Research ArticleENVIRONMENTAL STUDIES

Food web controls on mercury fluxes and fate in the Colorado River, Grand Canyon

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Science Advances  15 May 2020:
Vol. 6, no. 20, eaaz4880
DOI: 10.1126/sciadv.aaz4880
  • Fig. 1 Mercury food web fluxes over space and time.

    Hg fluxes in Colorado River food webs at the tailwater (A and B) and a representative (C and D) downstream site (site 3) before and after an experimental flood in the Grand Canyon. (Note scale differences in fluxes to invertebrates versus fishes). Arrows represent estimated total annual flows of Hg to consumers based upon their consumption rates and Hg concentrations of various diet items. Total Hg flux to invertebrates and fishes for each food web are summed in the center panel (red arrows) and labeled A to D to correspond with the detailed food web panels. Native fishes face left; non-native fishes face right. Numbers in (B) and (D) refer to animal key at bottom right (see table S3).

  • Fig. 2 Total Hg fluxes to invertebrates and fishes.

    Total fluxes of Hg to invertebrates, New Zealand mudsnail (NZMS), and fishes before and after an experimental flood. Fluxes at site 1 are graphed on a separate scale. Bars represent 95% bootstrap CIs. Flux to NZMS at sites other than site 1 was negligible (not shown).

  • Fig. 3 Fate of Hg in coupled food webs.

    (A) Amount of Hg in blackfly larvae (in μg m−1 of river per year) that is consumed by fishes (below the x axis, solid arrow) or is exported from the river via adult emergence (above the x axis, dashed arrow). (B) Proportion of Hg in blackfly larvae that is consumed by fishes, retained in adult blackflies, or excreted during metamorphosis.

  • Fig. 4 Species traits and predator-prey interactions drive contaminant fate in coupled food webs.

    (A) Productive, predator-resistant mudsnails are a contaminant trophic dead end in the tailwater. Dashed circular arrow indicates that Hg in their tissues is recycled to the detrital pool when they die. (B and C) Differences in production of blackflies relative to fish consumption determined whether blackfly Hg remained in the aquatic food web or was exported to land by adult blackflies.

Supplementary Materials

  • Supplementary Materials

    Food web controls on mercury fluxes and fate in the Colorado River, Grand Canyon

    D. M. Walters, W.F. Cross, T.A. Kennedy, C.V. Baxter, R.O. Hall Jr., E.J. Rosi

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    • Acknowledgements
    • Tables S1 to S4
    • Figs. S1 and S2

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