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Comprehensive assessment of hydro-climatic variations and change trends is essential for understanding, mitigating, and adapting to key water resource changes in different parts of the world. We performed such an assessment on Iran, as representative of an arid/semi-arid and geopolitically important world region. We acquired and calculated data time series of surface temperature (T), precipitation (P), runoff (R), evapotranspiration (ET), and water storage change (DS), to determine their status and changes in and among the 30 main hydrological basins in Iran over the period 1986–2016. From 1986–2000 to 2001–2016, the country warmed, P mostly decreased and R even more so, while water storage was depleted (DS < 0) and ET increased in some basins. Overall, the extra water provided from primarily groundwater depletion has fed and kept ET at levels beyond those sustained by the annually renewable water input from P. This indicates unsustainable use of water for maintaining and expanding human activities, such as irrigated agriculture, in this part of the world. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quantification framework for long-term soil moisture change in a changing climate. [•] Variable unsaturated-groundwater zone extents. [•] Historic and projected future soil moisture change can be screened. [•] Increased frequency of dry soil moisture events over the 20th century. [•] Drought risk increase even though precipitation increases. [ABSTRACT FROM AUTHOR]

The zinc load from the Dalãlven River to the Baltic Sea is greater than for any other watercourse in Sweden. This paper investigates zinc mass flows into and through the Dalälven River from major mining areas within its drainage basin. Reported zinc mass flow data for this river are re-analyzed using an input-output flow analysis approach. Results show major inconsistencies in previous data interpretations which totally neglected possible zinc mass load contributions from the groundwater system to the river. This paper quantifies significant subsurface zinc load contributions that are consistent with all independently available data. Furthermore, a possible explanation for why these subsurface contributions may have been missed in previous studies and by the prevailing Swedish environmental monitoring system is provided. The study indicates that the input-output flow analysis approach may be generally useful for identifying and quantifying diffuse, unmonitored and uncertain pollutant load contributions from ground- to surface water systems. [ABSTRACT FROM AUTHOR]

Abstract: We use input–output analysis of nitrogen flows between various sources–sectors and natural waters in the Swedish Norrström drainage basin for investigating and bounding the implication range of some uncertainty sources for results of subsurface nitrogen accumulation–depletion in this basin. We quantify different possible base and extreme assumptions of nitrogen discharges and transport pathways from agriculture to surface and groundwater in the basin. The results are robust in showing considerable nitrogen accumulation–depletion flow interactions taking place between the basin’s mobile water and accumulated nitrogen pools in soils, sediments and/or relatively immobile subsurface water zones for all different scenario assumptions. Similar scenario robustness is also found in resulting relative contributions of different active nitrogen source–sectors to nitrogen flows in natural water systems. In the Norrström basin, and possibly more generally, nitrogen accumulation–depletion flows to and from accumulated legacies for the future or from the past appear therefore to be more important for water quality than current nitrogen discharges from active source–sectors. [Copyright &y& Elsevier]

The dramatic shrinkage of the Aral Sea that has occurred after 1960 has affected also groundwater resources in the region, and this effect needs to be clarified and quantified because groundwater is essential for meeting freshwater demands in the area. We determine upper and lower limits for the groundwater discharge into the Aral Sea after 1960, by use of water balance expressions, treating the groundwater as a fitting parameter and considering the uncertainty of the dominant evaporation term in the Aral Sea water balance equation. We also independently analyze, from a pure groundwater hydraulic perspective, the relative effects of the on-going sea surface lowering since 1960 on the hydraulic gradient and thereby also the groundwater discharge into different regions of the Aral Sea. These independent analyses yield consistent results in terms of the total groundwater discharge into the Aral Sea being equal or greater than in 1960, with some relevant scenario results yielding increased groundwater discharge up to about 200% of the 1960 value. In terms of regional groundwater discharge distribution, the present (2002) discharge into the southeast part of Large Aral is not greater than it was 1960; analyses of about 3000 different and relevant parameter combinations show that this prediction is robust with respect to uncertainty in parameter values. The groundwater discharge into the northwest part of Large Aral and into the Small Aral, however, should have increased due to the on-going sea level lowering. Furthermore, for an unchanged absolute groundwater discharge, its relative importance for the Aral Sea(s) has increased dramatically, from being about 12% of the total river discharge in 1960 to about 100% of total river discharge presently, and constitutes now a critical factor for the fate of the present lake system. [Copyright &y& Elsevier]

Many environmental problems require assessment of extensive reaction systems within natural subsurface flow systems exhibiting large physical and biogeochemical heterogeneity. We present an approach to couple stochastic advective-reactive modeling of physical solute transport (LaSAR) with the geochemical model PHREEQC for modeling solute concentrations in systems with variable flow velocity and multicomponent reactions. PHREEQC allows for general and flexible quantification of a multitude of linear and nonlinear geochemical processes, while LaSAR efficiently handles field-scale solute spreading in stochastic heterogeneous flow fields. The combined LaSAR- PHREEGC approach requires very modest computational efforts, thereby allowing a large number of reactive transport problems to be readily assessed and facilitating handling of quantifiable uncertainty in environmental model applications. Computational efficiency and explicit handling of field-scale dispersion without introduction of excessive fluid mixing that may impair model results are general advantages of the LaSAR compared with alternative solute transport modeling approaches. The LaSAR-PHREEQC approach is restricted to steady or unidirectional flow fields, and our specific application examples are limited to homogeneous reaction systems without local or transverse dispersion-diffusion, although these are not general methodological limitations. As a comprehensive application example, we simulate the spreading of acid mine drainage in a groundwater focusing on Zn2+ and including relevant major-component geochemistry. Model results show that Zn2+ may be substantially attenuated by both sorption and precipitation, with flow heterogeneity greatly affecting expected solute concentrations downstream of the mine waste deposit in both cases. [ABSTRACT FROM AUTHOR]

Steffen et al. (Research Articles, 13 February 2015, p. 736) recently assessed current global freshwater use, finding it to be well below a corresponding planetary boundary. However, they ignored recent scientific advances implying that the global consumptive use of freshwater may have already crossed the associated planetary boundary. [ABSTRACT FROM AUTHOR]

Summary: Contamination of groundwater by intruding seawater is a major problem in many parts of the world. This work derives novel analytical solutions for addressing this problem by extending the Girinskii–Strack concept of discharge potential to represent regional, steady-state, sharp-interface seawater intrusion in a sloping unconfined coastal aquifer. The aquifer has hydraulic conductivity K, is recharged uniformly at the rate r, receives an inflow at its land boundary and has a collector trough (or well gallery idealised as line sink) located at the distance lw from the coastline that penetrates the aquifer and draws groundwater at the rate qw . The theory rests on the approximation of a linearised gravity-part of the hydraulic potential. Analytical solutions for the discharge potential are derived, through which the hydraulic head, the flow depth and the sharp interface, and particularly the location of the interface toe, lT , are also determined. These solutions simplify to known results for the horizontal aquifer case. The utility (and robustness to uncertainty regarding the base slope) of the results in applications is demonstrated in the regional example of the Akrotiri Coastal Aquifer, Cyprus. Recasting the problem in non-dimensional form provides a relationship for the dependence of the relative interface toe location lT /lw on the appropriately normalised difference between the groundwater flow just up-gradient of the collector trough, qo , and the pumping rate, qw , given values of the base slope, r/K and Hsea /lw , where Hsea is the sea-surface elevation above the aquifer base at the coastline. That relationship frames a common groundwater management problem in coastal aquifers subject to a certain exploitation scheme, with lT as decision variable. In an exploratory demonstration study, non-dimensional sets of performance curves are calculated for the regional Akrotiri aquifer. In general, the derived analytical solutions can be used for first-order assessments of seawater intrusion vulnerability and management possibilities across a wide range of current regional coastal aquifer conditions and/or projected water demand, groundwater management and climatic change scenarios. [ABSTRACT FROM AUTHOR]

Summary: We develop a modelling methodology and investigate how spatial data on catchment surface characteristics may be used for quantifying relative coastal discharge contributions of streams and diffuse submarine groundwater discharge along the coastlines of unmonitored near-coastal catchment areas. The methodology is applied to two small Swedish coastal catchments areas, considering also two different ways to estimate evapotranspiration and its spatial variation within the catchments. Despite considerable differences between the characteristics of the two catchment areas, their relative coastal distribution results are similar, with about 80% of the total coastal discharge occurring through focused flows in visible and permanent streams, whereas the remaining 20% is diffuse and may occur through submarine groundwater discharge (SGD), small transient streams or both at different points in time. Evapotranspiration differs between the two used models, which results in relatively uncertain local flux values within the diffuse flow fields. The large focused stream flows and the mean values and total sums of diffuse flows (such as SGD) along some considerable coastline length, however, are constrained by the catchment-scale hydrological balance and considerably more robust and certain to estimate than the spatially variable small local fluxes within the diffuse flow fields. [Copyright &y& Elsevier]

Summary Interface flow models that use the Dupuit–Forchheimer (DF) approximation for assessing the freshwater lens and the seawater intrusion in coastal aquifers lack representation of the gap through which fresh groundwater discharges to the sea. In these models, the interface outcrops unrealistically at the same point as the free surface, is too shallow and intersects the aquifer base too far inland, thus overestimating an intruding seawater front. To correct this shortcoming of DF-type interface solutions for unconfined aquifers, we here adapt the outflow gap estimate of an analytical 2-D interface solution for infinitely thick aquifers to fit the 50%-salinity contour of variable-density solutions for finite-depth aquifers. We further improve the accuracy of the interface toe location predicted with depth-integrated DF interface solutions by ∼20% (relative to the 50%-salinity contour of variable-density solutions) by combining the outflow-gap adjusted aquifer depth at the sea with a transverse-dispersion adjusted density ratio (Pool and Carrera, 2011), appropriately modified for unconfined flow. The effectiveness of the combined correction is exemplified for two regional Mediterranean aquifers, the Israel Coastal and Nile Delta aquifers. [ABSTRACT FROM AUTHOR]