Effects of elevated salinity from road deicers on Chironomus riparius at environmentally realistic springtime temperatures

We assessed the effects of road deicer (NaCl) on life-history traits (survival, emergence, development time, sex ratio, and size at emergence) of Chironomus riparius under laboratory conditions mimicking near-freezing overwintering temperatures and warmer temperature fluctuations during early spring. We added 1-d-old larvae to culture chambers and acclimated them for 1 wk at 22°C. We decreased the temperature over a period of 2 d to 1-2°C. After 1 wk, we added deicing salt (NaCl) to the chambers over a period of 4 d to expose the larvae (as 2^nd instars) to 0, 5, or 10 g/L salt (from deicer) concentrations. We then raised the temperature over a period of 1-2 d to fluctuate between 8-12°C and monitored adult emergence. All larvae in the 10-g/L chambers died when the temperature reached 12°C. The number of individuals that survived and the number that emerged were significantly lower, and development time was significantly longer in the 5-than in the 0-g/L chambers. Males and females emerged synchronously, sex ratio was 11, and females were significantly larger than males at 0 g/L. Males emerged only slightly before females, sex ratio was male skewed (21), and females were the same size as males at 5 g/L. Male size did not differ between 0 and 5 g/L, but females were significantly smaller at 5 than at 0 g/L. Road deicers can have significant lethal and sublethal population-level effects on chironomids in roadside wetlands, but these effects might be reduced if chironomids are present in nearby unaffected habitats that can act as source populations in late spring, summer, and autumn.