Assessment of mercury bioaccumulation within the lower food web of lakes in the western Great Lakes ...
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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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Kris Rolfhus, Britt Hall, Michael Paterson, and Bruce Monson

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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

  • 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


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…


  • 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


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…


  • 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


  • 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?


Data Sets


Sublethal & reproductive effects on fish

USEPA fish criterion for

MeHg (0.3 µg/g)

Voyageurs National Park--Northern Pike


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


VOYA Trophic Transfer Efficiency


Aqueous MeHg Concentration


Seston MeHg Concentration

N/A

N/A


Bulk Zooplankton MeHg Concentration

N/A

N/A


Seston/Water BAF Comparison

BAF range: 0.90

8-fold

N/A

N/A


Zooplankton/Water BAF Comparison

BAF range: 0.71

(5-fold)

N/A

N/A


BAF Comparisons

N/A

N/A


  • 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


  • 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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