Impacts of the Jessica oil spill on intertidal and shallow subtidal plants and animals

Densities of fishes, invertebrates and plants at rocky intertidal and shallow subtidal sites were censused 1-2 days prior to the Jessica oil spill and compared with information obtained for the same sites one month after the spill, both for sites impacted by oil and unaffected reference sites. While the availability of pre-spill data made this analysis one of the most powerful to date for testing impacts of oil on shoreline environments, no clear changes attributable to oiling could be identified. Discharged oil appeared to cause very little impact in the intertidal and shallow subtidal zones, with such impacts lying within the range of natural spatial and temporal variation at sites investigated. Factors considered to minimize impact in Galápagos included paucity of fully sheltered shores in spill path, moderate wave action, warm temperature, high levels of sunlight, and mixing of bunker oil with diesel.     

Oil persistence on beaches in Prince William Sound - a review of SCAT surveys conducted from 1989 to 2002

In 2002, 13 years after the Exxon Valdez oil spill (EVOS), 39 selected sites in Prince William Sound (PWS) were re-surveyed following established shoreline cleanup assessment team (SCAT) field observation procedures to document surface and sub-surface oiling conditions in shoreline sediments and to compare results with those from previous Shoreline Cleanup Assessment Team (SCAT) surveys and other surveys in PWS. The selected sites are locations where EVOS oil persisted in 1992, at the time the Federal and State On-Scene Coordinators determined that the cleanup was complete and that further cleanup activities would provide no net environmental benefit. These sites had been included in a 2001 NOAA survey of shoreline oiling conditions and account for 88% of the sub-surface oil residues (SSO) oil documented by that study. The 2002 field survey found isolated occurrences of residual EVOS surface oil residues (SO) in the form of weathered asphalt pavement at 15 of the 39 sites. This residual SO typically consisted of asphalt in mixed sand/gravel substrate, located within a wave shadow effect created by boulders or bedrock in the upper intertidal to supratidal zone. Residual SO, expressed as a continuous oil cover, was less than 200 m(2) within the approximately 111,120 m(2) surveyed. A total of 1182 pits were dug at locations where SSO residues were present in 1992. Six of the 39 sites and 815 (68%) of the pits contained no residual SSO. Eighty-three percent of pits with SSO residues were found primarily in middle to upper intertidal locations. SSO residues commonly occurred in a discontinuous approximately 3 cm thick band 5-10 cm below the boulder/cobble or pebble/gravel veneer. The SO and SSO occurrences in the 2002 survey closely match the locations where they were found in 1992 and earlier surveys; however, in 2002 residual SSO patches are more discontinuous and thinner than they were in the earlier surveys. These sites are biased toward SSO persistence; those that have SSO residues represent less than 0.5% of the originally oiled shorelines in PWS. Despite evidence of continued oil weathering, both at the surface and in the sub-surface, it is clear that the natural cleaning processes at these particular locations are slow. The slow weathering rates are a consequence of the oil residue being incorporated in finer sediments (fine sand, silt, mix) and isolated from active weathering processes as boulders and outcrops, shallow bedrock asperities, or boulder-armoring create wave shadows and limit effective physical action on shorelines.     

Response of Spartina alterniflora Vegetation to Oiling and Burning of Applied Oil

A field study evaluated Spartina alterniflora sensitivity to oiling and to in situ burning of applied crude oil. Experimental plots (2.4 m × 2.4 m × 0.6 m) were constructed in the salt marsh for control, oiling (natural clean-up) and oiling/burning treatments. South Louisiana Crude was applied to oiling and oiling/burning treatment plots at 2 l m⁻² and the burn conducted. S. alterniflora responses (height, live stem density, carbon fixation and biomass) were measured for 50 weeks after the August burn. Oiling and oiling/burning had short-term detrimental effects on the salt marsh. One year after the late summer burn, S. alterniflora responses measured in the oiled and oiled/burned plots were not significantly different compared to control values. Results suggest that, under our experimental conditions, intervention may not be required for marsh recovery. However, if spill conditions require a rapid response to control contaminant spread or protect other sensitive resources, burning may be a clean-up operation to consider.     

Effects of oil on mangrove seedlings grown under different environmental conditions

The effects of oil treatments (one-time addition of 120 ml per plant and weekly addition of 15 ml per plant) and environmental conditions at time of oiling (air conditioned laboratory/diffuse light vs hot, direct sunlight) on the survival and growth of Rhizophora mangle and Avicennia germinans seedlings were examined. No oiled A. germinans survived longer than a few weeks. Both one-time and weekly oiling depressed survival, stem growth, leaf production and maximum leaf size in R. mangle. Significant interaction terms between oil treatment and environmental conditions occurred later (50 and 59 weeks) for R. mangle stem growth and earlier (21 and 23 weeks) for leaf production. Relative to other treatment combinations, R. mangle mortality was greatest and growth lowest in the combination of one-time oiling under hot, bright outdoor conditions. Results indicate that synergistic interactions between oil effects and environmental conditions may contribute to the wide range of effects reported in the literature in studies of oil contamination of mangroves.     

Re-evaluating the use of beached bird oiling rates to assess long-term trends in chronic oil pollution

The oiling rate (oiled birds/total birds) has become the international standard to analyze beached bird survey data. However, this index may not reliably track long-term changes in marine oil pollution in regions where other activities that kill seabirds vulnerable to oil, such as hunting and gill-netting, are also changing. We compare the oiling rate from beached bird surveys conducted in southeastern Newfoundland between 1984 and 2006 to an alternative approach, namely trends derived from a model examining the linear density of oiled birds (birds/km). In winter, there was no change in the oiling rate since 1984, while in summer oiling rates significantly increased. In contrast, the number of oiled birds/km showed a significant decline in both winter and summer. The discrepancy in these trends was attributed to steep declines in the number of unoiled birds found in both seasons. In winter, the decline in unoiled birds/km was related to a reduction in the legal murre hunt and less onshore winds, while in summer a reduced cod fishery resulting in fewer murres drowning in nets and warming summers may have lead to the decline. The significant declines in oiled birds/km over the past three decades are hopefully an indication of less oil being present in the marine environment. Although oiled bird densities since 2000 have remained relatively low for the region (winter: 0.58 birds/km, summer: 0.27 birds/km), they still exceed densities reported elsewhere in the world.     

Declines in oil-rates of stranded birds in the North Sea highlight spatial patterns in reductions of chronic oil pollution

Strandings of oiled seabirds are used to signal the problem of chronic oil pollution. Species-specific oil rates reflect the risk for marine birds to become oiled at sea. High oil rates were characteristic for seabirds common in areas with frequent oil spills; low oil rates for birds wintering away from the busiest shipping lanes. Declining trends in oil-rates were found, reflecting a reduction in the amount of oil intentionally discharged over the past 50 years. Spatial patterns in the risk to become oiled could be identified, when the winter distribution patterns of the affected birds were incorporated in the analysis. Declines in oil rates were most pronounced in coastal birds. These trends were consistent with tendencies to police nearshore waters more effectively than offshore waters. While levels of chronic oil pollution are much reduced, future emphasis should be to reduce chronic oiling more effectively in offshore waters.     

Characterization and source of oil contamination on the beaches and seabird corpses, Sable Island, Nova Scotia, 1996-2005

During April 1996-May 2005, 2343 oiled seabird corpses were recorded in beach surveys conducted on Sable Island, Nova Scotia. One hundred eighty-three samples of oil were collected from the beaches and from the feathers of bird corpses. Gas chromatographic (GC/FID) analysis was used to identify generic oil type and likely marine source. During this period, at least 74 marine oil discharge events were probably responsible for beached pelagic tar and contamination of seabird corpses found on Sable Island, of which 77.0% were crude oils, 14.9% were fuel oils, and 8.1% were bilge oil mixtures. While fuel and bilge oils may be discharged by all vessel and platform types, crude oil discharges are associated with tanker operations. This study demonstrates that oiling of the sea from tankers remains a serious wildlife issue in the Northwest Atlantic.     

Long term monitoring for oil in the Exxon Valdez spill region

In the aftermath of the 1989 Exxon Valdez oil spill, a Long Term Environmental Monitoring Program (LTEMP) has been regularly sampling mussels (and some sediments) for polycyclic aromatic and saturated hydrocarbons (PAH and SHC) at sites in Port Valdez, Prince William Sound, and the nearby Gulf of Alaska region. After 1999, a decreasing trend appears in total PAH (TPAH) in tissues at all sites with current values below 100 ng/g dry weight (many below 50 ng/g). Currently, most samples reflect a predominantly dissolved-phase signal. This new low in TPAH likely represents ambient background levels. Synchrony in TPAH time-series and similarities in the hydrocarbon signatures portray regional-scale dynamics. The five inner Prince William Sound sites show similar composition and fluctuations that are different from the three Gulf of Alaska sites. The two Port Valdez sites represent a unique third region primarily influenced by the treated ballast water discharge from the Alyeska Marine Terminal. Prince William Sound has reverted to a stable environment of extremely low level contamination in which local perturbations are easily detected.     

Biodegradation of petroleum hydrocarbons at low temperature in the presence of the dispersant Corexit 9500

Our study examined the effects of Corexit 9500 and sediment on microbial mineralization of specific aliphatic and aromatic hydrocarbons found in crude oil. We also measured gross mineralization of crude oil, dispersed crude oil and dispersant by a marine microbial consortium in the absence of sediment. When provided as carbon sources, our consortium mineralized Corexit 9500 the most rapidly, followed by fresh oil, and finally weathered oil or dispersed oil. However, mineralization in short term assays favored particular components of crude oil (2-methyl-naphthalene > dodecane > phenanthrene > hexadecane > pyrene) and was not affected by addition of nutrients or sediment (high sand, low organic carbon). Adding dispersant inhibited hexadecane and phenanthrene mineralization but did not affect dodecane and 2-methyl-naphthalene mineralization. Thus, the effect of dispersant on biodegradation of a specific hydrocarbon was not predictable by class. The results were consistent for both high and low oiling experiments and for both fresh and weathered oil. Overall, our results indicate that environmental use of Corexit 9500 could result in either increases or decreases in the toxicity of residual oil through selective microbial mineralization of hydrocarbons.     

Oil pollution and seabirds: Atlantic Canada 1976–1977 and some implications for northern environments

Chemical analyses of the oils on dead or moribund seabirds from Atlantic Canada during the winter of 1976–1977 indicated that some of the birds were contaminated with oil spilled by the Argo Merchant grounding, some by oil probably from the Grand Zenith sinking, and still others by oil from various small local spills of unknown origin. These victims demonstrated that an extremely minute oiling may lead to the death of a seabird when the effects of the oil are synergistically combined with the stresses imposed by severe environmental conditions. This may intensify the impact of oil in the Arctic and thereby have a profound effect on seabird populations.     

Sediment penetration of Amoco Cadiz oil,potential for future release,and toxicity

Weathering states of oil ranging from sheen oil to mousse have significant effects during oil stranding on oil-water and oil-sediment interaction. Observations of oiled sandy beaches suggest two mechanisms of beach contamination—general penetration and contamination of beach substrate by films of sheen oil (probably partially emulsified), and secondly the burial of discrete layers of mousse. Depending on timing of oiling with respect to beach dynamics large amounts of stranded oil can be accommodated within beach sediments. These then become available for later long-term release.Acute lethal toxicity of stranded Amoco Cadiz oil is intermediate to Bunker C and Kuwait crude. Simulated weathering studies suggest that there may be some increase in toxicity with weathering.     

The impact of a minor oil spillage in the estuarine Niger delta

On 24 April 1984 a barge sank in the Bonny Estuary, spilling 250 barrels of Nigerian crude oil. The incident occurred in an area where a baseline survey was already in progress. These data, plus additional studies at the spill-site enabled the impact of the incident to be determined. At the spill-site there was a near to total elimination of the littoral infauna and a highly significant oyster mortality, plus a 30% oiling of mangrove prop roots and 32% oiling of seedlings, which resulted in partial defoliation and death of seedlings within a 500 m² area. There were no significant effects on Uca tangeri density at the spill-site, and no effects at the nearest baseline survey transect 5 km away. The spillage was considered to be minor in terms of the quantity spilled, the effects observed, and their ecological significance.     

Oil contamination of sedimentary shores of the Galápagos Islands following the wreck of the Jessica

Sediment samples were collected from sandy beaches at a variety of sites in the southern Galápagos Archipelago to assess levels of hydrocarbon contamination following the wreck of the oil tanker Jessica. Hydrocarbon levels in sediments were generally very low by international standards ranging between 0.4 and 48.9 ppm, with contamination attributable to the Jessica only detected at three sites Santa Fe, Playa Estación (Puerto Ayora, Santa Cruz) and Long Beach (Isabela). There was evidence of residual hydrocarbon contamination from sources other than the wreck of the Jessica.     

Assessing indirect effects of oil in the presence of natural variation: The problem of reproductive failure in South Polar Skuas during the Bahia Paraiso oil spill

A population-wide mortality of South Polar Skua chicks occurred during a small diesel-oil spill at Palmer Station, Antarctica in 1989. It was hypothesized that sublethal oiling of adult South Polar Skuas temporarily disrupted parental guarding of chicks. Unattended chicks were preyed on by other skuas, and all known chicks within the local population were lost. Subsequently, other researchers have proposed that this reproductive failure was unrelated to the presence of oil. Natural variation producing food shortages or storms in critical periods occasionally may result in reproductive failure among seabirds. Here, evidence for these alternative hypotheses is examined. This controversy illuminates the general problem of determining the effects of an oil spill on natural populations, whose numbers and reproductive success vary both in time and space.     

A hierarchical approach measures the aerial extent and concentration levels of PAH-contaminated shoreline sediments at historic industrial sites in Prince William Sound, Alaska

A field study was conducted in 2003 to estimate the areal distribution and concentrations of polycyclic aromatic hydrocarbons (PAH) in intertidal sediments at sites of past human and industrial activity (HA sites) in Prince William Sound (PWS), Alaska, the site of the 1989 Exxon Valdez oil spill. More than 50 HA sites, primarily in western PWS, were identified through analysis of historic records and prior field studies, and nine sites were selected for detailed surveys. The areal assessment process consisted of seven steps: (1) identify site from historic records and field surveys; (2) locate visual evidence of surface oil/tar at a site; (3) prepare a site map and lay out a sampling grid over the entire site with 10-m grid spacing; (4) excavate pits to 50 cm depth on the grid; (5) perform a field colorimetric test to estimate total PAH (TPAH) in sediments from the wall of each pit and record the results in the ranges <1 ppm; 1-10 ppm; >10 ppm TPAH; (6) expand grid size if necessary if elevated PAH levels are detected colorimetrically; (7) select 20 samples from each site for same-day shipboard PAH analysis by immunoassay (SDI RaPID PAH) and, based on these results, select sediment samples from each site for full PAH analysis in the laboratory to identify PAH sources. A total of 416 pits were dug at the nine sites. Nine acres of sediments with TPAH >2500 ppb dry wt. were mapped at the nine sites. TPAH concentrations obtained by immunochemical analysis of 181 samples from the nine sites ranged from 20 to 1,320,000 ppb (wet wt.). The contaminants are mixtures of petroleum products (2-3 ring PAH) and combustion products (4-6 ring PAH) unrelated to the 1989 Exxon Valdez oil spill. Mussels and clams collected at these sites have elevated levels of PAH that are compositionally similar to the PAH in the sediments. These findings indicate that at least a portion of the sediment PAH is bioavailable. The PAH sources at these historic industrial sites are chronic. They include relict fuel oil tanks and works located above and within the intertidal zone, with contamination at some locations extending into nearshore sub-tidal sediments. This study shows how a hierarchical approach can be used to quickly and successfully map, quantify, and subsequently, identify sources of PAH in shoreline sediments.     

Firth of Forth oil pollution incident, February 1978

Where seaducks and other waterfowl are highly concentrated, even small quantities of oil can be a major hazard. A pollution incident on the Firth of Forth in February 1978 was notable in that it affected 241 Great Crested Grebes Podiceps cristatus (a high proportion of those present at the time) as well as 700 diving ducks. Evidence is provided indicating that the slick passed close to the main wildfowl feeding area at night, oiling nocturnal-feeding Scaup Aythya marila and Pochard A. ferina and a raft of roosting grebes, while Eider Somateria mollissima and Goldeneye Bucephala clangula, which had moved elsewhere to roost, largely escaped. The behaviour of freshly oiled birds is described. Heavily oiled Pochard flew 7 km inland to a loch before they were incapacitated. This is the sixth oil pollution incident to affect a large number of birds on the Forth since January 1970.     

The extent of chronic marine oil pollution in southeastern Newfoundland waters assessed through beached bird surveys 1984-1999

The Grand Banks south of Newfoundland provide year-round feeding habitat for tens of millions of seabirds of numerous species, an abundance and diversity unparalleled in the North Atlantic. Dense ship traffic routes traverse this productive environment as vessels travel the Great Circle Route between Europe and North America. Oiled seabirds have washed up on beaches in Newfoundland for many decades. Most oil on their feathers is heavy fuel oil mixed with lubricants, the mixture found in bilges of large vessels. Beached bird surveys conducted between 1984 and 1999 indicate that chronic oil pollution along the southeast coast of Newfoundland is among the highest in world. Sixty two percent of all dead birds found over the 16-year period had oil on their feathers; 74% during the last five years. Auks, especially Thick-billed Murres (Uria lomvia), are the most affected. The mean number of oiled birds per kilometer was 0.77 and thus higher than in other regions of the world during a comparable time period (0.02-0.33). Oiling rates correlated with weather patterns and degree of the regional murre hunt, indicate that illegal dumping of oil may occur year round, and point out that it is critical to assess all possible environmental and anthropogenic factors influencing the number of clean and oiled dead birds found on beaches before inferring trends in oiling rates over time.     

Twenty years of Belgian North Sea aerial surveillance: a quantitative analysis of results confirms effectiveness of international oil pollution legislation

Over the years many policy measures have been taken to prevent illegal oil discharges from ships, like the MARPOL 73/78 Convention (1983) and the Bonn Agreement (1969/1983). However, the number of discharges remained high, leading to chronic oiling of seabirds and sensitive coastlines, therefore further measures were taken. The aim of this study is to quantify the effectiveness of two key legislative regulations: the IMO-designation of the North Sea as MARPOL Special Area which took effect in 1999, and the adoption of the EU Directive on Port Reception Facilities in 2000. Under study is the heavily navigated Belgian Surveillance Area, monitored since 1991, characterised by shallow waters with ecologically important sandbanks. The aerial surveillance data from 1991 to 2010 show a stepwise decrease in ship-source oil pollution. Three time periods can be distinguished with two turning points coinciding with the actual implementation of these key legislative measures, confirming their effectiveness.     

Comparison of mussels and semi-permeable membrane devices as intertidal monitors of polycyclic aromatic hydrocarbons at oil spill sites

Side-by-side comparisons of polycyclic aromatic hydrocarbon (PAH) concentrations in resident blue mussels (Mytilus trossulus) and in semi-permeable membrane devices (SPMDs) were made at four sites in Prince William Sound, Alaska. SPMDs were deployed for approximately 30 days on the surface of the beach sediment at three tidal elevations on each shore and in 0.5 m deep open pits in the middle intertidal zone. Total PAH (TPAH) concentrations in mussels and in SPMDs were correlated, but the PAH compositions were different. The lower molecular weight PAH were relatively more abundant in the SPMDs than in the mussels at oiled and HA sites. TPAH concentrations in SPMDs deployed in pits and mussels collected adjacent to those pits at oiled sites were higher than in SPMDs and mussels from non-pitted SPMD locations approximately 3-15 m from the pits. Pitting released buried oil making its PAH bioavailable. SPMDs deployed in the supratidal zone (+4.0 m tidal elevation) were exposed to atmospheric contaminants for a large fraction of the deployment time and accumulated primarily pyrogenic (combustion-sourced) PAH from the atmosphere. The SPMD strips supplied by the manufacturer contained significant amounts (approximately 125 ng/strip) of primarily alkylated 2-3 ring PAH. These blank levels make SPMDs unsuitable for shoreline assessments when environmental PAH concentrations are low. Consequently, where available, mussels are recommended for use in assessments of the bioavailability of buried oil residues sequestered in intertidal sediments following an oil spill. Mussels are the preferred monitoring tool when the assessments involve food-chain effects. At locations where the absence of mussels necessitates the use of SPMDs or other passive sampling devices, their limitations need to be carefully considered in the interpretation of results.