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Georgia's Marsh Die Back and Louisiana's Marsh BrowningNaturally Occurring Cycles or a Products of Human Disturbance? What can scientists in Georgia learn from Louisiana's efforts to understand a similar environmental disorder?
| By: Dorset Hurley, Research Coordinator, Sapelo Island National Estuarine
Research Reserve |
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Estuarine and marine scientists working in the marshes of the
southeastern United States became aware of vegetative denudation or "Marsh
Browning" areas in the coastal marshes of Louisiana in the fall of 2000.
By the Spring of 2001 in the Barataria-Terrebone salt marshes alone which comprise 390,000 acres of Louisiana's salt marsh systems, displayed vegetation declines in over 260,000 of those acres. The Governor of Louisiana declared the situation a "state of emergency" and obtained 3 million dollars in state and federal support to assist in the study, control and hopefully the reversal of the disorder.
In Louisiana, this ecosystem-level phenomenon seemed to exhibit similar symptoms within many of the affected estuarine areas of the state. However, its causal agents were unknown. Louisiana scientists termed the phenomena "Marsh Browning" due to the diseases early-stage symptoms which caused affected Spartina alterniflora or smooth cord grass, to turn brown as the aboveground vegetation died.
Georgia salt marshes started displaying similar vegetation disease symptoms in the Fall of 2001, about the same time that Louisiana's marshes began their slow, natural recovery. By the Summer of 2002 Georgia's Department of Natural Resources assessed "Marsh Die-Back" as affecting approximately 1500 acres of Georgia's 400,000 acres of salt marsh.
In Georgia however, the phenomena's genesis and epidemiology appeared different than that noted in Louisiana. Affected marshes in Georgia seemed to undergo dramatic shifts in vegetation coverage which displayed sharp transition zones between vegetated and non-vegetated areas.
Georgia's Die-Back disease was affecting both Juncus romarianis.( black needlerush) and Spartina alterniflora. Other symptoms that appear unique to Georgia's coastal Die-Back include: complete rhizome (root mass) failure in affected plants, the advance of the disease from tidal creek and low marsh areas toward high marsh areas and the sporadic nature of the disease's expression which seems to chronically affect smaller areas of both high and lower salinity marshes. These observations in the expression of the disease add to the mystery of Georgia's Marsh Die-Back and Louisiana's Marsh Browning which have scientists baffled as to whether or not they are:
- Studying the same marsh disease
- Studying the same symptoms of different
diseases
- Investigating closely related causal factors which express similar
but not identical symptoms.
Scientifically, an environmental situation of this magnitude represents a challenge that requires scholars of varying disciplines and programs to collectively partner and plan. This in-turn creates a sharing, intellectual environment, which much like the environmental system under study, responds to information input, energy flows and feedback loops.
In Louisiana, the issue was pervasive enough that the level of funding for studying the phenomena was sufficient in size to synthesize a wide range of applied science results. These results may provide future aid toward reversing the "Marsh Browning" trend
should it reappear in Louisiana. Additionally, many of the results among Louisiana
and Georgia scientists were shared in a very productive interactive two day forum
facilitated by the Georgia Coastal Research Council in Savannah this Spring.
After extensive aerial assessment of Louisiana's marshes, certain trends emerged
in the data related to coverage, extent and marsh condition of the states
affected area. These trends helped formulate the baseline of scientific
questions and management efforts directed at understanding Marsh Browning.
The following commonalities were noted in affected Louisiana salt marshes:
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 Jerico River Site
Teal Marsh 40 FT.
Jerico Site #2
PhotosÊtaken in September 2003, from the DNR helicopter by AIMEE GADDIS,
STEWARDSHIP COORDINATOR FOR SINERR
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- A landmark drought of three consecutive years precluded the occurrence of
Marsh Browning in Louisiana.
- High salinity marshes of near-Gulf waters seemed
most highly affected.
- Selective vegetative resistance to the disese was
noted with Spartina
alterniflora, or smooth cord grass being the only plant affected.
- Affected
areas seemed to demonstrate a browning of the Spartina often followed
by complete vegetative failure which affected both above ground and below
ground plant viability and seemed to follow an interior marsh genesis.
- Many of the affected sites were characterized by either excessive
submergence
(water logging) or excessive dryness (desiccation).
- Soil pH of
the affected marshes was typically acidic.
In Georgia, scientists collaborating with the states Coastal Zone Program and
Department of Natural Resources representing the organizations listed below,
mobilized a collective research approach through a venue provided by the Georgia
Coastal Research Council. With limited funding, the concerned agencies developed
an integrated research approach which led to the development of a standard monitoring
protocol. The monitoring effort includes simultaneously acquired, seasonal data,
submitted from several affected sites around the state, which is collated toward
characterizing Georgia's Marsh Die Back (MDB) phenomena. Parameters monitored
are vegetation type, stem density, pore water pH, temperature, salinity and macrofaunal
abundance. For more information on Georgia's research efforts view the Marsh
Die-Back Index pages.
The Sapelo Island National Estuarine Research Reserve
The Georgia Coastal
Research Council
The Georgia Department of Natural Resources: Coastal Resources
Division
The University of Georgia School of Marine Programs
Savannah State University
The Georgia Coastal Ecosystems Long-Term Ecological Research initiative
Much of the information provided by researchers in both states hold striking
similarities in conditions associated with the onset of the disease.
To date, a cause and effect relationship has not been established for
individual
or combinational factors due to the complexity that open systems such
as salt marshes present to environmental scientists. Most scientists
participating
in the research and information exchange related to the disorder agree
that combinations of environmental and biological factors are likely
the culprits.
Furthermore, as each system has different and unique environmental gradients
and biological constituents, it is likely that the expression of the
disorder assumes a unique form within each state's marshes. One overriding
environmental
theme common to both states occurrence of the disease is drought.
Dr. David Stooksbury , Georgia's state climatologist analyzed rainfall
data for the state from 1924- current and noticed that for four consecutive
years
preceding the expression of MDB, the Altamaha watershed had an average
compounded rainfall deficit of approximately 5" or 10% annually.
Stooksbury noted that the combined or cumulative effect of this type
of drought has tremendous potential to serve as a forcing mechanism upon
vegetation
declines. Dr. James Morris of South Carolina, a scientist specializing
in Spartina alterniflora responses offered concurring information based
upon his research.
Morris's work demonstrates that although Spartina alternifora is the
dominant vegetation of southeastern salt marshes it is highly stressed
by thermal
(heat) gradients found within these lower latitudes. In fact, the marshes
of Georgia and the Northern Gulf coast effectively constitute the southern
range limit of the plant.
Morris has documented that Spartina alterniflora from Northeast coastal
areas is much more efficient at absorbing photosyntheticly active radiation
(PAR). Simply stated, Spartina is best adapted to a cool climate, and
summer temperatures in the southeast are higher than its optimum temperature.
Coupling Morris's information with that of Stooksbury it is plausible
that
heat stress in combination with prolonged drought (desiccation stress)
and high salinities have collectively created a physio-chemical interaction
that is lethal to Spartina alterniflora under certain environmental conditions
such as drought, in areas close to its southerly limits.
Many other theories and combinations of theories have been discussed
and researched within scientific circles ranging from herbivory to soil
and
pore water chemistry. The reason for the occurrence of such a catastrophic
disease within our Southeastern marshes is alarming and still poorly
understood however, it has promoted some unique applied work that has
application
to many different aspects of coastal management.
One such product is the technology and methods developed by Louisiana's
Department of Agronomy that conducted large-scale restoration of Spartina
alterniflora in marsh settings by aerial seeding.
Mike Materne, the project leader conducted experimentation in two impacted
marshes and accomplished successful aerial seeding restoration projects
complete with cost analysis, expected germination rates, optimum seed
dispersal density and deployment methodology. This project developed
new restoration
tools for Spartina alterniflora establishment and as such is a landmark
agronomy study with far reaching future potential to coastal restoration
and management.
Regardless of your use of terms, the causal factors of Marsh Die Back
or Marsh Browning remain largely unknown. Salt marsh ecological studies
driven by concern over the heath of our valuable coastal systems continue
in both states. The products of these scientific efforts have allowed
for a more comprehensive understanding of issues related to the disease
and
the production of management tools which may someday help in controlling,
minimizing and understanding the effects and genesis of this disorder. |
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