Depositación atmosférica de nitrógeno en un transecto valle longitudinal-Cordillera de Los Andes, centro-sur de Chile

Abstract

Agricultural-livestock activities in south-central Chile, could result in elevated emissions of inorganic N (mainly NH3) compounds into the atmosphere. Ammonia can be transported via air currents and deposited on the vegetation and soil. The present study evaluates the atmospheric deposition of nitrogen compounds (NO3- y NH4+) in the precipitation, in an altitudinal transect of 66 km long, from the vicinity of Osorno (40° 35′ S, 72° 57′ W, 55 m of altitude) to Puyehue National Park, Cordillera de Los Andes (40° 46′ S, 72° 11′ W, 1,120 m of altitude). In seven sites, from June-1999 to May-2000, precipitation was recorded and water samples were collected monthly, for to determine pH, conductivity and NO3- and NH4+ concentrations. Annual precipitation increased from 1,103 mm near Osorno to 6,799 mm in Antillanca, Puyehue National Park. Annual mean values of pH showed little change from 6.3 in the central valley to 5.8 in the Cordillera de Los Andes. Conductivity showed the maximum values near Osorno (22.9 μS cm-1), intermediate values in transitional sites, and 11.3 μS cm-1 in the Cordillera de Los Andes. The annual mean concentrations of NO3- N changed between 52.3 μg L-1 in the agriculture-cattle area and 6.9 μg L-1 in temperate rainforests in Puyehue National Park. NH4+ concentrations changed between 699.4 μg L-1 in the Osorno sector to 37.8 μg L-1 in Cordillera de Los Andes. Inorganic-N values have a marked seasonal variation in the agricultural region with the maximum values in spring-summer and minimum in wintertime. Annual rates of atmospheric deposition of NO3-N fluctuated between 0.53 and 0.57 kg ha-1 yr-1, and the NH4-N between 6.4 and 2.8 kg ha-1 yr-1 for the agricultural region of Osorno and Puyehue National Park, respectively. These results are discussed in relation to the potential environmental effects of the increasing atmospheric deposition of nitrogen on the acidification and eutrophication of the soil and groundwater and runoff in the central valley of south-central Chile.