The hydrological regime of a forested tropical Andean catchment

Abstract

The hydrology of tropical mountain catchments plays a central role in ecological function, geochemical and biogeochemical cycles, erosion and sediment production, and water supply in globally important environments. There have been few studies quantifying the seasonal and annual water budgets in the montane tropics, particularly in cloud forests. We investigated the water balance and hydrologic regime of the Kosnipata catchment (basin area: 164.4 km(2)) over the period 2010-2011. The catchment spans over 2500 m in elevation in the eastern Peruvian Andes and is dominated by tropical montane cloud forest with some high-elevation puna grasslands. Catchment-wide rainfall was 3112 +/- 414 mm yr(-1), calculated by calibrating Tropical Rainfall Measuring Mission (TRMM) 3B43 rainfall with rainfall data from nine meteorological stations in the catchment. Cloud water input to streamflow was 316 +/- 116 mm yr(-1) (9.2% of total inputs), calculated from an isotopic mixing model using deuterium excess (Dxs) and delta D of waters. Field streamflow was measured in 2010 by recording height and calibrating to discharge. River runoff was estimated to be 2796 +/- 126 mm yr(-1). Actual evapotranspiration (AET) was 688 +/- 138mm yr(-1), determined using the Priestley and Taylor-Jet Propulsion Laboratory (PT-JPL) model. The overall water budget was balanced within 1.6 +/- 13.7 %. Relationships between monthly rainfall and river run-off follow an anticlockwise hysteresis through the year, with a persistence of high run-off after the end of the wet season. The size of the soil and shallow groundwater reservoir is most likely insufficient to explain sustained dry-season flow. Thus, the observed hysteresis in rainfall-run-off relationships is best explained by sustained groundwater flow in the dry season, which is consistent with the water isotope results that suggest persistent wet-season sources to stream-flow throughout the year. These results demonstrate the importance of transient groundwater storage in stabilising the annual hydrograph in this region of the Andes

Geomorphic regime modulates hydrologic control of chemical weathering in the Andes–Amazon

“…Because this complex behavior occurs at high runoff rates, it has an important impact on the total solute fluxes. Compared to the other sites, San Pedro has the highest annual precipitation (Lambs et al, 2012;Clark et al, 2014), which may be a factor contributing to its unique behavior at high runoff.…”

“…at the Wayqecha gauging station) in order to investigate mixing relationships. Following Clark et al (2014), samples collected between December and March are labeled wet season samples, samples collected in April are labeled wet-to-dry season transition samples, samples collected between May and September are labeled dry seasons samples, and samples collected between October and November are labeled dry-to-wet season transition samples. Samples for major and minor element analysis were collected from the river surface in a clean polypropylene (PP) bottle, filtered onsite with a 0.2 lm nylon filter and split into two aliquots stored in separate 60 mL high-density polyethylene bottles (HDPE).…”

“…Discharge was measured at each of the main sampling localities as described by Ballew (2011) and Clark et al (2014). Briefly, river level was monitored manually at all sites and converted to discharge using a rating curve.…”

“…During the study period (2010-2011), annual rainfall was 2519 ± 3 35 mm year À1 and 3112 ± 414 mm year À1 for the Way and SP catchments respectively, slightly above the long-term average . Like air temperature, rainfall also shows a strong elevational dependence (Lambs et al, 2012;Clark et al, 2014). For the same 2010-2011 period, annual runoff was estimated to be 3065 mm year À1 and 2796 ± 126 mm year À1 for the Way and SP catchments respectively .…”

“…Near the sampling locality, meteorological stations (data available from http://atrium.andesamazon.org) record temperatures that typically range from 21 to 26°C with a mean of $24°C and precipitation volumes that range from 2600 to 3500 mm/year, with mean values between 2700 and 3000 mm/year (Lambs et al, 2012). A majority of the annual rainfall in Peru occurs during the austral summer (Lambs et al, 2012;Clark et al, 2014). The catchment area of CICRA is largely underlain by sediments shed from the Andes with additional contributions from Cretaceous marine sediments and Cenozoic continental deposits (Räsänen et al, 1992;Mendívil Echevarría and Dávila Manrique, 1994;Carlotto Caillaux et al, 1996;Vargas Vilchez and Hipolito Romero, 1998;INGEMMET, 2013).…”