Articles | Volume 20, issue 4
Research article
27 Apr 2016
Research article |  | 27 Apr 2016

Factors influencing stream baseflow transit times in tropical montane watersheds

Lyssette E. Muñoz-Villers, Daniel R. Geissert, Friso Holwerda, and Jeffrey J. McDonnell

Abstract. Stream water mean transit time (MTT) is a fundamental hydrologic parameter that integrates the distribution of sources, flow paths, and storages present in catchments. However, in the tropics little MTT work has been carried out, despite its usefulness for providing important information on watershed functioning at different spatial scales in (largely) ungauged basins. In particular, very few studies have quantified stream MTTs or have related these to catchment characteristics in tropical montane regions. Here we examined topographic, land use/cover and soil hydraulic controls on baseflow transit times for nested catchments (0.1–34 km2) within a humid mountainous region, underlain by volcanic soil (Andisols) in central Veracruz (eastern Mexico). We used a 2-year record of bi-weekly isotopic composition of precipitation and stream baseflow data to estimate MTT. Land use/cover and topographic parameters (catchment area and form, drainage density, slope gradient and length) were derived from geographic information system (GIS) analysis. Soil water retention characteristics, and depth and permeability of the soil–bedrock interface were obtained from intensive field measurements and laboratory analysis. Results showed that baseflow MTTs ranged between 1.2 and 2.7 years across the 12 study catchments. Overall, MTTs across scales were mainly controlled by catchment slope and the permeability observed at the soil–bedrock interface. In association with topography, catchment form and the depth to the soil–bedrock interface were also identified as important features influencing baseflow MTTs. The greatest differences in MTTs were found both within groups of small (0.1–1.5 km2) and large (14–34 km2) catchments. Interestingly, the longest stream MTTs were found in the headwater cloud forest catchments.

Short summary
This study provides an important first step towards a better understanding of the hydrology of tropical montane regions and the factors influencing baseflow mean transit times (MTT). Our MTT estimates ranged between 1.2 and 2.7 years, suggesting deep and long subsurface pathways contributing to sustain dry season flows. Our findings showed that topography and subsurface permeability are the key factors controlling baseflow MTTs. Longest MTTs were found in the cloud forest headwater catchments.