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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

www.LAcoast.gov/brownmarsh


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.

www.LAcoast.gov/brownmarsh


Overview of Presentation

  • Extent of Brown Marsh

  • Coastal Conditions

  • Possible Causes

  • Nature of Recovery

  • Recommendations

  • Conclusions

www.LAcoast.gov/brownmarsh


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)

www.LAcoast.gov/brownmarsh


Sample point

www.LAcoast.gov/brownmarsh


Examples of Class Types

www.LAcoast.gov/brownmarsh


Percent Occurrence

www.LAcoast.gov/brownmarsh


Graph of Categories

www.LAcoast.gov/brownmarsh


Dist of Dead Patches

www.LAcoast.gov/brownmarsh


Dead Salt Marsh Patches

www.LAcoast.gov/brownmarsh


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

www.LAcoast.gov/brownmarsh


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

www.LAcoast.gov/brownmarsh


Drought Index

www.LAcoast.gov/brownmarsh


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

www.LAcoast.gov/brownmarsh


Low River Flow

7

8

9

6

3

5

2

1

4

www.LAcoast.gov/brownmarsh


Atch Slide

www.LAcoast.gov/brownmarsh


-1 SD

www.LAcoast.gov/brownmarsh


+1 SD

www.LAcoast.gov/brownmarsh


Historical Miss. River Discharge

www.LAcoast.gov/brownmarsh


Houma Canal DCP

www.LAcoast.gov/brownmarsh


Other Global Patterns of Coastal Wetland Dieback

www.LAcoast.gov/brownmarsh


Similar Local Patterns

www.LAcoast.gov/brownmarsh


Freshwater Diversions – Restoration Programs

www.LAcoast.gov/brownmarsh


Biotic Factors

Herbivory

Pathogens

Low Genetic Diversity

www.LAcoast.gov/brownmarsh


Abiotic Factors

Chemical Spills

Buildup of Sulfide

High Salinity

Extreme Water Levels

www.LAcoast.gov/brownmarsh


Low Water Levels

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

www.LAcoast.gov/brownmarsh


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

Tides

Rain

www.LAcoast.gov/brownmarsh


Some species of plants have been able to maintain a presence in brown marsh areas

  • Avicennia germinans.

  • Batis maritima

  • Juncus roemarianus

www.LAcoast.gov/brownmarsh


Avicennia

germinans

Distichlis spicata

www.LAcoast.gov/brownmarsh


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.

www.LAcoast.gov/brownmarsh


Summary

  • 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)

www.LAcoast.gov/brownmarsh


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

www.LAcoast.gov/brownmarsh


Recommendation

  • Identify extent and severity of damage

  • Identify causes

  • Identify impacts – economics, social, biological

  • Identify restoration strategies

www.LAcoast.gov/brownmarsh


Conclusions

  • 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

www.LAcoast.gov/brownmarsh


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