Road Salt Stress Induces Novel Food Web Structure and Interactions

Abstract

Freshwater salinization is an emerging global concern, and in northern latitudes can be largely attributed to road deicer applications during winter and spring. To investigate the effects of road salt contamination on pond food webs, we manipulated trophic structure and salt in experimental pond communities. In May 2008, we inoculated forty 600-L pond mesocosms with algae and zooplankton. Using a full-factorial design, we manipulated road salt presence (645 mg L−1 Cl−) and tadpoles (Hyla versicolor) in a food web that included two groups of primary producers (periphyton, phytoplankton) and two groups of primary consumers (tadpoles, zooplankton). Adult copepod density decreased significantly in the elevated chloride treatment (ANOVA P = 0.001). Tadpoles reared in the elevated chloride treatment grew larger (ANOVA P = 0.005) and metamorphosed sooner (ANCOVA P = 0.028) than those in the ambient treatment. Our results suggest there were more algal resources available to tadpoles as a result of declines in zooplankton, inducing a shorter time to and greater size at metamorphosis. While common pollutants such as road deicers are known to have direct effects on many taxa, the indirect effects on food web structure and interactions can be pronounced, even when pollutants occur at relatively low levels.