Index-based and compliance assessment of water quality for a Brazilian subtropical reservoir

ABSTRACT The Passaúna catchment is part of the Upper Iguaçu watershed and includes a water supply reservoir for over 500,000 inhabitants of Curitiba metropolitan region. The aim of this study was to establish the state of reservoir water quality, and whether it has undergone any recent medium- and long-term variations. A physical-chemical-biological assessment was undertaken using nine indicators and three indexes: Water Quality Index (WQI), Trophic State Index (TSI) and Shannon-Weaver Index (H’) for macroinvertebrate diversity. Compliance with the prescribed quality standards for the water body was verified using frequency curves. Two WQI calculation approaches were contrasted to test for conditions of partial data unavailability. Temporal trends in key parameters were assessed using Spearman’s rank correlation coefficient. WQI results from 1991-2014 indicated that the water quality may be classified as good and improved in the final decade of such period, while most TSI results were in the oligotrophic/mesotrophic range, but with no significant temporal trend. The biodiversity result of H’=1.6 obtained with data acquired in 2014 indicated a moderately degraded ecosystem that is typically associated with flow regulation and a degree of water quality impairment. Such a multi-indicator integrated physical-chemical-biological monitoring approach comprised a robust framework for assessments of medium-long term aquatic health.