RP-RainNet: The Rio de la Plata Atmospheric Deposition Network. Set up and Preliminary Results

PINEIRO G; JOBBAGY EG; JACKSON RB; SANTONI CS; PORTELA S; DI BELLA C

ACAPULCO MEXICO

Congreso; American Geophysical Union. Joint Assembly; 2007

American Geophysical Union

Resumen Atmospheric deposition is a key flux for understanding nutrient cycling in ecosystems. Southern South America almost completely lacks atmospheric deposition data. We began rain collections at three (9/2005) and then seven (9/2006) sites in Argentina and Uruguay across a west (dry) to east (wet) transect at latitude 34°S. Preliminary data showed a low and uniform NO3 deposition across the region in the first three study sites. Nitrate deposition was similar in populated (Buenos Aires, 13 million people) and unpopulated regions (Flores, less than 5 persons per km2), in spite of the relative high industrial activity of Buenos Aires, suggesting relative well mixed conditions. Ammonia deposition (6.0 kg/ha.year) doubled that of NO3 (3.2 kg/ha.year) with a high correlation between them across rain events (r=0.91), supporting a similar origin of both N forms, likely found in agricultural fields and rangelands. Chloride, Mg and Na concentrations were highly correlated suggesting a marine origin. Ca and K had lower correlations with other ions, but correlated better with land derived ions (NH4 and NO3). Correlations between ions were stronger in Montevideo (seaside site), weaker in Buenos Aires (estuary site) and medium in Flores (inland site). All ions concentrations in rain events decreased exponentially with precipitation amount. A Principal Component Analysis (PCA) showed a high variability in ions concentrations of rain events within each site but separated well rain events from different sites with the first component being driven by Cl concentration vs. other ions and the second by marine (Cl, Mg and Na) vs. land ions (NH4, NO3, Ca and K). Ongoing collections will expand or results in space and time including more continental situations.