FATE AND EFFECTS OF OIL AND DISPERSED OIL ON MANGROVE ECOSYSTEMS

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					FATE AND EFFECTS OF OIL AND
     DISPERSED OIL ON
 MANGROVE ECOSYSTEMS IN
        AUSTRALIA




                    Norman C. Duke
                   Kathryn A. Burns




         Australian Institute of Marine Science
                           and
              CRC Reef Research Centre




                      Final Report
                         to the
Australian Petroleum Production Exploration Association
                      12 June 1999
Effects of Oil and Dispersed Oil on Mangroves




An environmental research project with the AUSTRALIAN PETROLEUM PRODUCTION & EXPLORATION
ASSOCIATION L IMITED (APPEA) and the ENERGY RESEARCH AND DEVELOPMENT CORPORATION
(ERDC).




Scientific research conducted under the direction of the COOPERATIVE RESEARCH CENTRE FOR
ECOLOGICALLY S USTAINABLE DEVELOPMENT OF THE GREAT BARRIER REEF (Reef CRC) and the
AUSTRALIAN I NSTITUTE OF MARINE SCIENCE (AIMS).



Contact details:

AIMS    (local Australia)   —   Phone: 07 4753-4444        Fax: 07 4772-5852
        (International)     —   Phone: +617 4753-4444      Fax: +617 4772-5852

N.C. Duke           — n.duke@uq.edu.au

K.A. Burns          — kburns@aims.gov.au




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Effects of Oil and Dispersed Oil on Mangroves



Project Summary

      This three-year project (1995-1998) assessed short and long term effects of commonly transported
oils and dispersed oils on Australian mangrove flora and fauna. Short term studies were conducted in
planthouse and field conditions. Longer term effects were assessed from spill incidents which occurred
over the last 30 years in sites around Australia. Findings from all studies form the basis for improved
guidelines and recommendations for the protection, cleanup, and restoration of oiled mangrove habitat
around Australia, and elsewhere. For example, although there was no difference between oil only and
dispersed oil treatments in field trials where the impact on fauna was catastrophic, the death of mangrove
trees was significantly less in plots treated with dispersed oil. Partial recovery of fauna occurred after
approximately two years, but there was little sign of restoration of trees and damaged forest canopy. For
this reason, dispersion of spilled oil before it reaches mangroves is considered an effective strategy in
reducing the long term impact of oil on mangrove habitat. Such results have established the baseline for
future, on-going assessment of oil damaged sites for both natural recovery, and the application/testing of
remedial/restoration strategies and techniques; particularly for more sensitive and badly affected areas in
Australia.




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Effects of Oil and Dispersed Oil on Mangroves




CONTENTS

FATE AND EFFECTS OF OIL AND DISPERSED OIL ON MANGROVE
ECOSYSTEMS IN AUSTRALIA                                                              232

PROJECT SUMMARY                                                                      232


1. INTRODUCTION TO THE PROJECT                                                       236
       1.1 Structure of studies undertaken                                           237


2. SURVEYS OF OIL SPILL INCIDENTS AROUND A USTRALIA – AN ASSESSMENT OF INCIDENTS ,
  IMPACTS ON MANGROVES, & RECOVERY OF DEFORESTED AREAS                               240
       2.1 Summary Points                                                            240
       2.2 Introduction                                                              240
       2.3 Methods                                                                   242
               2.3.1 Australia-wide field surveys                                    242
               2.3.2 A standard protocol for site surveys                            242
               2.3.3 Measurements of tree and seedling condition                     244
               2.3.4 Sediment sampling and hydrocarbon analyses                      244
               2.3.5 Prior studies at each site                                      244
       2.4 Results                                                                   244
               2.4.1 Incidents                                                       244
               2.4.2 Impacts on mangroves                                            245
               2.4.3 Status and recovery of deforested mangroves                     245
       2.5 Discussion                                                                246


3. PLANTHOUSE EXPERIMENT – EFFECT OF OIL & DISPERSED OIL ON MANGROVE SEEDLINGS       248
       3.1 Summary points                                                            248
       3.2 Introduction                                                              248
       3.3 Methods                                                                   248
               3.3.1 The tidal system and establishment of mangrove seedlings        248
               3.3.2 Treatments of oil and dispersed oil                             248
               3.3.3 Elements in green leaves of treated seedlings                   250
       3.4 Results                                                                   250
               3.4.1 Overall effects of oil                                          251
               3.4.2 Overall effects of dispersed oil                                252
               3.4.3 Species and other seedling variables                            252
               3.4.3 Elements in leaves of seedlings                                 252
       3.5 Discussion                                                                252

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Effects of Oil and Dispersed Oil on Mangroves



4. GLADSTONE FIELD EXPERIMENT – EXPERIMENTAL SETUP AND METHOD                  256
      4.1 Summary points                                                       256
      4.2 Introduction                                                         256
      4.3 Methods                                                              261
              4.3.1 The study area and site selection                          261
              4.3.2 Experimental enclosures and oil treatments                 262
              4.3.3 Sediment sampling                                          262
      4.4 Results                                                              262
              4.4.1 Schedule of research activities                            262
              4.4.2 Physical description of treatment application              265
              4.4.3 Sediment cores                                             265
              4.4.4 Oiled sediment redox levels                                267
              4.4.5 Sediment nutrients                                         267
      4.5 Discussion                                                           267


5. GLADSTONE FIELD EXPERIMENT – WEATHERING OF HYDROCARBONS                     268
      5.1 Summary points                                                       268
      5.2 Introduction                                                         268
      5.3 Methods                                                              270
              5.3.1 Experimental design                                        270
              5.3.2 Analysis                                                   270
      5.4 Results & Discussion                                                 272
              5.4.1 General features                                           272
              5.4.2 Experimental loss rates                                    275
              5.4.3 Mass balance                                               275
              5.4.3 Changes in oil composition at 13 months                    275
              5.4.5 Further degradation at 22 months                           281
              5.4.6 Implications for treating oil spills impacting mangroves   281
      5.5 Conclusions                                                          281
      5.6 Notes on analytical quality assurance                                281


6. GLADSTONE FIELD EXPERIMENT – IMPACT, RESPONSE & RECOVERY OF PLANTS          284
      6.1 Summary points                                                       284
      6.2 Introduction                                                         284
      6.3 Methods                                                              284
              6.3.1 Surveys of plant condition                                 284
              6.3.2 Shoot observations                                         286
              6.3.3 Litter fall collection                                     286
              6.3.4 Allometric assessment of leaves                            286

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Effects of Oil and Dispersed Oil on Mangroves


              6.3.5 Derived measures of canopy standing biomass & density               286
              6.3.6 Indirect measurement of canopy density                              288
              6.3.7 Assessment of nutrients in green leaves                             288
              6.3.8 Seedling and tree demography                                        288
              6.3.9 Tree allometry                                                      288
      6.4 Results                                                                       288
              6.4.1 Impact on forest structure                                          288
                         6.4.1.1 Impact on trees                                        288
              6.4.2 Impact on seedlings                                                 290
              6.4.3 Canopy condition and growth                                         290
                         6.4.3.1 Litter fall                                            290
              6.4.4 Shoot observations                                                  295
              6.4.5 Allometric assessment of leaves                                     297
              6.4.6 Litter and shoot derivations                                        297
              6.4.7 Nutrients in leaves                                                 298
              6.4.8 Light penetration through the canopy                                298
      6.5 Discussion                                                                    299


7. GLADSTONE FIELD EXPERIMENT – IMPACT, RESPONSE & RECOVERY OF MACROFAUNA               302
      7.1 Summary points                                                                302
      7.2 Introduction                                                                  302
      7.3 Methods                                                                       302
              7.3.1 Canopy herbivory - caterpillars                                     302
              7.3.2 Macrobenthos epifauna - crustaceans                                 304
              7.3.3 Macrobenthos infauna - sipunculids                                  304
      7.4 Results                                                                       305
              7.4.1 Herbivory of canopy foliage by caterpillars                         305
              7.4.2 Biomass of crabs and other crustaceans living on the forest floor   306
              7.4.3 Leaf removal from the forest floor by crabs                         306
              7.4.4 Sipunculid worms in mangrove sediments                              308
      7.5 Discussion                                                                    310


8. RECOMMENDATIONS AND GUIDELINES                                                       314
      8.1 Summary points                                                                314
      8.2 Introduction                                                                  314
              8.2.1 Management protocol in oil spill response                           314
      8.3 Before an oil spill incident                                                  315
      8.4 During an oil spill – oil mobile phase                                        315
              8.4.1 Oil at sea – a threat to mangrove                                   315
              8.4.2 Oil into mangroves                                                  317

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Effects of Oil and Dispersed Oil on Mangroves


      8.5 After an oil spill – oil settled                                                             317
      8.6 Observations, recommendations and guidelines                                                 318


9. REFERENCES                                                                                          320


10. APPENDICES                                                                                         325
      10.1 Appendix 1
            Surveys of oil spill incidents which have affected mangrove habitats in Australia: a report on
            the incidents, impacts and recovery of affected areas.                                     325
      10.2 Appendix 2
            Current policies of key institutions in oil spill response, clean-up and management with
            regard to mangroves: the National Plan to Combat Pollution of the Sea by Oil.              361
      10.3 Appendix 3
            Revised dispersant use guidelines, approved by the GBRMPA on 5 December 1997.              362




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