Recovery of Intertidal Biotic Communities at Sullom Voe
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RECOVERY OF INTERTIDAL BIOTIC COMMUNITIES AT SULLOM VOE FOLLOWING THE ESSO BERNICIA OIL SPILL OF 1978 Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1991/1/461/1742866/2169-3358-1991-1-461.pdf by guest on 01 October 2021 Robert G. Rolan British Petroleum America 200 Public Square Cleveland, Ohio 44114 Ronald Gallagher Sullom Voe Oil Terminal Shetland, United Kingdom ABSTRACT: In December 1978, the Esso Bernicia spilled 8,000 bar- This program was organized by the Shetland Oil Terminal Environ- rels of Bunker C oil during a berthing accident near the Sullom Voe Oil mental Advisory Group (SOTEAG) which has an independent chair- Terminal. About 100 miles of shoreline were oiled, much of that span man and members drawn from the oil industry, the Shetland Islands heavily. Sullom Voe is a bay of the Shetland Islands, north of Scotland, Council, conservation groups, and local residents. Most of the mon- an area environmentally similar to Prince William Sound. The highly itoring studies have been carried out by independent groups such as indented, rocky shoreline is inhabited by typical intertidal communities university departments. characterized by fucoid algae (rockweed), barnacles, and snails. Bio- logical survey data for the intertidal communities had been collected for three years prior to the spill. During the cleanup, most of the shores that were accessible to heavy equipment were stripped of oily rock, cobble, and gravel. Other fairly accessible areas were hand-cleaned. Dispersants were tried on a few shores, but were ineffective. Many of the less accessible locations were not cleaned at all. The oiled shorelines were resurveyed every year from 1979 through 1987, except 1982 and 1983. Except for the mechanically cleaned areas, the biological communities in the rocky intertidal zone returned to very near normal within the first year, and have remained so in spite of the presence of traces of weathered oil. Normal populations of snails and small crustaceans have thrived in intimate contact with asphaltic residues that remain in some locations. In contrast, the biological communities at the sites that were cleaned mechanically were obliterated, and still had not fully recovered after almost nine years. The Shetland Islands, 130 miles north of Scotland, are the site of Europe's largest oil and liquefied gas terminal, at Sullom Voe (Figure 1). The terminal was built in the late 1970s to receive hydrocarbons from over a dozen fields in the East Shetland Basin of the North Sea, midway between Shetland and Norway. Operated by British Petro- leum, it handles nearly half of Britain's oil production. The Shetland Islands lie at approximately the same latitude as Prince William Sound, Alaska, i.e., just slightly north of 60°N. Owing to the influence of the Gulf Stream, it has a mild, oceanic climate and extremely high relative humidities. Summer temperatures are very similar to those in Prince William Sound (at Hinchinbrook Island), but average 13° to 14° F warmer in the winter. It is one of the windiest places in Britain, and averages 58 days a year of gales. Sullom Voe, a sea loch, is one of the more protected anchorages in Shetland due to its location on the windward side of Yell Sound. The shores are typically bedrock, boulders, and cobble, indicative of high wave energy levels.11 There has been a continuous program of environmental monitoring at the terminal and surrounding areas since the start of construction. Figure 1. Shetland Islands, showing location of Sullom Voe 461 462 1991 OIL SPILL CONFERENCE Because of this program of environmental monitoring, there were three years of data on the intertidal communities around the terminal area before it experienced its first and most serious oil spill. Although the intertidal studies had been established to document possible im- pacts from ongoing, routine operations at the terminal, the three years of baseline studies prior to the Esso Bernicia spill and biological recovery data, spanning nine years, provide a unique data set from which to evaluate the effects of a major spill and associated cleanup activities. This paper summarizes the results of these studies, here- tofore available only in unpublished SOTEAG reports. The spill and response Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1991/1/461/1742866/2169-3358-1991-1-461.pdf by guest on 01 October 2021 As a result of a fire aboard one of three attendant tugs, the 190,000- metric-ton tanker Esso Bernicia struck a mooring dolphin at the Sul- lom Voe Terminal on December 30, 1978, puncturing a fuel tank. Approximately 8,000 bbl (1,174 metric tons, t) of Bunker C oil were spilled. Initially, booming confined the oil to the immediate terminal area, but the boom failed on January 3,1979. Wind and strong tidal currents transported the oil widely throughout the Yell Sound area. Most of the oil stranded within Sullom Voe, and the most heavily oiled areas were in the vicinity of the terminal. The oil came ashore on a high tide in these areas, and, while stranding was confined to the upper shore, the covering was extensive. In all, some 100 miles (160 km) of coastline were oiled, about 20 percent of it heavily. Twenty-one intertidal survey sites had been established prior to the spill. Of these, all but four received some degree of oiling from the Esso Bernicia spill. A massive cleanup operation was mounted during the first half of Figure 2. Location of primary sampling sites in Sullom Voe and Yell 1979. The principal cleanup method was manual bagging of oil debris. Sound Roughly 1.3 million lb (600,000 kg) of oil material were collected. About 5,600 gal of BP 1100WD dispersant were used, with some success, to disperse oil on the water, but trial applications on the oiled primary sites. However, resampling of the two "reference sites" (3.8 shore were ineffective. At more remote locations on Yell Sound and its and 6.11) at Vidlin Voe was discontinued in 1985. Notably, of the five islands and many locations in Sullom Voe, very limited or no cleanup most heavily oiled sites in the Esso Bernicia spill, two had been was attempted, and the oil was left to degrade naturally. These shores mechanically cleared (5.2 and 6.12), two were cleaned manually (4.1 were predominantly bedrock or large boulders. and 4.3), and one was left to natural cleansing (6.13). The other two Most importantly, at certain accessible beaches near the terminal the mechanically cleared sites (6.2 and 6.4) were at locations which had beach material was stripped by bulldozer, dragline, and front-end been less heavily oiled. The degree of oiling of each site from the Esso loader. Survey sites 5.2, 6.2, and 6.4 were cleared in mid-January. Bernicia spill and whether it was mechanically cleared are indicated in Clearing was largely restricted to the upper shores, where the oil was Table l,8 along with years in which each of the sites were sampled. thickly deposited. At Scatsta Ness, another heavily oiled location, one stretch of shoreline was mechanically cleared in mid-May and an adjacent stretch was left uncleared in order to allow side-by-side com- parison of biological recovery following such fundamentally different Sampling methods treatments. At each of the 21 prespill sites, a permanent tidal datum marker was established. A transect was laid out from the low water of spring tide level to the splash zone. Stations were laid out along the transect at 20- Sampling sites cm vertical height intervals. The number of stations at each site ranged between 9 and 31, but typically were around 15 to 19. At the two new In 1976,18 primary intertidal sampling sites were established at the sites established following the Esso Bernicia spill, the locations of the locations indicated in Table 1 and Figure 2. In 1977, two additional stations were established at matching elevations relative to sea level. primary sites in Vidlin Voe (3.8 and 6.11) were established as reference Only stations above low water neaps were surveyed, because the lower sites because they were thought to be far enough from the terminal to shore had not been oiled and the communities were intact at both sites. be beyond any adverse influence. The 20 primary sites were to be Each year at sampling time, a tape was laid down the transect from resampled on an annual basis. A similar number of secondary sites the marker along exactly the same line as in previous years, as deter- were also established and sampled in the first year, but there was no mined by a combination of previous station marks, site photographs, intention to resample them every year and, in fact, most have not been and compass bearings. The sites were photographed each year, the resampled regularly or at all. marks were reestablished when necessary. At each station along the In 1979, following the Esso Bernicia spill, two new primary sampling tape, abundances of intertidal organisms were determined in a trans- sites were established at the heavily oiled shore at Scatsta Ness (sites verse swath 3 m wide (1.5 m on each side of the tape) by approximately 6.12 and 6.13). The sites were chosen because bedrock was present at 30 cm deep. Limpets and barnacle spat were counted at the same similar levels on the shore and the sites were as near to one another as stations each year using randomly located quadrats (20 cm by 20 cm possible. One of these sites had been mechanically cleared of oil and and 10 cm by 10 cm, respectively).