Total organic carbon concentrations in ecosystem solutions of a remote tropical montane forest respond to global environmental change.

The response of organic carbon (C) concentrations in ecosystem solutions to environmental change affects the release of dissolved organic matter (DOM) from forests to surface and groundwaters. We determined the total organic C (TOC) concentrations (filtered <1-7 µm) and the ratios of TOC/dissolved organic nitrogen (DON) concentrations, electrical conductivity (EC), and pH in all major ecosystem solutions of a tropical montane forest from 1998 to 2013. The forest was located on the rim of the Amazon basin in Ecuador and experienced increasing numbers of days with >25°C, decreasing soil moisture, and rising nitrogen (N) deposition from the atmosphere during the study period. In rainfall, throughfall, mineral soil solutions (at the 0.15- and 0.30-m depths), and streamflow, TOC concentrations and fluxes decreased significantly from 1998 to 2013, while they increased in stemflow. TOC/DON ratios decreased significantly in rainfall, throughfall, soil solution at the 0.15-m depth, and streamflow. Based on Δ14 C values, the TOC in rainfall and mineral soil solutions was 1 year old and that of litter leachate was 10 years old. The pH in litter leachate decreased with time, that in mineral soil solutions increased, while those in the other ecosystem solutions did not change. Thus, reduced TOC solubility because of lower pH values cannot explain the negative trends in TOC concentrations in most ecosystem solutions. The increasing TOC concentrations and EC in stemflow pointed at an increased leaching of TOC and other ions from the bark. Our results suggest an accelerated degradation of DOM, particularly of young DOM, associated with the production of N-rich compounds simultaneously to changing climatic conditions and increasing N availability. Thus, environmental change increased the CO2 release to the atmosphere but reduced DOM export to surface and groundwater.

Using isotope data to characterize and date groundwater in the southern sector of the Guaraní Aquifer System.

The Guaraní Aquifer System (SAG) is the largest transboundary aquifer in Latin America, extending beneath parts of Brazil, Paraguay, Argentina, and Uruguay. This paper presents the results of recent hydrogeological studies in the southern portion of the SAG. Locally, the abundance of surface water bodies precluded the use of conventional hydrological tools to characterize groundwater flows. Geological, hydrochemical and environmental isotope investigations were integrated to postulate a revised hydrogeological conceptual model. The revised geological model has provided a better definition of the geometry of the aquifer units and outlined the relevance of regional faults in controlling flow patterns. The new potentiometric map is consistent with groundwater flow from the SAG outcrops to the centre of the Corrientes Province, where upwards flows were identified. Hydrochemical and isotope data confirmed the widespread occurrence of mixing. Noble gas isotopes dissolved in groundwater (4He and 81Kr/Kr) provided residence times ranging from recent recharge up to 770 ± 130 ka. Groundwater age modelling confirmed the role of the geological structures in controlling groundwater flow. The southern sector of the SAG is a multilayer aquifer system with vertical flows and deep regional discharge near the Esteros del Iberá wetland area and along the Paraná and Uruguay rivers.

Isotopic characterisation and dating of groundwater recharge mechanisms in crystalline fractured aquifers: example of the semi-arid Banabuiú watershed (Brazil).

Sustainable groundwater management implies a good knowledge of recharge processes, especially in areas with water deficit, like the semi-arid region of Banabuiú watershed (Ceará State, Northeast of Brazil). In this zone, phreatic aquifers consist of Precambrian crystalline fractured reservoirs characterised by a high spatial anisotropy, both in terms of hydrodynamics and water quality. This study implemented a multi-tracer approach (18O, 2H, 14C, 3H, CFC, SF6), combined with hydrodynamic data (i.e. groundwater levels) to identify the groundwater recharge origin and the recharge mechanisms, and to estimate the groundwater residence time. At the basin scale, hydrodynamic data and local observations indicated the high reactivity of aquifers to precipitation and suggested that infiltration processes occur mostly through preferential infiltration zones. Stable isotope data showed a major contribution of evaporated surface water in the recharge process from many artificial or natural ponds. Groundwater residence time determination highlighted the spatio-temporal heterogeneity of flow path organisation within aquifers, with variable contributions between fast vertical flow (present-day end-member; 15-85 %) and a slower horizontal flow (old end-member <1960), underlining the vulnerability of aquifers to present-day environmental stress or pollution.

Geochemical evolution, residence times and recharge conditions of the multilayered Tubarão aquifer system (State of São Paulo - Brazil) as indicated by hydrochemical, stable isotope and 14C data.

The Tubarão aquifer system constitutes a very complex, multilayered aquifer enclosed in the Paraná basin (central-southern part of Brazil). Despite the relatively low productivity of wells, groundwater represents an important source of water for the very populated and industrialized zones of the State of São Paulo. An extensive water sampling campaign was carried out followed by hydrochemical and isotopic (δ 2H, δ 18O, δ 13C and 14C) studies, aiming at a better understanding of the aquifer's geochemical evolution, recharge processes, and its groundwater residence times. Two main hydrochemical facies were recognized and divide the aquifer in two portions. The shallow portion - the active hydrological zone of the aquifer - is characterized by the Ca-HCO3 water type, evolving as a system open to atmospheric CO2. Mean residence times are typically lower than 5000 years. The lower portion is mostly characterized by the stagnant, Na-HCO3 water type, evolving under closed system conditions. Residence times average up to 15,000 years, but can reach 44,000 years, which indicates the exploitation of (possibly non-renewable) fossil waters. This study contributes to the establishment of proper policies regarding the sustainable groundwater exploitation of the Tubarão aquifer system.

Application of isotope techniques to enhance the conceptual hydrogeological model and to assess groundwater sustainability in the Pampean plain in Córdoba, Argentina.

The objective of this work is to enhance the conceptual hydrogeological model in the Río Cuarto River basin by using isotope and hydrochemical techniques. The precipitation pattern, as reflected in the average values of δ 2H and δ 18O in stations located in the plains and in the mountains, showed an isotope depletion from the East to the West, attributed to continental and altitude effects. Groundwater quality is mainly the result of two controlling factors: lithology and flow distances from recharge. The aquifers show fresh calcium/sodium bicarbonate water in the upper and medium basin (coarse fluvial sediments) which evolve to sodium sulphate and chloride waters in the low basin (mainly loess and fine alluvial sediments). The confined aquifer systems in the lower basin (C and D systems) averaged more negative stable isotope values, indicating that groundwater recharged during colder climatic conditions (Pleistocene period). Groundwater dating with 14C confirmed that groundwater ages range from modern to 45,000 years BP showing that as the water flows towards deeper layers and farther from the mountainous recharge area, groundwater age increases. The confined aquifers can potentially be exploited in order to partly cover different water needs but they should be managed in a sustainable way.

Diagnóstico de infección por Helicobacter pylori mediante test de aliento con urea C-14 en población ecuatoriana / Diagnosis of Helicobacter pylori infection by C-14 urea breath test in Ecuadorian population

siendo el test de aliento con urea carbono-14 (C-14) uno de los métodos de diagnóstico no invasivos; sin embar-go, no ha sido comprobada su utilidad en la población ecuatoriana.Objetivo: Evaluar la sensibilidad y especificidad del test de aliento con urea C-14 para predecir la infección por HP en la población ecuatoriana.Métodos: Estudio de Pruebas Diagnósticas realizado en pacientes que acudieron a la consulta externa del servicio de gastroenterología del Hospital Teófilo Dávila de la ciudad de Machala, en el periodo abril 2018 a marzo 2019. Los pacientes se sometieron a una endoscopia superior de luz blanca (ES) con toma de biopsias para investigar la infec-ción por HP; además, se realizó un test de aliento con urea C-14, para compararla con los resultados de las biopsias.Resultados: Se estudiaron 78 pacientes con una edad media de 33.76±11.2 años. El diagnóstico de gastritis se confirmó a través de la ES e histopatología en el 100% de los pacientes. El test de aliento con urea C-14 fue positi-va en 47/78 (60.3%) pacientes. Se demostró evidencia de infección por HP en biopsias gástricas de 50/78 (64.1%) pacientes. La sensibilidad, especificidad, VPP, VPN, observada y la concordancia entre evaluadores fue de 94%, 100%, 100%, 90%, 96% y 92% (P <0.001), respectivamente.Conclusiones: El test de aliento con urea C-14, es una herramienta útil para predecir infección por HP en la población ecuatoriana

Background: Early detection of Helicobacter pylori infection has become more relevant, with urea carbon-14 (C-14) breath test as one of the non-invasive diagnostic methods; however, it has not been proven in Ecuadorian population.Objective: To evaluate the sensitivity and specificity of the C-14 urea breath test to predict HP infection in the Ecuadorian population.Methods: : Study of diagnostic tests performed on patients who attended the outpatient gastroenterology service of the Hospital Teófilo Dávila in the city of Machala, in the period April 2018 to March 2019. The patients underwent an upper endoscopy of white light (WLE) with biopsies taken to investigate HP infection. In addition, a breath test with C-14 urea was performed to compare it with the biopsies results.Results: 78 patients with a mean age of 33.76±11.2 years were studied. The diagnosis of gastritis was confirmed through endoscopy and histopathology in 100% of the patients. The breath test with urea C-14 was positive in 47/78 (60.3%) patients. Evidence of HP infection was demonstrated in gastric biopsies from 50/78 (64.1%) pa-tients. Sensitivity, specificity, PPV, NPV, and inter-rater reliability were 94%, 100%, 100%, 90%, 96%, and 92% (P <0.001), respectively.Conclusions: The C-14 urea breath test is a useful tool for predicting HP infection in the Ecuadorian population