CHRISTOPHER M. SWARZENSKI

UNITED STATES GEOLOGICAL SURVEY

LOUISIANA WATER SCIENCE CENTER BATON ROUGE

Extreme Climate Events and the Recurrent Sudden Dieback and Recovery of Salt Marshes in the Rapidly Subsiding Mississippi River Delta, Louisiana

Salt marshes in the Mississippi Delta in coastal Louisiana, rsl is around 1 cm per year

Map from Andrew Tweel, LSU

Mendelssohn and McKee. 1988. Spartina alterniflora die-back in Louisiana: Time-course investigation of soil waterlogging effects. Journal of Ecology 76: 509-521

“Non-acute” salt marsh dieback

Acute saltmarsh dieback

Dieback occurs quickly, from one growing season to next

Full recovery frequently occurs

Occurred in Gulf and Atlantic Coast marshes in 2000s, drought primary driver

Alber, et al. 2008. Salt marsh dieback; An overview of recent events in the US. Estuarine, Coastal and Shelf Science, 80: 1-11.

Acute salt marsh dieback

2000 2006

BACKGROUND

Timeline coastal Louisiana 1999-2009

CLIMATE

Exceptional drought (1999-2000, 2006)

Back to back hurricanes in 2005 and 2008

SALT MARSH DIEBACK

2000 (about 100,000 ha or 25%, widespread)

2009 (smaller area, regional distribution)

0.0

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MARSH SURFACE

MA

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S AVERAGE

DAILY HIGH

DAILY-AVERAGE WATER LEVEL

Range of marsh elevations with respect to local water levels

% T

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Seasonal marsh flooding, related to Gulf level

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Monthly mean sea level (light blue)

MSL

O N D J F M A M J J A S O N D J F M A M J J A S

Level in

feet

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-0.5

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1.0

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average 1999-2008

1999-2001

2007-2009

Gulf levels vary from year to year, with long stretches remaining higher or lower than average

Wa

ter

lev

el (

inch

es)

7/15/10 7/19/10 7/23/10 7/27/10 7/31/10

15

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35 Open water Marsh water

Microtidal flooding regime, daily flooding alternating with extended periods of drawdown

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Volume of free water greater in low elevation marshes

2000 DIEBACK

F I R S T N O T I C E D I N M A R C H / A P R I L , P O S S I B L E T H A T D I E B A C K O C C U R R E D A F T E R N E W G R O W T H F I R S T S T A R T E D

D I E B A C K L I N K E D T O D R O U G H T

O X I C S O I L S - > P H D R O P - > R E L E A S E O F M E T A L S T O T O X I C C O N C E N T R A T I O N S

McKee et al. 2004. Acute salt marsh dieback in the Mississippi River deltaic plain: a drought-induced phenomenon? Global Ecology and Biogeography 13(1) p.65-73

Dieback in interior areas Spartina alterniflora died back, Juncus roemerianus survived. Where both survived J. roemerianus taller than S. alt where both survived

2000 Dieback (widespread across elevation gradient)

(photo Karen Mckee, USGS)

Typical layout of study site

STUDY DESIGN developed to assess field conditions post-2000 dieback

- Locate paired interior dieback and surviving marshes (N=4) replicate high and low marshes - In field: compare relative elevations, soil salinity, drawdowns, specific yield - In lab: soil acidification potential, metal release

Comparisons at paired interior marshes

High B High A Low B Low A

Parameter live dead live dead live dead live dead

Relative Elevation (cm) + 3 + 5 +3 +3

Monthly Marsh flooding (%) 21 26 13 21 47 41 40 46

Maximum Drawdown (cm) 12 13.5 14 25 5 14 9 12

Specific Yield 0.03 0.08 0.03 0.03 0.09 0.10 0.18 0.17

Acidification Potential 2.6 2.8 2.9 3.2 n.s n.s 4.5 3.3

Average Soil

Salinity (ppt) 17.9 15.9 30.6 27.9 17.2 18.6 19.1 19.4

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0.3 Low A Low B

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n 2

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Patterns of drawdown at paired marshes

Low A Low B High A High B

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LIVE

DEAD

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Soil pore space volume during drawdowns

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ALUMINUM

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MANGANESE

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IRON

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Soil acidification potential and metal release

High marsh A

High marsh B

Low marsh A

Time Series of Soil Salinity in 10 cm increments (00-02)

1-10 cm

11-20 cm

21-30 cm

31-40 cm

41-50 cm

10

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60

SA

LIN

ITY

IN

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RT

S P

ER

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OU

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Surviving marsh Dieback marsh

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Depth interval

Drought as climate extreme

Key to survival was ability to maintain supply of water during periods of no marsh flooding

In one low elevation area dieback clearly related to soil acidification potential

In remaining three areas (high and low marsh) soil acidification and/or bound water combined with high soil salinity likely contributed to plant mortality

March 5, 2002 October 24, 2003

May 2006

Low Marsh A dieback site recovery; recovery by seedlings at all sites

F I R S T N O T I C E D I N F E B R U A R Y 2 0 0 9 , B E F O R E N E W G R O W T H

2009 Dieback

Dieback in interior areas S. alterniflora and Juncus roemerianus died back J. roemerianus no taller than S. alt where both survived

2009 dieback: limited to low elevation marsh

Hourly waterlevel at Grand Isle, August-October 2005 and 2008(Data from National Ocean Survey)

15-Aug-05

29-Aug-05

12-Sep-05

26-Sep-05

10-Oct-0

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A L

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2008

2005

Katrina

Gustav Ike

Rita

In 2005 hurricanes were spaced further apart and base water levels may have been a bit lower

Calculated % time flooded at indicated depths (cm)

>2.5 >7.5 >12.5 >17.5 >22.5 >27.5 >32.5 1 Aug- 31 Oct High marsh A

41 32 24 17 12 9 7 Low Marsh A 62 52 41 31 22 17 12 Sept 1-Oct 16 HM A 63 51 39 32 22 17 13

LM A 80 71 59 56 37 30 22

Patterns of dieback

Within both low marsh sites, areas at about 18-20 cm NAVD88 elevation died back; areas > 24 cm NAVD88 survived; measurements made after dieback occurred

Lake Felicity brown

1/1/09

7/1/09

1/1/10

7/1/10

1/1/11

7/1/11

1/1/12

# s

tem

s p

er

m2

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number of stems of S. alterniflora per m2 (average of four plots per site)

Lake Felicity green

1/1/09

7/1/09

1/1/10

7/1/10

1/1/11

7/1/11

1/1/12

# s

tem

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er

m2

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Bayou Sale brown

1/1/09

7/1/09

1/1/10

7/1/10

1/1/11

7/1/11

1/1/12

# s

tem

s p

er

m2

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300Bayou Sale green

1/1/09

7/1/09

1/1/10

7/1/10

1/1/11

7/1/11

1/1/12

# s

tem

s p

er

m2

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Stem density of S. alterniflora over time at plots established during 2000 dieback

Recovery at 2009 dieback sites

Storm surge as climate extreme

Dieback restricted to lower elevation marshes

Both S. alterniflora and J. roemerianus affected

Within a site, lowest elevation marshes affected

Wild cards – spacing of storm surge may play a role as may exact storm path

Re-growth 2009 to 2010 at Low marsh A

- D R O U G H T A F F E C T S M A R S H E S W I T H D I F F E R E N T E L E V A T I O N S E Q U A L L Y ; S T O R M S U R G E A F F E C T S L O W L Y I N G M A R S H E S

-C L I M A T E P E R T U R B A T I O N S D O N ’ T A F F E C T P L A N T S P E C I E S E Q U A L L Y

- R E G R O W T H T H R O U G H S E E D L I N G S ( S . A L T E R N I F L O R A )

- U N E X P E C T E D R E S I L I E N C E O F C O A S T A L L O U I S I A N A S A L T M A R S H E S T O C L I M A T E P E R T U R B A T I O N B E F O R E S E A L E V E L R I S E A C C E L E R A T E S

Summary

Healthy Die-Back

HIGH A HIGH B LOW A LOW B

2000 2006 2009 2011

- Tommy Michot, (ICEE, U. Louisiana Lafayette) - Richard Day (USGS-BRD) - Camille Stagg, USGS-BRD -Bob Gambrell (LSU)

MSL

O N D J F M A M J J A S O N D J F M A M J J A S

Level in

feet

-1.0

-0.5

0.0

0.5

1.0

1.5

average 1999-2008

1999-2001

2007-2009

Gulf levels vary from year to year, with long stretches remaining higher or lower than average