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Analysis of Plant Samples from 'Dead Marsh' Sites - A Pilot Study

PI: Chandra Franklin (Savannah State University, Savannah, GA, USA)

Support: Sea Grant College Program

Timeframe: 2003 - 2004

Project Overview:
The overall objectives of this project are to conduct relevant studies needed for investigating the cause(s) of vegetation loss in affected salt marshes, to evaluate the potential for natural recovery of affected plants, and to provide the technical support for developing meaningful, scientifically sound and feasible restoration projects.

Specific objectives:
1. To conduct morphological, anatomical and cytological analyses of plant samples at the organ, tissue and cellular levels in order to identify any unusual structural details and/or functional activities.
2. To perform vital stain tests to determine if plant parts (e.g. rhizomes, apical meristems, etc.) from affected areas are viable.
3. To identify a pattern, if present, in the progression of death of plants.
4. To predict the natural recovery of the salt marsh, or to determine if there is a potential for recovery.

Progress and Findings:
A total of 105 plant samples from 6 sites (from Glynn, Chatham, Liberty, and McIntosh counties) have been analyzed thus far. Samples consisted of 5 live plants from healthy marsh (healthy zone), 5 live plants from moderately impacted marsh (transition zone), and 5 dead plants from severely impacted marsh (dead zone).     

Decay of root mass. A key observation from the morphological analyses was that underground plant parts from dead marsh sites (where aboveground vegetation is destroyed) were dead as well. It is entirely possible that in some affected regions, there may be living underground material, and re-growth may occur in these marshes.
        Samples from different dead marsh sites showed varying degrees of decay. The rate of decay can provide an indication of the time it will take for the onset of erosion to occur. Soil/sediment erosion will lead to permanent loss of the salt marsh in affected areas.

Herbivory. The frequency of damage to aerial parts of plants caused by insect larvae was noticeably high. Of the 60 samples examined with intact aerial parts (i.e., those from healthy and transition zones), 29 showed a similar type of insect damage. Damage to vegetation caused by insect larvae is not uncommon in a natural setting (i.e. without the application of insecticide or other preventive measures), and under normal circumstances it may not lead to the destruction of an entire salt marsh. However, the frequency of insect damage observed in samples analyzed thus far appears to be unusually high indicating that insects may contribute to the loss of vegetation in salt marshes. This can only be confirmed by examining a large number of samples.

Damage at the cellular level. Analysis of plant samples at the cellular level revealed an unusual difference between samples from living and dead marshes. Xylem vessels in the rhizomes of samples from dead marshes (and in some cases transition zones as well) were clogged with a yellowish-brown colored substance. A xylem vessel is a type of cell in the vascular system of higher plants and is responsible for the transportation of water throughout the plant. In some plants, the clogging of xylem vessels may result from pathogen attack or from the presence of toxic substances. Whether the clogging of xylem vessels of S. alterniflora from dead or dying marshes is associated with a pathogen attack, or toxic substances (e.g. herbicides) is yet to be determined.


Related presentation:
August 2003, Vegetation Analysis (sorry, link has been inactivated)

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This page was updated October 13, 2006