Institute of Ecosystem Studies

2009 BES Annual Meeting Presentation and Poster Abstracts

Road deicers and gray treefrogs: Unexpected interactions in pond food webs
Van Meter, Robin
Co-Authors: Joel Snodgrass & Christopher M. Swan

Abstract: Freshwater salinization is an ongoing concern in northern latitudes where road deicers are applied in excess during the winter and spring months. Emerging data is showing that road salt has a high residence time, especially in urban areas, such that it is mobilized in pond habitats even during summer months. This study was designed to evaluate the direct and indirect effects of road salt on tri-trophic interactions in pond food webs. In May 2008, forty 600-L polyethylene mesocosms were filled with tap water and inoculated with algae and zooplankton. Using a 2x2x2 factorial design, 20 mesocosms received salt (645 mg/L Cl-), 100 gray treefrog tadpoles (Gosner 25), and/or 2 Dytiscid beetle predators. Periphyton, phytoplankton and zooplankton were measured weekly for 10 weeks. Upon metamorphosis, gray treefrogs were weighed, and all remaining tadpoles were staged and weighed. Tadpoles reared in the salt treatments metamorphosed both significantly faster and larger than those reared in non-salt treatments. The results suggest salt had negative direct effects on zooplankton, potentially releasing algae from grazing pressure by zooplankton. We hypothesize that as a result, gray treefrogs had more resources available to them, inducing a faster rate and size at metamorphosis. While common pollutants such as road deicers are known to have direct effects on taxa, the indirect effects can be pronounced, even at relatively low levels.