Hydrochemical fluxes in a Nothofagus pumilio forest in Puyehue National Park, southern Chile

Water and nutrient fluxes in a Nathofagus pumilio forest, located in the Pu yehue National Park (41 degrees S, 72 degrees W, 1120 m a.m.s.l.), during a 18-month period (July 1997-December 1998) were studied. Measurements of pr ecipitation, throughfall, stemflow, effective precipitation, soil water inf iltration and runoff were carried out in an experimental microcatchment. Si multaneously, monthly water samples were collected to determine the concent rations and fluxes of NO3-N, NH4-N, total-P, K+, Na+, Ca2+ and Mg2+. During 1997, precipitation was 5332 mm (78% as rain and 22% as snow). Throughfall was 4701 mm, stemflow 481 mm and runoff 4234 mm. The average pH of precipi tation, throughfall, stemflow and effective precipitation was 5.7, increasi ng their value in soil water infiltration (pH = 5.9) and runoff (pH = 7.0). The water in the forest was rich in cations, specially the runoff where K, Na+, Ca+ and Mg2+ concentrations were higher than those in the precipitat ion. NO3-N concentrations were higher in the forest, but lower in the runof f. However, NH3-N concentrations were lower in all levels of the forest in relation to precipitation. The total-P concentrations were higher in all le vels of the forest, compared to precipitation. The input of inorganic nitro gen via precipitation was 3.3 kg ha(-1) yr(-1) (NO3-N = 1.3 and NH4-N = 2.0 kg ha (-1) yr (-1)), and the output via runoff was 0.66 kg ha(-1) yr(-1) ( NO3-N = NH4-N = 0.31 kg ha(-1) yr(-1)), therefore the nitrate and ammonium retention efficiency were 72% and 85%, respectively.