Changing Land Use and the Anthropogenic Salinization of Inland Waters
Sujay Kaushal and Peter Groffman

Salinization of inland waters is recognized as a major problem in arid and semiarid environments throughout the world. Recent evidence suggests that anthropogenic salinization can also occur in humid watersheds of the eastern United States. Over a five- year period, we monitored concentrations of chloride on a weekly basis in streams draining watersheds across a gradient of land use (forest, agriculture, suburban, and urban) in Baltimore, Maryland, USA. The region receives both moderate snowfall and relatively low applications of road salt compared with other areas of the northeastern United States and Canada. Despite this, concentrations of chloride in urban streams can remain elevated during winters at almost 5 g/L, or approximately 1/4 its concentration in seawater. Concentrations of chloride in both suburban and urban streams showed declines throughout late spring and summer, but were still up to 100 times greater than concentrations found in streams draining forested and agricultural watersheds without roads. The mean annual concentration of chloride in streams increased strongly as a power function as the relative amount of impervious surface increased within watersheds. In developed areas with greater than 40% impervious surface, mean annual concentrations of chloride exceeded the threshold of tolerance for most land plants and freshwater life. Anthropogenic salinization from pavement may need to be considered as a disturbance, which can influence the distribution and abundance of freshwater species surrounded by increasing changes in land use.

Keywords: salinization, chloride, streams

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