Precipitation chemistry in deciduous and evergreen Nothofagus forests of southern Chile under a low-deposition climate

The chemistry of rainfall and its redistribution were studied during the periods July 1997-December 1998 in a Nothofagus pumilio (summergreen) forest and in April 1999-March 2000 in a Nothofagus betuloides (evergreen) forest in two experimental microcatchments, located in the Puyehue National Park, southern Chile (41 degreesS). Annual precipitation varied from 5406 to 6559 mm during the studied periods, with about 68-80% as rain and 32-20% as snowfall. The average pH of bulk precipitation was 5.7. In the N. pumilio forest, the pH of throughfall, stemflow and effective precipitation was 5.7. In the infiltrating water it increased to 5.9 and in the runoff to 7.0. In the N. betuloides forest, the pH value of the precipitation was 6.1 and showed a slight increase in throughfall and soil water to 6.2 and in runoff to 6.5. NO3-N concentrations increased inside of both forests, especially in stemflow, suggesting biological N fixation in the canopy due to the presence of epiphytic lichens of the genera Peltigera, Pseudocyphellaria and Sticta living on the trunks, but decreased in the runoff. NH4-N concentrations decreased in all compartments inside the forests, especially in runoff water, compared with bulk precipitation. Concentrations of K+, Na+, Ca2+ and Mg2+ were higher in throughfall, stemflow and soil solution than in the bulk precipitation. The runoff water both of the N. pumilio and the N. betuloides forest was enriched with cations, especially with Ca2+ and Mg2+, indicating active weathering processes. The input of inorganic nitrogen (NO3-N + NH4-N) via precipitation amounted 3.3 kg ha(-1)yr(-1) in the studied area, suggesting some anthropogenic contribution from the agricultural activities in the Central Valley and pointing at high levels of rainfall in the Cordillera de los Andes of southern Chile. The water chemistry data are compared with corresponding data from European and North American forests with a particular emphasis on nitrogen deposition.