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Western Canadian oil sands contain over 170 billion barrels of proven unconventional petroleum reserves currently extracted at 1.8 million barrels per day by either surface mining, or by in situ techniques that require subsurface injection of steam and hydrocarbon solvents. Natural high-salinity springs are known to add water and entrained inorganic and organic constituents to the Athabasca River and its tributaries in the region of ongoing bitumen production. However, the magnitude and synoptic distribution of these saline inputs has remained unquantified. Here, a chloride mass balance is used to estimate saline groundwater discharge to the Athabasca River from 1987 to 2010. Results show that the highest saline water discharge rate to the Athabasca River occurs between Ft. McMurray and the Peace-Athabasca Delta, supported by subcrop exposure of lower Cretaceous- and Devonian-aged formations bearing saline waters. Further, the input of saline groundwater is found to be an important control on the chemistry of the lower Athabasca River, despite comprising 10 � 1 to 3% of the Athabasca River’s discharge. The flux of natural saline groundwater entering the Athabasca does not appear to have increased or decreased from 1987 to 2010. The origin of seep salinity is interpreted as relict subglacial meltwater that has dissolved Devonian-aged evaporites, supported by saline Na-Cl type waters with low 18 O/ 16 O and 2 H/ 1 H ratios relative to modern precipitation. The magnitude of groundwater discharge and its impact on the Athabasca River’s chemistry in the area of ongoing bitumen development warrants the incorporation of natural groundwater seepages into surface water quality monitoring networks.

A compilation of 81 studies that have partitioned evapotranspiration (ET) into its components—transpiration (T) and evaporation (E)—at the ecosystem scale indicates that T accounts for 61% (±15% s.d.) of ET and returns approximately 39 ± 10% of incident precipitation (P) to the atmosphere, creating a dominant force in the global water cycle. T as a proportion of ET is highest in tropical rainforests (70 ± 14%) and lowest in steppes, shrublands and deserts (51 ± 15%), but there is no relationship of T/ET versus P across all available data ( R 2 = 0.01). Changes to transpiration due to increasing CO 2 concentrations, land use changes, shifting ecozones and climate warming are expected to have significant impacts upon runoff and groundwater recharge.

Groundwater resources are being stressed from the top down and bottom up. Declining water tables and near-surface contamination are driving groundwater users to construct deeper wells in many US aquifer systems. This has been a successful short-term mitigation measure where deep groundwater is fresh and free of contaminants. Nevertheless, vertical salinity profiles are not well-constrained at continental-scales. In many regions, oil and gas activities use pore spaces for energy production and waste disposal. Here we quantify depths that aquifer systems transition from fresh-to-brackish and where oil and gas activities are widespread in sedimentary basins across the United States. Fresh-brackish transitions occur at relatively shallow depths of just a few hundred meters, particularly in eastern US basins. We conclude that fresh groundwater is less abundant in several key US basins than previously thought; therefore drilling deeper wells to access fresh groundwater resources is not feasible extensively across the continent. Our findings illustrate that groundwater stores are being depleted not only by excessive withdrawals, but due to injection, and potentially contamination, from the oil and gas industry in areas of deep fresh and brackish groundwater.

In the version of this Article originally published, the wrong article was listed as ref. 33; it should have been “Oki, T. & Kanae, S. Global hydrological cycles and world water resources. Science 313, 1068–1072 (2006).” This has been corrected in the online versions of the Article.

En respuesta a las crecientes presiones sobre los recursos hidricos, los programas de gestion de servicios de cuencas hidrograficas se implementan en todo el tropico. Estos programas tienen como objetivo promover actividades de manejo de la tierra que mejoren la cantidad y calidad del agua disponible para las comunidades locales. El exito de estos programas depende de nuestra capacidad para (a) comprender los impactos de las intervenciones de cuencas hidrologicas en la ecohidrologia; (b) modelar estos impactos y disenar programas de gestion eficientes; y (c) desarrollar estrategias para superar las barreras al desarrollo practico de politicas, incluidas las limitaciones de recursos o la ausencia de datos de referencia. En este documento, revisamos las oportunidades en la ciencia ecohidrologica que ayudaran a abordar estos tres desafios. Las oportunidades se agrupan en tecnicas de medicion, enfoques de modelado y acceso a recursos en nuestro mundo hiperconectado. Luego evaluamos las implicaciones de gestion tanto de las brechas de conocimiento como de los nuevos desarrollos de investigacion relacionados con el efecto de la gestion de la tierra. En general, destacamos la importancia del conocimiento relevante para las politicas para implementar programas de servicios de cuencas eficientes y equitativos en los tropicos.

Declining groundwater levels are common in parts of the western US, but their impact on the ability of wells to pump groundwater is not known. Here we collate groundwater well records for the western United States and present the recorded locations, depths, and purposes of more than two million groundwater wells constructed between 1950 and 2015. We then use the well records to estimate the percentage of wells that were dry during the years 2013–2015. During the two year period, dry wells were concentrated in rural areas with high agricultural productivity, such as parts of the California Central Valley and the High Plains. Our results support anecdotal evidence that wells used for domestic purposes are more susceptible to drying than wells used for agricultural purposes throughout California's Central Valley because the former tend to be shallower. However, this is not the case in all regions. Our findings suggest that declining groundwater levels are threatening drinking water reliability and agricultural productivity, and consequently, have key implications for both domestic and agricultural water security. Ongoing reductions to groundwater storage are drying groundwater wells in the western US, and this manifestation of water scarcity warrants innovative groundwater management transcending status quos.

replying to A. M. J. Coenders-Gerrits et al. Nature506,http://dx.doi.org/10.1038/nature12925(2014) In their Comment, Coenders-Gerrits et al.1 suggest that our conclusion that transpiration dominates the terrestrial water cycle2 is biased by unrepresentative input data and optimistic uncertainty ranges related to runoff, interception and the isotopic compositions of transpired and evaporated moisture. We clearly presented the uncertainties applied in our Monte-Carlo sensitivity analysis, we reported percentile ranges of results rather than standard deviations to best communicate the nonlinear nature of the isotopic evaporation model, and we highlighted that the uncertainty in our calculation remains large, particularly in humid catchments (for example, figure 2 in our paper2).

[1] The hydrological fate of shallow tundra lakes and ponds under conditions of continued warming remains uncertain, but has important implications for wildlife habitat and biogeochemical cycling. Observations of unprecedented pond desiccation, in particular, signify catastrophic loss of aquatic habitat in some Arctic locations. Shallow tundra ponds are a ubiquitous feature in the western Hudson Bay Lowlands (HBL), a region that has undergone intense warming over the past ∼50 years. But it remains unknown how hydrological processes in these ponds have responded. Here, we use cellulose-inferred pond water oxygen isotope records from sediment cores, informed by monitoring of modern pond water isotope compositions during the 2009 and 2010 ice-free seasons, to reconstruct hydrological conditions of four shallow tundra ponds in the western HBL over the past three centuries. Following an interval of relative hydrological stability during the early part of the records, results reveal widely differing hydrological responses to 20th century climate change among the study sites, which is largely dependent on hydrological connectivity of the basins within their respective surrounding peatlands. These findings suggest the 20th century has been characterized by an increasingly dynamic landscape that has variably influenced surface water balance – a factor that is likely to play a key role in determining the future water balance of ponds in this region.

Dependence upon groundwater to meet rising agricultural and domestic water needs is expected to increase substantially across the tropics where, by 2050, over half of the world's population is projected to live. Rare, long-term groundwater-level records in the tropics indicate that groundwater recharge occurs disproportionately from heavy rainfalls exceeding a threshold. The ubiquity of this bias in tropical groundwater recharge to intensive precipitation is, however, unknown. By relating available long-term records of stable-isotope ratios of O and H in tropical precipitation (15 sites) to those of local groundwater, we reveal that groundwater recharge in the tropics is near-uniformly (14/15 sites) biased to intensive monthly rainfall, commonly exceeding the ~70th intensity decile. Our results suggest that the intensification of precipitation brought about by global warming favours groundwater replenishment in the tropics. Nevertheless, the processes that transmit intensive rainfall to groundwater systems and enhance the resilience of tropical groundwater storage in a warming world, remain unclear.

This paper summarizes various lines of evidence, including new geophysical and geochemical surveys indicating the discharge of naturally occurring saline formation water from Cretaceous and Devonian formations to the Athabasca River downstream of Fort McMurray — an active oil sands extraction area. The following features are indicative of saline water discharge: (i) the hydrogeological setting of the reach which is situated near the western, up-dip, and subcropping, edge of the Western Canada Sedimentary Basin; (ii) springs and seepage along area rivers and tributaries that have been observed and reported in previous studies; and (iii) a significant increase in dissolved solids in the river, particularly chloride, occurring in a downstream direction from Fort McMurray. Further evidence of the saline groundwater discharge was obtained from electromagnetic surveys conducted along a 125 km reach from the Clearwater River to the Firebag River. This technique was used to map the distribution of saline water in the riverbed hyporheic zone, and revealed broad zones of generally high terrain electrical conductivity values in deeply incised Cretaceous- and Devonian-aged subcrop areas, but with numerous point-source and lineal anomalies attributed to occurrence of saline water discharge in less incised areas. Porewater sampling using drive-point piezometers was then used to confirm the presence of saline water in selected zones. Depth-wise gradients in chemical parameters observed in the riverbed porewaters in these zones are interpreted as evidence of upward movement of saline formation water mixing with the Athabasca River. Geochemical properties of the porewater are consistent with natural sources of groundwater flow from the Cretaceous- and Devonian-aged formations discharging along various reaches of the river.