restoration of heavily oiled tidal flats and salt marshes
TRANSCRIPT
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Restoration of Heavily Oiled Tidal Flats and Salt Marshes 18
Years After The Gulf War Oil Spill Linos Cotsapas
Jason Hale, Christopher Cormack, Thomas Minter, and Jacqueline Michel
Research Planning, Inc. and Pandion
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Outline
• Introduction/Restoration Goals • Indicators of Stress • Remediation Activities • Results
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The Event and The Program
• Largest marine spill in history • Less than 10% of estimated spill volume
recovered • UN-sponsored; KSA-implemented
program governed by UN-set guidelines
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Guiding Principles • Decision 258 and F4 panel principles:
– Avoid techniques that pose unacceptable risks – Facilitate natural recovery to the extent possible – Rely on proven techniques – Utilize adaptive management – Be cost effective – Consider short- and long-term effects and
landscape connectivity – Result in more positive than negative results
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The Approach
• Target “Ecological Restoration” • Methods must:
– Understand and characterize conditions and site
– Identify stressors – Design appropriate remediation activities – Test and monitor effects of remediation
activities – Adaptively manage
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Heavily Impacted Tidal
Channels
Healthy Tidal Channels
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Achieving Restoration Goals
• Promote ecological restoration in contrast to “removal of contaminants”
– Ecological structure, what we see – Ecological function, the “jobs” that are done
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Achieving Restoration Goals
• Promote ecological restoration in contrast to “removal of contaminants”
• Ecological restoration and natural recovery – Remediation activities must promote or
accelerate rate of natural recovery – Remediation activities must conserve areas
exhibiting natural recovery
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Achieving Restoration Goals
• Promote ecological restoration in contrast to “removal of contaminants”
• Ecological restoration and natural recovery • “Removal of contaminants” implies oil is
the principle stressor – But is this the case after 20 years?
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Indicators of Stress • Ponding of upper marsh and channels at low tide • Widespread laminated algal mat • Widespread oil residues, surface and sub-surface • Tidal channel bank and bottom habitat degradation • Limited abundance and distribution of halophytes
(annual and perennial) • Limited abundance and distribution of key benthic
fauna
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How to Speed up Recovery
• Build on proven methods and adaptively manage to local conditions
• Practical methods that are readily implementable
• Assess results and adapt
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The Setting
Salt marshes and tidal flats: • Make up over 95%
of intertidal habitats between Jubail and Kuwait border
• Severely impacted by the spill
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Salt Marshes–Remediation Objectives
• Re-establish tidal channel function • Eliminate ponding - promote drying of part
of marsh surface between tidal cycles • Reduce total petroleum hydrocarbon levels • Remove/till barriers • Provide improved channel bank and bottom
substrate
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Salt Marshes – Techniques
• Channel excavation/refreshment • Tilling to break up algal mat and cohesive oiled
sediments • Removal/disposal of surface and cohesive
subsurface oiled layers • Microhabitat creation • Planting of marsh vegetation
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Tidal Flats–Remediation Objectives
• Increase suitable habitat for grazers and burrowing infauna
• Reduce total petroleum hydrocarbon levels • Improve drainage and reduce ponding
between tidal cycles • Tilling to break up algal mat and cohesive
oiled sediments
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Tidal Flats – Techniques
• “Dry” tilling of sediments followed by manual removal of remaining surface oil
• “Wet” tilling of sediments within constructed berms while flooded to liberate oil; and recovery by skimming/vacuuming
• Removal/disposal of surface and cohesive subsurface oiled layers
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Excavation of Tidal Channels
• Routing always follows natural cues – Priority - existing channels in salt marsh
habitat – Additional “straight” channels added to areas
with persistent ponding during low tide and where density was below average
• Rules of connectivity determined stream order
• Fixed dimensions for channel types
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After Excavation Before Excavation (line indicates location)
Excavation of Tidal Channels
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Excavation of Tidal Channels
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Channel Development
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Channel Development
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Point Bar Morphology
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Point Bar Micro-Habitat
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Pool Morphology
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Microhabitat Creation
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Mangrove Transplants
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Tilling and Mixing
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Wet Tilling
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Oil Liberation and Removal
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Results
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Project Site Plan
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Restoration Progress-Ecology
• Abundance and distribution of key benthic taxa that perform critical ecosystem functions:
– Grazing of microalgae substrate to keep channel bottom free from algal mat build-up
– Bioturbation for nutrient and carbon cycling; continued release/remediation of remaining residues
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Restoration Progress-Ecology
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Early Colonizers - Channel Bottom Habitat
• Grandidierella amphipod
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Early Colonizers - Channel Bottom Habitat
• Grandidierella amphipod
• Potamides mud snail
• Polychaete and other benthic infauna
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Nasima Burrowing Activity
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Monitoring Results
• Robust monitoring program established measuring physical, chemical, and ecological variables
• Monitoring program data indicate that remediation methods have increased rate of ecological recovery in both salt marshes and tidal flats
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Amphipods Snails
Nasima
South Channel North Channel
CRC1 Colonization – Two months post excavation
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CRC1 Colonization – Five months post excavation
Amphipods Snails
Nasima
South Channel North Channel
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CRC1 Colonization – 30 months post excavation
Amphipods Snails
Nasima
South Channel North Channel
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Program Achievements • Excavated +160 km of existing and new tidal
channels • Tilled +300 ha of marsh and unvegetated tidal
flats • Off-site disposal of 110,000 m3 oil-contaminated
substrate • On-site re-use of 45,000 m3 of “No” or “low”
contaminated substrate as micro-habitat • Transplanted 105,000 mangroves • Remediated 1,800 ha of salt marsh and tidal flat
habitat
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Conclusion Even after total devastation, with little if any natural recovery occurring 18 years after the spill, restoration of salt marshes and salt flats by re-establishing hydrological functioning and removal of physical barriers is possible with significant and quantifiable positive effects in the recovery of intertidal habitat functions