Seasonal characterization of the physical, chemical, biological and ecotoxicological variables in a stretch of the Paraíba do Sul River, SP, Brazil

Abstract The Paraíba do Sul River is located in a Brazilian region with high population density and great socio-economic importance. In the São Paulo stretch, the river is impacted and water quality is impaired due to the removal of riparian vegetation, increases in impermeable surfaces, industrial activity, the use of agricultural inputs, and the release of wastewater without proper treatment. This study characterized the physical, chemical, biological and ecotoxicological variables associated with the water quality of the Paraíba do Sul River in the upper-middle stretch during the dry and wet seasons. The sampling was carried out quarterly between August 2013 and August 2014. The variables evaluated were pH, temperature, conductivity, turbidity, dissolved oxygen (OD), biochemical oxygen demand (DBO), chemical oxygen demand (DQO), total phosphorus (PT), total solids (ST), fecal coliforms (CT), chlorophyll-a, acute toxic effect (ETA) and chronic toxic effect (ETC) and Trophic State Index (IET). The results showed that the variables OD, PT and CT were not in accordance with those established for a Class 2 aquatic environment, according to the National Counsel for the Environment 357/2005 (Portuguese acronym “CONAMA”). Some variables showed a reduction during the evaluated period, such as DBO (42.4%), ST (31.1%) and DQO (21.3%). Both ETA and ETC were observed in the rainy period. The statistical analysis showed that the rainfall has an influence on OD, DBO, ST, chlorophyll-a, ETA and ETC, acting as a possible intensifier agent of impacts on the river.

摘要 南帕拉伊巴河（Paraíba do Sul River）地处巴西人口密度极高、社会经济意义重大的区域。在圣保罗河段，河岸植被遭清除、不透水地表面积增加、工业活动频发、农业投入品使用以及未经妥善处理的废水排放，导致河流受干扰、水质恶化。本研究针对枯水期与丰水期的南帕拉伊巴河中上游河段水质相关的物理、化学、生物及生态毒理学变量开展特征表征分析。采样工作于2013年8月至2014年8月间按季度开展。本次评估的指标包括pH值、温度、电导率、浊度、溶解氧（Dissolved Oxygen, OD）、生化需氧量（Biochemical Oxygen Demand, DBO）、化学需氧量（Chemical Oxygen Demand, DQO）、总磷（Total Phosphorus, PT）、总固体（Total Solids, ST）、粪大肠菌群（Fecal Coliforms, CT）、叶绿素-a、急性毒性效应（Acute Toxic Effect, ETA）、慢性毒性效应（Chronic Toxic Effect, ETC）以及营养状态指数（Trophic State Index, IET）。研究结果显示，根据巴西国家环境委员会（CONAMA，葡萄牙语缩写）2005年第357号决议，溶解氧、总磷及粪大肠菌群三项指标未达到二类水生环境的标准要求。评估周期内部分指标呈下降趋势，其中生化需氧量降幅达42.4%，总固体降幅31.1%，化学需氧量降幅21.3%。丰水期可检测到急性毒性效应与慢性毒性效应。统计分析表明，降雨对溶解氧、生化需氧量、总固体、叶绿素-a、急性毒性效应及慢性毒性效应均存在影响，可能是加剧河流受干扰程度的驱动因素。