两类水质综合评价方法的特点及其在河流水环境管理中的作用

河流水质恶化已成为严峻的环境问题,针对河流开展水质综合评价对河流水环境管理具有重要意义。依据不同的评价目标,选择合理的综合评价的评估标准成为河流水质评价中重要的问题之一。通过基于期望值和阈值的水质健康综合评估法(ETI)和水质质量指数(WQI)两种水质综合评价方法对"引滦入津"工程重要水源地伊逊河水质进行评价,结果显示:1)伊逊河水质ETI评估结果为良好等级,WQI评估结果为一般等级;2)伊逊河采样点水质在ETI评价中分布于4个等级,WQI仅分布于2个等级;3)伊逊河自上游至下游水质显著降低,特别是ETI评估中由优秀等级转变为差等级;4)ETI和WQI评估结果显示极显著相关性(R=0.951,P0.01);5)通过逐步多元回归,ETI评估结果的主导因子是DO、EC、SS、BOD_5和TP(P0.05),WQI评估结果的主导因子是DO、SS、BOD_5、TP、TN和NH_3-N(P0.05)。进一步分析表明伊逊河水质恶化与其流域内土地利用情况密切相关。在河流水环境管理中,ETI作为一种水质相对值评估方法,能更好体现流域内水质差异的区分度,便于管理者迅速定位流域内亟需治理的河流或河段,同时能够根据河流自身特征制定管理目标,可作为河流管理绩效评估的有效手段;而WQI作为一种水质绝对值评估方法,更适用于河流水质时间变化评估,对河流经长期治理后的管理效果评价起到重要作用。

Characteristics of two comprehensive assessment methods for water quality based on different evaluation criteria and their applications in aquatic environment management

Water quality deterioration in rivers has become a serious environmental problem. It is of great significance for management to carry out comprehensive assessments of water quality. Due to different objectives, it is crucial to select reasonable evaluation criteria for a comprehensive assessment. In this study, we assessed the water quality conditions by the Water Health Assessment Index, based on the expectation and threshold value (ETI) and water quality index (WQI) in Yixun River, which is the water source for the "Water Diversion Project from Luanhe River to Tianjin City". The results showed that 1) the water quality rated at a "good" level for ETI, and "moderate" level for WQI; 2) the water quality in 24 sites was classed into four levels for ETI and only two levels for WQI; 3) the water quality decreased significantly from upstream to downstream in Yixun River. Especially for ETI, the water quality changed from "excellent" to "poor". 5) The two indices, ETI and WQI, showed a significant correlation (R=0.951, P < 0.01). From the results of the stepwise multiple regression, the dominant factors for ETI were DO, EC, SS, BOD₅, and TP (P < 0.05); and those for WQI were DO, SS, BOD₅, TP, TN, and NH₃-N (P < 0.05). These results suggested that 1) the water quality deterioration in Yixun River was closely related to the land use. 2) For aquatic environment management, ETI, as an assessment based on the relative state of water quality, could reflect spatial variation in river water quality better than WQI, which was more suitable for water quality management in a basin. Therefore, ETI can help managers to make and set management objectives for polluted rivers or streams based on the water quality, and can be used as an effective method to evaluate river management performance. Meanwhile, WQI, as a method for evaluating the absolute state of water quality, is more suitable for evaluating the temporal variation in river water quality, and plays an important role in evaluating the effect of aquatic environment management.