Abstract
Understanding how water moves through catchments - from the time it enters as precipitation to when it exits via streamflow - is of fundamental importance to understanding hydrological and biogeochemical processes. A basic descriptor of this routing is the Transit Time Distribution (TTD) which is derived from the input-output behavior of conservative tracers, the mean of which represents the average time elapsed between water molecules entering and exiting a flow system. In recent decades, many transit time studies have been conducted, but few of these have focused on snow-dominated catchments. We assembled a 10-year time series of isotopic data (δ18O and δ2H) for precipitation and stream water to estimate the characteristics of the transit time distribution in a boreal catchment in northern Sweden. We applied lumped parameter models using a gamma distribution to calculate the Mean Transit Time (MTT) of water over the entire period of record and to evaluate how inter-annual differences in transit times relate to hydroclimatic variability. The best fit MTT for the complete 10-year period was 650days (Nash-Sutcliff Efficiency=0.65), while the best fit inter-annual MTT ranged from 300days up to 1200days. Whilst there was a weak negative correlation between mean annual total precipitation and the annual MTT, this relationship was stronger (r 2 =0.53, p =0.02) for the annual rain water input. This strong connection between the MTT and annual rainfall, rather than snowmelt, has strong implications for understanding future hydrological and biogeochemical processes in boreal regions, given that predicted warmer winters would translate into a greater proportion of precipitation falling as rain and thus shorter MTT in catchments. Such a change could have direct implications for the export of solutes and pollutants.
Original language | English |
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Pages (from-to) | 7-16 |
Number of pages | 10 |
Journal | Journal of Hydrology |
Volume | 543 |
Issue number | A |
Early online date | 6 Feb 2016 |
DOIs | |
Publication status | Published - Dec 2016 |
Bibliographical note
AcknowledgementsThe presented data were collected and analysed with the help of a large number of colleagues in the Krycklan Catchment Study (KCS), all of whom deserve our gratitude and acknowledgement. We would especially like to thank Peder Blomkvist, Viktor Sjöblom and Ida Taberman. We would like to acknowledge Rene Capell who wrote the core script for the gamma model used. KCS is funded by the Swedish Science Foundation (VR) SITES, ForWater (Formas), Future Forest, Kempe Foundation, FOMA and SKB. Contributions from Aberdeen were funded by NERC (NE/M019896/1 project SIWA) and the European Research Council ERC (project GA 335910 VeWa).
Keywords
- Climate change
- Gamma model
- Isotopes
- Transit time