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Brown Marsh Update 14 September 2000. Dr. Robert R. Twilley University of Louisiana at Lafayette Center for Ecology and Environmental Technology. List of Panel Participants 12 September 2000.

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brown marsh update 14 september 2000

Brown Marsh Update14 September 2000

Dr. Robert R. Twilley

University of Louisiana at Lafayette

Center for Ecology and Environmental Technology

list of panel participants 12 september 2000
List of Panel Participants12 September 2000

Don Cahoon, Ph.D.Robert Chabreck, Ph.D.Woody Gagliano, Ph.D.Paul Kemp, Ph.D.Greg LinscombeMike MaterneIrv Mendelsohn, Ph.D.Jim Morris, Ph.D.Denise Reed, Ph.D.Robert Twilley, Ph.D.

overview of presentation
Overview of Presentation
  • Extent of Brown Marsh
  • Coastal Conditions
  • Possible Causes
  • Nature of Recovery
  • Recommendations
  • Conclusions

extent of salt marsh damage
Extent of Salt Marsh Damage
  • Aerial survey of salt marshes in the Barataria and Terrebonne basins

Greg Linscombe( Dept Wildlife & Fisheries)

Robert Chabreck (LSU -retired)

sample point
Sample point

examples of class types
Examples of Class Types

percent occurrence
Percent Occurrence

graph of categories
Graph of Categories

dist of dead patches
Dist of Dead Patches

dead salt marsh patches
Dead Salt Marsh Patches

local patterns of salt marsh dieback
Local Patterns of Salt Marsh Dieback
  • Pattern first observed in May 2000
  • Typical die-back of Spartina occurs in the marsh interior
  • Fringe Marsh usually remains healthy

coastal conditions la nina
Coastal Conditions - La Nina
  • Decrease in Precipitation over the last two years
  • Two Years of Water Deficits resulting in present condition of severe drought
  • Increased presence of Gulf High over coast of Louisiana
  • Increase number of clear days

drought index
Drought Index

coastal conditions river flow
Coastal Conditions - River Flow
  • River flow is one of lowest on record - probably between 8-10 lowest since 1931
  • Lack of seasonal flow in spring has resulted in the movement of salinity regimes inland

low river flow
Low River Flow










atch slide
Atch Slide

-1 SD

+1 SD

historical miss river discharge
Historical Miss. River Discharge

houma canal dcp
Houma Canal DCP

similar local patterns
Similar Local Patterns

biotic factors
Biotic Factors



Low Genetic Diversity

abiotic factors
Abiotic Factors

Chemical Spills

Buildup of Sulfide

High Salinity

Extreme Water Levels

low water levels
Low Water Levels
  • Evidence for low water levels: Records indicate low water levels at some locations during early part of year.

low water levels1
Low Water Levels

Marsh Drought - conditions with lower water level and increased temperatures have set up periods of water deficits in marsh soils - leading to toxic soil conditions - the exact nature of these soil conditions needs more information



some species of plants have been able to maintain a presence in brown marsh areas
Some species of plants have been able to maintain a presence in brown marsh areas
  • Avicennia germinans.
  • Batis maritima
  • Juncus roemarianus




Distichlis spicata

interacting environmental biotic factors
Interacting Environmental & Biotic Factors
  • Marsh drought, water level, and temperature are possibly all contributing factors that interact to develop stress plant conditions – the exact nature of which is not conclusive at this time.

  • Factors least likely to be involved: achemical spill, herbivory
  • Factors possibly involved, but with little or no data from a broad survey of current die-back sites: pathogens, low genetic diversity
  • Factors possibly involved, with some evidence from several sites: water level extremes, salinity, natural toxins (e.g., sulfide)

nature of recovery
Nature of Recovery
  • Some small patches have recovered
  • Recovery potential is unknown – limited by duration of La Nina
  • Extensive restoration programs are limited by the magnitude of dieback
  • Small scale restoration strategies do exist and are under consideration
  • Erosion control is a high priority

  • Identify extent and severity of damage
  • Identify causes
  • Identify impacts – economics, social, biological
  • Identify restoration strategies

  • Based on the combined scientific experience of panel members and participants – this dieback event is most unique in terms of temporal and spatial scale
  • Understanding the extent, causes, and consequences of this unique event will require the collaboration of State,Federal, and University scientists and natural resource managers