restoration of heavily oiled tidal flats and salt marshes
TRANSCRIPT
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
Outline
• Introduction/Restoration Goals • Indicators of Stress • Remediation Activities • Results
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
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
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
Heavily Impacted Tidal
Channels
Healthy Tidal Channels
Achieving Restoration Goals
• Promote ecological restoration in contrast to “removal of contaminants”
– Ecological structure, what we see – Ecological function, the “jobs” that are done
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
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?
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
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
The Setting
Salt marshes and tidal flats: • Make up over 95%
of intertidal habitats between Jubail and Kuwait border
• Severely impacted by the spill
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
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
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
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
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
After Excavation Before Excavation (line indicates location)
Excavation of Tidal Channels
Excavation of Tidal Channels
Channel Development
Channel Development
Point Bar Morphology
Point Bar Micro-Habitat
Pool Morphology
Microhabitat Creation
Mangrove Transplants
Tilling and Mixing
Wet Tilling
Oil Liberation and Removal
Results
Project Site Plan
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
Restoration Progress-Ecology
Early Colonizers - Channel Bottom Habitat
• Grandidierella amphipod
Early Colonizers - Channel Bottom Habitat
• Grandidierella amphipod
• Potamides mud snail
• Polychaete and other benthic infauna
Nasima Burrowing Activity
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
Amphipods Snails
Nasima
South Channel North Channel
CRC1 Colonization – Two months post excavation
CRC1 Colonization – Five months post excavation
Amphipods Snails
Nasima
South Channel North Channel
CRC1 Colonization – 30 months post excavation
Amphipods Snails
Nasima
South Channel North Channel
0
2000
4000
6000
8000
10000
12000
14000
TPH
(mg/
kg)
BeforeAfter
Average TPH Levels Before and After “Wet” Tilling
0
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350
10-M
ay-2
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ec-2
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10-Ju
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10-A
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10-S
ep-2
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10-N
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ec-2
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Num
ber o
f Bur
row
s pre
sent
in c
hann
el a
long
10
m tr
anse
ct
Date
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
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