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

Mercury and Selenium in the Colorado River Food Web, Grand Canyon

D.M. Walters, E. Rosi-Marshall, T.A. Kennedy, W.F. Cross, and C.V. Baxter

Key Findings · Mercury (Hg) and selenium (Se) concentrations are relatively high in the

Colorado River food web throughout Grand Canyon.

· Hg and Se in organic matter, algae, invertebrates, and fish exceed protective thresholds for fish, wildlife, and humans.

· Hg concentrations were low in rainbow trout in Glen Canyon, so human health risks associated with this popular sport fishery are low.

· However, Hg in trout was higher downstream. Some of these areas are targeted for trout removal, which are provided for human consumption.

· Managing exposure risks in Grand Canyon will be challenging, because sources of Hg and Se are beyond Park boundaries.

The Colorado River in Grand Canyon is an incredibly remote, but heavily altered ecosystem.

Glen Canyon Dam fundamentally changed the river’s physical template

Water is 1000X clearer

Filamentous algae

Voichick and Topping 2014

Glen Canyon Dam fundamentally changed the river’s physical template

Cold and constant water temperatures Voichick and Wright 2006

Altered Foodbase

Scuds

New Zealand mudsnails

Black flies

The dominant aquatic invertebrates in Glen and Grand Canyon are non-native.

? Humpback Chub

Losses

Razorback Sucker

Roundtail Chub

Bonytail Chub

Colorado Pikeminnow

Remaining Native Fishes

Flannelmouth Sucker

Bluehead Sucker

Speckled Dace

Rainbow Trout

Brown Trout

Common Carp

Fathead Minnow

Plains Killifish

Our new friends

Many invasive fish species.

On top of all this, chemical alteration?

Hg and Se data missing from Grand Canyon

piscivorous bird

piscivorous mammal

fish

piscivorous wildlife

larval fish

Why should we care about Hg and Se?

· Effects of Hg · Neurotoxin (cognition and behavior) · Lower reproductive success, growth, and survival

· Effects of Se · Deformities of embryo/larvae · Lower reproductive success, growth, and survival

· Hg –protective thresholds thoroughly vetted · Se –protective thresholds are preliminary

Objectives

· Sample Hg and Se along upstream-downstream gradient and throughout entire food web

· Compare Hg and Se concentrations to protective threshold to determine risk to humans and wildlife

· Examine potential sources

Approach

· Six sites (river mile 0, 30, 63, 125, 165, 225)

· Hg and Se concentrations – 1 season (Summer 2008)

· ~4 replicate samples of dominant types of organic matter, macroinvertebrates, and fish per site

· Endangered humpback chub not sampled

Hg and Se concentrations are relatively high throughout Grand Canyon, with no clear downstream patterns.

Cladophora Epilithon Epiphyton FBOM Seston

Hg

µg g

-1

0.0

0.1

0.2

0.3

0.4

0.5 RKM 0 RKM 48RKM 100 RKM 204 RKM 264RKM 362

Chironomid Gammarus mudsnail Simuliid Lumbricid

Hg

µg g

0.000

0.025

0.050

0.075

0.500

1.000

1.500

2.000

2.500

BHS CRP FHM FMS RBT SPD

Hg

µg g

-1

0.0

1.0

2.0

3.0

4.0

Hg

(µg

g-1 )

H

g (µ

g g-

1 )

Hg

(µg

g-1 )

Cladophora Epilithon Epiphyton FBOM Seston

Se

µg g

-1

0

1

2

3

4RKM 0RKM 48RKM 100RKM 204RKM 264RKM 366

Chironomid Gammarus mudsnail Simuliid Lumbricid

Se

µg g

-1

0.00

0.05

4.00

8.00

12.00

16.00

20.00

BHS CRP FHM FMS RBT SPD

Se

µg g

-1

0

1

2

3

4

5

6

Se (µ

g g-

1 )

Se (µ

g g-

1 )

Se (µ

g g-

1 )

RM 0 RM 30 RM 63 RM 127 RM 166 RM 225

RM 0 RM 30 RM 63 RM 127 RM 166 RM 225

Walters et al. 2015

Hg ug/g

0 1 2 3 4

Cladophora (24)

epilithon (23)

FBOM (22)

epiphyton (19)

seston (23)

mudsnail (3)

chironomid (14)

lumbricid (3)

Gammarus (7)

Simuliid (24)

common carp (17)

rainbow trout (20)

bluehead sucker (13)

flannelmouth sucker (21)

fathead minnow (16)

speckled dace (16)

A

BHg (µg g-1)

fish

piscivorous mammal kingfisher

human

Dietary risk thresholds

Hg concentrations among sites

Hg concentrations commonly exceed protective thresholds Walters et al. 2015

Se ug/g

0 2 4 6 8 10 12 14

Cladophora (19)

epilithon (24)

FBOM (22)

epiphyton (19)

seston (23)

mudsnail (3)

chironomid (13)

lumbricid (3)

Gammarus (8)

simuliid (23)

common carp (17)

rainbow trout (20)

bluehead sucker (13)

flannelmouth sucker (22)

fathead minnow (16)

speckled dace (16)

Se (µg g-1)

larval fish

piscivorous wildlife

Dietary and maternal risk thresholds

Se concentrations among sites

Se concentrations commonly exceed protective thresholds Walters et al. 2015

Where does Hg come from?

Humans have greatly increased atmospheric Hg, contaminating remote & protected areas.

“…human activities have increased atmospheric Hg concentrations 3- to 5-fold during the past 150 years.” “…[human activities] have resulted in some of the most remote and protected areas of the world becoming contaminated with Hg…”

Eagles-Smith and others 2014.

Where does Hg in Grand Canyon come from?

Atmospheric sources of Hg to Grand Canyon are likely a mixture of distant and nearbye sources.

Emissions from Navajo Generating Station are deposited in Grand Canyon and Lake Powell.

Seiler et al. 1999

Where does Se come from?

• Se is high where: – marine sedimentary

geology

– high evaporation index

– irrigation

areas susceptible to contamination

irrigated land

Se data 1985-94: Engberg,1999

How much Se enters Glen Canyon?

Glen Canyon

83 kg d-1

29.9 MT y-1

Lake Powell

100 kg d-1

Green R. 27%

Gunnison R. 31%

Grand Valley Pr. 30%

San Juan R. 8%

irrigation 71% natural weathering 21%

point source 8%

Hg and Se Transport Model Se & Hg

Hg

inorganic and organic Se & Hg

organic Se & Hg (bioavailable and toxic)

anaerobic conditions microbial activity

inorganic Se & Hg

Lake Powell likely plays a key role in Hg and Se cycling and transport

Hg/Se cycling

Key Findings

· Mercury (Hg) and selenium (Se) concentrations are relatively high in the Colorado River food web throughout Grand Canyon.

· Hg and Se in organic matter, algae, invertebrates, and fish exceed protective thresholds for fish, wildlife, and humans.

· Hg concentrations were low in rainbow trout in Glen Canyon, so human health risks associated with this popular sport fishery are low.

· However, Hg in trout was higher downstream. Some of these areas are targeted for trout removal, which are provided for human consumption.

· Managing exposure risks in Grand Canyon will be challenging, because sources of Hg and Se are beyond Park boundaries.

Acknowledgements

· Funding

· US EPA

· USGS