Anuran development, density and diversity in relation to agricultural activity in the Holland River watershed, Ontario, Canada (1990-1992)

Significantly lower anuran species diversity and density was recorded in a vegetable growing area relative to upstream and downstream sites in the Hol land River watershed, Ontario, Canada. Egg hatching success and tadpole def ormity rates of American toads (Bufo americanus americanus), green frogs (R ana clamitans melanota) and northern leopard frogs (Rana pipiens) eggs in w ater from field sites and control water were assessed. Compared to the cont rol and the upstream site, the total abnormality rate (unhatched eggs plus deformed tadpoles) was higher for American toads in water from the agricult ural and downstream sites. Total abnormality was higher in green frog eggs in water from the agricultural site and a downstream site. Trace concentrat ions of organophosphorus pesticides were detected most often in agricultura l zone water and sediments than in upstream and downstream sites. Organochl orine pesticide residues, especially in agricultural zone samples, exceeded the no effect level guidelines for the protection of aquatic life. Ammonia , phosphorus, particulates, BOD and TKN were highest in the agricultural zo ne. Significant correlations between these parameters and anuran developmen t suggest nutrient run-off as a causal or contributing factor in lower anur an diversity, density and reproductive success of American toads and green frogs in the site dominated by agriculture.