Rainwater geochemistry inside the Barcarena power station at the mouth of the Tocantins River

Abstract

Most of South America lacks studies on rainwater composition. The present study evaluates rainwater composition and bulk deposition inside Barcarena power station, located at the mouth of the Tocantins River with Amazon River in Brazil. In 2012, 24-h rainwater samples were collected inside the ELETRONORTE power plant (n = 93), and pH, EC, cations and anions were analyzed. In order of abundance, the rainwater ions were Na+ > Cl− > SO4−2 > Ca+2 > K+ > F− > Mg+2 > NH4+-N > NO3−-N. pH values ranged from 4.5 to 6.9, with 17 events with pH <5.6 and 5 events with pH < 5.0. Sodium and Cl− were the dominant ions with sea salt as main contribution. Acidity, enrichment factors and principal component analysis (PCA) indicate that F−, SO4−2 and NO3−-N in the rainwater came from anthropogenic sources. Fluoride correlated strongly (>0.85) with Ca+2 and Mg+2, likely originated from same source in the aluminum production chain. Potassium originated from a mixture of anthropogenic and natural sources, with a good correlation (>0.70) with NO3−-N and NH4+-N, indicating biomass burning and fertilizer origins. In 2012, Barcarena total bulk deposition ranged from 14,070 to 17,890 mg m−2 y−1 with significant contributions of SO4−2 (2,385 to 2,851 mg m−2 y−1), F− (419 to 479 mg m−2 y−1) and NO3−-N (128 to 280 mg m−2 y−1). EC values (4 to 254 µS cm−1) indicated a medium site pollution severity (> 175 µS cm−1), which increased the risk of damage to electrical components.