Little,C., Soto,D., Lara,A. and Cuevas,J.G.(2008): Nitrogen exports at multiple-scales in a southern Chilean watershed (Patagonian Lakes district). Biogeochemistry, 87, 297-309.

『南部チリ(パタゴニアの湖地方)の集水域における多規模での窒素排出』


Abstract
 We evaluated nitrogen (N) export for various catchments in the San Pedro River watershed of South-central Chile (39゜20' to 40゜12'S) during the dry season (February to March). We measured concentrations and export of the various N species at 16 points from the Andean headwaters to the lowland portion of the watershed: eight main nested points along the main watershed and eight secondary points on tributaries. We expected that, given a downstream increase in pastureland and decrease in native pristine forest cover, inorganic forms of N (DIN) would increase downstream, while conversely, dissolved organic nitrogen (DON) would decrease compared with concentrations in the forested headwaters. Nitrogen concentrations did not show statistically significant differences among the nested catchments. However, there were statistically significant differences in N concentrations associated with land cover among the tributaries. The results suggest that in the presence of base flow, natural landscape properties (barren land, lakes and rivers), explained most of the spatial variation in the N exports, while anthropogenic disturbance was not detectable. There was a negative relationship between DIN export and the coverage of lakes and rivers, suggesting that lakes might be acting as N traps. On the other hand, DIN, DON and total N exports were positively associated to barren land. Total nitrogen export during this 60-day dry season was less than 20 kg km-2 and the annual export was not larger than 100 kg km-2. This study documents the as yet pristine conditions of rivers in southern Chile.

Keywords: Catchment; Land cover; Nitrogen export; DIN/DON ratio』

Introduction
Study area
Methods
 Sampling design
 Water chemistry
 Streamflow
 Nitrogen export
 Data analysis
Results
 Land cover
 Hydrology
 Nitrogen concentration
 Nitrogen export
Discussion
 Magnitude of N exports and concentrations
 Trends in N concentration and exports
Conclusions
Acknowledgments
References


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