Salty summer streams - problem or opportunity?

Many streams in the Northeastern US show high summertime concentrations of chloride due to winter-applied road salt.  Mechanisms causing delayed flushing of salt from these streams are unknown and include longer hydrologic retention than expected or sorption to soils.  In several streams of Dutchess County, New York summer levels are as high, or higher than winter concentrations.  Peak concentrations are well over 100 mg/L Cl which have the potential to affect biota and are levels of concern for drinking water supplies.  For two local watersheds, summer baseflow sampling showed increasing concentration of chloride from 10 mg/L to > 100 mg/L along a downstream gradient of increasing human population density. From detailed sampling and experiments we have found some evidence to support both likely mechanisms (retention in groundwater and soil sorption).  Modeling of water fluxes through a local watershed will be used to better constrain hydrologic transit times.  This issue has proven to be an excellent opportunity to engage local decision makers, citizens and watershed groups because the ultimate cause, salting of roadways, is highly visible and familiar.  At present, elevated concentrations are not so widespread as to cause public health concerns or regulatory actions so this problem is generally non-threatening and non-confrontational allowing a more open discussion.