ABSTRACT
RESUMO O objetivo central deste trabalho foi realizar o mapeamento dos aspectos hidrogeoquímicos de águas subterrâneas usando a estatística multivariada e redes neurais artificiais como subsídio para identificação de padrões espaciais. Para tal, foi executado um estudo de caso em aquíferos no município de Lençóis, Bahia, na região da Chapada Diamantina, nordeste do Brasil. Foram realizadas campanhas de campo para coleta de coordenadas geodésicas e amostras de águas subterrâneas. Após análise laboratorial e determinação de dados analíticos, foi feita a interpretação dos processos ambientais com o uso da análise de agrupamentos e mapas auto-organizáveis, além de classificação das águas pela Resolução do Conselho Nacional do Meio Ambiente nº 396/2008. Para fins de mapeamento dos dados analisados, foram usadas técnicas de geoprocessamento no Sistema de Informação Geográfica. Os principais constituintes físicos e químicos analisados em dois períodos climáticos foram mapeados e divididos em sete agrupamentos. Foram identificadas quatro zonas no município, que apresentam diferentes contextos hidrogeoquímicos. As zonas dos setores leste/sudeste, sul (área urbana) e extremo sul apresentam as mais significativas alterações na hidrogeoquímica e qualidade das águas. O mapeamento, subsidiado pela estatística multivariada e redes neurais artificiais, se apresentou potencialmente útil em contribuir com as ações de gestão dos recursos hídricos subterrâneos, como delimitação de áreas prioritárias, monitoramento de zonas de riscos de contaminação, além de intervenções de engenharia que eventualmente busquem o saneamento ambiental das águas subterrâneas.
ABSTRACT The main objective this paper was to map the hydrogeochemistry aspects of groundwater using multivariate statistics and artificial neural networks as a subsidy to identify spatial patterns. For this, a case study was carried out in aquifers in the municipality of Lençóis (BA), in the region of Chapada Diamantina, Northeastern Brazil. Field campaigns were carried out to collect geodetic coordinates and groundwater samples. After laboratorial analysis and determination of analytical data, the environmental processes were interpreted by cluster analysis and self-organizing maps, as well as the waters classification through CONAMA Resolution no. 396/2008. For the purpose of mapping the analyzed data, geoprocessing techniques were used in GIS. The main physical and chemical constituents analyzed in two climatic periods were mapped and divided into seven clusters. Four zones that present different hydrogeochemical contexts were identified in the municipality. The zones of the east/southeastern, south (urban area) and south end sectors present the most significant changes in hydrogeochemistry and water quality. The mapping, supported by multivariate statistics and artificial neural networks, was potentially useful in contributing to the management actions of groundwater resources as delimitation of priority areas, monitoring of contamination risk zones and engineering interventions that eventually seek environmental groundwater sanitation.
ABSTRACT
The objective of this study was to analyze spatial-seasonal changes to identify the natural and anthropic processes that control groundwater hydrogeochemistry in urban aquifers in municipality of Lençóis (Bahia). Tourism is the main activity of this municipality, which is an important tourist destination in northeastern Brazil and which maintains its tourism infrastructure by using groundwater. Two field campaigns were conducted (dry and rainy seasons) in order to collect groundwater samples extracted from 15 tubular wells distributed over the urban area of the municipality. The Piper diagram, multivariate statistical analyses, and artificial neural networks indicated that there are two types of water (Na-Cl and Na-[Formula: see text]-), which were divided into five different clusters. Seasonal variation was observed to significantly alter groundwater hydrogeochemistry. According to the Gibbs diagram, groundwater within the urban area of Lençóis belonged to the rainfall dominance, demonstrating low water-rock interaction. Hydrogeochemical modeling results suggested hydrolysis as the main natural factors controlling process. However, mineral dissolution also occurred in one of the clusters. Human-originated trace contamination by nitrate, chloride, and sulfate occurred in a zone of the urban area. This contamination was observed regardless of climate seasonality, indicating that the main controlling process for groundwater hydrochemistry in this region is wastewater mobilization (indirect artificial recharge).
Subject(s)
Environmental Monitoring/methods , Groundwater/chemistry , Brazil , Cities , Groundwater/analysis , Minerals/analysis , Multivariate Analysis , Nitrates/analysis , Recreation , Sulfates/analysis , Water Pollutants, Chemical/analysisABSTRACT
RESUMO Este trabalho teve como objetivo investigar a geoquímica e a qualidade da água subterrânea no município de Serra do Ramalho, no oeste da Bahia, com ênfase nas concentrações de nitrato (N-NO3 -). Foi coletada água do Aquífero Bambuí, cárstico, em 26 poços tubulares nas campanhas de 2010 e 2011 (período chuvoso) e 2012 (período seco). Foram realizadas medidas in situ de variáveis físico-químicas e tomadas alíquotas para análises laboratoriais dos ânions (titrimetria e espectrofotometria) e cátions principais (ICP OES) e do fluoreto (SPANDS). O pH variou entre 6,6 e 8,7, cujos teores dos elementos principais foram, em ordem decrescente: rCa2+ > rNa+ > rMg2+ > rK+ e rCO3 2- - rHCO3 - > rCl- > rSO4 2- > rNO3- > rF-. As fácies hidrogeoquímicas bicarbonatadas cálcicas (49%), cloretadas cálcicas (21%) e mistas cálcicas (15%) foram as mais representativas. As concentrações de nitrato e fluoreto excederam o limite de potabilidade preconizado pela Portaria nº 2.914/2011 em 25 e 12% dos poços, respectivamente. A poluição da água subterrânea representa um desafio para a gestão dos recursos hídricos, o saneamento, o uso do solo e a saúde pública, devendo ser mais bem compreendida, monitorada e remediada.
ABSTRACT This study aimed to characterize groundwater geochemistry and quality in the municipality of Serra do Ramalho, west Bahia, with emphasis on nitrate (N-NO3 -) concentrations. Water was sampled from 26 tubular wells during 2010 and 2011 (rainy season) and 2012 (dry season). Physicochemical parameters were measured and groundwater was sampled in each sampling station for laboratory analyses of the main anions (titrimetry and spectrophotometry) and cations (ICP OES) and fluoride (SPANDS). The pH ranged from 6.60 to 8.70, with the following decreasing order of major elements: rCa2+ > rNa+ > rMg2+ > rK+ and rCO3 2- - rHCO3 - > rCl- > rSO4 2- > rNO3- > rF-. Calcic bicarbonated hydrochemical facies (49%), calcic chlorinated facies (21%) and calcic mixed facies (15%) were the most representative in the study area. Fluoride and nitrate concentrations were above potability limit in 25 and 12% of the wells, respectively. Groundwater pollution is a challenge to the management of water resources, sanitation, land use and public health, and should be better understood, monitored and remedied.
