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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

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Brown Marsh Update14 September 2000

Dr. Robert R. Twilley

University of Louisiana at Lafayette

Center for Ecology and Environmental Technology

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

  • Extent of Brown Marsh

  • Coastal Conditions

  • Possible Causes

  • Nature of Recovery

  • Recommendations

  • Conclusions

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

Examples of Class Types

Percent Occurrence

Graph of Categories

Dist of Dead Patches

Dead Salt Marsh Patches

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

  • 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

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










Atch Slide

-1 SD

+1 SD

Historical Miss. River Discharge

Houma Canal DCP

Other Global Patterns of Coastal Wetland Dieback

Similar Local Patterns

Freshwater Diversions – Restoration Programs

Biotic Factors



Low Genetic Diversity

Abiotic Factors

Chemical Spills

Buildup of Sulfide

High Salinity

Extreme 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 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

  • Avicennia germinans.

  • Batis maritima

  • Juncus roemarianus



Distichlis spicata

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

  • 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

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