Regional variation in the distribution of trace metals in modern intertidal sediments of northern Spencer Gulf, South Australia

Marine Geology, 61 (1984) 221--247 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

221

R E G I O N A L V A R I A T I O N IN T H E D I S T R I B U T I O N O F T R A C E M E T A L S IN M O D E R N I N T E R T I D A L S E D I M E N T S O F N O R T H E R N S P E N C E R GULF, SOUTH AUSTRALIA

P. HARBISON

Department of Geology and Mineralogy, The University of Adelaide, Adelaide, S.A. 5001 (Australia) (Accepted for publication March 19, 1984)

ABSTRACT Harbison, P., 1984. Regional variation in the distribution of trace metals in modern intertidal sediments of northern Spencer Gulf, South Australia. In: J.R. Hails and V.A. Gostin (Editors), The Spencer Gulf Region. Mar. Geol., 61: 221--247. Spencer Gulf, a sheltered marine inlet extending 270 km inland from the Southern Ocean is important to the maintenance of South Australia's commercial fishery. At the northern end of the Gulf, the tidal range of 3 m exposes 40% of the marine sediments at low water. These intertidal fiats vary from wide expanses of coarse sand to finer sediments colonized by blue-green algal mats or mangroves. Dissectingchannels are tidal, with virtually no terrestrial runoff. Intertidal sediments from industrial and undeveloped shorelines have been analysed to determine the concentration of trace metals in the surface layer, and factors influencing their local distribution. Physical and chemical characteristics of the depositional environment at sampling sites are defined by field measurements of temperature, salinity, pH, and dissolved H~S in overlying water, and by laboratory determination of the grain size, organic matter and total carbonate content of the sediment samples. Nitric acid soluble metal content of surface sediments is highly variable, with ranges of <0.2--23 ppm Cd, <0.2--50 ppm Cu, 0.1--17% Fe, 20--3000 ppm Mn, <1--600 ppm Pb, and 4--3200 ppm Zn. Generally, high metal concentrations have been found near

existing industries, and in sheltered, organic rich muds. The lowest metal concentrations were found in sandy sediments from exposed beaches. The measured ranges of 12--36°C temperature, 19--59%o salinity, pH 7--9.5, and < 0.1-->5 mg 1"~ ~lissolved H2S indicate the highly variable chemical environment in shallow water overlying the sediments. Proximity to a point source, the established pattern of littoral transport, and the physical and chemical features of the depositional environment apparently control the distribution of trace metals in sediments. INTRODUCTION N o r t h e r n S p e n c e r Gulf, a m a r i n e inlet e x t e n d i n g 2 7 0 k m inland f r o m the o p e n sea, is a n a r r o w , a l m o s t l a n d l o c k e d , w a t e r b o d y sheltered b y the C u l t a n a Hills t o the west, and t h e Flinders R a n g e s t o the east (Fig.l). T h e s u r r o u n d i n g terrain is arid, with an annual rainfall o f less t h a n 3 5 0 m m , a n d virtually n o f r e s h w a t e r r u n o f f t o the Gulf. T h e limited circula0025-3227/84/$03.00

© 1984 Elsevier Science Publishers B.V.

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Fig. 1. Northern Spencer Gulf, showing the intertidal zone and sediment sampling locations (adapted from Hails et al., 1983).

223 tion, high evaporation rate, and lack of freshwater ingress contribute to hypersaline conditions which persist throughout the year (Thomas and Edmonds, 1955). In the absence of river flow, the m o s t important influences on the physical characteristics of the Gulf are the wind, tides, and solar radiation (Stefanson, 1977), the tides having the greatest effect on water m o v e m e n t (Easton, 1978). Tidal amplitude within the Gulf increases from a b o u t 1.5 m at Port Lincoln, in the south, to 3.2 m at Port Augusta (Easton, 1978), and exposes banks, spits, and intertidal fiats up to 4 km wide at low water. Shipping in this region is confined to a main channel 20 m deep near the western shoreline, and relies on dredged access to Port Pirie and Whyalla (Fig.l). North of Point Lowly and Ward Spit, approximately 40% of the marine area of the Gulf is intertidal, a significant proportion of which is colonized by the white mangrove, Avicennia marina var. resinifera (Butler et al., 1977). The lower intertidal region supports seagrasses, usually Zostera, which extend seaward towards subtidal communities of Posidonia. Heterozostera and Halophila occur in deeper water (Shepherd, 1981; Gostin et al., 1984, this volume). Mangrove swamps and seagrass beds are important contributors to the f o o d chain of northern Spencer Gulf, and provide shelter and feeding grounds for a variety of juvenile fish (Jones, 1979; Shepherd, 1981; Thomas, 1981). Robertson (1977) made similar observations in Westernport Bay, Victoria, concerning the commercially important King George Whiting. The importance of northern Spencer Gulf to the South Australian prawn fishery has been indicated by the closure of all waters north of Point L o w l y and Ward Spit to prawn trawling from June 1978 (Thomas, 1981). The northern part of the Gulf is also a desirable location for industrial development, providing sheltered waters for shipping, and proximity to ore deposits as well as reserves of salt, oil and natural gas. Large metal smelters, with the associated shipping traffic, have operated on both sides of the northern Gulf for more than 50 years.

Industrial impacts in the Northern Gulf A t t e m p t s to assess the commercial value of gulf waters, and the impacts of development have resulted in a wide range of marine research during the last decade. A government survey initiated in 1973 to identify the origin and the nature of material discharged into Spencer Gulf reported the major industrial sources to be a lead/zinc smelter at Port Pirie, a steelworks at Whyalla, and a p o w e r station at Port Augusta (Deland and Jones, 1973). All these wastes discharge into the northern part of the Gulf, which according to Tronson {1974) and Bullock (1975), has a water circulation so limited as to form almost a closed system. Studies to determine the impact of effluent discharged from the lead zinc smelter at Port Pirie have been undertaken by the South Australian Department of Fisheries (Olsen, 1983), and also by Sims (1973), Depers

224 (1974), and by a number of Commonwealth Scientific and Industrial Research Organisation scientists {Tiller et al., 1975; Dossis and Warren, 1980, 1981; Warren, 1981; Ward, 1981; Ward and Young, 1981, 1982; Ferguson, 1983; Ferguson et al., 1983; K.G. Tiller, pers. commun., 1982). Much of this work has been briefly reviewed by Thomas (1981). Ward and Young {1981) inferred some atmospheric deposition of metals, in addition to the waste water source, from the results of the study carried out by Tiller et al. {1975) on the dispersal of lead emissions from the smelter into the surrounding agricultural region. Soil lead concentrations 100 X background levels were found within a radius of 2 km of the smelter, and also at Mt. Ferguson and Port Germein, north of Pt. Pirie {Tiller et al., 1975). Ward and Young (1981) reported a similar concentration of lead in shallow marine sediments about 4 km offshore from the m o u t h of First Creek (Fig.l). Sediments collected near the m o u t h of the Creek, which receives all drainage from the smelter, contained 3000--5000 ppm Pb. Aerial emissions from the stack have been considerably reduced in recent years, and Tiller et al. {1975) conclude that most of an estimated total fallout of 40,000 tonnes Pb on the land surface occurred before 1930. Other work undertaken in the Gulf near-shore zone, in the vicinity of Port Pirie, pertains to microbial and carbonate diagenetic processes in sediments with enhanced trace metal content (Bauld et al., 1980; Burne, 1981; Ferguson et al., 1983). The main o u t p u t from the coal-fired p o w e r station at Port Augusta is heated water, but water seeping from ashponds in the supratidal zone eventually reaches the Gulf and can contribute trace metals to intertidal sediments. Fly ash from the p o w e r station has also been considered a possible source, b u t in spring and summer prevailing winds carry the ash northwards over the town, and away from Gulf waters (Jordan, 1972). When winds blow from the north, it is possible for the plume to extend as far south as Port Pirie, b u t plume dispersion measurements carried o u t by the CSIRO indicate that emissions from the stacks at Port Augusta would make an insignificant contribution to trace metals in that part of the Gulf (Williams, 1979). Industrial discharges to the shallow subtidal zone at Whyalla include cooling water from the pellet plant, and cooling water and gas scrubber effluent from the blast furnace. Floating material is removed, and suspended matter allowed to settle, before final discharge into a shallow lagoon opening on its northern side to False Bay (Fig.2). Dust from the pellet plant, estimated by the company as a solid fallout of 2--7 t km -2 per month {Jordan, 1972), could contribute to sediments along the shoreline, depending on wind direction. This study investigates the impact of discharges from the Whyalla operation by determining the concentration of trace metals in the extensive intertidal sediments along the Gulf shoreline. Features of the depositional environment have been related to trace metal concentrations in an attempt to identify factors which influence the distribution of industrial discharges and the availability of trace metals to marine organisms in the near-shore zone.

225

Fig. 2. Aerial photograph showing the new embankment north of the steelworks in False Bay. Arrows show direction of wave fronts and white figures indicate sediment samples (South Australian Department of Lands Survey 2393--000, 10.3.79).

226 METHODS Sedimen~

Sediment sampling points were chosen on intertidal sandftats and in mangrove swamps within a 10 km radius of the steelworks at Whyalla, at Port Augusta and at Mt. Ferguson, 3 km north of the Port Pirie smelters (Fig.l). Chinaman's Creek and Fisherman's Bay, respectively 50 km north and south of Port Pirie, were considered to represent locations remote from industrial influences. Samples from Port Wakefield, a small fishing c o m m u n i t y at the head of Gulf St. Vincent, Port Gawler, an open beach area 25 km north of Adelaide, and Torrens Island, a power station site in extensive mangrove swamps near Adelaide, are included in the analyses to compare with Spencer Gulf sediments. Short, intact sediment cores were collected by pressing washed 50 cm lengths of 7 cm diameter PVC tubing into exposed sediment surfaces at low water. A hole was then dug beside the embedded tube so that its lower end could be capped before withdrawal from the surrounding material. Samples were collected at low, mid and high tidal levels from the exposed intertidal flats, and from those colonized by mangroves or seagrasses, then packed in ice, and later frozen until analyzed in the laboratory. A few subtidal samples were also collected in washed plastic bags from the top 10 cm of sediment. In the laboratory, the frozen samples were carefully extruded, and visually distinct colour horizons were separated for analysis. Colour was also used by HaUberg (1974) to differentiate layers in intertidal sediment cores. He attributed the colours to the presence of different iron minerals, ranging from brown (oxyhydroxides) to black (a mixture of sulphides), and grey (mainly pyrite). Smear slides of each horizon were also prepared for grain size estimation. Samples for trace metal analysis were taken from the approximate mid-point of each horizon and oven dried slowly at 60°--80°C to minimize the loss of volatile elements. Interstitial water and salts were n o t removed by washing, as preliminary tests showed considerable loss of zinc from the sample during this process. After drying, the sample was lightly crushed in an agate mortar, and sieved through a coarse nylon sieve (1 mm mesh) in order to remove shell fragments and pebbles. The whole sample was then reground in the agate mortar to homogenise it sufficiently for representative sampling. Metals were recovered by heating the dried sediments for two hours in concentrated nitric acid at 100°C, with another two hours heating after the addition of 30~o hydrogen peroxide, following the m e t h o d of Krishnamurty et al. (1976). Octan-2-ol was used to reduce frothing. Detailed descriptions of these methods have been given by Harbison (1980). Some samples were totally digested with nitric/perchloric/hydrofluoric acids under pressure (Agemian and Chau, 1976) to compare the total metal content of sediments with the amount of metal extracted by nitric acid. A reducing leach, consisting of a mixture of 0.2 M ammonium oxalate and 0.2 M oxalic

227 acid at pH = 3, was shaken with the sediments for 2 h in the dark to extract metals associated with amorphous iron oxides (Schwertmann, 1964). Blanks were included with each batch of samples. All extractions were made up to 100 ml volume with distilled water, and filtered to remove residues. Further dilution of some samples was necessary to measure high concentrations of iron and zinc. All measurements of metal concentration in solutions were made with a Varian Techtron Atomic Absorption S p e c t r o p h o t o m e t e r A.A.6, with simultaneous hydrogen lamp background correction for all elements except Fe and Cr. Methods were checked by analyses of USGS standard materials SCO-1 and MAG-1, b y replicate analyses of samples prepared by all extraction procedures, and by standard additions to the u n k n o w n solutions. The concentration of calcium in sediment extracts varied from 1300 ppm in solutions of clayey muds to 4500 p p m in shelly sands, so possible interferences were checked by preparing standards containing representative concentrations of cadmium, copper and lead in calcium solutions ranging from 1000 to 4000 ppm. With simultaneous background correction, there was no significant increase in absorbance for up to 4000 ppm calcium in solution. Without background correction, the increase in absorbance at 4000 ppm calcium was approximately 15% for cadmium, 12% for copper, and 25% for lead. Smear slides were examined microscopically to estimate predominant grain sizes, b u t only the broad categories " s a n d " ( > 1 0 0 p m ) and " m u d " (,:100 pm) have been used in this report. Because the study aimed to identify near-shore environments with an affinity for, or potential to accumulate metal wastes, the total sediment sample was analysed in each case. No attempt has been made to separate grain size, mineral, or organic components, as the enhanced accumulation of metals by any of these factors should also be apparent in the extent of accumulation and bioavailability of trace metals in the particular depositional environment. Dried sediment samples were ignited at 500 ° and 1000°C in order to determine the proportion of organic matter (O.M.) and the total carbonate c o n t e n t (T.C.), respectively (Dean, 1974). The weight loss (%} between 100 ° and 500°C is shown as organic matter (O.M.) in Tables I, II, VI and VII. The organic carbon content of sediments can be calculated from this figure by using the relationship organic C = 1 ignition loss 2.13 -+ 0.4

(Dean, 1974)

The weight loss (%) between 500 ° and 1000°C is corrected for the proportion of CO2 in CaCO3 (44%) to obtain the total carbonate c o n t e n t of sediments (Dean, 1974}, and is shown as T.C. in Tables I, II, VI, VII. These data are reported together with the metal content of sediments in Tables I and II. Aerial surveys of the nearshore zone at Whyalla (Fig.2) show the direction of wave fronts and the distribution of bare sand areas resulting from recent erosion or deposition. These features have been used in conjunction

228 with wind data for WhyaUa (Schwerdtfeger and Williams, 1975) to infer the net direction of longshore transport in the vicinity of the steel works, and the influence of a shore-connected breakwater (E1-Ashry and Wanless, 1977). Surface water parame ters

Several chemical parameters influence the depositional environment, the most important being the quantity of organic matter, oxidizing or reducing conditions in the water, pH, salinity, and temperature (Warren, 1981). Field pH measurements were made with a Metrohm AG CH-9100 Herisau E588 portable pH meter, using a combined glass electrode assembly. Conductivity was measured with a Townson portable conductivity meter 2103A, with full temperature compensation, using a TAO-type CG 210-p conductivity cell (K = 10). Water temperature was measured with a mercury bulb thermometer. The lead sulphide m e t h o d (Hatch DR-E1/2 portable test kit) was used to measure dissolved H2S and to identify redox state. The test relies on the use of reference colours from prepared standards, and allows immediate measurement of H2S in water at the test site. The range is limited to 0.1--5.0 mg 1-1, but could be extended by dilution of the sample. RESULTS The general distribution of metals in sediments

Complete dissolution of sediments collected near the blast furnace outfall with nitric, perchloric, and hydrofluoric acids (Agemian and Chau, 1976) indicated that approximately 25% of the total Cr, 45% total Cu and Fe, 60% total Mn, 80% total Pb and Zn, and all Cd were removed from samples by nitric acid extraction. The latter m e t h o d destroys organic matter and dissolves all precipitated and adsorbed metals, including those from industrial discharges, b u t does n o t completely dissolve silicate minerals (Agemian and Chau, 1976). Nitric acid soluble metal content, proportion of organic matter and total carbonate for sediment samples (surface 10 cm) collected near industrial centres in northern Spencer Gulf are shown in Table I. Samples from nonindustrial areas of the region and locations in Gulf St. Vincent, are recorded in Table II for comparison. A mean value for trace metal concentration in these sediment samples is used to represent a " b a c k g r o u n d " level in the following discussion of the distribution of metals in sediments. The values, shown at the b o t t o m of Table II, are 0.2 ppm Cd, 16 ppm Cr, 6 ppm Cu, 67 ppm Mn, 7 ppm Pb, and 27 ppm Zn. The full data on variations in metal concentration down the short cores are given by Harbison (1980), and analyses of five cores are shown in Table III. The general pattern of subsurface metal accumulation in the vicinity of the steelworks is exemplified by cores W2, W2M and F1. Core W l is from an eroding area, and reflects a change in the sedimentary regime.

Yellow sand White sand Yellow s a n d Brown sandy mud Brown sandy mud Brown sand Brown sand B r o w n silt Brown sand Black m u d Black m u d Brown sand Black m u d Brown sand Red sandy mud

Black s a n d y m u d Grey sandy mud Grey sand Grey sandy mud

Red mud

Grey mud

Whyalla FB33 F3 FB3 FB2 F2HW FBCr F1 FB1 Wl W2 Jan. W2 M a y W3 W3S W5 W7

P o r t Pirie WR2 WR3 WRB WRP

Port Augusta

T o r r e n s Island*

mid,

mid,

low, mid, mid, high,

mangroves

mangroves

seagrass mangroves mangroves mangroves

bare bare bare seedlings bare bare mangroves seagrass fibre bare mangroves mangroves mangroves mangroves bare mangroves

7

1

9 3 10 8

3 3 3 4 6 3 11 11 1 12 13 7 12 1 8

(%)

plant cover

high, low, mid, high, high, high, mid, sub, low, low, low, mid, high, low, high,

O.M.

Tidal level a n d

18

7

48 14 52 43

75 84 79 16 27 11 36 45 7 18 16 14 27 4 9

(%)

T.C.

0.2

--

23 3 2 --

---2 1 -3 3 1 6 6 7 7 1 --

Cd

31

41

20 16 7 26

8 10 8 -20 8 27 13 8 20 42 64 174 30 28

Cr

82

42

13 7 3 10

---6 9 3 13 13 5 18 19 15 27 3 50

Cu

7700

24000

8100 7000 1200 14600

1000 800 1000 4200 30300 2800 41300 11200 5600 69200 47000 29100 40000 166000 60800

Fe

p p m m e t a l in dried s e d i m e n t

O.M. = Organic m a t t e r , as i g n i t i o n loss at 500°C; T.C. = t o t a l c a r b o n a t e , f r o m i g n i t i o n loss at 1 0 0 0 ° C ; ( < 0 . 2 p p m Cd, Cu; < 1 p p m Cr, P b ) ; * T o r r e n s Island, G u l f St. V i n c e n t , n e a r Adelaide.

Sediment type

Sample

1540

320

148 950 113 378

75 70 100 67 540 50 810 340 235 908 981 825 800 3330 1473

Mn

113

38

335 208 113 329

24 -8 96 200 25 448 240 92 480 635 632 474 607 --

Pb

228

89

1090 196 87 170

128 134 130 675 1390 170 2880 1220 627 2280 2800 4977 3000 3240 492

Zn

= b e l o w d e t e c t i o n limit

Nitric acid soluble trace m e t a l c o n t e n t o f i n t e r t i d a l s e d i m e n t s ( t o p 10 c m ) near industrial o p e r a t i o n s in S p e n c e r G u l f

TABLE I

~v

Wakefield Gawler 1 Gawler 2 Gawler 3 Gawler 4

Grey mud Sandy mud Shelly sand Grey mud Grey muddy sand

Red sand Grey sand Grey sandy mud Grey sand Grey fine sand Grey sand Grey sand Grey sandy mud Grey sand Pink sandy mud Yellow sand Yellow sand Grey sand

Sediment type

mangroves seedlings

bare mangroves young mangroves

high, mid,

high, high, high,

rocky bare mangroves bare seagrass bare bare mangroves mangroves algal m a t bare bare seagrass

6 14 19

7

66 34 29

32

29

14 93 77 77 79 54 64 39 36 32 18

7 2 5 3 5 15 3 21 6 2 17

18

4 29

1

(%)

T.C.

2

(%)

plant cover

high, mid, mid, low, mid, low, mid, high, high, high, low, mid, low,

O.M.

T i d a l level a n d

----

--

--

------------

--

--

13 12 -11 14 ~ 6

16

--7 -3 3 2 8 -6 7 -17

Cu

31 24 5 25 27

--15 21 19 12 9 24 17 20 20 12 7

Cr

14900 10800 2500 11700 20400

1100 800 7600 1100 1800 2200 1700 7400 1600 11500 16600 2510 4600

Fe

p p m m e t a l in d r i e d s e d i m e n t Cd

~¢ 6 7

123 85 70 100 90

20 25 51 48 60 51 60 78 30 128 99 57 43

Mn

~ 7

4 5 3 10 7

------5 20 -29 -17 21

Pb

~ 27

34 28 8 38 28

10 30 25 19 37 16 30 16 4 57 21 36 44

Zn

O.M. = O r g a n i c m a t t e r as i g n i t i o n l o s s at 5 0 0 ° C ; T . C . = t o t a l c a r b o n a t e f r o m i g n i t i o n l o s s at 1 0 0 0 ° C ; - - = b e l o w d e t e c t i o n level ( < 0 . 2 p p m C d , C u ; < 1 p p m Cr, P b ) ; ~ = a v e r a g e m e t a l c o n t e n t o f s e d i m e n t s , u s e d as ' b a c k g r o u n d level'.

Port Port Port Port Port

G u l f St. V i n c e n t

Black Point 1 Black Point 2 Curlew Point TB1 TB2 Wl0 Wll W12M 8 mile Ck 2 Chinaman Ck C h i n a m a n Ck B Port Germein Fish Bay

Spencer Gulf

Sample

N i t r i c a c i d s o l u b l e t r a c e m e t a l c o n t e n t o f i n t e r t i d a l s e d i m e n t s ( t o p 10 c m ) f r o m n o n - i n d u s t r i a l a r e a s o f S p e n c e r G u l f a n d G u l f St. V i n c e n t

T A B L E II

b~ 5o O

231 TABLE III Subsurface variation in metal concentration (nitric acid soluble) in intertidal sediment cores (in ppm). Depth intervals are discrete colour horizons

-

Core

Depth from surface (cm)

Cd

Cr

Cu

Fe

8MC1 (south of Whyalla)

0--15 15--20 20--30 30--45

-----

-4 33 46

3 2 12 24

1600 2800 27100 21300

31 33 55 81

-----

3 1 35 48

W2 (works area)

0-8 8--20 20-35 35--40

6 2 1 1

20 10 13 18

18 8 13 15

69200 15500 5300 6400

908 274 72 28

480 110 3 50

2280 456 19 19

W2M

0-20 20-30 30-47

6 ---

42 21 33

19 7 17

47000 12500 10000

981 236 76

635 32 --

2800 150 16

Wl

0-6 6--20 20-32 32--45

1 -4 --

8 7 17 17

5 3 20 15

6900 4200 52000 10800

270 199 630 103

111 74 402 19

726 528 1584 73

F1

0-10 10-22 22--45

3 ---

27 13 17

13 ---

41300 3100 5000

810 47 43

448 ---

2880 65 5

-

Mn

Pb

Zn

= below detection limit (<0.2 ppm Cd, Cu; <1 ppm Cr, Pb).

C o r e 8MC1, f r o m E i g h t - M i l e C r e e k , s o u t h o f W h y a l l a ( F i g . l ) , s h o w s o n l y b a c k g r o u n d levels o f m e t a l s in r e c e n t s e d i m e n t s , b u t t h e h i g h e r c o n c e n t r a t i o n s o f Cr, C u a n d Zn a t 3 0 - - 4 0 c m m i g h t be r e l a t e d t o t h e g r e a t e r m e t a l c o n t e n t o f d i s c h a r g e s in e a r l i e r years. I n t e r t i d a l s e d i m e n t s r e m o t e f r o m i n d u s t r i a l l o c a t i o n s ( T a b l e II) h a v e l o w c o n c e n t r a t i o n s o f n i t r i c a c i d s o l u b l e Cd ( < 0 . 2 p p m ) , Cr a n d P b ( < 1 0 p p m ) , F e (< 2%), M n ( < 1 0 0 p p m ) a n d Z n (< 5 0 p p m ) . W h y a l l a s e d i m e n t s have h i g h e r c o n c e n t r a t i o n s o f Cd ( 2 - - 7 p p m ) , Cr ( 2 0 - 1 5 0 p p m ) , Mn ( 3 0 0 - - 9 0 0 p p m ) , Pb (100-600 ppm), Zn (2000--5000 ppm) and, near the steelworks, 2--16% Fe. S a n d y m u d from the intertidal zone at Mt Ferguson (WR2), a b o u t 7 km n o r t h e a s t o f t h e P o r t Pirie s m e l t e r , c o n t a i n s 23 p p m o f Cd, 3 3 0 p p m o f Pb, 1 1 0 0 p p m o f Z n , 0.8% F e a n d 1 5 0 p p m o f M n ( T a b l e I). The reducing oxalic acid/ammonium oxalate extraction, which removes i r o n p r e s e n t as a m o r p h o u s o x i d e p h a s e s , d i s t i n g u i s h e s t h e s e d i m e n t a c c m n u l a t i o n s o f F e a n d Mn a t W h y a l l a , f r o m F e a n d M n in s e d i m e n t s f r o m o t h e r areas. T h e p r o p o r t i o n o f n i t r i c a c i d s o l u b l e F e a n d M n r e m o v e d f r o m sedim e n t s b y o x a l i c a c i d is s h o w n in T a b l e IV. S e d i m e n t s in t h e v i c i n i t y o f t h e

232 TABLE IV Proportion of nitric acid soluble Fe and Mn removed by oxalic acid/ammonium oxalate from surface sediment Sample

Fe Nitric acid soluble Fe (ppm)

Mn Oxalic acid soluble fraction (%)

Nitric acid soluble Mn (ppm)

Oxalic acid soluble fraction (%)

A. S t e e l w o r k s area

F1 FB1 F2HW FB2 Wl W2M W3 W5 W2 W3S

41300 11200 30340 4170 5600 47000 29000 166000 69200 40000

57 45 45 30 53 62 49 39 51 50

810 340 540 67 235 981 825 3330 908 800

48

44 29 39 33 37 43 82 48 56 45 ~ 55

B. O t h e r areas

8MC W10 Wll W12 Bl. Pt. Curlew Pt. Ch. Ck. L. Ch. Ck. H. WR1 WR2 WR B

1600 2200 1700 11010 790 7600 16560 11470 2510 8160 1200

11 13 13 17 15 23 17 28 27 19 10 18

30 51 60 95 25 51 99 128 57 148 113

< 10 < 10 <10 10 20 24 24 30 21 18 <10 ~ 16

W h y a l l a s t e e l w o r k s y i e l d e d a m e a n 48% e a s i l y r e d u c i b l e F e , a n d 55% Mn, while s e d i m e n t s f r o m o t h e r areas, i n c l u d i n g P o r t Pirie, y i e l d e d 18% F e a n d 16% Mn ( F i g . 5 ) . C h a n g e s in t h e s o l u b i l i t y o f i r o n w i t h d e p t h in s h o r t c o r e s is also d e m o n s t r a t e d b y t h e o x a l i c acid e x t r a c t i o n o f s a m p l e s f r o m e a c h h o r i z o n , t h e p r o p o r t i o n o f e a s i l y r e d u c i b l e iron d e c r e a s i n g m a r k e d l y w i t h d e p t h ( T a b l e V). L o c a l e l e v a t i o n s in t h e t r a c e m e t a l c o n t e n t o f i n t e r t i d a l s e d i m e n t s a t P o r t A u g u s t a m a y be a t t r i b u t e d t o u r b a n r u n o f f , or t o e m i s s i o n s f r o m t h e p o w e r s t a t i o n s o u t h o f t h e t o w n , b u t w i t h t h e e x c e p t i o n o f Cr a n d Cu, t h e s e are l o w c o m p a r e d t o t h e m e t a l c o n t e n t o f s e d i m e n t s n e a r P o r t Pirie a n d W h y a l l a ( T a b l e I).

233 TABLE V Variation in recovery of iron with depth down core Sample

Depth from surface (cm)

Nitric acid soluble Fe (ppm)

Fraction dissolved in oxalic acid (%)

W2

0--8 8--20 20--35 35--40

69200 15540 5320 6360

51 43 5 3

W2M

0--20 20--30 30--47

46990 12460 10040

62 17 4

TB1

0--20 20--30

1120 1070

19 4

Wl0

0--2 2--24 24--32

1630 2700 6000

15 11 6

WR1

0--15 15--40

2510 10130

27 5

The distribution o f individual metals Possible influences on the distribution o f metals in sediments were examined by calculating correlations for the variables: trace metal c o n t e n t (ppm d ry weight), organic m a t t e r and total carbonate (% dry weight), and the e n v i r o n m e n t of deposition (Tables VI and VII). Organic m a t t e r (O.M.), measured as the weight lost by dried sediment between 100 ° and 500°C, varied from 1% in sands from exposed beaches to 15--20% in mangrove sediments or muds colonized by algal mats. The p r o p o r t i o n of weight lost by dried sediments between 500 ° and 1000°C was used to calculate the total carbonate c o n t e n t (Dean, 1974), which ranged f r o m 4 to 7% in sands of terrestrial origin to 90% in shelly sands f r o m exposed beaches. The variable De, a score t o describe the depositional e n v i r o n m e n t at the sampling point, is the sum of values assigned t o the p r e d o m i n a n t sediment grain size, tidal level, and presence of m a c r o p h y t e growth which baffles water movement. These features were scored 1, 2 and 3 points for sand, sandy mud, and m ud, with similar values for the low, mid, and high tidal levels. M a c r o p h y t e growth on the sediment surface was valued +2. T he total score is related inversely to the energy of deposition in the sampling area, e.g. a bare sand bar at the low tidal level has a De value = 2, while a sandy-mud covered with sea grasses at the same tidal level has a De value = 5. F o r mangrove muds at the u p p e r tidal level, De = 8.

234 TABLE VI C o r r e l a t i o n s for 10 variables in all N o r t h e r n S p e n c e r G u l f s e d i m e n t samples

Cd Cr Cu Fe Mn Pb Zn O.M.

T.C. De

Cd

Cr

1.000 x x x x 0.536 0.442 x x x

1.000 0.455 x x 0.507 0.566 x x 0.720

Cu

Fe

1.000 x 1.000 x 0.958 x 0.658 x 0.635 0.477 x --0.508 --0.462 0.643 x

Mn

1.000 0.660 0.627 x --0.476 x

Pb

Zn

1.000 0.916 1.000 x x --0.421 --0.410 x x

O.M.

T.C.

De

1.000 x 0.525

1.000 x

1.000

x = r < 0 . 3 5 , w h i c h is P = 0.05 for 30 df (n = 31 individual samples); O.M. = organic m a t t e r ; T.C. = t o t a l c a r b o n a t e ; D e = d e p o s i t i o n a l e n v i r o n m e n t ; C d - - Z n = p p m nitric acid soluble m e t a l in dried s e d i m e n t . T A B L E VII C o r r e l a t i o n m a t r i x for 10 variables in s e d i m e n t s f r o m n o n - i n d u s t r i a l areas in S p e n c e r G u l f a n d G u l f St. V i n c e n t ( n o d e t e c t a b l e Cd) Cd Cd Cr Cu Fe Mn Pb Zn O.M.

T.C. De

Cr

Cu

1.000 0.698 1.000 0.850 0.828 0.711 0.562 x x x x 0.657 0.830 x --0.678 0.724 0.584

Fe

1°000 0.796 x x 0.825 --0.660 0.718

Mn

1.000 x x 0.695 --0.424 0.764

Pb

Zn

1.000 0.701 0.569 x x

1.000 0.507 x x

O.M.

1.000 --0.568 0.644

T.C.

1.000 --0.418

De

1.000

x = r < 0 . 4 2 , w h i c h is P = 0.05 for 20 df; O.M. = organic m a t t e r ; T.C. = t o t a l c a r b o n a t e ; De = d e p o s i t i o n a l e n v i r o n m e n t ; C d - - Z n = p p m nitric acid soluble m e t a l in dried s e d i m e n t . The sheltered depositional environment (high De value) correlates with organic matter, but not with total carbonate, which correlates negatively with most metals (Cu, Fe, Mn, Pb, Zn). Correlations between all variables at the 95% level of significance (r = 0.35) shown for 31 Spencer Gulf sediment samples in Table VI, indicate common origins for trace metals in the ores processed at Whyalla (Fe and Mn) and Port Pirie (Cd, Pb and Zn). Other metal/metal correlations found for sediments from non-industrial areas are considered with results for individual metals below.

235

Cadmium correlates with Pb and Zn, and the highest concentrations in this study were found near Port Pirie (Fig.3). Ward and Young (1981) report very high concentrations of Cd (169 and 267 ppm), Pb (2630 and 5270 ppm) and Zn (7283 and 16667 ppm) in the intertidal sediments at the mouth of First Creek, into which effluent is discharged from the smelters at Port Pirie. As the aqua regia extraction used by these authors would remove approximately the same amount of metal from sediments as the nitric acid/hydrogen peroxide method (Bloom, 1975) the data can be compared. No correlation has been found between Cd and other metals, and except for the Port Pirie samples, the concentration of Cd exceeds 0.2 ppm only in sediments from the immediate vicinity of the steelworks outfall at Whyalla (Table I). Chromium concentrations exceeding 30 ppm are found only in sediments collected inside the embankment north of the steelworks, and probably come from that outfall. The absence of any correlation with Fe and Mn in industrial areas suggests that Cr is not associated with the ore. The correlation with organic matter and the depositional environment (Table VI) is supported

I ~ . ~

x 267 LI

II

xl

j/"

~,

b

J

.1 .,, -'"

20x

I

lOikm alB ii

XlO-

' .... •-.-

,lOx

• .

.

.- -"

x5 -

/:

--~ no data 0

" J: 138000 t

Fig.3. The general distribution of metal-enriched sediments in northern Spencer Gulf (enrichment = ppm metal in sediment/'background' concentration). (Data from D o ~ i s and Warren, 1980; Ward and Young, 1981; Ferguson et al., 1983; and Harbison, 1984, this volume).

236 by correlations with Fe, Mn, organic matter, and a high D e value in sediments from non-industrial areas (Table VII), and suggests that Cr discharged into Gulf waters will accumulate in the fine-grained, highly organic sediments deposited under sheltered conditions. Such conditions are found adjacent to the blast furnace outfall at WhyaUa, and probably confine the distribution of Cr wastes to that locality. C o p p e r correlates with Cr, organic matter and the depositional environm e n t in both industrial and more remote sediments and is associated with Fe and Mn in the latter (Table VII). This association suggests a controlling mechanism for both Cr and Cu, as well as a c o m m o n sedimentary sink in the highly organic muds. Ward and Young (1981) also conclude that the distribution of Cu at Port Pirie is probably controlled by features of the sedim e n t a r y environment, such as total organic carbon and fine grain size. Iron and manganese. In non-industrial areas, Fe and Mn correlate with each other, with organic matter in sediments, and with the sheltered depositional environment. A negative correlation is f o u n d with shelly sands. In industrial areas, the very high correlation with each other is related to the ore processed at Whyalla. Fe and Mn also correlate with Pb and Zn in industrial sediments, which at Whyalla contain Pb and Zn in concentrations up to 100 times background level. The absence of any correlation between Fe and Mn and organic matter or with the depositional environment in industrial sediments is probably due to the d o m i n a n t influence of the point source at Whyallm Wave erosion of the seaward side of the e m b a n k m e n t (Fig.2) also contributes a coarse brown sand to the longshore sediment budget. This sedim e n t (W5, Table I) contains more than double the a m o u n t of Fe and Mn found in sediments near the steel works outfall, and is derived directly from the rock used to construct the wall. The concentration of Pb and Zn in this material is similar to that in other sediments near the outfall, while Cd, Cr and Cu are lower, suggesting that they are not derived from the iron ore. L e a d and zinc. Pb and Zn are found in very high concentrations at Whyalla, and correlate with Fe, Mn and Cr (Table VI). No correlation has been found between these metals in sediments from non-industrial areas (Table VII) which suggests a c o m m o n origin in the Whyalla operation. Although the role of Mn and Fe in abstracting trace metals from the overlying water to the sediments has been extensively discussed (Theis and Richter, 1979), evidence from the present study does n o t distinguish between origin and control for the nitric acid soluble fraction in industrial sediment. Oxalic acid extraction of these samples, however, shows a correlation at the 99% significance level for Zn with Fe and Mn (0.57 and 0.56, d f = 19), but none for Pb. This may indicate that Zn occurs in association with the amorphous oxides, and could become available under reducing conditions, while Pb is more firmly bound in the nitric acid soluble fraction. Ward and Young (1981) found no

237 correlation for Pb and Zn with Mn in Port Pirie sediments and data for Fe were not reported. The possibility remains that amorphous iron oxides could influence the distribution of Zn, and that Zn and Pb have different forms in Whyalla sediments. The large transport vehicles constantly moving along the steelworks' shoreline are a possible source of Pb in sediments which has n o t been considered. Negative correlations of Cu, Fe, Mn, Pb and Zn with the carbonate content of sediments in industrial areas of Spencer Gulf probably reflect the low metal content of coarse grained shelly sands from exposed beaches, rather than the influence of any mineral c o m p o n e n t of the sediment. In fact, Dossis and Warren (1981) f o u n d that calcareous shells, analysed as a separate sediment component, had a large capacity for metals and, because of their abundance, were the main reservoir for these metals in contaminated sediments at Port Pirie. Chemical parameters in shallow water

Environmental factors considered to effect the migration of trace metals at the sediment/water interface are redox potential (Lu and Chen, 1977), pH (Salomons and Mook, 1980), salinity (McKelvie, 1979) and temperature (Warren, 1981). James (1978) considers pH and Eh to be the 'master variables' in describing the behaviour of metals in the natural environment. Changes in these parameters are particularly relevant in the northern part of the South Australian gulfs, where the p h e n o m e n o n known as " d o d g e tide" (Bye, 1976; Easton, 1978) can result in a layer of shallow water remaining stationary over the intertidal m u d flats for more than 24 h. This water m a y show wide variations in pH, temperature and dissolved H2S in the same 24-h period, and heavy rain can produce abrupt changes in salinity. Surface water parameters have been measured over a period of one year, January 1979--January 1980, in a variety of tidal and weather conditions. The range of temperature, pH, dissolved H2S and salinity recorded is given in Table VIII. Measurements of pH, Eh and solar irradiance (400--700 nm) have been made subsequently in water overlying intertidal sediments in Gulf St. Vincent, and are similar to the observations made in Spencer Gulf. Table IX shows changes in these parameters over a 24 h period during a TABLE VIII Range of temperature, pH, H2S and salinity in shallow water (< 10 cm)overlying intertidal sediments in Spencer Gulf Temp. (°C) low high

pH low

H~S (mg I~) low high

high

Day

15

36

7.5

9.5

<0.1

1.0

Night

12

20

7.0

8.1

<0.1

>5.0

Salinity (°/oo) low high 19 rain 34

58.5 47

238 TABLE IX Diurnal variation in water temperature, pH, Eh, and dissolved oxygen over intertidal sediments 29--30/8/82; water depth = 9 +~ 1 cm Time (h)

Water temperature (°C)

pH units

1500 1600 1700 1800 2100 2400 0200 0400 0600 0800 1000 1100 1200 1300 1400 1500

18 18 18 17 15 14 13 13 13 13 13 13 14 16 18 19

9.0 8.9 9.0 8.8 8.6 8.4 8.3 8.2 8.2 8.0 8.4 8.6 8.7 9.0 9.0 9.1

Eh (mV) + 250 + 240 + 230 + 180 + 70 + 70 +80 + 80 + 100 + 120 + 170 + 210 + 160 + 220 + 250 + 240

D.02* (% sat.) > 100 > 100 > 100 100 34 4 0 0 0 16 100 > 100 > 100 > 100 > 100 > 100

*Dissolved oxygen is measured with a gold membrane electrode as percent saturation using air as a standard 100%. " d o d g e " t i d e , w h e n t h e w a t e r d e p t h v a r i e d less t h a n 2 c m d u r i n g t h e 2 4 h. M e a s u r e m e n t s w e r e m a d e in a l a r g e p o o l s h e l t e r e d b y m a n g r o v e t r e e s . T h e sediment surface supported a mat of diatoms, blue-green algae, and some m a c r o s c o p i c g r e e n a l g a e (Enteromorpha). MAJOR INFLUENCES ON THE DISTRIBUTION OF METALS IN NEAI~SHORE SEDIMENTS

Point source P r o x i m i t y t o a p o i n t s o u r c e a p p e a r s t o b e a m a j o r i n f l u e n c e o n t h e dist r i b u t i o n o f m e t a l s in s e d i m e n t s a t W h y a l l a , w h e r e c o n c e n t r a t i o n s o f Z n , M n a n d P b a r e 5 0 - - 1 0 0 t i m e s g r e a t e r in s e d i m e n t s a d j a c e n t t o t h e s t e e l w o r k s a r e a t h a n in m o r e r e m o t e s e d i m e n t s . A t P o r t P i r i e , o n t h e e a s t e r n s i d e o f t h e g u l f ( F i g s . 3 a n d 4) W a r d a n d Y o u n g ( 1 9 8 1 ) a l s o r e p o r t a r a p i d d e c r e a s e in t h e c o n c e n t r a t i o n o f t h e s e m e t a l s in s e d i m e n t s w i t h i n c r e a s i n g distance from the effluent discharge point. C d , h o w e v e r , m a y b e m o r e w i d e l y d i s p e r s e d t h a n Z n a n d M n , w i t h inc r e a s e d m o b i l i t y d u e t o its c o m b i n a t i o n w i t h t h e c h l o r i d e i o n in s e a w a t e r (James, 1978; Warren, 1981). Analysis of sediments from transects across the nearshore zone at Port Pirie showed the highest concentrations of Pb, Z n a n d M n a t s t a t i o n A 1 , n e a r e s t t h e o u t f a l l , b u t t h e h i g h e s t C d c o n t e n t in

239

xi? 32 o

10

....

.........:.:i ........

,I

r Ix ....

Ill

f~

.......'~."~" ...'

.

.lOox

i

lOlk rn

.... ~.-,, • r'i

richment

--O no data

-

o

~

-sox

.o

1371°4s'

Jl

..j..r~

13~° ° ° '

Fig.4. The general distribution of metal-enriched sediments in northern Spencer Gulf. See further caption Fig. 3.

sediments from the second station out, where the element was found to be strongly associated with seagrass detritus (Ward and Young, 1981). From this point Cd decreased rapidly to an undetectable level in sediments a b o u t 10 km from the ouffall.

Littoral transport Circulation studies undertaken for the entire Spencer Gulf by Tronson {1974) and Bullock (1975) show a northward direction of water m o v e m e n t along the western shoreline for both wind-driven circulation and thermohaline current models. Aerial photographs of the coastal zone and wind data for Whyalla support the inference that the dominant longshore transport in this area is northwards, into False Bay (Schwerdtfeger and Williams, 1975). The nearshore distribution of metals is thus likely to be asymmetrical, skewed in a direction determined by the longshore current. The very low level of metals in intertidal sediments south of the steelworks, and high concentrations in False Bay Sediments to the north, support this suggestion (Fig.2). The proportion of oxalic acid soluble Fe and Mn, high in sediments from the works area, is also higher in False Bay sediments than in those south of the town (Table IV).

240 Longshore transport may also be redirected by man-made coastal structures. A shore connected breakwater functions as a barrier to the established pattern of littoral transport, resulting in the accumulation of material on the updrift side. If a narrow entrance is created by the breakwater, the increased velocity of the tidal current may also erode the opposite shoreline, and form a silted tidal delta in the semi-enclosed area (Johnson, 1956). Such changes in sedimentation have occurred at Whyalla, where a wall has been constructed along the shoreline to confine water discharged from the steel works into False Bay. The northern end of the wall (Fig.2) was left incomplete to maintain tidal circulation to mangroves growing on the opposite shoreline. Deep scouring of this intertidal mud flat (Wl) and undermining of mangrove trees is apparent opposite the end of the embankment, and the new area of deposition inside is clearly visible on recent aerial photographs (Fig.2). The trace metal content of cores from the Wl area is higher at 20--30 cm depth than at the surface, while cores from W2 and F1 on either side of the eroded area show the highest metal content in the surface sediments.

Environment of deposition Modification of prevailing winds and tidal currents by shoreline and nearshore features will also influence the sorting and distribution of grain size fractions in the sediment system, and ultimately determine the physical characteristics of the depositional environment. The well recognized enrichment of heavy metals in the finest size fraction of sediments (Warren, 1981) suggests that the sheltered environment of deposition will act as a sink for metals discharged into the marine environm e n t (Harbison, 1981). The correlations found for Cr, Cu, Fe and Mn with the low energy depositional environment (Tables VI and VII) in the present study support this suggestion, particularly where the source is more diffuse (Table VII). Proximity to a point source overrides this influence in the case of Pb and Zn at Port Pirie (Ward and Young, 1981) and at Whyalla. The fine sediment deposited in the sheltered environment also provides a substrate for a variety of micro and macro organisms, which m a y further reduce water movement, and encourage the deposition of still finer fractions. Sheltered intertidal zones in Spencer Gulf are colonized by seagrasses at the low tidal level, and by mangroves on the landward side. Both types of macrophyte growth baffle wave action, by a dense growth of strap-like leaf blades in seagrass areas, and by the vertical projection of mangrove pneumatophores, or aerial roots, from the m u d surface. The binding effect of gelatinous mats of blue-green algae is also apparent on the m u d surface where sufficient light is available. Exposure to air, and the presence of photosynthetic organisms, usually maintains an oxidized layer at the sediment surface. This layer varies in thickness, depending on the porosity of sediments, the activity of burrowing organisms, and the a m o u n t of organic matter present. Sandy sediments of

241

terrigenous origin, extensively irrigated by benthic fauna, may have an aerobic zone more than 20 cm thick. Fine clayey muds which are less permeable, and sealed at the surface by a gelatinous algal film, may have an oxidized layer only 1 mm thick overlying black anaerobic mud. This condition is typical of very sheltered environments, where the decaying organic matter contributed and trapped by mangroves and seagrasses supports intense microbial sulphate reduction, and facilitates the precipitation of metals as sulphides. The sheltered depositional environment, by the initial accumulation of the finest sediment fractions, appears to ultimately provide an optimum sink for the accumulation of metal wastes, and the availability of such locations could be an important influence on the final distribution of wastes discharged to the marine environment. The chemical environment in shallow water

The incorporation of transported metals into a sedimentary sink will be largely controlled by the chemical environment in the overlying water (Lu and Chen, 1977; McKelvie, 1979; Salomons and Mook, 1980). Photosynthetic organisms at the sediment/water interface can produce wide fluctuations in the Eh and pH of shallow overlying water with changes in light intensity (Table IX). During periods of high light intensity, the temperature and pH of water overlying seagrasses or algal mats is usually high, conditions which favour carbonate precipitation, and the adsorption of trace metals onto particulates (Farrah and Pickering, 1976; Salomons and Mook, 1980; Warren, 1981). Gnaiger et al. (1976) also recorded very high pH in the surface layer of sediments on an intertidal beach, and demonstrated the light dependency of the changes. Baas-Becking et al. (1960) referred to reductive photosynthesis by algae or photosynthetic bacteria as the "biogenic master reaction' in the environment, capable of producing significant changes in one or both parameters (Eh and pH). The dominance of cyanobacterial mats as primary producers (and their role in sulphate reduction) in intertidal sediments of northern Spencer Gulf, is described by Bauld et al. (1980) who also recorded high surface temperatures and salinity during bright sunlight. Field measurements show that the pH in shallow water declines after dark, and dissolved H2S in water overlying highly organic muds gradually increases (Table VIII). H2S exceeded 5 mg 1-1 over intertidal sediments at night, but was not recorded during the day, except where the surface layer was disturbed. Similar observations have been made by Bella et al. (1972) and Hansen et al. (1978). Friedman and Foner (1982) produced rapid changes in the Eh of seawater surrounding algal mats from Red Sea pools by alternating periods of sunlight and darkness in the laboratory. Present studies (Harbison, unpublished data) using laboratory cultures of intertidal muds with a variety of light sources suggest that diurnal changes in the Eh of shallow water are controlled

242

by photosynthetic sulphide oxidizing bacteria, and that pH changes are controlled by green algae. Similar results are reported by Blackburn et al. {1975) and by Baas-Becking and Mackay {1955). The chemical environment in shallow surface water under these conditions may affect the mobility of trace metals in surface sediments. Chemical models have shown that Cd, Cu, Pb and Zn increase in water overlying contaminated sediments as the environment becomes more oxidizing, while Mn and Fe increase under reducing conditions (Lu and Chen, 1977). Analyses of filtered water samples collected in a tidal swamp at dawn and in the early afternoon of the same day during a " d o d g e " tide showed marked decreases in the concentration of Fe and Mn as conditions became more oxidizing, supporting the observations of Lu and Chen (1977) (Harbison, unpublished data). Extremes of temperature and salinity also occur over the very wide expanses of tidal flat, particularly when there is little water movement (Table VIII). Rain is infrequent in the northern Gulf area ( < 3 5 0 mm yr-') b u t occasional very heavy showers may occur in summer, which can suddenly reduce the salinity of shallow surface water from a b o u t 50 to 20°/~. High temperatures and lowered salinity are known to increase the toxicity of trace metals to juvenile fish and crustaceans (Sullivan, 1977). Most epibenthic organisms and macroscopic infauna obtain their food from the sediment surface (James, 1978; L u o m a and Bryan, 1981; Warren, 1981). However, the surface layer of sediment often contains the highest concentration of trace metals. This has been demonstrated for 50 cm cores collected in the Whyalla area (Table III) and also for offshore vibrocores taken near Port Pirie (Ferguson et al., 1983). The sheltered depositional environments in Spencer Gulf support dense populations of marine and intertidal species, including juvenile fish and crustaceans, in shallow waters where chemical changes at the sediment/water interface could facilitate the release of trace metals from sediments, and enhance their impact on marine organisms.

Remobilization of sediments Metals incorporated in the sediments are subject to a variety of physical, chemical, and biological influences which could affect their solubility and redistribution (Luoma and Bryan, 1981; Warren, 1981). The chemical changes discussed above are most relevant to the sediment surface, b u t physical disturbance can result in the exposure of deeper layers of sediment. Turbulent conditions created in shallow water by strong winds or scouring tidal currents can disturb deeper anaerobic sediments, resulting in the oxidation or redistribution of sulphide minerals. Dredging is likely to remobilize large volumes of metal enriched sediment in areas where smelting operations are located near harbour facilities. The association of trace metals with fine grained anaerobic muds is now so well documented that sediment texture and colour from field observation

243

have been included in the guidelines for rapid classification of dredged material prepared by the United States Environmental Protection Agency (1977). These criteria, subject to review as additional data become available, are based on the total metal content of bulk sediment samples from more than 100 harbours analysed since 1967. The recommended levels refer to the acceptability of dredged sediments for open lake dumping, and may be lower than metal concentrations applicable to the marine environment. However, both Whyalla and Port Pirie rely on the regular dredging of channels through very shallow subtidal zones to maintain shipping access to the smelters, and to other loading facilities (Fig.l). These dredged channels are dee~ sections which act as sediment traps, accumulating the finer sediment fractions (Warren, 1981). The dredged spoil is then likely to contain a high l~roportion of fine material, and a potentially high accumulation of trace metals. At Whyalla, dredge spoil is dumped just below the 10 m contour, off the False Bay shoreline (Fig.l), and could be incorporated in the very wide intertidal fiats in that area. Concentrations of Pb, Zn, Cd and Mn in samples from the sediment surface near dredged shipping channels at Whyalla and Port Pirie are compared with USEPA guidelines in Table X. The Spencer Gulf samples generally far exceed the suggested limits for open water dumping (USEPA, 1977). TABLE X Pb, Zn, Cd and Mn content of Pt. Pirie and Whyalla sediments compared with USEPA guidelines for classification of dredged material (USEPA, 1977) Element

Pb Zn Cd Mn

USEPA guidelines (ppm metal)

Spencer Gulf sediments (ppm metal)

Unpolluted

Heavily polluted and unacceptable for open water dumping

Pt. Pirie WR2 WR3 2 km offshore*

Whyalla W2 W5

F1

60 200 6

335 1090 23

208 196 3

600* 1000" 105"

635 607 2800 3240 6 1

448 2880 3

500

148

950

no data

981 3330

810

40 90 No lower limit established 300

*Data from Ferguson (unpubl.).

CONCLUSIONS I n t e r t i d a l s e d i m e n t s n e a r m e t a l i n d u s t r i e s in n o r t h e r n S p e n c e r G u l f h a v e

surface enrichments of nitric acid soluble Cd, Cr, Fe, Mn, Pb and Zn up to two orders of magnitude greater than sediments from non-industrial areas

244

13710451

4*

[~!...

nitric solaci ublde3. Fe

*-.,

/'2O ,.

.,:"

~"

::.-~:.:~

...............

%Fe

...."

""

I

lokm I

I

Fig.5. The general distribution of metal-enriched sediments in northern Spencer Gulf. See further caption Fig.3.

(Figs.3--5). Controlling influences on the distribution of these metals appear to be: (1) proximity to the source; (2) the direction of littoral transport; and (3) the environment of deposition. Changes in sedimentation resulting directly from a shoreline construction at Whyalla are predictable, and suggest the use of such structures to direct the transport of contaminated particulates to desired locations. The sheltered environment of deposition presents optimum conditions for the accumulation of trace metals in the near-shore zone. These tidal flats and swamps comprise about one third of the marine environment in northern Spencer Gulf, and are known to maintain juvenile populations of fish and crustaceans. Natural fluctuations in the chemical environment, particularly during " d o d g e " tides, could facilitate the remobilization of metals from the sediments, and enhance their impact on marine organisms. The availability of such depositional environments, either natural or man-made, and the pattern of littoral transport, are factors which should be taken into account when coastal sites are considered for industrial development.

245 ACKNOWLEDGEMENTS T h e s t u d y was p a r t l y s u p p o r t e d b y a grant f r o m the B r o k e n Hill Propriet a r y C o m p a n y Ltd. at Whyalla t o the C e n t r e for E n v i r o n m e n t a l Studies at T h e University o f Adelaide. T h e assistance o f the f o r m e r D i r e c t o r , Dr. J.R. Hails, is a c k n o w l e d g e d in initiating the project. Dr. V.A. G o s t i n o f Adelaide University, Dr. H. V e e h o f Flinders University o f S o u t h Australia and Dr. D. S t e f f e n s e n of the S o u t h Australian D e p a r t m e n t o f E n g i n e e r i n g and Water S u p p l y are t h a n k e d f o r h e l p f u l advice and criticism. REFERENCES Agemian, H. and Chau, A.S.Y., 1976. Evaluation of extraction techniques for the determination of metals in aquatic sediments. Analyst, 101: 761--767. Baas-Becking, L.G.M. and Mackay, M., 1955. Biological processes in the estuarine environment. VA The influence of Enteromorpha upon its environment. Proc. Kon. Ned. Akad. Wet., Set. B, 59: 109--123. Baas-Becking, L.G.M., Kaplan, I.R. and Moore, D., 1960. Limits of the natural environment in terms of pH and oxidation reduction potentials. J. Geol, 68: 243--284. Bauld, J., Burne, R.V., Chambers, L.A., Ferguson, J. and Skyring, G.W., 1980. Sedimentological and geobiological studies of intertidal cyanobacterial mats in northeastern Spencer Gulf, South Australia. In: P.A. Trudinger, M.R. Walter and B.J. Ralph (Editors), Biogeochemistry of Ancient and Modern Environments. Australian Academy of Science, Canberra, A.C.T., pp.157--166. Bella, D.A., Ramm, A.E. and Peterson, P.E., 1972. Effects of tidal flats on estuarine water quality. J. Water PoUut. Control Fed., 44: 541--556. Blackburn, T.H., Kleiber, P. and Fenchel, T., 1975. Photosynthetic sulphide oxidation in marine sediments. Oikos, 26: 103--108. Bloom, H., 1975. Heavy Metals in the Derwent Estuary. Department of Chemistry, University of Tasmania, Hobart, Australia. Bullock, D.A., 1975. The general water circulation of Spencer Gulf, South Australia, in the period February--May. Trans. R. Soc. South Aust., 99: 43--53. Burne, R.V., 1981. Field Guide to the Coastal Complexes of Spencer Gulf. Baas-Becking Geobiological Laboratory, Canberra, A.C.T., 30 pp. Butler, A.J., Depers, A.M., McKillup, S.C. and Thomas, D.P., 1977. Distribution and sediments of mangrove forests in South Australia. Trans. R. Soc. South Aust., 101: 35--45. Bye, J.A.T., 1976. Physical oceanography of Gulf St. Vincent and Investigator Straight. In: C.R. Twidale, M.J. Tyler and B.P. Webb (Editors), Natural History of the Adelaide Region. Royal Society of South Australia, Adelaide, S.A., pp.143--160. Dean Jr., W.E., 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: comparison with other methods. J. Sediment. Petrol., 44: 242--248. Depers, A.M., 1974. Sedimentary facies at Yatala Harbour and Geochemical Comparison with Port Pirie sediments, Spencer Gulf, South Australia. B.Sc. (Hons) thesis, University of Adelaide, Adelaide, S.A., 35 pp. (unpublished). Deland, P. and Jones, R.M., 1973. Spencer Gulf Water Pollution Studies -- Reconnalsance Survey. Engineering and Water Supply Department, Adelaide, Publ. MW 473/72, 51 pp. Dossis, P. and Warren, L.J., 1980. Distribution of heavy metals between the minerals and organic debris in a contaminated marine sediment. In: R.A. Baker (Editor), Contaminants and Sediments. Ann Arbor Science Publishers, Ann Arbor, Mich., pp.119--139. Dossis, P. and Warren, L.J., 1981. Zinc and Lead in background and contaminated sediments from Spencer Gulf, South Australia. Environ. Sci. Technol., 15: 1451--1456.

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247 Olsen, A.M., 1983. Heavy metal concentrations of fish, other aquatic biota, River Murray and South Australian aquatic environments. Fisheries Res. Pap. 10, Department of Agriculture and Fisheries, South Australia. Robertson, I.A., 1977. Ecology of juvenile King George Whiting SiUaginodes punctatus (Cuvier and Valenciennes) (Pisces: Perciformes) in Westernport, Victoria. Aust. J. Mar. Freshwater Res., 28: 35--43. Salomons, W. and Mook, W.G., 1980. Biogeochemical processes affecting metal concentrations in lake sediments (IJsselmeer, The Netherlands). Sci. Total Environ., 16: 217--229. Schwerdtfeger, P. and Williams, S., 1975. Winds at Whyalla. Flinders Institute for Atmospheric and Marine Sciences. Res. Rep. 16, 11 pp. Schwertmann, V., 1964. The differentiation of iron oxide in soils by a photochemical extraction with acid ammonium oxalate. Z. Pflanzennaehr. Dueng., Bodenkd, 105: 194--201. Shepherd, S., 1981. Mapping the b o t t o m communities of upper Spencer Gulf. Safic, 5: 35--37. Sims, M.A., 1973. The impact of heavy metals on marine flora of an inlet at Port Pirie. B.Sc. (Hons) thesis, University of Adelaide, Adelaide, S.A., 84 pp. (unpublished). Stefanson, R., 1977. Spencer Gulf. A review of the oceanography, marine biology, and implications for development. 3rd Australian Conf. on Coastal and Ocean Engineering, 1977, 77/2, pp.13--16. Sullivan, J.K., 1977. Effects of salinity and temperature on the acute toxicity of cadmium to the estuarine crab Paragrapsus garmardii (Milne Edwards). Aust. J. Mar. Freshwater Res., 28: 739--743. Theis, T.L. and Richter, R.O., 1979. Chemical speciation of heavy metals in power plant ash pond leachate. Environ. Sci. Technol., 13: 2 1 9 - 2 2 4 . Thomas, I.M. and Edmonds, S.J., 1955. Chlorinities of coastal waters in South Australia. Trans. R. Soc. South Aust., 79: 152--165. Thomas, R.I., 1981. Upper Spencer Gulf coastal and marine environment. An overview and proposal for a management plan. Department of Environment and Planning, South Australia, 47 pp. Tiller, K.G., Merry, R.H., Cartwright, B. and Bartlett, N.R., 1975. Dispersal of lead emissions from an isolated lead smelter within an agricultural region of South Australia Search, 6: 437--439. Tronson, K., 1974. The hydraulics of the South Australian Gulf System. 1. Circulation. Aust. J. Mar. Freshwater. Res., 25: 413--426. United States Environmental Protection Agency, 1977. Guidelines for the pollution classification of Great Lakes harbour sediments. Reproduced in D.A. Bahnick et al. (1981), Development of Bioassay Procedures for Defining Pollution of Harbour Sediments, Part I. Report No. PB81-178261. Wisconsin University-Superior, Centre for Lake Superior Environmental Studies, 199 pp. Ward, T.J., 1981. The distribution of Cadmium in shallow marine sediments, flora and fauna near a lead smelter, Spencer Gulf, South Australia. 3rd Int. Cadmium Conf., Miami, Florida, February 1981. Ward, T.J. and Young, P.C., 1981. Trace metal contamination of shallow marine sediments near a lead smelter, Spencer Gulf, South Australia. Aust. J. Mar. Freshwater Res., 32: 45--46. Ward, T.J. and Young, P.C., 1982. Effects of sediment trace metals and particle size on the community structure of epibenthic seagrass fauna near a lead smelter, South Australia. Mar. Ecol. Progr. Ser., 9: 137--146. Warren, L.J., 1981. The contamination of sediments by lead, zinc and c a d m i u m - A review. Environ. Pollut., Ser. B, 2: 401--436. Williams, D.J., 1979. Measurements of the dispersion of the plume from Port Augusta Power Station. In: D.J. Swaine (Editor), Effects of Heavy Metals on Aquatic Life. CSIRO, Canberra, A.C.T., pp.83--84.