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Assessment of mercury bioaccumulation within the lower food web of lakes in the western Great Lakes Region. “Super Odon-8 Hotel”. Kris Rolfhus, Britt Hall, Michael Paterson, and Bruce Monson. Introduction. What controls Hg bioaccumulation in food webs? Food web structure

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slide1

Assessment of mercury bioaccumulation within the lower food web of lakes in the western Great Lakes Region

“Super Odon-8 Hotel”

Kris Rolfhus, Britt Hall, Michael Paterson, and Bruce Monson

slide2

Introduction

  • What controls Hg bioaccumulation in food webs?
  • Food web structure
  • Efficiency of transfer
  • Complexity of food web
  • Benthic vs. pelagic source
  • Inputs—processes affecting MeHg synthesis, transport
  • Atm deposition
  • Methylation rate
  • Speciation
  • Microbial abundance, activity
  • S, OM
  • Transport to base of food web
slide3

Trends observed in bioaccumulation studies

…within systems of similar [MeHg], trophic structure and transfer efficency may be most important…

…in systems that differ in multiple properties, MeHg supply to base of food web appears to be most important…

slide4

Why focus on lower food web?

  • Largest extent of bioaccumulation is in LFW
  • (water to particles in particular)
  • Least studied in terms of structure, function
  • …data sets are sparse, incomplete, and scattered
  • Pelagic:
  • Water/Seston/Zoops/Preyfish/Piscivores
  • Benthic:
  • Sediment/Invertebrates/Preyfish/Piscivores
  • Measures: MeHg, THg, 15N, 13C, ancillaries
slide5

Bioconcentration Factor (BCF)

accumulation due to respiratory/dermal source

= [tissue]/[water]

Biomagnification Factor (BMF)

accumulation due to dietary source only

= [tissue]/[diet]

Bioaccumulation Factor (BAF)

accumulation due to all sources

= [tissue]/[given trophic level]

…not all BAF’s are consistent or relevant…

slide6

Speciation Matters…

  • Use of MeHg rather than Total Hg…
  • Methylmercury is the accumulating form…
  • Data are less abundant for a number of reasons…
  • Difficulty/cost of MeHg analysis
  • Historically THg data
slide7

What are the important questions?

  • What has a bigger influence on predatory fish Hg,
  • trophic structure or supply of aqueous MeHg?
  • What is extent of spatial variation in
  • LFW bioaccumulation?
  • 3. Is benthic or pelagic food web more important?
slide9

Sublethal & reproductive effects on fish

USEPA fish criterion for

MeHg (0.3 µg/g)

Voyageurs National Park--Northern Pike

slide10

Mukooda Lake

Ryan Lake

181 ng/g

943 ng/g

Yellow Perch

17 ng/g

197 ng/g

Zooplankton

3.5 ng/g

8.3 ng/g

Seston

< 0.045 ng/L

Water

0.30 ng/L

2004 Collection

slide16

Seston/Water BAF Comparison

BAF range: 0.90

8-fold

N/A

N/A

slide17

Zooplankton/Water BAF Comparison

BAF range: 0.71

(5-fold)

N/A

N/A

slide19

Conclusions (thus far)…

  • BAFs are fairly consistent among contrasting sites
  • Sources of MeHg BAF variation to food web:
  • Aqueous [MeHg] 2.0 log units
  • Water to Seston 0.9
  • Seston to Zoop 1.0
  • Zoop to Preyfish 1.0
slide20

What’s next…

  • Sediment BSAFs involving benthic invertebrates
  • Compile further data from the literature
  • (do we have yours?)
  • Compare THg to MeHg BAFs
  • What is controlling [aqueous MeHg]?
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