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Factor analysis was applied to 56 groundwater samples collected from wells located in the Araripe Sedimentary Basin, in the north-east of Brazil. The parameters are a set of 9 physicochemical, chemical, and isotope data, constituted by electrical conductivity (EC), ionic concentrations of Ca2+, Mg2+, Na+, K+, Cl−, SO42−, alkalinity and δ18O0/00. In R-mode factor analysis, the first 3 factors explain 62% of the variance, their loadings allowing the interpretation of hydrogeochemical processes that take place in the area. Q-mode factor analysis on the 56 water samples decreases space dimensionality to 6, explaining 93% of the total database information. With the aid of a scalar and angular measurement method, objects were clustered, resulting in 11 groups classified according to their inherent characteristics, related to their hydrogeological origin.Keywords: hydrogeochemistry, R-mode factor analysis, Q-mode factor analysis, Araripe sedimentary basin, Cariri valley

To better know the aquifer system in the Maracanã Environmental Protection Area were collected samples in four campaigns; the first during the drought season and the others in the following rainy one. The water samples were analised for eleven hydrochemical parameters, CE, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, NO3-, Fe and P. Cluster analysis separated the wells in the area, identifing three different groups that exploit water with electrical conductivity in the ranges of 230 to 400 μS/cm, 87 to 210 μS/cm, and 22 to 64 μS/cm, respectively. Data show a predominance of sodium chlorinated water. With these results and identification of geochemical processes determined by changes in concentrations of Fe and P it was possible to develop a model that identifies the aquifer of the aquifer system exploited by each well. RESUMO Para conhecer o sistema aquífero na área de Proteção Ambiental do Maracanã foram coletadas amostras de água em quatro campanhas; a primeira no período seco e as outras no período chuvoso seguinte. Foram analisados nas águas amostradas onze parâmetros hidroquímicos CE, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, NO3-, Fe e P. A análise de agrupamentos separou os poços na área, identificando três grupos distintos que explotam águas com condutividade elétrica nas faixas de 230 a 400 µS/cm, 87 a 210 µS/cm e 22 a 64 µS/cm; os dados mostraram predominância de águas cloretadas sódicas e recarga rápida. Com estes resultados e identificação de processos geoquímicos determinados pelas mudanças nas concentrações de Fe e P foi possível desenvolver um modelo que identificou os aquíferos do sistema de aquíferos explotado por cada poço.

A matéria orgânica (MO) encontrada no solo pode ser uma ferramenta auxiliar na identificação de uma vegetação remota. Na Floresta Nacional do Araripe e circunvizinhança, na Chapada do Araripe, realizou-se o presente estudo, em que as medidas de d13C e d15N da MO dos solos foram utilizadas para: (i) avaliar os valores atuais desses parâmetros; (ii) analisar a variabilidade natural do d13C no solo de diferentes formações florestais e (iii) indicar o declínio de florestas. Verificou-se que os solos das áreas hoje preservadas e cuja MO na superfície mostra d13C tipo C3, da vegetação atual, e uma mistura C3-C4 em profundidade, correspondem a ecossistemas antropizados no passado por uso agrícola; já os solos que mantiveram o d13C tipo C3 em todo o perfil se referem a ecossistemas antropizados, porém por uso não agrícola. Na caatinga, o perfil do d15N indicou um solo mais mineralizado e com menos MO. As áreas reflorestadas e preservadas apresentaram recuperação da MO.

Flow modeling and hydrogeochemical inversion calculations were performed on the aquifer systems of the Crato-Juazeiro Graben in the Araripe Sedimentary Basin of the Cariri Valley, Northeast Brazil, in order to assess aquifer interconnections through an aquitard of the Araripe Plateau. Steady state hydraulic head numeric calculations with the finite difference method used Modflow software with hydrologically based boundary conditions and a piezometric surface as initial condition. Hydrogeochemical inversion with PHREEQC was performed for two water samples representing typical initial and final waters along the flow path. Flow simulation shows that approximately 20% of all recharge water from the superior aquifer system passes through the Santana aquitard reaching the middle aquifer system. Quantification of mineral dissolution/precipitation processes, ion exchange and microbiological redox reactions taking place in the aquifer systems also indicates hydraulic interconnection of the superior and middle aquifer systems through the Santana aquitard.

The objective of this research was to identify and quantify the primary processes responsible for the increase in salinity observed in the alluvial aquifer during the dry season. Multivariate statistical analysis and inverse geochemical modeling were used to simulate possible salinization mechanisms in the alluvial aquifer. For this, by quantifying electrical conductivity and the concentrations of the ions Ca2+, Mg2+, Na+, K+, Cl-, HCO3- and SO42- in waters from the crystalline basement near the study area, water reservoirs near the alluvial aquifer and the studied alluvial aquifer, groups were formed and discriminant analysis was applied. Significance tests showed that direct evaporation has not only an influence on the alluvial aquifer, but also a mean volumetric contribution of 15.8% from waters of the crystalline basement, accompanied by processes of salt dissolution and precipitation, which would also justify the increase in salinity observed in the alluvial aquifer in the dry period. Com o objetivo de identificar e quantificar os principais processos responsáveis pelo aumento da salinidade observada durante o período não chuvoso em um pequeno aquífero aluvial localizado no semiárido do Nordeste brasileiro utilizaram-se a análise estatística multivariada e a modelagem geoquímica inversa para simular prováveis mecanismos de salinização no aquífero; para isto e por meio da quantificação da condutividade elétrica e dos íons Ca2+, Mg2+, Na+, K+, Cl-, HCO3- e SO42- em amostras de águas do embasamento cristalino próximo à área de estudo, nos reservatórios próximos ao aquífero aluvial e do aquífero aluvial estudado, foram formados grupos e aplicada a análise discriminante. Testes de significância dos resultados demonstraram que a evaporação direta não apenas exerce influência sobre o aquífero aluvial mas ainda tem uma contribuição volumétrica média de 15,8% de águas do cristalino acompanhada de processos de dissolução e precipitação de sais, o que também justificaria o aumento da salinidade no aquífero aluvial no período seco.

Measurements of the environmental isotopes carbon-14 and oxygen-18 and of the electrical conductivity in ground water, together with MODFLOW-88 (DOS) simulations of pumping tests, were used to achieve a detailed understanding of the functioning of an aquifer in the area of a well field. The methodology was applied in the sedimentary basin of the Cariri region, in the south of Ceara State in Brazil. Localized hydraulic connections between adjacent aquifer units could be detected, and mixing ratios for the contributions from the units involved were determined. Cone of depression simulations for a three-year drought period revealed well interference and a drastic lowering of the piezometric level, thereby explaining the hydrogeologic changes and transformations in vegetation that were observed in the area of the well field. The combined use of the modeling tools and the geochemical field observations is shown to provide more detailed insight into the conceptual model of the groundwater flow system.

The Cariri region is the largest sedimentary basin in the state of Ceará, Brazil. Located in the southern portion of the state, it comprises the Araripe Plateau and the Cariri Valley on its northern foot. The region's groundwaters are being heavily exploited. Using electric conductivity (EC) and 18O, 14C and 3H data, we differentiate groundwaters from various origins. We identified three horizons of springs on the slope of the Plateau through their geologic environment and the EC of their waters. Groundwaters from wells in the Cariri Valley are classified according to the aquifers exploited as indicated by the drilling profiles. However, strong tectonic features and intense fracturing in the Valley produce a great many horizontal discontinuities, which result in a mixing of groundwaters from different aquifers. Mixing systems are described in terms of δ18O–14C and EC–14C linear trends.

The alluvial aquifers are of great importance for the economic development, because they to form an remarkable source of water for several uses, which should be controlled and they be in agreement with the potentialities of the resource, to avoid so much the degradation as the reduction of the water resource. In this paper we presented some aspects hydrogeologics of the alluvium of the river Janguaribe that facilitated to verify that the river Jaguaribe/Quixere doesn't receive significant contribution of the aquifers in any time of the year. In the simulation of the underground flow in the fluvial island, Island of Limoeiro do Norte, considering the river perennial as limit of the alluvial aquifer and 15% of the rains as recharge, was observed that the loads stabilizes forming a divisor of waters in the Island of Limoeiro do Norte, fact that it was not observed through the piezometric surface actual, which evidenced zones with over-exploitation of aquifer.

For an investigation in losses of river flow of Jaguaribe river, in the region of Limoeiro do Norte, surface and groundwater samples were taken, in dry and rainy seasons, during a period of 2 years. Oxygen-18 and hydrochemical analyses were performed to avaluate the origin of aquifer recharge and river/aquifer interaction. Results show pronounced differences in 18O between Jaguaribe river (mean: +1.6) and the Jandaira aquifer (mean:-2.4), strong seasonal variations in 18O in the river water, positive values for this parameter in some wells, indicating the influence of the river, and chemical homogeneity of Jaguaribe river water and those from the majority of wells. A general analysis of the data indicates a constant recharge to the alluvial aquifer though river water, however more pronounced during dry seasons.

Surface waters from three dams and groundwaters from three wells dug in alluvium, located in the Gameleira watershed in an area of restricted human action in the semi-arid Northeast of Brazil, were studied through chemical and physicochemical measurements for the identication of the origin of dissolved minerals and of the processes of salination. Results show that salts result from dissolution during water/rock interaction and from atmospheric precipitation. In both types of storage, evaporation is identified as an agent of salt enrichment, principally in surface waters. Waters sampled were chemically adequate for human consumption; however,anthropic action influences nitrate concentration.

Abstract The exploitation of an alluvial aquifer (2 × 106 m3) has been developed since 1998 in the Valley of Forquilha (Quixeramobim, State of Ceara). For this purpose, 165 wells were drilled along the 23 km of the valley that supplies 500 families and their farms. Monthly monitoring of piezometric and electrical conductivity (2000–2003) show seasonal variations in the water volume (35%) and in the mean value of the conductivity (800–1200 µS cm-1). A conceptual hydrogeological model was developed. Analysis of the data and simulations highlight that the recharge of the aquifer is mainly due to infiltration from the river in the rainy season, which is of the order of 1% of the rain over the catchment area (195 km2). The abstractions increase the recharge between 30 and 60%. The model makes it possible to propose scenarios of sustainable exploitation of the water resource in the catchment. For the period between 1970 and 1988, other simulations show that it would have been possible to maintain irrig...

RESUMO As aguas subterrâneas no municipio de Sao Luis/Maranhao estao, predominantemente, armazenadas nas formacoes Barreiras e Itapecuru. Medidas hidroquimicas foram utilizadas para entender os processos de recarga dos aquiferos. Os resultados mostram: (i) aguas de baixa salinidade com faixas diferentes de condutividade eletrica e de pH para cada aquifero; (ii) influencia dos aerossois marinhos nas aguas de recarga do aquifero Barreiras; (iii) dissolucao de carbonatos no aquifero Itapecuru e (iv) exploracao mais intensa do aquifero Barreiras do que do Itapecuru. As medidas isotopicas mostram: (i) recarga rapida dos dois aquiferos e (ii) semi-confinamento do aquifero Itapecuru com recargas regulares. ABSTRACT Ground water in the township of Sao Luis/ Maranhao is principally stored in the formations Barreiras and Itapecuru. We used chemical analyses and environmental isotopes (18O, D) in order to understand recharge mechanisms. Results shown: (i) waters are of low salinity, but have electric conductivity and pH completely different in the two principal aquifers; (ii) marine aerosol plays a role in the mineralization of Barreiras recharge water; (iii) dissolution of carbonate rock is the main contribution in the Itapecuru aquifer; (iv) the Barreiras aquifer is exploited with strong preference; (v) recharge is fast and without effects of evaporation on isotopes; (vi) the Itapecuru aquifer is semi-confined being recharged regularly.

The Araripe Plateau in northeastern Brazil has an area of about 8,000 km2, confined by 39°05′E and 40°55′E, and 7°10′S and 7°50′S. Due to high permeability of soils, a surface drainage system is practically inexistent. Water is stored in excavations with clayey soil, the “barreiros”. Monthly samples were taken for 18O measurements, from September 1999 to August 2000, from four barreiros, three dug wells and five drilled wells. Results show that (1) groundwaters in the eastern part of the plateau are derived from present-day rainfall (δ18O≈−3.2‰), whereas groundwaters in the western portion are isotopically different (δ18O≈−5.0‰); (2) barreiros are strongly marked seasonally by elevated δ18O during the dry period due to elevated evaporation; (3) a dug well at a distance of ≈30 m from a barreiro exhibits δ18O similar to that of the reservoir, indicating a strong interaction between groundwater and surface water; and (4) a tubular well of 242-m depth, located in a fault, exhibits strong seasonal changes in δ18O and electrical conductivity, revealing downward leakage between aquifers.

The Earth’s paleoclimate is not only a subject of human curiosity about the past, but has also become a matter of “understanding the past for predicting the future”. With the Earth facing the threat of a man-made global change in climate, caused by the “greenhouse effect”, the history ofthe world’s climate has found new interest. Science needs large-scale global as weH as specific regional values for the calibration of models designed to foresee and quantify future changes in climate. (Such as CLIMAP — Climate: Long Range Investigation and Prediction, CLIMAP 1981). As instrumental meteorology reaches back to the seventeenth century only (based on the invention of the thermometer by Galileo, around 1590, and of the barometer by Torricelli, in 1643), paleoclimatic evidence for remoter periods has to be based on indirect measurements (“proxy data”), analyzing the advance and retreat of glaciers, the stratification of loamy soils (varves), the width of annual growth-rings of trees, pollen as indicator for vegetation, historic records (for taxing normally) of crop yields, or the isotope composition of marine deposits, etc. Within this last category, the 18O/16O ratio of these stable oxygen isotopes is of special importance.

In the semi-arid Northeast of Brazil, the alluvial aquifers exploitation for irrigation and domestic supply of rural communities over the last decade has upset the traditional mechanisms of water resources management. This paper looks into this problem using as case of study the Forquilha watershed (221 km²; 5°17' S, 39°30' W). In the Forquilha watershed, main water resources are reservoirs (1 to 7 hm3), used for water supply only, and an alluvial aquifer (2,3 hm3), used for both irrigation and domestic water supply as well. From 1998 to 2006, the irrigated area by use of alluvial groundwater has increased from 0 to 75 ha and the percentage of population supplied with domestic water from both sources (reservoirs and alluvial aquifers) has increased from 1 to 70%. As one could expect, pressure on water resources is increasing and water availability for all the categories of uses and users is an open question. In this paper, an approach based on both physical and socio-economic issues was used in future availability simulations. Three main water territories ('aquifer', 'reservoirs' and 'disperse habitat') were identified, within which water related issues guide stakeholders actions. Different scenarios of water resources exploitation strategies were built for the next 30 years, considering a realistic population growth and multiple use hypotheses. Hydrological balance models were built and used to simulate the different impacts of different possible water management scenarios on water resources availability and salinity. The results of the simulations show that if the irrigated area remains the same (i.e. 75 ha), seasonal releases from the main reservoir higher than 50 l/s are necessary in order to sustain activities such as breeding and irrigation. This guarantees the recharge of the alluvial aquifer during dry season in 9 out of 10 years, keeping water salinity of the reservoir below 0,7 g/l. In the case of doubling irrigated areas to 150 ha, the use of water resources would lead to restrictions on irrigation, breeding and domestic water during 80% of time in the territory 'aquifer' and during 25% of time for the territory 'reservoirs'. As a consequence, the cost of palliative water supplying through bowsers would then increase 100% relative to the hypothesis of no increase of irrigated areas.