Water flow paths in soil control element exports in an Andean tropical montane forest

Abstract

We tested the hypothesis that concentrations of chemical constituents in stream water can be explained by the depth of water flow through soil. Therefore, we measured the concentrations of total organic carbon (TOC), NO 3 -N, NH 4 -N, dissolved organic nitrogen (DON), P, S, K, Ca, Mg, Na, Al and Mn in rainfall, throughfall, stemflow, litter leachate, mineral soil solution and stream water of three 8-13 ha catchments on steep slopes (1900-2200 m above sea level) of the south Ecuadorian Andes, from April 1998 to April 2003. Peak C (14-22 mg litre À1 ), N (0.6-0.9 mg litre À1 ), K (0.5-0.7 mg litre À1 ), Ca (0.6-1.0 mg litre À1 ), Mg (0.3-0.5 mg litre À1 ), Al (110-390 mg litre À1 ) and Mn (3.9-8.4 mg litre À1 ) concentrations in stream water were associated with lateral flow (fast near-surface flow in saturated topsoil) while the greatest P (0.1-0.3 mg litre À1 ), S (0.3-0.7 mg litre À1 ) and Na (3.0-6.0 mg litre À1 ) concentrations occurred during low baseflow conditions. All elements had greater concentrations in the organic layer than in the mineral soil, but only C, N, K, Ca, Mg, Al and Mn were flushed out during lateral-flow conditions. Phosphorus, S and Na, in contrast, were mainly released by weathering and (re-)oxidation of sulphides in the subsoil. Baseflow accounted for 32% to 61% of P export, while > 50% of S was exported during intermediate flow conditions (i.e. lateral flow at the depth of several tens of cm in the mineral soil). Near-surface water flow through C-and nutrient-rich topsoil during rainstorms was the major export pathway for C, N, Al and Mn (contributing > 50% to the total export of these elements). Near-surface flow also accounted for one-third of total base metal export. Our results demonstrate that near-surface flow related to storm events markedly affects the cycling of many nutrients in steep tropical montane forests.

Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador

“…3). As weather conditions in WET were likely to lead to episodic water saturation favoring lateral flow in topsoil (Boy et al 2008b) Mandernack et al 2000). The denit values of Mandernack et al (2000) are not directly comparable to ours because the authors reported the fractionation of several chemical reaction steps while we report fractionation during the first reaction step only.…”

“…DRY than in WET. Furthermore, lateral flow in the organic layer following water saturation of the soil is important at our study site (Goller et al 2005;Boy et al 2008b), which is likely to have occurred in WET. Lateral flow might have flushed NH 4 + quickly to the stream and consequently reduced its availability.…”

Land use alters dominant water sources and flow paths in tropical montane catchments in East Africa

“…We therefore conclude that the observed signatures were caused by shallow sub-surface flow during rainfall events, which agrees with findings in NF by Jacobs et al (in review) and is commonly observed in tropical montane forested catchments (e.g. Boy et al, 2008;Muñoz-Villers and McDonnell, 2012;Saunders et al, 2006). The extent to which the Hydrol.…”

The nitrogen cycle of tropical montane forest in Ecuador turns inorganic under environmental change

“…[Wilcke et al, 2001;Boy et al, 2008b]. Our own records show that annual precipitation ranged between 2000 and 2500 mm and that mean annual temperature was 14.9°C during 1999-2010.…”