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）地处巴西人口稠密、社会经济价值极高的区域。在圣保罗州河段，该河流因河岸植被清除、不透水面占比提升、工业活动、农业投入品使用以及未经妥善处理的废水排放等因素遭受干扰，水质已出现受损情况。本研究针对枯水期与丰水期的南帕拉伊巴河中上游河段，开展了与水质相关的物理、化学、生物及生态毒理学变量的表征分析。采样工作于2013年8月至2014年8月间按季度进行。本次评估的变量包括pH值、水温、电导率、浊度、溶解氧（dissolved oxygen，缩写OD）、生化需氧量（biochemical oxygen demand，缩写DBO）、化学需氧量（chemical oxygen demand，缩写DQO）、总磷（total phosphorus，缩写PT）、总固体（total solids，缩写ST）、粪大肠菌群（fecal coliforms，缩写CT）、叶绿素a、急性毒性效应（acute toxic effect，缩写ETA）、慢性毒性效应（chronic toxic effect，缩写ETC）以及营养状态指数（Trophic State Index，缩写IET）。研究结果显示，根据巴西国家环境委员会（葡萄牙语缩写CONAMA）颁布的第357/2005号决议，溶解氧（OD）、总磷（PT）及粪大肠菌群（CT）未达到二类水生环境的水质标准。部分评估变量在研究周期内呈下降趋势，其中生化需氧量（DBO）下降42.4%、总固体（ST）下降31.1%、化学需氧量（DQO）下降21.3%。丰水期可检测到急性毒性效应（ETA）与慢性毒性效应（ETC）。统计分析表明，降雨对溶解氧（OD）、生化需氧量（DBO）、总固体（ST）、叶绿素a、急性毒性效应（ETA）及慢性毒性效应（ETC）均存在显著影响，可能是加剧河流受干扰程度的潜在驱动因素。