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(49-11) Multiple Stressor Effects on Native Amphibians in Canada: Linking laboratory and field studies. Thompson, Dean1,2, Wojtaszek, Barbara1,2, Edginton, Andrea2, Chen, Celia3, Gerald, Stephenson2, Boermans, Herman*,2, 1 Canadian Forest Service, Sault Ste. Marie, Ontario2 University of Guelph, Guelph, Ontario3 Dartmouth College, Hanover, New Hampshire ABSTRACT- Ontario wetlands are critical habitat for numerous amphibian species and susceptible to contamination by forest-use herbicides and acid deposition. This collaborative project examined potential interactive and multiple stress effects of two herbicide formulations - VISION (glyphosate) and RELEASE (triclopyr) on native amphibians - northern leopard frog (Rana pipiens), green frog (Rana clamitans), - and on a laboratory surrogate - African clawed frog (Xenopus laevis) - under an environmentally relevant pH range 4.5 - 8.5. Laboratory studies focussing on species and life stage sensitivity indicated early larval stages are more sensitive than embryos and the amphibian species tested are equisensitive to the herbicides. There was significant but differential interaction among herbicide and pH stressors, with high pH enhancing VISION toxicity and low pH enhancing RELEASE toxicity. Herbicide, pH and food interactions suggested that food deprivation further increased toxicity. Laboratory studies indicated a substantial potential for deleterious effects at environmentally relevant pH and herbicide concentrations. Field enclosures in two different wetland ecosystems examined impacts on amphibians, phytoplankton and zooplankton. These studies confirmed that herbicide contamination, pH, food stress and anoxia were relevant and concomitant stressors in forest wetland ecosystems. However effects in field studies were moderated relative to effects predicted by laboratory studies. These data are being used to develop and validate multimedia chemical fate models suitable for predicting chemical fate in aquatic enclosures. In addition, chemical and biological monitoring of operational herbicide applications were carried out to quantify herbicide concentrations in a variety of natural wetlands within, adjacent to or buffered from forest regeneration sites receiving aerial herbicide treatments. This project demonstrates that multiple stressors occur concomitantly in natural wetlands associated with herbicide use that may have effects on native amphibians. Laboratory and field studies are required to fully characterize environmental risk associated with anthropogenic stressors in natural environments. Key words: Amphibians, Herbicides, pH, interactions |
