Nitrogen exports at multiple-scales in a southern Chilean watershed (Patagonian Lakes district) |
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Authors: | Christian Little Doris Soto Antonio Lara Jaime G Cuevas |
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Institution: | (1) Instituto de Silvicultura, Universidad Austral de Chile, Casilla 567, Valdivia, Chile;(2) Núcleo Milenio FORECOS, Iniciativa Científica Milenio, Valdivia, Chile;(3) Present address: Fisheries and Aquaculture Department, FAO of UN, Via delle Terme di Caracalla, 00100 Rome, Italy;(4) Instituto de Investigaciones Agropecuarias (INIA-Quilamapu), Chillán, Chile |
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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. |
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Keywords: | Catchment Land cover Nitrogen export DIN/DON ratio |
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