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.

Road Salts as Environmental Constraints in Urban Pond Food Webs

“…However, gray treefrog larvae that persist during these early developmental stages do have high survival rates as they develop through metamorphosis in high salt concentrations [31]. Furthermore, these individuals reared under elevated chloride conditions experience faster time to and larger size at metamorphosis [25], [31]. We obtained gray treefrog embryos for these previous studies from PWRC which is a rather pristine and protected environment.…”

“…Although we cannot rule out large changes in dissolved oxygen or pH over the course of the study, our previous research in these artificial pond systems suggested there would be no dramatic shifts in either of these parameters and no systematic shifts with our study treatments [25]. Given the high nitrogen content of waste released by developing tadpoles [36], we also collected water samples on day 45 to obtain nitrate estimates.…”

Occurrence of Amphibians in Saline Habitats: A Review and Evolutionary Perspective

“…Salinity is known as a driving force governing the composition of aquatic ecological communities (Gunter 1956), and recent work has suggested that salinity can affect the interactions of amphibians with other community members (e.g., food-web dynamics) both directly and indirectly (Petranka and Doyle 2010;Chambers 2011;Van Meter et al 2011;Petranka and Francis 2013;Moreira et al 2015;Van Meter and Swan 2014). Adaptation to salinity could certainly lead to novel predation opportunities for amphibians in these environments, as has been shown in some South American anurans eating marine invertebrates, for example (Sazima 1971;Brasileiro et al 2010;Ferreira and Tonini 2010).…”

Landscape level estimate of lands and waters impacted by road runoff in the Adirondack Park of New York State

“…Now, through this new work, we have estimated that 76 % of surface water area and at least 45 % of stream length (dependent on buffer width) in the Park may be receiving road runoff pollutants such as salt. Salt is one of the most widely studied road runoff pollutants, and the effects of salinization on freshwater ecosystems are well documented; for example, studies have reported reduced aeration and water circulation at depth (Fay and Shi 2012), decreased spotted salamander (Ambystoma maculatum) and wood frog (Rana sylvatica) survival (Karraker et al 2008), shifts in community structure (Collins and Russel 2009), reduced copepod density and changes in algal resources (Meter et al 2011), and decreased productivity at all trophic levels in model freshwater communities (Dalinsky et al 2014). A significant amount of road salt also enters groundwater where it can accumulate over years and exceed thresholds for potable water and aquatic organisms (Perera et al 2012).…”