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.

摘要 帕绍纳流域（Passaúna catchment）属于上伊瓜苏流域（Upper Iguaçu watershed），包含为库里蒂巴都会区（Curitiba metropolitan region）超50万居民提供供水服务的水库。本研究旨在明确该水库的水质现状，以及其近期是否发生了中远期变化。研究采用9项指标与3类指数开展理化生综合评估：水质指数（Water Quality Index, WQI）、营养状态指数（Trophic State Index, TSI），以及用于评估大型无脊椎动物（macroinvertebrate）多样性的香农-威弗指数（Shannon-Weaver Index, H’）。通过频率曲线验证了水体是否符合既定水质标准。对比了两种WQI计算方法，以测试部分数据缺失场景下的适用性。采用斯皮尔曼秩相关系数（Spearman’s rank correlation coefficient）分析关键参数的时间变化趋势。1991年至2014年的WQI结果显示，整体水质可评定为良好，且在该时段的最后十年水质有所改善；多数TSI结果处于贫营养/中营养区间，但未呈现显著的时间变化趋势。基于2014年获取的数据计算得到的香农-威弗指数H’=1.6，表明该生态系统处于中度退化状态，这通常与水流调控及一定程度的水质受损相关。这种多指标集成的理化生联合监测方法，为中远期水生生态健康评估提供了可靠的分析框架。