The solute budget of a forest catchment and solute fluxes within a Pinus radiata and a secondary native forest site, southern Chile

Abstract

AbstractSolute concentrations and fluxes in rainfall, throughfall and stemflow in two forest types, and stream flow in a 90 ha catchment in southern Chile (39°44′S, 73°10′W) were measured. Bulk precipitation pH was 6·1 and conductivity was low. Cation concentrations in rainfall were low (0·58 mg Ca2+ l−1, 0·13 mg K+ l−1, 0·11 mg Mg2+ l−1 and <0·08 mg NH4–N l−1), except for sodium (1·10 mg l−1). Unexpected high levels of nitrate deposition in rainfall (mean concentration 0·38 mg NO3–N l−1, total flux 6·3 kg NO3–N ha−1) were measured. Concentrations of soluble phosphorous in bulk precipitation and stream flow were below detection limits (<0·09 mg l−1) for all events. Stream‐flow pH was 6·3 and conductivity was 28·3 μs. Stream‐water chemistry was also dominated by sodium (2·70 mg l−1) followed by Ca, Mg and K (1·31, 0·70 and 0·36 mg l−1). The solute budget indicated a net loss of 3·8 kg Na+ ha−1 year−1, 5·4 kg Mg2+ ha−1 year−1, 1·5 kg Ca2+ ha−1 year−1 and 0·9 kg K+ ha−1 year−1, while 4·9 kg NO3–N ha−1 year−1 was retained by the ecosystem. Stream water is not suitable for domestic use owing to high manganese and, especially, iron concentrations.Throughfall and stemflow chemistry at a pine stand (Pinus radiata D. Don) and a native forest site (Siempreverde type), both located within the catchment, were compared. Nitrate fluxes within both forest sites were similar (1·3 kg NO3–N ha−1 year−1 as throughfall). Cation fluxes in net rainfall (throughfall plus stemflow) at the pine stand generally were higher (34·8 kg Na+ ha−1 year−1, 21·5 kg K+ ha−1 year−1, 5·1 kg Mg2+ ha−1 year−1) compared with the secondary native forest site (24·7 kg Na+ ha−1 year−1, 18·9 kg K+ ha−1 year−1 and 4·4 kg Mg2+ ha−1 year−1). However, calcium deposition beneath the native forest stand was higher (15·9 kg Ca2+ ha−1 year−1) compared with the pine stand (12·6 kg Ca2+ ha−1 year−1). Copyright © 2002 John Wiley & Sons, Ltd.