Temperature-dependent effects of road deicing salt on chironomid larvae

Road salt, a common pollutant in regions with snowy winters, enters roadside wetlands when temperatures are low and organisms are physiologically inactive and remains until flushed by snowmelt or rainfall. Flushing might not occur until spring temperatures rise and organisms are physiologically active. Thus, effects of road salt on aquatic organisms must be studied within the context of temperature. We monitored temperature and conductivity at the sediment—water interface from January to May 2004–2006 in two constructed wetlands in Erie, Pennsylvania. Runoff caused peaks in conductivity (up to ∼30 mS/cm) followed by exponential declines. Conductivity remained > 4 mS/cm during winter and returned to < 1 mS/cm in late spring (temperature > 10°C). Overspray caused lower peaks (< ∼6 mS/cm), and values reached baseline early in spring. Winter/spring chironomid abundance was significantly lower in wetlands that received salt than in other wetlands. We used a factorial-design laboratory study to test whether survival of chironomid larvae exposed to NaCl was temperature dependent. At 1°C and 5°C, low concentrations of salt appeared to increase survival; at 22°C all concentrations of salt significantly decreased survival. Salt might protect larvae in winter and increase survival if flushed before spring thaw, but could be detrimental after temperatures rise.