Abstract：
Understanding seasonal variations in water quality is crucial for effective management of freshwater rivers amidst changing environmental conditions. This study employed water quality index (WQI), metal index (MI), and pollution indices (PI) to comprehensively assess water quality and pollution levels in Nyabarongo River of Rwanda. A dynamic driver-pressure-state-impact-response model was used to identify factors influencing quality management. Over 4 years (2018-2021), 69 samples were collected on a monthly basis from each of the six monitoring stations across the Nyabarongo River throughout the four different seasons. Maximum WQI values were observed during dry long (52.90), dry short (21.478), long rain (93.66), and short rain (37.4) seasons, classified according to CCME 2001 guidelines. Ion concentrations exceeded WHO standards, with dominant ions being HCO 3 - and Mg 2 + . Variations in water quality were influenced by factors such as calcium bicarbonate dominance in dry seasons and sodium sulfate dominance in rainy seasons. Evaporation and precipitation processes primarily influenced ionic composition. Metal indices (MI) exhibited wide ranges: long dry (0.2-433.0), short dry (0.1-174.3), long rain (0.1-223.7), and short rain (0.3-252.5). The hazard index values for Cu2+, Mn4+, Zn2+, and Cr3+ were below 1, ranging from 8.89E - 08 to 7.68E - 07 for adults and 2.30E - 07 to 5.02E - 06 for children through oral ingestion, and from 6.68E - 10 to 5.07E - 07 for adults and 6.61E - 09 to 2.54E - 06 for children through dermal contact. With a total carcinogenic risk of less than 1 for both ingestion and dermal contact, indicating no significant health risks yet send strong signals to Governmental management of the Nyabarongo River. Overall water quality was classified as marginal in long dry, poor in short dry, good in long rain, and poor again in short rain seasons.
摘要：
了解水质的季节性变化对于在不断变化的环境条件下有效管理淡水河流至关重要。本研究采用水质指数(WQI)，金属指数(MI)，和污染指数（PI），以全面评估卢旺达Nyabarongo河的水质和污染水平。使用动态驾驶员-压力-状态-影响-响应模型来识别影响质量管理的因素。超过4年（2018-2021年），在四个不同的季节中，每月从Nyabarongo河的六个监测站中的每个监测站收集69个样本。在干燥过程中观察到最大WQI值(52.90)，干短(21.478)，长雨（93.66），和短雨（37.4）季节，根据CCME2001指南进行分类。离子浓度超过世卫组织标准,主要离子为HCO3-和Mg2+。水质变化受旱季碳酸氢钙占优势和雨季硫酸钠占优势等因素的影响。蒸发和沉淀过程主要影响离子组成。金属指数（MI）表现出广泛的范围：长干（0.2-433.0），短干燥（0.1-174.3），长雨（0.1-223.7），短雨（0.3-252.5）。Cu2+的危险指数值，Mn4+,Zn2+,Cr3+低于1，成人为8.89E-08至7.68E-07，儿童为2.30E-07至5.02E-06。通过皮肤接触，成人从6.68E-10到5.07E-07，儿童从6.61E-09到2.54E-06。摄入和皮肤接触的总致癌风险小于1，表明没有重大的健康风险，但向Nyabarongo河的政府管理发出了强烈的信号。总体水质被归类为长期干燥的边际水质，在短暂干燥中贫穷，在漫长的雨中很好，在短暂的雨季再次贫穷。
