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Characterising the variability of transit time distributions and young water fractions in a karst catchment using flux tracking
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  • Zhicai Zhang,
  • Xi Chen,
  • Qin-bo Cheng,
  • Chris Soulsby
Zhicai Zhang
Hohai University
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Xi Chen
Tianjin University
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Qin-bo Cheng
Hohai University
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Chris Soulsby
University of Aberdeen
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Peer review status:ACCEPTED

08 Jan 2020Submitted to Hydrological Processes
08 Jan 2020Submission Checks Completed
08 Jan 2020Assigned to Editor
08 Jan 2020Reviewer(s) Assigned
24 Feb 2020Review(s) Completed, Editorial Evaluation Pending
24 Feb 2020Editorial Decision: Revise Major
04 Apr 20201st Revision Received
05 Apr 2020Submission Checks Completed
05 Apr 2020Assigned to Editor
05 Apr 2020Reviewer(s) Assigned
13 May 2020Review(s) Completed, Editorial Evaluation Pending
18 May 2020Editorial Decision: Accept

Abstract

Water transit time and young water fraction are important metrics for characterizing catchment hydrologic function and understanding solute transport. Hydrological and biogeochemical processes in karst environments are strongly controlled by heterogenous fracture-conduit networks. Quantifying the spatio-temporal variability of water transit time and young water fractions in such heterogeneous hydrogeological systems is fundamental linking discharge and water quality dynamics in the karst critical zone. We used a tracer-aided hydrological model to track the fluxes of water parcels that entered a karst catchment as rainfall, time-stamping each hour of rain input individually. Using this approach, the variability of transit times and water age distributions were estimated in the main landscape units in the karst catchment of Chenqi in Guizhou Province, Southwest China. The estimated mean young water (i.e <~2 months old) fractions were 0.39, 0.31 and 0.10 for output fluxes from the hillslope unit, catchment outlet and slow flow reservoirs (matrix and small fractures), respectively. Marked seasonal variability in sources of runoff generation and associated hydrological connectivity between different conceptual stores were the main drivers of young water fraction dynamics in each landscape unit. The water age and travel time distributions were strongly influenced by the water storage dynamics reflecting catchment wetness conditions. Even though the contribution of young water to runoff was greater, the older water turnover was generally accelerated at moderately high flows during wet season.