Hydrochemical classification and nitrate contamination of the Barreiras unconfined aquifer in Capitão Pocinho river basin of the mid Guamá river region in eastern Amazonia

Abstract

The Capitão Pocinho river basin at the northeastern Pará constitutes one important area of orange production in Brazil, with use of herbicides and fertilizers in the management practice. This research analyzed the diffusion of nitrate ions and classified the occurrence of the most important ions. To collect the samples, 16 monitoring wells were dug in the citrus plantation in the Capitão Pocinho village. Water samples were collected during the wet and dry seasons of 2009. Even though the levels of nitrate detected were below the Maximum Allowable Value (MAV) of mg L-1 in all wells analyzed, there was evidence of nitrification in 60% of the wells. In 30% of the area surveyed, the levels of nitrate were higher than 2 mg L-1. The Na+, K+, Ca2+, Mg2+, HCO3- and NO3- showed a significant relation (p <0.05), while for the multivariate analyses of the remaining ions, the relationships were not significant at 95% confidence level and as well as for the population mean of each variable. The shallow ground waters of the Barreiras unconfined aquifer were classified as calcic bicarbonate and mixed.