CONICET | Buscador de Institutos y Recursos Humanos

Atmospheric depositions (AD) represent a significant input of nutrients to ecosystems. Southern South America almost completely lacks atmospheric deposition data. We present the first longtermdataset of ADmeasurements, on a netw ork of 6 sites located fromeast to west in Argentina and Uruguay. The network was started in 2006 and includes data for Ca, Mg, Na, K, PO4, NO3, SO4, NH4 and Cl. Measurements comprise both wet and dry per event deposition, obtained with a novel collector design that minimizes sample contamination and water evaporation fromthe collectors. Additionally, monthly collectors with this new design were also established at each site and compared w ith data obtained by per event collectors. Our results show a very close agreement of per event and monthly collectors, suggesting that this new collectors can be used for ADmeasurements in remote places on a monthly basis. Preliminary ADresults suggest higher SO4 and NO3 depositions in highly populated areas, although values are much lower that industrial regions of the Northern hemisphere (see Table). NH4 depositions seemto be high and similar to other regions of high cattle population and crop production. Marine elements are deposited in high quantities near costal sites, with very high Cl depositions near the ocean (see Rocha). ADvary between years depending on the site and element considered. Our data show s that in some cases elements deposition can be substantially increased (i.e Buenos Aires, Na : 2006= 1.99 and 2007=6.14 kg/ha.year) or be very stable between years (i.e Buenos Aires, NO3 : 2006= 2.28 and 2007=2.82 kg/ha.year). Dry deposition was a significant amount of total deposition (25% on average for all elements and sites), and tended to be lower in costal sites (16%) than in inland sites (34%).

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