Impact of crude oil on sulphate reduction and methane production in sediments impacted by the Amoco Cadiz oil spill

The activities of methane-producing and sulphate-reducing bacteria in intertidal sediments along the Brittany coast of France were examined in order to determine the effect of the Amoco Cadiz oil spill on sediment microbial processes. Porewater chemistry, methane production, sulphate rate and [2?¹⁴C]-acetate metabolism did not vary significantly between beach, estuary, and marsh sites, oiled or unoiled, after the Amoco Cadiz spill. Oiled sediments contained highly weathered oil of Amoco Cadiz origin, but unoiled comparison sites also contained hydrocarbons from anthropogenic sources. The additions of weathered Amoco Cadiz mousse, fresh and slightly weathered light Arabian crude oil, benzene or toluene to sediments from the oiled and unoiled marsh site did not significantly affect rates of sulphate reduction or methane production. The oxidation of [2?^14C]-acetate to ¹⁴CO₂, however, was significantly decreased when mousse, crude oil, benzene or toluene was added to sediments from the unoiled site. Inhibition seemed to be proportional to the extent of weathering. Sediments recently exposed to Amoco Cadiz crude oil were less affected by a second oiling, suggesting that the indigenous populations may have been replaced by organisms more resistant to oil toxicity. These results suggested that the Amoco Cadiz oil spill did not have major long-term effects on sulphate reduction or methane production.     

Sublethal effects of oiled sediment on the sand worm, Nereis (neanthes) virens: Induced changes in burrowing and emergence

The burrowing and emergence behavior of sand worms, Nereis (Neanthes) virens Sars, in sediment contaminated with sublethal concentrations of Prudhoe Bay crude oil ranging from 74 to 5222 ppm, was studied in the laboratory. Initial burrowing in oiled sediment did not differ from that observed in unoiled sediment. Emergence of exposed worms was related to the oil concentration and the extent of weathering of oiled sediment. Sand worms buried in unoiled sediment did not emerge. Worms dug from oiled sediment after 12 hours' exposure and placed on unoiled sediment were impaired, resulting in a significant increase in time to burrow. However, after 12h, they recovered and burrowed at normal rates. Worms held in oiled sediment for 96 h also recovered. Possible causes for recovery are discussed. Results suggest that oil-induced aberrations may increase vulnerability to predation.     

Weathered IXTOC I oil effects on estuarine benthos

The impact of weathered IXTOC I oil on experimental benthic communities colonized in the laboratory and in situ was observed. Test systems containing clean sand and receiving seawater from Aransas Pass Inlet were placed in the laboratory while similar systems were placed on the seafloor. All of these test systems were allowed to colonize for 8 weeks by settlement of planktonic larvae. Weathered IXTOC I oil was added to randomly selected laboratory and in situ replicate compartments within the test systems and these were then exposed to flowing seawater in the laboratory for an additional 4 weeks. Observations of the structure and biomass of the communities at the end of the 12-week period indicated no significant effects on the laboratory colonized communities. However, total density was significantly affected in the in situ colonized systems as was species composition. Although not significant, total biomass was substantially reduced by oiling. Eh measurements of sediments showed that the oil reduced the depth of the oxygenated layer approximately half. This reduction may reduce subsurface benthic production and alter processes such as nutrient regeneration.     

Effects of crude oil on the supralittoral meiofauna of a sandy beach

The supralittoral zone of an open sandy beach was dosed with crude oil and changes in the meiofauna monitored. Treatments included weathered and fresh oil on the surface, fresh oil mixed with dispersant on the surface and weathered oil at the water table, all in layers 0·8 cm thick. In all cases the meiofauna was reduced 1 month after dosing but numbers had returned to normal by 5 months except in the site dosed with fresh oil mixed with dispersant. Oil on the surface had greater effects than oil at the water table; fresh oil had a greater effect than weathered oil and fresh oil with dispersant was more toxic than fresh oil alone. Nematodes were least sensitive to the oil and oligochaetes more sensitive, their numbers being correlated with oil concentrations and depth in the substrate. It is concluded that, under all but the heaviest conditions of pollution in their environment, recovery from oil contamination should occur within 5 months in the meiofauna.     

Effects of oil exposure on pink salmon,Oncorhynchus gorbuscha,alevins in a simulated intertidal environment

Pink salmon, Oncorhynchus gorbuscha, alevins (5 and 60 days after hatching) were continuously or intermittently exposed for 30 days to the water-soluble fraction (WSF) of Cook Inlet crude oil in fresh water or in a simulated freshwater-seawater cycle. Alevins exposed to 0·7−2·4 mg/liter WSF in the simulated tidal cycle were more sensitive to oil, had reduced yolk reserves, and accumulated more hydrocarbons than did alevins exposed to the same concentrations in fresh water. Alevins in fresh water were more sensitive to continuous than to intermittent exposures. In all exposures, 60-day alevins were more severely affected than were 5-day alevins.     

Alternative interpretations as to the origin of the hydrocarbons of the Guajira Basin,Colombia

The origins of the hydrocarbon gases recovered from the Chuchupa, Ballena, and Riohacha fields, located in the Guajira basin, northeast Colombia, are examined. These gases are composed of methane with trace amounts of wet gas components (C₂₊<0.5%). The methane is isotopically light (δ¹³C₁<−50‰), as are the other hydrocarbon components. The Ballena and Riohacha fields are considered to have a biogenic origin and the Chuchupa gas is thought to have a mixed biogenic-thermogenic origin. The presence of a thermogenic contribution at Chuchupa need not, however, indicate that the sedimentary sequence was exposed to elevated temperatures. The generative kitchen located to the northwest of the three gas fields would preferentially feed into the Chuchupa Field.The gases recovered at three onshore seep localities appear to include a thermogenic component. As a result of fractionation it is unclear whether they represent ‘pure’ thermogenic gases or a mixed thermogenic-biogenic origin similar to Chuchupa.An examination of oil microseepage observed in soil samples recovered from the onshore Guajira region point to another hydrocarbon system apparently not related to the three gas fields. Some of these microseeps include ‘fresh’ (nonbiodegraded) oils. These microseeps did not correlate with either of the Tertiary oil families from the Sinú Urabá basin located to the southwest of the study area or with Cretaceous oils from that basin. A better correlation was observed with the La Luna Formation, but significant differences remain implying that the source for the microseeps was less calcareous and deposited in a less restricted environment than associated with ‘classical’ La Luna facies. This could indicate either a facies change or that a different source unit is present within the region.     

Exposure of pink salmon embryos to dissolved polynuclear aromatic hydrocarbons delays development,prolonging vulnerability to mechanical damage

Exposure to dissolved polynuclear aromatic hydrocarbons (PAHs) from crude oil delays pink salmon (Oncorhynchus gorbuscha) embryo development, thus prolonging their susceptibility to mechanical damage (shock). Exposure also caused mortality, edema, and anemia consistent with previous studies. Hatching and yolk consumption were delayed, indicating the rate of embryonic development was slowed by PAH exposure. The net result was that exposed embryos were more susceptible to shock than normal, unexposed embryos. Susceptibility to shock was protracted by 4–6 d for more than a month in embryos exposed to exponentially declining, dissolved PAH concentrations in water passed through oiled rock; the initial total PAH concentration was 22.4 μg L⁻¹ and the geometric mean concentration was 4.5 μg L⁻¹ over the first 20 d. Protracted susceptibility to shock caused by exposure to PAHs dissolved from oil could potentially increase the reported incidence of mortality in oiled stream systems, such as those in Prince William Sound after the Exxon Valdez oil spill, if observers fail to discriminate between direct mortality and shock-induced mortality.     

Respiratory changes and stability of haemocyanin—O2 binding capacity in the crab cancer irroratus exposed to Kuwait crude oil in sea water

To determine one possible mechanism of hydrocarbon toxicity, studies were carried out to establish: (a) the availability of hydrocarbons from sea water to the crab haemolymph, (b) the effects on respiration and (c) the possible effects on haemocyanin—O₂ binding characteristics in oiled crabs.Crabs incubated in ¹⁴C-naphthalene labelled oiled sea water (Kuwait crude) readily accumulated the isotope into the haemolymph, in concentrations exceeding those in the surrounding sea water medium with one-hour bioconcentration factors from 2·53 to 23·51. Respiration, as measured by uptake of O₂ from the respirometer sea water, was 12·5% lower in crabs held in 11·0 ppm Kuwait crude/sea water than in the same animals when held in unoiled sea water. Respiration levels returned to preoiling levels when the oiled sea water was replaced with fresh non-oiled sea water.Despite the observed effects of oiled sea water on respiration, the haemocyanin—O₂ binding potential, as well as the structural integrity of haemocyanin (as determined by its UV absorption spectrum, sub-unit dissociation and serum-free Cu⁺⁺ levels), remained unaltered. The results suggest that disruption of blood-oxygen transport via disruption of haemocyanin—O₂ binding as one possible mechanism of hydrocarbon toxicity is unlikely and that other alternatives must be considered.     

In situ microbial degradation of Prudhoe Bay crude oil in Beaufort Sea sediments

This study examined the fate of Prudhoe Bay crude oil in nearshore sediments of the Beaufort Sea, in situ, with emphasis on the rôle of microorganisms in the weathering process. The results indicate that oil is degraded in Arctic sediments very slowly; only after 1 year's exposure was biodegradation evident. Several factors probably contributed to the slow rate of microbial weathering, including: limited populations of hydrocarbon utilising microorganisms; localised high oil concentrations; low temperatures; limiting nutrient concentrations (unfavourable C:N and C:P ratios); low oxygen tensions and limited circulation of interstitial waters in fine-grained sediments. Abiotic weathering of the oil was also slow, with limited loss of low molecular weight aliphatic and aromatic hydrocarbons during 2 years' exposure. Significant features of the overall weathering process were: lack of initial loss of low molecular weight compounds; aliphatic compounds were not preferentially degraded over aromatic compounds and C₁₇, and lower molecular weight normal alkanes were preferentially degraded over higher molecular weight alkanes. The results of this study indicate that hydrocarbons will persist relatively unaltered for several years if Beaufort Sea sediments are contaminated with petroleum.     

Relative importance of hydrocarbon pollutants, salinity and tidal height in colonization of oyster reefs

The relative effects of hydrocarbon pollutants, salinity and tidal height on the invertebrates and fish that inhabit oyster reefs were studied along the Louisiana Gulf of Mexico coastline. Dried oyster shell (cultch) was first exposed to crude oil in the laboratory. In a series of experiments, plastic trays filled with control and oil-exposed cultch were then deployed at two locations differing in salinity, in two seasons and at two tidal levels. In experiments on hydrocarbon, salinity, and seasonal effects, trays were colonized for one month. To examine the effects of colonization time, half of the trays were retrieved after two and the rest after five weeks. Salinity dramatically affected oyster reef assemblages, with species richness and total abundance halved at the estuarine site. Hydrocarbon effects were less prominent, whether cultch was dosed with light or heavy crude oil. The sub-tidal site had higher colonization rates, but colonization interval did not affect colonization, and seasonal differences occurred only at the higher-diversity, sub-tidal site. To determine effects of cleaners, Corexit 9580 was applied alone and with oil on cultch, and trays were colonized for one month. At high concentrations, the cleaner ameliorated hydrocarbon effects. In general, hydrocarbon effects were less prominent than salinity and aerial exposure in explaining colonization of oyster reef assemblages. Gas chromatography/mass spectrometry analysis of oyster shells after one month immersion revealed considerable losses of oil, especially with higher flow at the inter-tidal site. Sediment on shell also diluted oil. We argue that oyster reef assemblages should recover from small-scale spills, unless they occur during periods of reproduction and dispersal.     

Effects of oil on phytoplankton metabolism in natural and experimental estuarine ponds

A low level oil spill was simulated in small shallow natural estuarine marsh ponds in Ocean Springs and in experimental impoundments near St. Louis Bay, Mississippi. In the natural tidal pond in situ light and dark BOD bottle experiments on the phytoplankton community revealed a 44 to 65 % reduction in primary production and a 30 to 50 % reduction in respiration 2 weeks after spillage of 1·45 mg Empire Mix crude oil per litre of water. Two months after the spill, primary productivity and respiration in the oiled pond were only 17% and 7% lower, respectively than in the control pond. In the experimental impoundments at a concentration of 0·2 mg Arabian, Empire Mix and Nigerian oil per litre of water, in situ radiocarbon uptake by phytoplankton was lower—but not significantly lower—than that of the control impoundment. One to two months later, primary productivity was significantly higher in the Nigerian and Arabian oil ponds than control and Empire Mix ponds. The changes in plankton metabolism in both natural ponds and impoundments were evaluated on the basis of data simultaneously obtained from adjoining control ponds.     

Changes in the volatile hydrocarbon content of Prudhoe Bay Crude Oil treated under different simulated weathering conditions

Changes have been determined in the concentrations of volatile saturate and aromatic hydrocarbons in Prudhoe Bay Crude Oil (PBC) weathered under three different simulated environmental conditions. A combination of light and water sprayed upon the surface of the oil produced the largest relative decreases in volatile saturate and most aromatic hydrocarbons. After 24 days, detectable amounts of monoaromatic hydrocarbons were absent in all three weathered oils, as were the saturate hydrocarbons from C₈ to C₁₀. Retention of aromatic hydrocarbons appeared to be related to molecular weight, as enrichments of triaromatics (phenanthrenes) were observed in weathered PBC relative to the original crude oil. These data are discussed with respect to effects resulting from spilled oil impacting benthic organisms residing in intertidal and shallow subtidal communities.     

Assessment of the effects of hydrocarbon contamination on the sedimentary bacterial communities and determination of the polar lipid fraction purity: Relevance of intact phospholipid analysis

This in situ study reports on the relevance of intact phospholipids as new biomarkers and highlights the limits of the classical fatty acid analysis after the hydrolysis of the polar lipid fraction. The analysis of polar lipid fractions revealed significant contributions of marine macrophytes with either non-phospholipid compounds (sulfoquinovosyl diacylglycerol) or with both non-bacterial phospholipid classes (phosphatidylcholine) and non-bacterial phospholipid molecular species (some molecular species of phosphatidylglycerol). The analysis of intact phospholipids showed also the predominance of gram-negative bacteria in sediments whereas the analysis of fatty acids alone cannot confirm such information. Lastly, as regard to the effects of petroleum hydrocarbons on the sedimentary bacterial communities, we observed a higher degree of saturation of the fatty acyl chains of the phospholipids extracted from sediment exposed to a massive and chronic crude oil contamination. Such a result was interpreted as an adaptive response resulting in higher membrane rigidity of the bacterial communities.     

Organic carbon stable isotope ratios of continental margin sediments

Stable isotope ratios (δ¹³C) of total organic carbon were measured in surface sediments from the continental margins of the northern and western Gulf of Mexico, the north coast of Alaska and the Niger Delta. Gulf of Mexico outer-shelf isotope ratios were in the same range as has been reported for Atlantic coastal shelf sediments, ?21.5 to ?20‰. Off large rivers including the Mississippi, Niger and Atchafalaya (Louisiana), δ¹³C values increased from terrigenous-influenced (around ?24‰) to typically marine ($\text{～?20‰}$) within a few tens of kilometers from shore. This change was accompanied by a decrease in the amount of woody terrigenous plant remains in the sediment. Alaskan continental margin samples from the cold Beaufort Sea had isotopically more negative carbon (?25.5 to ?22.6‰) than did warmer-water sediments. The data indicate that the bulk of organic carbon in Recent sediments from nearshore to outer continental shelves is marine derived.     

Relationship between hydrocarbons and bacterial activity in mediterranean sediments: Part 2—hydrocarbon degrading activity of bacteria from sediments

In marine sediments from the Mediterranean coast polluted by oil spills (Etang de Berre) high bacterial activity is responsible for self-purification, samples collected from these areas showing a bacterial density several orders of magnitude higher than samples from non-polluted areas (Isle des Embiez). Between 60 and 80 % of the heterotrophic bacteria in the polluted areas are hydrocarbon-degrading, compared with 0.01 % in the non-polluted area.Several strains of hydrocarbon utilisers were isolated, a mixture of strains from each biotope was taken to represent a ‘biotope population’ and their activity towards different types of hydrocarbons (n-alkanes, iso-alkanes, cycloalkanes, aromatics) was determined.With ammonia as the nitrogen source the ‘biotope population’ from the polluted area degraded hydrocarbons much more readily than the ‘biotope population’ from the non-polluted area. With nitrate as the nitrogen source the degradation was much reduced, and, for some hydrocarbons, ceased in both ‘populations’.Individual hydrocarbons encouraged the growth of individual strains in the ‘biotope population’. In natural mixtures of hydrocarbons all strains grew well and degraded aliphatics. There was a good correlation between the respiratory activity of the ‘biotope population’ and the ability of the ‘population’ to utilise hydrocarbons for growth.     

Method for assessing the chronic toxicity of marine and estuarine sediment-associated contaminants using the amphipod Corophium volutator

Acute sediment toxicity tests do not test key life stage events such as moulting and reproduction and therefore do not reveal the longer-term effects of contaminant exposure. A laboratory method is described for determining the chronic toxicity of contaminants associated with whole sediments. The test is conducted using neonates of the estuarine amphipod Corophium volutator at 15 degrees C, salinity 25 psu and a 12 h light:12 h dark photoperiod. The endpoints are survival and growth after 28 days and survival, growth and reproduction of amphipods upon termination of test i.e. reproduction within all control vessels (ca 75 days). The sediment chronic toxicity test was used to investigate the effects of sediments spiked with environmentally relevant preparations of slightly weathered Alaskan North Slope crude oil, including a water-accommodated-fraction (WAF) and a chemically-dispersed (Corexit 9527) WAF. Sediment oil concentrations were quantified using ultra-violet fluorescence. The amphipods exposed to chemically dispersed oil had higher mortality and lower growth rates than control-, Corexit 9527- and WAF-exposed organisms, resulting in reduced reproduction. The described method supplements the standard acute sediment test and would be particularly useful when long-term ecological effects are suspected but acute tests reveal no significant mortality. The sediment chronic test reported herein has shown that sediment that was not evidently toxic during 10-day acute tests could have population-level effects on sediment-dwelling amphipods.     

Recolonization of macrofauna in unpolluted sands placed in a polluted yachting harbour: A field approach using experimental trays

A field experiment using trays was conducted at Ceuta's yachting harbour, North Africa, to study the effect in recolonization of placing trays with unpolluted defaunate sediments (fine and gross sands with low contents of organic matter) inside an enclosed yachting harbour characterized by high percentages of silt and clay and high concentrations of organic matter. Sediment recolonization in the trays was mainly undertaken by the species living naturally at the yachting harbour, which recolonized both uncontaminated gross and fine sand trays (such as the crustaceans Corophium runcicorne, Corophium sextonae and Nebalia bipes, the mollusc Parvicardium exiguum and the polychaete Pseudomalacoceros tridentata). However, other species like the polychaetes Cirriformia tentaculata and Platynereis dumerilii, although also abundant in the yachting harbour, were unable to colonize the trays through transport of larvae and/or adults in the water column. The recolonization was very quick, and after the first month, the values of abundance, species richness, diversity and evenness were similar in the experimental trays and in the reference area (yachting harbour). Although the multivariate analysis showed that the species composition differed between the trays and the reference area, there were no significant differences in recolonization of gross and fine sands, indicating that other factors different from the granulometry are modulating the recolonization patterns.     

Physiological responses of Mytilus edulis during chronic oil exposure and recovery

Physiological responses of mussels Mytilus edulis were determined following 8 months' exposure to two oil concentrations (28 and 125 μg litre⁻¹ total hydrocarbons) and during the process of recovery. There was a significant inverse relationship between the performance of Mytilus edulis, measured in terms of scope for growth, and the concentration of aromatic hydrocarbons accumulated in the body tissues. The marked reduction in scope for growth of oil exposed mussels was primarily due to a reduction in feeding rate and food absorption efficiency. Recovery of physiological responses was coupled to the depuration of aromatic hydrocarbons from the body tissues. Mussels exposed to high-oil concentrations were found to recover more rapidly than those exposed to low-oil concentrations, both in terms of depuration and scope for growth, and there was evidence of ‘catch-up’ growth. Recovery of mussels from both oil conditions was complete after approximately 55 days.     

Sources of δ15N variability in sinking particulate nitrogen in the Cariaco Basin,Venezuela

Ten years of monthly observations of the δ¹⁵N of sinking particulate nitrogen (δ¹⁵N–PN (in ‰ versus atmospheric N₂)=[(¹⁵N/¹⁴N)_sample/(¹⁵N/¹⁴N)_standard)−1]1000) in the Cariaco Basin, Venezuela, confirm that the basin's bottom sediments store information about nitrogen dynamics related to seasonal and interannual variability in regional surface ocean processes. During the upwelling period of the southern Caribbean Sea (February–April), the δ¹⁵N–PN is similar to that of the thermocline nitrate (∼3.5‰). This nitrate is imported into the Cariaco Basin with Subtropical Underwater (SUW), which wells up near the coast. Thus, particles generated by phytoplankton photosynthesis during this productive period bear a sub-tropical North Atlantic isotopic imprint of N₂ fixation (low compared to the global average of nitrate δ¹⁵N≈5‰). During the non-upwelling period when surface waters are stratified (September–November), the δ¹⁵N–PN is also 3.5–4.0‰, and reflects a mixture of local N₂ fixation within the mixed layer, inputs of terrigenous organic matter and SUW nitrate consumption by phytoplankton below the mixed layer, which most likely exerts the strongest control on the δ¹⁵N–PN signal during this time. In the transition periods of May–July and December–January, the δ¹⁵N–PN increases to 4.5–6.5‰. This coincides with maxima of continental material fluxes (terrestrial PON δ¹⁵N is >6‰) into the Cariaco Basin. The δ¹⁵N signal in the sediments of the Cariaco Basin thus provides information about the relative strength of the local coastal upwelling, the relative input of continental material via river runoff, and local N₂ fixation. The findings contribute to interpretations of the basin's paleoclimatic nitrogen cycle variations based on observations of the sedimentary δ¹⁵N record at this location.