Mercury and Nutrient Transfer from the Deep Brine Layer to

Artemia franciscana in the Great Salt Lake, UT

Erin Jones and Wayne Wurtsbaugh Department of Watershed Sciences

Utah State University

Friends of the Great Salt Lake

Pre-Forum Session on Mercury

May 9, 2012

Formation of the Deep brine layer

(Monimolimnion)

• Railway causeway causes extensive

deep brine layer to form in Gilbert

Bay

• Insufficient light for photosynthesis,

but the deep brine layer is extremely

rich in sedimented organic material

• Total mercury, and especially

methyl mercury, very high in deep-

brine layer (Naftz et al. 2008)

• Because of the high density water,

the deep-brine layer has limited

ability to mix into the upper mixed

layer. However, some limited

mixing is expected, but the amount

is unknown.

• Determine if brine shrimp graze at the interface of

the deep brine layer and take up mercury there, or;

• If brine shrimp mercury uptake is enhanced if

deep brine layer is mixed into the upper layer

Objectives

7.8 108 m3/yr

Tentative Lake Mercury Budget

5

*

*

*Naftz et al. 2009

* *

*Naftz et al. 2009

Study Design

• Measure profiles of mercury and relevant limnological

parameters in an area of Gilbert Bay underlain by the

deep brine layer

• Measure mercury uptake in brine shrimp when deep

brine layer water is mixed with surface water

• Measure mercury uptake of brine shrimp in

mesocosms that simulated a water column with, and

without, a deep brine layer

Field Study (2010-2011)

Water

Mercury, Isotopes

Shrimp

Mixing Experiment (2009-2010)

0% Deep Brine

Mercury, Isotopes

10% Deep Brine

25% Deep Brine

Stratified Experiment (2009-2010)

Control

Mercury, Isotopes

Stratified

Field study

Sampling

Station

Pumped water

from ~2 m

intervals

for chemical

analyses & brine

shrimp counts

Collected water

from 3 m & 7 m

for laboratory

experiments

Deep Brine Water

Characteristics

Mixed layer

3 m

Mixed layer

3 m

Deep Brine

7 m

• High organic matter • Particulate

• Dissolved organic

carbon (DOC)

3 m – 42 mg C/L

7 m – 53 mg C/L • DOC binds with and

maintains mercury in

solution

• Anoxic

• H2S – rich (toxic) • Sulfide reduction

linked to production

of methyl mercury

• High mercury,

especially methyl

mercury

Field study (August 3, 2010)

Field study (August 3, 2010)

Field study (August 3, 2010)

Artemia Hg

(ng/g dry wt.)

620 ± 0.08

Water for

Laboratory

Experiments

• Three treatments (2 reps each) in 34-L aquaria • 0% deep brine layer; 100% mixed layer

• 10% deep brine; 90% mixed

• 25% deep brine; 75% mixed

• 18:6 light:dark

• 27

C

Mixing experiment design:

0% 10% 25%

Deep Brine Water

• 10 Artemia nauplii/L

• 14 day-long experiment

(Artemia mature)

• Aerated initially for 1 day

to remove H2S; 1 hr/day

subsequently

Mixing simulation

Percent Deep Brine Water

• Significantly higher mercury

with more deep brine water

Me

rcu

ry

( n

g / L

)

• Increasing

mercury from

beginning to end

of experiment

(due to

contamination

during aeration?)

Poor Artemia survival after 14 d

in treatments with higher

proportions of deep-brine water

ANOVA: p = 0.002

Mean weight and

final biomass were

not significantly

different, probably

due to large

standard

deviations

But, lower mercury levels in

Artemia in treatments with more

deep-brine water (higher mercury

concentrations)

ANOVA; p < 0.000

*Same trend seen in

preliminary study

done in 2009

Mercury, per unit of carbon (food), is

higher in the mixed layer than in the

deep brine layer

0.000

0.005

0.010

0.015

0.020

0.025

0% 10% 25%

Rati

o o

f H

g:P

OC

Percent Deep Brine Layer

Total Hg : POC

MeHg : POC

Stratified simulation experiment design:

Two treatments 46-L columns; 3 replicates of each

With or without deep brine water

18:6 light:dark regime to promote photosynthesis

27°C

10 Artemia nauplii/L

14 day-long experiment (Artemia mature)

Mercury Concentrations in Columns

Control columns Uniform

Concentrations

Methyl Hg: 0.7 ηg/L

Total Hg: 7.3 ηg/L

0

20

40

60

80

100

120

140

160

0 20 40 60 80

De

pth

(c

m)

Mercury (ng/L)

Control MeHg

Control MeHg

Mercury Concentrations in Columns

Control columns Uniform

Concentrations

Methyl Hg: 0.7 ng/L

Total Hg: 7.3 ng/L

Stratified columns High Hg in deeper

water

Methyl Hg: 1-22 ng/L

Total Hg: 6-56 ng/L

0

20

40

60

80

100

120

140

160

0 20 40 60 80

De

pth

(c

m)

Mercury (ng/L)

Stratified MeHg

Control MeHg

Stratified THg

Control MeHg

Deep Brine

Layer

Artemia Distribution in columns

• Mean distribution of day and night observations over 14 days

• Shrimp concentrated at top and bottom in mixed-layer treatments

• They concentrated at deep-brine interface in the stratified columns

0

20

40

60

80

100

120

140

160

0 10 20

Dep

th

( c

m )

Deep Brine

Mixed

Percent

Mercury in brine

shrimp adults

At end of

experiment brine

shrimp in deep

brine treatment had

lower levels of

mercury, despite

exposure to higher

mercury levels

ANOVA, p = 0.14

0.00

0.20

0.40

0.60

0.80

1.00

Deep Brine Mixed

Art

em

ia T

ota

l M

erc

ury

(m

g H

g/k

g)

Treatment

Conclusions for Deep Brine Layer Experiments

• In both experiments, mercury concentrations in Artemia

were lower when exposed to

deep brine layer water

• High POC in deep brine layer dilutes the mercury the

shrimp are consuming.

Ratios of total mercury to

particulate organic carbon

(Hg:POC) are lower in the

deep brine layer than in the

overlying mixed layer

Artemia enter upper layer of deep brine layer,

but do not penetrate far

In Column Experiment, growth and survival

unaffected by presence of deep brine layer

In Aquaria Mixing Experiment, survival much

lower in treatments with deep brine layer

water: toxic component unknown

Conclusions for Deep Brine

Layer Experiments

Acknowledgements:

- Dave Powelson, Craig Miller, George Aiken, Katie Fisher, Ryan Choi,

Michelle Kang, Brooks Rands lab, Jack Sheets and Sandra

Spence of the US EPA

- Funding provided by the Utah Division of Forestry, Fire and

State Lands

Questions?