Evaluation of water quality and trophic state in the Parnaíba River Delta, northeast Brazil

Abstract

This study aims to assess the water quality and trophic state of the Parnaíba River Delta, in the Brazilian northeast, under different hydrological conditions. Surface water samples were collected from 16 sites along the river during 2011 and 2012 at the dry and rainy seasons. The obtained data showed a strong fluvial influence in practically the entire extension of the two deltaic channels. The water quality and trophic state classification was performed by adapting and calculating the Water Quality Index (WQImin) and Trophic State Index (TRIXPD). A Principal Component Analysis (PCA) and a Hierarchical Cluster Analysis (HCA) were conducted in order to adjust the index parameters. The WQImin results presented medium to good (70 ≤ WQImin< 90) and bad to medium (26 ≤ WQImin< 70) water quality conditions for the different hydrological periods. The estuary is mainly limited by nitrogen (N:P < 10) in the dry season and by phosphorus (N:P > 20) in the rainy one. The results for TRIXPD, showed a predominance of mesotrophic to eutrophic conditions in the estuarine system (5 ≤ TRIXPD< 6). This integrated approach can be a promising tool for assessing water quality and trophic status in tropical estuaries.