Despite the importance of long-term atmospheric deposition of ions for vegetation productivity and biogeochemistry, southern South America lacks long-term deposition records. We report a 6-year-long record of atmospheric deposition measurements of Mg2+, Ca2+, Na+, K+, Cl−, SO42−, NO3− and NH4+ in the plains of southern South America, which encompass one of the most important agricultural basins and urban clusters of the continent. After establishing a deposition measurement network across four sites in Argentina and Uruguay, we collected bulk atmospheric deposition monthly form January 2007 through December 2012 in an east–west transect of 700 km. Spatial changes in the sea-salt component of atmospheric deposition were primarily associated with proximity to the sea—as observed in other regions of the world—whereas non-sea-salt components of atmospheric deposition of terrestrial origin were primarily associated with the size of the human population surrounding collection sites. Atmospheric deposition showed a strong interannual variability (CV 50%) mainly associated with variations in the non-sea salt components of terrestrial origin and were within observed values for other relatively unpolluted sites of South America and globally. However, atmospheric deposition appears to be increasing in the region, particularly for SO42− and other ions around Buenos Aires, Argentina, which may represent an early warning of increased air pollution in the area. Average annual regional deposition of sulfate (SO42−) was 12.7 kg S hectare−1 and nitrate (NO3−) was 9.2 kg N hectare−1. Weighted average concentrations of base cations (sum of Mg2+, Ca2+, Na+ and K+) was 0.27 mg L−1, and weighted average concentrations of SO42−, NO3− and NH4+ were 0.094, 0.018 and 0.046 mg L−1, respectively. Our work highlights the need for long-term networks recording atmospheric deposition in the region, increasing knowledge of nutrient cycling and establishing a baseline for future atmospheric pollution measurements.
Atmospheric deposition Soluble ion Regional patterns
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We gratefully acknowledge Enrique Piñeiro, Silvina Ballesteros, Héctor Banchero and Yolanda Gonzalez for helping with collections and analysis. Mercedes Peretti, Cristina Forti and Micael Abrigo, helped with sample processing and laboratory analysis. This article was performed with funds from INTA, CONCIET, PICT 205-2827 and IDRC (International Development Research Centre). This work was carried out with the aid of a Grant from the Inter-American Institute for Global Change Research (IAI) CRN III 3005 and 3095 which is supported by the US National Science Foundation (Grant GEO-1128040).
Supplementary material 1 (TIFF 372 kb). Figure SP1. Relationship between precipitation captured by bulk collectors and measured precipitation in the nearby weather station. The black line represents 1:1 relationship and the grey line represents the adjusted model. Regression parameters are shown in the top of the graph
Supplementary material 2 (TIFF 4161 kb). Figure SP2. Pearson’s correlation coefficients among annual mean deposition (mg L−1) of each element for all sites. Statistically significant regressions are shown with an “*”, using standard notation. Regression plots are show in the lower section
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