Atmospheric pollution in a tropical rain forest: Effects of deposition upon biosphere and hydrosphere I. Concentrations of chemicals

The effects of atmospheric deposition upon element cycling and turnover in three rain forest ecosystems of the Serra do Mar, a mountain range along th e atlantic coast of Brazil, have been investigated as part of an interdisci plinary German-Brazilian research project on dispersion, transformation and deposition of air pollutants in the vicinity the industrial complex of Cub atao, State of Sao Paulo. The project included on-site measurements from 19 91 to 1995, field experiments and mathematical modelling with the goal of p roviding damage evaluation and risk assessment, and elucidating damage mech anisms with respect to soils and vegetation. The role of the 'Soil Module' sub-project reported here was to assess atmospheric deposition and fluxes w ith precipitation and soil water, and to investigate possible soil changes induced by atmospheric deposition as well as biological effects of pollutan ts via the soil path. Part I of this paper deals with concentrations of che micals in precipitation, soil water, surface water and in litter. Part II w ill cover fluxes of chemicals and element budgets. Three sites were chosen which differed significantly with respect to pollution impact. Annual avera ges of ionic concentrations in precipitation found in open field and below the tree canopy amounted to 5 and 10 mg L-1, respectively, for sulfate-S, 0 .4 and 0.7 mg L-1 for nitrate, 0.65 and 1.1 mg L-1 for fluoride, 1.8 and 2. 6 mg L-1 for ammonium-N, 0.76 and 2.3 mg L-1 for Mg, and 3.5 and 7.5 mg L-1 for Ca at the most polluted site. The relatively 'clean' reference site at tained 1/3 to 1/9 of these averages, thus clearly reflecting the difference in air pollution load. Chemical composition in the liquid phase is complet ely changed when precipitation infiltrates the soil profile. Nitrate concen tration increases by the factor 5 to 20. A clear increase is also found for sulfate and chloride. Concentration changes during ecosystem passage of se epage are interpreted in relation to chemical reactions taking place in dif ferent compartments. They are characterized by an almost complete retention of ammonium and some retention of sulfate in the upper soil layers, and at the most polluted site by mobilization of Al from soil minerals and very h igh leaching of nitrate as a consequence of nitirification of organic matte r.