Using multiple sentinel species and stable isotopes to understand mercury sources and fate in temperate stream

The goal of this dissertation was to better understand mercury (Hg) dynamics in running waters. It employed two techniques, analysis of stable isotopes of carbon and nitrogen and the use of sentinel species, to achieve this goal. I began by learning about the feeding ecology of a common predatory insect, the water strider (Aquarius remigis) that I hoped to use as an indicator of aquatic Hg contamination. I found that water striders exhibited a strong connection to the riparian zone via consumption of terrestrial insects that made up a majority of their diet Water striders also had Hg concentrations that were weakly related to variables known to influence Hg in waterbodies, such as pH and dissolved organic carbon content. Instead water strider Hg concentrations were predicted by their body size, trophic level and proximity to a coal-fired power plant that annually emits ∼ 100 kg of Hg to the atmosphere. This suggests that striders are terrestrial organisms that happen to spend much of their time on the surface of the water, and they tell us little about processes occurring in the aquatic environment.;I then sampled algae, invertebrates and fishes from 60 stream and river sites in New Brunswick, Canada from 2004-2007. I found that the small minnow, blacknose dace, accumulated far more Hg than the larger species brook trout that is often caught by recreational anglers. Mercury concentrations in blacknose dace were predicted mainly by the pH of the water; acidic streams had dace with highest Hg concentrations. Trout Hg concentrations were determined more by their diet and their proximity to the coal-fired power plant. Trout that fed higher on the food chain and lived in streams within 50 km of the power plant had the highest Hg concentrations, but none of these concentrations were above the human health consumption guideline of 0.5 ug g-1 wet weight. Mercury increased four- to five-fold with each step in the food chain, similar to rates found in lakes and oceans, and differences in Hg concentrations in fishes were determined largely by differences at the base of the food chain.;All of these analyses suggest that patterns of Hg biomagnification in streams and rivers is similar to that observed in other ecosystems, and that Hg exposure will depend on the species that are present and the amount of Hg available at the base of the food chain.