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Ashton 95
Marine Pollution Bulletin, Vol. 31, Nos 4-12, pp. 334-340, 1995
Pergamon 0025-326X(95)0013414 Copyright © 1995 Elsevier Science Ltd
Printed in Great Britain. All rights reserved
0025-326X/95 $9.50+ 0.00
Biological Monitoring of the Marine
Ocean Outfall at Black Rock,
Victoria, Australia
PETER H. ASHTON* and BRUCE J. RICHARDSONt~
*Barwon Region Water Authority, P.O. Box 651, Geelong, Victoria 3223, Australia
"~School of Biological & Chemical Sciences, Deakin University, Geelong, Victoria 3217, Australia
~Author to whom correspondence should be addressed.
The Barwon Region Water Authority in Victoria, onshore treatment plant, which improves the quality of
Australia, commissioned a new subtidal ocean sewage the effluent by removing all floatable material, grit
outfall in February 1989. This ouffall replaced an old particles (>0.2 mm equivalent diameter) and visible
intertidal outfall, and presently discharges via a diffuser in floating oil and grease. The resultant effluent is buoyant,
an average depth of 15m some 1.2km offshore in Bass being more than 99% freshwater, and rises through the
Strait. Examination of biological communities around the water column to the surface, becoming mixed with
old outfall prior to the change revealed distinct differences ambient water by turbulent entrainment.
in biotic assemblages close to the ouffall. An ongoing The new subtidal outfall was designed to achieve a
monitoring programme, implemented in 1986, has rapid initial mixing ( > 100: 1; Ashton, 1991). During
assessed not only the recovery in this intertidal area, but the early phase of the study reported here, a model was
also the major changes to macroalgal communities on developed to predict effluent plume movement from the
surrounding reefs, subtidal infauna populations in sandy new subtidal outfall (see Ashton, 1986). This model
sediments, and rocky shore communities. defined a zone (zone 3: see Fig. l(a)) in which dilution of
the effluent field would not exceed 10 times that of the
initial dilution for 90% of the time. It was believed that
this zone would be the most likely area of adverse
The Black Rock sewage outfall services the city of impact.
Geelong and surrounding coastal townships in central The aims of this study were to examine the effects
Victoria, Australia (Fig. 1). The effluent passing of the submerged outfall on local subtidal assem-
through the system originates from industry (13% by blages, and the recovery from any impacts of the old
volume), domestic, commercial properties and perman- shoreline outfall on local intertidal and near-shore
ent infiltration (87%). The total population of the subtidal assemblages. The study was divided into four
region has increased from approximately 30 000 in 1910 sub-programmes on the basis of habitat types,
to around 200000 in 1990 (GDWB, 1991). Since 1916, including macroalgal communities on subtidal reefs;
sewerage services have been provided for a high infauna community structure in subtidal sediments;
percentage of the population in the region via an macroalgal and macroinvertebrate communities on the
intertidal outfaU which discharged up to 50 M1 d-1 of intertidal rock platforms; and infaunal community
coarsely-screened sewage effluent (CCE, 1979). With structure in the intertidal sandy sediments on
increasing volume of discharge, ecological and other surrounding beaches.
effects were reported from areas surrounding the outfall,
until eventually it was shut down in 1989 and a new
offshore ocean outfall was commissioned. The new
Subtidai Reef Monitoring
outfall discharges an average 55 M1 d -1 of finely- A flexible underwater strategy for monitoring the
screened sewage from a series of 27 diffuser ports which macroalgal communities was adopted to allow for a
are located 4 m apart on alternate sides of a pipeline, variable number of quadrats to be photographed,
situated, on average, at a depth of 15 m and depending upon the environmental conditions during
approximately 1.2 km from shore. the time of sampling. The photographic technique was
The old intertidal outfall discharged at the low water designed to permit 'single image analysis' of divisional
mark in a then remote area, 14 km south of Geelong. macroalgal coverage (i.e. red, green and brown algae)
Before discharge, the raw effluent passed through coarse over the reef substrate. Consideration was given only to
screen comminutors and was pumped to elevated levels total macroalgal cover, irrespective of canopy type (i.e.
via Archimedes screw pumps during flooding tidal turf, understorey or top). The monitoring strategy was
periods. The changes which have been effected in the designed to detect major changes, as monitoring subtle
new outfall include the passage of sewage through an population changes would not be cost-effective.
334
Volume 31/Numbers 4-12/April-December 1995
Melbourne
Geelong
38os ~
145 ° E
& ' "L, /
I /
M a p (a) "~ _ o)~ i,,,,,io,)o,,r,t) ~_._z~.__.~ ! //z
3 i
,oo.,
Bancoora Beach ' ~ - f + \ --- J ~r~6 I
Zone2 -~Subhdal Outfall
. ]nlertidal Beach Zones .......
Zooo~ Sublidal Sedime=ll Zones
0 I 2
/
M a p (b)
Black Rock
~ ~ o S l f T r ePla.t e r l l
alm • ,9
s; _s,S,
" ", , 1 1 , I'(ocky Sh oreline =>
R S5.~1~ • 52
~ -' Reef Sties (S#)
Rocky Shore Sites (RS#) => +
=> •
0 1 2
t .......... ~ t ........... .I
• St Km
Fig. 1 Location of the study area on the shores of Bass Strait. Map (a)
shows the subtidal soft-bottom samplingzones (Zones 1-6) and
the intertidal soft-s~Um~at sampling zones (Z1-ZS). Map (b)
shows the subtidal reef monitoring sites (S1-S12) and the
intertidal rocky shore sites (RS1-RS5).
Twelve sites were established (Fig. l(b)), nine o f and S11 were established to m o n i t o r the shallow waters
which were located in 15-20 m depth o f water. Two sites near the old outfall. Site S12 was established in
(S1 and $2) were established well away from the outfall shallower waters outside the predicted area o f influence.
area as controls. The locations o f the sites were based Flat areas o f reef were selected and locations fixed
directly u p o n possible impact zones predicted by a with a site marker. On each sampling occasion,
water quality model (Ashton, 1986). Following the transects were identified by a second m a r k e r 20 m
commissioning o f the new intertidal outfall, sites S10 away at a fixed compass bearing from the original site
335
Marine Pollution Bulletin
9S
100 I I I I I I I I
S12 Sl S3 S2 SI2 Sl S2 S7 S9 S9 SS S4 S3 S8 S4 S7 S6 S$ s 1 s6
Po¢ Post Po¢ po6tPre Pre Pie Pre pest Pre Pre Pie Pre Po~/ Post Poe Post Post Pie Pre
rF I
Reef Sites
Fig. 2 Bray--Curtis similarity dendrogram of macroalgal coverage in
the pre- and post-commissioning periods.
Percentage Algae Cover
100
80
60
40
20
ss (som) $4 (210m) s3 (540m) s9 (790m) s2 (4kin)
$6 (120m) $7 (390rn) $8 (630m) $12(2.1km) s l (5kin)
Reef Sites (distance from Ihe out'fall)
! Pre- Commissioning
mean value M Post-Commissioning
mean value
Bars = Standard Deviation
Fig. 3 Mean macroalgal coverage of sites during pre- and post-
commissioning periods.
marker. To minimize diver bottom times, photography abundances recorded at the two sites nearest the outfall
was carried out using a camera mounted on a grid (0.33 ($5 and $6) were attributed to construction activities in
m 2 in area). A minimum of 15 photographs were taken the pre-commissioning period and to sand accretion
at random along the transect, the exact number over the rocky substrate, driven by longshore sand
depending upon weather or sea conditions. shifts, in the post-commissioning period.
Raw data were group-averaged using mean percent- An assessment of reef macroalgae relative to
age canopy cover and analysed by hierarchical distance from the outfall was made using the mean
clustering. Figure 2 illustrates a Bray-Curtis similarity percentage macroalgal cover of each of the sites for
dendrogram of macroalgal coverage data for both the two monitoring periods. The results (Fig. 3) show
sampling periods (note that sites S10 and Sll are not that the two sites closest to the outfall ($5 and $6)
included, as there were no pre-commissioning data for had lower coverage for both monitoring periods. In
these sites). Macroalgal abundance was similar at all addition, both sites showed more variability during
sites in both sampling periods, although the lower the pre- and post-commissioning periods than the
336
Volume 31/Numbers 4-12/April-December 1995
other sites. All other sites showed an average of 75- and post-commissioning periods was undertaken separ-
90% macroalgal reef coverage for both monitoring ately to highlight individual zone differences between
periods, irrespective of distance or direction from the the two periods. Figure 4 indicates that changes have
out fall. occurred since the shutdown of the old intertidal outfall.
Whereas zone 5 was quite different in relation to other
zones in the pre-commissioning phase, it was similar to
Infauna Communities in the Subtidal Sediments zone 6 and closer in similarity to the other zones in the
post-commissioning period. These changes are due to
The monitoring strategy used in this habitat was the lower number of polychaete species collected in zone
designed to allow random sampling on a seasonal basis. 5 in the post-commissioning period.
Twenty locations were randomly selected within a Although elevated numbers of polychaetes were
kilometre-wide transect in the study area, and five detected in zone 4 in the pre-commissioning period,
replicate samples were taken at each location. A the multivariate analysis techniques were unable to
purpose-built venturi sampler was designed to enable differentiate distinct differences between this zone and
surface operation using small craft as a platform. The other unaffected zones, because of the presence of other
sampler covered an area of 0.05 m 2 (i.d. = 0.253 m) and dominant groups such as the amphipoda, isopoda and
sampled up to 0.20 m in depth, depending upon the the cumacea. Nonetheless, the mean number of
compaction of the substrate. polychaetes was still higher in this zone than in the
The sampling sites were catalogued into zones other zones in the pre-commissioning monitoring
corresponding to previously identified impacted areas period, but was no different to the other zones in the
and a single, predicted possible impact area, the latter post-commissioning period. This further strengthens the
based on the model produced during the study design assumption that the area around the old intertidal
(Ashton, 1986). The zones are shown in Fig. l(a). Major outfall is no longer impacted, and that population
animal groups (orders) were differentiated using multi- numbers have returned to baseline levels. On examina-
variate techniques. tion of the mean numbers of polychaetes in zones 5 and
A comparison was made between population data of 6, it is evident that they are above other zones; however,
animal groups collected from all samples taken during the numbers for zone 6 are similar in both periods.
the pre- and post-commissioning stages (Table 1). Slight Therefore, it may be assumed that the soft-bottom
differences in the percentages of the major groups of sediments to the east of the outfalls are able to harbour
animals were found. The population of amphipods was higher populations of these animals. There were no
reduced by 10% after the change of outfall. Isopods
increased from 4.6 to 11%, and the cumacea decreased (a)
from 7.5 to 3.3%. The polychaetes increased from 7.4 to 0
10%. In a dynamic environment such as that at Black 10
Rock, these differences are considered minor and are .£~0 20
probably due to natural changes (e.g. see Ferraro et al., 30
1991). r~ 40
To further elucidate differences between the six ._~
S0
defined zones, multivariate classification techniques
6o
were used and comparisons were based on the identity
of the major groups of animals in the collections. The
Bray-Curtis (B-C) similarity coefficient based on 80
abundance of the dominant groups of animals was 90 I
used to measure changes. The inter-group resemblance 100
Zone 6 Zone 4 Zone 3 Zone 2 Zone Zone
was defined as the mean of all resemblances between
one group of animals to those of another. Such group-
average clustering (Sneath& Sokal, 1973) has space
(b) 0
conserving properties, which produce clusters with little
10
distortion of the actual resemblance relationships
(Boesch, 1977). The hierarchical clustering of the pre- 20
30
9. 40
TABLE 1
Major animal group presence (descriptive statistical data only, 50
expressed as percentage population abundance for animals > 1 mm 60
< 10ram in size) in soft-bottom sediments throughout the study area. i. 70
Animal group
Amphipoda
Pre-commissioning
78
Post-commissioning
68
80
90
h
Isopoda 4.6 11 100
Cumacea 7.5 3.3 Zone 6 Zone 5 Zone 4 Zone 1 Zone 3 Zone 2
Decapoda 0.9 2.7
Polychaeta 7.4 10 Fig. 4 B r a y - C u r t i s s i m i l a r i t y d e n d r o g r a m o f the m a j o r s u b t i d a l
Others 1.6 4.0 a n i m a l g r o u p p o p u l a t i o n s b e t w e e n the z o n e s in t h e (a) p r e -
c o m m i s s i o n i n g p e r i o d a n d (b) the p o s t - c o m m i s s i o n i n g p e r i o d .
337
Marine Pollution Bulletin
obvious changes to polychaete numbers in the zone The discharge of sewage effluents to intertidal areas
nearest the subtidal outfall (zone 3), nor were any major has been associated with the stimulation of large crops
changes detected in other major population groups in of macroalgae, notably Enteromorpha spp. and Ulva
this zone. spp. (Wilkinson, 1963; Sawyer, 1965; Portsmouth
Polytechnic, 1976; Buttermore, 1977; Soulsby et al.,
1978; Montgomery & Soulsby, 1981). Although it was
Rocky Shores documented in the early studies (MSE, 1978a,b) that
Site selection was based upon the presence and primary production of macroalgal species, such as
location of permanently-exposed rocky shores in the Enteromorpha spp. and Ulva spp., was enhanced at
area, and the distance of these sites from the intertidal sites closer to the intertidal outfall at Black Rock, there
and subtidal outfalls (Fig. l(b)). Ten quadrats, each was some concern during the design stage of the
250x400 mm (0.1 m2), were permanently marked in programme in using these species to determine the
the mid to lower eulittoral zone at each site using recovery of rocky shore sites. These concerns were later
masonry nails. These quadrats were selected as justified, as certain sites well away from any area of
representative of the exposed areas of the cobbled or impact of the outfall (e.g. RS4 and RS5) showed periods
flat platform sites. Non-destructive methods (Gonor & of stimulated growth of these species.
Kemp, 1978) were used to estimate percentage cover of As the study required a monitoring programme that
macroalgae, mussel mats of Xenostrobus pulex and the would address 'recovery' of a rocky shore site (RS3)
sand mats of the spionid polychaete Boccardia following the shutdown of an intertidal outfall, special
proboscidea to the nearest 10%. Other groups of consideration was given to the opportunistic species B.
animals were counted individually. proboscidea (see Dorsey, 1982; Synnott & Brown,
Mean,'abundanceScore
2,500
2,000
15 0
,0
10 0
,0
500
0
1986 1987 1988 1989 1990 1991
Year
I G .r p d N Girrepedi N Polychaeta~
a o oa
t a
TubeWorrns
Polychaeta
SpionidWorms I B~vak'a
Fig. 5 Animal class abundance trends at rocky shore site RS3.
25
~52o
o0 lO
"6
o
RS1 RS2 RS3 RS4 RS5
Rocky Shores Site
[ ] 1986 [ ] 1988 [ ] 1989 [ ] 1990 [ ] 1991
Observationswerenotundertaken RS1,RS2,
at
RS4andat RS5in 1988.
Fig. 6 Macroalgal species richness trends on the rocky shore sites.
338
Volume 31/Numbers 4-12/April-December 1995
1985). Monitoring continued at this site during both (a)
the pre- and post-commissioning stages, and all other
organisms within the quadrat areas were documented.
Distinguishing between natural variability of plants -s0-
and animals and a 'recovery' response proved difficult
using the quadrat method alone, even though the '~
disappearance of B. proboscidea was evident (Fig. 5). ~ ss -
However, the results of annual macroalgal surveys .~
undertaken at each of the intertidal sites (Fig. 6)
reinforced the notion that site RS3 was recovering ~ 90-
¢1
slowly, with the gradual appearance of brown algae
which had not been previously documented, yet which
were common at other sites less than 1 km away. 95 -
Nevertheless, it was obvious, even 3 years after the
intertidal outfall shutdown, that the abundance of I00
macroalgal species was still well below expected levels.
Z$ Z4 ZI Z3 Z2
Subsequent studies have shown that macroalgal
abundance has increased to levels similar to that at MoniteringZoees
site RS1 (Barwon Water, 1994), which adds strength
to the conclusion that the RS3 site has recovered and (b)
now shows little evidence of past stress.
80-
Infauna Communities in the Intertidal
Sediments
The monitoring area of this habitat was divided into
zones relevant to direction and distance away from the I
outfalls. Each zone was sampled every season, using a
belt transect which ran from the previous high water 90- I
mark to the low water mark. To monitor populations
through the entire transect, stratified random samples
were taken along the belt transect. Ten sample units 95-
were randomly selected within the entire transect, with a
minimum of one sample unit being selected within each
100
subsampling area.
Z$ ZA 7.3 Z2 Zl
Locations where access pathways to the shoreline
existed were selected as sampling sites. One site per zone MonitoringZones
was randomly selected during each quarterly period.
Bancoora Beach, to the west of the outfall, was called Fig. 7 Bray~Curtis similarity dendrogram of major intertidal animal
group geometric mean populations in the (a) pre-eommission-
zone 1 (Z1); the 6.4 km of 13th Beach, to the east of the ing period and Co) the post-commissioning period.
rocky outcrops, was divided into four zones (Z2-Z5; see
Fig. l(a)). A sampler (0.05 m 2) was hand driven into the
sediment to a depth of 0.2 m and levered out with a differences between zones which could be attributed to
spade. The sample was sieved in situ and animals the old intertidal or new subtidal outfall. In addition,
retained on a 1.0 mm sieve were identified to the there were no significant differences detected in the data
taxonomic level of 'order' and counted. sets in each of the zones between the two monitoring
Geometric mean population data were assessed using periods.
multivariate cluster analysis to determine similarity
between zone changes in the pre- and post-commission-
ing monitoring periods. Figure 7 shows hierarchical
Conclusions
agglomerative clustering dendrograms calculated using
the Bray-Curtis similarity coefficient. The data were The monitoring programme showed that macroalgal
transformed by converting major animal group scores abundance has not been affected on either side of the
into logarithms to reduce the discrepancy between large new outfall, except for those sites directly affected by the
and small values. construction of the pipeline and subsequent longshore
The results show little difference in similarity sand shifts. Analysis of the infauna assemblages in areas
coefficients; however, there is a slight change of around the subtidal outfall indicated no outfall-related
hierarchical order with small changes occurring between impact on infaunal communities. Elevated numbers of
Z1, Z2 and Z3. Nevertheless, the subtle changes polychaetes found to the east of the intertidal ouffall
detected in this analysis were not considered significant. may reside naturally in this area. Further detailed
In brief, analyses of the data generated from this part of monitoring would be required to establish this;
the research revealed that there were no significant however, there is evidence that polychaete populations
339
Marine Pollution Bulletin
in a r e a s very close to t h e i n t e r t i d a l o u t f a l l h a v e Ferraro, S. P., Swartz, R. C., Cole, F. A. & Schults, D. W. (1991).
Temporal changes in the benthos along a pollution gradient:
decreased. discriminating the effects of a natural phenomena from sewage--
M o n i t o r i n g o f r o c k y shores h a s s h o w n t h a t the industrial wastewater effects. Estuar. Coastal ShelfSci. 33, 383-407.
p r e v i o u s l y identified a r e a s o f i m p a c t n e a r the o l d GDWB (1991). Annual Report. Geclong and District Water Board,
Geelong, Victoria, Australia.
i n t e r t i d a l o u t f a l l h a v e u n d e r g o n e significant change. Gonor, J. J. & Kemp, P. R. (1978). Procedures for Quantitative
O p p o r t u n i s t i c species, o n c e d o m i n a n t in the i n t e r t i d a l Ecological Assessments in Intertidal Environments. US EPA Report
areas, h a v e d i s a p p e a r e d . Species richness o f m a c r o a l g a e EPA-600/3-78-087.
Montgomery, H. A. C. & Soulsby, P. G. (1981). Effects of
in the a r e a has i n c r e a s e d to levels similar to o t h e r sites. eutrophication on the intertidal ecology of Langstone Harbour
A n a l y s i s o f the s a n d y b e a c h d a t a s h o w e d n o statistical UK and proposed control measures. Prog. War. Tech. 13, 287-
evidence to p r o v e t h a t either o u t f a l l i m p a c t e d u p o n 294.
MSE (1978a). Preliminary Investigation of the Environment and
s u r r o u n d i n g beaches. C o m m u n i t y v a r i a b i l i t y d i d occur, Ecology of the Geelong Waterworks & Sewerage Trust Sewer
b u t was e x p e c t e d in this e n v i r o n m e n t . Outfall. Report to GWST by Marine Science and Ecology, Geelong,
Victoria, Australia.
MSE (1978b). Distribution of the Benthic Communities at the
Ashton, P. H. (1986). Gcelong & District Water Board Ocean Geelong Waterworks & Sewerage Trust Sewer Outfall at Black
Outfall Biological Monitoring Program, 1986 Interim Report. Rock. Report to Caldwell Connell Engineers for GWSTG by
Report to Geelong & District Water Board, Geelong, Victoria, Marine Science and Ecology, Geelong, Victoria, Australia.
Australia. Portsmouth Polytechnic (1976). Langstone Harbour Study: The Effect
Ashton, P. H. (1991). Dilution Study Report. Report to Geelong & of Sewage Effluent on the Ecology of the Harbour. Portsmouth
District Water Board, Geelong, Victoria, Australia. Polytechnic Publication, Portsmouth, UK.
Barwon Water (1994). Barwon Region Water Authority, Ocean Sawyer, C. N. (1965). The sea lettuce problem in Boston Harbour. J.
Outfall Biological Monitoring Program. 1994 Interim Report. War. Pollut. Control Fed. 37, 1122-1133.
Barwon Water, Geelong, Victoria, Australia. Sneath, P. H. A. & Sokal, R. R. (1973). Numerical Taxonomy: The
Boesch, D. F. (1977). Application of Numerical Classification in Principles and Practice o f Numerical Classification. Freeman, San
Ecological Investigations of Water Pollution. Carvallis Environ- Francisco.
mental Research Laboratory, USEPA. Soulsby, P. G., Lowthion, D. & Houston, M. (1978). Observations on
Buttermore, R. E. (1977). Eutrophication of an impounded estuarine the effects of sewage discharged into a tidal harbour. Mar. Pollut.
lagoon. Mar. Pollut. Bull. $, 13-15. Bull. 9, 242-245.
CCE (1979). Geelong Ocean Outfall Study Report. Report to the Synnott, R. & Brown, V. (1985). The environmental effects of effluent
Geelong Waterworks & Sewerage Trust by Caldwell Connell discharge at Boags Rocks II. Results of monitoring program, 1980-
Engineers, Geelong, Victoria, Australia. 84. Working Paper 85/12. Melbourne & Metropolitan Board of
Dorsey, J. H. (1982). Intertidal community offshore from the Werribee Works, Melbourne, Australia.
sewage treatment farm: an opportunistic infaunal assemblage. Aust. Wilkinson, L. (1963). Nitrogen transformation in a polluted estuary.
J. Freshwat. Res. 33, 45--54. Int. J. Wat. Pollut. 7, 737-752.
340
Pergamon 0025-326X(95)0013414 Copyright © 1995 Elsevier Science Ltd
Printed in Great Britain. All rights reserved
0025-326X/95 $9.50+ 0.00
Biological Monitoring of the Marine
Ocean Outfall at Black Rock,
Victoria, Australia
PETER H. ASHTON* and BRUCE J. RICHARDSONt~
*Barwon Region Water Authority, P.O. Box 651, Geelong, Victoria 3223, Australia
"~School of Biological & Chemical Sciences, Deakin University, Geelong, Victoria 3217, Australia
~Author to whom correspondence should be addressed.
The Barwon Region Water Authority in Victoria, onshore treatment plant, which improves the quality of
Australia, commissioned a new subtidal ocean sewage the effluent by removing all floatable material, grit
outfall in February 1989. This ouffall replaced an old particles (>0.2 mm equivalent diameter) and visible
intertidal outfall, and presently discharges via a diffuser in floating oil and grease. The resultant effluent is buoyant,
an average depth of 15m some 1.2km offshore in Bass being more than 99% freshwater, and rises through the
Strait. Examination of biological communities around the water column to the surface, becoming mixed with
old outfall prior to the change revealed distinct differences ambient water by turbulent entrainment.
in biotic assemblages close to the ouffall. An ongoing The new subtidal outfall was designed to achieve a
monitoring programme, implemented in 1986, has rapid initial mixing ( > 100: 1; Ashton, 1991). During
assessed not only the recovery in this intertidal area, but the early phase of the study reported here, a model was
also the major changes to macroalgal communities on developed to predict effluent plume movement from the
surrounding reefs, subtidal infauna populations in sandy new subtidal outfall (see Ashton, 1986). This model
sediments, and rocky shore communities. defined a zone (zone 3: see Fig. l(a)) in which dilution of
the effluent field would not exceed 10 times that of the
initial dilution for 90% of the time. It was believed that
this zone would be the most likely area of adverse
The Black Rock sewage outfall services the city of impact.
Geelong and surrounding coastal townships in central The aims of this study were to examine the effects
Victoria, Australia (Fig. 1). The effluent passing of the submerged outfall on local subtidal assem-
through the system originates from industry (13% by blages, and the recovery from any impacts of the old
volume), domestic, commercial properties and perman- shoreline outfall on local intertidal and near-shore
ent infiltration (87%). The total population of the subtidal assemblages. The study was divided into four
region has increased from approximately 30 000 in 1910 sub-programmes on the basis of habitat types,
to around 200000 in 1990 (GDWB, 1991). Since 1916, including macroalgal communities on subtidal reefs;
sewerage services have been provided for a high infauna community structure in subtidal sediments;
percentage of the population in the region via an macroalgal and macroinvertebrate communities on the
intertidal outfaU which discharged up to 50 M1 d-1 of intertidal rock platforms; and infaunal community
coarsely-screened sewage effluent (CCE, 1979). With structure in the intertidal sandy sediments on
increasing volume of discharge, ecological and other surrounding beaches.
effects were reported from areas surrounding the outfall,
until eventually it was shut down in 1989 and a new
offshore ocean outfall was commissioned. The new
Subtidai Reef Monitoring
outfall discharges an average 55 M1 d -1 of finely- A flexible underwater strategy for monitoring the
screened sewage from a series of 27 diffuser ports which macroalgal communities was adopted to allow for a
are located 4 m apart on alternate sides of a pipeline, variable number of quadrats to be photographed,
situated, on average, at a depth of 15 m and depending upon the environmental conditions during
approximately 1.2 km from shore. the time of sampling. The photographic technique was
The old intertidal outfall discharged at the low water designed to permit 'single image analysis' of divisional
mark in a then remote area, 14 km south of Geelong. macroalgal coverage (i.e. red, green and brown algae)
Before discharge, the raw effluent passed through coarse over the reef substrate. Consideration was given only to
screen comminutors and was pumped to elevated levels total macroalgal cover, irrespective of canopy type (i.e.
via Archimedes screw pumps during flooding tidal turf, understorey or top). The monitoring strategy was
periods. The changes which have been effected in the designed to detect major changes, as monitoring subtle
new outfall include the passage of sewage through an population changes would not be cost-effective.
334
Volume 31/Numbers 4-12/April-December 1995
Melbourne
Geelong
38os ~
145 ° E
& ' "L, /
I /
M a p (a) "~ _ o)~ i,,,,,io,)o,,r,t) ~_._z~.__.~ ! //z
3 i
,oo.,
Bancoora Beach ' ~ - f + \ --- J ~r~6 I
Zone2 -~Subhdal Outfall
. ]nlertidal Beach Zones .......
Zooo~ Sublidal Sedime=ll Zones
0 I 2
/
M a p (b)
Black Rock
~ ~ o S l f T r ePla.t e r l l
alm • ,9
s; _s,S,
" ", , 1 1 , I'(ocky Sh oreline =>
R S5.~1~ • 52
~ -' Reef Sties (S#)
Rocky Shore Sites (RS#) => +
=> •
0 1 2
t .......... ~ t ........... .I
• St Km
Fig. 1 Location of the study area on the shores of Bass Strait. Map (a)
shows the subtidal soft-bottom samplingzones (Zones 1-6) and
the intertidal soft-s~Um~at sampling zones (Z1-ZS). Map (b)
shows the subtidal reef monitoring sites (S1-S12) and the
intertidal rocky shore sites (RS1-RS5).
Twelve sites were established (Fig. l(b)), nine o f and S11 were established to m o n i t o r the shallow waters
which were located in 15-20 m depth o f water. Two sites near the old outfall. Site S12 was established in
(S1 and $2) were established well away from the outfall shallower waters outside the predicted area o f influence.
area as controls. The locations o f the sites were based Flat areas o f reef were selected and locations fixed
directly u p o n possible impact zones predicted by a with a site marker. On each sampling occasion,
water quality model (Ashton, 1986). Following the transects were identified by a second m a r k e r 20 m
commissioning o f the new intertidal outfall, sites S10 away at a fixed compass bearing from the original site
335
Marine Pollution Bulletin
9S
100 I I I I I I I I
S12 Sl S3 S2 SI2 Sl S2 S7 S9 S9 SS S4 S3 S8 S4 S7 S6 S$ s 1 s6
Po¢ Post Po¢ po6tPre Pre Pie Pre pest Pre Pre Pie Pre Po~/ Post Poe Post Post Pie Pre
rF I
Reef Sites
Fig. 2 Bray--Curtis similarity dendrogram of macroalgal coverage in
the pre- and post-commissioning periods.
Percentage Algae Cover
100
80
60
40
20
ss (som) $4 (210m) s3 (540m) s9 (790m) s2 (4kin)
$6 (120m) $7 (390rn) $8 (630m) $12(2.1km) s l (5kin)
Reef Sites (distance from Ihe out'fall)
! Pre- Commissioning
mean value M Post-Commissioning
mean value
Bars = Standard Deviation
Fig. 3 Mean macroalgal coverage of sites during pre- and post-
commissioning periods.
marker. To minimize diver bottom times, photography abundances recorded at the two sites nearest the outfall
was carried out using a camera mounted on a grid (0.33 ($5 and $6) were attributed to construction activities in
m 2 in area). A minimum of 15 photographs were taken the pre-commissioning period and to sand accretion
at random along the transect, the exact number over the rocky substrate, driven by longshore sand
depending upon weather or sea conditions. shifts, in the post-commissioning period.
Raw data were group-averaged using mean percent- An assessment of reef macroalgae relative to
age canopy cover and analysed by hierarchical distance from the outfall was made using the mean
clustering. Figure 2 illustrates a Bray-Curtis similarity percentage macroalgal cover of each of the sites for
dendrogram of macroalgal coverage data for both the two monitoring periods. The results (Fig. 3) show
sampling periods (note that sites S10 and Sll are not that the two sites closest to the outfall ($5 and $6)
included, as there were no pre-commissioning data for had lower coverage for both monitoring periods. In
these sites). Macroalgal abundance was similar at all addition, both sites showed more variability during
sites in both sampling periods, although the lower the pre- and post-commissioning periods than the
336
Volume 31/Numbers 4-12/April-December 1995
other sites. All other sites showed an average of 75- and post-commissioning periods was undertaken separ-
90% macroalgal reef coverage for both monitoring ately to highlight individual zone differences between
periods, irrespective of distance or direction from the the two periods. Figure 4 indicates that changes have
out fall. occurred since the shutdown of the old intertidal outfall.
Whereas zone 5 was quite different in relation to other
zones in the pre-commissioning phase, it was similar to
Infauna Communities in the Subtidal Sediments zone 6 and closer in similarity to the other zones in the
post-commissioning period. These changes are due to
The monitoring strategy used in this habitat was the lower number of polychaete species collected in zone
designed to allow random sampling on a seasonal basis. 5 in the post-commissioning period.
Twenty locations were randomly selected within a Although elevated numbers of polychaetes were
kilometre-wide transect in the study area, and five detected in zone 4 in the pre-commissioning period,
replicate samples were taken at each location. A the multivariate analysis techniques were unable to
purpose-built venturi sampler was designed to enable differentiate distinct differences between this zone and
surface operation using small craft as a platform. The other unaffected zones, because of the presence of other
sampler covered an area of 0.05 m 2 (i.d. = 0.253 m) and dominant groups such as the amphipoda, isopoda and
sampled up to 0.20 m in depth, depending upon the the cumacea. Nonetheless, the mean number of
compaction of the substrate. polychaetes was still higher in this zone than in the
The sampling sites were catalogued into zones other zones in the pre-commissioning monitoring
corresponding to previously identified impacted areas period, but was no different to the other zones in the
and a single, predicted possible impact area, the latter post-commissioning period. This further strengthens the
based on the model produced during the study design assumption that the area around the old intertidal
(Ashton, 1986). The zones are shown in Fig. l(a). Major outfall is no longer impacted, and that population
animal groups (orders) were differentiated using multi- numbers have returned to baseline levels. On examina-
variate techniques. tion of the mean numbers of polychaetes in zones 5 and
A comparison was made between population data of 6, it is evident that they are above other zones; however,
animal groups collected from all samples taken during the numbers for zone 6 are similar in both periods.
the pre- and post-commissioning stages (Table 1). Slight Therefore, it may be assumed that the soft-bottom
differences in the percentages of the major groups of sediments to the east of the outfalls are able to harbour
animals were found. The population of amphipods was higher populations of these animals. There were no
reduced by 10% after the change of outfall. Isopods
increased from 4.6 to 11%, and the cumacea decreased (a)
from 7.5 to 3.3%. The polychaetes increased from 7.4 to 0
10%. In a dynamic environment such as that at Black 10
Rock, these differences are considered minor and are .£~0 20
probably due to natural changes (e.g. see Ferraro et al., 30
1991). r~ 40
To further elucidate differences between the six ._~
S0
defined zones, multivariate classification techniques
6o
were used and comparisons were based on the identity
of the major groups of animals in the collections. The
Bray-Curtis (B-C) similarity coefficient based on 80
abundance of the dominant groups of animals was 90 I
used to measure changes. The inter-group resemblance 100
Zone 6 Zone 4 Zone 3 Zone 2 Zone Zone
was defined as the mean of all resemblances between
one group of animals to those of another. Such group-
average clustering (Sneath& Sokal, 1973) has space
(b) 0
conserving properties, which produce clusters with little
10
distortion of the actual resemblance relationships
(Boesch, 1977). The hierarchical clustering of the pre- 20
30
9. 40
TABLE 1
Major animal group presence (descriptive statistical data only, 50
expressed as percentage population abundance for animals > 1 mm 60
< 10ram in size) in soft-bottom sediments throughout the study area. i. 70
Animal group
Amphipoda
Pre-commissioning
78
Post-commissioning
68
80
90
h
Isopoda 4.6 11 100
Cumacea 7.5 3.3 Zone 6 Zone 5 Zone 4 Zone 1 Zone 3 Zone 2
Decapoda 0.9 2.7
Polychaeta 7.4 10 Fig. 4 B r a y - C u r t i s s i m i l a r i t y d e n d r o g r a m o f the m a j o r s u b t i d a l
Others 1.6 4.0 a n i m a l g r o u p p o p u l a t i o n s b e t w e e n the z o n e s in t h e (a) p r e -
c o m m i s s i o n i n g p e r i o d a n d (b) the p o s t - c o m m i s s i o n i n g p e r i o d .
337
Marine Pollution Bulletin
obvious changes to polychaete numbers in the zone The discharge of sewage effluents to intertidal areas
nearest the subtidal outfall (zone 3), nor were any major has been associated with the stimulation of large crops
changes detected in other major population groups in of macroalgae, notably Enteromorpha spp. and Ulva
this zone. spp. (Wilkinson, 1963; Sawyer, 1965; Portsmouth
Polytechnic, 1976; Buttermore, 1977; Soulsby et al.,
1978; Montgomery & Soulsby, 1981). Although it was
Rocky Shores documented in the early studies (MSE, 1978a,b) that
Site selection was based upon the presence and primary production of macroalgal species, such as
location of permanently-exposed rocky shores in the Enteromorpha spp. and Ulva spp., was enhanced at
area, and the distance of these sites from the intertidal sites closer to the intertidal outfall at Black Rock, there
and subtidal outfalls (Fig. l(b)). Ten quadrats, each was some concern during the design stage of the
250x400 mm (0.1 m2), were permanently marked in programme in using these species to determine the
the mid to lower eulittoral zone at each site using recovery of rocky shore sites. These concerns were later
masonry nails. These quadrats were selected as justified, as certain sites well away from any area of
representative of the exposed areas of the cobbled or impact of the outfall (e.g. RS4 and RS5) showed periods
flat platform sites. Non-destructive methods (Gonor & of stimulated growth of these species.
Kemp, 1978) were used to estimate percentage cover of As the study required a monitoring programme that
macroalgae, mussel mats of Xenostrobus pulex and the would address 'recovery' of a rocky shore site (RS3)
sand mats of the spionid polychaete Boccardia following the shutdown of an intertidal outfall, special
proboscidea to the nearest 10%. Other groups of consideration was given to the opportunistic species B.
animals were counted individually. proboscidea (see Dorsey, 1982; Synnott & Brown,
Mean,'abundanceScore
2,500
2,000
15 0
,0
10 0
,0
500
0
1986 1987 1988 1989 1990 1991
Year
I G .r p d N Girrepedi N Polychaeta~
a o oa
t a
TubeWorrns
Polychaeta
SpionidWorms I B~vak'a
Fig. 5 Animal class abundance trends at rocky shore site RS3.
25
~52o
o0 lO
"6
o
RS1 RS2 RS3 RS4 RS5
Rocky Shores Site
[ ] 1986 [ ] 1988 [ ] 1989 [ ] 1990 [ ] 1991
Observationswerenotundertaken RS1,RS2,
at
RS4andat RS5in 1988.
Fig. 6 Macroalgal species richness trends on the rocky shore sites.
338
Volume 31/Numbers 4-12/April-December 1995
1985). Monitoring continued at this site during both (a)
the pre- and post-commissioning stages, and all other
organisms within the quadrat areas were documented.
Distinguishing between natural variability of plants -s0-
and animals and a 'recovery' response proved difficult
using the quadrat method alone, even though the '~
disappearance of B. proboscidea was evident (Fig. 5). ~ ss -
However, the results of annual macroalgal surveys .~
undertaken at each of the intertidal sites (Fig. 6)
reinforced the notion that site RS3 was recovering ~ 90-
¢1
slowly, with the gradual appearance of brown algae
which had not been previously documented, yet which
were common at other sites less than 1 km away. 95 -
Nevertheless, it was obvious, even 3 years after the
intertidal outfall shutdown, that the abundance of I00
macroalgal species was still well below expected levels.
Z$ Z4 ZI Z3 Z2
Subsequent studies have shown that macroalgal
abundance has increased to levels similar to that at MoniteringZoees
site RS1 (Barwon Water, 1994), which adds strength
to the conclusion that the RS3 site has recovered and (b)
now shows little evidence of past stress.
80-
Infauna Communities in the Intertidal
Sediments
The monitoring area of this habitat was divided into
zones relevant to direction and distance away from the I
outfalls. Each zone was sampled every season, using a
belt transect which ran from the previous high water 90- I
mark to the low water mark. To monitor populations
through the entire transect, stratified random samples
were taken along the belt transect. Ten sample units 95-
were randomly selected within the entire transect, with a
minimum of one sample unit being selected within each
100
subsampling area.
Z$ ZA 7.3 Z2 Zl
Locations where access pathways to the shoreline
existed were selected as sampling sites. One site per zone MonitoringZones
was randomly selected during each quarterly period.
Bancoora Beach, to the west of the outfall, was called Fig. 7 Bray~Curtis similarity dendrogram of major intertidal animal
group geometric mean populations in the (a) pre-eommission-
zone 1 (Z1); the 6.4 km of 13th Beach, to the east of the ing period and Co) the post-commissioning period.
rocky outcrops, was divided into four zones (Z2-Z5; see
Fig. l(a)). A sampler (0.05 m 2) was hand driven into the
sediment to a depth of 0.2 m and levered out with a differences between zones which could be attributed to
spade. The sample was sieved in situ and animals the old intertidal or new subtidal outfall. In addition,
retained on a 1.0 mm sieve were identified to the there were no significant differences detected in the data
taxonomic level of 'order' and counted. sets in each of the zones between the two monitoring
Geometric mean population data were assessed using periods.
multivariate cluster analysis to determine similarity
between zone changes in the pre- and post-commission-
ing monitoring periods. Figure 7 shows hierarchical
Conclusions
agglomerative clustering dendrograms calculated using
the Bray-Curtis similarity coefficient. The data were The monitoring programme showed that macroalgal
transformed by converting major animal group scores abundance has not been affected on either side of the
into logarithms to reduce the discrepancy between large new outfall, except for those sites directly affected by the
and small values. construction of the pipeline and subsequent longshore
The results show little difference in similarity sand shifts. Analysis of the infauna assemblages in areas
coefficients; however, there is a slight change of around the subtidal outfall indicated no outfall-related
hierarchical order with small changes occurring between impact on infaunal communities. Elevated numbers of
Z1, Z2 and Z3. Nevertheless, the subtle changes polychaetes found to the east of the intertidal ouffall
detected in this analysis were not considered significant. may reside naturally in this area. Further detailed
In brief, analyses of the data generated from this part of monitoring would be required to establish this;
the research revealed that there were no significant however, there is evidence that polychaete populations
339
Marine Pollution Bulletin
in a r e a s very close to t h e i n t e r t i d a l o u t f a l l h a v e Ferraro, S. P., Swartz, R. C., Cole, F. A. & Schults, D. W. (1991).
Temporal changes in the benthos along a pollution gradient:
decreased. discriminating the effects of a natural phenomena from sewage--
M o n i t o r i n g o f r o c k y shores h a s s h o w n t h a t the industrial wastewater effects. Estuar. Coastal ShelfSci. 33, 383-407.
p r e v i o u s l y identified a r e a s o f i m p a c t n e a r the o l d GDWB (1991). Annual Report. Geclong and District Water Board,
Geelong, Victoria, Australia.
i n t e r t i d a l o u t f a l l h a v e u n d e r g o n e significant change. Gonor, J. J. & Kemp, P. R. (1978). Procedures for Quantitative
O p p o r t u n i s t i c species, o n c e d o m i n a n t in the i n t e r t i d a l Ecological Assessments in Intertidal Environments. US EPA Report
areas, h a v e d i s a p p e a r e d . Species richness o f m a c r o a l g a e EPA-600/3-78-087.
Montgomery, H. A. C. & Soulsby, P. G. (1981). Effects of
in the a r e a has i n c r e a s e d to levels similar to o t h e r sites. eutrophication on the intertidal ecology of Langstone Harbour
A n a l y s i s o f the s a n d y b e a c h d a t a s h o w e d n o statistical UK and proposed control measures. Prog. War. Tech. 13, 287-
evidence to p r o v e t h a t either o u t f a l l i m p a c t e d u p o n 294.
MSE (1978a). Preliminary Investigation of the Environment and
s u r r o u n d i n g beaches. C o m m u n i t y v a r i a b i l i t y d i d occur, Ecology of the Geelong Waterworks & Sewerage Trust Sewer
b u t was e x p e c t e d in this e n v i r o n m e n t . Outfall. Report to GWST by Marine Science and Ecology, Geelong,
Victoria, Australia.
MSE (1978b). Distribution of the Benthic Communities at the
Ashton, P. H. (1986). Gcelong & District Water Board Ocean Geelong Waterworks & Sewerage Trust Sewer Outfall at Black
Outfall Biological Monitoring Program, 1986 Interim Report. Rock. Report to Caldwell Connell Engineers for GWSTG by
Report to Geelong & District Water Board, Geelong, Victoria, Marine Science and Ecology, Geelong, Victoria, Australia.
Australia. Portsmouth Polytechnic (1976). Langstone Harbour Study: The Effect
Ashton, P. H. (1991). Dilution Study Report. Report to Geelong & of Sewage Effluent on the Ecology of the Harbour. Portsmouth
District Water Board, Geelong, Victoria, Australia. Polytechnic Publication, Portsmouth, UK.
Barwon Water (1994). Barwon Region Water Authority, Ocean Sawyer, C. N. (1965). The sea lettuce problem in Boston Harbour. J.
Outfall Biological Monitoring Program. 1994 Interim Report. War. Pollut. Control Fed. 37, 1122-1133.
Barwon Water, Geelong, Victoria, Australia. Sneath, P. H. A. & Sokal, R. R. (1973). Numerical Taxonomy: The
Boesch, D. F. (1977). Application of Numerical Classification in Principles and Practice o f Numerical Classification. Freeman, San
Ecological Investigations of Water Pollution. Carvallis Environ- Francisco.
mental Research Laboratory, USEPA. Soulsby, P. G., Lowthion, D. & Houston, M. (1978). Observations on
Buttermore, R. E. (1977). Eutrophication of an impounded estuarine the effects of sewage discharged into a tidal harbour. Mar. Pollut.
lagoon. Mar. Pollut. Bull. $, 13-15. Bull. 9, 242-245.
CCE (1979). Geelong Ocean Outfall Study Report. Report to the Synnott, R. & Brown, V. (1985). The environmental effects of effluent
Geelong Waterworks & Sewerage Trust by Caldwell Connell discharge at Boags Rocks II. Results of monitoring program, 1980-
Engineers, Geelong, Victoria, Australia. 84. Working Paper 85/12. Melbourne & Metropolitan Board of
Dorsey, J. H. (1982). Intertidal community offshore from the Werribee Works, Melbourne, Australia.
sewage treatment farm: an opportunistic infaunal assemblage. Aust. Wilkinson, L. (1963). Nitrogen transformation in a polluted estuary.
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340