Saltwater intrusion alters nitrogen and carbon export from a restored coastal plain wetland

(North Carolina, USA)

Marcelo Ardón1, Emily S. Bernhardt2, Ashley Helton2, Amy Burgin3, Robert Payn4, and Geoffrey Poole4

1. Department of Biology, East Carolina University, Greenville NC, USA 2. Biology Department, Duke University, Durham NC, USA 3. School of Natural Resources, University of Nebraska-Lincoln NE, USA 4. Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT, USA

Wetland restoration

Agriculture

Development

Restoration

Carter 1975 Science

Sea level rise

Climate driven changes in hydrology

How do drought and saltwater intrusion alter carbon and nitrogen retention in a coastal plain freshwater restored

wetland?

Timberlake Restoration Project

• Privately owned 1000ha mitigation bank • Focus 440ha agricultural field (formerly pumped) • Two constrained inflows – single outflow • Surrounded by preservation wetlands • <5 m range in surface elevation • Freshwater with wind-driven tides & bidirectional flow

OUTFLOW

Mass balance

MIDPOINT 2 INFLOWS

Water budgets

Inflows

Inflows

2/07 8/07 2/08 8/08 2/09 8/09 2/10 8/10 2/11 8/11 Dai

ly d

isch

arge

(m3 d

ay-1

)

-40000

-20000

0

20000

40000

InflowPump station

Outflow

2/07 8/07 2/08 8/08 2/09 8/09 2/10 8/10 2/11 8/11

Dai

ly d

isch

arge

(m3 d

ay-1

)

-200000

20000400006000080000

100000

Rainfall

Date

2/07 8/07 2/08 8/08 2/09 8/09 2/10 8/10 2/11 8/11

Rai

nfal

l (m

m)

0

50

100

150

200

Ardón et al. 2010 Ecosystems

3/07 9/07 3/08 9/08 3/09 9/09 3/10 9/10 3/11 9/11

Wat

er e

leva

tion

(m)

-0.8

-0.4

0.0

0.4

0.8

1.2

Con

duct

ivity

(mS/

cm3 )

0

6

12

Water elevationInflow MidpointOutflow

Drought-induced saltwater intrusion 5.0

Outflow

Midpoint Inflows SWI

Cl- concentrations are higher at the soil surface

Transect 1

Depth (cm)

20 40 60 80 100 120

Cl (

mg/

L)

0

500

1000

1500

Transect 3

Depth (cm)

20 40 60 80 100 120

Cl (

mg/

L)

0

50

100

150

200

250

300

Outflow

Cl (mg/L)

0 1000 2000 3000 4000

SO4

(mg/

L)

0

100

200

300

400

500

600

Midpoint

Cl (mg/L)

0 1000 2000 3000 40000

100

200

300

400

500

600

Inflow

Cl (mg/L)

0 1000 2000 3000 40000

100

200

300

400

500

600

Cl- travels farther upstream than SO4

R2=0.89 slope= 0.10

R2=0.81 slope= 0.04

R2=0.24 slope= 0.02

oxic anoxic

SO42-

OC

CO2

H2S

CO2

CARBON NITROGEN SULFUR IRON PHOSPHORUS

Fe-PO43-

Fe3+ PO43-

Fe2+

Fe-S

N2, N2O

NO3- NH4

+,N2

Predictions

oxic anoxic

SO42-

OC H2S

CO2

CARBON SULFUR

POC

C+

Predictions DOC

oxic anoxic

SO42-

OC

CO2

H2S

CO2

NITROGEN SULFUR

N2, N2O

NO3- NH4

+,N2

Predictions

CARBON

DOC

NH4

C+

Budget year

2007 2008 2009 2010 2011

DO

C (k

g ha

-1 y

-1)

0

50

100

150

200

250InputsOutputs

Outflow

Date

2/07 8/07 2/08 8/08 2/09 8/09 2/10 8/10 2/11 8/11 2/12

DO

C (m

g/L)

0

10

20

30

40

50

60

70

80

Con

duct

ivity

(mS/

cm)

0

2

4

6

8

10

12DOCConductivity

Source of DOC DOC export with SWI

POC formation with increasing conductivity Floc yeah!

Conductivity (mS/cm)

0 2 4 6 8 10 12 14

POC

form

atio

n (%

initi

al D

OC

)

0

5

10

15

20

24º C30º C

+ Conductivity

2007 2008 2009 2010 2011

NH

4 (k

g ha

-1 y

-1)

0

2

4

6

8

10 2007 2008 2009 2010 2011

NO

3 (k

g ha

-1 y

-1)

0

2

4

6

8

10InputsOutputs

Budget year

2007 2008 2009 2010 2011

TDN

(kg

ha-1

y-1

)

0

5

10

15

20

NO3 sink

TDN sink

NH4 sink/source

[NH4] with Conductivity

Outflow

Date

2/07 8/07 2/08 8/08 2/09 8/09 2/10 8/10 2/11 8/11 2/12

NH

4 (m

g/L)

0

2

4

6

8

10

Con

duct

ivity

(mS/

cm)

0

2

4

6

8

10

12NH4

Conductivity

Outflow

1/07 7/07 1/08 7/08 1/09 7/09 1/10 7/10 1/11 7/11 1/12

NH

4 (k

g m

onth

-1)

0

50

100

150

200

250

300

Con

duct

ivity

(mS/

cm)

0

2

4

6

8

10

12NH4 Conductivity

Control (DI)

Sep Oct Nov Dec

Cl (

mg/

L)

0

1000

2000

3000

4000

DroughtFlooded

ASW with SO4

Sep Oct Nov Dec 0

1000

2000

3000

4000ASW without SO4

Sep Oct Nov Dec

Y D

ata

0

1000

2000

3000

4000SO4

Date

Sep Oct Nov Dec 0

1000

2000

3000

4000

Control (DI)

Sep Oct Nov Dec

SO4

(mg/

L)

0

100

200

300

400

DroughtFlooded

ASW with SO4

Sep Oct Nov Dec 0

100

200

300

400ASW without SO4

Sep Oct Nov Dec 0

100

200

300

400SO4

Date

Sep Oct Nov Dec 0

100

200

300

400

Manipulative Experiments Hydrology x Water chemistry

SW decreased DOC concentrations

Control (DI)

Sep Oct Nov Dec

DO

C (m

g/L)

0

20

40

60

80

100

120

DroughtFlooded

ASW with SO4

Sep Oct Nov Dec 0

20

40

60

80

100

120ASW without SO4

Date

Sep Oct Nov Dec 0

20

40

60

80

100

120SO4

Sep Oct Nov Dec 0

20

40

60

80

100

120

SWI with and without SO4 increase NH4

+ concentrations

Control (DI)

Sep Oct Nov Dec

NH

4 (m

g/L)

0

1

2

3

4

5

Drought

Flooded

ASW with SO4

Sep Oct Nov Dec 0

10

20

30

40ASW without SO4

Sep Oct Nov Dec 0

10

20

30

40

SO4

Date

Sep Oct Nov Dec 0

1

2

3

4

5

Predictions

• DOC decline • NH4 increase

Microcosm

Cl (mg/L)

0 500 1000 1500 2000 2500 3000 3500

NH

4 (

mg

/L)

0

5

10

15

20Field data

Cl (mg/L)

0 500 1000 1500 2000 2500 3000 3500

NH

4 (m

g/L)

0

1

2

3

4

5

Conclusions • Saltwater intrusion decreases DOC export and N

retention

• Saltwater intrusion can lead to NH4 release

• Caution for wetland restoration and hydrologic reconnection

• Important to understand both the biotic and

geochemical effects of saltwater intrusion

Acknowledgments • Great Dismal Swamp Mitigation Bank

• Thanks to: K.R. Balance, R. Bier, M. Burke, Bernhardt Lab, Doyle Lab, Jackson

Lab, Wright Lab, and Duke University Wetland Center

• External funding: GDSMB, EPA STAR, NC WRRI, NC EEP, DOE NICCR, NCALM, Lindbergh Foundation, NSF, and NSF Postdoc Fellowship

Rob Payn Ashley

Helton

Geoff Poole

Amy Burgin

Jen Morse

Marcelo Ardon