Coastal Marsh Dieback

Doug Atkinson

Marine Extension Service,The University of Georgia

What is Marsh Dieback?

• Marsh dieback is the phenomena in which intertidal marsh grass, usually Spartina alterniflora (smooth cord grass) but sometimes also Juncus roemerianus, thins or disappears.

• The disappearance sometimes involves the death of the root structures and sometimes not.

What is Marsh Dieback? (cont’d.)

• In some places, the marsh grass is still standing but is mostly or entirely brown.

• In other places, there is no above-ground vegetation remaining and the roots may be live, dead or no longer present.

• Dieback areas may be bare, may be composed completely of affected plants, or may be areas that have a mix of dieback plants and healthy plants.

Where Has Dieback Occurred?

• the entire Georgia coast.

• Louisiana and Texas

• South Carolina, North Carolina, Virginia, Long Island

• all five New England states

What is Being Done To Study Dieback in Georgia?

• Marsh Dieback Committee formed in 2002

• The committee established monitoring protocols in 2002.

• Georgia Coastal Resources Consortium (GCRC) is best source of information

Marsh Monitoring Program Sites in Georgia

•Chatham County– Isle of Hope, Ossabaw Island, Talahi Island

•Glynn County– Hwy 17

•Liberty County– Isle of Wight Road, Melon Bluff Plantation

•Liberty/Bryan County– Jerico River area

•McIntosh County– Sapelo Island

Some Study Results

• In one study, researchers (Ogburn and Alber, 2003) transplanted the two dieback species into dieback areas.

• They monitored the sites for 6 months for plant height, stem density, porewater ammonium, and the soil characteristics of reduction potential, pH and salinity.

• Transplant survival was nearly 100%. • Results suggested that the cause of the dieback

was no longer present at the time of the study and that transplanting is a possibility for restoring affected areas.

Some Study Results (cont’d.)

• A study in SW Lousiana looked at ecological and genetic measures to compare sites in their dieback stage and to their successive 'recovered' stages.

• The study determined dieback did not affect genetic diversity.

• It also determined that in all study sites, seedling recruitment contributed to recovery and in some sites the survival of below-ground plant structures also contributed to rapid recovery.

• (This study was forthright in declaring that the Louisiana dieback was an apparent response to a prolonged and severe drought.)

Here is what part of the Jerico River dieback site looks like on an oblique photo....

Some Study Results (cont’d.)

• A 2-year study (McFarlin, Ogburn, Alber, 2005) looked at two dieback sites, one with extensive Spartina alterniflora and one with extensive Juncus roemerianus.

• Both sites experienced regrowth, but both still showed significant differences between healthy and dieback areas.

• Dieback areas had lost more sediment, had lower snail densities, had higher densities of crab holes, and had more mussels (than healthy sites) and the plants at those areas had lower stem densities and were shorter.

• The regrowth was progressing faster in the Juncus site than the Spartina site.

What Does Marsh Dieback Look Like?

Here is what the same Jerico River site looks like Here is what the same Jerico River site looks like on an aerial photo....on an aerial photo....

Here is an oblique shot of a dieback area on Sapelo Island....

Here is the same area on the 02/03 aerial photography....

What is the Marine Extension Service's Involvement

with Studying Marsh Dieback in Georgia?

MAREX is working to create an inventory of marsh dieback for the

entire Georgia coast.• We have coastwide aerial photography for

2002/2003. As we map the dieback using the 02/03 aerial photography, we will be mapping the dieback for a time period soon after it was at its worst.

• Also, we have acquired coastwide aerial photography for 2005. We're experimenting with using the 02/03 aerial photography to assist us with mapping the dieback from the 2005 aerial photography.

Here is a 2005 aerial photo shot of the same area on Sapelo Island, that we saw on 02/03 photography....

How Are We Doing the Mapping?

• We could hire technicians to delineate the dieback polygons manually (on-screen digitizing).

• But this would be time consuming. • And it would incur a great deal of human

error.

• Instead we are using software to do the mapping for us.

How Does the Software Do the Mapping?

• We provide the software with a training set.

• A training set is a collection of dieback areas (polygons) that have been mapped correctly (digitized) by us.

• Then, using the training set, the software searches the photography, looks for areas that are spectrally similar to the training set and maps the rest of the dieback.

Where Does the Training Set Come From?

• We have gathered a collection of oblique photographs of marsh dieback that were shot at the time of our aerial photography.

• We examine the obliques, compare them to the aerial photography, and then manually digitize the dieback against the aerials.

What Is The Software and How Does It Work?

• Definiens Professional, by the German company Definiens

• The process of using software to map something (such as dieoff) automatically is called ‘feature extraction’

Two Steps to Feature Extraction using Definiens Professional

• Segmentation

• Classification

Segmentation

• The software 'examines' the entire aerial photograph and then divides the entire map area into polygons or 'segments'.

• The segmentation process uses certain parameters that are controlled by the software user:– scale parameter– shape/color ratio– compactness/smoothness ratio

• The results of the segmentation are visually compared to the original image to determine whether to proceed with the classification step

Classification

• Classification is the process of grouping the segments into similar categories

• The training set is used on the segmentation result to classify the original image

What Kind of Results Have We Been Getting?

• Our initial accuracy assessment, in a small test area in the 02/03 photography, has yielded an overall accuracy of 91%.

• We are planning to switch to a different method of accuracy assessment (stratified random sampling) which will not yield such a high accuracy.

• Also, the success could be lower when we get to the point where we're doing the extraction for the entire coastal area.

APPENDIX

What is the Geographic Extent of the 2002/2003

Aerial Photography?

Geographic Extent of the 2002/2003

Aerial Photography

Why Does the Photography Look Different or Inconsistent?

• It's because the some of the photography was shot in December 2002…

• …and some of it was shot in December 2003.

What is the Distribution of the Oblique Photographs?

• We have 161 oblique photographs....

What is the Geographic Extent of the 2005 Aerial Photography?

Are the two set of aerial photographs comparable in terms of quality?

(quality = resolution)

• Somewhat.

• The resolution of the 02/03 photography ranges from 0.6 meters to 1 meter.

• The resolution of the 2005 photography is 2 meters.

• Here is the pier and park in the village on St. Simon's Island…..

On this shot from 2002, each pixel represents 0.8 meters....

… and on this shot from 2005, each pixel represents 2 meters.

• Here are the shots we saw earlier of an area on Sapelo Island….

On this image from 2003, each pixel represents 1 meter....

… and on this image from 2005, each pixel represents 2 meters.