The Recent Status and Trends of Two Georgia Marsh Dieback Sites
Caroline McFarlin, Matt Ogburn, and Merryl Alber, Department of Marine Sciences, The University of Georgia
Results
Abstract
1
35
Healthy
Melon Bluff
Melon Bluff
Healthy
Dieback
Dieback
35
35
30
30
Melon Bluff
Melon Bluff
1.4
1.4
1.2
1.2
Isle
of Wight
Isle of
Wight
Rd. Rd.
Isle of Wight Rd.
1.4
Isle of Wight Rd.
0.5
15
ND
2
ND
1
ND
-0.5
0.8
-1
25
20
Littoraria per m
20
0
2
Littoraria per m
25
1.2
Elevation Change (cm)
30
15
25
1
1
20
0.8
0.8
15
0.6
0.6
10
0.4
0.6
5
10
-1.5
10
-2
0.2
ND
ND
ND
0
160
Crab holes per m2
Salinity (psu)
ND
ND
ND
180
0
0
30
25
20
15
Isle of Wight
Road
0.2
ND
0
200
35
0
0.2
ND
0
5
40
5
0.4
ND
0.4
140
120
100
80
60
10
40
5
20
Isle of Wight Rd, June 2005
ND
ND
Jun-05
Mar-05
Dec-04
Sep-04
Jun-04
Mar-04
Jan-04
Sep-03
Jun-03
Jun-05
Mar-05
Dec-04
Sep-04
Jun-04
Mar-04
Jan-04
30
•At Melon Bluff, there were significantly more Littoraria
Melon Bluff
in healthy as compared to dieback areas (p < 0.01). At
Isle of Wight (Juncus site) fewer snails were present
(note scale change), but when observed they were
associated with healthy areas.
25
Geukensia per m2
Isle of Wight Road
Sep-03
Jun-03
Jun-05
Mar-05
Sep-04
Dec-04
22.1±5.7 at Melon Bluff and
22.0±6.6 and Isle of Wight Road;
pH was 6.7±0.2 and 6.2±0.4,
respectively. There were no
differences between healthy and
dieback areas
Isle of Wight Rd, June 2004
ND
0
•Mean soil temperature was
between healthy and dieback areas
in salinity. However, salinity at
Melon Bluff showed a decrease
between June 2004 and June 2005.
This trend was not as apparent at
Isle of Wight, although salinities did
decrease in June 2005.
showed a decrease over
time at both sites, with
greater losses in dieback
as compared to healthy
areas.
ND
Jun-04
Sep-03
•There were no overall differences
•Sediment elevation
ND
Mar-04
ND
Jun-03
June-05
Mar-05
Sept-04
June-04
Mar-04
Jan-04
Sept-03
Jun-03
ND
Jan-04
ND
0
Dec-04
Melon Bluff
Physical Setting
2
Littoraria per m
In 2001 and 2002, Georgia experienced the largest dieback of
salt marsh vegetation ever recorded, with ≥ 800 ha affected.
Although the ultimate cause of the dieback was never established, the
event has been linked to a severe drought. Two dieback sites located
in Liberty County, GA have been monitored quarterly since 2003, one
with extensive Spartina alterniflora dieback and a second with
extensive Juncus roemerianus dieback. There were no consistent
differences in porewater chemistry between healthy and dieback areas
at either site, but there were increased densities of crab burrows in
dieback as compared to healthy areas. Snail abundance was
extremely low in the Juncus site whereas at the Spartina site densities
were elevated in healthy areas. Both sites have exhibited signs of regrowth since March 2004. In the Spartina site plant density in the
dieback transects increased from 0 stems/m2 in March 2004 to 18  36
stems/m2 in June 2005. Over this same period average soil salinity
decreased from 22.6  5.8 to 13.3  3. At the Juncus site, re-growth
has been more substantial, with densities in dieback transects
increasing from 88  111 to 670  611 since March 2004, but salinities
were variable and did not show consistent trends.
Fauna
20
•The number of crab holes tended to be higher in
15
dieback as compared to healthy areas. This trend was
significant at the Isle of Wight Road site (p<0.05).
10
Melon Bluff
5
•Geukensia density was higher in dieback areas at
ND
Jun-05
Mar-05
Dec-04
Sep-04
Jun-04
Mar-04
Jan-04
JuncusDominated
Sep-03
SpartinaDominated
Jun-03
0
Melon Bluff as compared to healthy areas. No mussels
were ever observed in the Isle of Wight (Juncus) site.
Vegetation
Healthy
400
35
Melon Bluff
Melon Bluff
Dieback
1.4
1200
1.2
1000
1
800
•Stem densities were higher in
healthy versus dieback areas at
both sites throughout the
monitoring period. T-tests
comparing values averaged across
all healthy plots within a site were
significantly greater than those
from dieback plots: Spartina at
Melon Bluff (p < 0.0001); Juncus at
Isle of Wight (p < 0.01).
Isle of Wight Rd.
Isle of Wight Rd.
350
0.8
200
150
0.6
400
100
0
ND
9
8
ND
7
6
ND
5
0
ND
120
4
8
ND
7
6
5
4
3
2
120
9
0.2
0
3
ND
200
2
0.4
50
1
10
5
600
0
100
100
80
80
60
60
40
40
20
20
ND
ND
ND
Jun-05
Mar-05
Dec-04
Sep-04
Jun-04
Mar-04
Jan-04
Sep-03
Jun-05
Mar-05
Dec-04
Sep-04
Jun-04
Mar-04
Jan-04
0
Sep-03
0
Jun-03
15
250
1
Plot Monitoring Protocol:
•Physical Setting
•Surface elevation (marked PVC pipe, cm)
•Soil temperature (°C)
•Salinity (refractometer, psu)
•pH (handheld probe)
•Marsh vegetation
•Stem density (living, no./m2)
•Height of the 5 tallest plants (cm)
•Faunal Density
•Snails (Littoraria irrorata) >10 mm (no./m2)
•Fiddler crabs (Uca) (using crab holes >5 mm as a proxy)
•Mussels (Geukensia demissa) (no./m2)
•Site and Plot Observations:
•Distance to healthy marsh (m)
•Soil firmness, smell
•Vegetation color, health
•Dead fauna
•Other plant and animal species
20
300
Jun-03
Site Setup: plots (0.5-m x 0.5-m) were spaced 10 m apart along 3
healthy and 3 dieback transects (3 plots/transect = 18 plots/site)
25
Plant Height (cm)
Methods
2
Littoraria per m
2
Number of Stems per m
30
•The heights of the 5 tallest plants,
when present, were greater in
healthy versus dieback areas, with
one exception (Melon Bluff, June
2005). T-tests comparing values
averaged across all healthy plots
within a site were significantly
greater than those from dieback
plots: Spartina at Melon Bluff (p <
0.05); Juncus at Isle of Wight (p <
0.0001).
•Between June 2004 and June
2005, Juncus density and heights at
Isle of Wight showed significant
increases in both healthy (p <
0.001, p < 0.0001, respectively)
and dieback plots (p < 0.05, p <
0.01, respectively). No significant
differences were observed for
Spartina at Melon Bluff.
Conclusions
•After 2 years, both sites monitored for this project still showed
significant differences between healthy and dieback areas. In
comparison to healthy areas, dieback areas had lost more sediment,
had lower stem density and shorter plants. In terms of fauna,
dieback areas had lower snail densities, higher densities of crab
holes, and more mussels (when present).
•There were no apparent differences in terms of pore water salinity,
pH or temperature between healthy and dieback areas within each
site.
•Long-term trends are difficult to discern, but in the Juncusdominated site (Isle of Wight), plants were significantly denser and
taller in June 2005 as compared to June 2004. These trends were not
observed in the Spartina-dominated site (Melon Bluff).
•Monitoring is scheduled to continue on an annual basis (during the
fall).
Acknowledgments
This study was supported by the Georgia Coastal
Management Program (NOAA Award NA170Z2331), the
Georgia Coastal Ecosystems Long Term Ecological
Project (NSF Award OCE 99-82133), the Georgia College
Sea Grant Program (NOAA Award NA06RG0029), and
the EPA (EPA Star Grant). We thank Jenny Fenton,
Janice Flory, Ben Maher, Chip McFarlin, Steven
O'Connell, Monica Watkins, and Susan White for help in
the field and the Devendorf family for hosting us at the
Melon Bluff Plantation and allowing access to field sites.