Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Hydrol. Earth Syst. Sci., 20, 2987-3004, 2016
https://doi.org/10.5194/hess-20-2987-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
26 Jul 2016
Insights into the water mean transit time in a high-elevation tropical ecosystem
Giovanny M. Mosquera1,2, Catalina Segura3, Kellie B. Vaché2, David Windhorst4, Lutz Breuer4,5, and Patricio Crespo1 1Departamento de Recursos Hídricos y Ciencias Ambientales & Facultad de Ciencias Agropecuarias, Universidad de Cuenca, Av. 12 de Abril, Cuenca, 010150, Ecuador
2Department of Biological and Ecological Engineering, Oregon State University, Corvallis, 97331, USA
3Department of Forestry Engineering, Resources, and Management, Oregon State University, Corvallis, 97331, USA
4Institute for Landscape Ecology and Resources Management (ILR), Research Centre for Biosystems, Land Use and Nutrition (IFZ), Justus Liebig University Gießen, Gießen, 35392, Germany
5Centre for International Development and Environmental Research, Justus Liebig University Gießen, Gießen, 35392, Germany
Abstract. This study focuses on the investigation of the mean transit time (MTT) of water and its spatial variability in a tropical high-elevation ecosystem (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in southern Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs under steady-state conditions (i.e., baseflow MTT). We used a unique data set of the δ18O isotopic composition of rainfall and streamflow water samples collected for 3 years (May 2011 to May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to explore controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15–0.73 years, 53–264 days). Regression analysis revealed a negative correlation between the catchment's average slope and MTT (R2 =  0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables, whereas MEC increases with MTT (R2 =  0.89, p < 0.001). Overall, we conclude that (1) baseflow MTT confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; (2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and (3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.

Citation: Mosquera, G. M., Segura, C., Vaché, K. B., Windhorst, D., Breuer, L., and Crespo, P.: Insights into the water mean transit time in a high-elevation tropical ecosystem, Hydrol. Earth Syst. Sci., 20, 2987-3004, https://doi.org/10.5194/hess-20-2987-2016, 2016.
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Short summary
This study focuses on the investigation of baseflow mean transit times (MTTs) in a high-elevation tropical ecosystem (páramo) using stable water isotopes. Results showed short MTTs (< 9 months) and topographic controls on their spatial variability. We conclude that (1) the hydrology of the ecosystem is dominated by shallow subsurface flow and (2) the interplay between the high storage capacity of the páramo soils and the catchments' slopes provides the ecosystem with high regulation capacity.
This study focuses on the investigation of baseflow mean transit times (MTTs) in a...
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