Effects of aquatic herbicides on abundance of pond-breeding frogs
Aquatic herbicides are often applied to control nuisance vegetation in lakes and ponds, and they can be re-applied over many years. This study compares the abundance of five frog species in treated and untreated lakes in Ashburnham, MA. At each lake the density of human housing and lake area were also assessed for their relationship with frog abundance. The abundance of each frog species was estimated with a standard calling index, and the sum of calling indices from all species served as a measure of total frog abundance at each survey site.
The sum of calling indices declined with increasing density of human housing, while herbicide treatment was not an important main effect. However there was marginal interaction between herbicides and housing density: lakes with moderate-high housing densities seemed to have lower frog abundance with herbicide treatments. The small data set here also suggests that frogs may benefit from permanently untreated refuge zones on lakes. When frog species were assessed individually, none of the five frog species were less abundant in herbicide-treated lakes. While long-term use of aquatic herbicides did not generally reduce abundance of adult frogs, more studies are needed to determine whether some herbicides may impair frog populations that are already stressed by housing development.