Surface-water-quality indices for the analysis of data generated by automated sampling networks

To date, different water-quality indices (WQIs) categorizing water bodies have flourished in the literature. While this type of index has normally been applied to data sets from manual monitoring programs, we focus attention on the analysis of data from automated sampling networks, from which measurements of a small number of physico-chemical variables are usually obtained from different locations with high temporal resolution.To deal with data of this nature, we compare different indices for the physico-chemical evaluation of water quality. As a result, we select the WQI of the Canadian Council of Ministers of the Environment (CCME WQI) as the most suitable. Our interest in using this WQI rests on its flexibility for selecting parameters as well as the possibility of modifying the objectives to be met by each variable according to the specific end use of the water.We perform a sensitivity analysis for the CCME WQI in order to select the best procedure for calculating it according to input data.Finally, we apply the CCME WQI to simulated data sets describing three different environmental scenarios corresponding to episodes of discharge of urban wastewater, eutrophication and risk to fish. From this comparison and according to the specific objectives we define in this work, we rank sensitivity in CCME WQI performance in the following order: (1) urban wastewater; (2) eutrophication; and, finally, (3) risk to fish.