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Influences of Salinity Intrusion on Belowground Decomposition: Implications for Surface
Elevation Change
Camille L. Stagg1
Nicole Cormier1, Ken Krauss1, William Conner2, Don Cahoon3
1U.S. Geological Survey, National Wetlands Research Center, Lafayette, LA2Clemson University, Baruch Institute of Coastal Ecology and ForestScience, Georgetown, SC
3U.S. Geological Survey, Patuxent Wildlife Research Center, Beltsville, MD
Sea-level Rise
River Flow Nutrients
Plant Growth
Salinity
Biomass Accumulation
Soil Redox
Sedimentation
Temperature
Surface Elevation
Subsidence
Decomposition
Waccamaw River
Savannah River
2.6 (0.16) ppt
Upper LowerMiddle Marsh
Rive
r 1Ri
ver 2
Salinity Gradient
Depth
10 25 50
Roots and Rhizomes• Litterbags• Labile and refractory materials• Long-term = 1 year• Single exponential decay model: Y= ae-kt
Cellulose• Cotton Strips• Labile material only• Short-term ~ 14 days• %Tensile strength lost
Sea-level Rise
River Flow Nutrients
Plant Growth
Salinity
Biomass Accumulation
Soil Redox
Sedimentation
Temperature
Surface Elevation
Subsidence
Decomposition
Organic Matter
Composition
• 10 cm depth• April 2011-Ocotber 2011Temperature
• 10cm, 25cm 50 cm depth• October 2010, 2011Redox
• October 2010-2011, 60 cm well depthSalinity
• Root and Rhizomes, initial material• Lignin, Cellulose, Total Carbon, Total Nitrogen
Organic Matter Composition
Soil Depth (cm)
10 25 50
% M
ass
Rem
aini
ng
0
20
40
60
80
100P = 0.7609
A A A
Soil Depth (cm)
10 25 50
Red
ox (m
V)
-300
-250
-200
-150
-100
-50
0
P = 0.5768
CSTL day-1
2.0 2.5 3.0 3.5 4.0 4.5
Soi
l Dep
th (c
m)
0
10
20
30
40
50
P < 0.0001
-505
101520253035
01-
Oct
-201
0 2
6-O
ct-2
010
20-
Nov
-201
0 1
5-D
ec-2
010
09-
Jan-
2011
03-
Feb-
2011
28-
Feb-
2011
25-
Mar
-201
1 1
9-Ap
r-20
11 1
4-M
ay-2
011
08-
Jun-
2011
03-
Jul-2
011
28-
Jul-2
011
22-
Aug-
2011
16-
Sep-
2011
11-
Oct
-201
1
Waccamaw Marsh
-10
-5
0
5
10
15
20
25
30
01-
Oct
-201
0 1
3-O
ct-2
010
26-
Oct
-201
0 0
7-N
ov-2
010
20-
Nov
-201
0 0
2-D
ec-2
010
15-
Dec
-201
0 2
7-D
ec-2
010
09-
Jan-
2011
21-
Jan-
2011
03-
Feb-
2011
15-
Feb-
2011
28-
Feb-
2011
12-
Mar
-201
1 2
5-M
ar-2
011
06-
Apr-
2011
19-
Apr-
2011
Waccamaw Lower
-10
-5
0
5
10
15
20
01-
Oct
-201
0 2
4-O
ct-2
010
16-
Nov
-201
0 1
0-D
ec-2
010
02-
Jan-
2011
25-
Jan-
2011
18-
Feb-
2011
13-
Mar
-201
1 0
5-Ap
r-20
11 2
9-Ap
r-20
11 2
2-M
ay-2
011
14-
Jun-
2011
08-
Jul-2
011
31-
Jul-2
011
23-
Aug-
2011
16-
Sep-
2011
09-
Oct
-201
1
Waccamaw Upper
-15-10-505
1015202530
01-
Oct
-201
0 2
3-O
ct-2
010
14-
Nov
-201
0 0
6-D
ec-2
010
28-
Dec
-201
0 1
9-Ja
n-20
11 1
0-Fe
b-20
11 0
4-M
ar-2
011
26-
Mar
-201
1 1
7-Ap
r-20
11 0
9-M
ay-2
011
31-
May
-201
1 2
2-Ju
n-20
11 1
4-Ju
l-201
1 0
5-Au
g-20
11 2
7-Au
g-20
11 1
8-Se
p-20
11 1
0-O
ct-2
011
Waccamaw Middle
Time (Days)
0 100 200 300 400
% M
ass
Rem
aini
ng
60
70
80
90
100
110
UpperMiddleLowerMarsh
P<0.0001
P=0.0203
AA
A
B
Landscape Salinity Gradient
Upper Middle Lower Marsh
% M
ass
Rem
aini
ng
0
20
40
60
80
100
Landscape Salinity Gradient
Upper Middle Lower Marsh
Sal
inity
(ppt
)
0
1
2
3
4
P < 0.0001
SalinityA
B
C
D
Landscape Salinity Gradient
Upper Middle Lower Marsh
Soi
l Tem
pera
ture
( C
)
0
5
10
15
20
25
30
35
P = 0.0856
Soil Temperature
Landscape Salinity Gradient
Upper Middle Lower Marsh
Red
ox (m
V)
-300
-250
-200
-150
-100
-50
0
Redox
P = 0.0663
Salinity (ppt)
0 1 2 3 4 5
% M
ass
Rem
aini
ng
40
50
60
70
80
90
100
r = 0.38309P = 0.1430
Pearson Product-Moment Correlations
Redox Potential (mV)
Temperature(°C)
PorewaterSalinity (ppt)
% Mass Remaining r = -0.18041P = 0.5037
r = 0.47682P = 0.2322
r = 0.38309P = 0.1430
P=0.0203
AA
A
B
Landscape Salinity Gradient
Upper Middle Lower Marsh
% M
ass
Rem
aini
ng
0
20
40
60
80
100
> 3ppt
Site Lignin Cellulose Carbon : Nitrogen Lignin : Nitrogen
Upper 35.1 (3.9) a 20.3 (0.9) bc 44.5 (1.2) bc 35.8 (1.5) b
Middle 34.9 (0.6) a 22.4 (0.9) ab 48.7 (3.8) b 38.6 (2.9) a
Lower 26.5 (6.0) b 18.0 (1.7) c 41.1 (0.9) c 29.0 (3.4) d
Marsh 22.3 (1.3) b 24.2 (0.5) a 61.6 (2.9) a 32.0 (3.1) c
Different letters indicate significant differences between site/salinity treatments
Landscape Salinity Gradient
Upper Middle Lower Marsh
CS
TL d
ay-1
0
1
2
3
4
5
C
B
A
B
P < 0.0001
• Sulfate Introduction – Stimulated respiration– C- mineralization: Weston et al., 2011; Weston et al., 2006
• Nitrogen Availability– Salinity-induced plant mortality or stress with subsequent nutrient
pulse, or lower Nitrogen uptake and increased Nitrogen availability.
Pearson Product-Moment Correlations (n=120)
Total sulfur Conductivity
N mineralization flux(µmol m-2 d-1)
r = -0.088P = 0.338
r = -0.076P = 0.412
N turnover(d-1)
r = 0.017P = 0.852
r = 0.055P = 0.551
Noe et al., in review
Salinity (ppt)
0 1 2 3 4 5
CS
TL d
ay-1
12
14
16
18
20
22
24
26
28
Pearson Product-Moment Correlations
Redox Potential (mV)
Temperature(°C)
PorewaterSalinity (ppt)
CSTL day-1 r = -0.03203P = 0.9063
r = 0.39566P = 0.3319
r = 0.08374P = 0.7578
r = 0.08374P = 0.7578
NutrientsPlant
Growth/Mortality
Salinity Decomposition+- +
+
Landscape Salinity Gradient
Upper Middle Lower Marsh
% M
ass
Rem
aini
ng
0
20
40
60
80
100
Landscape Salinity Gradient
Upper Middle Lower Marsh
CS
TL d
ay-1
0
1
2
3
4
5
CB
A
B
Refractory + Labile Labile
A A AB
> 3ppt
N
Primary Production
Decomposition
Landscape Salinity Gradient
Upper Middle Lower Marsh
Ele
vatio
n C
hang
e (c
m)
0
1
2
3
4
Accretion Surface Elevation Change
SLR 0.3 - 0.4 cm y-1
Time (year)
0.0 0.5 1.0 1.5 2.0
Sur
face
Ele
vatio
n C
hang
e (c
m)
-1
0
1
2
3
4
Upper MiddleLowerMarsh
P < 0.001
• Decomposition of refractory organic matter is limited when salinity exceeds 3ppt.
• There is not effect of salinity on decomposition of refractory material between 0-3ppt
• Decomposition of labile organic matter is stimulated in the degraded forest. Stimulation may be due to nutrient pulse/ increased nutrient availability resulting from salinity-induced plant mortality or stress.
• Decomposition of labile organic matter is limited in the marsh, either from adverse impacts of salinity on microbial activity or lack of nutrient availability.
• Marsh elevation is increasing and likely due to a combination of decreased organic matter decomposition and increased primary production.
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