺ dissolution as often reported from theoretical constraints.     

Hydrochemical considerations and heavy metal variability in the middle Paraná River

The Paraná River is one of the largest drainage systems in the Americas. Its hydrology is characterized by an active teleconnection with the ENSO, and by a significant discharge increase trend, evident since the mid-1970s. An Eh–pH data set collected in the Paraná’s middle stretch suggests that large flood events, such as the one triggered by the 1982–1983 ENSO, are discernible in the plot, probably due to the influx of water draining flood plain water bodies. The total (particulate + dissolved) concentration of a set of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) was determined in a downriver survey of the middle stretch. With the exception of Cu, Cd, and Pb, the metals exhibit a significantly increasing concentration trend towards the river mouth. The slopes of the regression lines imply that Zn and Ni, on one hand, and Mn and Cr, on the other would have common controlling sources. Another set of analyses were performed during the 1982–1983 flooding event; besides an increased variability observable during the flood arrival, most elements, with the only exception of Pb, did not show a variability coherent with the discharge series.     

Absolute Dating of Permian Ash-Fall in the Rio Bonito Formation,Paraná Basin,Brazil

The Rio Bonito Formation in southern Paraná basin contains a set of tonsteins interbedded with coal-seams. These tonsteins are composed mainly of kaolinite with zircon, apatite and beta-quartz paramorphs as accessory minerals, and were interpreted as volcanic ashes deposited by ash falls over pits protected by barrier islands in a barrier-lagoon system. A U-Pb dating of zircons in the tonstein A, which furnished an age of 267.1 ± 3.4 Ma (Early Permian) confirming previous age-dates based on palynology and correlating them with one of the main periods of volcanic activity in the Gondwana.The source of the pyroclastic material was attributed to the early Permian Choiyoi magmatic arc in Argentina, developed during the Sanrafaelic orogeny, and with a main peak of volcanic activity between 260 and 272 Ma.     

The fluoride in the groundwater of Guarani Aquifer System: the origin associated with black shales of Paraná Basin

This work presents petrological and geochemical results of the black shales interval from Permian and Devonian strata of the Paraná Basin, Brazil and its relationships with fluoride of groundwater from Guarani Aquifer System. The Guarani Aquifer, located in South Brazil, Uruguay, Paraguay and Argentine, presents contents of fluoride higher than the Brazilian accepted potability limits. Several hypotheses have been presented for the origin of the fluoride in the groundwater of the Guarani Aquifer. Microcrystalline fluorite was registered in black shales of Ponta Grossa and Irati formations from Paraná Basin. The results shown in this work suggest that fluoride present in groundwater of Guarani Aquifer can be originated in deeper groundwater that circulates in Ponta Grossa and Irati formations. The interaction of the groundwater coming from deeper black shales with the groundwater-bearing Aquifer Guarani System occurs through regional fragile structures (faults and fractures) that constitute excellent hydraulic connectors between the two sedimentary packages. The microcrystalline fluorite registered in Ponta Grossa and Irati Formations can be dissolved promoting fluoride enrichment in groundwater of these black shales and Guarani Aquifer System.     

Geophysical signatures of the alkaline intrusions bordering the Paraná Basin

Alkaline intrusions at the edges of the Paraná Basin are mostly grouped in provinces, but occur in a few cases as isolated bodies. All of these intrusions surround the edge of the basin and intrude into weak zones, such as belts and arches. In rare cases, the intrusions are covered by basin sediments, but they are mainly found in the exposed crystalline basement. In this study, we discuss the gravimetric and magnetic signatures of the alkaline intrusions in the Ponta Grossa Arch, Alto Paranaíba and Goiás provinces. The provinces ages range from 120 to 60 Ma, and are thus contemporary or subsequent to the Serra Geral magmatic event. The magnetic signature of the province intrusions indicates a strong residual magnetization, as observed on maps of the anomalies reduced to the pole, which were different from the anomalies resulting only from induced field. The residual magnetization was often verified by magnetic measurements in the laboratory. Some of the studied intrusions have reverse magnetization. Other intrusions shows two magnetization directions, normal and reverse, indicating the likely presence of carbonatite. With the exception of the intrusions containing carbonatite, anomalies reduced to the pole are characterized by highly concentrated magnetization and well-defined 3D geometry. Intrusions with carbonatite usually exhibit dual polarization. The gravimetric signature is a positive anomaly of great magnitude. When carbonatite is present, a negative anomaly within the positive anomaly is observed, where the negative anomaly is associated with carbonatite. The gravimetric anomalies are also highly localized, indicative of 3D bodies. Gravimetric and aeromagnetic maps of the provinces show a coincidence between the location of the mapped intrusions and the anomalies. These maps also show anomalies that have the same signature but are not related to the mapped outcrops. This result suggests that these anomalies are indicative of the presence of alkaline intrusions that are covered by sediments (from either the Paraná Basin or alluvial sources) or are not emergent from the basement. The analysis of these maps and the inversion of the anomalies allows inference of the subsurface geometry, and thus also calculation of the body volume and its emplacement mechanism, which are elements necessary for mineral deposit evaluation. The maps also allow the identification of pre-existing faults and those formed during the emplacement. We compare geophysical models developed for gravimetric and magnetic data for the intrusions of the Ponta Grossa Arch, Alto Paranaíba and Goiás provinces in order to identify physical similarities and differences in the alkaline intruded into lithospheric segments with different tectonic histories.     

Geological Features of Devonian Sedimentary Basins in South China and Their Deposition and Mineralization

The Devonian succession in South China is well-known for its complete development, vari-fied sedimentary types, remarkable lithofacies variation and abundant mineral resources. The South China plate was formed by the collision and collage of the Yangtze plate and the Cathaysian plate. The collision began approximately at the Jinningian stage and the collage was not finalized until the Guangxian movement. It was on the South China plate with a somewhat different nature of the basement that the Devonian deposition formed.     

Time series analysis of daily rainfall and streamflow in a volcanic dike-intruded aquifer system, O��ahu, Hawai��i, USA

A conceptual model of groundwater occurrence was developed for a dike-intruded aquifer system in M??kaha valley, O??ahu, Hawai??i, USA, and used to explain the impacts of water resource development on groundwater levels and streamflow. Time-series analyses were applied to two subsets of daily rainfall, total flow, and baseflow??from the third (1946?C1968) and fourth (1968?C1991) periods of development??to evaluate changes in streamflow response. Autocorrelation, cross-correlation, squared coherency and phase functions were used to estimate the decorrelation lag time, and the correlation length, linearity with frequency, and frequency response delay between rainfall and streamflow. The decorrelation lag time for total flow and baseflow declined by 16?C20?days (d). The correlation length between rainfall and streamflow declined 4?C7?d for total flow and 10?C13?d for baseflow. The squared coherency function indicates an overall decline in linearity between rainfall and total flow across most frequencies. The changes in hydrologic response following increased water-resource development is consistent with a model of groundwater depletion resulting in less groundwater discharge and more induced groundwater recharge. Changes in streamflow response are inconsistent with observed changes in rainfall and imply that streamflow decline is more likely to be the result of groundwater pumping.     

High-resolution aquifer analog of fluvial–aeolian sediments of the Guarani aquifer system

The Guarani aquifer system (GAS) represents one of the biggest aquifers in the world and is the most relevant groundwater resource in South America. For the first time, by combining field and laboratory measurements, a high-resolution aquifer analog model of fluvial–aeolian sediments of the GAS in São Paulo State (Brazil) is constructed. Three parallel sections of frontal outcrops, 28 m × 5.8 m, and two parallel sections of lateral outcrops, 7 m × 5.8 m, are recorded during open-pit mining of sandy sediments and describe in detail the three-dimensional distribution of the local lithofacies and hydrofacies. Variations of hydraulic conductivity, K, and porosity, n, are resolved on the centimeter scale, and the most permeable units of the fluvial–aeolian facies association are identified. The constructed aquifer analog model shows moderate hydraulic heterogeneity and a mean K value of 1.36 × 10^?4 m/s, which is greater than the reported range of K values for the entire GAS in São Paulo State. The results suggest that the examined sedimentary unit constitutes a relevant portion of the GAS in São Paulo State in the context of groundwater extraction and pollution. Moreover, the constructed aquifer analog is considered an ideal basis for future numerical model experiments, aiming at in-depth understanding of the groundwater flow and contaminant transport patterns at this GAS portion or at comparable fluvial–aeolian facies associations.     

Stable isotope and mineralogical investigation of the genesis of amethyst geodes in the Los Catalanes gemological district,Uruguay, southernmost Paraná volcanic province

Stable isotopes (C, O, S) and mineralogical studies of the world-class amethyst-geode deposits of the Los Catalanes gemological district, Uruguay, constrain processes operative during mineral deposition. The mineralized basaltic andesites from the Cretaceous Paraná volcanic province are intensely altered to zeolites (clinoptilolite) and clay minerals. Variations in the δ¹⁸O values of silica minerals in geodes (chalcedony, quartz, and amethyst) are much larger and the values generally somewhat lower (21.2–31.5‰) in the Uruguayan deposits than in the Ametista do Sul area of southern Brazil. The range of δ³⁴S values (−15.0 to −0.3‰) of altered basaltic rocks requires (in addition to sulfur of magmatic origin) the involvement of ³⁴S-depleted sedimentary sulfur from bacterial sulfate reduction. The results delimit the mineralizing processes to a post-eruption environment characterized by low temperature and strong interaction of the lava flows with meteoric water.     

Epigenetic hydrothermal origin of native copper and supergene enrichment in the Vista Alegre district,Paraná basaltic province,southernmost Brazil

Native copper is widespread in the Lower Cretaceous Paraná basaltic province, southern Brazil, both as films in fractures and as massive balls in amygdules. The focus of this investigation is on the large concentration of occurrences (n = 85) that forms the Vista Alegre district in the border region of Rio Grande do Sul and Santa Catarina states. The high average of 220 ppm Cu content of the basalts resulted in ore of native copper, Cu oxides, abundant chrysocolla in the top of mineralizations, and minor malachite and azurite. Native copper is associated with dioctahedral and trioctahedral smectites, zeolites (heulandite and clinoptilonite), quartz, and calcite, typical of a low-T (100–150°C) hydrothermal alteration assembly. The PGE distribution shows enrichment in Pd in relation to Pt both in basalts and in native copper, supporting the hypothesis of hydrothermal origin of the mineralization. No evidence was found of direct precipitation of copper from the lava; based on field and petrographic evidence, integrated with BSE images, EPMA analyses, EGP contents of native copper, and bulk rock analyses, this is an epigenetic hydrothermal copper mineralization, followed by supergene enrichment.     

Geochemical evolution of groundwater in the Cambrian–Vendian aquifer system of the Baltic Basin

The shallowly buried marginal part of the Cambrian–Vendian confined aquifer system of the Baltic Basin is characterised by fresh and low δ¹⁸O composition water, whereas the deeply settled parts of the aquifer are characterized by typical Na–Ca–Cl basinal brines. Spatial variation in water geochemistry and stable isotope composition suggests mixing origin of the diluted water of three end-members—glacial melt water of the Weichselian Ice Age (115 000–10 000 BP), Na–Ca–Cl composition basin brine and modern meteoric water. The mixing has occurred in two stages. First, the intrusion and mixing of isotopically depleted glacial waters with basinal brines occurred during the Pleistocene glacial periods when the subglacial melt-water with high hydraulic gradient penetrated into the aquifer. The second stage of mixing takes place nowadays by intrusion of meteoric waters. The freshened water at the northern margin of the basin has acquired a partial equilibrium with the weakly cemented rock matrix of the aquifer.     

Geological sources of boron and fluoride anomalies in Silurian–Ordovician aquifer system,Estonia

The objective of this study was to examine the possible natural sources of fluorides and boron in Silurian–Ordovician (S–O) aquifer system, as the anomaly of these elements has been distinguished in groundwater of western Estonia. Water–rock interactions, such as dissolution and leaching of the host rock, are considered to be the main source of high fluoride and boron concentrations in groundwater. Altogether 91 rock samples were analysed to determine if high F⁻ and B levels in groundwater could be attributed to certain aquifer forming rock types. Fluorine and boron contents in limestones and dolomites vary from 100 to 500 mg/kg and 5 to 20 mg/kg, reaching up to 1,000 and 150 mg/kg in marlstones, respectively. K-bentonites, altered volcanic ash beds, are rich in fluorine (400–4,500 mg/kg) and boron (50–1,000 mg/kg). Thus, clay-rich sediments, providing ion-exchange and adsorption sites for F⁻ and B, are the probable sources of both elements in S–O aquifer system in western Estonia.     

U-Pb geochronology of Paraná volcanics combined with trace element geochemistry of the zircon crystals and zircon Hf isotope data

The Paraná volcanic province is a window into mantle and crustal processes in the Cretaceous. The variability and complexity of this province can be determined through the study of minerals. An integrated study of zircon from Paraná lavas (one high-Ti basalt, one low-Ti andesite, one high-Ti rhyodacite and one high-Ti andesite sill) was achieved using backscattered electron imaging, sensitive high resolution ion microprobe (SHRIMP-IIe) for U-Pb geochronology, and laser ablation inductively coupled mass spectrometer (LA-ICPMS) to determine the Lu-Hf isotopes and the trace-element compositions. U-Pb-Hf and trace-element data indicate that zircon crystallized from the magma at approximately 134 Ma. This South American large igneous province originated from the mantle and was contaminated by crust either in the mantle or during ascent and crystallization of magma. Contaminant continental crust had Precambrian age. Trace elements point to a new compositional field for zircon, different from other types of provinces. Examination of volcanic zircon improves our understanding of age and contamination of the Paraná volcanics.     

Simulating the impacts of groundwater pumping on stream–aquifer dynamics in semiarid northwestern Oklahoma,USA

Visual MODFLOW, a numerical groundwater flow model, was used to evaluate the impacts of groundwater exploitation on streamflow depletion in the Alluvium and Terrace aquifer of the Beaver-North Canadian River (BNCR) in northwestern Oklahoma, USA. Water demand in semi-arid northwestern Oklahoma is projected to increase by 53% during the next five decades, driven primarily by irrigation, public water supply, and agricultural demand. Using MODFLOW’s streamflow routing package, pumping-induced changes in baseflow and stream leakage were analyzed to estimate streamflow depletion in the BNCR system. Simulation results indicate groundwater pumping has reduced baseflow to streams by approximately 29% and has also increased stream leakage into the aquifer by 18% for a net streamflow loss of 47%. The magnitude and intensity of streamflow depletion, however, varies for different stream segments, ranging from 0 to 20,804 m³/d. The method provides a framework for isolating and quantifying impacts of aquifer pumping on stream function in semiarid alluvial environments.

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Résumé  Visual MODFLOW, un modèle numérique d’écoulement des eaux souterraines, a été utilisé pour évaluer les impacts de l’exploitation de l’eau souterraine sur la réduction du régime de la rivière dans un aquifère d’alluvions et de terrasse de la Rivière canadienne Beaver-North (BNCR) au nord-ouest de l’Oklahoma, aux USA. La demande d’eau dans le nord-ouest semi-aride de l’Oklahoma devrait augmenter de 53% durant les cinq prochaines décennies, essentiellement du fait de l’irrigation, la demande en eau potable et la demande agricole. En utilisant le module numérique traitant les rivières dans MODFLOW, les changements sur le régime de base des cours d’eau induits par le pompage et la recharge par la rivière ont été analysés pour estimer la réduction du régime de la rivière du système BNCR. Les résultats de la simulation indiquent que le pompage de l’eau souterraine réduit le débit de base de la rivière de 18% pour une perte nette du débit de la rivière de 47%. L’importance et l’intensité de la réduction du débit de base, toutefois, varie selon le bief, de 0 à 20,840 m³/d. La méthode apporte un cadre pour isoler et quantifier les impacts sur le pompage de l’aquifère sur le fonctionnement de la rivière dans un environnement alluvial semi-aride.

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Resumen  El Visual MODFLOW, que es un modelo numérico de flujo de agua subterránea, fue usado para evaluar los impactos de la explotación del agua subterránea, en la disminución de la cantidad de flujo de una corriente superficial, relacionada al acuífero del aluvión y de la terraza del Río canadiense Beaver-North (BNCR) en Oklahoma del noroeste, EUA. Se proyecta que la demanda de agua aumentará en un 53%, en el sector semiárido de Oklahoma del noroeste, durante las próximas cinco décadas, principalmente debido a la irrigación, suministro de agua público, y la demanda agrícola. Mediante el uso del paquete especial para relaciones corriente superficial- acuífero (SFR) de MODFLOW, se analizaron cambios inducidos por el bombeo, tanto en el flujo base, como en el goteo del río, para estimar la disminución del flujo de la corriente en el sistema de BNCR. Los resultados de la simulación indican, que el bombeo de agua subterránea ha reducido el flujo base a los arroyos aproximadamente en un 29% y también ha aumentado el goteo del arroyo hacia el acuífero en 18%, resultando una pérdida neta del flujo del río de un 47%. La magnitud e intensidad de la disminución del flujo del río, sin embargo, varía en sus diferentes segmentos, oscilando de 0 a 20,804 m³/d. El método suministra un marco, para aislar y cuantificar los impactos del bombeo del acuífero, sobre el funcionamiento de una corriente superficial en los ambientes aluviales semiáridos.

     

Chloride as tracer of solute transport in the aquifer–aquitard system in the Pearl River Delta,China

A 1D numerical model is constructed to investigate the impact of sedimentation and sea level changes on transport of Cl^? in the aquifer–aquitard system in the Pearl River Delta (PRD), China. The model simulates the evolution of the vertical Cl^? concentration profiles during the Holocene. Sedimentation is modeled as a moving boundary problem. Chloride concentration profiles are reconstructed for nine boreholes, covering a wide area of the PRD, from northwest to southeast. Satisfactory agreement is obtained between simulated and measured Cl^? concentration profiles. Diffusion solely is adequate to reproduce the vertical Cl^? concentration profiles, which indicates that diffusion is the regionally dominant vertical transport mechanism across the aquitards in the PRD. The estimated effective diffusion coefficients of the aquitards range from 2.0?×?10^–11 to 2.0?×?10^–10 m²/s. The effective diffusion coefficients of the aquifers range from 3.0?×?10^–11 to 4.0?×?10^–10 m²/s. Advective transport tends to underestimate Cl^? concentrations in the aquitard and overestimate Cl^? concentrations in the basal aquifer. The results of this study will help understand the mechanisms of solute transport in the PRD and other deltas with similar geological and hydrogeological characteristics.     

Review: groundwater management practices, challenges, and innovations in the High Plains aquifer, USA—lessons and recommended actions

The US High Plains aquifer, one of the largest freshwater aquifer systems in the world, continues to decline, threatening the long-term viability of the region’s irrigation-based economy. The eight High Plains States take different approaches to the development and management of the aquifer based on each state’s body of water laws that abide by different legal doctrines, on which Federal laws are superposed, thus creating difficulties in integrated regional water-management efforts. Although accumulating hydrologic stresses and competing demands on groundwater resources are making groundwater management increasingly complex, they are also leading to innovative management approaches, which are highlighted in this paper as good examples for emulation in managing groundwater resources. It is concluded that the fragmented and piecemeal institutional arrangements for managing the supplies and quality of water are inadequate to meet the water challenges of the future. A number of recommendations for enhancing the sustainability of the aquifer are presented, including the formation of an interstate groundwater commission for the High Plains aquifer along the lines of the Delaware and Susquehanna River Basins Commissions in the US. Finally, some lessons on groundwater management that other countries can learn from the US experience are outlined.