Abstract
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 language | English |
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Pages (from-to) | 3824-3841 |
Number of pages | 18 |
Journal | Hydrological Processes |
Volume | 34 |
Issue number | 18 |
Early online date | 9 Jul 2020 |
DOIs | |
Publication status | Published - 30 Aug 2020 |
Bibliographical note
ACKNOWLEDGEMENTSA.C. acknowledges a UCR‐funded postdoctoral research fellowship. C.B. would like to acknowledge the Advanced Studies of the University of Costa Rica UCREA (B8276) and UCR support of the projects B8709 and the Water and Global Change Observatory (ED‐3319). We also thank the IAEA for support with CRP 22009 and 22760 research grants and the staff at the Soltis Center for rainfall sampling. The data that was developed and used in this study is publicly available: Birkel, C. (2020). San Carlos_Costa Rica database for HYP‐20‐0127, HydroShare, http://www.hydroshare.org/resource/e6b38a2999354626a36058676f916a47
Keywords
- Bayesian mixing model
- Costa Rica
- headwater
- humid tropics
- stable isotopes
- tracers