THE ROLE OF ROAD SALT DEICER AND RESOURCE BIODIVERSITY ON AQUATIC CONSUMER FEEDING DYNAMICS

Abstract

Road salt deicer is a growing pollutant of concern in the United States as urbanizationand human expansion continues at a rapid rate. Deicer infiltrates surface waters through stormwater runoff and increases chloride concentrations in freshwater ecosystems. The purpose of this study was to evaluate the effects of road deicer on a critical function of freshwater ecosystems - leaf litter breakdown. I hypothesized that increased chloride concentrations would decrease breakdown rates through decreased invertebrate consumer activity. To examine the impacts of chloride breakdown rates, a multi-factorial laboratory experiment was designed to test the effect of chloride on aquatic consumer feeding rates and examine the role of heterogeneous leaf litter under these conditions. Leaf litter and aquatic invertebrates (Gammarus sp.) were collected from headwater streams in Maryland (USA). Microcosms were inoculated with stream water and subjected to a chloride treatment (0 or 600mg/L), a leaf litter treatment (F. grandifolia, A. rubrum, or "mixed”), and an invertebrate treatment (presence or absence). After 28 days, mass loss rate was calculated for all treatments. In the single-species litter treatments, mass loss increased under the presence of chloride in both the presence and absence of the invertebrate consumer. Regardless of invertebrate presence, chloride only decreased mass loss in the mixed leaf litter assemblages. Further, the results showed a diversity effect between the single and mixed-species litter treatments but only in the invertebrate absent treatments. Therefore, the presence of an invertebrate eliminated the diversity effect regardless of chloride concentration. In short, increased chloride concentrations altered feeding rates though differently than predicted while a diversity effect was observed only in the absence of the invertebrate. The results suggest a complex interaction between chloride, heterogeneous leaf litter, and aquatic consumers that requires additional research to further understand the relationship between these factors.