Impact of sediment and nutrient inputs on growth and survival of tadpoles of the Western Toad

1. Sediment and nutrient loading in freshwater systems are leading causes of aquatic habitat degradation globally. We investigated the impacts of fine-sediment and nutrient additions on the growth and survival of western toad ( Bufo boreas ) tadpoles and emergent metamorphs in mesocosm and exclosure experiments.
2. Mesocosm tanks received weekly pulses of fine sediments to create initial concentrations of 0, 130 and 260 mg L⁻¹ of suspended sediment and either bi-weekly additions of nutrients (N = 160 μg L⁻¹, P = 10 μg L⁻¹) or no additions in a factorial design. Within mesocosms, tadpole exclosures allowed for quantification of tadpole grazing pressure on periphyton biomass, chlorophyll- a and sediment deposition.
3. Tadpoles receiving sediment additions experienced slower growth rates and reduced survival to metamorphosis, although no effects of treatment were detected on size at metamorphosis or time to metamorphosis. Nutrient additions also lowered survival, but had no impact on other measured parameters of tadpole fitness. Dissections and gut content analysis revealed that tadpoles ingested sediment in large quantities altering the proportion of the organic content of ingested food.
4. Together these results suggest that although sediment was readily consumed by tadpoles, its presence in the larval environment had an overall negative effect on tadpole growth and survival, although not as severe as predicted.