Effects of Land Use Conversion from Native Forests to Exotic Plantations on Nitrogen and Phosphorus Retention in Catchments of Southern Chile

Abstract

In six small catchments located at the Cordillera de la Costa in southern Chile (40°S), concentrations and fluxes of NO 3 -N, NH 4 -N, organic-N, total-N and total-P in bulk precipitation and runoff water were measured. The main objective of this study was to compare nitrogen and phosphorus retention of catchments with varying land cover of native forest and exotic plantations, in order to evaluate possible effects of land use change. Nitrate-N was the dominant fraction (>50%) of nitrogen loss, especially in the catchments dominated by exotic plantations. In the catchment with native forests, NO 3 − only contributed with 34% of the nitrogen loss and DON was the main output with 55%. Annual NO 3 − export was lower in the catchment with native forest compared to the catchments with exotic plantations where the streamflow output exceed the precipitation input. Average inputs of total-N were 2.6 kg ha −1 year −1 (DIN=1.4 kg ha −1 year −1 , DON=1.2 kg ha −1 year −1 ) and outputs were 1.7 kg ha −1 year −1 (DIN= 1.2 kg ha −1 year −1 , DON=0.5 kg ha −1 year −1 ). Annual retention of total nitrogen fluctuated between 61% in a catchment dominated by native forests to 15% in catchments dominated by exotic plantations of Eucalyptus sp. Nitrogen retention was positively related with native forest coverage. The N retention capacity of the catchments could be both attributed to consequences of clear cutting practices and differences in vegetation cover.

Ecohidrology and Nutrient Fluxes in Forest Ecosystems of Southern Chile

“…Studies in watersheds in the United States [34] reported that thin or porous soils and high infiltration rates have less capacity to retain N. However, in our study, catchments with high infiltration rates, such as NE and ND showed greater N retention than soils with very low infiltration rates, such as EG. In our study, the differences in DIN retention were evident between native forests and Eucalyptus plantation, as also has been described previously by [12]. However, [35] observed using land cover, watershed area and precipitation as predictors for water quality (nitrate, ammonia, DON, TDP and electric conductivity) for local models explained 79.5% of the variance.…”

“…[6] described that the dominant form of N leaching was dissolved organic nitrogen (DON) for unpolluted forests of southern Chile. Other studies in the area had reported that conversion from native forests to exotic fast-growing plantations is likely to decrease N retention on catchments [12].…”

Mineralización del nitrógeno, carbono y actividad enzimática del suelo en un bosque de Nothofagus obliqua (Mirb) Oerst y una plantación de Pinus radiata D. Don. del centro-sur de Chile

“…La menor CHM del suelo en la plantación de P. radiata en comparación a N. obliqua se relaciona con el bajo nivel de MOS, expresado en los contenidos de C y N del suelo superficial. Una mayor evapotranspiración es consecuencia directa de las plantaciones forestales con una consecuente disminución de la disponibilidad de agua en el suelo, acoplada con la compactación del suelo, producto del uso agrícola y forestal (Oyarzún et al 2007). …”

“…En Chile, la sustitución de bosques nativos por plantaciones de P. radiata ha sido un proceso importante, con consecuencias sociales, económicas y ambientales (Oyarzún et al 2007). Frank & Finckh (1997) evaluaron el impacto de las plantaciones de Pseudotsuga menziesii (Mirb) Franco sobre la vegetación y las propiedades del suelo en un Andisol de Chile, señalando para este último cambios significativos en la química, particularmente en el empobrecimiento de bases, cationes básicos y contenido de fósforo.…”

Propiedades hidrológicas del suelo y exportación de sedimentos en dos microcuencas de la Cordillera de la Costa en el sur de Chile con diferente cobertura vegetal

“…Esta conversión a plantaciones forestales ha resultado en tasas de deforestación de 4,5 % al año en la región del Maule (35° S) entre 1975 y 2000 (Echeverría et al 2006). Estudios recientes en el sur de Chile han mostrado los efectos negativos de la conversión de bosques nativos por plantaciones exóticas sobre las reservas de agua del suelo (Oyarzún y Huber 1999), rendimiento hídrico (Huber et al 2008) y retención de nitrógeno a nivel de cuencas (Oyarzún et al 2007). Brown et al (2005) indican que los resultados de experimentos de cambio en la cobertura vegetal, realizados en diversas partes del mundo (Australia, Nueva Zelanda, Sudáfrica y Estados Unidos), dependen principalmente del almacenamiento de agua en los suelos y de las variaciones en las tasas de transpiración en función de la edad de la vegetación.…”