Variable fish mercury concentrations in the Dehcho: effects of catchment control and invertebrate community composition

During a previously conducted study, we found that some Dehcho lakes have high mercury concentrations in top predator food fish species, such as Northern Pike (exceed consumption guidelines), whereas other lakes have relatively low mercury concentrations in these species. Among-lake variability in fish mercury concentrations are not fully explained by any of the variety of variables we investigated, including fish growth rates, fish trophic position, fish age, and fish size. We also found an interesting decoupling between mercury concentrations in water and mercury concentrations in fish, and that lakes with high fish mercury concentrations do not necessarily have high rates of mercury biomagnification through the food web. Our aim is to understand what the key drivers of fish mercury concentrations are in traditional fishing lakes in the Dehcho region, and how/if these drivers vary predictably among lakes. We will build upon our previous research and conduct a paired-lakes study (2 lakes with relatively high mercury concentrations, 2 lakes with relatively low mercury concentrations) that is designed to address the following monitoring- and management-relevant research questions:1.Knowing that mercury concentrations in water, variables related to fish ecology (e.g., growth rates, trophic position), and rates of biomagnification do not fully explain among-lake differences in fish mercury levels ([Hg]) in Dehcho lakes, are fish [Hg] better explained by catchment and lake morphometry variables (e.g., catchment slope, mercury in influent wetlands, catchment land cover, lake depth) or by invertebrate community composition and the amount of bioavailable mercury at the bottom of the food chain? 2. Do lake productivity, quantity and quality of dissolved organic carbon (DOC), and sediment conditions explain why [Hg] in water are not related to [Hg] in fish?Results will allow more informed predictions of the effects of climate change and other anthropogenic stressors on mercury concentrations in food fishes.