Evaluating oil spill effects and restoration potential of Alabama salt marshes using

experimental wetlands

Thomas Hess and Christopher J. AndersonSchool of Forestry and Wildlife Sciences

Auburn University

Alabama Water Resource Conference5 September 2013

2010 Deepwater Horizon Oil Spill

• ~4.5 million barrels of oil spilled in May 2010

• Impacted coastal areas without a history of oil spills from petroleum production

• Some exposure to Alabama salt marshes

2011 Mesocosm Research GoalsResearch Goals:

Determine how Juncus roemerianus marshes responds to dose and weathered condition of oil

2011 Mesocosm Methods• 32 wetland mesocosms were developed

using Juncus sod and designed to mimic tides • 3 dose treatments– Low (6 L /m2)– Medium (12 L /m2)– High (24 L /m2)

• 3 weathering treatments– None (full strength)– 3 days– 3 weeks

• Oil was applied to wetland mesocosms in July 2011

2011 Mesocosm Methods

Series10.0

10.0

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50.0

60.0

Low Med HighTP

H (m

g g-

1 dr

y so

il)

a

b

c

July 16 Sep 1Aug 4

2011 Mesocosm Results

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160

7/30/2011 8/16/2011 9/27/2011

(2 wks post oil) (4 wks post oil) (10 wks post oil)

% st

ems a

live

(rel

. to

June

cou

nt)

Cont

Low

Med

High

Mean (±SE) percent no. of live stems compared to pre-oil count

a

aa

b

a a

bb

c

b

bcc

2011 Mesocosm ResultsStem survival (Dose)

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7/30/2011 8/16/2011 9/27/2011

(2 wks post oil) (4 wks post oil) (10 wks post oil)

% st

ems a

live

(rel

. to

June

cou

nt)

Cont3W3DFS

Mean (±SE) percent no. of live stems compared to pre-oil count

a

a a

bb b

b b

bb b

b

2011 Mesocosm ResultsStem survival (Weathering)

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120

6/29/2011 7/30/2011 8/16/2011 9/27/2011

(pre oil) (2 wks post oil) (4 wks post oil) (10 wks post oil)

Phot

osyn

thes

is ra

te (%

con

trol

)

Low

Med

High

Mean (±SE) percent photosynthesis rate compared to control

a a aa

bb

NS b

a

ab

2011 Mesocosm ResultsPhotosynthetic rate

2012 Microcosm Research GoalsResearch Goals:

Determine how amenable salt grass (Distichlis spicata) would be for remediation of oiled marshes.

2012 Microcosm Project• Continuation of the mesocosm

study aimed at determining the restoration potential of salt grass (Distichlis spicata) on oiled marshes.

• Potential bioremediation:

• Improved degradation of subsurface oil through root aeration of soil.

• Reducing coastal erosion by re-establishing a root matrix.

2012 Microcosm Methods• 84 marsh plugs from the

2011 mesocosm experiment

• Used 2011 dosage treatments:– Control– Low – Medium – High

• Hoses and drip irrigation valves used to recreate tidal fluctuations

2012 Microcosm Methods• Planted- September 4, 2012• Half of the pots were

fertilized- September 18, 2012• Pulsed with 50 gallons of

brackish water two to three times a week

• Stem counts and heights were taken once every three weeks• Final plant heights and

biomass measured- December 17, 2012

Fig. 6

Total Petroleum Hydrocarbons (TPH)

Low Med High0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

TPH

(mg

g-1

dry

soil)

• Average TPH concentration for microcosms based on analyses in June 2012 (n=24) and December 2012 (n=18)

2012 Microcosm ResultsInfluence of oil on stem heights

27-Sep 11-Oct 7-Nov 17-Dec0

50

100

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450

500

Stem

Hei

ght (

mm

)

Non-Fertilized

27-Sep 11-Oct 7-Nov 17-Dec

Control Low Medium High

Fertilized

2012 Microcosm ResultsInfluence of oil on stem counts

27-Sep 11-Oct 7-Nov 17-Dec0

5

10

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25

30

35

40

45

Stem

Cou

nt

27-Sep 11-Oct 7-Nov 17-Dec

Control Low Medium High

FertilizedNon-Fertilized

2012 Microcosm ResultsAboveground plant biomass

Cont Low Med High0.0

2.0

4.0

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Abov

egro

und

biom

ass (

g)

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16.0

Abov

egro

und

biom

ass (

g)

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a

bb

b

Non-Fertilized Fertilized

2012 Microcosm ResultsFinal plant biomass

Cont Low Med High0.0

2.0

4.0

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16.0

Tota

l bio

mas

s (g)

Cont Low Med High0.0

2.0

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16.0

Tota

l bio

mas

s (g)

FertilizedNon-Fertilized

a

b

abab

NS

n=8n=8 n=8n=4

Summary

2011 Mesocosm Study• Oil had a negative effect on

stem survival – High dose wetlands had the most

rapid decline in survivorship • Weathering seemed to have

little effect on Juncus

• Oil exposure had a negative effect on plant photosynthetic rates– Four weeks after application

Summary 2012 Microcosm Study• Soil TPH was substantially

lower than concentrations in the 2011 study

• Combination of lower soil TPH, and fertilizer produced the most grass stems

• Control microcosms tended to produce greater below ground biomass

Questions

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6/29/2011 7/30/2011 8/16/2011 9/27/2011

(pre oil) (2 wks post oil) (4 wks post oil) (10 wks post oil)

CO2

upta

ke ra

te (u

mol

CO 2

s-1

)

ContLowMedHigh

Mean (±SE) CO2 uptake rate per mesocosm

a

bb

bNS

bbc

c

a a

b

c c

2011 Mesocosm ResultsCO2 uptake rate

Cont Low Med High0.0

2.0

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Abov

egro

und

biom

ass (

g)

Cont Low Med High0.0

2.0

4.0

6.0

8.0

10.0

12.0

Belo

wgr

ound

bio

mas

s (g)

2012 Microcosm ResultsFinal plant biomass

Cont Low Med High0.0

0.1

0.2

0.3

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0.5

0.6

0.7

0.8R:

S ra

tio

2012 Microcosm ResultsRoot to Shoot Ratio