An assessment of the chemical composition of precipitation and throughfall in rural-industrial gradient in wet subtropics (southern Brazil)

Abstract

The chemical composition of bulk precipitation and throughfall were analyzed, during a 1-year period (2002), in rural–urban-industry gradients with similar forest cover (Eucalyptus spp.) in southern Brazil (Rio Grande and Porto Alegre cities). Values of pH varied from 5.0–5.1 in rural to 5.4–6.1 in industrial sites, and were intermediate in urban sites. The major ions in bulk precipitation were Na⁺, Cl⁻, ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$, ${\text{NO}}^{{\text{ - }}}_{{\text{3}}}$ and ${\text{PO}}^{{{\text{3 - }}}}_{{\text{4}}}$, and concentrations increased in urban and industrial sites. Principal component analysis identified the local main anthropogenic sources. Estimated annual amounts of dry deposition were generally greater in both industrial and urban sites than in rural sites. Areas close to industrial activity showed greater S and N total deposition (10.4–10.9 and 20.2–30.6 kg/ha, respectively) than in urban (3.4–7.3 and 14.6–24.1 kg/ha) and in rural (1.7–2.6 and 8.9–12.1 kg/ha) sites. Annual deposition of Ca and P varied from 0.6 and 3.0 kg/ha in rural to 45.4 and 32.4 kg/ha in industrial sites, maximum values being observed closed to the phosphate fertilizer plant of Rio Grande. Deposition in urban and industrial sites may be balanced by the alkaline cations, as bulk precipitation pH varied from 5.4 to 6.1, and was greater than in rural sites (5.0–5.1).