DEVELOPMENT OF A WATER QUALITY INDEX WITH A REDUCED NUMBER OF PARAMETERS

ABSTRACT The development of water quality indices (WQIs), duly modified and using a small number of parameters, may be of great economic use. The purpose of this work was to develop a WQI with a reduced number of parameters (WQIred), in relation to what is used in the Brazilian state of Minas Gerais (WQIIGAM), in the basin of the Doce River. Four different scenarios were analysed, with the absence of the following parameters for the calculation of the WQIred: BOD, E. coli and phosphate; BOD and E. coli; BOD, E. coli and total solids (TS); BOD, E. coli, phosphate and TS. The redistribution of the weight attributed to the eliminated parameters was done according to the following methods: (i) in weighted form, through optimisation of the correlation between the WQIred and the WQIIGAM; (ii) based on the cluster analysis. The best scenario found was that of the WQIred considering only DO, pH, temperature variation, nitrates and turbidity, with the weights being redistributed based on cluster analysis. This scenario maintained satisfactory performance, with a minimum difference being observed between WQIIGAM and WQIred, in terms of management purpose. The WQIred as proposed makes it possible to establish a monitoring control system operating in real time in the Doce river basin, as all the parameters considered can be obtained with the use of multiparameter probes.摘要 经过合理修正且采用少量参数的水质指数（Water Quality Indices, WQIs）开发具有重要的经济应用价值。本研究以多西河流域为研究对象，旨在开发一种参数精简型水质指数（WQIred），以对比巴西米纳斯吉拉斯州现行的水质指数（WQIIGAM）。本研究分析了四种不同的情景，即构建WQIred时分别剔除以下参数组合：生化需氧量（Biochemical Oxygen Demand, BOD）、大肠杆菌（Escherichia coli, E. coli）与磷酸盐；生化需氧量（BOD）与大肠杆菌（E. coli）；生化需氧量（BOD）、大肠杆菌（E. coli）与总固体（Total Solids, TS）；生化需氧量（BOD）、大肠杆菌（E. coli）、磷酸盐与总固体（TS）。针对被剔除参数的权重重新分配，采用以下两种方法完成：（1）加权优化法，通过优化WQIred与WQIIGAM之间的相关性实现权重分配；（2）聚类分析法，基于聚类分析完成权重分配。最终筛选得到的最优情景为仅保留溶解氧（Dissolved Oxygen, DO）、pH值、水温变化、硝酸盐与浊度的WQIred，其权重通过聚类分析法完成重新分配。该情景表现优异，从水环境管理的应用角度来看，WQIIGAM与WQIred之间的差值极小。本研究提出的WQIred可用于在多西河流域搭建实时运行的水质监测控制系统，因其纳入的所有参数均可通过多参数探头获取。