Abstract
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.
Highlights
Water quality assessments of rivers and reservoirs may support management decision-making and is key for achieving the sustainable balance of multiple water resource uses (VON SPERLING, 1999)
Excess phosphorous could be originated in uncontrolled agricultural activities in the watershed and enter the reservoir primarily via Passaúna river (VEIGA; DZIEDZIC, 2010)
The corresponding exceedance probability of 31% is remarkably close to the one calculated using a different, longer and larger dataset
Summary
Water quality assessments of rivers and reservoirs may support management decision-making and is key for achieving the sustainable balance of multiple water resource uses (VON SPERLING, 1999). Context-specific assessments usually involve indexes formed by the aggregation of a number of such indicators. The Water Quality Index (WQI) was developed by the United States National Sanitation Foundation (NSF) for assessing the quality of source waters prior to treatment for public supply, being adapted to suit a variety of application contexts (e.g., ABTAHI et al, 2015; FINOTTI et al, 2015; SUN et al, 2016), including a version for reservoirs (IAP, 2004; 2009; 2017). Several Trophic State Index (TSI) versions have been developed to assess the eutrophication risk or state of a water body (CARLSON, 1977; LAMPARELLI, 2004). The trophic response of temperate reservoirs may differ significantly from that of their tropical or subtropical counterparts (CUNHA et al, 2013)
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