Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time

Abstract

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km2) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub‐páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C‐horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.

Impact of elevation and weather patterns on the isotopic composition of precipitation in a tropical montane rainforest

“…They found that near-surface event water dominates runoff in these pristine rainforest-covered micro-catchments. In contrast, groundwater dominated fluxes tend to govern runoff generation on larger scales as revealed by geogenic tracer analyses (Bücker et al, 2010;Crespo et al, 2012). Surprisingly, Crespo et al (2012) derived MTTs of up to 260 to 350 days, despite the very responsive, flashy hydrographs that tend to react within a few hours to precipitation inputs.…”

“…In contrast, groundwater dominated fluxes tend to govern runoff generation on larger scales as revealed by geogenic tracer analyses (Bücker et al, 2010;Crespo et al, 2012). Surprisingly, Crespo et al (2012) derived MTTs of up to 260 to 350 days, despite the very responsive, flashy hydrographs that tend to react within a few hours to precipitation inputs. The uncertainty of this estimate remains unknown, given the limited information of stable isotopes in precipitation that the authors used.…”

Stable water isotope tracing through hydrological models for disentangling runoff generation processes at the hillslope scale

“…This study is conducted in a 75 km 2 montane rain forest catchment in south Ecuador, the upper part of the Rio San Francisco, which has been under investigation since 2007 (Bogner et al, 2014;Boy et al, 2008;Bücker et al, 2011;Crespo et al, 2012;Fleischbein et al, 2006;Goller et al, 2005;Timbe et al, 2014;Windhorst et al, 2013b). The findings of those studies (briefly synthesized in Sect.…”

“…Large shares of the soil water percolate to deeper horizons, thereby creating long mean transit times (MTT) (Crespo et al, 2012;Timbe et al, 2014). 4.…”

Sampling frequency trade-offs in the assessment of mean transit times of tropical montane catchment waters under semi-steady-state conditions

“…The stream waters of the river and its tributaries are perennial and baseflow dominated. Previous research accounted the groundwater contribution in 85 % of the total runoff, characterized by MTTs on the order of 2 to 4 years (Timbe et al, 2014;Crespo et al, 2012). A detailed description of the physical, hydro- logical and land cover characteristics of the catchment and main tributaries are given in Timbe et al (2014), whereas additional information on the climate and ecosystem gradients of the research area can be found in Bendix et al (2008), Fiedler and Beck (2008) and Wilcke et al (2008).…”