Mercury bioaccumulation in stream ecosystems—Detailed studies, spatial assessments,

and trend monitoring

Mark E. Brigham

U.S. Department of the InteriorU.S. Geological Survey

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What drives mercury bioaccumulation

in stream ecosystems?

Methylation efficiency

Mercury source strength

Food chain —

specific interactionslength

—

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Hydrology Aquatic chemistry Atmospheric chemistry Ecological function Land cover/land use

Mercury cycling is interrelated with numerous environmental

issues…

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In aquatic ecosystems, mercury runoff may be…

• Increased by:– Erosion & weathering of soils – Low-intensity fires?– Urbanization & increase in

impervious surfaces– Increased inputs

• Decreased by:– Soil restorative processes– Intense fires– Decreased inputs

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Notes related to previous slide, including selected references [page 1 of 2]

• Soil erosion and increased Hg runoff:

(See: Balogh et al., 1997, Environ. Sci. Technol., v 31, p. 198; Balogh et al., 1998, Environ. Sci. Technol., v 32, p. 456; Balogh et al., 2000, J. Environ. Qual., v 29, p. 871).

• Fires and mercury runoff: The effect of fires is likely complex, temporally dynamic, and likely depends on more environmental variables than can be summarized herein. Fire likely affects both mercury speciation and total mercury concentration in runoff. Low-intensity fires may promote runoff of higher methylmercury concentrations (see: Amirbahman et al., 2004, Water, Air, & Soil Pollut., v 152, p. 313), possibly due to enhanced methylation. Hotter fires volatilize mercury (Sigler et al., 2003, Environ. Sci. Technol., v 37, p. 4343; Cannon W.F. et al., 2002, Geological Society of America Annual Meeting, Oct. 22-27, 2002, http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_40419.htm), and may affect mercury bioaccumulation (Garcia & Carignan, 1999, Can. J. Fish. Aquat. Sciences, v 56, p. 339). More research is needed to describe the role of fire on mercury runoff and speciation.

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Notes related to previous slide, including selected references [page 2 of 2]

• Mercury runoff and urbanization (See: Mason and Sullivan, 1998, Water Resources, v 32, p. 321-330)

• Mercury runoff and soil restorative processes: This argument is the converse of the above notes on erosion processes that exacerbate mercury runoff. Soil erosion increases mercury runoff to aquatic ecosystems; controlling erosion in a highly erodible setting would tend to decrease mercury runoff. Also, soil organic carbon holds a large reservoir of mercury at the earth’s surface. Mineralization of this soil organic matter is exacerbated with many land use and intensive cultivation practices, implying potential for release and runoff of soil-bound mercury. Conversely, conservation-minded land use and cultivation practices can restore soil organic matter (Tilman, Nature 1998, v 396, p. 211), implying potential for retention of atmospherically deposited mercury on the land surface.

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Erosion mobilizes mercury and carbon from soils to natural waters.

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Numerous influences alter methylation…

• New impoundments (reservoirs, wetlands)

• Cycles of wetting and drying – Sulfur recycling

• Sulfate loading • Temperature

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• Wealth of expertise to inform ecosystem management.– Existing literature– New research– Adaptive

management

Consider mercury in resource management decisions…

particularly in ecosystems with mercury advisories

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Mercury bioaccumulation in stream ecosystems—

Detailed studies

• Barb Scudder• Lia Chasar• Dennis Wentz• Mark Brigham • Rod DeWeese• Amanda Bell• Michelle Lutz• Dave Krabbenhoft• Mark Marvin-DiPasquale• George Aiken• Carol Kendall • Robin Stewart• Bill Orem• Others…

• NAWQA Program• Toxic Substances

Hydrology Program• National Research

Program• Geology • Biological Resources• And USEPA

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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

Detailed

mercury

studies(USGS-NAWQA study areas)

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Urban settings…

Photos: Dennis Wentz

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Relative reference settings…range from high-topographic gradient / low organic carbon streams

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…to low-topographic gradient, high-carbon streams

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Detailed studies

Urban sites– Presumed higher

loading; proximity to many sources

– Not targeted to point sources!

– Enhanced runoff – Disturbed

ecosystems

Undisturbed rural sites– Low-moderate

Hg loading– Not “negative

control” for urban sites

– Natural runoff pathways

– Undisturbed ecosystems

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Sources anthropogen

ic and natural

Hgº Hg+2 MeHg

Methylation

Hgº Hg+2

Biomagnification

PHg (particulate Hg)

PHg

Sed. Hg

Hgº Hg+2

MeHg

Hg+2 MeHg

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Food web sampling

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• Start simple…

Intensive study area

Modified from Reed Harris, Tetra Tech Inc.

River mercury studies & model development—

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• Build complexity over time…

Intensive study area

Modified from Reed Harris, Tetra Tech Inc.

River mercury studies & model development—

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Spatial assessments—National synoptic for mercury

• One-time, multimedia sampling of streams

• Spatial coverage; diverse settings• Correlative analysis

(biogeochemical; spatial)• Refs:

http://toxics.usgs.gov/pubs/wri99-4018/Volume2/sectionB/2301_Krabbenhoft/pdf/2301_Krabbenhoft.pdf

http://www.cerc.usgs.gov/pubs/center/pdfdocs/BSR2001-0009.pdf

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USGS national mercury synopticStreams sampling in most NAWQA study

areas, in 1998, 2002, 2004-05

USGS NAWQA Program

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Trends…

• A national network of multimedia Hg-trend sites to assess ecosystem responses to emission reductions in: – Precipitation (MDN)– Surface water– Fish

• Contact Mark Brigham(mbrigham@usgs.gov)

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Summary

• USGS is studying methylmercury in key components of stream ecosystems, at selected sites across the nation. – several temporal and spatial scales– Detailed studies– Spatial (synoptic) assessments– Trend sampling