Investigation of correlation between remotely sensed impervious surfaces and chloride concentrations

Abstract

The main objective of this study is to verify the often assumed correlation between impervious surfaces and chlorides that result from the application of road salts, focusing on a case study in the selected six major watersheds within the Greater Toronto Area. Landsat-5 Thematic Mapper images collected in 1990, 1995, 2000, and 2005 and the unsupervised classification technique were utilized in the estimation of percentage imperviousness for each watershed. Chloride concentrations collected at water quality monitoring stations within the watersheds were then mapped against impervious surface estimates and their spatiotemporal distribution was assessed. The remotely sensed impervious surface maps and chloride maps were overlaid in a geographical information system environment for the investigation of their potential correlation. The main findings of this study indicate an average of 12.9% increase in impervious surface areas as well as a threefold increase in chloride concentrations between 1990 and 2005. Water quality monitoring stations exhibiting the highest amounts of chloride concentration correspond with the most impervious parts of the watersheds. The results also show that the increase in imperviousness does generate higher chloride concentrations. Correspondingly, the higher levels of chloride can potentially degrade the quality of surface waters. Through developing a novel integrated remote-sensing approach, the study was successful in identifying areas most vulnerable to surface water quality degradation by road salts.