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Tracer-aided modelling reveals quick runoff generation and groundwater losses producing young streamflow ages in a tropical rainforest catchment
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  • Leia Mayer-Anhalt,
  • Christian Birkel,
  • Ricardo Sanchez-Murillo,
  • Stephan Schulz
Leia Mayer-Anhalt
Technical University of Darmstadt Institute of Applied Geosciences

Corresponding Author:[email protected]

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Christian Birkel
University of Costa Rica
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Ricardo Sanchez-Murillo
Universidad Nacional de Costa Rica
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Stephan Schulz
Technische Universität Darmstadt
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Abstract

There is still limited understanding of how waters mix, where waters come from and for how long they reside in tropical catchments. In this study, we used a tracer-aided model (TAM) and a gamma convolution integral model (GM) to assess runoff generation, mixing processes, water ages and transit times (TT) in the pristine humid tropical rainforest Quebrada Grande catchment in central Costa Rica. Models are based on a four-year data record (2016 to 2019) of continuous hydrometric and stable isotope observations. Both models agreed on a young water component of fewer than 95 days in age for 75% of the study period. The streamflow water ages ranged from around two months for wetter years (2017) and up to 9.5 months for drier (2019) years with a better agreement between the GM estimated TTs and TAM water ages for younger waters. Such short TTs and water ages result from high annual rainfall volumes even during drier years with 4,300 mm of annual precipitation (2019) indicating consistent quick near-surface runoff generation with limited mixing of waters and a supra-regional groundwater flow of likely unmeasured older waters. The TAM in addition to the GM allowed simulating streamflow (KGE > 0.78), suggesting an average groundwater contribution of less than 40% to streamflow. The model parameter uncertainty was constrained in calibration using stable water isotopes (δ2H), justifying the higher TAM model parameterization. We conclude that the multi-model analysis provided consistent water age estimates of a young water dominated catchment. This study represents an outlier compared to the globally predominant old water paradox, exhibiting a tropical rainforest catchment with higher new water fractions than older water.
27 May 2021Submitted to Hydrological Processes
29 May 2021Submission Checks Completed
29 May 2021Assigned to Editor
29 May 2021Reviewer(s) Assigned
09 Jul 2021Review(s) Completed, Editorial Evaluation Pending
14 Jul 2021Editorial Decision: Revise Major
30 Sep 20211st Revision Received
01 Oct 2021Assigned to Editor
01 Oct 2021Submission Checks Completed
01 Oct 2021Reviewer(s) Assigned
25 Nov 2021Review(s) Completed, Editorial Evaluation Pending
30 Nov 2021Editorial Decision: Revise Minor
23 Jan 20222nd Revision Received
24 Jan 2022Assigned to Editor
24 Jan 2022Submission Checks Completed
24 Jan 2022Reviewer(s) Assigned
24 Jan 2022Review(s) Completed, Editorial Evaluation Pending
29 Jan 2022Editorial Decision: Accept