Caroline McFarlin, Matt Ogburn, and Merryl Alber, Department of Marine Sciences, The University of Georgia

ResultsResults

Physical SettingPhysical Setting

The Recent Status and Trends of Two Georgia Marsh Dieback SitesThe Recent Status and Trends of Two Georgia Marsh Dieback Sites

AbstractAbstract 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 re-growth 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.

Methods Methods 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)

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

Melon BluffMelon Bluff Isle of Wight Isle of Wight RoadRoad

Spartina-Spartina- DominatedDominated

ConclusionsConclusions•After 2 years, both sites monitored for this project still showed After 2 years, both sites monitored for this project still showed significant differences between healthy and dieback areas. In significant differences between healthy and dieback areas. In comparison to healthy areas, dieback areas had lost more sediment, comparison to healthy areas, dieback areas had lost more sediment, had lower stem density and shorter plants. In terms of fauna, had lower stem density and shorter plants. In terms of fauna, dieback areas had lower snail densities, higher densities of crab dieback areas had lower snail densities, higher densities of crab holes, and more mussels (when present). holes, and more mussels (when present).

•There were no apparent differences in terms of pore water salinity, There were no apparent differences in terms of pore water salinity, pH or temperature between healthy and dieback areas within each pH or temperature between healthy and dieback areas within each site.site.

•Long-term trends are difficult to discern, but in the Long-term trends are difficult to discern, but in the Juncus-Juncus-dominated site (Isle of Wight), plants were significantly denser and dominated site (Isle of Wight), plants were significantly denser and taller in June 2005 as compared to June 2004. These trends were not taller in June 2005 as compared to June 2004. These trends were not observed in the observed in the Spartina-Spartina-dominated site (Melon Bluff).dominated site (Melon Bluff).

•Monitoring is scheduled to continue on an annual basis (during the Monitoring is scheduled to continue on an annual basis (during the fall). fall).

Juncus-Juncus- DominatedDominated

AcknowledgmentsAcknowledgments

This study was supported by the Georgia Coastal This study was supported by the Georgia Coastal Management Program (NOAA Award NA170Z2331), the Management Program (NOAA Award NA170Z2331), the Georgia Coastal Ecosystems Long Term Ecological Georgia Coastal Ecosystems Long Term Ecological Project (NSF Award OCE 99-82133), the Georgia College Project (NSF Award OCE 99-82133), the Georgia College Sea Grant Program (NOAA Award NA06RG0029), and Sea Grant Program (NOAA Award NA06RG0029), and the EPA (EPA Star Grant). We thank Jenny Fenton, the EPA (EPA Star Grant). We thank Jenny Fenton, Janice Flory, Ben Maher, Chip McFarlin, Steven Janice Flory, Ben Maher, Chip McFarlin, Steven O'Connell, Monica Watkins, and Susan White for help in O'Connell, Monica Watkins, and Susan White for help in the field and the Devendorf family for hosting us at the the field and the Devendorf family for hosting us at the Melon Bluff Plantation and allowing access to field Melon Bluff Plantation and allowing access to field sites.sites.

•At Melon Bluff, there were significantly more At Melon Bluff, there were significantly more LittorariaLittoraria in healthy as compared to dieback areas (p < 0.01). At in healthy as compared to dieback areas (p < 0.01). At Isle of Wight (Isle of Wight (JuncusJuncus site) fewer snails were present site) fewer snails were present (note scale change), but when observed they were (note scale change), but when observed they were associated with healthy areas.associated with healthy areas.

•The number of crab holes tended to be higher in The number of crab holes tended to be higher in dieback as compared to healthy areas. This trend was dieback as compared to healthy areas. This trend was significant at the Isle of Wight Road site (p<0.05).significant at the Isle of Wight Road site (p<0.05).

•GeukensiaGeukensia density was higher in dieback areas at density was higher in dieback areas at Melon Bluff as compared to healthy areas. No mussels Melon Bluff as compared to healthy areas. No mussels were ever observed in the Isle of Wight (were ever observed in the Isle of Wight (JuncusJuncus) site. ) site.

FaunaFauna

Melon Bluff

0

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Littoraria p

er

m2

ND

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Jun-03

Sep-03

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Mar-04

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Cra

b h

ole

s p

er

m2

ND

Jun-03

Sep-03

Jan-04

Mar-04

Jun-04

Sep-04

Dec-04

Mar-05

Jun-05

ND ND

Isle of Wight Rd.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

ND ND

Melon Bluff

0

5

10

15

20

25

30

35

Littoraria

per

m2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Healthy Dieback

Melon Bluff

0

5

10

15

20

25

30

Jun-03

Sep-03

Jan-04

Mar-04

Jun-04

Sep-04

Dec-04

Mar-05

Jun-05

Geukensia

pe

r m

2

ND

Melon Bluff

Isle of Wight Road

VegetationVegetation

•Stem densities were higher in Stem densities were higher in healthy versus dieback areas at healthy versus dieback areas at both sites throughout the both sites throughout the monitoring period. T-tests monitoring period. T-tests comparing values averaged across comparing values averaged across all healthy plots within a site were all healthy plots within a site were significantly greater than those significantly greater than those from dieback plots: from dieback plots: SpartinaSpartina at at Melon Bluff (p < 0.0001); Melon Bluff (p < 0.0001); JuncusJuncus at at Isle of Wight (p < 0.01).Isle of Wight (p < 0.01).

•The heights of the 5 tallest plants, The heights of the 5 tallest plants, when present, were greater in when present, were greater in healthy versus dieback areas, with healthy versus dieback areas, with one exception (Melon Bluff, June one exception (Melon Bluff, June 2005). T-tests comparing values 2005). T-tests comparing values averaged across all healthy plots averaged across all healthy plots within a site were significantly within a site were significantly greater than those from dieback greater than those from dieback plots: plots: SpartinaSpartina at Melon Bluff (p < at Melon Bluff (p < 0.05); 0.05); JuncusJuncus at Isle of Wight (p < at Isle of Wight (p < 0.0001).0.0001).

•Between June 2004 and June 2005, Between June 2004 and June 2005, JuncusJuncus density and heights at Isle density and heights at Isle of Wight showed significant of Wight showed significant increases in both healthy (p < increases in both healthy (p < 0.001, p < 0.0001, respectively) 0.001, p < 0.0001, respectively) and dieback plots (p < 0.05, p < and dieback plots (p < 0.05, p < 0.01, respectively). No significant 0.01, respectively). No significant differences were observed for differences were observed for SpartinaSpartina at Melon Bluff. at Melon Bluff.

Nu

mb

er o

f S

tem

s p

er m

2P

lan

t H

eig

ht

(cm

)

Melon Bluff

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1 2 3 4 5 6 7 8 9

ND

Isle of Wight Rd.

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1 2 3 4 5 6 7 8 9

ND ND

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120

Jun-03

Sep-03

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Mar-04

Jun-04

Sep-04

Dec-04

Mar-05

Jun-05

ND0

20

40

60

80

100

120

Jun-03

Sep-03

Jan-04

Mar-04

Jun-04

Sep-04

Dec-04

Mar-05

Jun-05

ND ND

Melon Bluff

0

5

10

15

20

25

30

35

Littoraria

per

m2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Healthy Dieback

Isle of Wight Rd, June 2004Isle of Wight Rd, June 2004 Isle of Wight Rd, June 2005Isle of Wight Rd, June 2005

•Sediment elevation Sediment elevation showed a decrease over showed a decrease over time at both sites, with time at both sites, with greater losses in dieback greater losses in dieback as compared to healthy as compared to healthy areas.areas.

•There were no overall differences There were no overall differences between healthy and dieback areas between healthy and dieback areas in salinity. However, salinity at in salinity. However, salinity at Melon Bluff showed a decrease Melon Bluff showed a decrease between June 2004 and June 2005. between June 2004 and June 2005. This trend was not as apparent at This trend was not as apparent at Isle of Wight, although salinities did Isle of Wight, although salinities did decrease in June 2005. decrease in June 2005.

•Mean soil temperature was Mean soil temperature was 22.122.1±5.7 at ±5.7 at Melon Bluff and Melon Bluff and 22.022.0±6.6±6.6 and Isle of Wight Road and Isle of Wight Road; ; pH was 6.7±0.2 and 6.2±0.4, pH was 6.7±0.2 and 6.2±0.4, respectively. There were no respectively. There were no differences between healthy and differences between healthy and dieback areasdieback areas

Isle of Wight Rd.

ND ND

Melon Bluff

-2

-1.5

-1

-0.5

0

0.5

1

ND

Jun-03

Sep-03

Jan-04

Mar-04

Jun-04

Dec-04

Sep-04

Mar-05

Jun-05

ND ND ND ND0

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25

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40

Jun-03

Sept-03

Jan-04

Mar-04

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Sept-04

Dec-04

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June-05

ND

Sal

inity

(psu

)E

leva

tion

Cha

nge

(cm

)

Melon Bluff

0

5

10

15

20

25

30

35

Littoraria

per

m2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Healthy Dieback