- Email: [email protected]
Effects of south Louisiana crude oil and dispersants on Rhizophora mangroves
Marine Pollution Bulletin Cook, C. B. & Knap, A. H. (1983). The effects of crude oil and chemical dispersant on photosynthesis in the brain coral, Diploria strigosa. Mar. BioL 78, 21-27. Dodge, R. E., Wyers, S. C., Knap, A. H., Frith, H. R., Sleeter, T. D. & Smith, S. R. (1984). The effects of oil and oil dispersants on hermatypic coral skeletal growth (extension rate). Coral Reefs 3,191-198. Knap, A. H., Sleeter, T. D., Dodge, R. E., Wyers, S. C., Frith, H. R. & Smith, S. R. (1983). The effects of oil spills and dispersant use on corals--a review and multidisciplinary experimental approach. Oil and Petrochemical Pollution 1, 157-169. Knap, A. H., Solbakken, J. E., Dodge, R. E.. Sleeter, T. D., Wyers, S. C.
& Palmork, K. H. (1982). Accumulation and elimination of (9--14C) phenanthrene in the reef-building coral (Diplorla strigosa). Bull. Environm. Contain. and Toxicol. 28, 281-284. LcGore, R. S., Marzalek, D. S., Hoffman, J. E. & Cuddeback, J. E. (1983). A field experiment to assess the impact of chemically disperscd oil on Arabian Gulf corals. Soc. Petrol. Engs. SPE no. 11444, 51-55. Wyers, S. C., Frith, H. R., Dodge, R. E., Smith, S. R., Knap, A. H. & Sleeter, T. D. (1986). Behavioural effects of chemically dispersed oil and subsequent recovery in Diploria strigosa. Mar. Ecol. 7, 23-42.
1)1125-326X/87S3J)O+O.O0 O 1987 PergamonJournalsLtd.
MarinePollutionBulletin.Vol. 18, No. 3. pp. 122-124. 1987. Printedin Great Britain.
Effects of South Louisiana Crude Oil and Dispersants on Rhizophora Mangroves HOWARD J. TEAS, EIRIK O. DUERR* and J. ROSS WlLCOXt
Biology Department, Universityof Miami, Coral Gables, Florida 33124; t Florida Power&Light Co., P.O. Box 14000, Juno Beach, Florida 33408, USA *Present address: The Ocean Institute, Makapun Point, Waimanalo, Hawaii 96795, USA
Sprays of seawater or dispersant were found to have no value in saving oiled Rhizophora mangroves. However, mangroves treated with dispersed oil showed no greater mortality than was found in untreated control plots. It is concluded that every effort should be made to protect mangroves from oil, including offshore dispersal.
Mangroves are trees and shrubs that grow along low energy tropical and subtropical shorelines of the world. Although there are at least 15 genera and more than 50 species of mangroves worldwide (Chapman, 1970), species of the genus Rhizophora are dominant in areas adjacent to open water over much of the more tropical parts of the range of mangroves. Rhizophora mangroves are important protectors of shorelines from storms and currents, they can be harvested for timber and firewood, they provide shelter and habitat for many animal species, and they are a source of primary productivity for food webs that serve as a base for the production of marine and estuarine organisms such as lobsters, prawns, finfish, and shellfish (summarized by Teas, 1979). Rhizophora mangroves have arching, stilt-like aerial roots, called prop roots, that serve as anchoring structures, and contain tissues that conduct air to the subsurface roots. They occur near many tropical oil production areas and shipping lanes, and are often found at low-energy sites where spilled oil accumulates. As a consequence, Rhizophora mangroves are frequently oiled from shipping accidents, oil well blowouts, tanker bilge washings, etc. 122
Although many cases of oil damage to mangroves have been tabulated (e.g. Lewis, 1983), no systematic experiments have been reported on the effects of dispersed oil on mangroves or on attempts to reduce mangrove mortality by post-oiling treatments. Leaf fall and the related death of apical buds were found to be indicators of tree stress. All oiled trees showed increased leaf loss, but some recovered. The reliable criterion for oil damage to Rhizophora mangroves was therefore taken to be tree death. The present study reports on the mortality in Rhizophora mangroves from oil under controlled conditions. The oil treatment corresponds to a spill in which the oil is carried into the mangroves by the tide. Under real-life situations, such oil would often have been partially weathered before impacting the mangrove communities. Because fresh, rather than weathered, oil was applied in the present study, the results obtained may be considered to be 'worst case' effects. The non-ionic waterbased dispersant (NIWBD) and seawater (SW) washes represent an attempt to save oiled trees by washing the oil from the trees and soil with high-pressure sprays applied the next day. Except for the lack of weathering, the oil dispersed with glycol ether-based dispersant (GEBD) corresponds to a well-dispersed oil slick being brought ashore into mangroves by the tide. Materials and M e t h o d s The mangroves used for the experiment were Rhizophora mangle;, the experimental plots were almost a monoculture of this species. The trees are located along the sloping bank of a canal that was dug through the
Volume 18/Number 3/March 1987
area approximately 14 years ago. The canal, which is about I5 m wide and 1.5 m deep, was formerly part of a thermal discharge canal system that emptied into Biscayne Bay. The site is on the grounds of the Florida Power & Light Co.'s Turkey Point Power Plant, which is located 40 km south of Miami, Florida, at c. 80 ° 20' W and 25 ° 26' N. The water in this canal has very limited connections with the present cooling canals and the whole system is isolated from Biscayne Bay by earth dikes. The water in the canal is not tidal, but its level varies approximately 0.6 m during a year. The canal salinity during the period of the experiment varied from 30-42%0, as a function of rainfall and evaporation. This salinity range is similar to that of Biscayne Bay. The mangrove plots were each enclosed by a semicircular boom (radius of 1.37 m) located on the water side (Fig. 1). The number of trees per plot varied from 8-50. Tree size varied but each plot had at least one tree 2 m tall and many trees in the plots were more than 2.5 m tall. Each plot had an area of 3.0 m 2. Plots were separated from the canal by a 4.3 m length of oil boom; in addition each plot that received oil was provided with an arc section of oil boom 6-9 m long located on the canal edge for containment of any splash or runoff oil. Plots were laid out so that all the prop roots of the experimental trees were within the area of the plot; nearby trees and intruding prop roots from outside were removed for a distance of 0.5 m. Trees that shaded the plots at any time of day were pruned or removed. The chain-weighted skirts of the inner and outer oil booms were buried in the muddy soil. The relationships of plots, trees, and oil booms are illustrated in Fig. 1. Plots differed in numbers of crab burrows. In order to assure uniform penetration o f oil into the substrata
Aerial view of plot
~
for all treatments, 36 'artificial crab holes' each 3 cm in diameter and 0.5 m deep were bored into the soil of each of the 24 plots at least 2 weeks before oiling. These holes were spaced to avoid, so far as possible, the subsurface roots near prop roots. Experiments were set up in July 1983. Oil treatment consisted of unweathered South Louisiana crude oil applied at the rate of 114 1. per plot (38 1. m--~). These treatments were administered in three 38 1. applications about 1! h apart. The oil was poured onto the soil and over the lower about 30 cm of the prop roots by hand using metal cans and buckets. Treatments were randomized among the plots and replicated three times. In the case of post-oiling washes with NIWBD, the dispersant was educted into a stream of SW (Canal water) provided by a gasoline powered pump as described by Canevari (1979). The SW and dispersant was sprayed on the soil and prop roots at a pressure of about 325 kg cm -2. Each plot so treated received 3.8 I. NIWBD in about 389 1. SW during 2 rain. and then a 3 rain. wash with only SW. The NIWBD in SW wash treatment was repeated 2 h later for a total of 7.6 1. NIWBD per plot. SW washes involved the same SW volumes and were also repeated afier2 h. In the case of GEBD, 114 1. of oil mixed with 5.7 1. of G E B D was educted into a stream of SW which was sprayed at low pressure or poured on the soil and prop roots. Leaf fall, apical bud death and tree death were scored for 30 months and tree death for 36 months. Only tree death is included in this report.
Results The percentages of trees that died from each treatment are plotted in Fig. 2. It is obvious that oil treatments, whether or not there was an attempt to wash away the oil, caused much higher mortality than occurred in treated controls, or the simple NIWBD or SW washes. The differences in mortality between oiled plots and controls were significant (P ~<0.05) by the Student-Newman-Kuels multiple range test at 12 months and thereafter. Both wash treatments following oil had significantly higher mortalities than controls at 6 months and thereafter. The plots treated with the same amount of oil, but dispersed by G E B D , had mortalities that did not differ significantly from the control, SWwashed, or NIWBD-washed plots.
Summary and Conclusions ongroves
~
oik boom PLot
SectionoL view of plot
Fig. l Experimental plot arrangement.
South Louisiana crude oil killed Rhizophora mangroves. High pressure washes with SW or NIWBD in SW applied the day after oiling were ineffective in reversing oil toxicity; indeed, they increased mortality compared to treatments with oil only. Oil pre-dispersed by G E B D caused no more mortality than that observed in untreated controls. These experiments indicate that: 1. every possible effort should be made to keep spilled oil from reaching mangroves, including offshore dispersal, and 2. washing oiled mangroves apparently has no value for saving the trees.
123
M a r i n e Pollution Bulletin
60--
• /
50--
•~
~....~ • OiL+SW
•
Oi(+NIWBD
40
./
50--
•
20--
•
I0--
J
..,,,r
6
"
L 12
'
l
,,~.~-----
~
~ 18
• Sea w a t e r
• '~ ' ' ' ~ - ~ 24
• Oit +GEBD ~ 30
-
?
Control 36
T i m e in m o n t h s
Fig. 2 M a n g r o v e mortality at 6 m o n t h intervals for e x p e r i m e n t a l treatments.
The authors.wish to express their thanks to the Florida Power & Light Co. ['or permission to carry out the experiment on their property; Earl Baker of Florida Power & Light Co. for logistic support of field operations; Gerald P. Canevari for the loan of the gasoline-powered pump used for spray treatments; Daniel Cary for assistance with statistical analyses; Exxon Chemical Company and Texaco, Inc. for materials; the American Petroleum Institute (API) for financial support of the investigations; the API Task Force members (Stuart Horn, Gerald E Canevari, June Lindstedt-Siva, C. Bruce Koons, Albert Lasday, Clayton McAuliffe and James Marum) for advice and field assistance; Donald Casey and Jack R. Gould, API staff, for advice and administrative support; and Michael de Grood, Carlos Manalich, George Concepcion, Clorinda Roblcs, and Marie Morgan for technical assistance.
Canevari, G. P. (1979). Restoration of oiled shorelines by proper use of chemical dispersants. Proceedings ot 1979 Oil Spill Conference, pp. 443-446. American Petroleum Institute, Washington, D.C. Chapman, V. J. (1970). Mangrove phytosociology. Tropical Ecology 11, 1-19. Lewis, R. R. (1983). Impact of oil spills on mangrove forests. In Tasks for Vegetation Science (H. J. Teas, ed.), pp. 171-183. Dr. W. Junk Publishers, The Hague. Teas, H. J. (1979). Silviculture with saline water. In The Biosaline Concept (A. Hollacndcr, ed.), pp. 117-161. Plenum Publishing Corporation, New York.
~hlrine Pollunon Btdletin, Vol. 18, No. 3. pp. 124-126. 1987.
()025-326X/87 $3.00+0.00 © 1987 PergamonJournals Lid.
Printed in Great Britain.
Oil Spill Clean-up: The effect of Three Dispersants on Three Subtropical/Tropical Seagrasses A. T H O R H A U G *
a n d J. M A R C U S
Florida International University, Tamiami Campus, Miami FL 33199, USA *On leave to United Nations Food and Agriculture Organization
Three seagrasses found throughout the Greater Caribbean tropical/subtropical region as major critical habitat organisms were tested in the laboratory for toxicity limits to three dispersants commonly stockpiled in the region. At concentrations in the recommended dosage level, that is, below 1 ml dispersant with 10 ml oil in 100 000 ml seawater, even for 100 h no large mortality occurred (15-18 barrels per acre as calculated by Exxon, 1985). At an order of magnitude higher, especially for longer time periods, the more sensitive seagrasses Syringodium filiforme and then Halodule wrightii succumbed. The dispersants had widely differing effects, with Corexit 9527 and Arco124
chem D609 having far less toxic effect than Conco K(K) at the same exposure time and concentration. There was comparatively little difference between effects of oils (Louisiana crude versus Murban). Types and brands of dispersants should be referred to specifically in oil spill contingency plans since such widely varying ecological toxicity occurs among various dispersants. Use of the word 'dispersant' as a policy tool should be used with caution, realizing that dispersants vary widely in toxicity effects. Further testing of seagrasses in other ocean basins and those dispersants to be used there is highly recommended.
& Palmork, K. H. (1982). Accumulation and elimination of (9--14C) phenanthrene in the reef-building coral (Diplorla strigosa). Bull. Environm. Contain. and Toxicol. 28, 281-284. LcGore, R. S., Marzalek, D. S., Hoffman, J. E. & Cuddeback, J. E. (1983). A field experiment to assess the impact of chemically disperscd oil on Arabian Gulf corals. Soc. Petrol. Engs. SPE no. 11444, 51-55. Wyers, S. C., Frith, H. R., Dodge, R. E., Smith, S. R., Knap, A. H. & Sleeter, T. D. (1986). Behavioural effects of chemically dispersed oil and subsequent recovery in Diploria strigosa. Mar. Ecol. 7, 23-42.
1)1125-326X/87S3J)O+O.O0 O 1987 PergamonJournalsLtd.
MarinePollutionBulletin.Vol. 18, No. 3. pp. 122-124. 1987. Printedin Great Britain.
Effects of South Louisiana Crude Oil and Dispersants on Rhizophora Mangroves HOWARD J. TEAS, EIRIK O. DUERR* and J. ROSS WlLCOXt
Biology Department, Universityof Miami, Coral Gables, Florida 33124; t Florida Power&Light Co., P.O. Box 14000, Juno Beach, Florida 33408, USA *Present address: The Ocean Institute, Makapun Point, Waimanalo, Hawaii 96795, USA
Sprays of seawater or dispersant were found to have no value in saving oiled Rhizophora mangroves. However, mangroves treated with dispersed oil showed no greater mortality than was found in untreated control plots. It is concluded that every effort should be made to protect mangroves from oil, including offshore dispersal.
Mangroves are trees and shrubs that grow along low energy tropical and subtropical shorelines of the world. Although there are at least 15 genera and more than 50 species of mangroves worldwide (Chapman, 1970), species of the genus Rhizophora are dominant in areas adjacent to open water over much of the more tropical parts of the range of mangroves. Rhizophora mangroves are important protectors of shorelines from storms and currents, they can be harvested for timber and firewood, they provide shelter and habitat for many animal species, and they are a source of primary productivity for food webs that serve as a base for the production of marine and estuarine organisms such as lobsters, prawns, finfish, and shellfish (summarized by Teas, 1979). Rhizophora mangroves have arching, stilt-like aerial roots, called prop roots, that serve as anchoring structures, and contain tissues that conduct air to the subsurface roots. They occur near many tropical oil production areas and shipping lanes, and are often found at low-energy sites where spilled oil accumulates. As a consequence, Rhizophora mangroves are frequently oiled from shipping accidents, oil well blowouts, tanker bilge washings, etc. 122
Although many cases of oil damage to mangroves have been tabulated (e.g. Lewis, 1983), no systematic experiments have been reported on the effects of dispersed oil on mangroves or on attempts to reduce mangrove mortality by post-oiling treatments. Leaf fall and the related death of apical buds were found to be indicators of tree stress. All oiled trees showed increased leaf loss, but some recovered. The reliable criterion for oil damage to Rhizophora mangroves was therefore taken to be tree death. The present study reports on the mortality in Rhizophora mangroves from oil under controlled conditions. The oil treatment corresponds to a spill in which the oil is carried into the mangroves by the tide. Under real-life situations, such oil would often have been partially weathered before impacting the mangrove communities. Because fresh, rather than weathered, oil was applied in the present study, the results obtained may be considered to be 'worst case' effects. The non-ionic waterbased dispersant (NIWBD) and seawater (SW) washes represent an attempt to save oiled trees by washing the oil from the trees and soil with high-pressure sprays applied the next day. Except for the lack of weathering, the oil dispersed with glycol ether-based dispersant (GEBD) corresponds to a well-dispersed oil slick being brought ashore into mangroves by the tide. Materials and M e t h o d s The mangroves used for the experiment were Rhizophora mangle;, the experimental plots were almost a monoculture of this species. The trees are located along the sloping bank of a canal that was dug through the
Volume 18/Number 3/March 1987
area approximately 14 years ago. The canal, which is about I5 m wide and 1.5 m deep, was formerly part of a thermal discharge canal system that emptied into Biscayne Bay. The site is on the grounds of the Florida Power & Light Co.'s Turkey Point Power Plant, which is located 40 km south of Miami, Florida, at c. 80 ° 20' W and 25 ° 26' N. The water in this canal has very limited connections with the present cooling canals and the whole system is isolated from Biscayne Bay by earth dikes. The water in the canal is not tidal, but its level varies approximately 0.6 m during a year. The canal salinity during the period of the experiment varied from 30-42%0, as a function of rainfall and evaporation. This salinity range is similar to that of Biscayne Bay. The mangrove plots were each enclosed by a semicircular boom (radius of 1.37 m) located on the water side (Fig. 1). The number of trees per plot varied from 8-50. Tree size varied but each plot had at least one tree 2 m tall and many trees in the plots were more than 2.5 m tall. Each plot had an area of 3.0 m 2. Plots were separated from the canal by a 4.3 m length of oil boom; in addition each plot that received oil was provided with an arc section of oil boom 6-9 m long located on the canal edge for containment of any splash or runoff oil. Plots were laid out so that all the prop roots of the experimental trees were within the area of the plot; nearby trees and intruding prop roots from outside were removed for a distance of 0.5 m. Trees that shaded the plots at any time of day were pruned or removed. The chain-weighted skirts of the inner and outer oil booms were buried in the muddy soil. The relationships of plots, trees, and oil booms are illustrated in Fig. 1. Plots differed in numbers of crab burrows. In order to assure uniform penetration o f oil into the substrata
Aerial view of plot
~
for all treatments, 36 'artificial crab holes' each 3 cm in diameter and 0.5 m deep were bored into the soil of each of the 24 plots at least 2 weeks before oiling. These holes were spaced to avoid, so far as possible, the subsurface roots near prop roots. Experiments were set up in July 1983. Oil treatment consisted of unweathered South Louisiana crude oil applied at the rate of 114 1. per plot (38 1. m--~). These treatments were administered in three 38 1. applications about 1! h apart. The oil was poured onto the soil and over the lower about 30 cm of the prop roots by hand using metal cans and buckets. Treatments were randomized among the plots and replicated three times. In the case of post-oiling washes with NIWBD, the dispersant was educted into a stream of SW (Canal water) provided by a gasoline powered pump as described by Canevari (1979). The SW and dispersant was sprayed on the soil and prop roots at a pressure of about 325 kg cm -2. Each plot so treated received 3.8 I. NIWBD in about 389 1. SW during 2 rain. and then a 3 rain. wash with only SW. The NIWBD in SW wash treatment was repeated 2 h later for a total of 7.6 1. NIWBD per plot. SW washes involved the same SW volumes and were also repeated afier2 h. In the case of GEBD, 114 1. of oil mixed with 5.7 1. of G E B D was educted into a stream of SW which was sprayed at low pressure or poured on the soil and prop roots. Leaf fall, apical bud death and tree death were scored for 30 months and tree death for 36 months. Only tree death is included in this report.
Results The percentages of trees that died from each treatment are plotted in Fig. 2. It is obvious that oil treatments, whether or not there was an attempt to wash away the oil, caused much higher mortality than occurred in treated controls, or the simple NIWBD or SW washes. The differences in mortality between oiled plots and controls were significant (P ~<0.05) by the Student-Newman-Kuels multiple range test at 12 months and thereafter. Both wash treatments following oil had significantly higher mortalities than controls at 6 months and thereafter. The plots treated with the same amount of oil, but dispersed by G E B D , had mortalities that did not differ significantly from the control, SWwashed, or NIWBD-washed plots.
Summary and Conclusions ongroves
~
oik boom PLot
SectionoL view of plot
Fig. l Experimental plot arrangement.
South Louisiana crude oil killed Rhizophora mangroves. High pressure washes with SW or NIWBD in SW applied the day after oiling were ineffective in reversing oil toxicity; indeed, they increased mortality compared to treatments with oil only. Oil pre-dispersed by G E B D caused no more mortality than that observed in untreated controls. These experiments indicate that: 1. every possible effort should be made to keep spilled oil from reaching mangroves, including offshore dispersal, and 2. washing oiled mangroves apparently has no value for saving the trees.
123
M a r i n e Pollution Bulletin
60--
• /
50--
•~
~....~ • OiL+SW
•
Oi(+NIWBD
40
./
50--
•
20--
•
I0--
J
..,,,r
6
"
L 12
'
l
,,~.~-----
~
~ 18
• Sea w a t e r
• '~ ' ' ' ~ - ~ 24
• Oit +GEBD ~ 30
-
?
Control 36
T i m e in m o n t h s
Fig. 2 M a n g r o v e mortality at 6 m o n t h intervals for e x p e r i m e n t a l treatments.
The authors.wish to express their thanks to the Florida Power & Light Co. ['or permission to carry out the experiment on their property; Earl Baker of Florida Power & Light Co. for logistic support of field operations; Gerald P. Canevari for the loan of the gasoline-powered pump used for spray treatments; Daniel Cary for assistance with statistical analyses; Exxon Chemical Company and Texaco, Inc. for materials; the American Petroleum Institute (API) for financial support of the investigations; the API Task Force members (Stuart Horn, Gerald E Canevari, June Lindstedt-Siva, C. Bruce Koons, Albert Lasday, Clayton McAuliffe and James Marum) for advice and field assistance; Donald Casey and Jack R. Gould, API staff, for advice and administrative support; and Michael de Grood, Carlos Manalich, George Concepcion, Clorinda Roblcs, and Marie Morgan for technical assistance.
Canevari, G. P. (1979). Restoration of oiled shorelines by proper use of chemical dispersants. Proceedings ot 1979 Oil Spill Conference, pp. 443-446. American Petroleum Institute, Washington, D.C. Chapman, V. J. (1970). Mangrove phytosociology. Tropical Ecology 11, 1-19. Lewis, R. R. (1983). Impact of oil spills on mangrove forests. In Tasks for Vegetation Science (H. J. Teas, ed.), pp. 171-183. Dr. W. Junk Publishers, The Hague. Teas, H. J. (1979). Silviculture with saline water. In The Biosaline Concept (A. Hollacndcr, ed.), pp. 117-161. Plenum Publishing Corporation, New York.
~hlrine Pollunon Btdletin, Vol. 18, No. 3. pp. 124-126. 1987.
()025-326X/87 $3.00+0.00 © 1987 PergamonJournals Lid.
Printed in Great Britain.
Oil Spill Clean-up: The effect of Three Dispersants on Three Subtropical/Tropical Seagrasses A. T H O R H A U G *
a n d J. M A R C U S
Florida International University, Tamiami Campus, Miami FL 33199, USA *On leave to United Nations Food and Agriculture Organization
Three seagrasses found throughout the Greater Caribbean tropical/subtropical region as major critical habitat organisms were tested in the laboratory for toxicity limits to three dispersants commonly stockpiled in the region. At concentrations in the recommended dosage level, that is, below 1 ml dispersant with 10 ml oil in 100 000 ml seawater, even for 100 h no large mortality occurred (15-18 barrels per acre as calculated by Exxon, 1985). At an order of magnitude higher, especially for longer time periods, the more sensitive seagrasses Syringodium filiforme and then Halodule wrightii succumbed. The dispersants had widely differing effects, with Corexit 9527 and Arco124
chem D609 having far less toxic effect than Conco K(K) at the same exposure time and concentration. There was comparatively little difference between effects of oils (Louisiana crude versus Murban). Types and brands of dispersants should be referred to specifically in oil spill contingency plans since such widely varying ecological toxicity occurs among various dispersants. Use of the word 'dispersant' as a policy tool should be used with caution, realizing that dispersants vary widely in toxicity effects. Further testing of seagrasses in other ocean basins and those dispersants to be used there is highly recommended.