Groundwater provides a critical buffer for urban water security, yet contamination by nitrate from deteriorating sewer networks poses a persistent and globally underestimated threat. Unlike agricultural pollution, urban-derived nitrate is sustained by diffuse, chronic leakage from buried infrastructure, producing plumes that can persist for decades. Here, coupled groundwater flow and solute transport models (MODFLOW–MT3D) were applied to simulate 30-year scenarios of aquifer response in a Brazilian city where a nitrate plume exceeding 1.5 km2 has been sustained for over 20 years. Modeled results revealed that maintaining current leakage rates ( 11

Following recent prolonged regional droughts, reliance on groundwater resources in São Paulo State, Brazil, has increased, emphasizing the need for robust evaluations of groundwater availability to support integrated water resources management. For this purpose, dependable methods for estimating groundwater recharge were applied. This paper focuses on one of the region’s most important aquifers, the Bauru Aquifer System (BAS), which spans roughly 42

Characterizing hydraulic parameters in urban aquifers is a persistent global challenge, as conventional pumping tests are frequently impractical due to operational constraints and complex inter-well interference (IWI). This study introduces a novel, universally applicable artificial intelligence (AI)-driven methodology that circumvents these limitations by estimating the hydraulic properties of confined aquifers directly from passively collected operational monitoring data. The approach integrates a robust algorithm for extracting high-quality recovery events from raw water-level time series with a differential evolution (DE) metaheuristic optimization framework. Crucially, the framework explicitly models IWI using a physics-informed superposition model, representing a significant advancement over traditional single-well analytical solutions. Applied to the heavily exploited Guarani Aquifer System (GAS) in a dense urban setting, the method successfully identified 70 high-quality recovery events across 16 wells. The DE-based calibration, which explicitly accounted for IWI, yielded a 442.7% average reduction in root mean square error compared to a classical Theis-based model. Results demonstrate that neglecting IWI leads to non-unique and physically implausible parameter estimates, underestimating hydraulic conductivity by up to three orders of magnitude while overestimating storativity. The phenomenon of equifinality was clearly observed, where models with identical errors produced vastly different parameters, highlighting the proposed method’s utility as a diagnostic tool for identifying parameter uncertainty. This research establishes a scalable, cost-effective framework for continuous, non-invasive aquifer characterization, enabling the development of high-resolution numerical models and supporting adaptive groundwater management in complex urban environments worldwide.

Over recent decades, the Amazon region has faced an alarming escalation in anthropogenic forest fires, which, while human-initiated, are catastrophically amplified by climatic conditions. This chapter delves into the complex interplay between meteorological and hydrological droughts and their impact on forest fires, with a specific focus on the often-underestimated role of groundwater and the influence of El Niño-Southern Oscillation (ENSO) events. Drawing from a detailed analysis of the Amazon Basin from 2004 to 2016, an innovative approach centered on groundwater dynamics is presented. By utilizing comprehensive drought indicators at various soil depths, including surface soil moisture, root zone soil moisture, and groundwater storage, alongside the Standardized Precipitation Index (SPI), a consistent and troubling decrease in humidity conditions across all levels is revealed. The findings demonstrate that groundwater storage (gws), with its slower response to precipitation anomalies, is a pivotal factor governing the severity and duration of hydrological drought. The very strong 2015–2016 El Niño event serves as a stark case study, drastically amplifying the burned area and underscoring the vulnerability of the ecosystem. This chapter highlights the imperative to integrate groundwater monitoring into fire risk management, proposing the development of a tailored fire risk index for the Amazon to create more effective early warning systems and enhance regional preparedness against the growing threat of catastrophic fires.

Estimating potential aquifer recharge is vital for water resource management in Brazil, where groundwater is a key source for drinking water and irrigation. This study aims to evaluate the potential aquifer recharge of unconfined aquifers by utilizing a GIS-based distributed water balance model in the Metropolitan Region of Natal. The methodology was developed using water balance parameters, including surface runoff, actual evapotranspiration, and percolation, which were calculated using Thornthwaite and Mather’s method. The analysis of annual rainfall revealed significant spatial variability, with higher precipitation noted near the coastline, particularly in the city of Natal, and a marked decline toward the interior. A similar trend was observed for water surplus, with the highest values situated along the coast, and gradually decreasing toward the western regions, where water surplus was minimal. The results indicate substantial spatial variations in potential recharge across the region. In the eastern area, recharge exceeds 600 mm/year, accounting for approximately 30

Karst aquifers are highly vulnerable to contamination due to their unique hydrogeological characteristics and increasing anthropogenic pressures. Given the challenges and costs associated with remediation, this study evaluates the groundwater vulnerability of karst formations in the Western Amazon Basin using three assessment methods: EPIK, DRASTIC, and DRASTIC-LUC. Geospatial data and sensitivity analysis were employed to assess the Napo Karst Formation. The results show that DRASTIC and EPIK classified 45.76

Microplastics (MPs), defined as plastic particles between 5 mm and 0.001 mm, are transported through the atmosphere and detected in diverse ecosystems, including remote cryospheric environments. However, their atmospheric accumulation rates remain largely unquantified. This study presents the first reconstruction of the accumulation of atmospheric MPs in a tropical Andean glacier over the course of a hydrological year, defined as the annual cycle delimited by δ18O isotope depletion rather than the calendar year. An 8-m ice core was collected from Glacier 15-α on the Antisana volcano in Ecuador and dated with δ18O values to cover this cycle. MPs were visually identified and quantified, and polymer types were determined via micro-FTIR analysis. Accumulation rates were estimated by modeling a linear correlation between concentration of MPs and core depth, where surface layers are the most recent. A total of 1762 MPs were identified in the ice core, classified as fibers and fragments. Polyethylene and polymethyl methacrylate were the most common polymers throughout the core. The accumulation rate more than doubled, rising from 140 MPs/L at the beginning to 292 MPs/L at the end. These results indicate progressive atmospheric deposition of MPs, with persistent accumulation recorded in the upper troposphere, above boundary layers where turbulent mixing and frequent Amazonian rainfall would typically remove particles. Persistent MPs in the upper troposphere underscore the atmosphere's role as both a global vector and reservoir, with wide-ranging implications for ecosystems and long-range exposure risks to humans and wildlife.

Over recent decades, anthropogenic forest fires have significantly altered vegetation dynamics in the Amazon region. While human activities primarily initiate these fires, their escalation is intricately linked to climatic conditions, particularly droughts induced by the warm El Niño phase. This study investigates the impact of meteorological and hydrological drought on forest fires in the Amazon, focusing on the role of groundwater and El Niño events. Utilizing comprehensive drought indicators at various soil depths and standardized precipitation indexes, the research spans from 2004 to 2016, revealing a consistent decrease in humidity conditions across surface soil moisture, root zone soil moisture, and groundwater storage levels. With its slower response to precipitation changes, groundwater emerges as a crucial factor influencing hydrological drought patterns in the Amazon. The spatial distribution of drought conditions is explored, highlighting areas with lower humidity concentrations in the northeast and a correlation between forest fires and positive rates of change in burned area fraction during El Niño events. Notably, the study underscores the substantial increase in burned area during the 2015–2016, characterized by a very strong El Niño. This nuanced understanding of groundwater dynamics and its interplay with El Niño events provides critical insights for developing a tailored fire risk index in the ecologically significant and vulnerable Amazon basin, subsidizing strategies for mitigating fire risk and enhancing preparedness.

Karst terrains can undergo geotechnical issues like subsidence and collapse, occurring both naturally and anthropogenically. The municipality of Sete Lagoas, in the State of Minas Gerais, Brazil, is notable for overexploiting a karst aquifer, resulting in adverse effects such as drying lakes and geotechnical problems. This study aims to assess the progression of geotechnical risk areas in the central urban area from 1940 to 2020 and simulate future scenarios until 2100. To achieve this, historical hydraulic head data, a three-dimensional geological model, and a karst geotechnical risk matrix were used to develop a calibrated FEFLOW numerical model. Results show that before the installation of the first pumping well in 1942, the natural groundwater flow direction was primarily northeast. However, in the 1980s, a cone of depression emerged in the city, creating a zone of influence (ZOI) with a surface area of around 30 km2. Between 1940 and 2020, twenty geotechnical collapse events occurred in defined risk zones, often in regions where limestone outcrops or is mantled in association with the ZOI. In future scenarios, if the 2020 total annual groundwater pumping rate (Q = 145,000 m3/d) remains constant until 2100, the geotechnical risk zones will continue expanding laterally. To establish a sustainable risk state, a 40% decrease in the pumping rate (Q = 85,500 m3/d) is necessary.

Abstract Karst environments are susceptible to contamination and directly affected by anthropogenic pressures. Remediation efforts are expensive, time-consuming, and often impractical. Hence, vulnerability maps can be valuable tools for protecting and preventing the aquifer’s degradation. This study aims to evaluate the vulnerability of the Napo Karst Formation (NKF), in the western Amazon basin in Ecuador, using three vulnerability models: EPIK, DRASTIC, and DRASTIC-LUC. The difference between the three models lies in the parameters used and how each one of them address the vulnerability. Because assigning values to each parameter depends on the author's expertise and the available data, these models can produce varying outcomes, which we analyze using spatial and sensitivity analysis. Our results showed that DRASTIC and EPIK classified 45.76% and 35.38% of the NKF area as highly vulnerable, respectively, while DRASTIC-LUC classified most of the NKF areas under moderate vulnerability (57.47%). The sensitivity analysis determined that the depth to water table (D) and the infiltration conditions (I) were the most critical parameters for the vulnerability assessment. The moderate-to-high vulnerability of the NKF raises a warning, as the impacts on surface and groundwater may affect local populations that directly depend on its water. This is the first study that evaluates the vulnerability to the contamination of karst formation in the Ecuadorian Amazon. The results of this research can be used as a baseline for future research and as technical information for decision-makers to reduce the activities that could aggravate surface and groundwater quality in Western Amazonia.

Future groundwater recharge estimations are helpful tools for water resources management. However, there is a need for more information about it in many parts of the world, including the Portoviejo River watershed (PRW) in the West of Ecuador, a semi-arid zone with a water deficit where climate change impacts could increase pressure on groundwater resources. Geographical Information Systems were used in this paper, owing to their simplicity of inputs and accuracy of outputs, to estimate current and future (2021–2070) groundwater recharge in the PRW. The study is divided into two stages: 1) a runoff map based on soil permeability, land use, and terrain slope, and 2) current and future recharge calculations using the Thornthwaite and Mather water balance method. Future precipitation and temperature data from an ensemble of four Global Circulation Models were used as inputs, along with a map of runoff spatial distribution. The representative concentration pathways (RCP) 4.5 and 8.5 were the climate change scenarios used in this study. The results showed that the location of the groundwater recharge zone would be impacted by future precipitation and temperature variability in both scenarios for the next fifty years. For the decade 2060–2070 and the scenario RCP 4.5, the highest recharge rate zones were located in the lowlands of the PRW surrounding Portoviejo city. In scenario RCP 8.5, the highest groundwater recharge areas increase considerably in the entire PRW. Currently, the highest groundwater recharge zones are in the highlands of the PRW. The future groundwater recharge scenarios provide information to decision-makers regarding land use, since the future groundwater recharge zones will be in the expansion areas of Portoviejo city.

The correct management of groundwater depends on information regarding the evolutionary processes of groundwater and the characterization of spatial variability of recharge mechanisms. GIS-based index models have become a reliable alternative for mapping and interpreting recharge models due to their adaptability and reliability in estimating recharge. Furthermore, stable isotopes of hydrogen and oxygen in water (δ 2 H and δ 18 O) help determine the origin and monitoring of water in the hydrological cycle. This paper aims to contribute to the knowledge of groundwater recharge by developing a conceptual recharge model using stable isotopes and estimating the recharge amount using a spatially distributed water balance model based on GIS for the Zamora River Basin (ZRB) in Ecuadorian Amazon. Due to the basin's size and geography, it was necessary to divide it into six precipitation blocks. The high precipitation rates resulted in high (18.22%) and moderate (30.93%) recharge zones across the basin. The analysis of stable isotopes in water indicates that precipitation water comes from the east, from the Amazon plain. In the valleys, precipitation enriched in δ 18 O suggests that it has undergone a recycling process in the basin; groundwater recharge comes from these precipitations. This analysis provides a simplified representation of reality that can assist in predicting the impacts of human activities on the basin.

A hydraulic interaction between a pond and shallow aquifer in a watershed surrounded by cultivations of sugarcane and eucalyptus trees was evaluated in a tropical zone in Brazil. The pond, located in lower topographic levels, was prematurely interpreted as the local shallow unconfined aquifer's discharge area, suggesting the groundwater could flow toward the pond. However, water table gradients indicated opposite directions, bringing up questions about the eucalyptus root's potential to access groundwater, consequently lowering the water level and changing the groundwater flow directions. Physicochemical parameters, stable isotopes of δ18O and δ2H, major ions analysis were determined in samples of groundwater and pond water; geophysical surveys and groundwater level measurements were performed before and after the eucalyptus cutting. The results showed (1) the eucalyptus does not have a significant influence on the groundwater dynamic; (2) the pond behaves as a recharge, not a discharge area; and (3) previously considered as a local flow, the interaction between groundwater and pond is determined by an intermediate flow system, controlled by a near spring, independently of the seasonal variation and land uses.

Native forest deforestation has been identified as one of the main land cover changes affecting flood risk specially during small and moderate storm events. In this regard, forest protection and reforestation are considered a nature-based solution (NbS) for flood regulation. However, there is a lack of knowledge about the effects of different deforestation spatial patterns over floods. Effects of land cover changes on floods in a humid tropical basin within the Ecuadorian Amazon are assessed distinguishing forest location and forest fragmentation. The hydrological distributed model TETIS was applied to simulate the hydrological response of a basin to extreme storms having return periods of 1, 10 and 100 years, considering five land cover scenarios. The model was calibrated and validated using nine storm samples collected at a gauge station during the years 2018 and 2020. The simulated overland flow in hillslopes and stormflows within the river channel were analyzed to i) assess the statistical differences among all land use scenarios with the Kruskal-Wallis test; ii) assess the statistical differences among pairs of both location and fragmentation scenarios through the post-hoc evaluation Dunn test; iii) assess the statistical differences in relation to the baseline. Obtained results indicate that stormflow is less sensitive than overland flow to land cover changes. Forest location have more influence than forest fragmentation over both, overland flow and storm flows. Deforestation of the upper basin represents the worst scenario for flood regulation, thus protection of existing forest, as well as reforestation of deforested areas located in the upper watersheds is a priority for flood risk mitigation and forest conservation. The results enhance our understanding of ecosystem services provided by tropical Andean foothills forests.

Oxygen isotopes delta O-18 from a 13 m ice core derived from the Antisana volcano ice cap (0 degrees 28'S, 78 degrees 08'W), Ecuador, were analyzed to generate an age model based on isotopic fluctuations. The inferred age model spans c. 3.6 years, from 1993 to mid-1996, and corresponds to 3.6 cycles of isotopic fluctuations driven by seasonal change in precipitation in western Amazonia. A logarithmic transformation (LT) was performed on the ice core density data to remove the compression effect of accumulated snow affecting the temporal fluctuation of the isotopic signal. A wavelet analysis run on the decompressed isotope signal (LT) showed periodicities of 80, 40, and 20 corresponding to 12, 6, and 3 months, respectively. The results were compared against the isotopic record from the Chimborazo ice core data to validate its temporal match with a hydrological year. The LT isotopic signal showed a significant correlation with the Chimborazo isotopic data (r = 0.69 and p-value < 0.001). The methodology applied in this study allowed the reconstruction of 3.6 cycles (3.6 years), showing that age models can be derived from ice cores using oxygen isotope annual fluctuations in tropical glaciers.

Monitoring studies are necessary to better understand the hydrological processes affecting the isotopic signature of cave waters, which are ultimately recorded in speleothems that are used as paleoclimate archives. This research examines changes in the isotopic composition (delta O-18 and delta H-2) of precipitation as it infiltrates through the epikarst and into the Jumandy cave, located in the western Amazon Basin (Ecuador). Meteorological and hydrological parameters were monitored outside and inside the cave, and isotope analyses were carried out in waters from rainfall, an underground river, and drip-water at two sampling sites in the cave between April 2019 and February 2020. At monthly timescale, the rainfall weighted isotopic composition monitored at our stations was strongly correlated with the mean precipitation amount. However, when considered at weekly time-steps, the correlation is only moderate. This implies that the variation of the isotopic composition in the study area cannot be interpreted exclusively as an amount effect. Isotopic values and back-trajectory modeling show that the isotopic signature was affected by the moisture source effect associated with upstream rainout. The moisture flux is dominantly from an east to northeast direction and moisture mainly originates over the Atlantic Ocean, passing through the Amazon Basin. A significant fraction of moisture is associated with local sources within the Amazon Basin. This aspect is confirmed by d-excess values of rainfall and the Local Meteoric Water Lines (LMWLs) that indicate an influence of the high evapotranspiration rate of the Amazon region on the isotopic composition of local rainfall. The infiltrated water resides for about three weeks in the epikarst and then pre-cipitates forming speleothems (residence time). However, this short residence time needs to be confirmed with a longer monitoring period. Despite the different magnitudes of the dripping rates, the isotopic values at the two monitored sites are similar. This suggests that the dripping discharge rate is affected by the karst structure, but the isotopic signature reflects the mixing of individual rainfall events above the cave. Therefore, ?18O in spe-leothems from these caves is mainly recording short-term precipitation changes linked to regional and large-scale atmospheric circulation.

Microplastic (MPs) contamination is ubiquitous in most terrestrial and aquatic ecosystems. Recently MPs have been reported at high altitudes which indicates that air masses can transport and deposit MPs in the surface snow of high mountain ecosystems, however, whether MPs typification and abundance can be influenced by direction and origin of air masses still remains an open question. Here we present the first report of MPs above 5000 m a.s.l from surface snow of a glacier in the tropical Andes. We collected surface snow along an elevational gradient, from 5000 to 5400 m a.s.l., in the Antisana Glacier, in the northern Andes cordillera of Ecuador to analyze MPs abundance and polymeric identification with the Fourier Transform Infrared (FTIR) and also to hypothesized the possible MPs sources in this remote area by comparing the oxygen and hydrogen stable isotopic ratio composition of the snow samples and by analyzing the wind direction. We observed an average of 131 +/- 24 MPs L-1 in our samples. Fibers corresponded to 70% of all MP shapes; FTIR results showed that MPs composition mainly included polyurethane, polyethylene, polyamide, polyester, and high-density polyethylene in surface snow. There were no statistically significant differences of MPs abundance among sampled elevations, and the isotopic ratio composition did not differ among locations. Our results suggest that MP that accumulated in the glacier may be transported from the east, across the Amazonia, by the prevalent eastward air flow. The absence of industrial cities at least 2000 km further east from Antisana, indicates that the remote Andean glaciers could constitute important depositional zones for long-distance transported contaminants. (c) 2021 Elsevier B.V. All rights reserved.

In Brazil, there are about 2.5 million tubular wells in which 88% of them are illegal, extracting more than 17,580 Mm3/yr. This irregular use may cause sustainability issues that may be economic, social, or environmental (overexploitation, well losses and associated increases of water conflicts; aquifer contamination; and land subsidence). This paper aims to address the illegal wells in Brazil and discuss measures to minimize it. Conclusions indicate that users do not understand the aquifer dynamic and, therefore, do not have a proper understanding of problems such as loss of water quality and quantity caused by the excess of groundwater exploitation. This creates a false idea that there are no water conflicts among users, which causes a lack of engagement by society. Without groundwater users and stakeholder pressure, the government does not aim to control or close illegal wells, and the “vicious cycle” persists. The one way to break this “vicious cycle” would be programs of social communication and users’ participation, coupled with improvements to the control apparatus and inspection from State institutions, making sure that there is correct management and not only legislations that are not applied.