Biogeochemical cycles, contaminant transport and chemical weathering are regulated by the speed at which precipitation travels through landscapes and reaches streams1. Streamflow is a mixture of young and old precipitation2, but the global proportions of these young and old components are not known. Here we analyse seasonal cycles of oxygen isotope ratios in rain, snow and streamflow compiled from 254 watersheds around the world, and calculate the fraction of streamflow that is derived from precipitation that fell within the past two or three months. This young streamflow accounts for about a third of global river discharge, and comprises at least 5% of discharge in about 90% of the catchments we investigated. We conclude that, although typical catchments have mean transit times of years or even decades3, they nonetheless can rapidly transmit substantial fractions of soluble contaminant inputs to streams. Young streamflow is less prevalent in steeper landscapes, which suggests they are characterized by deeper vertical infiltration. Because young streamflow is derived from less than 0.1% of global groundwater storage, we conclude that this thin veneer of aquifer storage will have a disproportionate influence on stream water quality.
At a glance
- 818 (Freeman, 1978). & Water in Environmental Planning
- Flow path of rain from the soil surface to the water table. Soil Sci. 100, 377–383 (1965). &
- A review and evaluation of catchment transit time modeling. J. Hydrol. 330, 543–563 (2006). &
- Estimates of freshwater discharge from continents: latitudinal and seasonal variations. J. Hydrometeorol. 3, 660–687 (2002). &
- Debates—The future of hydrological sciences: a (common) path forward? A call to action aimed at understanding velocities, celerities, and residence time distributions of the headwater hydrograph. Wat. Resour. Res. 50, 5342–5350 (2014). &
- The role of groundwater in storm runoff. Dev. Water Sci. 12, 45–65 (1979). &
- The role of event water, a rapid shallow flow component, and catchment size in summer stormflow. J. Hydrol. 217, 171–190 (1999). , , &
- Hydrograph separation using stable isotopes: review and evaluation. J. Hydrol. 505, 47–64 (2013). &
- How old is the water? Open questions in catchment transit time conceptualization, modelling and analysis. Hydrol. Process. 24, 1745–1754 (2010). et al.
- Aggregation in environmental systems – Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments. Hydrol. Earth Syst. Sci. (in the press).
- Aggregation in environmental systems – Part 2: Catchment mean transit times and young water fractions under hydrologic nonstationarity. Hydrol. Earth Syst. Sci. (in the press).
- Seasonality of isotopes in precipitation: a global perspective. J. Geophys. Res. 114, D08116 (2009). , &
- Amount-weighted annual isotopic (δ18O) values are affected by the seasonality of precipitation: a sensitivity study. Geophys. Res. Lett. 34, L21707 (2007). , , &
- Application of flow models in an alpine catchment area using tritium and deuterium data. J. Hydrol. 66, 319–330 (1983). , , &
- Seasonal isotope hydrology of three Appalachian forest catchments. Hydrol. Process. 11, 1895–1906 (1997). , , , &
- Fractal stream chemistry and its implications for contaminant transport in catchments. Nature 403, 524–527 (2000). , &
- Generality of fractal 1/f scaling in catchment tracer time series, and its implications for catchment travel time distributions. Hydrol. Process. 24, 1660–1671 (2010). et al.
- Hydrology: the sting in a fractal tail. Nature 403, 493–495 (2000). &
- A simplified approach to analysing historical and recent tritium data in surface waters. Hydrol. Process. 29, 572–578 (2015). et al.
- Mapping of snow water equivalent and snow depth in boreal and sub-arctic zones by assimilating space-borne microwave radiometer data and ground-based observations. Remote Sensing Environ. 101, 257–269 (2006).
- Streamflow generation in a large, alpine watershed in the southern Rocky Mountains of Colorado: is streamflow generation simply the aggregation of hillslope runoff responses? Wat. Resour. Res. 47, W06512 (2011). , , , &
- Regional groundwater flow in mountainous terrain: three-dimensional simulations of topographic and hydrogeologic controls. Wat. Resour. Res. 44, W10403 (2008). &
- Classifying the water table at regional to continental scales. Geophys. Res. Lett. 38, L05401 (2011). , , &
- Global patterns of groundwater table depth. Science 339, 940–943 (2013). , &
- A glimpse beneath earth’s surface: GLobal HYdrogeology MaPS (GLHYMPS) of permeability and porosity. Geophys. Res. Lett. 41, 3891–3898 (2014). , , &
- The dependence of chemical weathering rates on fluid residence time. Earth Planet. Sci. Lett. 294, 101–110 (2010).
- On the role of aspect to quantify water transit times in small mountainous catchments. Wat. Resour. Res. 45, W08427 (2009). , &
- A new time-space accounting scheme to predict stream water residence time and hydrograph source components at the watershed scale. Wat. Resour. Res. 45, W07401 (2009). &
- Truncation of stream residence time: how the use of stable isotopes has skewed our concept of streamwater age and origin. Hydrol. Process. 24, 1646–1659 (2010). , &
- The global volume and distribution of modern groundwater. Nature Geosci. http://dx.doi.org/10.1038/ngeo2590 (2015). , , , &
- Deuterium and oxygen-18 isotope composition of precipitation and atmospheric moisture. Hydrol. Process. 14, 1341–1355 (2000). , &
- Global Network for Isotopes in Precipitation (International Atomic Energy Agency, accessed November 2014); http://www-naweb.iaea.org/napc/ih/IHS_resources_gnip.html
- The Global Network of Isotopes in Rivers (GNIR): integration of water isotopes in watershed observation and riverine research. Hydrol. Earth Syst. Sci. 19, 3419–3431 (2015). , , , &
- Global Network for Isotopes in Rivers (International Atomic Energy Agency, accessed November 2014); http://www-naweb.iaea.org/napc/ih/IHS_resources_gnir.html
- Distribution of oxygen-18 and deuterium in river waters across the United States. Hydrol. Process. 15, 1363–1393 (2001). &
- Isotopic (δ18O) characteristics of weekly precipitation collected across the USA: an initial analysis with application to water source studies. Hydrol. Process. 14, 1449–1464 (2000).
- Atmospheric circulation controls on precipitation isotope–climate relations in western Canada. Tellus B 61, 566–576 (2009). &
- A high-resolution data set of surface climate over global land areas. Clim. Res. 21, 1–25 (2002). , , &
- Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000. Glob. Biogeochem. Cycles 22, GB1003 (2008). , , &
- Development and validation of a global database of lakes, reservoirs and wetlands. J. Hydrol. 296, 1–22 (2004). &
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