POREWATER CHEMISTRY AND QUALITY OF ORGANIC MATTER IN SOILS OF COASTAL LOUISIANA MARSHES

Christopher M. Swarzenski, Louisiana Water Science Center, Baton Rouge

TOPICS

BACKGROUND

POREWATER AND SOIL CHARACTERIZATION OF HEALTHY PEAT-BASED MARSHES

RESPONSE TO RIVER WATER INFLUX

POREWATER RESPONSE TO EXTREME CLIMATE EVENTS

• ONE WAY TO EXPRESS SOIL ORGANIC MATTER QUALITY

Rain waterRiver water

Occurrence of organic-rich marshes in the Louisiana Delta Plain

from Chabreck, Brubacher and others

COASTAL LOUISIANA MARSH SOILS

- in Louisiana, as elsewhere, marsh soils rely on organic matter to add volume and keep pace with relative sea level rise

-- accrete about 175-250 g C m2 y-1

- accretion rates (~ 0.4-1 cm-1)

- sulfate: influences humification of soil organic matter

TOPICS

BACKGROUND

POREWATER AND SOIL CHARACTERIZATION OF HEALTHY PEAT-BASED MARSHES

RESPONSE TO RIVER WATER INFLUX

POREWATER RESPONSE TO EXTREME CLIMATE EVENTS

Location of porewater sampling sites at Jean Lafitte National Historic Park

Increasing exposure to salt pulses

Salinity regime at JELA: interior and exposed marsh

interior site

exposed site

1/1/95 7/1/95 1/1/96 7/1/96 1/1/97 7/1/97 1/1/98

SA

LIN

ITY(

PS

U)

0

1

2

3

5 cm15 cm45 cm

1/1/95 7/1/95 1/1/96 7/1/96 1/1/97 7/1/97 1/1/98

SA

LIN

ITY(

PS

U)

0

1

2

3

Differential exposure to marine influence influential in Differential exposure to marine influence influential in controlling occurrence of different plant speciescontrolling occurrence of different plant species

Plant communityPlant community

S. patens/S. patens/S.americanusS.americanus

P. hemitomonP. hemitomon(non floating)(non floating)

P. hemitomonP. hemitomon(floating)(floating)

Eleocharis Eleocharis mixmix

Eleocharis Eleocharis dominantdominant

S. S. falcatafalcata

0.4 0.6 0.8 1.0 1.2 1.4

CHLORIDE

0.4 0.6 0.8 1.0 1.2 1.4

SULFIDE

02468

1012

CALCIUM TO MAGNESIUM RATIO

500

1000

1500

2000

2500

0

mg/

L

JELA: BARATARIA PRESERVE

Averaged porewater concentrations (5,15 and 45 cm depth, 2000-2002)

--average S

mg/L0 2 4 6 8 10

average DOC

mg/L0 20 40 60

average pH

Units5.0 5.5 6.0 6.5 7.0

Incr

easi

ng e

xpos

ure

to s

alt p

ulse

SagittariaPanicum S.Patens(most exposed)

TOPICS

BACKGROUND

POREWATER AND SOIL CHARACTERIZATION OF HEALTHY PEAT-BASED MARSHES

RESPONSE TO RIVER WATER INFLUX

POREWATER RESPONSE TO EXTREME CLIMATE EVENTS

ONE PURPOSE OF A RIVER DIVERSION

BUILD MARSH SOILS

1) RESILIENT IN TERMS OF DAY-TO-DAY (TIDES) AND EXTREME EVENTS (STORM SURGE, DROUGHTS) -- focus on organic matter quality: decomposition, shear strength

2) ACCRETE IN BALANCE WITH APPARENT SEA LEVEL RISE- focus on organic matter quantity: accretion rates

Organic-rich marshes have experienced extensive conversion to open water and degraded marsh in Penchant basin, an area where influx of Mississippi river water predominates. Why?

Porewater sulfide and chloride in relation to calcium/magnesium ratio: comparison rain vsriver water

0.5 1.0 1.5 2.0 2.5 3.00.0

0.5

1.0

Sulfi

de in

mg/

l0.5 1.0 1.5 2.0 2.5 3.0

0

200

400

600

Chl

orid

e m

g/l

Calcium:magnesium ratioRiver waterRain water floating

Rain water non-floating

Porewater S and Fe

S-

0 10 20 30 40 50

mic

rom

olar

S

01020304050

Sulfide concentrations are much higher; Fe concentrations much lower in Penchant marshes

Probably iron-phosphate complexes are broken, and iron complexes with S- internal eutrophication, release of phosphate

Fe

0 10 20 30 40 50

mic

rom

olar

Fe

0

20

40

60

Penchant study

COMPARING NITROGEN AND SULFUR TO CARBON RATIOS IN SOILS FROM JEAN LAFITTE NATIONAL PARK AND PENCHANT BASIN

Sulfur:Carbon

0.000.01

0.020.03

0.040.05

0.060.07

-100

-80

-60

-40

-20

0

Barataria Preserve Panicum hemitomon Penchant Panicum hemitomon

Nitrogen:Carbon

0.04 0.05 0.06 0.07

DEP

TH IN

CM

-100

-80

-60

-40

-20

0

Soil Quality: with long-term (30+ years) river water influx decomposition appears enhanced (same plant community, Panicum hemitomon)

River water Rain water- No difference in year-end standing biomass

- No difference in accretion rates

BUT:- Soil is much more decomposed

- links to river water include sulfate, nitrate, alkalinity

Swarzenski et al (2008), Biogeochemistry

Marshes at outfall and east control

Marshes on the east side of Delacroix road survived the storm surge fairly intact. The east side is isolated from river influx.

Marshes on the west side of Delacroix road were picked apart, leaving only scattered remnants. These marshes have been in the diversion outfall path since 1992.

Caernarvon study

POST KARINA, SOILS IN AREA RECEIVING RIVER WATER EXHIBITED DIFFEREING POREWATER RESPONSE: OXIDATION OF FeS?

POREWATER SULFATE/CHLORIDE

Chloride in mg/l0 1000 2000 3000 4000 5000

Sul

fate

in m

g/l

0

500

1000

1500

2000River subsidy sulfate values are higher and spread over a larger range relative to chloride compared with the two control areas.

Caernarvon study

TOPICS

BACKGROUND

POREWATER AND SOIL CHARACTERIZATION OF HEALTHY PEAT-BASED MARSHES

RESPONSE TO RIVER WATER INFLUX

POREWATER RESPONSE TO EXTREME CLIMATE EVENTS

In area with controlled river influx P. HEMITOMON MARSHES(average of four locations)

7/98 1/99 7/99 1/00 7/00 1/01 7/01 1/02 7/02 1/03 0

62.5

125M

ICR

OM

OLA

R S

0

1.9

3.8

5.8

7.7

9.6

11.5M

ICR

OM

OLA

R Fe

Fe at 45 cm

S-- at 5 cm

EXTREME DROUGHT

In reference area (without river influx)

LEV

EL

IN IN

CH

ES

10

20

30

40

50MARSH WATERMAT

SULF

IDE

MG

/L

0.0

0.5

1.0

1.5

MORONENFM6FMUNIT 4

1/1/1998

7/1/1998

1/1/1999

7/1/1999

1/1/2000

7/1/2000

1/1/2001

7/1/2001

1/1/2002

7/1/2002

1/1/2003

CH

LRO

IDE

IN M

G/L

0

500

1000

1500MORONENFM6FMUNIT 4

shift

EXTREME DROUGHT

SOIL QUALITY: EXTREMES BASED ON MARINE INFLUENCE

DROUGHT (NOV 2000)

DEP

TH

BELO

W M

AR

SH

IN

CEN

TIM

ETER

S0 2 4 6 8 10

-80

-60

-40

-20

0

AVERAGE(1995-1999)

SALINITY IN PSU0 2 4 6 8 10

-80

-60

-40

-20

0

POST RITA

POST KATRINA

P. hemitomon

S. patens

JELA: BARATARIA PRESERVE

Interior marsh water-level fluctuations; note impounded condition with occasional short drawdowns, and long periods of inundation

M o ron e (s ta rt Ja n 98 , e n d S e p 0 2 )no n -flo a tin g P . h e m ito m on m a rsh

1 /1 /1 998 7 /1 /199 8 1 /1 /1 999 7 /1 /199 9 1 /1 /20 00 7 /1 /2 000 1 /1 /200 1 7 /1 /20 01 1 /1 /2 002 7 /1 /20 02 1 /1 /200 3

LEV

EL

IN C

EN

TIM

ETE

RS

2 0

4 0

6 0

8 0

10 0

12 0

14 0

Jean Lafitte P. hemitomon marsh (water level movement)

DATE

4/1/05 7/1/05 10/1/05 1/1/06 4/1/06 7/1/06 10/1/06 1/1/07 4/1/07 7/1/07 10/1/07 1/1/08 4/1/08 7/1/08 10/1/08 1/1/09 4/1/09

LEV

EL

IN IN

CH

ES

90

100

110

120

130

140

150

160

170

90

100

110

120

130

140

150

160

170

shallow watermarsh surfaceMercury sampling

RESEARCH NEEDS

Improved techniques to characterize organic matter quality

Understanding processes that control organic matter quality: linking porewaters to organic matter quality

Complete overlap with understanding mercury cycle