# Presentation: 271243

## Mercury cycling and bioaccumulation in streams in Oregon, Wisconsin, and FloridaMark E. Brigham5th National Monitoring ConferenceSan José, CaliforniaMay 7-11, 2006

**U.S. Department of the Interior**
**U.S. Geological Survey**

**Notes:**
Today I’m going to provide an overview of a USGS study of mercury in stream ecosystems in Oregon, Wisconsin, and Florida.  

## Mercury: A leading water-quality impairmentData source: EPA 303(d) list (http://oaspub.epa.gov/waters/national_rept.control)

- Mercury: A leading water-quality impairmentData source: EPA 303(d) list (http://oaspub.epa.gov/waters/national_rept.control)

-   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. 13-16, 2002

- Hg(II)  MeHg

**Notes:**
Main study objective: Describe the importance of key factors in determining mercury concentrations in fish in stream ecosystems.   Our initial conceptual framework was that mercury concentrations in top predator fish was controlled by three primary factors:  
  Source-strength, or how much mercury is entering the watershed and the stream; 
  Methylation efficiency, or how effectively a given ecosystem converts inorganic mercury to methylmercury; 
  And biological factors such as food-chain length and specific food-web interactions—who is eating who.  There is some evidence from the literature that lakes with longer food chains yield higher mercury levels in the top predator fish.  

## USGS NAWQA mercury  study areas

- 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**

**Notes:**
With this framework in mind, we selected streams that span large gradients in factors we believed to be important in the mercury cycle.  
--2003-05 studies—focus of today’s presentation.
--point out next round of studies.

## Sites span gradient of wet Hg deposition 

**Notes:**
Our sites span the national gradient in wet deposition of mercury. 
Nationally, the mercury issue is driven by modest Hg loading from atmospheric transport & deposition.  
Numerous waters are also affected by point sources, such as mining inputs. 

## 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...

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

## ...to low-gradient, high-carbon streams

- ...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

**Notes:**
This slide encompasses many of the components of our mercury studies.  We selected stream basins mercury from atmospheric inputs is thought to be the dominant source of mercury.
  We used standard Mercury Deposition Network sites to monitor mercury in precipitation.  This is a key measure of mercury load to ecosystem, but ignores dry-deposition inputs, which are much more difficult to characterize.  
 Water column monitoring, with ancillary water chemistry measures and flow
 Sediment & porewater geochemistry: in addition to concentrations of mercury and related constituents, also measured rates of mercury methylation; demethylation of  methylmercury; sulfate reduction. 
Measure Hg in key components of food-web, including periphyton, invertebrates, small fish, and predator fish—Chasar presentation.  
FOCUS of remainder of my presentation is mainly on mercury in stream water, and comparison of stream-water data to other key media.  

## 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]

**Notes:**
Understanding controls on aqueous MeHg is key to understanding:
--Fish mercury concentrations.
--How ecosystems may respond to changes in mercury deposition

## Stream sediment geochemistry

- Characterize channel substrate.
- Detailed geochemical measures:
- Concentrations: MeHg, THg, carbon, S, etc.
- Rates:
- Methylation:  Hg(II)  MeHg
- Demethylation:  MeHg  Hg(II), Hg°
- Sulfate reduction:  SO4-2  S-2

## Sediment methylation rate and MeHg concentration strongly relate to texture & organic content

**0**

**50**

**100**

**150**

**200**

**250**

**0**

**10**

**20**

**30**

**40**

**50**

**60**

- Loss On Ignition (% dry weight)

- Methylation rate
- (from 203Hg experiment)
-  (ng • g dry sed-1 • d-1)

**y = 4.36x + 9.7**
**R****2**** = 0.95**

**Evergreen**

**Oak Creek**

**Pike Creek**

## Stream sediment characterization

- Fines

- Mixed sand & fines

- Sand

- Gravel & cobble

- Simplified channel cross section

## Sediment & porewater geochemistry sampling

- Sand

- Fines

- Sand & fine mixture

## Large range in dominant channel substrate(grain size; organic content)

- 0

- 10

- 20

- 30

- 40

- 50

- 60

- 70

- 80

- 90

- 100

**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

**0**

**0.1**

**0.2**

**0.3**

**0.4**

**St Marys**

**L Wekiva**

**Santa Fe**

**Pike**

**Evergr.**

**Oak Cr**

**Lookout**

**Beaver.**

- Mean aqueous  MeHg (ng/L)

**0**

**1**

**2**

**3**

**4**

**5**

**6**

**7**

**8**

**9**

**Florida sites**

**Wisc. sites**

**Oregon**
**sites**

- Sediment  MeHg (ng/g dry sed)

**Notes:**
Make color stand Bill.

## Fluvial MeHg yield unrelated to stream-sediment methylation rate

## 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

- 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