Headwaters drive streamflow and lowland tracer export in a large-scale humid tropical catchment

Christian Birkel* (Corresponding Author), Alicia Correa-Barahona, Marco Martinez-Martinez, Sebastian Granados-Bolaños, Nelson Venegas-Cordero, Kenneth Gutiérrez-García, Sara Blanco-Ramírez, Rafael Quesada-Mora, Vanessa Solano-Rivera, Jasson Mussio-Mora, Andres Chavarría-Palma, Katherine Vargas-Arias, Georgianne W. Moore, Ana Maria Durán-Quesada, Javier Vasquez-Morera, Chris Soulsby, Dörthe Tetzlaff, Edgar Espinoza-Cisneros, Ricardo Sánchez-Murillo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


Headwaters are generally assumed to contribute the majority of water to downstream users, but how much water, of what quality and where it is generated are rarely known in the humid tropics. Here, using monthly monitoring in the data scarce (2,370 km2) San Carlos catchment in northeastern Costa Rica, we determined runoff-area relationships linked to geochemical and isotope tracers. We established 46 monitoring sites covering the full range of climatic, land use and geological gradients in the catchment. Regression and cluster analysis revealed unique spatial patterns and hydrologically functional landscape units. These units were used for seasonal and annual Bayesian tracer mixing models to assess spatial water source contributions to the outlet. Generally, the Bayesian mixing analysis showed that the chemical and isotopic imprint at the outlet is throughout the year dominated by the adjacent lowland catchments (68%) with much less tracer influence from the headwaters. However, the headwater catchments contributed the bulk of water and tracers to the outlet during the dry season (>50%) despite covering less than half of the total catchment area. Additionally, flow volumes seemed to be linearly scaled by area maintaining a link between the headwaters and the outlet particularly during high flows of the rainy season. Stable isotopes indicated mean recharge elevations above the mean catchment altitude, which further supports that headwaters were the primary source of downstream water. Our spatially detailed “snap-shot” sampling enabled a viable alternative source of large-scale hydrological process knowledge in the humid tropics with limited data availability.

Original languageEnglish
Pages (from-to)3824-3841
Number of pages18
JournalHydrological Processes
Issue number18
Early online date9 Jul 2020
Publication statusPublished - 30 Aug 2020


  • Bayesian mixing model
  • Costa Rica
  • headwater
  • humid tropics
  • stable isotopes
  • tracers


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