Chilean basins have long been exposed to nutrient discharges from human activities and land use changes. A historical seasonal NO(3)(-)-N and PO(4)(3-)-P database of the last 23 years of the main nine rivers of central-southern region of Chile was analysed. Generalized additive models indicated that annual trends in NO(3)(-)-N and PO(4)(3-)-P are nonlinear. River basins such as Bío-Bío, Bueno, Imperial, Maule, Rapel and Valdivia showed a clear increase in NO(3)(-)-N, while PO(4)(3-)-P increased only in the Rapel and Maule basins. Although no seasonal difference in NO(3)(-)-N and PO(4)(3-)-P was found in the analysed basins, there was a negative relation between these nutrients and water flow. Sampling stations with high NO(3)(-)-N concentration were found mostly in sub-basins located in the "central valley" of central Chile, while several PO(4)(3-)-P "over-concentrated" sampling stations were located mostly upstream. If NO(3)(-)-N emissions into Chilean river basins continue at current rates it is probable that the concentration of this nutrient will tend to match that of the most "polluted" rivers around the world.
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