Nutrients dynamics in the main river basins of the centre-southern region of Chile

Chilean basins have long been exposed to nutrient discharges from human activities and land use changes. A historical seasonal NO3--N and PO43--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 NO3--N and PO43--P are nonlinear. River basins such as Bio-Bio, Bueno, Imperial, Maule, Rape] and Valdivia showed a clear increase in NO3--N, while PO43--P increased only in the Rapel and Maule basins. Although no seasonal difference in NO3--N and PO43--P Was found in the analysed basins, there was a negative relation between these nutrients and water flow. Sampling stations with high NO3--N concentration were found mostly in sub-basins located in the central valley of central Chile, while several PO43--P over-concentrated sampling stations were located mostly upstream. If NO3--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. (C) 2009 Elsevier B.V. All rights reserved.