Marine Environments of the Southeast Australia (Gippsland Shelf and Bass Strait) and the impact of offshore petroleum exploration and production activity

This article was downloaded by: [UNSW Library]On: 17 March 2015, At: 17:42Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Marine Georesources & GeotechnologyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/umgt20

Marine environments of Southeast Australia (GippslandShelf and Bass Strait) and the impact of offshorepetroleum exploration and production activityIan H. Lavering aa Exploration and Production Impacts Section, Petroleum Resources Branch , Bureau ofResource Sciences , P.O. Box Ell, Queen Victoria Terrace, Parkes, Canberra, ACT, 2600,AustraliaPublished online: 23 Dec 2008.

To cite this article: Ian H. Lavering (1994) Marine environments of Southeast Australia (Gippsland Shelf and Bass Strait) andthe impact of offshore petroleum exploration and production activity, Marine Georesources & Geotechnology, 12:3, 201-226,DOI: 10.1080/10641199409388263

To link to this article: http://dx.doi.org/10.1080/10641199409388263

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Marine Georesources and Geotechnology, Volume 12, pp. 201-226 1064-119X/94 $10.00 + .00Printed in the UK. All rights reserved. Copyright © 1994 Taylor & Francis

Marine Environments of Southeast Australia(Gippsland Shelf and Bass Strait) and the

Impact of Offshore Petroleum Exploration andProduction Activity

IAN H. LAYERING

Exploration and Production Impacts SectionPetroleum Resources BranchBureau of Resource SciencesParkes, Canberra, ACT, Australia

Marine environments of the Gippsland Shelf (Gippsland Basin) and Bass Strait(Bass Basin) are described and an exploratory (preliminary) assessment of thepotential effects of petroleum exploration and production activity are outlined.Exploration activity has been undertaken in both areas and inferred environmentalimpacts are typically short term. Production activities are restricted to the GippslandBasin, have potential for long-term impact, and are likely to result in trace levels ofhydrocarbons being present within 1 km of the point(s) of discharge of drilling wasteor wastewater. The inferred impact of produced wastewater, which may contain upto a maximum of 30 ppm of produced hydrocarbons, on waters of the GippslandShelf is presently being modeled and quantified. Results indicate that the backgroundlevel of produced petroleum in waters of the Gippsland Shelf is less than in areasaround Sydney and Melbourne affected by urban runoff. Potential strategies formonitoring environmental quality on the Gippsland Shelf include a biologicallybased "mussel watch"program.

Keywords environmental impact, environmental monitoring, marine environ-ments, petroleum exploration and production

Living marine communities in the Gippsland Shelf and Bass Strait regions ofAustralia (Figure la) are complex and diverse. They, like all naturally occurringcommunities, are subject to natural change and, in some cases, changes resultingfrom human activities. The effects of man-made disturbance are difficult toquantify in settings where natural changes and processes have not been assessed in

Received 18 February 1994; accepted 2 June 1994.The comments and assistance of Alan Williams, Russ Temple, Paul Williamson, Barry

West, Tony Stephenson, Madeleine Jones, Kevin McLoughlin, and Russell Reichelt of theBureau of Resource Sciences, and Russell Tait of Esso Australia Ltd., in the development ofthis work is gratefully acknowledged. Drafting of text figures was undertaken by theCartographic Services Unit of the Australian Geological Survey Organisation, under thedirection of Brian Pashley. This article is published by permission of the Director of thePetroleum Resources Branch of BRS. The comments of two anonymous reviewers are alsogratefully acknowledged.

Address correspondence to Ian H. Lavering, Exploration and Production ImpactsSection, Petroleum Resources Branch, Bureau of Resource Sciences, P.O. Box Ell , QueenVictoria Terrace, Parkes, ACT, 2600 Australia.

201

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

202 I. H. Lavering

nB W 1 T x l l

— • Basin margin

• Bathymetry in metres

42° 0 400 km

142°

(a)

Figure la. Location of Bass Strait and Gippsland Shelf, southeast Australia.

detail. The assessment presented in this study is essentially exploratory becauseenvironmental data are scattered or are of variable quality. Because the mostdetailed data are limited to the immediate surroundings of petroleum productionfacilities, quantified assessment of the impact(s) of various human activities on thetwo regions is of limited value and reliability. All assessment must have somestarting point, however, and this study seeks to place available information andresults in perspective, albeit an exploratory one.

This article considers the marine environments of two major water bodies ofsoutheast Australia and their underlying sedimentary basins (Bass and GippslandBasins), drawing from geological, biological, and environmental monitoring studies(Figure la). Such data provide a profile of environmental features, as well asinformation on the operations of the petroleum exploration and production indus-try in the region(s). Océanographie and biological data are used as a starting pointfor this discussion.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 203

The marine biological communities most likely to reflect the impact ofpetroleum exploration and production activities are benthic filter-feeding popula-tions (Hyland et al., 1990; Middleditch, 1981). Pelagic populations may reflectimpacts on oceanic and biochemical processes rather than site-specific data.Chemical, physical, and biological data from similar studies in North Americaindicate that the subtle environmental effects of petroleum exploration and pro-duction activity are difficult to distinguish apart from natural changes. Monitoringstudies of petroleum-producing continental shelf areas of North America indicatethat the level of carbon derived from fossil sources (petroleum production) andpreserved in seabed sediments is minute compared with the amount of carbonderived from local biotic and other sources (Hyland et al., 1990; Schimmelmann &Tegner, 1991; Wolfson et al., 1979).

Past assessment of the environmental impact of the Australian petroleumindustry by the Independent Scientific Review Committee (ISRC, 1993) is largelybased on extrapolation from studies conducted in other parts of the world. TheISRC (1993) concluded that the environmental effects and fate of waste productsgenerated by the Australian petroleum exploration and production industry areminor and localized. However, until such findings are reinforced by additionaldetailed surveys and critical review, their validity will remain the subject of ongoingdiscussion. Differences due to the uniqueness of local conditions and faunas are,alone, sufficient to require detailed monitoring and surveillance (Buckley, 1991;Constable, 1991).

143* Í44e

• • • • • " • ' . - ' " • ' • • • . : ' -

:'\-:':•&:'•£•• s

\ 9 * - Cape Ohvay

• «\ ^S' * %98 \ « '&%

í ) i/1( •

\\

'.'• ; ' • • ' • • - i / "..•'•:¿sR*t

0«

O9

* 9

9 9

KingIsland

*

HUNTERGBOUP

« «

\ '

145"

ilefboufne-

9

9

O

O

9O

9

« O . •ö_«9

Ais

O

0 ®

®

«A

146*. • V ; V . ; - . • . . ; • - • . • : • - • . . • ' . • . - . • .

Wilsons 1 ••(Promontory \J

9

BXSS STTMfJ-

o ••

9 O

147* M8*

1*, 1 ffOIPPSUWO gjfe

" f ft / */W1

HCX3AN GBOUP <> \ 9

*® ¿yKENT * ®)GROUP • /

e ,̂ -v Flinders L r i• i^\tsland F|S

FURNEAU^^'v^i Ä \GROUP X.v'y 1 % \

9 V:>J® \9 J!j3-q ®

9 Ç7

9 * BANKS STRAIT ¿

s* / x ««/

I491 1ST• •-••/.•:•. •:-:r--y>/Cape'Howe

ii^—^y , 1/ „%^— •

* snap

SH PLATFORM•

9

^ TASMAN SEA

i8

9

0 100 kmi i

» Biological sample <> Petroleum exploration well Production facility - Seabed pipeline

(b)

Figure lb. Location of petroleum exploration wells in Bass Strait and Gippsland Shelf;production platforms on the Gippsland Shelf, and biological samples in the Bass Straitbenthic sampling survey by the Museum of Victoria. (After Wilson & Poore, 1987.)

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

204 I. H. Lavering

Even though no major problems have been identified to date (ISRC, 1993),ongoing monitoring programs are required to satisfy both public and privateinterests in the environmental record of the Australian petroleum exploration andproduction industry. No comprehensive data is available to test the validity of theinference in the ISRC (1993) report that, as no evidence of major impacts havebeen noted under local conditions, such impacts are minor, localised or do not existin the long-term. Monitoring also provides knowledge of local environmentalconditions and help in assessment and forecasting of natural biological cycles.Monitoring studies are also essential to demonstrate that ongoing (sustainable)resource management is practicable while satisfying much of Australia's currentcrude oil requirements (Spellerberg, 1991). The approach used in this study isinterpretation of available data, from local and foreign sources, and estimation ofthe relative probability and severity of risks associated with the direct environmen-tal effects, impacts, or by-products of these activities.

Location and Setting

Bass Strait and the Gippsland Shelf are the widest areas of continental shelf in thetemperate part of Australia (Kershaw & Nanson, 1993; Wilson & Poore, 1987). Seafloor investigations have been undertaken (Blom & Alsop, 1988; Jones & Davies,1983) along with reconnaissance sampling of benthic and demersal populations(Wilson & Poore, 1987). Sediments on the sea floor are largely sand, but silt andclay dominate the central part of Bass Strait and deeper waters of the GippslandShelf (Wilson & Poore, 1987).

Ongoing petroleum exploration and production activity on the Gippsland Shelf(overlying the Gippsland Basin) supplies much of Australia's domestic crude oilrequirements (Figure lb). In 1992 Gippsland Basin oil fields produced 68% ofAustralian crude oil requirements (Australian Institute of Petroleum [AIP], 1993).Approximately 150 geophysical surveys have been conducted in waters of theGippsland Shelf for the purpose of both exploration and delineation of knownfields (PEDIN, 1993). A moderate level of data coverage from seismic survey andwells is available, but less than for most other major petroleum-producing regionsof the world.

More than 150 exploration wells have been drilled to test the fluid content ofsubsurface reservoirs (PEDIN, 1993). Exploration wells that identify a majorpetroleum accumulation are used to guide drilling of development and productionwells, which tap into reservoirs and may be used to produce petroleum. The latterwells are drilled from, or close to, purpose-designed man-made structures, whichseparate petroleum from produced wastewater and are the focus of the productionprocess. Sixteen man-made structures are present on the Gippsland Shelf andproduce petroleum to onshore facilities, via a network of pipelines, and otherseabed facilities (Russ, 1991).

Petroleum industry activity and facilities only occupy a small surface area ofsea bed, and above the water, even though the Gippsland Basin is the mostintensively explored and prolific petroleum-producing area of Australia. Eachexploration well site is occupied by a moveable platform on an anchored vessel.These facilities remain in place for short periods to undertake drilling of explo-ration wells. Such sites occupy several tens of square meters of sea bed and initialdrilling takes place over a period of up to 40 days. In contrast, production facilities

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 205

occupy up to 300 m2 of sea bed, and much of the overlying space, above sea level,is taken up by production and drilling equipment. Pipelines and other subsurfaceequipment associated with production facilities, including well heads and gatheringsystems, lie across the sea floor and may over time become covered by sediment orencrusted with marine growth (Figure lb).

In the Bass Strait region (overlying the Bass Basin) 30 exploration wells havebeen drilled and 67 geophysical surveys undertaken. Several petroleum accumula-tions have been discovered but none produce petroleum or have permanentproduction equipment installed on location. The Bass Strait region provides auseful contrast with the Gippsland Shelf in that it is an area where only explorationactivity (seismic surveys and drilling) has been undertaken.

Climate and Oceanography

Early Europeans noted that waters of Bass Strait and the Gippsland Shelf were thelocation of frequent storms and strong tidal flows (Jones, 1980). Bass Strait is ashallow coastal sea where current patterns follow strong diurnal tidal flows andexhibit uniform temperature and salinity for most of the year (Jones, 1980)(Figures 2 and 3). Bass Strait waters cool more rapidly in winter than do those ofthe Gippsland Shelf. As a consequence, slightly denser Bass Strait waters can spillover the marginal ridge between the two regions (Bassian Rise; Figure la) and flowunderneath waters of the Gippsland Shelf, generating a "winter cascade" in thelower part of the water column (Godfrey et al., 1980). In summer, tidal flowsdominate Bass Strait resulting in stronger residence time for that period anddevelopment of some stratification in the water column, a pattern which mayreinforce the cascade effect (Godfrey et al., 1980).

The fate of fluids and wastewater discharged during exploration and produc-tion activities in the Gippsland and Bass regions depends on regional patterns oftidal as well as oceanic circulation. The internal flow patterns within Bass Straitand the Gippsland Shelf are affected by the circulation of four major water masses:

(a)

Figure 2a. Local pattern of summer water circulation. (After LCC, 1993.)

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

206 I. H. Lavering

I f East Australian"!^

• . GIPPSLAND . * * 5 O O m

, SHELF \ Cascade

.¿%*

(W

Figure 2b. Local pattern of winter water circulation. (After LCC, 1993.)

the east Australian current (EAC), Tasman Sea, subantarctic water, and a circum-polar current (Land Conservation Council [LCC], 1993XFigures 3a and 3b).

The EAC is a current of relatively high temperature and salinity that is low innutrients. It comes from the tropical Coral Sea and moves southward down theNew South Wales coast and into the Tasman Sea, generating eddies or warm-corerings (Figures 2 and 3). It mixes with the Tasman Sea between Australia and NewZealand. According to the LCC (1993), when the EAC extends into Bass Strait,

V^7 o * 3 ^Papua

|NewC

SUBANTARCTIC

{a)

Figure 3a. Regional summer pattern of surface circulation.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 207

(b)

Figure 3b. Regional winter pattern of surface circulation.

subtropical species such as leatherback turtles, manta rays, marlin, and hammer-head sharks may consequently be found in waters off western Victoria andTasmania.

Bass Strait

Water depths in much of Bass Strait range from 40 to 60 m, but in the central partof the strait are 80 to 90 m (Malikides et al., 1988) (Figure 1). Around the marginof Bass Strait, on both the western and eastern sides, relatively shallow waters( < 50 m) surround major islands such as the Hogan, Kent, Flinders Island, KingIsland, and Hunter groups (Figures la and lb). Coastlines on these island groupsare affected by periodic, vigorous storms generated by southwest gales (Figures 2and 3). Consequently, the eastern coastline of such islands have better developedbeach systems, dunes, cusps, and spits than those on the exposed western sides(Bird, 1981; Gill, 1972). Greater exposure to prevailing wind and weather patternsystems also results in the development of narrow supratidal platforms and boulderbeds on the western sides of each island (Edgar, 1984).

Tidal ranges in Bass Strait are small, with about 1 m along most sandycoastlines and 2 m at Wilsons Promontory. Tidal currents within the central part ofBass Strait are generally larger than the currents induced by prevailing windregimes (Fandry et al., 1985). Tidal influence enters Bass Strait from both the westand east, combines in the center, and produces an amplitude twice that ofshoreline tides (Fandry', 1981; Fandry et al., 1985). Surface currents in Bass Strait

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

208 I. H. Lavering

flow from west to east of approximately 0.5 km/h (Department of Transport,Australia [DTA], 1976).

Mean surface sea temperature in Bass Strait is 14°C in August and 19°C inFebruary. Tidal standing waves noted at the east and west entrances of Bass Straitrestrict surface water movement for a large part of the year (Boland, 1971; Edgar,1984; Gibbs et al., 1986; Godfrey et al., 1980). Summer upwelling takes place alongthe Victorian coastline of Bass Strait and the Gippsland Shelf (LCC, 1993). Suchupwelled water has low temperature and high salinity and is low in nutrients (LCC,1993).These patterns have implications for the distribution of sediments and solidwaste derived from exploration and other drilling operations.

Gippsland Shelf

At the shoreline the Gippsland Shelf is separated from Bass Strait by WilsonsPromontory and mangrove salt marshes of Corner Inlet (Bird, 1981). To thenortheast of these features an extensive system of coastal dunes has formed underthe influence of longshore drift currents, wave patterns, and the availability of finequartz sand. The Gippsland Shelf narrows from 100 nautical miles off WilsonsPromontory to 10 nautical miles east of Cape Howe. During summer the shelf issubject to mild easterly winds, which produce less vigorous wave systems than thosedeveloped in Bass Strait. As a result, the Gippsland coast is essentially depositionalwith long beach systems, dunes, cusps, and spits, and some fringing mangroves andsalt marshes (Bird, 1981). Tidal ranges are small, about 1 m along most of the coastand 2 m at Wilsons Promontory. Tidal currents at the shoreline are limited, exceptat the mouth of the Gippsland Lakes, where flood and ebb tidal deltas have formedland and seawards of narrow, man-made tidal channels.

The vertical structure of water in Bass Strait and the Gippsland Shelf is morecomplicated than surface current and circulation patterns indicate (Fandry, 1983).At the Kingfish petroleum production platform (Figure lb), on the GippslandShelf, an upper water layer flows in response to tide-induced velocity plus 2% ofwind velocity while the lower boundary layer is driven by tides (Jones, 1980). As aconsequence, cold water can build up on the northern shores of Bass Strait at theend of summer and add to the development of the winter cascade across theGippsland Shelf.

Moreover, currents at the Kingfish production platform change with depth(Fandry et al., 1985; Jones & Gerlach, 1980). Westerly winds result in a subsurfaceflow to the northeast at 2% of wind speed. Water column stratification notedat Kingfish platform has the potential to selectively trap some components of drill-ing waste and produced wastewater and limit distribution and dilution of suchmaterial.

The circulation pattern in the Tasman Sea east of the Gippsland Shelf is themain local influence on circulation through Bass Strait and the Gippsland Shelf(Figures 2 and 3). Andrijanic (1988) has identified major water masses in theTasman Sea by the composition of their planktonic foraminiferal faunas. Twospecies common in the Tasman Sea are Globigerina bulloides and Globorotaliainflatia, which is more abundant below the surface (Albani & Yassini, 1989). Thefirst is prevalent in surface subantarctic water, the second is typical of transitional

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 209

water, which develops when cold and subtropical water masses mix. These twospecies reflect the influence in the Tasman Sea of two major oceanic systems: theEAC, which circulates down from the Coral Sea, and colder southern oceancurrents.

Subantarctic water originates in high southerly latitudes and is rich in nutri-ents. It reaches the east and west entries to Bass Strait and supports high levels ofpelagic productivity. The deeper waters of the Tasman Sea are, according to LCC(1993), cold, low in salinity, and have a high level of nutrients. They are subject tothe interaction of the EAC, and flow through Bass Strait as well as subantarcticwater.

The Tasman Sea exceeds 4,000 m in depth and is the location of southwardmeanders of the EAC, which forms deeply circulating warm-core rings (Mulhearn,1983). "Pinch-off eddies from the EAC can also develop northeast of theGippsland Shelf (Mulhearn, 1983; Nilsson & Cresswell, 1981). Otherwise the shelfis under the influence of northwest flowing currents from Bass Strait and thesouthern part of the Tasman Sea (Mulhearn et al., 1986). These major patternsprovide the driving mechanisms for current regimes on the Gippsland Shelf.

Modeling of stratified and well-mixed water bodies by Simpson and Bowers(1981) provides an indication of how Gippsland and Bass water bodies function as areceptor of sedimentary and water input, particularly fine clay particles fromdrilling waste or wastewater from production operations. Well-mixed water bodiestend to be under the influence of major oceanic currents. Stronger mixing takesplace in the restricted passages of Bass Strait (Fandry, 1983), but some stratifica-tion can develop during summer and autumn. The boundary between stratifiedparts of Gippsland Shelf waters and mixed eddies of the EAC changes positionfrom summer to winter as a result of the changing pattern of water circulation(Figures 2 and 3).

Sedimentary Environments

Muddy sediments are present on much of the continental shelf of eastern Australia(Figures 4 and 5). Davies (1979) suggests that these sediments are relics of pastprocesses, because their textures are similar to those of mixed coastal barrier sandsand back-barrier muds. Most sand grains sampled are of carbonate origin (Jones &Davies, 1983). Some concretionary limestone and relict beach rock is present onthe middle and outer Gippsland Shelf but otherwise the carbonate is largelyskeletal debris from mollusks, bryozoans, and foraminifera.

Mud is present on the sea floor in Bass Strait at depths of 44 to 90 m.According to Blom and Alsop (1988), calcitic muds are now accumulating in thecentral part of the basin at 75 to 80 m of water depth over an area of 20,000 km2.The calcitic muds are a product of the remains of nanoplankton (coccoliths) as wellas skeletal carbonate grains. Depositional rates are < 12 cm per 1,000 years in thebasin center but decrease to < 6 cm per 1,000 years around the margin (Blom &Alsop, 1988).

Several large fields of sandwaves are evident at water depths of 40 to 46 m inand around the islands of Bass Strait (Malikides et al., 1988). The fields are coarsesand and gravel consisting of 50 to 92% biogenic carbonate, derived from the

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

210

144° 145°

/. H. Lauering

146° 147" 148°

Melbourne

41°

GRAJNSIZE 0

1-2 2-3 3-4 4-5 >5 Rock outcrop

Figure 4. Seafloor sediment types. (After Blom & Alsop, 1988, Jones & Davies, 1983.)

remains of mollusks, bryozoans, and echinoderms. They appear to be modernactive bedforms with ripples, crest megaripples, trough megaripples, and sandwavespresent on their surface (Malikides et al., 1988). In total they cover an areaexceeding 400 km2 in eastern Bass Strait. Sandwaves and their superimposedmegaripples are aligned approximately transverse to ebb tidal flow. Large megarip-ples located in the troughs between sandwaves are aligned transverse to flood tidalflow.

Along the Gippsland Shelf there is a transitional change at depths of 40 to 45m from wave-like or sand-rippled bedforms to irregular substrates colonized bysedentary marine forms (Jones & Davies, 1983). The boundary between thesebedforms is governed by storm wave-base. Exon et al. (1992) identified sedimentsin waters deeper than those of the Bass Basin, 100 km west of King Island, andnoted a change from bryozoan, coral, pelecypod, and gastropod gravels, in water800 m deep, to fine sands, sandy calcareous oozes, and heavily bioturbated mudsand oozes, down the continental slope in water 4,500 m deep. Exon et al. (1992)suggest that the shelly bryozoan sands reflect higher energy conditions than those

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 211

presently evident on the continental shelf and may be the remnant of past lower(interglacial) sea level(s).

Biological Environments

The marine ecosystem of Bass Strait and Gippsland Shelf is complex and dynamic.The intertidal zone is a potential accumulation point for flotsam and jetsam, andoil spills, derived from shipping or other sources. Intertidal benthic communitieshave significant filter-feeding populations, which are useful monitors of sea waterquality (Burns & Smith, 1980, 1981) but also may be the first affected by man-madedisturbance.

According to Edgar (1984) and Rice (1989), the upper intertidal zone of Bass isthe location of extensive populations of barnacles and mollusks, whereas the lowerintertidal zone, and below, is dominated by algae. In deeper subtidal waters of theGippsland Shelf and outer parts of the Bass Basin numerous bivalve, brachiopod,gastropod, and scaphopod species are evident (Jones & Davies, 1983; Richardson,1987).

144° 145° 146° 148°

100 kmMelbourne

— Z&< GIPPSLAND: : • ' • : : . SHELF ~

40°

41'

% CaCo3

f: .•:•! 90-70 70-50 r-_r <50 Rock outcrop

Figure 5. Percent calcium carbonate in seafloor sediments. (After Blom & Alsop, 1988.)

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

212 I. H. Lavering

At least five brachiopod species are common to the sandy patches of sea floorin Bass Strait. Most use their attachment mechanism (pedicle muscle) to maintaina stable position at the sediment/water interface but another sedentary formattaches itself to bryozoan colonies (Richardson, 1987). The shell form comprisinga biconvex shape, with an oval outline, lacks significant external ornament andensures ease of movement in maintaining position in rapidly migrating carbonatesands.

According to Jones and Davies (1983), the foraminifera present in shallow( < 20 m) seafloor sediments of the outer Gippsland Shelf are largely calcareousbenthic types; arenaceous and planktonic forms are less common. Shoreward of themid-shelf ( < 80 m) are quartz-rich sediments in which a sparse fauna dominatedby Elphidium is present.

Benthic invertebrates in waters ranging from 20 to 80 m deep compriseforaminifera, bryozoans, mollusks, echinoids, brachiopods, ostracods, and burrow-ing worms (Blom & Alsop, 1988). Bryozoans are dominant and include erect,flexible forms typically found on fine sand and silty substrates. Encrusting anderect branching forms are present in shallow sandy substrates, particularly in thenorthern part of and around islands of Bass Strait (Blom & Alsop, 1988).

The Bass Strait and Gippsland Shelf regions are noted for their significant fishand seafood stocks. At depths of up to 30 m the green and blacklip abaloneHaliotis ruber and Haliotis laevigata inhabit reefs, crevices, and the sheltered partsof rocks and boulders. Moderate water movement is a feature of its habitat and itmay also be present along the margin of seagrass beds (Winstanley, 1981).

Commercial exploited populations of scallops {Pectén alba) inhabit fine tocoarse sandy substrates within 20 nautical miles of Lakes Entrance, and near theKingfish oilfield (Winstanley, 1981). The transient nature of the scallop beds isapparently due to the patchy distribution of larval settlement (Winstanley, 1981).Squid are caught throughout the year in waters 60 to 90 m deep, but fewer catchesare made in winter. Octopi are caught in shallow waters in traps and on sandy orgravel substrates.

Trawling for prawn (shrimp) is done in estuaries and inlets and coastal waters 2to 40 m deep adjacent to Lakes Entrance. Lobster and crab species support sometrapping operations and inhabit hardgrounds and sandy substrates in waters 30 to80 m deep. Giant crabs and swimmer crabs are caught by trapping in water depthsof up to 420 m (Winstanley, 1981). A wide variety of fish stocks are successfullyexploited by both commercial and recreational fishing on the Gippsland Shelf(Winstanley, 1981).

Petroleum Exploration

Exploration activity typically begins with seismic survey traverses, followed byselection of sites for the drilling of exploration wells. Discovery of potentiallycommercial petroleum in an exploration well is generally closely followed byinstallation and commissioning of petroleum production facilities, along withassociated pipeline or other processing hardware. The Gippsland Shelf has beenthe location of major petroleum production activity for more than 20 years. Duringthis period, more than 2,800 million barrels of crude oil have been extracted, butonly approximately 350 barrels of this has been lost by spillage (Griffiths, 1991).With such a record, the major environmental impacts of industry activity, evident

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 213

to date, are those that result from the presence of the industry, rather than as adirect consequence of petroleum extraction or accidental spillage.

Seismic Surveys

Parts of the Gippsland Shelf and Bass Strait have been the location of intermittentexploration activity for nearly 30 years. Geophysical (largely seismic) surveys arethe most widespread activity and consist of the collection of seismic data overparticular areas of potential interest. The surveys involve the pulsing of acousticsignals to penetrate and image geological structure below the sea bed. Acousticenergy is reflected back to sensitive receiver equipment by subsurface layers belowthe sea bed. The reflected signals are used to evaluate the subsurface geologicalstructure and to determine potential to host petroleum accumulations. Survey datacollection is generally limited to periods of less than 40 days per survey. The mainquestion related to such surveys is their possible sublethal or disturbance effects onsea life.

Marine mammals and vertebrates can apparently habituate to low levels ofbackground noise (Geraci & St. Aubin, 1987). Marine habitats on the GippslandShelf and Bass Strait are not without significant levels of noise from other sources,such as those associated with wind and wave movement, sea-bottom sedimenttransport, feeding, and other activities of marine life (Harris et al., 1991). Migratingsandwaves have been observed to produce noise levels of the order of 140 to 180db (Harris et al., 1991)

Acoustic pulses from modern seismic sources do not appear to have a majoreffect on fish or invertebrate populations, at ranges of greater than several metersfrom source (Neff et al., 1987). For efficiency and technical control, potentiallylethal explosive seismic sources have not been used in surveys since the late 1960s.The disturbance effects of acoustic signals on larger marine mammals at closerange is not accurately known but appears to be comparable with that generated bymammals during periods of vigorous activity. Like seismic surveying in other partsof the Australian continental shelf, noise levels generated by seismic survey workundertaken in the Bass Strait and Gippsland Shelf regions could be calibrated tolocal conditions to assess any disturbance effect they may represent to marinemammals and sea life.

Drilling Operations

Drilling in the Bass Strait and Gippsland Shelf regions has been accomplishedusing drillships, jackups, semisubmersible vessels, or rigs mounted on fixed produc-tion facilities. The type of vessel used depends on water depth, cost, and availabil-ity. Anchoring of the vessel represents a potentially localized disturbance to the seafloor in the vicinity of the drill site. Extendible legs used to support a jackup vesselsit on the sea floor, causing indentation and compaction of several square metersof the substrate.

The impact of offshore exploration drilling operations is largely related to thefate and effects of drilling muds and excavated rock fragments discharged into thesea. Drilling mud, largely barite (barium sulfate) is mixed with water and used as aweighting agent to maintain control over pressurized subsurface fluids. Circulationof the drilling mud to the drill bit, at the base of the well and back to the surface,allows fragments excavated by the drill bit to be separated from the mud and

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

214 I. H. Lavering

discharged overboard (Chilingarian & Vorabutr, 1983). A typical well discharges atotal of 1,000 to 2,500 tons of rock fragments, each of which may be coated withtraces of drill mud (Gettleson, 1980). Much of the mud that coats each fragment iswashed off in the sea, and the fragments settle to the sea floor. Drilling mud isconstantly conditioned and treated to maintain required engineering properties,but it may be discharged into the sea if a different type of fluid is required fordrilling or completion of a well (Gettleson, 1980).

Field data from studies outlined in Boesch and Rabalais (1987) indicate thatwaste disposed of during drilling operations would be distributed by local tidal andcurrent patterns. Dilution and dispersion of drilling mud and rock fragments, at thetime of disposal, takes place at rates dependent on prevailing hydrographie condi-tions (Neff, 1987). Low-energy sites may show evidence of discharged materialwithin 1,000 m of the point of discharge; high-energy sites show little if anymaterial except within several meters of discharge.

Long-term effects of prolonged drilling are difficult to estimate (Thompsonet al., 1980). The major potential for any visible impact is when peak concentra-tions of material are discharged and little, if any, dilution and dispersion takesplace. Plumes formed by discharged rock fragments and drilling mud may beslender and highly concentrated rather than broad and diffuse. As a result, theextent of areas affected depends on the "visitation frequency" of the plumes ofwaste material (Churchill, 1987). Settling times for fine, suspended mud and clayparticles follow Stokes' law (1 to 2 m/day settling rate; Sackett, 1978).

The fate of discharged drill cuttings and associated mud in the water column issuch that rock cuttings and other coarse solids fall rapidly to the sea floor andsuffer only relatively minor deflection by the prevailing currents in the watercolumn, even in water up to 80 m deep. Fine grains and particles can, however,remain in suspension and be distributed downcurrent of the point of release. Spoilwith a high silt content is likely to be transported to the bottom as a turbulent jet(Gordon, 1974). When such a jet impacts the sea floor it spreads in a circularpattern, to a distance equivalent to 30% of the water depth. Turbidity in the watercolumn will carry less than 1% of the silt material in suspension, which settles overa wide area. According to Bokuniewicz and Gordon (1980), these processes areindependent of water depth and current speed. Wilson (1979) suggests thatsuspended material will develop a plume related to settling velocity and theadvective/diffusion effects of ambient water flow.

Lytle and Lytle (1979) compared the changes evident after 2 months of oil rigdrilling operations at a location on the Texas Shelf in 25 m of water. Theyconcluded that only slight changes in the level of trace hydrocarbons were evidentclose to the rig site; minor increases in the concentration of barium sulfate wereevident. Exposure to even very low concentrations of some trace elements can,over time, lead to their buildup in the tissues of clams and other invertebratedeposit feeders and filter feeders (Romeril, 1979).

Petroleum Production

Studies of the ecological impact of production facilities have been performed for arange of marine habitats (Boesch & Rabalais, 1987). Some ecological changes dooccur, and these are largely related to artificial reef effects or changes due to the

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 215

presence of cuttings or drilling waste on the sea floor. Other changes are subtle,not readily detectable without detailed sampling and analysis (Spies, 1987). Thedischarge into the sea of processed subsurface water (separated from the crude oil)is expected to be the largest single environmental impact of the oil productionprocess, largely because of the volume of fluid discharged and the longevity of theprocess.

Produced Wastewater

The volume of wastewater discharged from the Gippsland Shelf production facili-ties from 1988 to 1990 increased from approximately 28 to 48 ML/day (Russ,1991). Oil concentration levels in the wastewater were generally below 20 ppm or20 mg/L (O'Byrne, 1988), although peak levels of 60 to 75 ppm were attained forshort periods (up to 30 minutes) (Russ, 1991). Wastewater temperatures at the timeof discharge are inferred to be above 60°C, and salinity levels vary.

Wastewater from some Gippsland fields is largely positively buoyant (lowerdensity than seawater), whereas that of other fields may have neutral or negativebuoyancy at the time of discharge. Buoyancy of the wastewater plumes may varywith wastewater temperature and salinity. Kuttan et al. (1986) identified 30,000 to40,000 ppm NaCl equivalent as the formation water salinities of some of the majorGippsland Basin (Shelf) producing fields. The large volume of wastewater from allfields is likely to have nil or slightly positive buoyancy and spread in plume-likeflows as it mixes and entrains ambient seawater after discharge.

Gippsland Shelf fields closer to the coast have (low) salinities of less than 4,000ppm NaCl equivalent, due to influx of freshwater into the oil-bearing reservoirs(Kuttan et al., 1986). In contrast, Roder and Sloan (1986) suggest that the salinityof oil-bearing reservoirs in such fields is actually higher and that only reservoirsunderlying the oil-bearing intervals have been affected by the influx of low-salinitywater.

Wastewater from most Gippsland reservoirs would have positive buoyancywhen released in seawater. Diffusion and mixing of produced wastewater would beaided by local tide and surface wind-induced currents. The low salinity and hightemperature ( > 50°C) of wastewater cause positive buoyancy and rapid spreadingin the water column. Rapid cooling of highly saline (brine) wastewater could,however, result in negative buoyancy. Such brines can form plumes on the sea floor(Randall, 1981), where they are slowly diffused by advection and dispersion. Thewinter cascade of water out of Bass Strait and across the shelf may contribute toflushing of any high-salinity wastewater buildup on the sea floor of the GippslandShelf, should it ever occur.

Subsurface reservoir temperatures of oil and water in Gippsland fields areestimated to be of the order of 80 to 120°C (Ozimic et al., 1987), which would resultin a temperature for wastewater discharged from such fields of 60 to 80°C. Theupper temperature limit tolerated by most marine plants and animals is about40°C, and prolonged exposure to elevated temperatures above this results indisturbed metabolic functions, if not death (Kinne, 1970). Some bacteria andprotozoa are, however, apparently well adapted to living in water temperaturesabove 30°C (Martinez, 1980).

Although the temperature of Gippsland wastewater may be below 40°C shortlyafter release, the driving effects of temperature and salinity on the plumes are

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

216 I. H. Lavering

similar (Bowman & Iverson, 1977; Smith, 1978). Hot wastewater undergoes buoy-ant spreading. There has been considerable concern expressed about the tempera-ture dependence of metal accumulation in marine organisms, particularly in caseswhere hot wastewater is discharged into marine environments (Romeril, 1979).Zooplankton populations, in particular, are likely to find the zone where waste-water and ambient water mixes to be the most favorable, if foreign examples are aguide (Youngbluth, 1976).

Routine reconnaissance studies of the Gippsland production facilities and theirsurroundings are warranted if such subtle effects of wastewater discharge are to beidentified and monitored. The effects may be detectable in simple pelagic formssuch as bacteria, algae, Zooplankton, and protozoa, as well as in organisms higherin the food chain (Smith, 1978). Intertidal and subtidal benthic populations onplatform surfaces and mooring buoys provide additional scope for assessing waterquality at the sea surface. Such filter-feeding benthic organisms provide an indica-tion of seawater quality (Boesch & Rabalais, 1987). In contrast, sediment-feedingforms reflect changes to the quality and chemistry of sedimentary particles on thesea floor, and such data can be better assessed using sediment sampling programs.

Domestic Wastewater

Detailed studies of the impact of discharged domestic wastewater effluent onbenthic communities in Victorian waters are restricted to Port Phillip Bay andWestern Port; hence it is necessary to refer to these results to assess the likelyeffects of such discharges from offshore platforms. Dorsey and Synnot (1980)investigated the impact of domestic wastewater outside Port Phillip Bay (waters 2to 5 m deep) on substrates populated by a diverse crustacean and polychaeteinfaunal assemblage, living in fine, sandy sediments. Most of the organisms aredetritus or suspension feeders, with detritus coming from planktonic or suspendedsources (Poore & Rainer, 1979).

The influx of nutrients in domestic wastewater affects the composition of suchnatural benthic communities by increasing the production of benthic algae and theabundance of deposit- and suspension-feeding invertebrate species (Dorsey &Synnot, 1980). The nature of changes triggered by urban runoff and sewage-relatedeffluent can be clearly distinguished from that of petroleum production effluentbecause of the more severe and obvious effects of the high nitrate and phosphatelevels in urban effluent.

Intertidal areas of Bass Strait impacted by urban sewage effluent show areduction of the intertidal brown alga Hormosira banksii and the coral algaCorallina officinalis and a reduction in cover of turfing algäe (LCC, 1993). Speciesrichness declines by at least 50% near the points of discharge. These effects are farmore concentrated than those likely to develop near offshore petroleum produc-tion platforms, but they serve as a guide to the specific impact of such material(Chiffings et al., 1992).

Borowitzka (1972) found similar results in the case of an intertidal rockplatform 3 m above a domestic wastewater ocean outfall, in the Sydney region. Thenumber and types of algal species encrusting varied with proximity to the outfall.Close and concentrated exposure to domestic grease and detergents reducedspecies close to the outfall, although green algae were capable of colonizing even

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 217

the most polluted sites. Such conditions are unlikely to develop in the vicinity ofGippsland Basin platforms because of the low discharge volume and rapid dilution.

Surface Coatings

Considerable attention has been given in marine studies to ways in which encrust-ing marine growth can be prevented from building up on maritime vessels andman-made marine structures such as offshore petroleum production facilities.Surface coatings, mechanical growth inhibitors in the wave zone (barnacle bashers),and paint compounds are used because they can retard the growth of marineorganisms. Since the early 1980s the primary growth retardant in some paints,tributyltin, has been known to cause growth abnormalities in oysters and othershellfish, at very low concentrations, particularly in areas of limited water circula-tion or where there are large numbers of moored craft. The extent and use of anysuch material remains to be identified together with any specific effects it may haveon benthic forms on the Gippsland Shelf.

Corrosion Inhibitors

Metal pipes and other equipment on offshore production facilities often havebiocide compounds added to product streams to inhibit corrosion (Middleditch,1981). While such compounds are potentially a minute component of any effluentdisposed of, their demonstrated toxicity is such that any application must remainlimited. Middleditch (1981), in assessing effluent from the offshore Buccaneer oiland gas field of the U.S. Gulf Coast, noted that biocides used in the product streamto inhibit bacterial growth were present as trace amounts in the produced waste-water. The presence, or concentration, of such compounds in Gippsland wastewa-ter is not presently known.

Marine Growth

Despite attempts at redemption, some marine "fouling" growth inevitably buildsup on the large surface areas of production facilities. A key observation ofmonitoring studies in North America has been the artificial reef effect of produc-tion platforms and fixed structures in attracting both encrusting organisms andhigher levels of the food chain (Middleditch & Galloway, 1981). In most settingsthe reef effect is observably greater than the negative impact of dischargedformation water and drilling waste on local and benthic populations (Lytle & Lytle,1979; Wolfson et al., 1979).

Monitoring of fouling communities on man-made structures in Australianwaters has been undertaken by Lewis (1991), who identifies both soft- andhard-bodied organisms as potential problems for immersed man-made structures.Locations in Port Phillip Bay and Sydney Harbor are identified as having thepotential to produce between 200 and 1,200 g/m2 per month of dry weight hardfouling material such as tubeworms, shells, and skeletons, which can weigh as muchas 17 kg/m3. Most growth takes place in the summer months but may also occur inspring and autumn.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

218 I. H. Lavering

Assessment of the buildup of fish stocks around man-made reefs suggests thatthe structures increase the standing stock of marine organisms by concentratingthem in a smaller area, but this observation may not apply in all cases (Kerr, 1992).It is not possible to extend results from shallow water concrete, vessel, vehicle, ortyre-based artificial reefs to production platforms because the latter extend fromthe sea bed into the intertidal zone and artificial reefs in Australia are limited toseafloor depths of 5 to 45 m (Kerr, 1992).

Shallow water (12 to 14 m) concrete reefs in the Mediterranean Sea exhibitthree distinct assemblages over a 5-year period without reaching ecological equilib-rium (Gravina el al., 1989). The initial pioneer assemblage was mostly sessile filterfeeders, dominantly serpulids. The second was dominated by mussels and poly-chaetes common on subtidal hard-bottom communities, and the third occurredwhen mussels were reduced in number due to the buildup of surface sediment, andcarnivores and omnivores were more numerous. The overall trend was for thepercentage of filter feeders to decrease with time (Gravina et al., 1989). Differ-ences in water depth and the nature of man-made production facilities on theGippsland Shelf result in assemblages that do not proceed past the second stagenoted by Gravina et al. (1989).

Hydrocarbon Input Levels

Long-term assessment of the fate of carbon inputs into the ocean, including theGippsland Shelf area, is a key feature of the study of long-term effects ofproduction in the region. Schimmelmann and Tegner (1991), in the offshore SantaBarbara Basin of California, have examined in detail the fate of major sources ofnatural organic carbon, including that derived from marine phytoplankton andsubtidal kelp forests, and compared them with the levels derived from onshorevegetation and oil production. The Santa Barbara Basin is a region that experi-ences considerable natural seepage of crude oil from the sea floor (Stuermer et al.,1982). The oil is evident as droplets in the water column, weathered oil residues insediments, and tar balls on the substrate (Stuermer et al., 1982). The Santa BarbaraBasin region could be expected to have a relatively high level of background fossilcarbon (petroleum) in the water column and seafloor sediments. Input of carbonderived from onshore sources (e.g., in urban runoff, wastewater, and atmosphericfallout) or offshore petroleum production facilities would complement that fromnatural oil and gas seepages (Hyland et al., 1990).

The results outlined by Schimmelmann and Tegner (1991) show that the levelof carbon inputs into the offshore Santa Barbara Basin from onshore vegetationand oil products (natural seepages, onshore effluent, and petroleum productioneffluent) is negligible compared with those derived from kelp and marine phyto-plankton. Most of the Santa Barbara Basin carbon input derived from kelp andphytoplankton over the last 143 years (1844-1987) exhibits distinct climatic cycles,particularly the El Nino-Southern Oscillation (ENSO) and occasionally an associ-ated sporadic kelp "dieback" caused by bacterial disease.

No direct comparison is suggested here between the level of fossil organiccarbon currently being deposited in the Gippsland Shelf from petroleum produc-tion activity and the Santa Barbara Basin. Instead, Shimmelmann and Tegner's(1991) Santa Barbara Basin results serve as a guide to the upper limit of petroleum(carbon) inputs from production operations likely to be detected on the Gippsland

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 219

Shelf. The Santa Barbara Basin region shows a limited regional input of fossil(petroleum) carbon, despite the presence of major natural offshore oil and gasseepages (Stuermer et al., 1982) and offshore petroleum production (Hyland et al.,1990).

Bishop et al. (1992), Heggie and O'Brien (1988), and O'Brien and Heggie(1989) surveyed parts of the Gippsland Shelf for natural seepages of petroleum.They concluded that a 5- to 10-ppm background concentration of thermogenichydrocarbons was present in samples collected from the water column and thatpetroleum sourced from both wet gas and liquids (oil) was evident. A previousstudy by Burns and Emmett (1984) suggested that although such trace quantitiesand several anomalous concentrations are evident above background levels in theGippsland Shelf, they are sourced from hydrocarbons in produced wastewater.

A water column sampling survey on the Gippsland Shelf reported by Heggie(1989) identified several elevated CX-CA concentrations over distances of about 10km. Peak total hydrocarbon levels of 60 to 120 ppm were recorded in samplesextracted from seawater along traverses located near several producing fields andother known accumulations. Normal background concentrations in the watercolumn were 5 to 10 ppm. It remains to be seen whether the water column surveyreadings are due to wastewater or natural seepage.

The concentrations of hydrocarbons in Gippsland Shelf seawater comparefavorably with those measured in a 1992 survey by Heggie et al. (1992) of majorurban discharges—plumes of wastewater released by ocean outfalls offshore fromSydney. Background readings of 20 to 30 ppm hydrocarbons and peak levels of 70ppm evident plumes formed by mixing of processed urban wastewater and seawa-ter. The same survey was able to detect anomalous concentrations of ethane andbutane in seawater (0.1 to 1.0 ppm) near the entrance to Botany Bay (Heggie et al.,1992), but from different urban sources, possibly refinery effluent or atmosphericfallout from aviation exhaust emissions.

Sampling of sediments and oysters from islands along Australia's North WestShelf by Pendoley (1992), to determine baseline concentrations of THCs (saturaten-alkanes and polycyclic aromatic hydrocarbons [PAHs]), revealed very low levels.The THCs come from fishing boats, commercial shipping, or petroleum industrywork boats. The concentrations were similar to those measured in other (unpol-luted) areas of the world: n-alkanes ranged from 1.0 to 4.9 ppm in oysters and 0.015to 0.050 ppm in sediments; PAHs were < 0.010 to 0.150 polynuclear aromatichydrocarbons (ppm) in oysters and < 0.005 ppm in sediments (Pendoley, 1992).

Petroleum from Urban Sources

The concentration of petroleum from urban and onshore sources in all Victoriancoastal waters is low, on the order of 0.1 fim/L. This is equivalent to thebackground concentration in the major oceans of the world (Myers & Gunnerson,1976). In some Victorian coastal locations, such as those proximal to operatingpetroleum refineries along the shores of Port Phillip Bay and Western Port,elevated hydrocarbon concentrations have been identified by analysis of seawater,sea-bottom sediment, and the body tissues of invertebrate filter-feeding species(Burns & Smith, 1980). Readings were relatively low (up to 22 jug/L), but typicalof levels derived from refinery effluent and areas around fuel loading facilities.Sampling in adjoining water bodies indicates that the petroleum is rapidly diluted

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

220 I. H. havering

and dissipated in the water column by tidal circulation. The results suggest thathydrocarbons circulating in the water column are eventually sorbed onto sedimentparticles located on the sea floor.

Burns and Smith (1980) showed that hydrocarbons discharged into Victoriancoastal waters can only be detected above background levels where samples arecollected close to the original source. Populations of bivalve mussels (the bivalveMytilus edulis) are useful in assessing and monitoring areas affected by repeated,low-level, urban and industrial hydrocarbon input. Sediment samples collectedproximal to sources of refinery effluent have low concentrations of petroleumabove background readings (Burns & Smith, 1980). Dilution and seawater circula-tion after discharge result in only trace concentrations in the water column, levelsdifficult to detect over analytical background using normal collection techniques(Burns & Smith, 1981).

Burns and Smith (1981) recommend M. edulis as a local biological monitor ofseawater quality in areas subject to petroleum input, as an alternative to morecomplex and labor-intensive approaches. According to Broman and Ganning(1985), the bivalve bioaccumulates petroleum in proportion to the concentration ofpetroleum in seawater. Short-term variations in petroleum concentration areleveled by a long uptake period and persistence in the body tissues of M. edulis,which is a filter feeder that inhabits hard substrates, including man-made struc-tures. It is potentially useful as an indicator or monitoring species (Burns & Smith,1981). This species has a considerable advantage in assessing the concentration ofpetroleum in wastewater from Gippsland Shelf production platforms.

Long-Term Issues

Oil spills are an infrequent, low-risk event in exploration and production activity,particularly in the case of offshore oil and gas fields on the Gippsland Shelf. Theconsequences of a major oil spill from such offshore facilities are, however,potentially severe and could have major consequences. A long-term effect is heretaken as any notable change that persists over a period of greater than 2 years(Boesch & Rabalais, 1987). To date only a very small quantity of the total volumeof crude oil produced has suffered this fate and none has been recorded as havingany evident environmental impact (Griffiths, 1991).

Despite the low levels of risk posed from oil spillage during exploration and,production activities, the major environmental impacts of such spills might includephysical fouling of coastlines and a notable impact on biota close to the source ofthe spill. Residual biological damage to benthic communities, reefs, mammals,birds, fish, and reptiles and the chronic effects of crude oil weathering productsand their potential for impacts along the food chain, particularly their potential forbioaccumulation, are all possible (Warren, 1989). The introduction of petroleuminto the marine environment does cause environmental damage, mainly in local-ized areas where input rates are high. The detrimental effects are usually of shortduration and environmental conditions can readily recover if the stress (oil) isremoved or greatly reduced.

A variety of physical, chemical, and biological processes act on spilled petroleumimmediately on and after its release into the environment, including spreading,drifting, evaporation, dissolution, dispersion, emulsification, sedimentation,biodégradation, photochemical oxidation, and autooxidation. The physical pro-

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 221

cesses are important at the time of the spill, whereas the chemical and biologicalones become more significant as time passes.

Evaporation is one of the most important processes for removal of hydrocar-bons from the ocean; it is most significant during the initial stages and isaccelerated by wind, sea state, temperature, and solar radiation. Drifting anddispersion become more important after the initial spill, and biodégradation ispredominant after several days. Petroleum biodegrading microorganisms arewidespread throughout the seawater column and seafloor sediments. Althoughpresent in all oceans, they proliferate in oil-polluted waters and are ultimatelyresponsible for removal of petroleum and petroleum residues from the oceans.Bays, marshes, and estuaries are the areas most vulnerable to the impact of oilslicks because they lack the natural cleansing action of significant wave energy; oilimpinging on these areas takes longer to break down. They also tend to be themost biologically nutrient-productive areas.

One of the most adverse effects of petroleum released into the marineenvironment is the modification of benthic communities along coastlines, particu-larly the intertidal to subtidal zones. Recent research suggests that the effects of oilon these organisms is not as catastrophic as was generally thought (Teal &Howarth, 1984). Field studies in the North Sea, offshore California, and the Gulf ofMexico show that on a regional scale the distribution, density, and diversity ofbenthic organisms remain largely a product of the natural environment and arenot affected by either drilling or production activities (Lytle & Lytle, 1979;Middleditch, 1981; Wolfson et al., 1979).

Fortuitously, local Gippsland Basin crude oil accumulations discovered to datelack the more toxic compounds such as sulfur dioxide and other componentspresent in accumulations in other parts of the world. As a result, if a significantspill takes place, it should have less detrimental or long-term effects than aheavy-grade crude. All possible measures should, however, continue to be taken toavoid such spills and to maintain the excellent safety record of the industry on theGippsland Shelf (Griffiths, 1991).

Conclusions

Although this study highlights some of the potential impacts petroleum explorationand production activity may have in areas of the Bass Strait and Gippsland Shelf,the quantification of any long-term effects is a matter of ongoing effort. It is thelack of specific notable impacts and limited availability of monitoring data that arethe major results evident to date.

Natural variability accounts for much of the changes evident in marine ecosys-tems in the Bass Strait and Gippsland Shelf regions. The recognition of suchnatural variability versus the impacts of human activity can test the limits ofstatistical variability. To avoid such limits, semiquantitative measures are suggestedhere to outline the broad effects of subtle environmental disturbance.

The complexity of Bass Strait and Gippsland Shelf marine ecosystems and thesubtle nature of any impacts resulting from exploration and production activitymake initial conclusions difficult to quantify. Only by long-term assessment will itbe possible to develop an understanding of the unique features of the Bass andGippsland regions and to determine whether man-made disturbances are havingany effects beyond those noted in this study.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

222 I. H. Lavering

Wastewater disposal represents an activity where more detailed study andmonitoring is desirable. As more of our known fields approach depletion theyproduce higher volumes of wastewater, particularly in the final phase of petroleumproduction. In the long term, the need to identify the precise effects of wastewaterdisposal may necessitate more detailed, field-by-field monitoring.

References

AIP. 1993. Australian Institute of Petroleum, News. March/April. Melbourne.Albani, A. D. and L. Yassini. 1989. Taxonomy and distribution of shallow water Lagenid

Formaniferida from the south-east coast of Australia. Australian Journal of Marine andFreshwater Research 40:369-401.

Andrijanic, S. 1988. Geographical distribution of living planktonic foraminifera (protozoa)off the east coast of Australia. Australian Journal of Marine and Freshwater Research39:71-85.

Bird, E. C. F. 1981. Victorian coastal geomorphology. Proceedings of the Royal Society ofVictoria 91:19-35.

Bishop, J. H., G. P. Bickford, and D. T. Heggie. 1992. South-eastern Australia surfacegeochemistry. II: Light hydrocarbon geochemistry in bottom waters of the Gippsland Shelf,Eastern Otway Basin, Torquay Sub-Basin and the Durroon. Sub-Basin. Bureau Of MineralResources, Geology and Geophysics, Record 1992/54.

Blom, W. A. and D. B. Alsop. 1988. Carbonate mud sedimentation on a temperate shelf,Bass Basin, southeastern Australia. Sedimentary Geology 60:269-280.

Boesch, D. F. and N. N. Rabalais, eds. 1987. Long-term effects of offshore oil and gasdevelopment. London: Elsevier Applied Science.

Bokuniewicz, H. J. and R. B. Gordon. 1980. Deposits of dredged sediment at open watersites. Estuarine and Coastal Marine Science 10:289-303.

Boland, F. M. 1971. Temperature-salinity anomalies at depths between 200m and 800m inthe Tasman Sea. Australian Journal of Marine and Freshwater Research 22:755-762.

Borowitzka, M. A. 1972. Intertidal algal species diversity and the effect of pollution.Australian Journal of Marine and Freshwater Research 23:7-84

Bowman, M. J. and R. L. Iverson. 1977. Estuarine and plume fronts. In Ocean fronts incoastal processes, eds. M. J. Bowman and E. Esaias, pp. xx-xx. Berlin: Springer-Verlag.

Broman, D. and B. Ganning. 1985. Bivalve molluscs (Mytilus edulis and Macoma baltica) formonitoring diffuse oil pollution in a Northern Baltic Archipelago. Ambio 14(1):23-28.

Buckley, R. 1991. Perspectives in environmental management. Berlin: Springer-Verlag.Burns, B. J. and J. K. Emmett. 1984. Final report GE 83B geochemical (sniffer) survey,

offshore Gippsland Shelf, November 1983. Report submitted as a result of workprogram undertaken under the Petroleum (Submerged Lands) Act. Copy retained byBureau of Resource Sciences, Reference No. PSLA 83/47.

Burns, K. A. and J. L. Smith. 1980. Hydrocarbons in Victorian coastal waters. AustralianJournal of Marine and Freshwater Research 31:251-256.

Burns, K. A. and J. L. Smith. 1981. Biological monitoring of ambient water quality: The casefor using bivalves as sentinel organisms for monitoring petroleum pollution in coastalwaters. Estuarine, Coastal and Shelf Science 13:433-443.

Chiffings, A. W., A. J. Bremner, and V. B. Brown. 1992. A review of the scientific studiesand the management of nutrient loads to Port Phillip Bay. Proceedings of the RoyalSociety of Victoria 104:57-65.

Chilingarian, G. V. and P. Vorabutr. 1983. Drilling and drilling fluids. Developments inPetroleum Science, 11. Amsterdam: Elsevier.

Churchill, J. H. 1987. Assessing hazards due to contaminant discharge in coastal waters.Estuarine, Coastal and Shelf Science 24:225-240.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 223

Constable, A. J. 1991. The role of science in environmental protection. Australian Journal ofMarine and Freshwater Research 42:527-538.

Davies, P. J. 1979. Marine geology of the continental Shelf off southeast Australia. Bureau ofMineral Resources, Geology and Geophysics, Bulletin 195.

Dorsey, J. H. and R. N. Synnot. 1980. Marine soft-bottom benthic community offshore fromBlack Rock Sewage outfall, Connewarre, Victoria. Australian Journal of Marine andFreshwater Research 31:151-162.

DTA, Department of Transport, Australia. 1976. Marine information manual, 2nd Ed.Canberra: Australian Government Publishing Service.

Edgar, G. J. 1984. General features of the ecology and biogeography of Tasmanian subtidalrocky shore communities. Papers and Proceedings of the Royal Society of Tasmania118:173-186.

Exon, N. F., C.-S. Lee, E. A. Felton, D. T. Heggie, D. McKirdy, C. Penney, S. Shafik, A. E.Stephenson, and C. Wilson. 1992. BMR Cruise 67: Otway Basin and West TasmanSampling. Bureau of Mineral Resources, Geology and Geophysics, Report 306.

Fandry, C. B. 1981. Development of a numerical model of tidal and wind-driven circulationin Bass Strait. Australian Journal of Marine and Freshwater Research 32:9-29.

Fandry, C. B. 1983. Model for the three-dimensional structure of wind-driven and tidalcirculation in Bass Strait. Australian Journal of Marine and Freshwater Research34:121-141.

Fandry C. B., G. D. Hubbert, and P. C. Mclntosh. 1985. Comparison of predictions of anumerical model and observations of tides in Bass Strait. Australian Journal of Marineand Freshwater Research 36:737-752.

Geraci, J. R. and D. J. St. Aubin. 1987. Effects of offshore oil and gas development onmarine mammals and turtles. In Long-term effects of offshore oil and gas development,eds. D. F. Boesch and N. N. Rabalais, pp. 587-618. London: Elsevier Applied Science.

Gettleson, D. A. 1980. Effects of oil and gas drilling operations on the marine environment.In Marine environmental pollution, 1, hydrocarbons, Elsevier Oceanography Series, 27A.ed. R. A. Geyer, pp. 371-412. Amsterdam: Elsevier.

Gibbs, C. F., R. A. Cowdell, and A. R. Longmore. 1986. Seasonal variations of densitypatterns in relation to the Bass Strait Cascade. Australian Journal of Marine andFreshwater Research 37:21-25.

Gill, E. D. 1972. Application of recent hypotheses to changes of sea level in Bass Strait,Australia. Proceedings of the Royal Society of Victoria 85:117-123.

Godfrey, J. S., I. S. F. Jones, J. G. H. Maxwell, and B. D. Scott. 1980. On the winter cascadefrom Bass Strait into the Tasman Sea. Australian Journal of Marine and FreshwaterResearch 31:275-286.

Gordon, R. B. 1974. Dispersion of dredge spoil dumped in near-shore waters. Estuarine andCoastal Marine Science 2:349-358.

Gravina, M. F., G. D. Ardizzone, and A. Belluscio. 1989. Polychaetes of an artificial reef inthe Central Mediterranean Sea. Estuarine, Coastal and Shelf Science 28:161-172

Griffiths, A. 1991. Principal address—Opportunities for Australian companies. APEAJournal 31(2):27-31.

Harris, P. T., E. K. Baker, and A. R. Cole. 1991. Physical sedimentology of the Australiancontinental Shelf with emphasis on Late Quaternary deposits in major shipping channels,port approaches and choke points. Ocean Sciences Institute Report No. 51, University ofSydney.

Heggie, D. T. 1989. Project 131.20: Southeastern Australia geochemistry BMR 89. Yearbookof the Bureau of Mineral Resources, Geology and Geophysics, Canberra, pp. 76-77.

Heggie, D. T. and G. W. O. O'Brien. 1988. Hydrocarbon gas geochemistry in sediments of theoffshore Otway and Gippsland Shelf. Preliminary post-cruise report. Bureau of MineralResources, Geology and Geophysics, Record 1988/32.

Heggie, D. T., G. Bickford, and J. H. Bishop. 1992. BMR detects hydrocarbon pollution offSydney. BMR Research Newsletter 16:23-24.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

224 I. H. Lavering

Hyland, J. D., D. Hardin, E. Crecelius, D. Drake, P. Montagna, and M. Steinhauer. 1990.Monitoring long-term effects of offshore oil and gas development along the SouthernCalifornia outer continental Shelf and slope: Background environmental conditions inthe Santa Maria Basin. Oil and Chemical Pollution 6:195-240.

ISRC, Independent Scientific Review Committee Report. 1993. Offshore Petroleum Environ-mental Review Project—A project for the Australian Petroleum Exploration AssociationLtd., Sydney.

Jones, I. S. 1980. Tidal and wind-driven currents in Bass Strait. Australian Journal of Marineand Freshwater Research 31:109-117.

Jones, H. A. and P. J. Davies. 1983. Superficial sediments of the Tasmanian continental shelfand part of Bass Strait. Bureau of Mineral Resources, Geology and Geophysics, Bulletin218.

Jones, I. S. and H. O. Gerlach. 1980. A current prediction scheme to assist platformplacement in Bass Strait. Proceedings of the 17th International Conference on CoastalEngineering, Sydney.

Kerr, S. 1992. Artificial reefs in Australia, their construction, location and function. Bureau ofRural Resource working paper WP/8/92.

Kershaw, A. P. and G. C. Nanson. 1993. The last full glacial cycle in the Australian region.Global and Planetary Change 7:1-9.

Kinne, O. 1970. Temperature. General introduction. In Marine ecology: A comprehensiveintegrated treatise on life in oceans and coastal waters, Volume 1, Environmental Factors,Part 1, ed. O. Kinne, pp. 321-396. London: Wiley-Interscience.

Kuttan, K., J. B. Kulla, and R. G. Neumann. 1986. Freshwater influx in the Gippsland Shelf:Impact on formation evaluation, hydrocarbon volumes, and hydrocarbon migration.APEA Journal 26(1):242-249.

LCC, Land Conservation Council. 1993. Marine and coastal special investigations descriptivereport. June, Melbourne, Victoria.

Lewis, J. A. 1991. Marine biofouling in Australian waters—Composition, geographic variationand methods of prevention. First Offshore Australia Conference, Australian ExhibitionServices Pry Ltd., X23-X26.

Lytle, T. F. and J. S. Lytle. 1979. Sediment hydrocarbons near an oil rig. Estuarine andCoastal Shelf Science 9:319-330.

Malikides, M., P. T. Harris, C. J. Jenkins, and J. B. Keene. 1988. Carbonate sandwaves inBass Strait. Australian Journal of Earth Sciences 35:303-311.

Martinez, E. A. 1980. Sensitivity of marine ciliates (Protozoa, Ciliophora) to high thermalstress. Estuarine and Coastal Marine Science 10:369-381.

Middleditch, B. S., ed. 1981. Environmental effects of offshore oil production: The Buccaneergas and oilfield study, Marine Science 14, New York: Plenum Press.

Middleditch, B. S. and B. J. Galloway. 1981. Prologue. In Environmental effects of offshore oilproduction: The Buccaneer gas and oilfield study, Marine Science 14, ed. B. S. Middled-itch, pp. 1-14. New York: Plenum Press.

Mulhearn, P. J. 1983. Deep currents of the northern Tasman Sea Basin. Deep-Sea Research30(11A):1119-1126.

Mulhearn, P. J., J. H. Filloux, F. E. M. Lilley, N. L. Bindoff, and I. J. Ferguson. 1986.Abyssal currents during the formation and passage of a warm core ring in the EasternAustralian Current. Deep-Sea Research 33(11/12):1563-1576.

Myers, E. P. and C. G. Gunnerson. 1976. Hydrocarbons in the ocean. Special report ofMarine Ecosystems Analysis Program, U.S. Department of Commerce, National Oceanicand Atmospheric Administration, Boulder, CO.

Neff, J. M. 1987. Biological effects of drilling fluids, drill cuttings and produced waters. InLong-term effects of offshore oil and gas development, eds. D. F. Boesch and N. N.Rabalais, pp. 469-537. London: Elsevier Applied Science.

Neff, J. M., N. N. Rabalais, and D. F. Boesch. 1987. Offshore oil and gas activities

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

Gippsland Shelf and Bass Strait 225

potentially causing long-term environmental effects. In Long-term effects of offshore oiland gas development, eds. D. F. Boesch and N. N. Rabalais, pp. 149-174. London:Elsevier Applied Science.

Nilsson, C. S. and G. R. Cresswell. 1981. The formation and evolution of East AustralianCurrent warm-core eddies. Progress in Oceanography 9:133-183.

O'Brien, G. W. and D. T. Heggie. 1989. Hydrocarbon gases in seafloor sediments, Otwayand Gippsland Shelfs: Implications for petroleum exploration. APEA Journal 29:96-113.

O'Byrne, M. J. 1988. Bass Strait gas lift and water handling development. In Petroleum inAustralia, the first century, pp. 353-358. Australian Petroleum Exploration AssociationLtd. MacArthur Press.

Ozimic, S., E. Nicholas, L. Pain, and V. Vuckovic. 1987. Australian Petroleum AccumulationsReport 3 Gippsland Basin, Victoria. Bureau of Mineral Resources, Geology and Geo-physics.

PEDIN. 1993. National Petroleum Database Index. Canberra: Petroleum Resource Branch,Bureau of Resource Sciences.

Pendoley, K. 1992. Hydrocarbons in Rowley Shelf (Western Australia) oysters and sedi-ments. Marine Pollution Bulletin 24(4):210-215.

Poore G. C. B. and S. Rainer. 1979. A three-year study of benthos of muddy environments inPort Phillip Bay, Victoria. Estuarine and Coastal Marine Science 9:477-497.

Randall, R. E. 1981. Measurement of a negatively buoyant plume in the coastal waters offFreeport, Texas. Ocean Engineering 8:407-419.

Rice, E. L. 1989. An analysis of the community composition of the Xiphophora gladiatadominated subzone of the Tasmanian Sublittoral fringe. Papers and Proceedings of theRoyal Society of Tasmania 123:191-209.

Richardson, J. R. 1987. Brachiopods from carbonate sands of the Australian Shelf. Proceed-ings of the Royal Society of Victoria 99:37-50.

Roder, G. H. and M. W. Sloan. 1986. Barracouta: History of exploration and development, andgeology of the field. Second South-Eastem Australian Oil Exploration Symposium, ed.R. C. Glenie. Technical papers presented at PESA Symposium, 14-15 November 1985,Melbourne.

Romeril, M. G. 1979. The occurrence of copper, iron and zinc in the hard shell clam,Mercenaria mercenaria, and sediments of Southampton water. Estuarine and CoastalMarine Science 9:423-434.

Russ, P. R. 1991. Improvements in offshore water handling systems. First Offshore AustraliaConference, Australian Exhibition Services Pty Ltd, VI17-VI23.

Sackett, W. M. 1978. Suspended matter in sea water. In Chemical oceanography 7, eds. J. P.Riley and R. Chester, pp. 127-172. London: Academic Press.

Schimmelmann, A. and M. J. Tegner. 1991. Historical oceanographic events reflected in13C/12C ratio of total organic carbon in laminated Santa Barbara Basin sediment.Global Biogeochemical Cycles 5(2):173-188.

Simpson, J. H. and D. Bowers. 1981. Models of stratification and frontal movement in Shelfareas. Deep-Sea Research 28A(7):727-738.

Smith, R. 1978. Effect of salt on hot-water dispersion in well-mixed estuaries. Estuarine andCoastal Marine Science 7:445-454.

Spellerberg, I. 1991. Monitoring ecological change. London: Cambridge University Press.Spies, R. B. 1987. The biological effects of petroleum hydrocarbons in the sea: Assessment

from field and microcosms. In Long-term effects of offshore oil and gas development, eds.D. F. Boelsch and N. N. Rabalais, pp. 538-586. London: Elsevier Applied Sciences.

Stuermer, D. H., R. B. Spies, P. H. Davis, D. J. Ng, C. J. Morris, and S. Neal. 1982. Thehydrocarbons in the Isla Vista marine seep environment. Marine Chemistry 11:413-426.

Teal, J. M. and R. W. Howarth. 1984. Oil spill studies: A review of ecological effects.Environmental Management 8(1):27-44.

Thompson, J. H., E. A. Shinn, and T. J. Bright. 1980. Effects of drilling mud on seven species

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015

226 I. H. Lavering

of reef-building corals as measured in the field and laboratory. In Marine environmentalpollution, 1, hydrocarbons, Elsevier Oceanography Series, 27A, ed. R. A. Geyer, pp.413-437. Amsterdam: Elsevier.

Warren, R. P. 1989. Offshore oil and gas exploration: What are the environmental effectsand do they justify limitations on access to coastal waters? APEA Journal 29(1):84-95.

Wilson, R. E. 1979. A model for the estimation of concentrations and spatial extent ofsuspended sediment plumes. Estuarine and Coastal Marine Science 9:65-78.

Wilson, R. S. and G. C. B. Poore. 1987. The Bass Strait Survey: biological sampling stations,1979-1984. Occasional Papers from the Museum of Victoria 3:1-14.

Winstanley, R. H. 1981. Fisheries resources of Victoria's coastal and offshore waters.Proceedings of the Royal Society of Victoria 91:81-92.

Wolfson, A., G. Van Blairom, N. Davis, and G. S. Lewbel. 1979. The marine life of anoffshore oil platform. Marine Ecology—Progess Series 1:81-89.

Youngbluth, M. J. 1976. Zooplankton populations in a polluted, tropical embayment.Estuarine and Coastal Marine Science 4:481-496.

Dow

nloa

ded

by [

UN

SW L

ibra

ry]

at 1

7:42

17

Mar

ch 2

015