Water flow paths in soil control element exports in an Andean tropical montane forest |
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| Authors: | J Boy C Valarezo W Wilcke |
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| Institution: | aProfessorship of Soil Geography/Soil Science, Geographic Institute, Johannes Gutenberg University, 55099 Mainz, Germany, and bUniversidad Nacional de Loja, Area Agropecuaria y de Recursos Naturales Renovables, Programa de Agroforestería, Ciudadela Universitaria Guillermo Falconí, Loja, Ecuador |
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| 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), NO3‐N, NH4‐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?1), N (0.6–0.9 mg litre?1), K (0.5–0.7 mg litre?1), Ca (0.6–1.0 mg litre?1), Mg (0.3–0.5 mg litre?1), Al (110–390 μg litre?1) and Mn (3.9–8.4 μg litre?1) 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?1), S (0.3–0.7 mg litre?1) and Na (3.0–6.0 mg litre?1) 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. |
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