Streamflow observations from near-natural catchments are of paramount importance for detection and attribution studies, evaluation of large-scale model simulations, and assessment of water ...management, adaptation and policy options. This study investigates streamflow trends in a newly-assembled, consolidated dataset of near-natural streamflow records from 441 small catchments in 15 countries across Europe. The period 1962-2004 provided the best spatial coverage, but analyses were also carried out for longer time periods (with fewer stations), starting in 1932, 1942 and 1952. Trends were calculated by the slopes of the Kendall-Theil robust line for standardized annual and monthly streamflow, as well as for summer low flow magnitude and timing. A regionally coherent picture of annual streamflow trends emerged, with negative trends in southern and eastern regions, and generally positive trends elsewhere. Trends in monthly streamflow for 1962-2004 elucidated potential causes for these changes, as well as for changes in hydrological regimes across Europe. Positive trends were found in the winter months in most catchments. A marked shift towards negative trends was observed in April, gradually spreading across Europe to reach a maximum extent in August. Low flows have decreased in most regions where the lowest mean monthly flow occurs in summer, but vary for catchments which have flow minima in winter and secondary low flows in summer. The study largely confirms findings from national and regional scale trend analyses, but clearly adds to these by confirming that these tendencies are part of coherent patterns of change, which cover a much larger region. The broad, continental-scale patterns of change are mostly congruent with the hydrological responses expected from future climatic changes, as projected by climate models. The patterns observed could hence provide a valuable benchmark for a number of different studies and model simulations.
In many of the alpine watersheds of Sierra Nevada (Southern Spain) exists an ancient network of dug canals that collect, transport and facilitate the recharge the snowmelt in the underlying aquifer ...during the spring season. This practice, known as careos, in the lower part of the watersheds supply drinking water as spring discharge during the dry season. To study how this managed recharge technique modifies the natural response of these basins this work focuses on characterizing the hydrological behavior of one of the sites, the Berchules watershed. The mechanisms for mineralization of groundwater are based on geochemical processes such as evapo-concentration in the soil layer and silicate mineral weathering due to dissolved CO2 originated from both soil biogenic processes and the atmosphere. Groundwater presents a main hydrogeochemical calcium‑magnesium-bicarbonate type facies, which is associated to groundwater flowing through the upper weathered silicates and quickly drained through springs located in the uplands and in the intermediate altitude catchment zone. Additionally, in the lower part of the basin some springs discharge mineralized groundwater with a sodium–calcium–bicarbonate composition associated to regional groundwater flow. In natural conditions, this hydrogeological system behaves as a sloping aquifer, occurring recharge between 1400 and 2500 m a.s.l. The springs discharge groundwater with an isotopic content and temperature in coherence with the local rainfall isotopic and thermal atmospheric altitudinal lines. Nevertheless, once the careo recharge begins the affected springs reveal the fingerprint of the concentrated recharge system by blurring the fingerprint of both the isotopic and thermal altitudinal dependence in the springs discharge. This validates the previous conceptual model and supports average recharge values of 141 ± 140 mm/yr and total average water resources of 181 ± 111 mm/yr which include a 40% increase in the study period due to the effect of the acequias de careo.
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•The acequias de careo is a water management system that enhances aquifer recharge.•The ancient managed aquifer recharge ensures water availability downstream.•Environmental tracers are essential to study alpine hydrologic systems.•Concentration by evaporation controls the dissolved salts content in groundwater.•Chemical weathering of silicate minerals is behind GW mineralization.
The Ordesa and Monte Perdido National Park, located in the Southern Pyrenees, constitutes the highest karst system in Western Europe. No previous studies regarding its geochemical and isotopic ...groundwater characterization are available in this area. This work presents the results of field and sampling campaigns carried out between July 2007 and September 2013. The groundwater presents high calcium bicarbonate contents due to the occurrence of upper Cretaceous and lower Paleocene-Eocene carbonate materials in the studied area. Other relevant processes include dissolution of anhydrite and/or gypsum and incongruent dissolution of Mg-limestone and dolomite. The water stable isotopes (δ(18)O, δ(2)H) show that the oceanic fronts from the Atlantic Ocean are responsible for the high levels of precipitation. In autumn, winter, and spring, a deuterium excess is found in the recharge water, which could be related to local atmospheric transport of low-altitude snow sublimation vapour and its later condensation on the snow surface at higher altitude, where recharge is mostly produced. The recharge zones are mainly between 2500m and 3200ma.s.l. The tritium content of the water suggests short groundwater transit times. The isotopic composition of dissolved sulphate points to the existence of regional fluxes mixed with local discharge in some of the springs. This work highlights the major role played by the altitude difference between the recharge and discharge zones in controlling the chemistry and the vertical variability of the isotopic composition in high-altitude karst aquifers.
•Brines chlorine calcium type have been identified in deep coastal boreholes in the Atacama Desert.•The combined application of lithium, boron and strontium isotopes has made it possible to recognize ...an ancient marine origin of deep brines.•The combined application of the isotopes δ11B and δ7Li allows an indirect approximation of the age of groundwater of marine origin to be made.
This paper presents a multi-isotopic study to investigate the origin of saline groundwater in the Cordillera de la Costa, in the arid Atacama Desert region in northern Chile. Understanding the origin of deep saline groundwater can be challenging using only hydrogeochemical and common isotope methods. New 87Sr/86Sr, δ11B, δ7Li, and 234U/238U values of dissolved salts have been added to previously known chemical and isotopic compositions of groundwater, inorganic dissolved carbon, and sulfate. In this extremely arid area, the chemical and isotopic compositions of coastal springs primarily reflect the concentration of salts from atmospheric wet and dry deposition, which accumulate in the topsoil and dissolve during the occasional heavy rainfall events. These events recharge the aquifer with sodium-chloride type, high salinity water, with rock weathering contributing minimally to the chemical composition of groundwater. However, high salinity water of the calcium chloride and sodium-calcium chloride types in the deep fractured aquifer have a significantly different chemical and isotopic composition. In this investigation, it has been concluded that the salinity of these last waters is due to remnants of ancient marine water, mineral alteration and interaction with predominantly andesitic volcanic rocks in the Cordillera de la Costa. The deep saline groundwater has δ11B values between 17.3‰ and 20.7‰, and 87Sr/86Sr values below 0.706, suggesting mixing with recharge groundwater. The δ7Li composition of the deep groundwater varies between 23.5‰ and 31.5‰, pointing to a contribution of salts of marine origin and mineral alteration. However, the low Li concentrations relative to B in recharge water and in deep groundwater shows a preferential Li removal from pore water. Uranium and uranium isotopes data are limited to shallow groundwater due to the very low U concentrations in deep groundwater following reduction of U, and point to enhanced water–rock interaction in a rock-dominated environment. The dissolution of old buried saline deposits at shallow depth as a source of salinity is ruled out.
The objective of this work is to characterize the impact of climate change in the karst aquifer of the Port del Comte Massif (PCM). Six regional climate models (RCMs) from CLYM'PY Project are used to ...analyse the magnitude and trends of changes on precipitation and temperature (RCP4.5 and RCP8.5 scenarios) and how these changes propagate through the hydrogeological system as groundwater resources availability and the associated water isotopic content. The study uses the RCMs climate change forcings as input data to a combination of (1) a semi-distributed hydrological model for simulating the hydrodynamical response of the aquifer, and (2) a lumped parameter model for simulating the isotopic content in groundwater at the outlet of the aquifer. A mean decrease of 2.6% and 1.9% in yearly precipitation and a mean increase of 1.9 and 3.1 °C in average temperature is expected in PCM at the end of the 21st century in the RCP4.5 and RCP8.5 scenarios, respectively. This climate signal entering the hydrogeological system results in a mean decrease in recharge of 3.9% and 0.5% from rainfall and of 59.3% and 76.1% from snowmelt, and a decrease of 7.6% and 4.5% in total system discharge, but also generates an isotopic enrichment in groundwater discharge (δ18OGW) of 0.50‰ and 0.84‰, respectively. Moreover, from a long-term (2010−2100) perspective, the mean trend in δ18OGW is 0.7‰/100 yr and 1.2‰/100 yr for RCP4.5 and RCP8.5, respectively, resulting in easily measurable annual lapse rates with the current analytical methods.
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•Water resources generated in the Port del Comte aquifer will decrease in the future.•Future system discharge during both the thaw and the low flows seasons will be lower.•Multi-model and multi-scenario used to assess isotopic content trends in groundwater.•The Isotopic content in groundwater (δ18OGW) shows trends statistically significant.•Trends in δ18OGW can be used as proxy of Climate Change impact in aquifer systems.
Water resources in high mountain karst aquifers are usually characterized by high rainfall, recharge and discharge that lead to the sustainability of the downstream ecosystems. Nevertheless, these ...hydrological systems are vulnerable to the global change impact. The mean transit time (MTT) is a key parameter to describe the behavior of these hydrologic systems and also to assess their vulnerability. This work is focused on estimating MTT by using environmental tracers in the framework of high-mountain karst systems with a very thick unsaturated zone (USZ). To this end, it is adapted to alpine zones a methodology that combines a semi-distributed rainfall-runoff model to estimate recharge time series, and a lumped-parameter model to obtain ΜΤΤ. The methodology has been applied to the Port del Comte Massif (PCM) hydrological system (Southeastern Pyrenees, NE Spain), a karst aquifer system with an overlying 1000 m thick USZ. Six catchment areas corresponding to most important springs of the system are considered. The obtained results show that hydrologically the behavior of the system can be described by an exponential flow model (EM), with MTT ranging between 1.9 and 2.9 years. These ΜΤΤ values are shorter than those obtained by considering a constant recharge rate along time, which is the easiest and most applied aquifer recharge hypothesis when estimating ΜΤΤ through lumped-parameter models.
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•Amplitude of seasonal isotopic composition of rainfall depends on elevation.•Moisture generating rainfall in the study zone comes from the Mediterranean.•The aquifer main recharge zones located at elevations between 2050 and 2387 m a.s.l•Considering transient recharge improves the estimations of mean transit times.•Transit times in agreement with the karstic nature of the aquifer system
Modern irrigation technologies and tools can help boost fertigation efficiency and sustainability, particularly when using irrigation water of varying quality. In this study, a high-tech irrigation ...head using a new fertigation optimization tool called NutriBalance, which is designed to manage feed waters of different qualities, has been evaluated from technical and economic perspectives. NutriBalance computes the optimal fertigation dose based on specific data about the equipment, the crop, the irrigation water, and the fertilizers available, in order to enable autonomous and accurate water and fertilizer supply. The system was trialed in a grapefruit orchard irrigated with fresh and desalinated water for several values of crop nutritional requirements and considering different fertilizer price scenarios. The results showed the good interoperability between the tool and the irrigation head and the nearly flawless ability (error below 7% for most ions) of the system to provide the prescribed fertigation with different combinations of irrigation water. Fertilizer savings of up to 40% were achieved, which, for the lifespan of the equipment, were estimated to correspond to around 500 EUR/ha/year. The results of this study can encourage the adoption of novel technologies and tools by farmers.
•Tracer content and derived age in GW not related to the time since recharge happened.•Chemical and isotopic GW composition reveals different aquifer recharge periods.•Chloride content in GW may keep ...memory of the origin of moisture producing rainfall.•14C activity from TIDC in GW is not a good proxy of the age of past recharge events.
The concentration of atmospheric tracers in groundwater samples collected from springs and deep wells is, in most cases, the result of a mixture of waters with a wide range of residence times in the ground. Such is the case of an unconfined aquifer recharged over all its surface area. Concentrations greatly differ from the homogeneous residence time case. Data interpretation relies on knowledge of the groundwater flow pattern. To study relatively large systems, the conservative ion chloride and the decaying radiocarbon (14C) are considered. Radiocarbon (14C) activity in groundwater, after correction to discount the non-biogenic contribution, is often taken as an indication of water age, while chloride can be used to quantify recharge. In both cases, the observed tracer content in groundwater is an average value over a wide range which is related to water renewal time in the ground. This is shown considering an unconfined aquifer recharged all over its area under arid conditions, in which a period of greater recharge happened some millennia ago. The mathematical solution is given. As the solution cannot be made general, to show and discuss the changes in water reserve and in chloride and radiocarbon concentration (apparent ages), two scenarios are worked out, which are loosely related to current conditions in Northern Chile. It is shown that tracer concentration and the estimated water age are not directly related to the time since recharge took place. The existence of a previous wetter-than-present period has an important and lasting effect on current aquifer water reserves and chloride concentration, although the effect on radiocarbon activity is less pronounced. Chloride concentrations are smaller than in current recharge and apparent 14C ages do not coincide with the timing, duration and characteristics of the wet period, except in the case in which recharge before and after the wet period is negligible and dead aquifer reserves are non-significant. The use of chloride concentration in springs as a proxy of chloride concentration in recharge to estimate recharge from atmospheric deposition leads to recharge value larger than the real one and it approaches the wet period recharge. Drawing inferences about radiocarbon data and recharge by the chloride balance method has rarely been taken into account before. It is important to consider the variable aquifer groundwater reserve. Current recharge estimation can be improved by careful selection of groundwater samples, supported by tritium and radiocarbon measurements.
The time series of stable water isotope composition relative to IAEA-GNIP meteorological stations located in alpine zones are analyzed in order to study how the amplitude of the seasonal isotopic ...composition of precipitation (Aδ) varies along a vertical transect. A clear relationship between Aδ and local evaporation is obtained, with slopes of −0.87 ‰/100mm/yr and −7.3 ‰/100mm/yr for Aδ18O and Aδ2H, respectively. When all sampling points of the vertical transect receive the same moisture sources, then a linear relationship between Aδ and elevation is obtained, with vertical gradients of 0.16 ‰/100mm/yr and 1.46 ‰/100mm/yr forAδ18O and Aδ2H, respectively.
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•Amplitude of seasonal isotopic composition of rainfall depends on local evaporation.•Isotopic amplitude depends on elevation if the air moisture sources are common.•Local evaporation is controlled by atmospheric local and synoptic conditions.
Sierra Nevada, Spain.
The local communities of the Sierra Nevada mountain range adapted to recurrent dry periods by spreading water along hillslopes with unlined channels that deviate surface runoff ...from headstreams during high flow periods. However, the impact of the so-called careo practice on river regimes in Sierra Nevada remains mostly unquantified. This work aimed to fill this gap by monitoring and analyzing streamflow in a major careo channel and river during three consecutive years (2021–2023) in the Mecina watershed (51 km², Las Alpujarras).
This study reveals unexpectedly high proportions of groundwater and human influence in total basin runoff within the hard rock environment of the Sierra Nevada. The data shows consistent streamflow gains between controlled river sections despite experiencing three years of below average precipitation, most remarkably below high infiltration channel stretches. The relationship between careo recharge and river flow kept constant even during the driest of the observed years. The influence from careo recharge was most noticeable during the low flow period (summer) when it represented between 40 % and 60 % of river streamflow. In addition, about 32 % of the total recharge to the aquifer in the basin comes from water transported and infiltrated by just one of the basin's careo channels, which means that such a careo recharge channel increases the natural infiltration of meteoric water by 47 %.
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•Streamflow monitoring shows importance of hard-rock slope aquifers in river baseflow.•Traditional low-cost human practice enhances total basin aquifer recharge by 82 %.•Careo recharge accounts for 45 % of total aquifer recharge during dry years.•Artificial recharge constitutes up to 79 % of the river´s low flow rates.•Drinking and irrigation water supply depend on local ecological knowledge.
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