Experimental Application of Oil—Based Muds and Cuttings to Seabed Sediments

Dixon, I. M. T.

doi:10.1007/978-94-009-3573-0_12

Cited by 6 publications

(2 citation statements)

References 6 publications

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“…Furthermore, one cannot be sure that an apparently explanatory variable was not a proxy for an unmeasured variable that really was causal. As Dixon (1987) has pointed out, long-term comparative studies using experimental systems such as mesocosms are needed to determine cause and effect relationships. Whilst we agree with this, at the same time the recent change to water-based drilling muds on the Norwegian continental shelf is in itself a fieldexperiment.…”

Section: Trmentioning

confidence: 99%

A comprehensive analysis of the effects of offshore oil and gas exploration and production on the benthic communities of the Norwegian continental shelf

Olsgard¹,

Js²

1995

Mar. Ecol. Prog. Ser.

259

157

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ABSTRACT. Multivariate statistical analyses of data on environmental variables and benthic fauna from 14 oil and gas fields obtained from 24 surveys collected between 1985 and 1993 are presented. At all fields oil-based drilling mud was used. The purpose of this study was to investigate contamination gradients, assess effects on benthic fauna both spatially and temporally and to evaluate measures such as diversity indices, indicator species and multivariate analysls techniques in assessment of pollution. Results from analyses of baseline surveys of environmental variables and fauna were charactensed by a lack of distinct gradients in station placement, having a typical shot-gun pattern in PCA-, DCA-and MDS-ordination analyses. Likewise there was no consistency in which environmental variables correlated with the fauna. Contamination was assessed using all the physical and chemical data in classification and PCA-ordination analyses Clear patterns were found using 4 categories, conveniently termed initial, moderate, severe and gross. The categories were usually apparent as rings radiating from the platform. Initial contamination of the outermost areas at most fields was shown as elevated levels of barium and total hydrocarbons (THC) and sometimes also by elevated levels of zinc, copper, cadmium and lead. Three fields were studied in particular and showed contaminated areas of over 100 km2 (Valhall), over 15 km2 (Gyda) and over 10 km2 (Veslefrikk). After a period of 6 to 9 yr contamination had spread, so that nearly all of the outermost stations 2 to 6 km away from the platforms showed evidence of contamination. Thus, the existing sampling design is no longer suitable for assessment of the area contaminated. Effects on the fauna showed, as with contamination, 4 categories. Analyses hnking fauna and environmental variables indicated that the effects were mainly related to THC, barium and strontium, but also to metals like zinc, copper, cadmium and lead, which are all discharged in drill-cuttings. Effects on the fauna closely followed the patterns of contamination with only a few stations at each field that were contaminated not showing effects. Thus the areas showing effects were only slightly less than the areas contaminated. Subsequent to cessation of discharges biodegradation of oil and reduced concentrations of THC were observed. Yet there was an extension of areas where the fauna was affected several years after cessation of dnll-cutting discharges This may indicate that barite and related compounds associated with the discharges also have an environmental impact. However, preliminary results from fields using only water-based mud clearly indicate a reduction in environmental contamination and biological Impact, compared to effects reported here, for oil-based drill-cuttings. Diversity indices appl~ed to the data did not show the extent of effects and such Indices alone should not be used to interpret changes. The consistent patterns that the multlvariate techniques were able to detect showed that these methods...

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Section: Trmentioning

confidence: 99%

A comprehensive analysis of the effects of offshore oil and gas exploration and production on the benthic communities of the Norwegian continental shelf

Olsgard¹,

Js²

1995

Mar. Ecol. Prog. Ser.

259

157

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“…Thus restoration of major biological features of the community took less than 3 mo in an area with a benthic fauna typical for a eutrophicated fjord. Based on reported effects of hydrocarbons on benthic communities (Dixon 1987) it was surprising that the effect of the added oil was not dramatic, especially as the oil content in the sediment was high (3920 ppm wet wt) and was not reduced during the experimental period (Berge et al 1987). Despite the fact that densities were reduced for some of the taxa for the total box samples (Berge unpubl.…”

Section: Experimental Designmentioning

confidence: 99%

Macrofauna recolonization of subtidal sediments. Experimental studies on defaunated sediment contaminated with cruce oil in two Norwegian fjords with unequal eutrophication status. I. Community responses.

Berge¹

1990

Mar. Ecol. Prog. Ser.

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Experiments were performed by placing oiled and unoiled defaunated sediment in boxes (0.2 m2) on the sea floor in 2 Norwegian fjords, the eutrophicated Oslofjord (4 boxes, April to July 1980) and the non-eutrophicated Rauneflord (12 boxes, February 1981 to March 1982. In the Oslofjord no negative effects of the added oil (3920 ppm wet weight sediment) on macrofauna community structure were seen after 3 mo. Thus restoration of the community took less than 3 mo during a spring/summer situation in a soft bottom area with a species composition dominated by opportunistic species (Polydora spp.). In the Raunefjord the effect of the added oil (4520 ppm) was shown in reduced species diversity after 4 mo, and altered k-dominance curves, distribution of individuals among species, Hurlbert's rarefaction curves and multidimensional scaling plots. The added oil reduced the mean equilibrium number of species per box from 80 to 55. The time needed to reach 90 % of this equilibrium was shorter in the oiled boxes (259 d) than in the control boxes (466 d). Effects were most severe after 4 mo on the f~lter-feeders and surface deposit feeders, after 9 and 13 mo on subsurface deposit feeders. Immigration rates were similar (0.27 species d-' box-') m both treatments during June to November; however, from November to March the rate was higher in control boxes (0.24) than in oiled boxes (0.17). Mean extinction rates in boxes (species/species d-' box-') were, however, larger in the oiled boxes than in the control boxes during both periods (Oil: 0.0048, 0.0033; Control: 0.0027, 0.0024). For both fjords animals retained on a 250 Km sieve generally showed higher densities in the oiled sediment. It is concluded that restoration of the benthic macrofauna after oil contamination of sediment takes longer in a noneutrophicated area than in a eutrophicated area. The reduced density of macrofauna in the oiled boxes in the Raunefjord was caused by toxic response to oil directly, or by secondary effects leading to increased mortality, rather than by reduced settlement. Macrofauna recolonization is easily affected by oil-contamination in a non-eutrophicated area; however separation of oil-specific responses in benthic communities from responses to other disturbances can hardly be demonstrated without relevant controls

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Mining and Mineral Processing

Govorushko

2011

Natural Processes and Human Impacts

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Experimental Application of Oil—Based Muds and Cuttings to Seabed Sediments

Cited by 6 publications

References 6 publications

A comprehensive analysis of the effects of offshore oil and gas exploration and production on the benthic communities of the Norwegian continental shelf

A comprehensive analysis of the effects of offshore oil and gas exploration and production on the benthic communities of the Norwegian continental shelf

Macrofauna recolonization of subtidal sediments. Experimental studies on defaunated sediment contaminated with cruce oil in two Norwegian fjords with unequal eutrophication status. I. Community responses.

Mining and Mineral Processing

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