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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