Stream water quality is controlled by the interaction of natural and anthropogenic factors over a range of temporal and spatial scales. Among these anthropogenic factors, land cover changes at catchment scale can affect stream water quality. This work aims to evaluate the influence of land use and seasonality on stream water quality in a representative tropical headwater catchment named as Córrego Água Limpa (Sao Paulo, Brasil), which is highly influenced by intensive agricultural activities and urban areas. Two systematic sampling approach campaigns were implemented with six sampling points along the stream of the headwater catchment to evaluate water quality during the rainy and dry seasons. Three replicates were collected at each sampling point in 2011. Electrical conductivity, nitrates, nitrites, sodium superoxide, Chemical Oxygen Demand (DQO), colour, turbidity, suspended solids, soluble solids and total solids were measured. Water quality parameters differed among sampling points, being lower at the headwater sampling point (0m above sea level), and then progressively higher until the last downstream sampling point (2500m above sea level). For the dry season, the mean discharge was 39.5ls⁻¹ (from April to September) whereas 113.0ls⁻¹ were averaged during the rainy season (from October to March). In addition, significant temporal and spatial differences were observed (P<0.05) for the fourteen parameters during the rainy and dry period. The study enhance significant relationships among land use and water quality and its temporal effect, showing seasonal differences between the land use and water quality connection, highlighting the importance of multiple spatial and temporal scales for understanding the impacts of human activities on catchment ecosystem services.

Nitrogen (N) pollution in shallow groundwater within the Jianghan Plain—a depositional basin along the Yangtze River in China—is a serious issue affecting the local water supply. There is little concern regarding temporal variation patterns of groundwater N in regions with intensive groundwater/surface-water interactions thus far. In this study, a 2-year field monitoring program and a set of incubation experiments were jointly applied to characterize the seasonal variation mechanisms of groundwater N. Groundwater monitoring suggested that temporal N variations in monitoring wells of 25 and 10-m depth were correlated with fluctuations in water levels, with lower NH₄-N and higher NO₃⁻-N concentrations corresponding to groundwater discharge during the dry season, and with higher NH₄-N and lower NO₃⁻-N concentrations corresponding to groundwater recharge during the wet season. Batch sediment incubation experiments showed that buried organic carbon in sediments from the field site could not promote NH₄-N release, but exogenous organic carbon and oxidant input could catalyze organic N mineralization, resulting in NH₄-N release. Nevertheless, NO₃⁻-N release was limited in all incubations. Thus, the temporal variation patterns could be divided into (1) groundwater N in type-1 wells (25 and 10 m), controlled by the annual reversal of groundwater flow gradient, which determined whether there was input of exogenous organic carbon or oxidants, ultimately affecting organic N mineralization, denitrification and other transformation processes, and (2) groundwater N in type-2 wells (<4 m depth), which showed no significant seasonal variation, implying the process is mainly controlled by surface inputs in the shallower subsurface.

Since the end of the Cambodian Civil War in 1998, the population of the Oddar Meanchey province has drastically increased despite the lack of adequate infrastructure, including basic amenities such as drinking-water supply. To improve the access to drinking water, governmental and aid agencies have focussed on drilling shallow boreholes. The use of groundwater for irrigation is also a growing concern to cope with the occasional late arrival of the rainy season or to produce food during the dry season. Since the groundwater resource in the province has not been documented, a 4-year study was undertaken (2011–2014), aiming to estimate the capability of groundwater to supply domestic needs and supplementary irrigation for rice production. Aquifer properties were estimated by combined use of hydrogeological techniques with the geophysical magnetic resonance sounding method. Groundwater storage and recharge were estimated based on new developments in the application of the geophysical method for quantifying specific yield. The median groundwater storage of the targeted sandstone aquifer is 173 mm, the recharge is diffuse and annually ranges from 10 to 70 mm, and the transmissivity is low to medium. Simulations of pumping indicate that the aquifer can easily supply 100 L of drinking water per capita daily, even considering the estimated population in 2030. However, the shallow aquifer can generally not deliver enough water to irrigate paddy fields of several hectares during a 2-month delay in the onset of the monsoon.

Drinking water monitoring plans are important to characterize both treated and untreated water used for drinking purposes. Access to drinking water increased in recent years as a response to the Millennium Development Goals set for 2015. The new Sustainable Development Goals aim to ensure universal access to safe drinking water by 2030. Within the framework of these global goals, it is crucial to monitor local drinking water systems. In this paper, treated and untreated water from different sources currently consumed in a specific town in Salta, northern Argentina, was thoroughly assessed. Monitoring extended along several seasons and included the physical, chemical and microbiological variables recommended by the Argentine Food Code. On the one hand, treated water mostly complies with these standards, with some non-compliances detected during the rainy season. Untreated water, on the other hand, never meets microbiological standards and is unfit for human consumption. Monitoring seems essential to detect anomalies and help guarantee a constant provision of safe drinking water. New treatment plants are urgently needed to expand the water grid to the entire population.

Mandalay is a major city in central Myanmar with a high urban population and which lacks a central wastewater management system, a solid waste disposal process, and access to treated drinking water. The purpose of this study is to investigate the groundwater quality of local dug wells and tube wells, determine quantitative data on characteristics of the Amarapura Aquifer, and compare seasonal variations in groundwater flow and quality. Water samples were collected during the dry and wet seasons, then analyzed for major ion chemistry using ion chromatography to identify indicators of wastewater contamination transport to the shallow aquifer and to compare seasonal variations in groundwater chemistry. An open-source analytic element model, GFLOW, was used to describe the physical hydrogeology and to determine groundwater flow characteristics in the aquifer. Hydrogeochemistry data and numerical groundwater flow models provide evidence that the Amarapura Aquifer is susceptible to contamination from anthropogenic sources. The dominant water types in most dug wells and tube wells is Na-Cl, but there is no known geologic source of NaCl near Mandalay. Many of these wells also contain water with high electrical conductivity, chloride, nitrate, ammonium, and E. coli. Physical measurements and GFLOW characterize groundwater flow directions predominantly towards the Irrawaddy River and with average linear velocities ranging from 1.76 × 10⁻² m/day (2.04 × 10⁻⁷ m/s) to 9.25 m/day (1.07 × 10⁻⁴ m/s). This is the first hydrogeological characterization conducted in Myanmar.

During the rainy season of 1998, a field experiment was established in Cocula, Guerrero (hot subhumid climate, Awo) and in Montecillo, México (semiarid climate, BS₁), to evaluate the effect of nitrogen (0, 10 and 20 g m⁻²) and environment on phenology, yield and its components, water use efficiency (WUE), and crop evapotranspiration (ETc) and heat units (HU) accumulated during the growth cycle of sunflower (Helianthus annuus L.) cv. Victoria. The crop was planted on June 1 at a density of 7.5 pl m⁻² in both climates. In Cocula, maximum and minimum temperatures were more extreme and rainfall was more intense, while soil was poor in total nitrogen, compared with Montecillo. Crop growth, yield and its components, and water use efficiency were affected significantly by the environment, nitrogen and the interaction environment * nitrogen. The crop cycle in the hot environment was 36 days shorter, with a greater accumulation of HU and ETc. Yield and its components and water use efficiency were significantly higher in Cocula. Nitrogen positively affected the evaluated variables. The interactive effect of environment * nitrogen was observed clearly, since in Cocula there was response to the application of nitrogen in most of the variables evaluated, while in Montecillo there was not.

Understanding the hydrological functioning of the scarce freshwater bodies of semiarid regions is crucial, especially in those areas affected by anthropic activities involving land-use changes. In the dry western edge of the Argentina Pampean plains, a system of more than 100 shallow lakes of remarkable stability occurs. These lakes exhibit low salinity compared to those located in the more humid belt. This system has constituted the main water resource for humans from prehispanic times to the present. Stable isotopes were used to establish the seasonal surface-water/groundwater interactions and the hydrological conditions in a lake of the Dry Pampean Plain (DPP), i.e., Lake Los Pocitos, to understand the mechanism that guarantees such a resource. Results indicate that evaporation mainly controls the isotopic composition of lake water, overwhelming the effect of higher rainfall inputs during the wet (but also most evaporative) season. The δ¹⁸O mass balance model indicates greater groundwater inflow to the lake during the dry season (~0.4 m month⁻¹) compared to the wet season (~0.2 m month⁻¹). Lake level decreased in the wet season due to the lowest groundwater inflow and the greatest evaporation rate. Based on the proportion of water entering a lake that leaves through evaporation, Los Pocitos corresponds to a throughflow lake with a short water residence time (~0.47 years). These hydrologic conditions, along with freshwater inputs from a dune located at the western margin of the lake, determine the existence of this relatively stable and freshwater lake in the DPP where high evaporation rates are registered.

High-frequency time series analysis and cross-correlation identified the relationship between precipitation and water-level responses at 16 sandstone wells in southern California, USA. The time series analysis suggested that the water table rises only when a threshold value of precipitation is reached during the rainy season that likely represents the water content deficit from the previous 7-month dry season being replenished before generating a water-table response. The cross-correlation indicates two statistically significant lag-times: 0–3 and 20–50 days. Confidence in these results was augmented by unprecedented and exceptionally high-resolution sampling frequency. Water pressure readings were collected every second and then analyzed to identify and remove the effects of barometric pressure changes, Earth tides and earthquakes on water levels. These effects are usually considered “noise” in recharge studies, but their accurate quantification helped assess the unconfined nature of the wells, minimize uncertainties of the results, and isolate the groundwater responses to precipitation. Diffusivity values for the thick unsaturated zone, based on the time lags, suggest quick responses are related to flow through fractures and longer time lags are associated with piston-type movement in the matrix. Fast responses were more likely for shallow water tables in response to high-intensity precipitation events and vice versa. These findings are consistent with those found, using lower resolution data, for the Chalk aquifer in England (UK), despite the contrasting fracture and matrix properties, hydrogeological setting and climatic conditions. Thus, the same style of response to precipitation is expected globally where similar fractured porous media are present.

Stable isotopic composition (δ²H, δ¹⁸O) of river water, groundwater, and paddy water in the Mun River catchment, northeast Thailand, were determined to investigate the hydrological processes and the impacts of natural and anthropogenic activities on the water cycle. Quantities of δ²H (−93.9 to −25.4‰) and δ¹⁸O (−12.24 to −2.22‰) in river water in the wet season follow the trend: upper reaches > middle reaches ≈ lower reaches. Trends for δ²H (−52.3 to −22.0‰) and δ¹⁸O (−6.37 to −1.36‰) in the dry season are: upper reaches ≈ middle reaches > lower reaches. In the dry season, groundwater (δ²H: −57.5 to −34.6‰, δ¹⁸O: −8.24 to −4.40‰) shows a lighter isotopic composition, and paddy water (δ²H: −18.2‰, δ¹⁸O: −0.72‰) shows the highest isotopic composition. Spatial variation of δ¹⁸O and deuterium excess suggests that groundwater exchanges with surface water frequently. Rainfall and river water recharge groundwater in the wet season, and groundwater flows back to the river in the dry season, especially in the middle reaches. This process is most likely related to impoundment of the rivers by large dams. On the other hand, the lowest values of stable isotopes of river water are coincident with the extreme flooding that was produced by Tropical Storm Sonca in July 2017. This study contributes to a better understanding of hydrological processes in the Mun River catchment and provides a perspective on the application of stable isotopes to other large tropical monsoon catchments around the world.

Overexploitation of groundwater resources in Sana’a Basin, Yemen, is causing severe water shortages associated water quality degradation. Groundwater abstraction is five times higher than natural recharge and the water-level decline is about 4–8 m/year. About 90 % of the groundwater resource is used for agricultural activities. The situation is further aggravated by the absence of a proper water-management approach for the Basin. Water scarcity in the Wadi As-Ssirr catchment, the study area, is the most severe and this area has the highest well density (average 6.8 wells/km²) compared with other wadi catchments. A local scheme of groundwater abstraction redistribution is proposed, involving the retirement of a substantial number of wells. The scheme encourages participation of the local community via collective actions to reduce the groundwater overexploitation, and ultimately leads to a locally acceptable, manageable groundwater abstraction pattern. The proposed method suggests using 587 wells rather than 1,359, thus reducing the well density to 2.9 wells/km². Three scenarios are suggested, involving different reductions to the well yields and/or the number of pumping hours for both dry and wet seasons. The third scenario is selected as a first trial for the communities to action; the resulting predicted reduction, by 2,371,999 m³, is about 6 % of the estimated annual demand. Initially, the groundwater abstraction volume should not be changed significantly until there are protective measures in place, such as improved irrigation efficiency, with the aim of increasing the income of farmers and reducing water use.