Characteristics of chloride loading from urban and agricultural watersheds during storm and non-storm periods

The chloride ion (Cl−) can adversely affect an aquatic ecosystem, but it is not clear how Cl− moves with runoff and how its transport processes are related to land uses and land cover. This study investigated how the loading characteristics of Cl− vary depending on storm events and land cover in a temperate region. We monitored Cl− concentrations in three study watersheds that have different compositions of urban and agricultural land uses. In addition, a Mass First Flush ratio (MFFn) was determined to quantify the effect of first flush on Cl− loading. Overall, the observed concentrations and loadings in this study were found to be less than those reported in cold northern regions. The monitoring data showed that Cl− concentrations and loads observed in an urban watershed were significantly larger than those of a rural watershed. The results suggest water management plans should focus on urbanized areas and their storm water to efficiently reduce chloride loading to downstream waterbodies. However, a further study is recommended to identify the sources and pathways of Cl− loaded to waterbodies. HIGHLIGHTS Cl− loading varies depending on storm events and land cover.; The first flush effect on Cl− loading was strong in urban storm runoff.; The urban watersheds had significantly larger Cl− loads than the rural watershed.