Evaluation of alternative oil spill cleanup techniques in a Spartina alterniflora salt marsh

Environmental Pollution 55 (1988) 221-238

Evaluation of Alternative Oil Spill Cleanup Techniques in a Spartina alterniflora Salt Marsh Russell W. Kiesling, Steve K. Alexander* & James W. Webb Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas 77553-1675, USA (Received 22 October 1987; accepted 20 April 1988)

ABSTRACT Three oil spill situations which cause long-term impact were simulated in 1 m 2 salt marsh plots to evaluate the effectiveness of alternative cleanup techniques at removing oil and reducing damage to Spartina alterniflora. Cleanup techniques, implemented 18-24 h after oiling, were not effective at removing oil after sediment penetration. When oil remained on the sediment surface, flushing techniques were most effective at removal, reducing levels of added oil by 73% to 83%. The addition of dispersant to theflushing stream only slightly enhanced oil removal Clipping of vegetation followed by sorbent pad application to sediment was moderately effective, reducing added oil by 36% to 44%. In contrast to flushing and clipping, burning increased the amount of oil in sediment by 27% to 72%. Although flushing and clipping were effective at oil removal, neither technique reduced initial damage to plants or enhanced long-term recovery. Whileflushed plots sustained no additional plant damage due to cleanup, clipped and burned plots sustained additional initial plant damage. Based on these results,first consideration should be given to natural tidalflushing as the means to remove oil, especially in salt marshes subject to ample tidal inundation. Although our results do not support cleanup in salt marshes with ample tidal inundation, low pressure flushing may be warranted when fuel oils or large quantities of crude oil impact salt marshes subject to reduced tidal flushing. Flushing, when warranted, should be initiated prior to oil penetration into the substrate. Clipping may be considered as a cleanup response only when heavy oil cannot be effectively removed from vegetation by flushing. Burning is not recommended because it enhances oil penetration into sediment and causes substantial initial plant damage. * To whom correspondence should be addressed. 221 Environ. Pollut. 0269-7491/88/$03"50 © 1988 Elsevier Science Publishers Ltd, England. Printed in Great Britain

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Russell W. Kiesling, Steve K. Alexander, James W. Webb

INTRODUCTION Gulf coast salt marshes form valuable nursery grounds for a variety of species (Lindall & Saloman, 1977). They also act to stabilize shorelines against erosion as well as enhance water quality through immobilization of nutrients and filtering of heavy metals and toxic materials from the water column (Getter et al., 1984). Because of these values, salt marshes receive the highest priority for protection in comprehensive oil spill response plans for coastal areas (Lindstedt-Siva, 1977; Gundlach & Hayes, 1978). However, despite their priority in the implementation of protection efforts, salt marshes are still occasionally impacted by oil (Crow, 1974; Hershner & Moore, 1977; Mattson et al., 1977; Ayers, 1978; Hampson & Moul, 1978; Holt et ai., 1978; Sanders et al., 1980; Webb et al., 1981; Alexander & Webb, 1987). Cleanup is often attempted after oil enters a salt marsh. However, improper cleanup activities can be harmful. For example, cleanup activities on the Ile Grande marsh following the A m o c o Cadiz spill resulted in severe long-term damage to the marsh (Long & Vandermeulen, 1983). Because of damage frequently associated with oil cleanup in salt marshes, some researchers have recommended natural cleansing, i.e. the 'do nothing' approach (Westree, 1977; Lindstedt-Siva, 1979; 1984). Others have examined oil spills and subsequent cleanup efforts in salt marshes and have reported good recovery (Mattson et al., 1977; Holt et al., 1978; Webb et al., 1981; Alexander & Webb, 1983). However, others have reported detrimental effects associated with cleanup activities (Crow, 1974; Holt et al., 1978; Long & Vandermeulen, 1983; Getter et al., 1984; Lane et al., 1987). Still others have conducted field experiments in which cleanup had no detrimental or beneficial effects (DeLaune et aL, 1984; Smith et al., 1984). As a result of these studies, there is some information to draw upon when implementing a cleanup response. Yet, a number of questions regarding the use of alternative cleanup techniques in salt marshes remain unanswered: (1) should cleanup be attempted at all in salt marshes, and, if so, under what conditions?; (2) do cleanup techniques simultaneously remove oil and decrease damage to vegetation? and (3) which of the alternative cleanup techniques is most useful? After a careful research of the literature, Alexander & Webb (1985a) concluded that rapid recovery occurred in a number of oil spill situations in salt marshes without cleanup. Cleanup is clearly not warranted in these situations because of damage associated with cleanup activities. In addition, they were able to identify spill situations where impact was long-term; when No. 2 fuel oils were involved and when large quantities of oil penetrated the sediment. In a later study, they identified oil completely covering plant surfaces during active growth periods as a third long-term impact situation

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(Alexander & Webb, 1985b). It is for these situations that they recommend consideration of a cleanup response. The purpose of the present study was to evaluate the effectiveness of alternative cleanup techniques in a Spartina alterniflora salt marsh exposed to these three long-term impact situations. The oils chosen in the present study were No. 2 fuel oil and Isthmus (Mexico) crude oil. Both oils are transported in the Gulf of Mexico and, if spilled, could cause long-term impact in salt marshes in the situations described above. Isthmus crude is imported from Mexico for local refining, while No. 2 fuel oil is shipped to markets primarily on the east coast. Both oils were obtained from Exxon Company, USA, with the following information: Isthmus crude oil--33-0 API gravity, 1.5% sulfur and 0"9% aromatics; No. 2 fuel oil--a light, low sulfur content heating oil. Although the aromatic content was not provided, refined oils such as No. 2 fuel oil typically have a much higher aromatic content than crude oils (Evans & Rice, 1974; Ryan, 1977).

MATERIALS AND METHODS Three series of 24 1 m 2 plots (with 10 m between series and 1 m between plots in a series) were established in a row 4-10 m from the shoreline of a S. alterniflora dominated salt marsh located on the northern edge of Pelican Island in Galveston Bay, Texas (Fig. 1). All three series were established in an area of S. aiterniflora marsh where visual inspection indicated uniform plant height and density and uniform sediment type. Homogeneity of vegetation in this area was later verified by comparison of control plots during analysis of data. The three series of plots were treated as follows: (1) No. 2 fuel oil applied at 2 liters/m 2 on sediment and lower plants on 15 November, 1985; (2) Isthmus (Mexico) crude oil applied at 4 liters/m 2 on sediment and lower plants on 14 January, 1986; and (3) Isthmus (Mexico) crude oil applied at 2 liters/m 2 on sediment and entire plants on 19 May, 1986. Each series was treated with oil (with respect to type, amount, degree of plant coverage, and date of application) to simulate one of the three long-term impact situations reported in the literature (cited earlier). Specifically, the first series was designed to simulate a No. 2 fuel oil spill in the fall. The second series simulated a winter crude oil spill with dormant marsh plants and large quantities of oil penetrating the sediment surface, while the third series simulated a crude oil spill during an active plant growth period with oil completely covering plant surfaces. A randomized block design with four replications of six treatments was used for each series of plots. These treatments were: 1--no oil/no clean (control); 2--oil/no clean; 3--oil/flushing with sea water; 4~oil/flushing

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Russell W. Kiesling, Steve K. Alexander, James W. Webb

9'5° ~ ' ~

~

Gulf

of Mexico

/

1 mile

Fig. 1.

Location (X) of study site on Pelican Island.

with sea water plus dispersant; 5--oil/clipping and sorbent pads; 6--oil/ burning. Before oil application, retaining structures of plywood which projected 50 cm above the marsh surface were placed around each 1 m 2 plot. These structures prevented normal tidal exchange for 18-24h while ensuring oil retention in plots until cleanup. For the November spill, these retaining structures were assembled on site in the marsh. Corner stakes (122 x 10 x 5cm) were driven 61 cm into the sediment. Plywood backing and identification tags were attached at each corner. When this construction method was used, oil leaked from some of the plots due to difficulties encountered in sealing the edges. For the two remaining spills, oil retaining structures were assembled beforehand and transported to the marsh. When this construction method was used, no oil leakage was noted. After retaining structures were in place, oil was sprayed into all plots (except controls) within 1 h. Oil was applied with commercial hand sprayers to ensure uniform coating of sediment and plant surfaces. Sediment surfaces were oiled uniformly within these plots while plants were covered either partially (lower 20-30 cm) or completely (May simulated spill). Since oil was

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225

applied only during low tide, oil came into direct contact with both sediment and plant surfaces. Because of retaining structures, oil remained in contact with these surfaces until cleanup. To duplicate approximate response time in an actual oil spill, retaining structures were not removed until 18-24 h after each simulated spill. After this time, retaining structures were removed and oil cleanup began. Plots treated by low pressure flushing were washed using a Wayne portable p u m p (GP300) for 60 s with 300 liters of sea water. Since the nozzle diameter was 5 cm, this flow created minimal disturbance of sediment and plants. For plots flushed with sea water and added dispersant, a water-based chemical dispersant (Corexit 7664, Exxon Chemical Americas) was introduced into the stream by means of a chemical eductor for the first 15 to 20 s at the recommended dilution rate of 1-2%. Clipped vegetation was removed at sediment level and the substrate was treated with sorbent pads (Type 157 oil sorbent, 3M Company). Sorbent pads were stepped on to simulate trampling by workers during normal cleanup operations. Propane torches were used to ignite oil in the burned plots. Plants were burned to a uniform level with actual burning lasting from several minutes to approximately I h for each plot. The effectiveness of each cleanup technique was assessed by its ability to remove oil from the sediment and reduce damage to S. alterniflora. Sediment samples were removed from each plot immediately after cleanup to determine ability of each cleanup technique to remove oil. A sediment sample of each plot consisted of three cores (5 cm wide x 5 cm deep) pooled from one 0.25 m E subplot. Sediment samples were frozen until hydrocarbon extractions could be performed. Hydrocarbons were extracted from 100 g wet sediment by washing with 75 ml methylene chloride in an extraction flask. Extractions were repeated until the decanted solvent was clear. The resulting solvent was filtered through a W h a t m a n G F / C glass microfiber filter and transferred to a 500 ml round bottom evaporating flask. The flask was attached to a Buchler portable flash-evaporator with the bottom submerged in a 60°C water bath. After solvent evaporation, the residue was transferred to a tared 8.5 m! drying vial with the aid of several solvent rinses. The vial remained open at r o o m temperature until only oil residue remained. The quantity of oil residue was then determined gravimetrically with measurements continuing until a constant weight was obtained. Hydrocarbon content of the sediment was reported as mg hydrocarbon per g dry sediment. Total hydrocarbon content of the sediment from each plot was analyzed with SAS (Statistical Analysis System) using the Duncan's Multiple Range Test for significant differences between treatments. Nonoiled plots were compared to the oiled, non-cleaned plots to determine total a m o u n t of hydrocarbons in the sediment due to the simulated oil spill. The

Russell W. Kiesling, Steve K. Alexander, James W. Webb

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cleaned plots were compared to the oiled, non-cleaned plots to determine the effectiveness of each cleanup technique at removing oil. Plant samples were collected l, 5 and 12 months after each spill from the three remaining 0.25 m 2 subplots. All vegetation was removed by clipping at sediment level and separated as live and dead on the basis of coloration. Plant material containing green color was considered live. Separated plant samples were placed in tared paper bags and dried at 80°C to constant weight. Live and dead plant biomass data were analyzed with SAS using the Duncan's Multiple Range Test for significant differences between treatments. The effectiveness of each cleanup technique at reducing damage to plants was assessed by comparison of live and dead biomass among treatments as described for the hydrocarbon data. RESULTS No. 2 fuel oil

Oil levels in study plots immediately after cleanup of the three simulated spills are presented in Table 1. For the No. 2 fuel oil spill, oil levels in oiled/ TABLE 1 Sediment Oil Content (mg/g dry sediment)a in Salt Marsh Plots Immediately after Cleanup

Treatments b

Simulated oil spill ~ No. 2 fuel oil

Isthmus crude (4 liters/m 2)

Isthmus crude (entire plants)

1

0"6

0-I

2 3 4 5

1-8 0-4 0-3 1-0

5-3n 3'6 d 5-3a 4-0n

0.2 1.1 0"3 0"2 0"7

6

3"ln

4.5 n

1-44

° Values represent the mean of four replications. b 1 - - n o oil, no clean (control); 2--oil, no clean; 3--oil/flush with sea water; 4--oil/flush with sea water plus dispersant; 5--oil/clip and sorbent pads; 6 - oil/burn. c No. 2 fuel oil (2 liters/m 2) was applied on sediment on lower plants (15 November 1985); Isthmus crude oil (4 liters/m 2) was applied on sediment and lower plants (14 January 1986); Isthmus crude oil (2 liters/m 2) was applied on sediment and entire plant surfaces (19 May 1986). d Significant difference (P < 0.05) in sediment oil content between control and oil treatment as determined by analysis of variance and Duncan's Multiple Range Test.

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227

non-cleaned plots were three times higher than in the non-oiled plots. However, this difference could not be termed significant (p < 0.05) due to oil leakage from plywood enclosures which caused high variability within some treatments. Oil leakage from some plots was likely due to improper sealing of retaining structure edges and not to the light nature of the oil. Of the cleanup techniques employed, flushing with sea water and sea water plus dispersant reduced oil levels to the background levels of non-oiled plots. Clipping also removed oil, but not to the degree of flushing. In contrast, burning increased mean oil content of the sediment when compared to oiled/non-cleaned plots. Standing crop measurements ofS. alterniflora 1, 5 and 12 months after the No. 2 fuel oil spill are presented in Table 2. Damage to S. alterniflora, as TABLE 2

Spartina alterniflora S t a n d i n g C r o p (g/m2) a in Salt M a r s h Plots 1, 5 a n d 12 M o n t h s after the 15 N o v e m b e r 1985 A p p l i c a t i o n o f No. 2 Fuel Oil (2 liters/m 2) o n Sediment a n d L o w e r Plants

Months after spill

Treatments ~

Biomass (g/m 2) Live

Dead

1

1 2 3 4 5 6

686 504 c 654 577 0~ 189 c

156 335 c 309 219 tY 576 c

5

1 2 3 4 5 6

304 101 c 98 c 120 52 ~ 77 c

315 55@ 467 460 1c 536 c

12

1 2 3 4 5 6

475 401 366 443 401 422

132 107 103 78 108 111

a Values represent the m e a n o f four replications. b See T a b l e 1 for treatments. c Significant difference ( P < 0"05) between oil t r e a t m e n t a n d the control as determined by analysis o f variance a n d D u n c a n ' s Multiple R a n g e Test.

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Russell W. Kiesling, Steve K. Alexander, James I4I. Webb

indicated by a significant (p < 0.05) decline in mean live biomass and increase in mean dead biomass, was evident in oiled/non-cleaned plots when compared to non-oiled plots one month after cleanup. Of the cleanup techniques employed, none significantly reduced this initial plant damage. Although mean live biomass was greater in plots flushed with and without dispersant when compared to oiled/non-cleaned plots, these differences were not significant. Dead plant biomass in both types of flushed plot was also comparable to the oiled/non-cleaned plots. Since all vegetation was removed during cleanup, clipped plots contained no biomass one month later. Burned plots contained significantly lower live biomass and higher dead biomass than oiled/non-cleaned plots. Five months after cleanup, live and dead plant biomass comparisons between oiled/non-cleaned and non-oiled plots still indicated plant damage. Only plots flushed with dispersant added appeared to enhance recovery of plant growth. None of the remaining cleanup techniques significantly altered levels of live biomass when compared to oiled/non-cleaned plots. Dead biomass after five months in both flushed and burned plots was not significantly different from oiled/non-cleaned plots. Clipped plots contained all new growth and essentially no dead biomass. There were no significant differences in mean live or dead plant biomass in any of the plots 12 months after cleanup.

Isthmus (Mexico) crude oil (4 liters/m 2) Immediately after cleanup of the Isthmus crude oil spill of 4 liters/m 2, oil levels in oiled/non-cleaned plots were significantly higher (p < 0"05) than in non-oiled plots (Table 1). Most of the cleanup techniques did remove some oil, but all cleaned plots still had an elevated oil content comparable to the oiled/non-cleaned plots. S. alterniflora standing crop measurements 1, 5 and 12 months after the Isthmus crude oil spill of 4 liter/m 2 are presented in Table 3. Live biomass comparisons between non-oiled and oiled/non-cleaned plots indicated significant plant damage due to oil one month after cleanup. There was a corresponding increase in dead biomass. Of the cleanup techniques employed, none significantly reduced this initial plant damage. Clipped plots had experienced some new growth. Burned plots contained significantly lower live biomass than oiled/non-cleaned plots. Five months after cleanup, damage to S. alterniflora was still evident. Comparisons of live biomass indicated that none of the cleanup methods reduced this plant damage. There were no detectable differences in dead biomass other than in clipped plots. Twelve months after cleanup, there was still significantly less (p < 0.05)

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TABLE 3 Spartina alterniflora Standing Crop (g/m2) a in Salt Marsh Plots 1, 5 and 12 Months after the 14 January 1986 Application of Isthmus (Mexico) Crude Oil (41iters/m 2) on Sediment and Lower Plants Months after spill

Treatments b

Biomass (g/m 2) Live

Dead

1

1 2 3 4 5 6

378 23@ 258 c 256 c 14c 34c

514 716 844c 678 17c 626

5

1 2 3 4 5 6

361 68c 23~ 29~ lilY 94~

212 256 247 259 21 c 250

12

1 2 3 4 5 6

130 6lY 51 c 52c 95 51c

237 94c 78¢ 97~ 142 82~

a Values represent the mean of four replications. See Table I for treatments. c Significant difference (P < 0"05) between oil treatment and the control as determined by analysis of variance and Duncan's Multiple Range Test. live b i o m a s s in o i l e d / n o n - c l e a n e d p l o t s t h a n in n o n - o i l e d plots, i n d i c a t i n g l o n g - t e r m o i l - i n d u c e d d a m a g e t o S. alterniflora. L i v e a n d d e a d b i o m a s s in all c l e a n e d p l o t s w e r e c o m p a r a b l e t o levels in o i l e d / n o n - c l e a n e d p l o t s i n d i c a t i n g n o b e n e f i t d e r i v e d f r o m c l e a n u p a f t e r o n e year.

Isthmus (Mexico) crude oil (entire plants) I m m e d i a t e l y a f t e r c l e a n u p o f t h e I s t h m u s c r u d e oil spill w i t h e n t i r e p l a n t c o v e r a g e , oil levels in o i l e d / n o n - c l e a n e d p l o t s w e r e a p p r o x i m a t e l y five t i m e s h i g h e r t h a n in n o n - o i l e d p l o t s ( T a b l e 1). F l u s h i n g t e c h n i q u e s r e d u c e d oil c o n t e n t t o t h e b a c k g r o u n d levels o f n o n - o i l e d plots. C l i p p i n g r e m o v e d s o m e

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Russell W. Kiesling, Steve K. Alexander, James W. Webb

oil, while b u r n i n g i n c r e a s e d oil in s e d i m e n t w h e n c o m p a r e d to oil levels o f o i l e d / n o n - c l e a n e d plots. S t a n d i n g c r o p m e a s u r e m e n t s o f S. alterniflora 1, 5 a n d 12 m o n t h s a f t e r the I s t h m u s c r u d e oil spill w i t h entire p l a n t c o v e r a g e are p r e s e n t e d in T a b l e 4. O n e m o n t h a f t e r c l e a n u p , d a m a g e to S. alterniflora w a s e v i d e n t b y significantly l o w e r live b i o m a s s a n d h i g h e r d e a d b i o m a s s in the o i l e d / n o n c l e a n e d p l o t s w h e n c o m p a r e d to n o n - o i l e d plots. N o n e o f the c l e a n u p m e t h o d s e m p l o y e d r e d u c e d this initial d a m a g e to plants. F l u s h e d p l o t s c o n t a i n e d levels o f live a n d d e a d p l a n t b i o m a s s similar to t h o s e in the oiled/ n o n - c l e a n e d plots. B o t h clipped a n d b u r n e d p l o t s c o n t a i n e d little o r n o live biomass. TABLE 4 Spartina alterniflora Standing Crop (g/m2) a in Salt Marsh Plots, 1, 5 and 12 Months after the 19 May 1986 Application of Isthmus (Mexico) Crude Oil (2 liters/m 2) on Sediment and Entire Plant Surfaces

Months after spill

Treatments b

Biomass (g/m 2) Live

Dead

2 3 4 5 6

271 118c 152c 139c 0c 3~

241 547c 378 437 c 0~ 521 c

5

1 2 3 4 5 6

694 446 ~ 497 502 59c 149c

329 328 329 268 24~ 224

12

1 2 3 4 5 6

320 324 323 328 275 341

304 151Y 173¢ 18(Y 55c 78c

1

1

a Values represent the mean of four replications. b See Table 1 for treatments. c Significant difference (P < 0-05) between oil treatment and the control as determined by analysis of variance and Duncan's Multiple Range Test.

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Five months after cleanup, damage to plants in oiled/non-cleaned plots was still evident. However, dead biomass levels in oiled/non-cleaned and non-oiled plots were virtually identical. Cleanup did not aid in plant recovery. Mean live and dead biomass levels for flushed plots were similar to oiled/non-cleaned plots. Clipped and burned plots still had significantly lower levels of live biomass. There was no detectable difference in mean live biomass between oiled/ non-cleaned and non-oiled plots 12 months after cleanup. Flushed plots contained live and dead plant biomass similar to oiled/non-cleaned plots. Clipped and burned plots contained live biomass similar to oiled/noncleaned plots and dead biomass significantly (p < 0.05) lower than oiled/ non-cleaned plots. DISCUSSION Flushing was the most effective technique at removing oil from the sediment surface of the salt marsh. Oil visibly flowed from the study plots during flushing. This field observation was subsequently verified by sediment analysis which indicated that flushing reduced levels of added oil by 73-83%. DeLaune et al. (1984) reported flushing to be less effective in an experimental spill of South Louisiana crude oil, removing only 36% of the added oil. Comparisons between flushing alone or with added dispersant in this study indicated that use of the dispersant only slightly increased the amount of oil removed. DeLaune et aL (1984) and Smith et al. (1984) reported flushing with added dispersant reduced sediment oil levels by 33 %. Once oil penetrated the sediment surface, not even flushing was effective at removal. None of the cleanup techniques removed much oil after the January 1986 spill where large amounts of crude oil penetrated the marsh surface. At the time oil was applied, both the water table and tide were extremely low. Oil quickly penetrated the sediment as it was applied. Cleanup procedures the following day were of limited effectiveness at removing oil as indicated by elevated sediment hydrocarbon content in all oiled plots even after cleanup. Clipping of vegetation followed by sorbent pad application on the sediment removed some surface oil from the marsh. Oil adhering to plant surfaces was removed when the plants were clipped. Sorbent pads also removed visible amounts of oil from the bare sediment surface. Sediment hydrocarbon levels, as determined by laboratory analysis, verified that some oil had been removed although in lesser concentrations than by flushing. Clipping followed by sorbent pad application on the substrate removed 36--44% of added oil. DeLaune et al. (1984) found a 31% reduction in sediment oil after clipping.

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Russell W. Kiesling, Steve K. Alexander, James W. Webb

Of the cleanup techniques employed, burning proved least effective at removing oil. Burning actually increased oil content in sediment by 27-72%. Lindstedt-Siva (1984) cautions against burning oiled vegetation as a cleanup alternative in salt marshes because it may promote oil penetration into the sediment. This study verified her suggestion. Burning did not increase the amount ofoil in the sediment following the January 1986 spill because large amounts of oil had already penetrated into the sediment prior to cleanup. Although flushing was able to remove oil from the marsh, it was unable to significantly reduce initial oil-induced damage to S. alterniflora or enhance long-term plant recovery. Flushed plots did not sustain any additional plant damage due to cleaning, since amounts of live and dead biomass in flushed plots were generally equal to amounts in oiled/non-cleaned plots. Also, the addition of dispersant did not alter plant response to flushing since amounts of live and dead biomass in flushed plots were generally equal regardless of dispersant. Although clipping was able to remove some oil from the marsh, it was unable to reduce plant damage or enhance recovery. Instead, clipping vegetation resulted in considerable initial damage to S. alterniflora. Clipped plots generally took up to one year for biomass levels to reach those of oiled/ non-cleaned plots. Also, damage to plants associated with foot traffic around study plots was noted following oil application and cleanup. DeLaune et al. (1984) reported considerable damage to marsh vegetation associated with cleanup activities and sampling in areas around study plots. Other investigators have indicated traffic in the marsh as an additional source of damage to vegetation (Westree, 1977; Holt et aL, 1978; Long & Vandermeulen, 1983; Getter et al., 1984; Lindstedt-Siva, 1984). In addition to proving ineffective at oil removal, burning was unable to reduce plant damage or enhance recovery. Instead, burning caused considerable initial damage to S. alterniflora. Live biomass levels in burned plots took up to one year to reach those of oiled/non-cleaned plots. Detrimental effects have been associated with burning of salt marsh vegetation in other attempts to remove spilled oil (Crow, 1974; Westree, 1977; Lindstedt-Siva, 1984). There is a possible explanation why oil removal by flushing and clipping did not reduce initial damage to vegetation or enhance recovery. It is likely that substantial oil-induced damage to S. alterniflora occurred during the 18-24 h period prior to cleanup. For example, in the spill involving No. 2 fuel oil, the light nature of the oil may have promoted rapid penetration of a portion of the applied oil into plant tissue (Baker, 1971; Webb et al., 1985) resulting in damage upon contact. Also in the spill where oil completely covered plants, the oil could have resulted in a sudden reduction of oxygen transport to the roots. S. alterniflora is dependent on oxygen transported to

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233

its roots to supply aerobic metabolic processes and to oxidize the surrounding sediment. Productivity of the plant has been directly correlated with its ability to transport oxygen to its roots for maintenance of a favorable (high) redox potential in the surrounding sediment (Howes et al., 1981). Complete blockage of air-space openings with oil would limit the ability of the plant to transport oxygen to the roots and could have resulted in the rapid development of an unfavorable (low) redox potential toxic to the roots (Alexander & Webb, 1985b). In the present study, none of the alternative cleanup techniques simultaneously removed oil and reduced plant damage. The only benefit derived from cleanup was the removal of oil by flushing and clipping. Natural tidal flushing can achieve the same result as cleanup in those areas subject to ample tidal exchange. Therefore, our results indicate that cleanup is not recommended in salt marshes subject to good tidal flushing. In these salt marshes, there is no additional benefit derived from cleanup, while tidal flushing both alleviates the need for traffic on the marsh and removes substantial quantities of oil with no added expense. Our recommendation of the 'do nothing' approach in marshes with ample tidal flushing agrees with others who have advocated natural cleansing based on arguments that cleanup is damaging (Westree, 1977; Lindstedt-Siva, 1979, 1984). Although our results do not support cleanup in salt marshes with adequate tidal flushing, cleanup may be warranted when fuel oils or large quantities of crude oil impact salt marshes subject to reduced tidal flushing. For example, reduced tidal cycles are common along the Gulf coast during winter. Also, localized weather conditions such as prolonged 'northerns' can reduce water levels in salt marshes (Stinckney, 1984). Cleanup may be warranted under such conditions because oil would otherwise remain and eventually penetrate into sediment resulting in long-term damage to both plants and animals. Once oil has penetrated the surface, it is retained in salt marsh sediment for years (Blumer & Sass, 1972; Nadeau & Roush, 1973; Lytle, 1975; Alexander & Webb, 1978; Teal et al., 1978; Burns & Teal, 1979; Milan & Whelan, 1979; DeLaune et al., 1980; Hershner & Lake, 1980; Sanders et al., 1980; Lee et al., 1981; Macko et al., 1981) causing adverse effects on benthic fauna (Bender et al., 1977; Hershner & Moore, 1977; Krebs & Burns, 1977) and S. alterniflora (Hampson & Moul, 1978; Alexander & Webb, 1987). Removal of oil by cleanup techniques in these situations may lessen impact on such communities by preventing the amount removed from penetrating into the sediment. When the use of cleanup techniques is warranted, low pressure flushing should be given primary consideration. In the present study, flushing most effectively removed oil while causing no additional damage to plants. Flushing also minimized the amount of foot traffic in the marsh during

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cleanup operations. Several other authors have advocated flushing techniques for oil removal from salt marshes (Westree, 1977; Texas Engineering Extension Service, 1978; Lindstedt-Siva, 1979; Getter et al., 1984; Lindstedt-Siva, 1984). If flushing is to be effective, it must be implemented while oil remains on the surface of the marsh. Once oil penetrates the sediment, as occurred after the January 1986 spill, surface cleanup techniques will not be effective. Obviously, quick response time is critical. This is especially true where oil spills impact gravel, sandy, and peat substrates, as these will have higher rates of oil penetration than finer silts and clays (Texas Engineering Extension Service, 1978). Regardless of sediment type, if cleanup response is delayed and oil is allowed to penetrate the substrate, oil removal will be greatly hindered. When the use of cleanup techniques is warranted, clipping of vegetation should be given consideration only when substantial quantities of oil adhere to plant surfaces and flushing is ineffective at dislodging it. If clipping can be accomplished without substantial trampling of the marsh, it can be considered as a method to prevent oil penetration into the sediment, because it did remove some oil in the present study. However, large-scale clipping operations should be avoided since trampling by workers may cause extensive damage to root and rhizome structures (Holt et aL, 1978; Getter et al., 1984). Others have recommended clipping under certain conditions. For example, Mattson et al. (1977) recommends clipping of vegetation soon after a spill to reduce mortality. Based on the results of this study, burning of salt marsh vegetation to remove spilled oil should not be considered as a cleanup alternative. Burning increased initial mortality of plants as well as oil penetration into sediment. Increased oil penetration is undesirable because oil may be retained in the anaerobic sediments for years as a long-term source of potential impact (Blumer & Sass, 1972; Nadeau & Roush, 1973; Lytle, 1975; Alexander & Webb, 1978; Teal et al., 1978; Burns & Teal, 1979; Milan & Whelan, 1979; De Laune et al., 1980; Hershner & Lake, 1980; Sanders et al., 1980; Lee et al., 1981; Macko et al., 1981). CONCLUSIONS In the present study, none of the alternative cleanup techniques simultaneously removed oil and decreased damage to S. alterniflora. Although flushing and clipping were effective at removing oil, they were unable to reduce damage to S. alterniflora. Since cleanup responses have limited effectiveness at reducing oil-induced damage to plants, primary emphasis

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should be placed on contingency planning and protection of salt marsh habitat. In those situations where protection is too late or has failed, natural cleansing by tidal flushing should be given first consideration, i.e. the 'do nothing' approach. This recommendation agrees with the others who have recommended natural cleansing based on the damage associated with cleanup. While the present results do not support cleanup in salt marshes with ample tidal inundation, cleanup may be warranted when fuel oils or large quantities of crude oil impact salt marshes subject to poor tidal flushing. In these situations, low pressure flushing should be given first consideration and should be initiated prior to oil penetration into the sediment. If oil cannot be removed effectively from plants by flushing, clipping may be considered as a cleanup alternative. Burning should not be considered as a cleanup technique because it enhances oil penetration into sediment and causes substantial initial damage to plants.

A C K N O W L E D G E M ENTS This research was supported by the state of Texas through the Center for Energy and Mineral Resources at Texas A & M University as well as by the Harris and Eliza Kempner Fund, National Wildlife Federation, and American Petroleum Institute. Special thanks is extended to Exxon Corporation for supplying oils and chemical dispersant and to 3M C o m p a n y for supplying oil sorbent pads. The technical assistance of Daniel Avery, Carlos Vanoye-Trevino, Cecelia Miles, and Chiara Jones is gratefully acknowledged. REFERENCES Alexander, S. K. & Webb, J. W. (1978). Oil in the salt marsh: Damage assessment, cleanup, and restoration. In Oil Spill Control Course Handbook, revised edn. Texas Engineering Extension Service, Texas A&M University, College Station, Texas, Section M, pp.l-14. Alexander, S. K. & Webb, J. W. (1983). Effects of oil on growth and decomposition of Spartina alterniflora. In Proceedings of the 1983 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 529-32. Alexander, S. K. & Webb, J. W. (1985a). Oil in the salt marsh! What have we learned? In Proceedings of the Fourth Coastal Marsh and Estuary Management Symposium, ed. C. F. Bryan, P. J. Zwank & R. H. Chabreck. Louisiana State University, Baton Rouge, Louisiana, pp. 49-62. Alexander, S. K. & Webb, J. W. (1985b). Seasonal response of Spartina alterniflora to oil. In Proceedings of the 1985 Oil Spill Conference. American Petroleum Institute, Washington, DC., pp. 355-7.

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Alexander, S. K. & Webb, J. W. (1987). Relationship ofSpartina alterniflora growth to sediment oil content following an oil spill. In Proceedings of the 1987 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 445-9. Ayers, R. W. (1978). The effects of the barge STC-101 oil spill on shallow water invertebrates of lower Chesapeake Bay. In Proceedings of the Conference on Assessment of Ecological Impacts of O i l Spills. American Institute of Biological Sciences, Arlington, Virginia, pp. 280-310. Baker, J. M. (1971). Comparative toxicities of oils, oil fractions, and emulsifiers. In The Ecological Effects of Oil Pollution on Littoral Communities, ed. E. B. Cowell. Institute of Petroleum, London, pp. 78-87. Bender, M. E., Shearls, E. A., Ayers, R. P., Hershner, C. H. & Huggett, R. J. (1977). Ecological effects of experimental oil spills on eastern coastal plain estuarine ecosystems. In Proceedings of the 1977 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 505-9. Blumer, M. & Sass, J. (1972). Oil pollution: Persistence and degradation of spilled fuel oil. Science, 176, 1120-2. Burns, K. A. & Teal, J. M. (1979). The West Falmouth oil spill: Hydrocarbons in the salt marsh ecosystem. Estuar. Coast. Mar. Sci., 8, 349-60. Crow, S. A. (1974). Microbiological aspects of oil intrusion in the estuarine environment. Dissertation, Louisiana State University, Baton Rouge, Louisiana. DeLaune, R. D., Hambrick, G. A. & Patrick, W. H. (1980). Degradation of hydrocarbons in oxidized and reduced sediments. Mar. Pollut. Bull., 11, 103-6. DeLaune, R. D., Smith, C. J., Patrick, W. H., Fleeger, J. W. & Tolley, M. D. (1984). Effect of oil on salt marsh biota: Methods for restoration. Environ. Pollut. (Ser. A), 36, 207-28. Evans, D. R. & Rice, S. D. (1974). Effects ofoil on marine ecosystems: A review for administrators and policy makers. Fish. Bull., 72(3), 625-38. Getter, C. D., Cintron, G., Dicks, B., Lewis, R. R. & Seneca, E. D. (1984). The recovery and restoration of salt marshes and mangroves following an oil spill. In Restoration of Habitats Impactedby Oil Spills, ed. J. Cairns & A. L. Buikema. Butterworth Publishers, Boston, pp. 65-113. Gundlach, E. R. & Hayes, M. O. (1978). Vulnerability of coastal environments to oil spill impacts. Mar. Technol. Soc. J., 12(4), 18-27. Hampson, G. R. & Moul, E. T. (1978). No. 2 fuel oil spill in Bourne, Massachusetts: Immediate assessment of the effects on marine invertebrates and a three-year study of growth and recovery of a salt marsh. J. Fish. Res. Board Canada, 35, 731--44. Hershner, C. & Lake, J. (1980). Effects of chronic oil pollution on a salt marsh grass community. Mar. Biol., 56, 163-73. Hershner, C. & Moore, K. (1977). Effects of the Chesapeake Bay oil spill on salt marshes of the lower bay. In Proceedings of the 1977 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 529-33. Holt, S., Rabalais, S., Rabalais, N., Cornelius, S. & Holland, J. S. (1978). Effects of an oil spill on salt marshes at Harbor'Island, Texas. I. Biology. In Proceedings of the Conference on Assessment of Ecological Impacts of Oil Spills. American Institute of Biological Sciences, Arlington, Virginia, pp. 344-52. Howes, B. L., Howarth, R. W., Teal, J. M. and Valiela, I. (1981). Oxidation-reduction potentials in a salt marsh: Spatial patterns and interactions with primary production. Limnol. Oceanog., 26, 350-60.

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Krebs, C. T. & Burns, K. A. (1977). Long-term effects of an oil spill on populations of the salt marsh crab Uca pugnax. Science, 197, 484-7. Lane, P. A., Vandermeulen, J. H., Crowell, M. J. & Patriquin, D. G. (1987). Impact of experimentally dispersed crude oil on vegetation in a Northwestern Atlantic salt marsh--preliminary observations. In Proceedings of the 1987 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 509-14. Lee, R. F., Dornseif, B., Gonsoulin, F., Tenore, K. & Hanson, R. (1981). Fate and effects of a heavy fuel oil spill on a Georgia salt marsh. Mar. Environ. Res., 5, 125-43. Lindall, W. N. & Saloman, C. H. (1977). Alteration and destruction of estuaries affecting fishery resources of the Gulf of Mexico. Mar. Fish. Rev., 39(9), 1-7. Lindstedt-Siva, J. (1977). Oil spill response planning for biologically sensitive areas. In Proceedings of the 1977 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 111-4. Lindstedt-Siva, J. (1979). Ecological impacts of oil spill cleanup: Are they significant? In Proceedings of the 1979 Oil Spill Conference, American Petroleum Institute, Washington, DC, pp. 521-4. Lindstedt-Siva, J. (1984). Oil spill response and ecological impacts: 15 years beyond Santa Barbara. Mar. Technol. Soc. J., 18(3), 43-50. Long, B. F. & Vandermeulen, J. H. (1983). Geomorphological impact of cleanup of an oiled salt marsh (Ile Grande, France). In Proceedings of the 1983 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 501-5. Lytle, J. S. (1975). Fate and effects of crude oil on an estuarine pond. In Proceedings of the 1975 Conference on Prevention and Control of Oil Pollution. American Petroleum Institute, Washington, DC, pp. 595-600. Macko, S. A., Parker, P. L. & Botello, A. V. (1981). Persistence of spilled oil in a Texas salt marsh. Environ. Pollut. (Ser. B), 2, 119-28. Mattson, C. P., Vallario, N. C., Smith, D. J., Anisfield, S. & Potera, G. (1977). Hackensack estuary oil spill: Cutting oil-soaked marsh grass as an innovative damage control technique. In Proceedings of the 1977 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 243-6. Milan, C. S. & Whelan, T. (1979). Accumulation of petroleum hydrocarbons in a salt marsh ecosystem exposed to steady state oil input. In Proceedings of the Third Coastal Marsh and Estuary Management Symposium, ed. J. W. Day, D. D. Culley, R. E. Turner & A. J. Mumphrey. Louisiana State University, Division of Continuing Education, Baton Rouge, Louisiana, pp. 65-87. Nadeau, R. J. & Roush, T. H. (1973). A salt marsh microcosm: An experimental unit for marine pollution studies. In Proceedings of the 1973 Conference on Prevention and Control of Oil Spills. American Petroleum Institute, Washington, DC, pp. 671-83. Ryan, P. R. (1977). The composition of oil--a guide for readers. Oceanus, 20(4), 4. Sanders, H. L., Grassle, J. F., Hampson, G. R., Morse, L. S., Garner-Price, S. & Jones, C. C. (1980). Anatomy of an oil spill: Long-term effects from the grounding of the barge Florida offWest Falmouth, Massachusetts. J. Mar. Res., 38, 265-380. Smith, C. J., DeLaune, R. D., Patrick, W. H. & Fleeger, J. W. (1984). Impact of dispersed and undispersed oil entering a gulf coast salt marsh. Environ. Toxicol. Chem., 3, 609-16. Stinckney, R. R. (1984). Estuarine Ecology of the Southeastern United States and Gulf of Mexico. Texas A & M University Press, College Station, Texas.

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Teal, J. M., Burns, K. & Farrington, J. (1978). Analysis of aromatic hydrocarbons in intertidal sediments resulting from two spills of No. 2 fuel oil in Buzzards Bay, Massachusetts. J. Fish. Res. Board Canada, 35, 510-20. Texas Engineering Extension Service. (1978). Oil Spill Control Course Handbook, revised edn. Oil and Hazardous Material Control Training Division, College Station, Texas. Webb, J. W., Alexander, S. K. & Winters, J. K. (1985). Effects of autumn application ofoil on Spartina alterniflora in a Texas salt marsh. Environ. Pollut. (Ser. A), 38, 321-37. Webb, J. W., Tanner, G. T. & Koerth, B. H. (1981). Oil spill effects on smooth cordgrass in Galveston Bay, Texas. Contrib. Mar. Sci., 24, 107-14. Westree, B. (1977). Biological criteria for the selection of cleanup techniques in salt marshes. In Proceedings of the 1977 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 231-5.