Fish are known conduits of metal exposure to humans and wildlife. Forty-eight states currently issue public advisories limiting fish consumption to reduce human exposure to Hg and other toxins. Yet, there is much unexplained variation in metal levels in fish from different lakes even within the same region. Project 7 studies mechanisms driving lake-to-lake variation in burdens of top priority metals (Hg, As, Cd, Zn, Pb) in aquatic organisms. We focus on the trophic transfer !of metals (i.e., movement of metal from water through the food chain to fish) in a multiple stressor context (e.g. multiple metals, pH, DOC, nutrients, low food) across a gradient of lake types. We hypothesize that much variation in fish metal burdens is driven by fundamental differences in the food web structure among lake types and in the ability of particular taxa to accumulate, magnify or dilute metals. We will predict this variation based on environmental properties that vary across lakes, such as lake productivity, adjacent land use, dominance of """"""""key conduit"""""""" species, use of """"""""conduit"""""""" habitats for foraging, timing and nature of metal inputs, and the toxicological responses of the conduit organisms. Our research across 60+ lakes identifies three aspects of food web structure that increase trophic transfer of metal to fish: (1) larger bodied, lower complexity zooplankton food webs, (2) dominance of key conduit zooplankton taxa (e.g., Daphnid), and (3) lower algal biomass and zooplankton abundance. We also plan to test for additional influences of factors including lake productivity, use of the littoral zone for feeding, presence of other environmental stressors. We further seek to strengthen the scientific basis for lake-specific management and public health warnings and plan to develop Daphnia as a model organism for toxicogenomic analysis to understand gene-environment interactions underlying effects of multiple metal stressors in aquatic ecosystems. This proposal has five specific aims.
Aim 1 characterizes metal trophic transfer pathways in the field and tests whether the transfer to fish diminishes!in eutrophic or urbanized lakes.
Aim 2 determines strength and consistency of specific taxa and specific lake habitats (littoral Vs. pelagic) as conduits of metals to fish.
Aim 3 links temporal patterning in deposition of multiple metals to watersheds and inputs to lakes, and determines the source of key depositional events using multielement emission source fingerprinting, a new stable Hg isotope technique, and meteorological trajectory analysis.
Aim 4 quantifies combined toxic effects of multiple environmental stressors associated with metal burdens in situ on Daphnia.
Aim 5 characterizes genomic response to metals among natural populations of Daphnia, in order to further the development of Daphnia as a general toxicogenomic model species for assessing metal exposure and effects in natural field populations.
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