The Impact of Pollution on the Meiofaunal Densities of an ... PAPERS/PERT Vol... · THE IMPACT OF POLLUTION ON THE MEIOFAUNAL DENSITIES OF AN ESTUARINE MUDFLAT MATERIALS AND METHODS

Pertanika 10(2), 197-208 (1987)

The Impact of Pollution on the Meiofaunal Densitiesof an Estuarine Mudflat

SHABDIN B. MOHD LONGMarine Science Department,

Faculty of Science and Natural Resources,Universiti Kebangsaan Malaysia, Sabah Campus,

88996-Kota Kinabalu, Sabah,

Key words: Hydrocarbon; redox potential discontinuity; meiofaunal densities.

ABSTRAK

Kajian ini dilakukan pada dataran lumpur di muara sungai Forth (Scotland) untuk melihatkesan daripada buangan industri ke atas kepadatan meiofauna, dengan membuat tinjauan he ataskomuniti meiofauna dan parameter kimia yang tertentu. Dataran lumpur ini menerima buanganberminyak darikilangpenapis minyak B.P. Ltd.; buangan darikilang kimia B.P. Ltd. (terutamanyapelarut organik dan garam ammonia) dan dua buangan kumbahan. Buangan kilang penapis minyakdan kimia didapati memberi kesan ke atas kepadatan meiofauna. Ini dapat dilihat dengan jelas ter-utamanya di kawasan yang berhampiran dengan tempat buangan pada bahagian paling atas dataranlumpur ini, di mana kandungan bahan organik yang tinggi menyebabkan pembentukan sedimenyang berwarna hitam dan tanpa oksigen dengan kedalaman di bawah daripada 1 — 2mm dari per-mukaan, dalam musim panas. Kepadatan meiofauna adalah sangat berkurangan. Pengurangankepadatan nematoda dan kopepoda adalah merupakan tindak balas biasa kepada kewujudanminyak; itu pun hanya apabila minyak wujud dalam kepekatan yang tinggi. Kesan keracunan danfizikal minyak ke atas meiofauna di Kinneil, adalah kurang penting akibat kesan tidak langsungdaripada minyak menerusipengeluaran sedimennya yang kurang oksigen dan berbelerang.

ABSTRACT

A study was carried out in the Forth estuary (Scotland) to determine the impact of industrial effluentson the meiofaunal density of an estuarine mudflat, through a survey of the meiofauna communitiesand certain chemical parameters. The mudflat has been subjected to oily effluents from the B.P.Refinery Ltd., effluents from B.P. Chemicals Ltd. (chiefly organic solvents and ammonium salts) andtwo sewage discharges. The refinery and chemical discharges were shown to have a marked impact onthe density of meiofauna. This was most marked near the points of discharge at the top of the shorewhere the high organic content caused the formation of black, reduced sediment below a depth of 1 -2mm in the summer. Meiofaunal density was grossly reduced. It seemed that reductions in nematodeand copepod densities were common responses to the presence of oil, although only when present athigh concentrations. At Kinneil, the toxic and physical effects of the oil on the meiofauna seemed lessimportant than the indirect effects of the oil through its production of oxygen-deficient, sulphuroussediments.

INTRODUCTION cause mortality among meiofauna (Rutzler andThe results of oil pollution studies on meiofauna Sterrer, 1970; Wormald, 1976; Giere, 1979;generally seem contradictory. Several studies Boucher, 1980). Some studies have shown thehave shown that oil mixed with the sediment can effects of acute oil pollution on the meiofauna to

SHABDIN B. MOHD LONG

be a reduction in density of all taxa followed byrapid recovery of the nematodes (McLachlanand Harty, 1982; Boucher, 1980; Bonsdorff,1981), followed by slower recovery of the othertaxa. The study by Rutzler and Sterrer (1970)showed that the oil inflow into the sand beachecosystem along the Atlantic seaboard ofPanama resulted in a dramatic reduction of themeiofauna population. A similar case was foundby Wormald (1976) in Hong Kong where, within4 days of pollution by a heavy marine diesel fuel,meiofauna was almost totally destroyed. How-ever, the effects of oil on meiofauna have alsobeen shown to stimulate an increase in density ofmeiofauna (Naidu et aL, 1978; Fleeger andChandler, 1983). Giere (1979) noted thatmeiofaunal oligochaetes, p >lychaetes, halacaridsand turbellarians appeared to be generallyresistant to oil pollution. The effects seem to bedependent on spill size and habitat charac-teristics as well as taxonomic grouping (Deckerand Fleeger, 1984).

The impact of oil on nematode commu-nities has been examined on several occasions(Wormald, 1976; Giere, 1979; Boucher, 1980;Fricke et al.f 1981, Bonsdorff, 1981; Alongi etaL, 1983; Fleeger and Chandler, 1983), al-though results have been inconsistent. Wormald(1976) found that a few nematodes at oil spillsites recovered within one month of the spill,whilst Giere (1979) found low nematodes densi-ties 6 weeks after the La Coruna blowout. How-ever, Fleeger and Chandler (1983) showed signi-ficant increases 5 — 20 days after sediments wereexperimentally sprayed with South Louisianacrude oil. Boucher (1980) found that a generaldecrease in the nematode density in intertidalsand was obvious seven months after the oilpollution. Decker and Fleeger (1984) performeda study to see the effects of South Louisianacrude oil on the colonization of meiofauna, andfound that nematode densities were significantlylower in highly oiled sediments (288mg oil: lOOgdry sediment) than in lightly oiled sediments(ISSmgoil: lOOg dry sediment). However, Frickeet aL, (1981) found no difference in nematodedensity between oil polluted and referencebeaches. Similarly, Alongi et aL (1983) alsonoted no significant differences in densitiesbetween oiled and non-oiled sediments. It seems

that oil spill effects on nematodes depend on thehabitat type as well as the dosage and kind of oilspilled (Decker and Fleeger, 1984).

The study of the reaction of benthic harpac-ticoid copepods to the presence of oil has beenexamined by a number of workers (Kontagianisand Barnett, 1973; Wormald, 1976; Naidu etaL, 1978; Giere, 1979; Ustach, 1979; DallaVenezia and Fossato, 1977; Alongi et aL, 1983;Fleeger and Chandler, 1983; Decker andChandler, 1984), although the results have beeninconsistent. Giere (1979) rarely found harpac-ticoid copepods in the zone of heavy oil pollu-tion, and Bonsdorff (1981) found them reducedin sublittoral soft bottoms polluted by oil andWormald (1976) found them slow to recoverfrom an oil spill. However, Naidu et aL (1978)reported that an increase in copepod densityoccurred in an experimentally oiled site on anAlaskan mudflat. Fleeger and Chandler (1983)again found significant increases of harpacti-coids (specifically Enhydrosoma woodini) bydays 30 — 60 after the sediments were sprayedwith South Louisiana crude oil. However, Alongiet aL (1983) found the difference between colo-nization rates into experimentally oiled and un-oiled sediment to be not significant. In thelaboratory, studies by Ustach (1979) on theharpacticoid copepod, Nitocra affinis, showedthat copepods reacted to the presence of oil byreduction in brood size. However, Dalla Veneziaand Fossato (1977) found no significant diffe-rence with respect to the number of eggs ornauplii or percent hatching of Tisbe bulbisetosawhich had been subjected to different concen-trations of a suspension of Kuwait crude oil.Decker and Fleeger (1984) found that all benthiccopepods, except Enhydrosoma woodini,appeared unaffected by the presence of oil in saltmarsh sediments.

Despite all the studies mentioned above,studies are still lacking on the meiofauna ofestuarine mudflats. Moreover, meiofaunal pollu-tion studies to date have generally, considered atmost, only one or two of the major meiofaunaltaxa. The objective of the present study then wasto examine the impact of chronic oil pollution onthe densities of all major meiofaunal taxa of amudflat in the Forth estuary.

198 PERTANIKA VOL. 10 NO, 2, 1987

THE IMPACT OF POLLUTION ON THE MEIOFAUNAL DENSITIES OF AN ESTUARINE MUDFLAT

MATERIALS AND METHODSDescription of the Study AreaThe Forth estuary (Fig. 1) extends from Stirlingdownstream to South Queensferry and receivesdomestic and industrial effluent at severalpoints, notably domestic sewage and waste fromthe distilling industry in the Alloa area, andindustrial waste in the Grangemouth area. Italso receives the heated cooling water fromLongannet and Kincardine power stations. Thefauna, especially the macrofauna, and theimpact of pollution on the intertidal areas hasbeen described by McLusky et al (1976, 1978,1980) and McLusky (1978, 1982). The intertidalareas comprise approximately 22.6km2, of whichthe largest single region is the Kinneil mudflat,having an area of 5.71km 2at mean low neap tide(MLWN) and 6.42km2 at mean low spring tide(MLWS) (McLusky, 1982).

Attention in this study has been concentrat-ed on Kinneil mudflats. The area is divided bythe River Avon, which meanders across theintertidal area en route to the low water channelof the Forth estuary. The Kinneil area receiveseffluent from several sources. The biggestsources are those from B.P. industries which dis-charge effluent at the high tide mark at positions

shown in Figure 1. The volume of effluent fromB.P. Oil Grangemouth Refinery Limited isabout 15-25 X 106 1 d"1 comprising ballastwater, boiler and cooling tower blowdown andprocess water. B.P. Chemical Limited Grange-mouth discharges effluent of 6 - 9 X 1061 d ',which is mainly hot freshwater with chemicalcontaminants including organic solvents andammonium salts (McLusky, 1982). The area alsoreceives treated domestic effluent from Kinneiland Bo'ness sewage works and contaminatedwater from Grangemouth docks and the RiverCarron. The mudflats may also be influenced bya subtidal discharge from I.C.I, near the mouthof the Carron, which contains mercury. Thesalinity in the area varies between 15-20%(Stout, 1976; FRPB annual report, 1979).

Much of the upper shore at Kinneil hasbeen reclaimed, the mudflats extending upwardsonly as far as MTL-MHWN for much of thearea. The highest mudflats occur west of theAvon in the vicinity of the B.P. discharges,where the shore extends beyond MHWN. Skin-flat mudflats lie to the west of Grangemouthdocks. Here the shore is backed by saltmashabove MHWN. No effluent discharges arepresent at the top of the shore here.

Fig. 1: Map of the study area showing the location of three longitudinal transects at .approximatelyMean Low Water Neap (MLWN; stations 1 to 10), Mid Tide Level (MTL; stations 11 to 19) and Mean HighWater Neap (MHWN, stations 20 to 28) at Grangemouth mudflats. C — chemical discharge,G — Grangebum, O — oil refinery discharge and S — sewage discharge

PERTANIKA VOL. 10 NO. 2, 1987 199


Station LocationThe Kinneil mudflat area was surveyed formeiofauna and environmental factors on the25th-27th July, 1984. Prior to sampling, 3longitudinal transects were marked out along thelower, middle and upper shore by positioning3 - 4m stakes at the sampling stations (Fig. 1).

SamplingCollection of core samples for chemical and bio-logical studies was carried out by using a modifi-cation of a flow-through corer by Frithsen et al.(1983).

RedoxOne core of area 5.5cm 2was taken to a depth of7 —10cm for the determination of the redoxpotential vertical profile. Samples for redoxmeasurement were immediately brought back tothe laboratory where Eh was measured at 0.5cmintervals to a depth of 5cm using the method ofPearson & Stanley (1979).

HydrocarbonTwo cores of area 5.5cm2 were taken to a depthof 3cm for the hydrocarbon analysis. Coringtubes and extrusion pistons were cleaned in 95 %ethanol and wrapped in aluminium foil to ex-clude dust. Each core was used for one stationonly. The sediment in the cores was pushed outwith an extrusion piston into a glass container,previously cleaned with dichloromethane.

Samples were stored deep frozen. All glass-ware was washed twice with dichloromethaneand covered with foil caps prior to use. Totalaliphatics and aromatics were measured usinginfra-red and ultra-violet fluoresence spectro-photometers respectively.

MeiofaunaTriplicate 5.5cm2cores were taken to a depth of3cm for meiofauna and the sediment preservedin 4% buffered formalin.

The meiofauna was extracted from the sub-strate by a combination of sieving and centri-fugation. The preserved samples were washedthrough sieves of 500um and 63um using a finejet of tap water. The material retained on the63um sieve was concentrated by washing it to theedge of the sieve and then excess water removed

by placing absorbant paper beneath the sieve,This is important in order to minimise subse-quent dilution of the floatation medium. Thescreenings were then carefully washed into a250ml centrifuge bottle using colloidal silica in awash bottle. The colloidal silica used was Ludox-TM and spun for 5 minutes at 2709g. The super-gravity of 1.115 with 4% formalin. The 250mlcentrifuge bottle was then 3/4 filled with Ludox-TM and spun for 5 minutes at 270g. The super-natant was carefully decanted into a 63um netheld over a beaker whilst rotating the centrifugebottle to wash off material adhering to the wall.The net screenings were then rinsed free ofLudox and stored in 4% formalin. The centri-fuge bottle was then refilled again with Ludox-TM and the process was repeated once more.The method used was 95% efficient (Mr. DJ.Mills, pers. comm.).

Sorting and CountingThe meiofauna was scattered in a gridded petridish under a stereomicroscope. Using a finetungsten needle, bent at the tip, all taxa exceptnematodes were counted and transferred tosmall glass vials containing 4% formalin. Thenthe total number of nematodes in the petri dishwas counted. Numbers were averaged for thethree scores and finally converted to densities inunits of individuals 10cm ~\

RESULTS

RedoxThe depth of the redox potential discontinuitylayer (RPD) was taken here as the depth at whichthe Eh is zero. The sediment of the middletransect was the most oxygenated with the RPDdepth varying between 22-25mm. The RPDwas a little shallower along much of the lowertransect at 20 — 22mm except near the Avonchannel where it rose markedly to 5mm. Alongthe upper transect the RPD depth was 20 -21mm at Skinflats but rose to within 1 - 2mm ofthe surface at Kinneil (Table 1, Fig. 2).

The Eh at a depth of 5mm showed the samegeneral pattern as the RPD but showed there wasa little recovery in the oxic state of the sedimentbetween the chemical and refinery discharges onthe upper transect (Table 1, Fig. 2). Along the

200 PERTANIKA VOL. 10 NO. 2, 1987


TABLE 1The location of sampling stations and some chemical characteristics of the sediment along three transects

at approximately Mean Low Water Neap (MLWN), Mid Tide Level (MTL)and Mean High Water Neap (MHWN) at Grangemouth mudflats

Transect

Mean LowWaterNeap(MLWN)

Mid TideLevel(MTL)

Mean HighWaterNeap(MHWN)

1 ND - not

Station

123456789

10

111213141516171819

202122232425262728

determined.

Distancealong

transect(meter)

4639.04325.03414.02746.02236.01820.01454.01191.0470.0

0.0

0.0500.0794.0

1051.01293.01621.02069.02797.03699.0

988.0766.0631.0496.0353.0173.0

0.0control 2

control

Redoxpotentialat 5mm

depth (mV)

240.0251.6256.6

- 4.0222.8157.9137.9120.0180.2238.6

280.6250.0270.1240.0280.3270.0240.0243.0275.3

- 23.7- 46.9- 31.9- 42.2- 62.2- 31.7- 21.7

280.3308.2

Redoxpotential

discontinuitydepth (mm)

2121215

212121202122

242325242323232422

2111112

2120

Aliphatichydrocarbon

(ppm)

1232.6841.5

1754.51086.1ND 1

1564.91080.9628.3

1132.2622.3

512.5689.7946.5

1128.61994.51787.51389.41022.2892.5

2450.73761.94300.85981.05108.15175.33879.51616.91249.2

Aromatichydrocarbon

(ppm)

2.09.94.73.5

ND ]

Ift.l5.18.02.30.6

4.58.5

10.816.737.821.418.211.715.0

6.445.396.4

158.2143.2

19.839.829.3

ND *

z control — control station.

lower transect, in addition to the indication of ahighly reduced sediment in the Avon channel,there was a clear depression in redox potential inthe vicinity of the refinery channel.

Aliphatic and Aromatic HydrocarbonThe level of aliphatic hydrocarbons showed avery strong gradient along the upper transectwith a peak of 5981 ppm near the oil refinery dis-charge and falling off to either side. The mini-mum value of 1617ppm was recorded at Skin-

flats (Table 1, Fig, 3). The concentration wasmuch lower along the middle shore transect butthere was a clear gradient with a peak of1995ppm at station 15 near to the refinerychannel, falling to 513 — 893ppm at the ends ofthe transect. The reduction in concentrationwith distance from the refinery channel was lesson the downstream side of the channel. Theconcentration along the lower transect wassimilar to the middle transect but there was noobvious pattern. The concentration lay between622-1755ppm.



25,

201

15'

10

5

0

0

\

\

W . 5 2k 23

MHWNC A1 • ,

22 a ff

MHWN

403

300

200

100

0

-100150 360 450 600 7*0 960 1050 1200

0 C AI • ! MTL 16

600 750 900 X)50 1200MTL

400

150

128

96

64

32

00

160

-123

96

64

32

25

20-

15

10

5

0 400 800 1200 1600 2toO 24bO 2800 3200 3600 4000G 0

400

300

200

100

0

-1000 500 1000 1500 2030 2500 3D00 3500 4000 4500 5000

Distance along transect (m)

Fig. 2: Redox potential (Eh) at a depth of 5mm anddepth of redox potential discontinuity (RPD)along three transects at approximately MeanHigh Water Neap (MHWN), Mid TideLevel (MTL) and Mean Low Water Neap(MLWN) at Grangemouth mudflats. Stationnumbers are given. A — River Avon, C —chemical effluent channel, G — Grange burnand O — oil refinery channel, (depth of RPD, Eh)

6000

49 00

3800

270OJ

)fj-=^ ^*r f J

0 400 800 1200 1600 2to0 2400 2&00 3*X> 3600 40000 Q

MLWN T160

128

95

.64

0 S ) KfeO 1500 2d00 S c T x t o 3̂ 00 4000 i * 0 5000"


Fig. 3: Concentration of aliphatic and aromatichydrocarbon in the sediment along threetransects at approximately Mean HighWater Neap (MHWN), Mid Tide Level(MTL) and Mean Low Water Neap(MLWN) at Grangemouth mudflats. Stationnumbers are given. A — River Avon, C —chemical effluent channel, G -~ Grangeburnand O — oil refinery channel, (aliphatic, aromatic)

The aromatic hydrocarbon level alsoshowed a very strong gradient along the uppertransect with a peak of 158ppm near the refinerydischarge declining off to either side. The mini-mum value was 6ppm at 870m from the refinerydischarge (station 20), (Table 1, Fig 3). The con-centration was much lower along the middleshore transect but there was a clear gradient witha peak of 38ppm at station 15 near to therefinery channel, falling to 5-15ppm at the

ends of the transect. The concentration alongthe lower transect was slightly lower than themiddle shore transect but there was no obviouspattern. The concentration lay between 1 —lOppm.

Meiofaunal DensitiesThe composition of meiofauna at all stations isstrongly dominated numerically by nematodes,followed by harpacticoid copepods, polychaetes,



TABLE 2Density of meiofauna (no. 10cm ~2) along three transects at approximately Mean Low Water Neap (MLWN),

Mid Tide Level (MTL) and Mean High Water Neap (MHWN) at Grangemouth mudflats.Values given are means of three replicate cores

TransectStation

Taxon

Nematodes

Oligochaetes

Polychaetes

Harpacticoid copepods

Nauplii

Amphipods

Unidentified soft fauna

Total

TransectStation

Taxon

Nematodes

Oligochaetes

Polychaetes


Nauplii


Total

TransectStation

Taxon

Nematodes

Oligochaetes

Polychaetes


Nauplii


Total

1

3532

10

—

45

41

32

3660

2

4787

16

7

49

23

—

27

4909

11

1927

16

192

274

49

9

2467

20

1130

-

298

4

-

5

1439

3

2643

25

83

154

69

—

7

2981

12

1396

20

245

289

69

—

2019

21

20

—

—

1

-

-

21

Mean Low4

1572

7

9

1

1

-

12

1603

Mid Tide

13

1743

60

181

409

74

-

2467

Water5

247

1

-

9

5

-

4

266

Level

14

1121

27

323

320

27

-

1818

Neap (MLWN)6

1423

9

1

60

23

—

-

1516

(MTL)

15

1025

10

181

230

54

-

1500

7

345

2

260

34

4

-

2

647

16

565

12

409

300

32

-

1318

8

999

10

9

61

5

-

1084

17

1332

7

136

141

2

-

1618

Mean High Water Neap (MHWN)22

82

-

-

4

-

-

86

23

38

-

—

4

-

-

42

24

31

-

-

-

—

—

31

25

29

-

—

—

—

—

29

26

303

4

—

5

—

—

312

9

666

7

4

27

1

-

-

705

18

1150

9

5

150

21

-

1336

27

7107

16

38

29

25

77222

10

702

5

192

69

16

1

-

985

19

713

9

-

354

10

12

1098

28

2235

11

87

138

50

69

2590



oligochaetes and others (nauplii, amphipods,halacarids and unidentified soft fauna) (Table2).

NematodesThe density of nematodes along the lowertransect was variable with fair numbers ofnematodes west of the River Avon but very highdensities towards Bo'ness (Fig. 4). The density ofnematodes varied between 247 ind. 10cm ~2

at station 5 to 4787 ind. 10cm "2at station 2. The

MHWN

27c.

AI

24 23 2220

1 432<>

>. 2880

I 1440-

« o

0 150 300 450 600 750 900 1050 1200

? S i

1719

—I

0 4C0 860 1200 1600 2000 2400 2&0 3300 3600

7200T ' ^ ^ M l W N

<5 500 COO 15C0 2000 2500 3GC0 3$00 4000 4500 5000

Distance along transact (m)

Fig. 4: The mean density of nematodes (no.10cm ~2) along three transects atapproximately Mean High Water Neap(MHWN), Mid Tide Level (MTL) andMean Low Water Neap (MLWN) atGrangemouth mudflats. Station numbers aregiven. A — River Avon, C — chemicaleffluent channel, G — Grange burn and O— oil refinery channel, (error bars represent± 1 standard error)

nematodes on the middle shore transect fluctuat-ed between 713 ind. 10cm 2at station 19 to 1927ind. 10cm ~2at station 11. Nematode densitieswere very low on the upper shore in the vicinityof the outfalls (21 to 303 ind. 10cm 2), butnormal abundances were found at the stationbordering the River Avon (station 20), and onSkinflats (1132 to 7107 ind. 10cm 2). Althoughnematode abundance was drastically reduced inthe vicinity of the outfalls, they were not absent,even at the stations closest to the outfalls.

400

30O

800 1200 1600 2000 2400 2800 3200 3600 4X0A• MLWN

0 500 1000 1500

Distance

2 1

3500 3£O0 45aT

along transect (m)"Ito

Fig. 5: The mean density of harpacticoid copepods(no. 10cm ~2) along three transects atapproximately Mean High Water Neap(MHWN), Mid Tide Level (MTL) andMean Low Water Neap (MLWN) atGrangemouth mudflats. Station numbers aregiven. A — River Avon, C — chemicaleffluent channel, G — Grange burn and O— oil refinery channel, (error bars represent± 1 standard error)



Harpacticoid CopepodsAlong the lower shore harpacticoid copepoddensity fluctuated around an average of 51 ind.1 0 c m 2 but crashed to virtual extinction nearthe Avon channel (Fig. 5). The density was muchhigher along the middle shore (mean, 274 ind.10cm ~2) but again declined to a minimum inthe vicinity of the Avon. Along the uppertransect copepods were virtually absent atKinneil but present in moderate numbers (mean131 ind. 10cm ~2) at Skinflats.

PolychaetesPolychates were patchily distributed along thelower shore but were abundant on the middleshore upstream of the Avon (mean, 186 ind.10cm 2), (Fig. 6). On the upper shore they werepresent in moderate numbers at Skinflats (mean,62.5 ind. 10cm ~2), completely absent in thevicinity of the refinery discharge but abundantjust 200m east of the chemical discharge.

OligochaetesOligochaetes were present throughout themiddle and lower transects but at densities most-ly below 20 ind. 10cm ~2 although a peak of 60ind. 10cm ~2 occurred 250m upstream of the

5 4&0 860 1200 1600 2000 2400 2800 3200 3600 400C

MHWNC A

23 22 21 20150 3CG 450 600 7S0 900 10$0 1200

17 18

f \19

300

200

100

1200 1600 2000 2400 2800 3200 3600 4&0r\ A

MLWN

6 5 2 110 9

' 0 500 1000 1500 2000 2500 3000 3500 4)00 <kw 5*XX)

Distonce olong tronsc-ct (m)

Fig. 6: The mean density of polychaetes (no.10cm ~2) along three transects atapproximately Mean High Water Neap(MHWN), Mid Tide Level (MTL) andMean Low Water Neap (MLWN) atGrangemouth mudflats. Station numbers aregiven. A — River Avon, C — chemicaleffluent channel, G — Grange burn and O— oil refinery channel, (error bars represent± 1 standard error)

0 500 1000 1500 2C00 2500 3000 3500 « 0 0 4^00 50C0


Fig. 7: The mean density of oligochaetes (no.10cm 2) along three transects atapproximately Mean High Water Neap(MHWN), Mid Tide Level (MTL) andMean Low Water Neap (MLWN) atGrangemouth mudflats. Station numbers aregiven. A — River Avon, C — chemicaleffluent channel, G — Grangeburn and O— oil refinery channel, (error bars represent± 1 standard error)



refinery channel on the middle transect (Fig. 7).On the upper shore oligochaetes were present inmoderate numbers at Skinflats (mean, 14 ind.10cm 2). At Kinneil, however, they were com-pletely absent from the vicinity of the refineryand chemical discharges, only being recordedsome 300m west of the refinery discharge in lownumbers.

DISCUSSIONLaw and Fileman (1985) recorded hydrocarbonlevels of 0.4 — 2.0ppm in superficial sediments ofthe Dogger Bank (North Sea), which they con-sidered to be typical of unpolluted sediments.Boucher et ai (1981) recorded aliphatic hydro-carbon levels greater than lOOOppm on mudflatsin the River Morlaix (France) in July 1978, thevery high levels resulting from the Amoco Cadizoil spill which took place 4 months previously.Wharfe (1975), studying the impact of refineryeffluent in the Medway estuary, Kent (England),recorded levels of up to 13100ppm on mudflatsin the vicinity of the discharge and somewhatlower levels subtidally (1000-6400ppm). Thehydrocarbon levels at Grangemouth, rangingfrom 513 - 6139ppm are clearly enhancedthroughout the area. The very high levels at thetop of the shore (mean, 4452ppm) possibly resultfrom ponding of the effluent in this deeplyembayed area of the mudflat.

On the middle and lower shore at Kinneilhydrocarbon levels are similar (means, respec-tively 1168 and lllOppm), however, the patternsof hydrocarbon contamination with distancefrom the refinery channel differ. Both the upperand middle shore transects clearly display apattern of decreasing aliphatic and aromatichydrocarbons with distance from the refinerychannel. The erratic pattern of hydrocarbonlevels along the shore transect might be causedby the stranding of oils patches which wash upand down the main estuary channel. Some ofthese may be derived from Grangemouth docksand other sources. Patches of oil have indeedbeen observed on the mud near the bottom ofthe mudflats.

Both the refinery and chemical dischargescan influence the biota of the mudflats indirectlythrough the reduction of the sediment that theycause. This is particularly marked at the top of

the shore where the RPD layer occurs within thetop few millimetres in summer along the entireupper shore area at Kinneil (a distance of lkm).This contrasts strongly with the deep RPD layerfound at a similar tidal height at Sinflats.Despite similar hydrocarbon levels the redoxstate of the sediment differs on the middle andlower shore. Whereas there is a slight and verylocalized reduction in Eh adjacent to the refinerychannel on the middle shore, both effluentchannels appear to cause marked reductions inEh on the lower shore. About 1.5km of the lowershore transect display reduced Eh levels in thevicinity of the refinery channel and a furthergrossly reduced area of sediment is located justbelow the confluence of the chemical channelwith the Avon. The different redox conditionson the middle and lower shore transects may becaused by differences in hydrodynamism. Tidalcurrents are stronger at mid than at low tide andthe frequency of emersion/immersion is greaterat mid tide than at low tide. Thus, hydro-dynamic forces may lead to greater sedimentmixing and hence increased oxygenation on themiddle shore.

Whilst it is likely that the chemical dis-charge contributes to the production of thegrossly reduced area of sediment just below theconfluence of the chemicals channel with theRiver Avon, other discharge into the Avon mayalso be important in this regard. The dischargeof treated domestic effluent from Kinneil sewageworks may be a significant factor.

The meiofauna of Grangemouth mudflats isstrongly dominated numerically by nematodes,followed by harpacticoid copepods, polychaetesand oligochaetes. Nematodes have generallybeen found to be dominant in muddy sediments.Capstick (1959) recorded mean densities in theRiver Blyth (Britain) varying from 300 ind.10cm 2in muddy sand to 2590 ind. 10cm "2inmud. Similarly, Rees (1940) recorded an averagedensity of nematodes on a mudflat in the Bristolchannel (Britain) in the surface 3cm of 3589 ind.10cm ~2 Bouwman (1983) recorded an averagedensity of nematodes in the tidal flats of the Emsestuary (France) of 2000 ind. 10cm ~2. Generally,the nematode density on the middle and lowershore at Kinneil was similar to the othermudflats in temperate regions. Average densities



of harpacticoid copepods from similar habitatsinclude 171 ind. 10cm 2in the Bristol channel(Rees, 1940), 279 ind. 10cm ~2 in the Lynherestuary, United Kingdom (Warwick et al.,1979), 389 ind. 10cm 2 on a danish mudflat(Smidt, 1951) and 47-87 ind. 10cm ~2 in aNew England (U.S.A.) estuary, (Tietjen, 1969).The average density of copepods on the lowerand middle shore at Kinneil was 51 and 274 ind.10cm respectively, similar to the otherestuaries. Hence the nematode and copepoddensities on the lower and middle shore atKinneil mudflats seem typical of estuarinemuddy sediments.

Oil has often been found to cause a reduc-tion in meiofaunal densities (Smith, 1968;Rutzler and Sterrer, 1970; Wormald, 1976;Giere, 1979; Boucher, 1980; 1985). Wormald(1976) found that within 4 days of pollution byheavy diesel fuel, sandy shore meiofauna wasalmost totally destroyed. A few nematodes start-ed to appear within one month of the spill butharpacticoid copepods did not return in anynumbers for 8 months, by which time the oilcontent had decreased by 50%. Giere (1979)found low nematode densities 6 weeks after theLa Coruna blowout and he rarely found harpac-ticoid copepods in the zone of heavy oil pollu-tion. Decker and Fleeger (1984), when they per-formed a study to see the effects of SouthLouisiana crude oil on the colonization ofmeiofauna, found that nematode densities weresignificantly lower in highly oiled sediments.They also found that the harpacticoid speciesEnhydrosoma woodini was significantly reducedin density in highly oiled sediments until 60 daysafter the oiling. Boucher (1980) found that ageneral decrease in the nematode density ofintertidal sand was obvious 7 months after oilpollution from the Amoco Cadiz. Bonsdorff(1981) found harpacticoid copepods. werereduced in density in a sublittoral soft sedimentpolluted by oil.

Virtually the entire upper shore area atKinneil exhibits a severely impoverished meio-fauna although some recovery occurs at themouth of the River Avon. The nematode andharpacticoid copepod populations appear to bestrongly affected by pollution. Harpacticoidcopepods were grossly reduced in density and

only a small population of nematodes waspresent. In view of the fact that nematode andcopepod densities were high at similar tidal levelat Skinflats, it seems that the oil and chemicaldischarges were clearly responsible for the reduc-tion of nematode and copepod densities atKinneil. Elsewhere on the middle and lowershore, the pollution impact on meiofaunaldensity was not marked except for the virtual dis-appearance of harpacticoid copepods in thereduced sediments near the confluence of thechemical channel and the River Avon at thebottom of the shore. Hence it seems that a reduc-tion in nematode and copepod densities are acommon response to the presence of oil,although only when present at high concentra-tions. At Kinneil the toxic and physical effects ofthe oil on the meiofauna seem less importantthan the indirect effects of the oil through itsproduction of oxygen deficient, sulphuroussediments.

ACKNOWLEDGEMENTSThe author wishes to thank to Dr. Colin G.Moore of the Department of Brewing and Bio-logical Sciences, Heriot-Watt University for hiscomments and advice throughout this study.This work is a part of a thesis submitted for aMSc. degree to the Heriot-Watt University,Edinburgh, Scotland.

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(Received 4 March, 1987)


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