Abstract

Stream nutrient loads are heavily dependent on catchment vegetation. Alteration of canopies and the soil under it have a significant impact on nitrogen (NO3--N; NH4+-N; DON and TDN), phosphorus (PO43+-P and TDP) and base cations (Ca2+, Mg2+, Na+ and K+) reaching the stream. The objective of this study was to assess hydrology affected stream nutrient load responses and canopy effects on nutrients concentrations in five watersheds dominated by native old-growth evergreen rainforests, native secondary evergreen, native deciduous and exotic plantations of Eucalyptus nitens and Eucalyptus globulus, located at the Coastal mountain range of southern Chile (40° S). The mixed-deciduous (ND) and old-growth evergreen (ONE) forests show the highest canopy enrichment for throughfall, while the Eucalyptus plantations (FEP and EG) showed the minimum enrichment. The highest enrichment was DON (10.3 times) for ONE; and TDP (10.7 times) for ND catchment. The relations of TDN and TDP with catchment discharge were positive for all nutrients except NO3--N, which showed a negative association with discharge, during the dry season, and were observed negative correlations between stream discharge and base cations concentrations. Our results suggest that in native forests, rainfall water was infiltrating and percolating (subsurface flow) exporting less N in contrast to Eucalyptus plantation in which as the soil has less porosity and infiltration rates due to land-use history.