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Abstract

Throughfall enrichment and stream nutrient chemistry in small headwater catchments with different land cover in southern Chile.

Abstract

Land cover changes have a great impact on nitrogen (N) and phosphorous (P) fluxes catchments. In this study, we wanted to compare different land covers: deciduous (D), evergreen (E) (both native forests), and exotic Eucalyptus globulus plantation (EP), affected precipitation, and stream discharge on N and P species concentrations and fluxes, under a low deposition climate in south-central Chile. For this, we collected bulk precipitation, throughfall, and stream water samples after 41 rainfall events in E and EP, during the period June 2009-March 2011, and 31 rainfall events in D, during the period October 2009-March 2011. The highest canopy enrichment of N and P species for throughfall was observed in deciduous forest, while E. globulus showed the minimum enrichment. Total nitrogen (total-N) discharge in EP was about 8.6 times higher than that of E and D catchments. Total-N annual retention was positive only in E and D catchments. However, EP catchment showed a net loss (-4.79 kg N ha/year). The biggest difference was observed in nitrate stream concentrations, which showed low values for E (3.4±1.3 µg/L), while EP and D showed higher nitrate concentrations (84.9±16.7 and 134.7±36.7 µg/L, for EP and D, respectively). Total phosphorous (total-P) discharge flux was low in EP (0.4 kg P ha/year), and negligible in E and D forests (<0.1 kg P ha/year). Total-P annual retention was near to 1.0 kg N ha/year (on E and D), while a net loss (-1.5 kg N ha/year) was observed for EP. We attribute the observed differences in nutrient throughfall enrichment due to high multi-stratified canopies in the native forests. Both deciduous and evergreen native forest-covered catchments showed the highest retention of total-N and total-P, in contrast to Eucalyptus-covered plantation.