Considerations on the monitoring of water quality in urban streams: a case study in Portugal

Monitoring water quality in urban stream is of utmost importance for water resources managers, who are pressured to optimize monitoring schemes in order to reduce costs. The present study aims to use the results of a 2-year-long water quality monitoring pro- gram of an urban stream in Portugal to identify improve- ment opportunities. The urban stream under study was subjected to wastewater treatment plants effluent dis- charges, leachates from a major sealed landfill, low- class housing effluents, and nonpoint sources of pollu- tion. Contributing watersheds are mostly artificial sur- faces and agricultural land, which irrigate directly from the river. River water quality was evaluated on 11 sam- pling locations for 24 months from October 2013 to September 2015. The present paper describes statistical analysis of the results obtained for 12 physicochemical parameters in order to optimize the monitoring scheme. Cluster analysis detected a seasonal variation in the water quality and a spatial pattern based on the major point sources of pollution. A factor analysis showed that the parameters that mostly contribute to water quality assessment in this urban river are alkalinity, ammonia, electrical conductivity, pH, temperature, and dissolved oxygen. Results suggest that the monitoring efforts— and associated costs—may be reduced by decreasing monitoring frequency, sampling points, and monitored parameters. The statistical analysis described in this study may be replicated in other water quality monitor- ing programs, providing useful and important informa- tion for the systematic and iterative assessment of the adequacy of water quality sampling programs towards a sustainable management of water quality surveillance.