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Sounding outlake beds

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AUSGEOnewsDecember 2003 ISSUE No. 72

Also: Seabed in detai l , r ich bottom l i fe , sediment loads checked, & lots more inside…

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Sounding outlake beds

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plant growth

A U S G E O N e w sDecember 2003 Issue no. 72

Editor Julie Wissmann

Graphic Designer Katharine Hagan

This publication is issued free ofcharge. It is published four times a yearby Geoscience Australia.

The views expressed in AusGeoNews are not necessarily those ofGeoscience Australia, or the editor, andshould not be quoted as such. Everycare is taken to reproduce articles asaccurately as possible, but GeoscienceAustralia accepts no responsibility forerrors, omissions or inaccuracies.

© Commonwealth of Australia 2003ISSN 1035-9338

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AusGeo News is available on the web at www.ga.gov.au/about/corporate/ausgeo_news.jsp

In many Australian coastal waterways plant growthis stimulated by nutrients that come from thecatchment. Large increases in plant growth cancause clogged waterways and algal blooms.

But some estuaries and coastal lakes remain‘clean’ despite lots of nutrient or sediment.

Something is happening at the bottom of theselakes or in their water that allows them to handlebig sediment–nutrient loads without threateningecosystem health. These factors are discussed in thisissue of AusGeo News.

Photo: Arthur Mostead

CONTENTS

Comment 3

Reefs found in murky Carpentaria depths 4

Sonar mapper reveals seabed in unprecedented detail 6

Census of tiny marine species in Torres Strait 7

Bottom life quite rich in gulf 9

Why estuaries are green or clean 10

Trapped nitrogen throws out estuary balance 12

Fitzroy under scrutiny for catchment loads 14

In brief… 16

Land clearing swells sediment loads in WA estuaries 18

SeaBat trial echoed from coast to coast 20

Sounding out lake bed habitats 22

Smelly conditions perfect for estuary work 23

Conferences 25

Events calendar 26

Regional-scale seabed map a first 27

Product news 29

AusGEO News 72 December 2003 3

N E I L W I L L I A M SCEO Geoscience Australia

Australia is preparing a bid to host the prestigious International GeologicalCongress (IGC) in Brisbane in August 2012. The IGC is held every four yearsand this is the next available slot.

This congress attracts more than 5000 delegates from around the world,so if Australia is successful it will lift the profile of geoscience at home andpresent some wonderful opportunities internationally.

The 2004 IGC will be in Florence and the 2008 IGC is set for Oslo. Likethe Olympics, bidding occurs well in advance and our bid must be submittedin February because a decision will be made at the Florence IGC in August.

Australia’s IGC Organising Committee comprises senior GeoscienceAustralia and State Geological Survey people, academics and representativesof professional geoscience bodies. Two committee positions have beenendorsed: Ian Lambert as Secretary General, and I have the honour of beingelected President. New Zealand is represented by Alex Malahoff, ChiefExecutive of the Institute of Geological and Nuclear Sciences. Others will beadded at a later stage.

The Australian Geoscience Council will be the incorporated body for thecongress so that anticipated profits are channelled into Australian geoscience.

Our theme is: ‘Earth dreaming – Unearthing our past and future’. Thiscaptures the concept of an ancient land in which geoscience helps to meetsocietal needs and to look after planet Earth. These needs include effectivemanagement of natural resource problems; groundwater supplies;discovering the next generation of mineral and energy resources beneathcover; dealing with greenhouse emissions and climate change; making urbandevelopments more sustainable; and managing and applying geospatialinformation for an increasing range of stakeholders.

Our bid is an outcome of deliberations leading up to the recentpublication of the National Strategic Plan for the Geosciences. It wasproduced by the National Committee for Earth Sciences, Australian Academyof Science.

A successful bid will give us an enormous opportunity to demonstratethe importance of the earth sciences and provide the geoscience fraternitywith a scientifically rewarding and enjoyable international event.

And talking about looking after planet Earth: this issue of AusGeo Newsfocuses on our work around Australia’s coastline, mapping our seabed andestuaries to help the National Oceans Office, Environment Australia, localcouncils, and many others better understand ecosystems and manage ournatural resources.

The articles illustrate howgeological information providesenvironmental managers with acontext and baseline data for thedistribution of ecosystems and theirbiota, and for measuring humanimpacts. The articles also highlightour recent and ongoing work in anumber of Cooperative ResearchCentre (CRC) projects.

In fact, all this work is done incollaboration with partners fromother federal agencies, universities,and state and local governmentgroups that have banded togetheras the ‘Coastal and MarineEnvironmental Geoscience Group’.This group provides governmentwith advice and products to meetits goals regarding its NationalOceans Policy, and the preservationand maintenance of biodiversity,and ecosystem-based management.

Some future work will involveGeoscience Australia in the TorresStrait (through the Reef CRC), aswell as in the Gulf of Carpentaria,Recherche Archipelago off south-western Australia, and various baysand estuaries (through the CoastalZone CRC).

I hope you enjoy reading ourDecember issue, and I’d like tothank you for supportingGeoscience Australia in 2003 andwish you the very best for thefestive season.

murkyReefs

4 December 2003 AUSGEO News 72

Thoughts about reef growth are changing after the discovery of healthycorals in unlikely conditions off far north Queensland.

Geoscience Australia scientists discovered uncharted bryomol reefs andplatforms of hard coral in murky, warm water near Mornington Island in theGulf of Carpentaria on their recent Southern Surveyor voyage.

They made the discovery in June using multibeam sonar to mapunderwater sandstorms and sediment movement from rivers entering thegulf.

Finding living corals was an even bigger surprise because the turbidwater and large sediment input would generally smother hard corals, and thesurface water temperature of 28–30º C was too warm for coral survival.

Unlikely condit ionsThe gulf is a shallow sea between York Peninsula and Cape Arnhem. Itsdeepest point is 65 metres below the surface.

For 10 thousand years, sediment has discharged into it from chenierplains and deltas so that more than half of the sediment in the gulf is fromadjacent land.

The southern Gulf of Carpentaria, an area of more than 100 thousandsquare kilometers, is Australia’s largest shelf province of ‘terrigenous-dominated’ sediments.

The reef depths are unusual because corals typically grow upwards tothe surface. The Carpentaria reefs are at depths of 25–30 metres, with thehighest point 18 metres down.

Reef age and sea levels over the past 120 thousand years provide someclues (figure 1).

Sea levels are not constant over time. When sea level rises, corals growupwards. When sea level is stable, corals grow outwards. As sea levels fall,exposed reefs die leaving cliffs of limestone that can be re-colonised whensea level rises again.

Ancient reefsThe Carpentaria reefs were established when sea levels were much lowerthan present, such as those between 50 and 120 thousand years ago. Theclimate was cooler and drier, and the gulf was a large lagoon with oneentrance via the Arafura Sea. Torres Strait was a land bridge.

During low sea-level phases, reefs built adjacent to the eastern margin ofMornington Island (figure 2, BR). On the Southern Surveyor voyage

bryozoans and molluscs weredredged from these reefs, but nolive specimens were recovered.

These bryomol reefs are now at30-metres depth and have a pock-marked surface. There are large,bowl-shaped depressions ofweathered limestone up to half akilometre wide that probablyformed at the surface whenrainwater dissolved the exposedlimestone.

The unusual swirl patterns inthe bathymetric image of the area(figure 3) are similar to the cometmarks (also called obstacle marksor current crescents) seen in manyhigh-energy, subaqueousenvironments. They suggestsediment moves northwards, butthe marks are probably from fluvialerosion during low sea level ratherthan from tidal scour or sedimentdeposition in the past 10 thousandyears.

A closer look at the bryomolsamples and radiocarbon dates willestablish a better history for thesereefs, but early results suggest thatthey are mostly relict.

0

50

100

1500 50 100 150

Thousand years before present

Previous phases of reef growth

R1 R2 R3

0

N-S reef profiles

4 km N

Dep

th b

elow

)

03-268-1

Figure 1. Sea levels for the past 150thousand years show when the Carpentariareefs were near the surface. Reef growthand main deposition probably occurredduring the three high stands from 50 to120 thousand years ago.

▼

murkyReefs found in

Carpentaria depthsphoto: C

SIRO

Coral surpr iseAbout 100 kilometres north-east of Mornington Island are three coral reefsthat probably formed when sea level was 25 metres lower than today (figure2). Together they are 80 square kilometres in size (72.5, 5.5 and 1.6 km2).Each is oval-shaped with steep, almost vertical sides.

In this area the Southern Surveyor dredged a live specimen of plate coral(Turbinaria) and hard corals (Leptoseris), and videoed fan and barrelsponges, starfish, soft coral, anemones, and many colourful fish.

These reefs are mostly relict even though there are live corals. Only afew small areas of live reef rise above the otherwise flat surfaces, which areplatforms (at 27 m depth) and three- to four-metre-high terraces (at 30 mdepth) that were shaped by sea-level oscillations (figure 4).

The sluggish growth of corals in the past few thousand years could bedue to environmental factors such as temperature, current, turbidity, ornutrient levels. But the live reefs are on a platform and distant from the verycloudy, inshore waters.

Corals may have only recentlyre-colonised the reefs and so theyhave not had time to growupwards.

Whatever the reason for thepresent-day corals, it could beanswered in future samplingexpeditions.

More submerged reefs couldalso be found because shoals aboutthe same depth as these reefs aremarked on navigation maps of thesouthern gulf.

The seed stock for the coralshas drifted on currents from warmtropical waters somewhere north ofthe gulf and when the Carpentariareefs flourished previously, theTimor or Arafura seas perhaps hadabundant reefs.

Submerged reefs at about 30-metres depth have been identifiedin the Gulf of Papua, Great BarrierReef, and Indian Ocean.


Figure 2. Mornington Island (MI), bryomol reef (BR) and three submerged coral reefs(R1, R2 & R3) are marked on this false-colour bathymetry map of the south-east Gulfof Carpentaria. SR indicates other possible submerged reefs.

139 51’ 139 55’139 53’ 139 57’

16 26’

16 28’

16 30’

16 32’

▼

Figure 4. A detailed colourbathymetry map of reef R1, mappedusing a 240 kHz multibeam sonarsystem. Survey lines were spaced at100–150 metres and adjustedaccording to water depth.

Figure 3. A false-colour bathymetrymap of thebryomol reef (BR)and erodedseafloor areaadjacent toMornington Islandwith sand waves(S) and cometmarks (C) shown.

▼

14

15

16

17

136 138 140 142

▼

Australia is building amazing images of its seabedsince multibeam sonar was added to its researchvessel Southern Surveyor.

This imaging technology is allowing Geoscience Australia to createbathymetry models of the seafloor in detail never before possible, andrecently helped it discover uncharted reefs in the Gulf of Carpentaria (figure 1).

The image quality and resolution depend on sea conditions and thedepth in which the multibeam sonar is operating.

Topographic features smaller than 10 centimetres were discernable fromthe Southern Surveyor in ideal conditions in the gulf’s shallow water (20–50 m).

As the Southern Surveyor traverses the sea surface, a fan (or swath) ofsonar beams bounce off the sea bottom like echoes, to produce an image ofthe seabed.

The beams (orientated port/starboard across the survey track) generatenear-immediate, accurate, seafloor bathymetry maps.

Raw data from the beams are combined with data from other equipment(gyrocompass, motion sensor, GPS, sound-velocity profiles, and tide models)to accurately position bathymetry soundings on the seafloor. The soundingsare ‘cleaned and gridded’ to produce a seafloor model.

Sonar energy As the multibeam unit processes bathymetry data, the returned energy of thesonar beam (acoustic reflectivity) is recorded. The image of the returnedenergy, known as sidescan or backscatter, is also gridded.

Sidescan is used with bathymetry to identify changes in benthic habitats,rock types, or topography, such as that caused by tidal currents andtransported sediment (figure 2). It is often logged at a much higherresolution than the bathymetry to identify small-scale features.

Figure 2. A sidescan reveals a rippledseabed east of Mornington Island inthe Gulf of Carpentaria. The ripplessuggest that tidal currents aretransporting sediment in the area.

Figure 1. A coral reef in the south-eastGulf of Carpentaria was uncharted untilmultibeam sonar was added to theSouthern Surveyor. The reef isapproximately 120 square kilometres. Itlies at 40 metres depth and rises to 19meters below the surface.

Sonar mapperreveals seabed inunprecedented

Future plansBy 2100 global warming isexpected to increase sea-surfacetemperatures by 1–2° C, which willprobably kill many coral reefsworldwide. Submerged reefs thatare protected from sunlight and hotsurface water by a thick, overlyingwater column could survive andprovide important seed stock.

Clearly, more information isneeded about the distribution ofsubmerged coral reefs, and whyreef growth has not kept pace withsea-level rise in the gulf.

The Carpentaria reefs are toodeep to be detected by satelliteremote sensing or aerialphotographs, but they wereidentified as reefs by ship-mountedmultibeam sonar and confirmedwith seabed sampling andunderwater video footage.

Geoscience Australia is stillanalysing data and samplescollected in May and June on itsmonth-long voyage that embarkedfrom Cairns and berthed in Darwin.

It plans to map and build a 3Dmodel of the gulf floor. These toolswill help local councils and marineagencies better understand theprocesses that control seagrassgrowth and coral development, andthe fisheries that rely on thosehabitats for their reproductive cycle.

For more information phonePeter Harris on +61 2 6249 9611or e-mail [email protected] visit www.ga.gov.au/oceans/projects/20010917_12.jsp

▼ ▼


detail


The waters of the Torres Strait–Gulf of Papuaregion are very energetic and difficult fortiny marine life.

Warm, salty water is diluted by heavy, equatorial rain, and Papua NewGuinea’s Fly River flushes about 120 million tonnes of sediment annuallyinto the strait. Much of this sediment is swept through the strait by strongtidal currents that scour the seafloor.

Some tiny marine organisms float in deep water; others cling to therocky bottom for stability, or burrow in the muddy sand. But just howabundant are these organisms in the tough conditions?

Early last year on the Franklin voyage, Geoscience Australia collectedmore than 60 grab samples from the Fly River delta, Torres Strait and Gulfof Papua (figure 1, A–C) to determine their distribution.

Fifteen different groups of organisms in the classic micropalae-ontological size fraction (150 �m–2 mm) were quantified (figure 2).

Two of these groups live in the water column (planktonic foraminiferaand pteropods). The others live on the seafloor and/or within a fewcentimetres of sediment.

Census of tinymarine speciesin Torres Strait

Wide use Multibeam sonar technology isbeing applied in resource andwaterways management, regionalmarine planning, habitat mapping,and mapping sediment distributionsand mobility. At present GeoscienceAustralia is using multibeam sonardata to:

• update bathymetry grids for theAustralian exclusive economiczone;

• ‘characterise’ the seabed bymapping areas of similaracoustic response orgeomorphological shape;

• map sediment facies andbenthic habitats for RegionalMarine Planning;

• generate maps and 3D displaysfor scientific and educational purposes; and

• produce environmentalassessments.

In December additionalmultibeam sonar equipment will beinstalled on the Southern Surveyorby Geoscience Australia, NationalOceans Office and CSIRO MarineResearch for mapping thebathymetry and seabed character indeeper water.

The Simrad EM300 will map inwater as deep as 3000 metres with aswath width of up to 7000 metresand 1x1 degree beam-widths formaximum resolution in idealsurveying conditions.

This state-of-the-art mappingtechnology is available to allresearch institutes in Australia,which should boost the scope ofresearch happening in Australianwaters.

For more information phone James Daniell on +61 2 6249 9691 or [email protected]

Figure 1. On the Franklin voyage, Geoscience Australia collected more than 60 grabsamples from the Fly River delta (A), Torres Strait (B) and Gulf of Papua (C) todetermine the distribution of tiny marine organisms.

▼


Organism dis tr ibut ionThe bottom-dwelling foraminiferaare by far the most abundantgroup sampled (figure 2), but theydecrease towards the inner shelf(Areas B and C). Bivalves,ostracods and porifera also steadilydecrease from Area A to C.

Only fragments of bryozoa,halimeda and corals (including softcorals) were in the sizes analysed,but they increase in abundancetowards the shelf edge.

In the water column,planktonic forams show a markedand constant increase towards thegreater depths of Area C, whilepteropods are abundant in allareas.

Various factors influenceabundance patterns. In the regionsampled, water depth has thestrongest influence overall,followed by water temperature,salinity and mud content and,lastly, calcium carbonate content.

Water depthNumbers of bottom-dwellingforams (e.g. Amphistegina,Elphidium and Ammonia spp) thatlike brackish and shallow waterrapidly decline as water deepens.Amphistegina lessonii, for example,is commonly found at water depthsof five–40 metres, which is typicalof Area A.

This water-depth trend isopposite for the other tiny marineorganisms, which also respondnegatively to salinity increases.

The planktonic foraminifera aremore abundant in deeper water asmany species descend toconsiderable depths during theirlife cycle—a process that is difficultin the shallower parts of Areas Aand B.

Condit ion changesSmall changes in water temperature and salinity, which are mostly driven bybathymetry changes, cause strong variations in the distribution andabundance of organisms.

The bryozoa and corals are the most sensitive, favouring stableenvironments with well-defined ranges in temperature and salinity. Asbrackish and very shallow water inhibit coral growth, any fragments countedin innermost areas were probably transported and reworked by currents andwave scour.

Bivalves and ostracods are the least sensitive, their prevalence onlyweakly associated with the sedimentary mud content. They are filter feedersconsuming detritus stirred up by their antennae or mandibles, and thrive bestin muddy sands and silts. Very high percentages of mud, however, canprevent their full development.

Pteropods and planktonic forams are affected by salinity, temperatureand water depth. Pteropods react less strongly to these factors, and adaptbetter than forams to shallow-water environments.

The tiny marine organisms of the Torres Strait–Gulf of Papua regionprovide useful information about their adaptability to ecosystem variations.Quantifying their response to different conditions provides reference data formonitoring ecological changes, even though the region’s complexsedimentary and oceanographic dynamics are not yet completely understood.

For more information phone Alix King on +61 2 6249 9127or e-mail [email protected]

Area A

Pteropods

Bivalves

Bryozoa

Gastropods

Soft coralsOstracods

Other arthropods

EchinodermsSerpulids

Brachiopods

Corals

Porifera

Benthic forams

Plank foramsCoralline algae(Halimeda)

Area B Area C

03-233-2

Fly River Torres Strait Gulf of Papua

Figure 2. The distribution of 15 groups of marine organisms (150 �m–2 mm in size)from three areas, expressed as percentages based on the number of specimens/gram.

▼

The coral species recovered,which are typical of an inner-shelfreef, comprised three species ofhard corals, seven species ofgorgonians (sea ferns), and onespecies of soft coral. Four speciesof sponge and a starfish species(Linkia sp) commonly found oncoral reefs were also collected.

Two species of fan sponge(Ianthella basta and I.flabelliformis), a barrel sponge(Xestospongia sp) and the sea fernsthat were recovered are found onseabed channels in Torres Strait andthe Great Barrier Reef.

Animals generally live on theseabed in the gulf’s rough ground,and it seems to be a refuge formany mobile seabed animals. Inthe muddy trawl-grounds animalsmostly live within the seabed.

The Southern Surveyor voyageled by Geoscience Australia wassponsored by the National OceansOffice and the Department ofEnvironment and Heritage.

For more information aboutCarpentaria benthic habitats andfauna phone Ted Wassenberg on+61 7 3826 7217 or [email protected]


▼

The Gulf of Carpentaria seabed was considered flat and muddy and hometo prawns and mud burrowers until the recent Southern Surveyor voyage,despite fisher reports of rough ground at 20–40 metre depths.

Geoscience Australia’s 3D mapping on the voyage targeted prawn-trawlgrounds as well as uncharted rough seabed, providing an opportunity toexplore unknown parts of the gulf floor.

It allowed CSIRO Marine Research to systematically sample areas passedover by biological researchers in the past 25 years.

Biological samples were collected from muddy-sand seabed, steep rockcliffs, gorges and plateaux using a short tow with a benthic sled, rockdredge or sediment sampler (table 1).

Diverse fauna were collected with a total of 569 taxa (species groups)identified within 64 major taxonomic groups (family level or higher).

Crustaceans provided the greatest variety (139 species), followed by thebivalves (64), sponges (60), and soft corals (56). Gastropods (39), tunicates(32), starfish (28), bryozoans (26), sea cucumbers (24), hydroids (19) andfish (15) were also plentiful. There was also a variety of hard corals (12)and worms (12), and five algal species (figure 1).

Some animals collected from very rough seabed were indicative of aliving coral reef.

A live specimen of plate coral (Turbinaria sp) was dredged from 20metres depth and lots of hard corals (Leptoseris sp) were observed onunderwater video.

Table 1. Summary of samples collected by eachdevice, the number of species collected and theaverage number of species per sample for sixregions in the eastern Gulf of Carpentaria

Area Samples Species Av number species

Area B dredge x 5 78 16

Area B grab x 35 83 2

Area B sled x 18 553 31

Area C dredge x 6 79 13

Area C grab x 25 20 <1

Area C sled x 12 347 29

Area D grab x 5 8 2

Area E grab x 6 2 <1

Central east gulf grab x 9 4 <1

Central east gulf sled x 8 237 34

South-east gulf grab x 28 35 1

South-east gulf sled x 23 589 26

Figure 1. Species collected by the Southern Surveyor in the eastern Gulf of Carpentariausing three sampling devices.

03-2

68-5

0

20

40

60

80

100

120

140

160

Num

ber o

f spe

cies

24.4%

19.0%

13.5%

10.5% 9.8%

5.6% 4.6%2.6% 2.1% 2.1%

0.7%

4.9%

Total species = 569

Crabs (Crustacea)

Sponges (porife

ra)

Fish (Telle

ostii)

Worms (P

olychaeta)

Starfish & urchins (E

chinodermata)

Snail & clams (M

ollusca)

Soft corals (O

ctocorallia)

Sea squirts (A

scidiacea)

Lace corals (Ectoprocta)

Hard corals (Scleractin

ia)

Macroalgae

Undetermined

Bottom life quite rich in gulf


In Australian coastal waterways plant growth isstimulated by nutrients such as nitrogen andphosphorus that come from the catchment. Howprolifically plants grow because of these nutrientsand whether ecosystem health is threatened dependon a number of factors.

The physical characteristics of the waterway are important including howoften water flushes through the system and how sediments and nutrients aretrapped, buried and washed to sea.

Sunlight is a big influence. If the water is turbid, not much sunlightpenetrates the water for plant photosynthesis.

Also important is how much nutrient is processed by microbes in thesediment and dissolved in the water or released as nitrogen (N2) gas into the atmosphere.

Eutrophic waterwayLarge increases in plant growth can cause clogged waterways and nuisanceor toxic algal blooms, indicating the waterway is eutrophic.

When large quantities of plants die and decay, oxygen is depleted fromthe water column and without enough oxygen fish and other marine animalsdie. Sometimes the waterway smells of rotten egg gas (hydrogen sulphide).

Geoscience Australia has developed some generalisations forenvironmental managers to show how prone seven types of coastalwaterways are to eutrophication (figure 1).

Eutrophication in any system is determined by the balance betweennutrient (particularly nitrogen) inputs and exports (flushing to the sea, burialin the sediments, and transformed to N2 gas).

Once a waterway becomes eutrophic, it is difficult to re-establish itsoriginal conditions.

Tidal systemsIn northern Australia there are many tide-dominated deltas, estuaries andtidal flats. They have a low-to-moderate susceptibility to eutrophicationbecause they are naturally turbid and not much sunlight penetrates the watercolumn for plant growth. Mangroves are the most abundant plants in thelarge intertidal areas.

Estuaries are more susceptible than the deltas and tidal flats. They havethe capacity to trap more nutrients and they are flushed less frequently—roughly every few weeks.

Tide-dominated systems, particularly the deltas, tend to export much oftheir sediment–nutrient loads to the near-shore shelf in northern Australia.This has ecological implications for adjacent shallow continental-shelf areasthat support seagrass and coral reef ecosystems.

These areas off northern Australia include the inner Great Barrier Reeflagoon, the Gulf of Carpentaria and the Arafura Sea.

Microbial processes in sediments and dissolved nutrients (particularly

nitrogen) in the water can changethe ecosystem. Nutrient-poor watersthat support seagrasses and coralreef growth could become nutrient-rich waters that encourage nuisancealgae.

The susceptible offshore areasare most likely adjacent tocatchments with intensiveagriculture.

Wave systemsIn the temperate climates of south-west and south-east Australia, thereare many wave-dominated deltas,estuaries, coastal lakes, strandplains and lagoons. Some estuaries,lagoons and strand plains arereferred to as ICOLLS (intermittentlyclosed and open lakes andlagoons), and as a group aremoderately to highly susceptible toeutrophication.

Wave-dominated estuariesaccumulate river and catchmentrunoff. They have a central basin toaccommodate a lot of sediment andnutrients. The nutrient-laden waterstays in the system for weeks tomonths and sometimes years,because the estuaries are poorly flushed.

Plant growth occurs in thewater column (phytoplankton) andon the sediment surface in theshallow areas. Plants formed in situand their debris stay in thesediments where sunlight, dissolvednutrients and low turbidityencourage algae and macrophytegrowth.

Why estuaries aregreen or clean


Coastal lakesCoastal lakes are a type of wave-dominatedestuary, but the entrance to the sea hasclosed. They are highly susceptible toeutrophication.

Flushing is negligible so water andother material remain in the lake for years,waiting for a large rainfall event to breachthe barrier and flush accumulated organicdebris and nutrients to the sea.

LagoonsLagoons do not receive fluvial discharges.Sediment–nutrient retention is high becausethey are not flushed very often.

Nutrient loads to lagoons are generallylow because most sediment is from the seaand it comprises mineral grains that areusually low in organic carbon andnutrients.

Unless they receive local surface runoffthat is high in dissolved nutrients, lagoonsare moderately susceptible toeutrophication.

Strand plainsStrand plains are ‘ponds’ of water trappedbetween beach ridges. They are usuallyvery shallow, poorly flushed and receiveonly local runoff.

Because they are small, there is littlespace for sediment–nutrient retention. Theyare moderately susceptible toeutrophication unless local runoff is rich innutrients.

For more information phone DavidHeggie on + 61 2 6249 9589 or [email protected]

Figure 1. Why some coastalwaterways are more susceptible thanothers to excessive plant growth

03-237-6

Waterway type

Particulate

retention Turbidity FlushingEutrophication

susceptibility

Tide-

dominated

delta

Wave-

dominated

delta

Tide-

dominated

estuary

Wave-

dominated

estuary &

coastal lake*

Tidal

flats

Strand

plains

Lagoon

Low Moderate High

very high*

▼


gBenthic algaeBenthic algaeBenthic algaeBenthic algaeB hi l

Sediments

Burial

Microbialprocessing

N2

03-237-103-237-103 237 1

flushing

p ymacroplytesmacroplytesmacroplytesmacroplytesl t

f

Figure 1. Major processescontrolling nitrogen cycling inestuaries and coastal lakes

▼

Trapped nitrogen throws outTrapped nitrogen throws out

estuary balance

Yet some environments seem tohave the capacity to handle morenitrogen than others.

Nitrogen trapMost nitrogen added to an estuaryis from land-use practices andurban runoff into the catchment.Some is flushed to sea but quite alot is trapped in estuaries andcoastal lakes in temperate Australia.

Some of the trapped nitrogen isburied in the sediment, but mostbolsters plant growth includingphytoplankton, macroalgae,macrophytes and mangroves. Theplants eventually die and sink tothe bottom to be degraded bybacteria (figure 1).

Sediment reactions areimportant. Microbial processes inthe sediments recycle nitrogenprincipally as either N2 gas (by areaction known as denitrification)which is lost to the atmosphere, oras ammonia (NH3) which isrecycled to the overlying water.

Some estuaries and lakes willeventually choke on their plant lifeif they are too enriched in nitrogen.

Sediment s tudiesGeoscience Australia has been using benthic chambers to study thedegradation of plant material in coastal sediments. These chambers capture aparcel of seawater overlying the sediments and measure the organic carbonbeing degraded during ‘incubation’ (<24 hours).

The microbes consume oxygen from the water and liberate carbondioxide, nitrate, ammonia, nitrogen gas, phosphate and silicate into thechambers.

The chambers have been deployed about 350 times in various Australianestuaries and coastal waterways.

In about half of the sampling, phytoplankton was the major organicsource being degraded in the sediments. It seems to be the main plantbiomass forming in estuaries and coastal lakes in temperate Australia.

Benthic f luxesThe nitrogen recycled in sediments and into the overlying water is measuredas a flux. Plots of the ammonia (NH3) versus carbon dioxide (CO2) fluxesfrom various Australian waterways are shown in figure 2.

Because carbon and nitrogen in phytoplankton are in the proportion ofC:N::106:16, the maximum nitrogen released per unit of CO2 can bepredicted and this is shown as the Redfield line in figure 2. Four things areevident in the data.

1. All measured ammonia fluxes fall below the Redfield line indicatingthat some nitrogen is missing. In the benthic chambers N2 gas was formingin the sediments.

2. The ammonia fluxes for Myall Lakes and the Swan River estuary showthat denitrification is not very efficient (<50%) at carbon oxidation rates <60mmol m-2 day-1.

3. In Port Phillip Bay and Moreton Bay denitrification efficiency is highat carbon oxidation rates below 40 mmol m-2 day-1 and <50% at carbonoxidation rates >80 mmol m-2 day-1.

4. Most nitrogen is lost by denitrification in Wilson Inlet, at carbonoxidation rates <150 mmol m-2 day-1, and only at higher oxidation rates isammonia release important.

These results show that some environments such as Wilson Inlet have agreater natural capacity to handle more nitrogen than others.

The burrowing of animals, which ventilates the sediments withoxygenated bottom waters, is important for high rates of nitrogen loss to theatmosphere. An active benthos is probably a good indicator of highdenitrification rates.

Toxic algal blooms,anoxic water, fish killsand the smell of rottenegg gas in an estuarysuggest something is outof balance, and the mostlikely culprit is nitrogen.


Eff ic iency gaugeGeoscience Australia has developed a 12-zone classification to describe howsusceptible sites are to changes in nitrogen levels and how efficiently theyget rid of it. (See figure 3: The trophic state refers to the organic carbonrecorded in benthic CO2 fluxes).

Sites in zones one to four are quite robust to nitrogen loading and‘stable’ trophically. Those in zones nine to 12 recycle significant amounts ofammonia back into the overlying waters and are potentially ‘unstable’ ormore susceptible to nutrient enrichment and more likely to changeecologically.

Some sites in Wilson Inlet are in zone one because they efficiently ridthe system of nitrogen when carbon input rates are high.

Wilson Inlet has not had nuisance algal blooms and apparently remainsin good condition even though it experiences a lot of microphytobenthosgrowth in autumn and supports abundant Ruppia production.

Sites from the Swan estuary and from the Bombah Broadwater of MyallLakes (zones seven to 12) though have problems, even with low carboninput. These waterways had nuisance algal blooms when the measurementswere taken.

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Nitrogen modelGeoscience Australia has developeda model that can be used toinvestigate whether nitrogen in anestuary will remain in steady state(inputs balance outputs) or increase(be assimilated into macro-plants)as a result of different nitrogenloads.

Consider a bogus site in zonethree (the solid dot in figure 3),which has a high capacity fordenitrification.

If 10 per cent of the nitrogenload was flushed to the sea andburied in the sediments, this sitewould remain in near steady stateeven with a 20 per cent increase innitrogen. However, the net nitrogenflux would rise rapidly—promotingadditional plant growth—if thenitrogen load increased 50 per cent.

Excess nutrients, sedimentationand declining water quality areserious issues affecting Australiancoastal waterways. GeoscienceAustralia’s work on nitrogenrecycling provides valuable dataand new insights on how to bettermanage them.

For more information phoneDavid Heggie on +61 2 6249 9589or e-mail [email protected]

Figure 2. Data from the Swan Riverestuary (WA) and Myall Lakes(NSW), Port Phillip Bay (Vic) andMoreton Bay (Qld), and Wilson Inlet(WA) showing ammonia releasedfrom the sediments and organiccarbon degradation rates. Thestraight line is the Redfield line.

Figure 3. A classification of estuarine sitesbased on ammonia release rates from thesediments and organic carbon degradationrates. The various states are shown withthe 0–30%, 40–60% and 70–100%denitrification efficiency boundaries. Thesolid dot shows a hypothetical site with anitrogen loading of 7 mmol m-2 day-1 and adenitrification efficiency of 70%.

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With major fisheries relying on a healthy estuary and the Great Barrier Reefoffshore, the Fitzroy River in central Queensland is under the scrutiny ofenvironmental managers and local stakeholders.

In September the Coastal Cooperative Research Centre began a series ofstudies into how nutrients, fine sediment and agricultural chemicals aretransported, stored and transformed in the Fitzroy estuary, and perhapscarried to the reef.

The study collaborators (called the Fitzroy Contaminants Dynamicsproject) are Geoscience Australia, CSIRO, Griffith University, CentralQueensland University and Queensland Department of Natural Resourcesand Mines.

Samples and other data collected in the first surveys are currently beingassessed by project members.

Water and bottom sedimentGeoscience Australia and CSIRO Land and Water charted a local vessel fromSeptember 5–12 to survey the Fitzroy estuary and Keppel Bay. Seventy-twostations were sampled to assess dry-season water column and bottomsediment properties (figure 1).

At each station, various combinations of the following were targeted:• bottom sediments;• water-column nutrients (total and dissolved), organic carbon (total and

dissolved), and phaeophytin and chlorophyll a;• total suspended matter and its grain size;• water clarity; and • algal pigments and dissolved organic matter.

At some stations a vertical profile of the water column was undertakento assess dissolved oxygen, turbidity, light absorption and conductivity.

Floodpla in In the same period, the floodplainwas cored to determine what sortof sediment has been transportedfrom the catchment into the estuaryover the past 5000 years.

Cores were taken frombillabongs along the Fitzroy Riverand from a small tidal creek, usinga small boat and a push corer (ahand-operated device that canretrieve two-metre cores from softsediments).

Sites included Crescent Lagoonand Frogmore Lagoon near thetown of Rockhampton. Localreports suggest that these lagoonsnever completely dry out, providinga continuous and undisturbedsedimentary record.

Soft sediment cores were alsotaken from Casuarina Creek, a largetidal creek fringed by mangroveforest (figure 2).

In the hard, clay-rich areas ofthe floodplain a Geoprobepercussion corer was used.

Geoscience Australia andCSIRO are currently analysing thegeochemistry and grain-sizedistribution of the cores, mainly todetermine the sediment ages andaccumulation rates.

Beach r idgesAdjacent to the river mouth is aseries of beach ridges (figure 2).These ridges show that Long Beachis prograding towards the sea, andprobably because of Fitzroy Riverand Keppel Bay sediments.

Sediment was collected fromthe first 11 major ridges landwardfrom the beach (figure 3), using ahand-auger.

The sediment samples arebeing dated to find out the rate ofshoreline progradation. Traceelements will be analysed todetermine any changes in thesource and character of sedimentsover time.

The elevation and shape of theridges and swales (shallowdepressions between ridges) that

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Figure 1. Daily ship tracks and the station locations for the water-column survey

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Fitzroy under scrutinyccaattcchhmmeenntt llooaaddss

Fitzroy under scrutinyfor


extend inland from Long Beach were also measured. This informationindicates the rates at which sediment was delivered to the shoreline (e.g.low-amplitude, well-spaced ridges = rapid sediment accumulation; high-amplitude, closely spaced ridges = slow accumulation).

Intert idal zoneIn October, the intertidal areas and mangrove wetlands were assessed fortheir role in estuarine productivity and nutrient cycling (particularlynitrogen). The nitrogen from the intertidal mudflats is thought to be asignificant component of the overall biogeochemical nutrient budget in theFitzroy.

Surface sediment samples werecollected along the mudflats of theFitzroy River and major creeks. Ateach site, multiple samples werecollected for chlorophyll andbiomarker analysis, and nitrogenfixation experiments.

Determining speciescomposition is important becausecyanobacteria and eukaryotic algaeplay a significant role in themudflats and when one dominates,the nitrogen levels (and chlorophyllproduction) differ.

Samples are being analysed atCSIRO Marine’s Hobart laboratory:chlorophyll as a basic measure ofprimary production; sterol and fattyacid biomarkers and algal pigmentsto quantify broad classes ofeukaryotic algae (diatoms,dinoflaggellates and green algae)from cyanobacteria.

Nitrogen fixation was measuredusing the acetylene reductiontechnique. This involves incubatinga small (about 20 gm) of surfacesediment in a gas-tight glass bottleand injecting acetylene into thehead-space. If nitrogen-fixingbacteria are present in thesediments, some of the acetyleneshould be reduced to ethylene.

Ethylene will show thatbiological nitrogen fixation occursat sites where these sediments weretaken.

For more information phoneBrendan Brooke on + 61 2 6249 9434 or [email protected]. Also see: www.coastal.crc.org.au/fitzroy/index.html

Figure 3. A vertically exaggeratedrepresentation of the surveyed beachridges (see figure 2 for location). Surveymeasurement sites are represented by redtriangles. Sediment auger sample sites areshown as black arrows.

Figure 2. Location of the floodplain sediment core sites and beach-ridge auger sites

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MARine SedimentdatabaseGeoscience Australia is creatingthe MARS database so thatresearchers have a secure, centralrepository of sediment data fromAustralia’s marine jurisdiction.

All sorts of data will be storedin MARS, ranging from ship-deckdescriptions of grab samples to thelatest underwater video footage.

MARS data will be used tomap seafloor properties and buildwhat is known about marineecosystems and benthic habitats indifferent regions of Australia. Thedata will be vital to regionalmarine planning.

The National Oceans Officehas provided funds to fast-trackMARS development.

Some marine sediment datamay have research, commercial orsecurity restrictions. However allopen-file data, includingGeoscience Australia’s extensivedatasets, will be promoted as the‘National Fundamental MarineDataset’ which can be viewed anddownloaded from the web nextyear.

The database is beingdeveloped in line with ANZLICdata standards.

Visualisation E D G EGeoscience Australia has the edge on others exploring Australia’s geologywith a new theatre and a state-of-the-art stereo visualisation system thatallows people to ‘experience’ data in true 3D.

The EDGE 3D theatre (for Enhanced Discovery of Geosciences) is awork room for scientists to view and analyse models of the subsurface, aswell as a display venue for visitors.

The 3D visualisation adds reality to subsurface models and helpsscientists discuss their ideas about natural hazards and resource potential andcommunicate them to non-scientists.

For example, a slice of the Earth can be rotated and layers of data canbe added or removed for discussions about mineral and petroleumexploration, earthquake monitoring and problems such as salinity.

The EDGE has already been used to fine tune a preliminary 3D model ofthe Yilgarn geology, a major gold mining region in Western Australia.

3D images and digital movies are projected onto a 2 x 2.4 metre screen,and viewed using passive polarising glasses. The viewing systemincorporates a PC, a signal splitter, and two projectors with polarising filters.

The EDGE was officially opened on November 26 by the AustralianGovernment Minister for Industry, Tourism and Resources, Ian Macfarlane.

Geoscience Australia plans to develop the EDGE so that data can bemanipulated virtually and people can simultaneously interact with the samemodel in a teleconference.

M a r i n eM a r i n esc ience meet ingA French–Australian science meeting was held in Geoscience Australiaheadquarters in Canberra on October 15 to discuss marine research prioritiesfor the next five years.

Presently there are more than 100 cooperative research projectsinvolving scientists from both nations in coral reef, geoscience, climate,fisheries and aquaculture studies.

Australia and France share sea borders in the New Caledonian andKerguelen Plateau regions, and have interests in Antarctica.

France has superb blue-water research vessels with cutting-edgegeophysical systems, submersibles, remotely operated vehicles and longcoring equipment.

Australia has the vast marine jurisdiction that extends from the tropics tothe poles, in which many global scientific problems can be researched.

Together French and Australian researchers and marine managementagencies can ensure that a large part of the world’s oceans are betterunderstood and properly managed.

All major French and Australian government marine agencies werepresent including Geoscience Australia, the Australian Antarctic Division,National Oceans Office, CSIRO, the largest French marine research agency(IFREMER) and the French Polar Institute (IPEV).

Reference databaseAll major Australian geosciencepublications are being added to theinternational GeoRef database. Thisshould be good news for thosewho have struggled to find relevantreference material since AESIS(Australian Earth SciencesInformation Service) folded in2001.

GeoRef contains 2.4 millionreferences to geoscience journals,books, maps, conferenceproceedings and reports, making itthe world’s best geosciencedatabase. References can be foundby searching for title, author,subject, or publication date.

Users will be able to subscribeto the full GeoRef database, theAustralian content only(AusGeoRef), or to a customisedalert service via the web or on CD.Subscription details are available atwww.geoscience.gov.au

GeoRef was established in1966 by the American GeologicalInstitute.

I n B r i e f

Left to right: ITRSecretary MarkPaterson, MinisterIan Macfarlane,and GeoscienceAustralia CEONeil Williams.

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SHIP UPGRADEA major refit of the 66-metre-long research vessel Southern Surveyor in Decemberwill improve its capability, particularly for marine geoscience.

A Simrad EM300 multibeam sonar swath mapper will be installed for detailedmapping of the seabed in water depths of 15 to 3000 metres. Soon afterwards aSimrad Topas PS18 sub-bottom profiler will be added for high-resolution images ofseabed strata down to about 80 metres. This technology will help scientists bettertarget seabed coring.

Geoscience Australia, the National Oceans Office and CSIRO purchased the newequipment.

The mid-range swath mapper will be used for the first time in February–Marchnext year by Geoscience Australia in the Bremer Basin, a frontier area off Albany.The voyage will run seismic profiles on the first leg and then dredge rocks fromsubmarine canyon walls on the second leg, aiming to understand the geologicalhistory of the basin and assess its petroleum potential.

In May both the swath mapper and sub-bottom profiler will be used byGeoscience Australia to survey the deep-water Kenn Plateau north-east of Brisbane.

The survey aims to assess the geological history of this continental fragmentwhich separated from mainland Australia about 95 million years ago, and what thismeans for the region’s petroleum prospects.

Topo map checkMost topographic mappingnowadays is done by satellite. Theposition of big features like hills,lakes and reserves are confirmed bygovernment and the private sector.

Local knowledge is needed forthe small landmarks and easilyoverlooked changes such as a roadbeing sealed.

Geoscience Australia’s RachelleNevin and Matt Barwick are talkingwith local map users such ascouncils, Rural Fire Services, andNational Parks and WildlifeServices, and checking somechanges first hand.

They use a car navigationsystem and digital software(OziExplorer and NATMAP Raster250K) to track their location andidentify inaccuracies in the positionof local features such as mines,towers, homesteads and landingstrips.

The pair spent two weeks inthe Armidale region of New SouthWales at the end of October and inmid-November travelled around theKalgoorlie district in WesternAustralia. Generally each district isvisited about every five years.

In September, GeoscienceAustralia completed the topographicmapping of the entire Australiancontinent (all 7.66 million km2) at1:250 000 scale.

The field work to date verifiesthe maps are accurate and easy touse. They are available from theGeoscience Australia web site.

Season’s GreetingsBest wishes for the festive season.

Thank you for your interest in Geoscience Australia and your readership of AusGeo News. We look forward to your support in 2004.

Mutant pollenMutations found recently in prehistoric conifer tree pollen are the same asthose in modern pines suffering environmental stress.

Some 250 million years ago, it is thought that gas and dust frommassive volcanic eruptions damaged Earth’s ozone layer and changed itsatmosphere, causing mass extinction.

The extreme change in environment caused conifers to producemutant pollen.

Instead of the usual two-wing sacks that help the pollen drift throughthe air, the stressed prehistoric conifers produced pollen with one, noneor three or more wing sacks.

Modern pines show these mutations in response to such stresses asextreme cold, dryness and fallout from the Chernobyl nuclear power plantdisaster.

The prehistoric mutant pollen was found in ancient lake sediments inChina and Russia and is being studied by a team ofinternational scientists including Geoscience Australia’sClinton Foster and Sergey Afoin from thePalaeontological Institute of Moscow.

It is speculated that similar mutant pollens will befound in sediments dating back to the dinosaur-extinctionevent about 65 million years ago.

I n B r i e f


Just months before hispassing in 1998, ErnestHodgkin suggested that

increased sedimentationfrom land clearing was

the main long-termthreat to estuaries and

tributaries in southWestern Australia.

He called for research into the effects of catchment clearing on estuaries andon sediment transport.

Geoscience Australia in collaboration with Western Australia’s Waters andRivers Commission collected surface sediment samples from the centralbasins of 12 estuaries in south Western Australia (figure 1).

The two water-quality monitoring surveys conducted in 1997 and 2002were part of a broader initiative to develop geochemical indicators ofsediment condition for monitoring Australia’ coastal waterway health.

The sediment was analysed for grain size, total nitrogen (TN) and totalphosphorus (TP), total organic carbon (TOC) and major element oxides(including total sulphur, TS).

Some of the Commission’s long-term water quality data (TN, TP anddissolved nutrients), and CSIRO sediment-yield data were also used.

From the data, Geoscience Australia calculated the sediment load, carbonand nitrogen accumulation rates, TOC:TS ratio, and a weathering index foreach estuary.

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Figure 2. The National Land and WaterResources Audit found that land clearinghas changed the amount of sediment inestuaries in south Western Australia overthe past 200 years. In the estuariesinvestigated, it is now 15–75 times higherthan prior to European settlement.

Land clearing swells sedimentloads in WA estuaries

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Huge sediment increase Since European settlement, the amount of sediment in the estuariesinvestigated has increased 15–70 times because of land clearing (figure 2).

It is estimated that up to seven kilograms of sediment per square metreof estuary are added yearly to some Western Australian estuaries (sedimentloads range from 0.1 to 7.8 kg m-2 y-1).

In the Swan Canning estuary, Hardy Inlet and Oldfield Inlet in particular,land clearing practices in their catchments have added a lot of sediment tothe waterway. Organic debris, nutrients such as nitrogen and phosphorus,and other contaminants travel with sediments into the estuaries.

Oldfield and Hardy inlets have high levels of carbon and nitrogenaccumulation that could affect ecosystem health (figure 3). The nutrientloads of a couple of others are also a concern particularly as some of thesecarbon accumulation rates would be lower than actual carbon loads becausethey do not account for carbon oxidised at the sediment–water interface.


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Poor water qual i ty There is a distinct relationship between the weathering index and sedimentloads (curve in figure 4).

Soil erosion probably explains the rising phase of the curve. Thedeclining phase that occurs when sediment loads are even higher isprobably bedrock erosion (i.e. the transport of more primary minerals andless clay).

Overall, eroded soil contributes to poor water quality in south WesternAustralia’s estuaries.

Nutrient concentrations (TN and TP) in the water column tend to bemore than double levels recommended by the Australian and New ZealandWater Quality Guidelines, when sediment loads are in the range 2–4 kg m-2

y-1 and weathering indices are higher than 67 (figure 3). In these situationsminerals in the soil have helped transport organic matter and nutrients.

Chlorophyll a levels and algal blooms are also typically higher inestuaries with these sediment loads (figure 4).

Figure abbreviations: HAM = Hamersley Inlet, WI = Wilson Inlet, IRW = IrwinInlet, WELL = Wellstead Inlet, WN = Walepole–Nornalup Inlet, GOR = GordonInlet, PAR = Parry Inlet, TOR = Torbay Inlet, BEAU = Beaufort Inlet, SW = SwanCanning estuary, OLD = Oldfield Inlet, and HAR = Hardy Inlet

Figure 3. Median inorganic(nitrogen):organic (carbon) ratios inestuarine sediment loads, whichprovide insights into estuarine health

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Figure 4. Changes in the weathering index with sediment loads. Changes in waterand sediment quality are displayed as horizontal bars.

Water qual i ty surpr iseThe inlets with the highest sedimentloads (Oldfield and Hardy inlets)have good water quality based ontotal nutrients and chlorophyll, buttheir sediment quality is poor fromtheir TOC:TS ratios.

These ratios are at their lowestin the estuaries with highersediment loads (figure 3: higherthan 3 kg m-2 y-1).

The TS in sediment shows thatorganic matter has beendecomposed by sulphate-reducingbacteria. The bacteria oxidiseorganic matter under anoxic (nooxygen) conditions and in theprocess produce hydrogen sulphide.Some hydrogen sulphide convertsto sulphides (TS) upon reactionwith iron minerals in the sediment.

Hydrogen sulphide can betoxic. It can also inhibit thewaterway’s ability to transform andget rid of nitrogen.

Rapid burial seems to reducethe time available for organic matterto be oxidised in the water columnso it builds in the sediment,allowing bacteria to decompose it.The bacteria use the oxygen,causing sediment anoxia.

Geoscience Australia continuesits work on the impacts of sedimen-tation on coastal waterways, atpresent in south-east Australia.

Ernest Hodgkin was a marineecologist who pioneered researchinto Western Australian estuaries.He continued his work long afterretirement and until his death.

For more information phoneLynda Radke on +61 2 6249 9237or e-mail [email protected]

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The Coastal Cooperative ResearchCentre is addressing the problemwith the latest sonar mappingtechnology: a SeaBat swathmapping system mounted on asurvey boat.

After trials in known areas likeSydney Harbour, the Reson SeaBat8125 will move to other coastalwaters around Australia over thenext three years.

This Coastal CRC work, calledthe Coastal Water Habitat Mappingproject, heavily involves GeoscienceAustralia.

Sonar mappingA swath mapper uses sonar to maplarge areas of seabed underneathand on both sides of the surveyboat.

SeaBat 8125 is capable ofmapping the depth of the seabedup to 60 metres below the watersurface.

It emits 455 kHz pulses ofsonar energy, which echo from theseabed. The returning echo signalsare resolved into 240 narrowbeams, in a 120° arc under theboat. The arc allows a swath orstrip of seabed approximately 3.5times the water depth to bemapped.

Seabed features can beresolved to about six-millimetreaccuracy.

SeaBat 8125 also records theproperties of sound waves thatbounce back from the seabed(acoustic backscatter information),which highlight different textureson the seafloor. This data can beused later to classify sediment typesand define seafloor habitats.

By using 3D technology withthe system, images of the seabedcan be viewed in near real-time asthe boat carries out the survey.

Sydney Harbour tr ia lSeaBat 8125 was tested in Sydney Harbour during August. The harbour wasideal because it has been surveyed with numerous other techniques andresults could be compared with SeaBat 8125 data.

The main test site was an area of high seabed diversity in the outersection of Sydney Harbour known as Sow and Pigs Reef (figure 1). The reefis exposed during low tide and can be a shipping hazard.

An area of approximately one square kilometre (one-third the surveyarea) was mapped (figure 1). Survey lines were spaced so that beamsoverlapped to get total seabed coverage and to minimise outer-beamdistortion.

A 3D bathymetry image from SeaBat data shows there is a shoal aroundSow and Pigs Reef (figure 2, red area to the left) that comprises a smallbedrock outcrop surrounded predominantly by sand. The sand is fromlandward-migrating continental shelf sediments and is mixed with river mud.

The deepest point in the survey area was 24 metres (blue area at thebottom left of figure 2). This area borders the dredged Western shippingchannel. The channel allows safe access to Sydney Harbour, and cutsthrough the region from the north-west to the south-east.

Another dredged area, the Deviation Cut, appears as rough areas in the3D image, at about 12 metres water depth.

Ground-truth workThe acoustic diversity in the SeaBat echoes can be used to form proxy mapsof the seafloor and its habitats, such as the location of seagrasses, reef,sponge gardens, sand and mud.

These maps are validated through ‘ground truthing’, generally bygrabbing sediment samples from the seabed and taking underwater videofootage.

Video transects were recorded of the Sydney Harbour study area, andseabed samples were collected from 21 sites. The primary sampling tool wasa 60 kilogram Smith-Mackintyre grab sampler that returns large, relativelyundisturbed sand and muddy sand samples. A box-corer collectedundisturbed samples from muddier areas.

Samples from the deeper ‘holes’ (blue area in figure 2) comprise softblack mud, whereas the shoal areas typically had sands with molluscs andother invertebrate fauna. Samples from the harbour’s dredged areas typicallycomprised a mixture of sands and gravels.

The grab samples are undergoing sediment and geochemical analysis atGeoscience Australia and will be compared with video footage andbackscatter data to improve interpretation of SeaBat data and seabed models.

SeaBat trial echoed fromcoast to coast

Habitat maps of shallowmarine environments

are in demand forenvironmental planning

and managing Australia’snatural resources.

But good-quality maps are scarce.


Futher seabed mapping In mid-November, SeaBat 8125 moved to the Recherche Archipelago, southof Esperance in Western Australia, to be tested in different conditions outsideof shallow harbours and estuaries.

In deep water near the Woody and Remark Island groups, the mappingand sampling work found the seafloor comprises a mix of calcium-carbonate-based sand, reef with algae and sponges, and massive graniteboulders.

Plans are under way to useSeaBat 8125 for seafloor habitatmapping again in Sydney Harbour,as well as Cockburn Sound inWestern Australia, Keppel Bay andMoreton Bay in Queensland, andpossibly the Derwent River inTasmania.

Others involved withGeoscience Australia in the CoastalWater Habitat Mapping project areCurtin University, the University ofWestern Australia, Defence Scienceand Technology Organisation,Reson, Fugro, Sonardata andGeoReality.

For more information phone Brendan Brooke on + 61 2 6249 9434 or [email protected]

Figure 2. A 3D image from SeaBat 8125 data collected over the Sowand Pigs Reef area in Sydney Harbour

Figure 1. The trial swath mapping area for SeaBat 8125 in Sydney Harbour isindicated by the yellow box. Sow and Pigs Reef is also shown.

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Large areas of the lake were rapidly mapped by Geoscience Australia usingQuester-Tangent single-beam acoustic equipment (figure 1). The results werethen field tested.

Geoscience Australia found that the lake bed produced six distinctiveacoustic responses to the echo-sounder signal. These were ‘ground truthed’to find out what features in different areas of the lake floor influenced theacoustic response.

The track of the echo-sounder was combined with a GIS of the lake(figure 2) so that a range of habitats would be sampled. Once in the field,the sampling sites were located using a very accurate global positioningsystem (DGPS).

Bottom sediment was collected from more than 100 sites using a push-corer. At most sites, divers provided extra information about the lake bed,such as the density of seagrass and animal burrows. Underwater photographswere also taken.

Back in the laboratory, each sample was measured for grain size, wetbulk density, total organic carbon, CaCO3 content, and coarse shell material(>2 mm diameter).

There were four predominant sediment types: organic-rich sandy mudwith a lot of shell, organic-rich mud, medium-grained sand, or fine- tomedium-muddy sand.

Other features of the lake bed had to influence the acoustic signal toproduce six distinctive responses.

MuddiedBoth sediment and biophysical (morphology and biota) features haveaffected acoustic signals. Bottom types and even similar sites were notnecessarily associated with one acoustic class. For example: • Acoustic classes 1 and 6 are related to muddy basins, which comprise

fine, low-density muds and abundant animal burrows but no seagrass.• Acoustic classes 2 and 5 generally represent shell-rich sandy muds, and

occur mostly in deeper channels.• Acoustic class 3 is indicative of coarse sediments with low organic

carbon and seagrass beds, typically the marine-derived sands in the maininlet channels.

• Acoustic class 4 generally represents shelly muds with patches ofseagrass, although this class was sedimentologically similar to classes 1 and 6.

The extensive muddy environments, although acoustically different fromsandy areas, were particularly hard to differentiate by acoustic class. Burrowsize and density might better differentiate the muddy habitats and show whythey produce a range of acoustic responses. Also, other unmeasured featuresof the lake bed may have influenced the echograms, such as gas bubblesproduced by plants or evolved from within the organic-rich muds.

The seagrass areas are largely restricted to the shallow margins of thebasins and the inlet channels. There are also dense beds in the marine tidal

delta which consists of clean, well-sorted sand.

Most of the broad basins suchas Pipers Bay and the area west ofWallis Island are dominated by veryfine sediments with varyingconcentrations of shell materialoften densely populated by variousinfaunal organisms (ones that livewithin the sediments).

The intricate network ofchannels in the northern section ofWallis Lake are the deepest parts(up to 8 m), and they compriserelatively dense sandy mud andmuddy sand, often with a relativelyhigh concentration of shell material.

Sounding outlake bed habitats

WallisLake

WallambaRiver

WallingatRiver

Forster

PACIFICOCEAN

STUDYAREA

Many parts of Wallis Lake, a largeestuary on the central New South

Wales coast, are turbid and difficultto map so new echo-sounder

equipment was trialled last year.

Figure 1. An Aster satellite image ofWallis Lake estuary, northern NewSouth Wales, shows the estuary shapewith the study area marked by a whitebox.

▼


Potent ia lSingle-beam acoustic mapping invery shallow water such asestuaries still has some challenges,but it also has much potential.

Large areas of Wallis Lake wererapidly mapped and sampled withthis technology and the resultsindicate the diversity andabundance of habitats in areas ofthe lake that are difficult to mapusing traditional techniques.

This survey is the firstquantification of non-seagrasshabitats in the deeper, often highlyturbid areas of the lake.

For more information phoneDavid Ryan on +61 2 62499257or e-mail [email protected] of the survey can soonbe viewed on the web atwww.ozestuaries.org/

Figure 2. Colour-coded acoustic responses are plotted on an aerialphotograph of Wallis Lake supplied by Land and PropertyInformation, NSW.

▼

Bacter ia at workWhen organic matter settles to the bottom of an estuary, it is broken downin several ways (figure 2). If there is enough oxygen in the water, aerobicbacteria in the sediment go to work. These nitrifying bacteria use oxygen tobreak down organic matter, producing carbon dioxide, phosphate and nitrate(table 1, equation 1).

The nitrate produced is then used by denitrifying bacteria to breakdownorganic matter and produce carbon dioxide, phosphate and mostimportantly, nitrogen gas (table 1, equation 2). The nitrogen gassubsequently escapes to the atmosphere (figure 2).

Nitrogen is an essential nutrient of life. But too much of a good thingcan have negative consequences such as excessive plant growth or algalblooms, which can deplete oxygen levels and result in poor water quality.

Denitrification is one way estuaries can get rid of some nitrogen andlimit excessive plant growth. Water exchange with the ocean is anothermeans of losing nutrients (figure 2).

But if excessive amounts of organic matter are deposited, the aerobicbacteria will use up the oxygen in the water and so anaerobic bacteria, suchas sulphate-reducing bacteria, take over the work of breaking down organicmatter.

Sulphate-reducing bacteria produce hydrogen sulphide, which smells likerotten eggs, and in the process carbon dioxide, phosphate, and ammonium(equation 3). Ammonium is a form of nitrogen which remains in the system(figure 2), perpetuating cycles of excessive plant growth and depletedoxygen levels.

Smelly conditions perfect for estuary work

Marine sandsCentral basin muds

0

03-217-1

D

H

1 km

Fluvial sands andmuds

150 45’ 150150 4646’

34 5655 ’

34 57’

343434 58’

CulburraCulburra

Wattle CornenerCreek

DowDownsCreeke

CooonemC ia Creekreek

Sitee 1

Site 2

LAKE

WOLLUMBOOLA

CC

Figure 1. Map of LakeWollumboola and the benthic-chamber sampling sites

▼

Acoustic c lass 1 2 3 4 5 6

Table 1. Bacteria at workEquation 1: Nitrification106(CH2O)16(NH3)(H3PO4) + 138O2 →106CO2 + 16HNO3 + H3PO4 + 122H2O(phytoplankton) (oxygen) (carbon dioxide) (nitrate) (phosphorus) (water)Equation 2: Denitrification106(CH2O)16(NH3)(H3PO4) + 94.4HNO3 →106CO2 + 55.5N2 + H3PO4 + 177H2O(organic matter) (nitrate) (carbon dioxide) (nitrogen gas) (phosphorus) (water)Equation 3: Sulphate reduction106(CH2O)16(NH3)(H3PO4) + 53SO4

2- →106CO2 + 16NH3 + H3PO4 + 106H2O(organic matter) (sulphate) (carbon dioxide) (ammonium) (phosphorus) (water)

Geoscience Australia has beenprobing the bottom sediments of asmelly, saline lagoon on the NewSouth Wales south coast.

Lake Wollumboola has highconcentrations of hydrogensulphide, or rotten egg gas, in thesediment porewaters and lake-bottom waters. Periodically thehydrogen sulphide escapes to theatmosphere making it unpleasantfor the residents of Culburra(figure 1).

This pristine but sometimessmelly lake provides the idealenvironment for finding out aboutnutrient cycling and nitrogenrelease in hydrogen sulphide-richestuaries.


Organic sourceBenthic chambers were dropped at two sites in the central basin of LakeWollumboola in November 2002 to determine how nutrients are cycled inthe lake (figure 1).

Benthic chambers isolate a volume of water in contact with thesediment. Changes in oxygen, carbon dioxide, and nutrient concentrationsinside the chamber are measured over time.

At first glance, ‘weeds’ (that are really macroalgae) appeared to providemost of the organic matter for bottom sediments of Lake Wollumboola. Themacroalgae looks like green hair and forms a one-metre-thick layer acrossmost of the lake’s central basin.

The benthic chamber data revealed, however, that phytoplankton(microscopic algae) was the major source of organic matter at the time of thesurvey.

Miss ing ni trogenTwo methods were used to determine what was happening to the nitrogenin Lake Wollumboola. The first measured ammonia and nitrate in the benthicchambers (figure 3) and the second measured the increase in nitrogen gasover time.

Denitrification rates could be measured because phytoplankton has acarbon: nitrogen: phosphorus ratio of 106:16:1 (Redfield line, figure 3). The‘missing nitrogen’, or the difference between the measured dissolvedinorganic nitrogen flux and the expected nitrogen flux (Redfield line), isassumed to be nitrogen gas produced via denitrification.

Denitrification efficiencies calculated using the two different methodswere comparable for most chambers. The average denitrification efficienciesfor sites 1 and 2 were 61 per cent and 65 per cent respectively.

In Lake Wollumboola more than 60 per cent of nitrogen is being lost asnitrogen gas and around 40 per cent is being recycled into the water columnand available for plant growth.

Figure 3. Graph of dissolved inorganicnitrogen (DIN) flux, against carbondioxide (CO2) flux. The differencebetween the DIN flux and the expectedtotal nitrogen flux (Redfield line) is thenitrogen gas flux (denitrification). Violetdata points are for site 1 and orange datapoints are for site 2.

High concentrat ionsAverage hydrogen sulphideconcentrations in the surfacesediment porewaters were 412 �mat site 1 and 44 �m at site 2.Despite these high concentrations,denitrification occurs in LakeWollumboola. This is surprising asresearch elsewhere reports thathydrogen sulphide concentrationsabove 100 �m inhibitnitrification/denitrification.

Perhaps the bottom sedimentsof Lake Wollumboola areheterogeneous—that is, made up ofhydrogen sulphide-rich patcheswhere denitrification does not occurand hydrogen sulphide-free patcheswhere denitrification does occur.Such patches may be due to theactivity of organisms living in thesediment.

Burrows, for example, can takeoxygen deeper into the sediment,allowing nitrification/denitrificationto occur immediately around theburrow. Sulphate reduction couldbe occurring in anoxic sedimentaway from the burrow.

For more information phone Emma Murray on +61 2 6249 9019 or [email protected]

NH +4 N2

Sediments

Loss of N

Export

Organic matter inestuary eg. algae,

n

r

nutrients

03-244-1

-2-1

2-2 -1CO flux (mmol m day )

Redfie

ld

12

8

4

00 40 80 120

03-244-3

DIN

flux

(m

mol

m

day

)

Figure 2. Diagram showing how nitrogen is lost or recycled in the waterway

▼

▼


SPATIAL CONFERENCEwell attended

Inaugural

This year COGS (Consortium forOcean Geosciences for AustralianUniversities) held its three-dayconference in conjunction with theAustralian Sedimentologists Groupand it was jam-packed withpresentations.

The COGS conference is amajor forum for presenting theresearch of marine geoscientists andstudents in Australia. It was held atthe Kioloa field research station onthe New South Wales south coastfrom July 7–9.

Most of Australia’s leadingocean and coastal geoscientistsattended and there were 19presentations from GeoscienceAustralia.

Some research outlined in thisissue of AusGeo News waspresented, including estuary habitatmapping, the production of ageomorphic features map for theentire Australian margin, andriverine sediment loads in estuariesin southern Western Australia.

Other Geoscience Australia work presented at COGS 2003 involved:• A geophysical survey of the seafloor east of Norfolk Island, across the

Three Kings Ridge and northwards to the Cook Fracture Zone, whichrevealed a series of broad plateaux separated by depressions and atrench-like feature west of the ridge.

• High-quality deep seismic of the western Antarctic margin that providesdetails about the continental–ocean boundary, and the break-up ofAustralia and Antarctica and subsequent slow seafloor spreading.

• Swath mapping the Murray Canyons system off South Australia todetermine sedimentation patterns, sea-level fluctuations andenvironmental changes in the Murray–Darling Basin.

• Sediment transport studies in the northern Great Barrier Reef whichshow that Fly River sediment is not being transported to the reefbecause of tidal current scour and channels.

The 38 presentations and six posters delivered over the three dayswere testament to the exceptional quality of marine geoscience researchhappening in Australia. COGS 2005 conference in Townsville should beequally successful.

For more information phone Andrew Heap on +61 2 6249 9111 or e-mail [email protected]

For five days in September, Canberra hosted the inaugural Spatial SciencesConference which was an amalgam of the conferences of five professionalassociations (AURISA, IEMSA, ISA, MSIA and RSPAA).

Leading experts from around the world were among the 830 registrants.They included the UK Ordinance Survey Director-General, Dr VanessaLawrence, the US Geological Survey’s Associate Director for Geography,Barbara Ryan, and Australia’s Chief Scientist, Dr Robin Batterham.

Geoscience Australia supported the conference with speakers andpresenters, as well as a display that exhibited a new Raster mosaic product.

This product was launched at the conference by Geoscience AustraliaCEO Dr Neil Williams.

Many delegates took the opportunity to visit Geoscience Australia’sheadquarters and the Australian Centre for Remote Sensing (ACRES) tocheck out the latest mapping and visualisation activities.

Inaugural

Marine research forum abig success

C o n f e r e n c e s

North American ProspectsExhibition 2004American Association ofProfessional Landmen5 & 6 February, Houston, Texas Contact: AAPL, 4100 Fossil CreekBoulevard, Fort Worth, Texas 76137USAphone +1 817 847 7700fax +1 817 847 7704e-mail [email protected]

17th Australian GeologicalConventionGeological Society of Australia8 to 13 February, Hobart Contact: Conference Design, POBox 342, Sandy Bay, Tas 7005phone +61 3 6224 3773fax +61 3 6224 3774 e-mail [email protected]

PDAC 2004 Prospectors & DevelopersAssociation of Canada7 to 10 March, Toronto, CanadaContact: Prospectors & DevelopersAssociation of Canada, 34 KingStreet East, Suite 900, Toronto,Ontario M5C 2X8, Canadaphone +1 416 362 1969fax +1 416 362 0101 e-mail [email protected]

NZSEE Annual Conference 2004New Zealand Society forEarthquake Engineering19 to 21 March, Rotorua, NewZealandContact: Derek Wilshere, NZSEE,PO Box 2193, Wellington, NewZealandphone +64 4 562 7920fax +64 4 562 7920 www.nzsee.org.nz/EVENTS/events.html

APPEA 2004 Australian Petroleum Production &Exploration Association 28 to 31 March, Canberra Contact: Julie Hood, APPEA Ltd,GPO Box 2201, Canberra ACT 2601phone +61 2 6267 0907fax +61 2 6247 0548e-mail [email protected] www.appea.com.au

AAPG 2004 American Association of PetroleumGeologists 18 to 21 April, Dallas, Texas Contact: AAPG Convention, PO Box 979, Tulsa Oklahoma74101-0979 USAphone +1 918 560 2679fax +1 918 560 2684e-mail [email protected]

Petroleum Open DayCanberra April 1

The Petroleum Open Day gives you the chance to discuss GeoscienceAustralia’s program over the next four years with petroleum researchersand government decision makers. This event immediately follows APPEA 2004 in Canberra and is held atGeoscience Australia’s headquarters. The Open Day costs $33, which includes lunch and morning andafternoon tea, and it must be paid by March 12.

The proposed program is available at www.ga.gov.au

Call for researchproposals for

EXPERIMENTSin 2004&beyond

The Australian National SeismicImaging Resource (ANSIR), a majornational research facility, seeksbids for research projects forexperiments in 2004 and beyond.

ANSIR operates a pool ofstate-of-the-art seismic equipmentsuitable for experiments designedto investigate geological structures.ANSIR is operated jointly byGeoscience Australia and theAustralian National University.

ANSIR equipment is availableto all researchers on the basis ofmerit, as judged by an AccessCommittee.

Demand for broad-bandequipment is very high. Thisshould be taken into considerationin the design of experiments.ANSIR provides training in the useof its portable equipment, and afield crew to operate its seismicreflection profiling systems.Researchers have to meet projectoperating costs.

Applicants should consult theweb (http://rses.anu.edu.au/seismology/ANSIR/ansir.html) fordetails of the equipment available,access costs, likely field projectcosts, and the procedure forsubmitting bids. This site includes anindicative schedule of equipment forprojects that arose from previouscalls for proposals.

Researchers seeking to useANSIR equipment from mid-2004should submit research proposalsto the ANSIR Director by February16, 2004.

Enquiries should be directed to:

Prof Brian Kennett, ANSIRDirector, Research School ofEarth Sciences, AustralianNational University, Canberra ACT 0200. Tel. +61 2 6215 4621 or e-mail [email protected]

Submissions by February 16, 2004

ANSIR AUSTRALIAN NATIONALSEISMIC IMAGINGRESOURCE

e-mail [email protected]


EVENTS calendar compiled by Steve Ross


For the first time, the ‘landscape’ of

Australia’s seabed hasbeen mapped at a large

scale in a GeoscienceAustralia–National

Oceans Office project.

The geomorphic map for a majorpart of Australia’s exclusiveeconomic zone is crucial for propermanagement of offshore resources,as each feature is home to verydifferent ecosystems and marinelife.

The map is a major referencefor regional marine planning and isheld in a geographic informationsystem for updating.

Map construct ionGeoscience Australia addedapproximately 289 millionsoundings from swath surveys, shipecho sounders, and Navy fair-sheetsto its existing bathymetric database.From these data, it generated abathymetric grid (250 metrehorizontal cell size) for definingseabed features.

Published information andbathymetry were used to determinefeatures, which are based on theInternational Hydrographic Officedefinitions. They include majorgeomorphic provinces (continentalshelf, slope, rise and abyssal plain),as well as individual features (e.g.reef, canyon, fan and terrace).Sandwaves/sand banks were addedeven though they are not in theIHO scheme, because they are amajor feature of the continentalshelf.

Boundaries separating the shelf,slope, rise and abyssal plains weredetermined by changes in slope.

The geomorphic map wasconstructed at a scale of 1:5 million,so the smallest unit size that couldbe reliably resolved was about 10square kilometres. Some featuresthat are even larger could not bemapped because no data areavailable.

The boundaries of the featureswere digitised and stored in a GISand their surface areas werecalculated from the GIS polygons.

Different composi t ionAustralia’s seabed is quite varied even on a regional scale (figure 1). Thenorthern margin is more than 70 per cent continental shelf, whereas theeastern margin and the island regions are more than 80 per cent abyssalplain environments.

The continental rise along the western margin is better developed thanalong the southern and south-east margins.

The most abundant feature are plateaus (about 22% of the area mapped,see table 1), but they are not uniformly distributed. The largest are thecarbonate-dominated Queensland and Marion plateaus in the north-east.

The second most abundant feature is basins (657 600 km2; 9.1%) andthere are two types: shallow basins on the continental shelf in the Gulf ofCarpentaria, Bass Strait and Bonaparte Gulf, and deeper ocean basins suchas the Coral Sea Basin. Knowing the distribution and abundance of shallowshelf basins is important because these are principal repositories for river-borne nutrients and contaminants.

Shallow sills separate basins from the deeper ocean. The sills profoundlyinfluence basin habitats. They have regulated the transfer of water andsediments between the basins and adjacent oceans over many sea-level cycles.

Terraces are the third most abundant feature (591 500 km2; 8.2%),particularly in the west and southern margins where they comprise extensivelow-gradient mid-slope surfaces.

Habitats on these margins will be more affected by depositionalprocesses than the rest of the mid-slope which is characterised by gravityflows and submarine canyons and their dynamic habitats.

Submarine canyons are numerous and occur in all regions except forCocos-Keeling Islands. They are most extensive on the south-east margin (50 536 km2), followed by the west (23 232 km2), south (21 227 km2), north(15 873 km2), north-east (6798 km2) and east (5116 km2) margins.

The relationship between the distribution of submarine canyons andonshore drainage and regional rainfall patterns (i.e. river discharge) is notstraightforward. The canyons occur where the slope is steepest. But thegeomorphic map data could be biased, so questions about canyons willneed to wait until there are more high-resolution bathymetric data (e.g. frommultibeam swath surveys).

Regional-scaleseabed map a first

Shelf Basin

Slope Reef

Rise Canyon

Abyssal plain Knoll

Bank/shoal Ridge

Deep/hole/valley Seamount/guyot

Trench/trough Pinnacle

Plateau

Saddle

Apron/fan

Escarpment

Sill

Terrace

Sandwave/sand bank

10°

110° 120° 130° 140° 150° 160°

110° 120° 130° 140° 150° 160°

20°

30°

40°

50°

10°

20°

30°

40°

50°

10°

104° 106° 108°

12°

100 km

CHRISTMAS ISLAND

100 km

14°

94° 96° 98° 100°

12°

10°

COCOS-KEELING ISLAND

32°

30°

26°

28°

166° 168° 170°

NORFOLK ISLAND100 km

52°

154° 156° 158° 160° 162° 164°

54°

58°

60°

MACQUARIE ISLAND

56°

200 km

N

500 km

Figure 1. The first geomorphic map for a large part of Australia’s exclusive economiczone mapped at 1:5 million scale

▼


Management f rameworkBased on the distribution and abundance of seabed geomorphic features,Geoscience Australia divided the mapped area into eight regions (figure 2).

For example, the north-east margin is defined by an abundance ofmarginal plateaus, coral reefs, and large submarine troughs. In contrast, theeastern margin has seamounts and a relatively narrow shelf cut by numeroussmall but steep submarine canyons.

This breakdown is useful for identifying unique seafloor regions thatmay require protection. It has already been used to define Broad Areas ofInterest, or candidates for marine protected areas, on the south-east margin.

The information also allows quantitative comparisons of features. Forexample, coral reefs in the north-east margin, which are an extremelyvaluable resource are in area only about three per cent of the region.

Future workHigh-quality multibeam swath data are not available for most of Australia’soffshore jurisdiction. The areas with high-quality data coverage are mostlyalong the upper slope of the southern margins. Sensitive management areassuch as the Great Barrier Reef have not been comprehensively swathmapped.

Geoscience Australia is creating a national repository for multibeamsurvey data, and has contributed to a new sonar mapping system that will beinstalled on the research vessel Southern Surveyor in December.

Early next year, Geoscience Australia will use the equipment to collectdetailed bathymetric data in the Bremer Basin on the south-west margin andKenn Plateau on the north-east margin.

The geomorphic map will be updated as new data become available.Geoscience Australia is seeking the science community’s input into newerversions of the map.

Figure 2. The prevalence of seabed geomorphicfeatures showed there were eight main regionsaround the Australian continent.

Table 1. Surface areas of majorgeomorphic features on Australia’s seabed

For more details or if you wouldlike to contribute data for themap contact Andrew Heap on+61 2 6249 9790 or [email protected]

-

Mid slope

terraces

+

rise

+

abyssal

plain

Narrow

shelf

+

seamountsMid-slope

terrace+

canyons

Numerous

canyons

+

rugged deep

seafloor

Complex shallow shelf

Plateaux

+

troughs

+

coral reefs

Plateaux

+

seamounts

Narrow

shelf+

canyons

Feature Km-2 Area%

1. Shelf 1 973 879 27.402. Slope 2 636 416 36.593. Rise 97 099 1.354. Abyssal plain 2 496 205 34.65

Total 7 202 700 1005. Bank/shoals 51 600 0.726. Deep/hole/valley 176 300 2.457. Trench/trough 189 000 2.638. Basin 657 600 9.139. Reef 58 700 0.8210. Canyon 125 100 1.7411. Knoll/hill/peak/mountain 120 800 1.6812. Ridge 111 200 1.5413. Seamount/guyot 103 700 1.4414. Pinnacle 5600 0.0815. Plateau 1 603 600 22.2616. Saddle 160 200 2.2317. Apron/fan 17 700 0.2518. Escarpment 22 900 0.32 19. Sill 17 400 0.2420. Terrace 591 500 8.2221. Tidal sandwave 25 200 0.35

▼


Data from Geoscience Australia’s airborne geophysics and gravity databasesare now delivered using a new system called GADDS (Geophysical ArchiveData Delivery System).

To access these databases enter the address www.ga.gov.au/gadds intoa standard web-browser and follow four simple steps:1. Define the area of interest on a map of Australia.2. Choose the data types (magnetics, radiometrics, elevation or gravity), and

the format (ASCII columns or Intrepid Database).3. Choose the dataset of interest and the dataset columns.4. Supply your e-mail address for data delivery.

You will receive only the required data. Both vector (line and point)and raster (grid) datasets are available.

For raster data files either the entire dataset or a sub-sample (every 2ndor every 10th cell) dataset can be supplied. You can preview a colour imageof the dataset prior to downloading.

Vector data files are supplied at the full dataset resolution. The columnsrequired from each vector dataset are selected by clicking on the correspon-ding check box. All check boxes are left unchecked if all fields are required.

An estimate is given for how much of the chosen dataset is in theregion of interest. The ‘survey extents’ and ‘survey metadata’ links are also afeature of the data delivery.

The ‘survey extents’ link displays a map of the full extent of the chosensurvey relative to the extent of the interest area entered by the user. The‘survey metadata’ link queries the airborne metadata database and displaysall available survey metadata relating to the chosen survey.

An estimate of the unzipped file size and the time to complete therequest is also displayed—with a warning about download time if the filesize is greater than 200 Mb.

Data for individual surveys usually cover one or more 1:250 000 sheetareas. Most surveys prior to 1990 in the databases have flight-line spacingsof 1500 metres or more. From 1990 they usually have flight-line spacings of400 metres or less.

For more information phone Murray Richardson on +61 2 6249 9229or e-mail [email protected]

Web delivery ofairborne survey data streamlined

P r o d u c t N e w s

Geochemicalplotting on-lineGeoscience Australia hasredeveloped its Geochemical DataAnalysis (GDA) system andreleased it as an on-line packagefor retrieving and plottinggeochemistry data it holds in acorporate database.

Originally programmed inFORTRAN, the application hasbeen rewritten in Java to run on astandard web browser.

The current version allowsusers to retrieve data fromGeoscience Australia’s OZCHEMdatabase as well as files from alocal file system via the web. Theretrieved data can be filtered andgrouped, and plotted as X-Ygraphs, Ternary diagrams,spidergrams and histograms.Overlays can be added to the X-Yand Ternary diagrams.

Other features include: linesof best fit, stacked plotting,logarithmic scales, zoom in/out ofselected parts of a graph,enlarge/reduce graph size, modifysymbol colours, and retrievesample information fromindividual graph points.

Filtered and grouped dataand plotted graphs can be savedto a PC.

Java Runtime Environment(Version 1.4.2 or above) is neededto take advantage of all thefeatures. But if users do not havethis software, a simplified (htmlonly version) provides access tothe same data.

Although the GDAredevelopment deals specificallywith the extraction and display ofgeochemical data, the applicationis sufficiently generic to be usedfor the retrieval and plotting ofdata types from other datasources.

For more information phoneNeal Evans on +61 2 6249 9698or e-mail [email protected] visit the Plot-It web site atwww.ga.gov.au/gda/


Geoscience Australia has re-processed seismic data from two large regional-scale reflection surveys that were carried out in Queensland in the early 80s.This is more than 2100 kilometres of seismic data acquired for crustalstructure studies.

Data were recorded to 20-seconds two-way time on a 48-channel DFSIV system. The group interval was generally set at 83 metres with a shotinterval of 333 metres. Dynamite was used as the energy source (drill holes40 m deep and a charge size of 8 kg).

Eromanga Basin (L115, 116 & 118): Over three years (from 1980 to1982), 1382 kilometres of data were acquired from 13 traverses in the centralEromanga Basin to investigate the basin’s structure with a view to futurehydrocarbon exploration.

South-east Queensland (L120): Eight hundred kilometres of six- or 12-fold CDP reflection data were recorded over eight months in 1984 from aline near Charleville in south-west Queensland to Ipswich in the east. Thiswas the first of the Australian Continental Reflection Profiling (ACORP)initiatives to study critical transects of the Australian lithosphere.

Generally speaking data quality was good to fair and has been used indetailed stratigraphic and structural studies of the sedimentary basins as wellas deep crustal studies.

Long line: A continuous traverse is available from Mt Howitt, in thewestern part of the Eromanga Basin, to Ipswich in the Clarence-MoretonBasin (figure 1). This traverse is 1067 kilometres long and comprisesapproximately 3200 drill holes (figure 1).

The data are available in SEG Y format, as ‘shot’ records or enhanced‘final stack’ records, and are easily read on any seismic viewing package andplotted/viewed/interpreted at any required scale. They have beenconsiderably improved with the recent re-processing (figure 2).

Ancillary data, including drill-hole logs, operations reports and potentialfield profiles are also available.

Figure 1. Location map of recentlyreprocessed seismic data

For more information phone David Johnstone on +61 2 6249 9446 or [email protected]

Long lines of seismic data refreshed

The National Land and Water Resources Audit says that about half ofAustralia’s 1048 estuaries are ‘near-pristine’—that is, they have had little or noapparent human impact.

These estuaries are mostly along the remote and least-explored coastline,such as far northern Australia and south-west Tasmania, so little is knownabout them.

A new Coastal CRC project aims to increase knowledge of Australia’spristine and near-pristine estuaries. The two-year ‘Near-pristine Estuaries’project is collating existing information, and mapping the sedimentaryenvironments and habitats of some using satellite images and aerial photos.

The characteristics of near-pristine estuaries are needed for comparisonwith modified estuaries—as an environmental benchmark to assess thedegree of alteration that has occurred.

Much of what is known about Australian estuaries comes from studiesdone in more accessible areas, such as along the south-east and south-westcoasts. These estuaries are often quite altered due to human activities likenative vegetation clearing.

If you have worked in or studied a near-pristine estuary, the Coastal CRCwould like to know about your findings.

Maps, information andmanagement tools from this workwill eventually be available on theOzEstuaries database(www.ozestuaries.org). In themeantime, you can receive updatesvia e-mail on project progress, andmaps which invite feedback.

Geoscience Australia ismanaging the Near-pristine Estuariesproject in collaboration with CSIROLand and Water and theQueensland EnvironmentalProtection Authority.

For more details, or tocontribute to the project orreceive e-mail updates, phone Emma Murray on +61 2 6249 9019 or [email protected]

Pristine estuaries being mapped

EROMANGA

BASIN

MORRRTONOR

-SURATBASIN

03-260-1

28

24

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Figure 2. Example of improved datafrom Moonie area, Surat Basin

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P r o d u c t N e w s

Yilgarn exposedA new on-line GIS uncovers one of Australia’s key mineral provinces, theYilgarn Craton in Western Australia (N Lat -24º; S Lat -36º; W Long 114º; ELong 126º).

The Yilgarn attracts more than half the mineral exploration expenditure,and produces two-thirds of the gold and most of the nickel mined inAustralia.

The problem is bedrock exposure is extremely poor throughout theYilgarn and most known mineral deposits occur within or adjacent to sparseoutcrop.

The on-line GIS allows users to display all deposits in the region or justthe gold or nickel deposits. Mineral deposit distributions can be comparedto other data layers such as geology.

The GIS uses standard browser technology with in-built pan, zoom,query and select tools. Dataset themes include geology, topography,

The proceedings of the Coastal GIS 2003 Workshop held at WollongongUniversity on July 7–8 have just been published.

Australia is very actively involved in numerous issues in its coastal zone,and this workshop explored what spatial information technology has tooffer for the rapid dissemination and effective use of geographical data.

Papers included in the proceedings examine such topics as: Coastaldata—hydrography, data conversion and marine cadastre; Near-shoremapping; Coastal assessment and databases; Coastal morphology andhydrodynamics; Estuarine mapping; and Coastal management.

The proceedings show that Australia is well placed to become aninternational leader in the development and adoption of GIS as an effectivecoastal research and management tool.

The workshop was sponsored by Geoscience Australia, the NationalOceans Office, HSA Systems and ESRI Australia. Participants were from awide range of Australian research institutes, including leading Australianfederal, state and local government agencies, and from New Zealand andSouth Korea. It was organised by Colin Woodroffe, from the School of

Geosciences at WollongongUniversity, and Ron Furness, aformer director with the AustralianHydrographic Office.

Copies of Coastal GIS 2003: Anintegrated approach toAustralian coastal issues areavailable from Myree Mitchell atthe Centre for Maritime Policy,University of Wollongong, [email protected]

potential field geophysics, seismictraverses, whole-rock geochemistry,and geochronology.

One of the main features is thecraton-wide aeromagneticinterpretation (lithology distributionand structure), revealing theprospective Archaean bedrockdistribution under the relatively thinregolith cover. Interpreted structuralelements include lithologicallayering, faults, and dyke swarms.Also presented are severalsurrounding and partially overlyingProterozoic and Phanerozoic basinsand provinces.

There is also a detailed solidgeology interpretation of theLeonora–Neale Transect fromseismic reflection profiles acquiredin 2001 (01AGS-NY1 and NY3).

This GIS is a product of theNorseman-Wiluna Synthesis project,a National Mapping Agreementproject involving GeoscienceAustralia and the Geological Surveyof Western Australia.

For more information phone Richard Blewett +61 2 6249 9713 or [email protected]. Alsovisit ww.ga.gov.au/map/yilgarn

Coastal GIS proceedings released

OzEstuaries is a national repository for information about Australian estuariesand coastal waterways, which Geoscience Australia has been improving withnew geographical and geochemical data, and models of estuary function andecosystem health.

‘Funct ion’ models Geomorphic conceptual models for the seven types of Australian estuariesand coastal waterways (e.g. wave- and tide-dominated estuaries, deltas, andlagoons) have been added. The models provide insights into estuarinefunction, particularly the estuary’s capacity to trap sediments and processpollutants.

Each model comprises a 3D block diagram that summarises the estuary’sphysical form, hydrology, and sediment and nutrient dynamics.

These diagrams are useful tools for assessing relationships amongcomponents in an ecosystem. They will be improved over time throughtesting and user review. A report on estuary models can be downloaded atwww.ozestuaries.org/oracle/ozestuaries/document/.

Fact sheets Biophysical indicators, coastal issues and human pressures on the coastalzone are summarised as fact sheets in the module ‘Coastal IndicatorKnowledge and Information System’. There are also fact sheets to describethe economic and social consequences (or impact) of changed ecosystemhealth and how these may be managed.

The sheets are linked to other indicator fact sheets and to the estuarinefunction models to show the interconnectedness of different measures and,where possible, the coastal settings where they best apply.

There are also external links to web information such as CatchmentCondition On-line Maps and Water Quality Targets On-line.

On-l ine GISAn on-line GIS allows users to check the location of individual estuaries on aLandsat satellite mosaic, and to pan and zoom at different scales. TheLandsat image has a spatial resolution of 25 metres and shows the details ofmost estuaries. For some estuaries the geomorphic habitat mapping can bedisplayed along with cadastral features.

A variety of other imagery isalso available, from regionaloverviews of ocean condition andproperties to aerial photographyand other satellite images. Theattributes of estuaries held in thedatabase, such as geometry orhabitat type, can be queried fromthe on-line GIS.

Other featuresIn OzEstuaries there is now a‘condition assessment’ for mostAustralian estuaries, which wascompiled as part of the NationalLand and Water Resources Audit. Itprovides information about physical,chemical and biological aspects ofthe estuaries.

There is also a link to CSIRO’sSimple Estuarine Response Model(SERM). This model predicts anestuary’s response to changes fromvarying input. SERM is particularlyuseful for gaining a betterunderstanding of the interconnec-tedness of estuary processes.

The ‘Links’ page enable users tolocate other relevant informationand documentation about Australia’sestuaries and coastal waterways.

OzEstuaries represents thecollaborative efforts of more than100 coastal scientists from a rangeof government agencies anduniversities.

For more information phoneCraig Smith on + 61 2 6249 9650 or e-mail [email protected] visit www.ozestuaries.org


Mosaic of Australia now on

The Landsat 7 Mosaic of Australia was releasedon DVD in November. It is derived from the ACRESLandsat 7 Y2K Mosaic data produced by the AustralianGreenhouse Office in 2000.

This beautiful but inexpensive satellite image of Australia displaysground features in photographic-like perspective. It is particularly useful asdigital background information for GIS applications.

The mosaic contains two different 3-band image combinations that havebeen compressed to reduce image size yet retain high quality. The firstimage combines spectral bands 2, 4 and 7 (blue, near infrared, middleinfrared) which results in a pseudo-natural colour image. The second imageis a combination of spectral bands 1, 2 and 3 (blue, green, and red) whichresults in a natural colour image.

Pixel size is an impressive 25 metres using GDA94 datum and LambertConformal Conic projection. The image is ortho-corrected.

The product comes with ERViewer software that allows theuser to load, open, display, viewand save images into a wide rangeof formats including tiff, jpg andWindows bmp.

The Landsat 7 Mosaic ofAustralia on DVD costs $99through ACRES Landsat datadistributors (www.ga.gov.au/acres/distributor/landdis.htm)or phone the GeoscienceAustralia Sales Centre on 1800800 173 (Freecall in Australia)or +61 2 6249 9966, or [email protected]

SEE AUSTRALIA FOR $99

estuaries databaseLots more in estuaries database

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