Mercury bioaccumulation in stream ecosystems—Detailed studies, spatial assessments, and trend monitoring Mark E. Brigham U.S. Department of the Interior U.S. Geological Survey

2 What drives mercury bioaccumulation in stream ecosystems?

3 Hydrology Aquatic chemistry Atmospheric chemistry Ecological function Land cover/land use Mercury cycling is interrelated with numerous environmental issues…

4 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

5 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 , 2002, 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.

6 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 ) 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.

7 Erosion mobilizes mercury and carbon from soils to natural waters.

8 Numerous influences alter methylation… New impoundments (reservoirs, wetlands) Cycles of wetting and drying –Sulfur recycling Sulfate loading Temperature

9 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

10 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

11 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)

12 Urban settings… Photos: Dennis Wentz

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

14 …to low-topographic gradient, high-carbon streams

15 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

16 Sources anthropogenic and natural Hgº Hg +2 MeHg Methylation Hgº Hg +2 Biomagnification PHg (particulate Hg) PHg Sed. Hg Hgº Hg +2 MeHg Hg +2 MeHg

17 Food web sampling

18 Start simple… Intensive study area Modified from Reed Harris, Tetra Tech Inc. River mercury studies & model development—

19 Build complexity over time… Intensive study area Modified from Reed Harris, Tetra Tech Inc. River mercury studies & model development—

20 Spatial assessments—National synoptic for mercury One-time, multimedia sampling of streams Spatial coverage; diverse settings Correlative analysis (biogeochemical; spatial) Refs:

21 USGS national mercury synoptic Streams sampling in most NAWQA study areas, in 1998, 2002, USGS NAWQA Program

22 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

23 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