Mercury cycling and bioaccumulation in streams in Oregon, Wisconsin, and Florida Mark E. Brigham 5 th National Monitoring Conference San José, California May 7-11, 2006 U.S. Department of the Interior U.S. Geological Survey

Mercury: A leading water-quality impairment Data source: EPA 303(d) list ( ) Mercury: ~ 6,000 Metals impairments ~ 2,100 Fish consumption advisories >8,100 impaired waters

Factors that control mercury levels in fish After: Mumley & Abu-Saba, WEF National TMDL Science and Policy Conference Proceedings, Nov , 2002 Hg(II)  MeHg

Willamette Basin Hudson River Basin Lake Erie Basin Santee Basin Georgia-Florida Coastal Plain Western Lake Michigan Drainages Long Island- New Jersey Reference stream Urban stream USGS NAWQA mercury study areas

Sites span gradient of wet Hg deposition

Settings Urban sites –Presumed higher loading; proximity to many sources –Not targeted to point sources! –Enhanced runoff –Disturbed ecosystems Reference sites – Low-moderate Hg loading – Not “control” for urban sites – Natural runoff pathways – Minimally disturbed ecosystems

Comparison of Basin Sizes

Reference settings: streams range from high-topographic gradient / low organic carbon…

…to low-gradient, high-carbon streams

Main study components: THg, MeHg, and related measures in: Stream water filtered & particulate phases Precipitation aquatic food web Hg +2 MeHg Sediment & pore water

Aqueous methylmercury (MeHg) is a major control on mercury bioaccumulation Hg in forage fish (μg/g wet wt.) [mean of N ≈ 24 at each site] Aqueous MeHg (ng/L) [mean of N ≈ 35 at each site]

Stream sediment geochemistry 1.Characterize channel substrate. 2.Detailed geochemical measures: Concentrations: MeHg, THg, carbon, S, etc. Rates: –Methylation: Hg(II)  MeHg –Demethylation: MeHg  Hg(II), Hg° –Sulfate reduction: SO 4 -2  S -2

Sediment methylation rate and MeHg concentration strongly relate to texture & organic content Loss On Ignition (% dry weight) Methylation rate (from 203 Hg experiment) (ng g dry sed -1 d -1 ) y = 4.36x R 2 = 0.95 Evergreen Oak Creek Pike Creek

Stream sediment characterization Fines Mixed sand & fines Sand Gravel & cobble Simplified channel cross section Substrate characterization sampling points

Transect Sediment & porewater geochemistry sampling Sand Fines Sand & fine mixture

Large range in dominant channel substrate (grain size; organic content) L. Wekiva Santa Fe St. Mary's Beaverton Lookout Evergreen Oak Cr. Pike R. Percent of channel substrate Sand High organic - Fine High org-Sand/Fine Larger than sand Low organic - Fine

MeHg in sediment (spatially weighted) unrelated to stream-water MeHg St MarysL WekivaSanta FePikeEvergr.Oak CrLookoutBeaver. Mean aqueous MeHg (ng/L) Florida sitesWisc. sites Oregon sites Sediment MeHg (ng/g dry sed) Note extremes

Fluvial MeHg yield unrelated to stream-sediment methylation rate Fluvial MeHg yield (μg/m 2 /year) Sediment methylation rate (spatially weighted; potential rate from 203 Hg experiment, μg/m 2 /year)

Summary & Implications (1) Aqueous MeHg is strongly related to fish-Hg concentrations. –Therefore, efforts to better understand MeHg production and transport are important for ecosystem management

Summary & Implications (2) Sediment MeHg unrelated to fluvial MeHg concentration and yield. Evidence suggests stream sediments play weak role in MeHg mass balance –Demethylation – high in sandy sediments. –Methylation – high in organic-rich sediments. –Difficult to scale isotope experiments to mass-balance context. It’s the watershed—Thursday’s presentation.

Future directions: Move toward more complete mass balance: --Net role of sediments & periphyton --Dry deposition? Evasion? --Watershed retention / delivery / methylation Integrate with model development Intensive study area

Acknowledgments USGS: Dennis Wentz, Barb Scudder, Lia Chasar, Amanda Bell, Michelle Lutz, Dave Krabbenhoft, Mark Marvin- DiPasquale, George Aiken, Robin Stewart, Carol Kendall, Bill Orem, Rod DeWeese, Jeff Isely, and many others… USGS: NAWQA and several other programs USEPA: support for periphyton study MDN site support: Wisconsin DNR, Oregen DEQ, Forest Service, US Fish & Wildlife Service, St. John’s River Water Management District (Florida), USGS NAWQA Menomonie Indian Tribe of Wisconsin