Department of Health Library Services ePublications - Historical Collection
Please Note: Aboriginal and Torres Strait Islander people should be aware that this publication may contain images, voices or names of deceased persons in photographs, film, audio recordings or printed material.
Purpose
To apply preservation treatments, including digitisation, to a high value and vulnerable Historical collection of items held in the Darwin and Alice Springs libraries so that the items may be accessed without causing further damage to the original items and provide accessibility for stakeholders.
Reference and Research Disclaimer
Please note: this document is part of the Historical Collection and the information contained within may be out of date.
This copy is a reproduction of an original record. Please note that the quality of the original record may be poor and cannot be enhanced with the scanning process.
Northern Territory Department of Health Library Services Historical Collection
DE
Q(,ilt~,_TW(pr,ff 0# I"( .t.l Tt1 N4J C(')MiUlan 51.llllvCll
MOSQUITO BREEDING IN SEWAGE PONDS AT BATCHELOR, ADELAIDE RIVER AND
PINE CREEK.
F0R FURiTHER INFORMATION:
DL HIST
595. 772
BOO
1988
CCNTACT: MEDICAL ENTOWOLOGY BRANCH
DEPARTMENT OF HEALTH AND COMMUNITY SERVICES GPO BOX 1701
DARWIN NT 0801
=LEPHONE: 20 8333 Peter Whelan
Senior Medical Entomologist
HISTORICAL COLLECTION
.:::ibn'::>- - 52
3o~
T 1 111 11~n111 1Hll 1H1r~1[ 111~1 ~1
I19, 2 ~ -
3 0820 00005697 3
CENTRAL LIBRARY - 7 APR 1998
TERRITORY HEAL TH SERVICES
MOSQUITO BREEDING IN SEWAGE PONDS AT BATCHELOR, ADELAIDE RIVER AND PINE CREEK
July/ August, 1988 D. Booth
&W. Kelton
Medical Entomology Branch
Department of Health and Communit
yServices
DATE DUE
. ..
,~ ~
RA£CO
1:>L Htsr
5::,5_-r72
44098
O?L{<c:,0/1
~ .
INTRODUCTION
As part of the Medical Entomology Branch's ongoing assessment of mosquito breeding in the Darwin Region the sewage ponds at Batchelor, Adelaide River, and Pine Creek were visited.
This report discusses the mosquito breeding detected at these ponds and assesses likely problem areas so that management of the ponds with respect to mosquito breeding can be optimised.
In general, mosquito breeding following circumstances:
occurred in the
- where floating debris in the primary pond had been allowed to accumulate;
- where margins were lined with vegetation;
- where effluent is discharged into areas such that the margins of the pooling were shallow and lined with vegetation;
- where sewage was leaking from a broken main.
The discharged effluent is probably the most important source of mosquitoes from sewage ponds generally, and certainly at Batchelor and Pine Creek.
Specific aspects of the above points are discussed in this report.
•
N. T. SEWAGE PONDS
1. BATCHELOR
The Batchelor sewage ponds were inspected for mosquito breeding on the 19-20th July, 1988 C see Figure 1, Map 1 for diagram and location of ponds). Previous inspections C June, 1987; September, 1983) had found Culex annulirostris breeding in the primary and evaporation ponds, and had suggested alterations to pond structure and maintenance to prevent mosquito breeding.
Cx annulirostris was again collected in the primary ponds. It breeds in the areas where wave action is disrupted by floating debris. There was more floating debris here than at the Adelaide River sewage primary pond <where no Cx annulirostris were collected).
The secondary pond was covered in very dense A2olla which would have prevented larval access to the surface. Hence no mosquito breeding was detected.
There was some grass growing in the crevices of the concrete apron around this and the other two ponds. No mosquito breeding was detected near these at this time but i t is likely that unchecked growth of these weeds may later encourage mosquito breeding.
Hater in the evaporation pond was covered in a dense layer of A2olla and the edges were lined with Typha This vegetation was too dense to allow mosquito breeding, though at the higher water levels in the wet and early dry season i t is likely that mosquitoes would breed in the Typha
Dry ice baited traps indicated a number of mosquito species were present in the area, including Cx annuli rostri s C Table 1). However, the numbers were not high, particularly compared to the trap 500 metres from the ponds (69 cf 132 per trap/night).
Although there was l i t t l e mosquito breeding in the ponds at the time of the visit, a number of features of the sewage ponds could be altered to reduce the risk of mosquito breeding at other times of the year.
Recommendations:
1. The Typha in the evaporation pond be killed and removed before the next wet season.
2. A partitioning of the evaporation pond to control the dispersal of the effluent.
3. More regular removal of the floating debris in the primary pond.
4. More regular removal of weeds from the concrete margins of the ponds .
•
---
..._,,, - - '
---"' ',
I I I I I
'
I Me."Sl.1tk:\~---~-
...'
\'
I.S.EALE.b RoAt>5
Du~.T 'lo~o~ /TAACAt;s
R.AILWP.Y
.b~1,U~,t::f.. LIN!.
\.lET SEA!>Orl LAGOOt.l {u~"'-'-Y O~y) Ps.RtvlANli'NT" ~~Tfrfl.
\.
\
t.
~-
...,.-- '
--- ,
...'
\ I--- ... _.__>
,
,,.--,--~
- ,,__
_.,\ \_,,
,Map 1 .
I
Location of Batchelor Sewage Ponds
l,
3 ""'·
I
'
Figure 1. Batchelor Sewage Ponds
Trap Bl
Primary Pond j..
some sludge
Cx annulirostris breeding Secondary Pond
I
.dense growth of duckweed
dense :E.Xpha
Trap B2 500m S E /
Evaporation Pond
Legenci
r~] Fl
effluent 1'ypha
Table 1. Batchelor Sewage Ponds - Mosquito Breeding Female mosquitoes trapped in dry ice baited EVS traps near Batchelor Sewage
Ponds, 18-19 July, 1988
Species Trap B1 Trap B2
C at sewage C 500m SE ponds) ponds)
An bancroftii 1
Cx annulirostris 69 132
Cx pullus 2
Cq xanthogaster 208 333
Ma uniformis 2
Total 281 466
2. ADELAIDE RIVER
The Adelaide River sewage ponds were inspected on the 19-20th July, 1988 (see Figure 2 and Map 2 for diagram and location of ponds). The last inspection of these sewage ponds for mosquito breeding was in April, 1983.
In contrast to that visit, there was no grassy margin to the primary pond, and no mosquito breeding in it.
The effluent was bounded by the concrete wall. There was less floating debris in this pond than at Batchelor.
The secondary pond remains as described in the 1983 visit. However, there was no mosquito breeding. This was due to the dense layer of Azolla covering most of the surface of the pond, and preventing mosquito breeding, even at the grassy edges. The level of effluent was very low, and there was a 1-2 metre grassy margin between the concrete apron and effluent.
Seasonal fluctuations in the water level may inundate the grassy edge, or may provide an ideal mosquito breeding area. A wet season inspection of the ponds is needed to assess this. Also, i f the Azolla were less dense, as i t probably is at certain times of the year, i t is probable that Cx annulirostris could breed in the secondary pond.
No effluent was discharged into the evaporation pond at the time of the visit or for some months prior to it.
Dry ice baited traps run overnight confirmed that there was no significant mosquito breeding in these ponds (Table 1). Only 24 Cx annulirostris / trap night were collected at the ponds, compared with 79/trap night 500m from the ponds. Very high numbers of Psychodids were collected at the ponds, but these have no public health importance.
Mosquito breeding was not a problem in the Adelaide River sewerage ponds at the time of the visit. A number of measures could be employed to ensure this continues.
Recommendations
1. The floating debris in the primary pond needs to be regularly removed Ctherw was no evidence that this was not happening at present).
2. All vegetation will need to be removed from the edges of the secondary pond.
3. If the evaporation pond is to be used, i t needs to be compartmentalised so that pooling at the inlet is bound by a formalised margin.
Map 2. Location of Adelaide River Sewage Ponds
t
to DarwinTrap A2
Stuart Highway
service Station
•
'l'rap Al
~
Adelaide River Township
Service Station Pub
Sewage Ponds
O. 5km
Figure 2. Adelaide River Sewage Panas
Trap A2 500m S
'
some sludge \
Primary Pond
i\
dense growth of duckweed
Secondary Pond
\
I
"-\
Trap Al
grassy edges (l-2m) '\ ..,.
·, I
\ ----:;
\.
Evaporation Pond
dry ..
i
N•
Table 2. Adelaide River Sewage Ponds - Mosquito Breeding Female mosquitoes trapped in dry ice
baited EVS traps at Adelaide River sewage ponds, 18-19 July, 1988
Species Trap A1 Tra:e A2
C at sewage (500m s ponds) of ponds)
An bancroftii 2
An annulipes 1
Cx annulirostris 24 79
Cq xanthogaster 47 11 9
Total 71 199
Chironomids 8
Psychodids - 200
•
3. PINE CREEK
An inspection was made of the Pine Creek sewage ponds (see Figure 3 and Map 3 for diagram and location of ponds) and effluent disposal system on 10th and 11th August, 1988. A previous survey in April, 1983 had found the ponds to have prolific weed growth around the margins, and resultant breeding of large numbers of Culex annulirostris mosquitoes. At that time, i t appears that some of the ponds had a small concrete border at the margins, but this apparently had broken down in places and allowed weed growth. It had also retained pockets of effluent cut off from the main body of the pond, and these small pockets had been found to be breeding huge numbers of mosquitoes.
This inspection found the ponds to have been upgraded, and new concrete margins put in around each pond. A concrete apron has been laid around each pond and is approximately 50cm wide and slightly sloping (probably less than 20 degrees slope). The first three ponds were full, margins were weed free and no mosquito breeding was located. The final evaporation pond was only partially full, withearth exposed between the concrete apron and the water level, and there was a dense weed growth at the edges and extending about 2m into_ the pond. Mosquito breeding was prolific amongst the vegetation, being in excess of SO/dip for early instar larvae, and considerably lower numbers of later instar larvae and pupae (less than 1/dip).
Results of the larval survey are set out in Table 4. No predators were seen in several dips made, and during observation.
During later discussion with the contractor responsible for maintenance, advice was received that the weed growth had 'recently' been sprayed with Ustil an. Inspection showed that while weeds growing on earth exposed just below the concrete apron had died, those in the water appeared unaffected. The contractor was unable to be more specific about the actual date of spraying. When weeds are killed in the final pond, they will need to be removed due to their large biomass, otherwise the dead lodged vegetation will s t i l l provide suitable breeding sites for mosquitoes.
Some solids and floatables were collecting in the corner of the first pond, and a scum was beginning to form in the corner of the second pond. Care needs to be taken to prevent this occurring. No discharge of effluent was occurring into the open drain adjacent to the ponds, but there was some underground discharge to a more formalized point approximately 100m from the ponds. The effluent was piped underground and discharged via an energy dissipation structure, into an open concrete-lined drain, which in turn discharged into an open unlined drain. This unlined drain had numerous animal hoof prints and some grass and green algae growth. Cx. annulirostris was found breeding here
"
in minor numbers at less than 1/dip. There was free water for only about 25m in length of the drain due to the dry conditions pre~ailing, but this area could be a problem during the wet season.
The two borrow pits adjacent to the ponds, found to contain water at past inspections,
which have been were both dry.
Approximately half way between the ponds and the town, close to the sewage pumping station, there was a broken sewer main. Effluent was rising to the ground surface, flowing under the road via a culvert, and finally along a shallow flow line into a depression on the flat. The water in this final holding area was vegetation-free but had green algal growth. Minor numbers of Culex annulirostris were found breeding in this area. Where the effluent flowed under the road there was dense grass growth, shade from overhanging trees and huge numbers of Culex guinquefasciatus were found to be breeding in this area.
John Robertson, contractor to the Department of Transport and Works for maintenance of the sewage ponds, advised that the broken main had been repaired, and that he would either pump the effluent out onto higher ground or treat the surface with diesel to prevent mosquito breeding.
Inspection later revealed that the effluent was s t i l l flowing along the rocky section of the drain, suggesting that there was s t i l l a leak.
Pine Creek Creek was dry, except for a dammed section immediately to the west of the Stuart Highway. The dam was free of vegetation at the margins. This area was not examined for mosquito breeding.
The Pine Creek Gold Mine personnel advise that the old tailings dam and evaporation areas adjacent to the highway are being phased out of operation, and a new dam further to the west is now being used. Access to the new area was not sought, but a brief inspection of the old evaporation area showed only a minimal amount of water and no marginal vegetation.
Four carbon-dioxide baited mosquito traps were set at the sewage ponds, sewer main leak area and the edge of town and the trapping results may be seen in Table 3. Table 4 details mosquito larvne collected in the locality.
Cx. annulirostris accounted for 85% of the total adult collections, with the highest numbers occurring close to the sewage ponds and the leaking main. Numbers of Cx. quinquefasciatus were low, but this species is not highly attracted to carbon dioxide mosquito traps, and the numbers collected would be an underestimate of actual population figures. Both of these species of mosquitoes are potential disease vectors, and high numbers close to
•
O?Cf40 /1?
areas of habitation are undesirable. Repair and maintenance of the sewage system in Pine Creek would reduce the current high mosquito numbers.
Rec omme nda-t ions:
1. Weed should be removed immediately from the evaporation pond to reduce mosquito breeding. Until the pond is restored to weed free condition, temporary insecticidal control should be carried out. Periodic inspections should then be carried out in all ponds to ensure that mosquito breeding is not re-established.
2. The open should be maintained not occur.
earth drain which receives excess effluent formalized for its whole length, and in a state such that mosquito breeding does
3. Some provision needs to be made to dispose of excess effluent before the wet season, as i t appears now that effluent is simply dispersed down a drain to an i l l - defined drainage line about 100m from the ponds (See Map 3). One suitable method of excess disposal would be to formalise the two borrow pits immediately west of the pond system. They would need to be excavated to a suitable depth, and have steep sides to prevent weed growth. Excess could then be directed into them, thus increasing the total evaporation area of the system.
4. Immediate steps need to be taken to completely repair the faulty sewer main and prevent sewage from pooling near the pump station. In the meantime, insecticidal treatment should be carried out as a matter of urgency, to prevent mosquito breeding in high numbers close to the town .
i
'
LEc:;ewt>.
~--5it:
..,.0 ; _ _ _ _ _ ___.L.--_ _ _ ____,
-*
L~~ ~ P L . 1 ~ O,TI!I.I ,1- --~\
• >
I
Li:"ar.;."'b
• CO2. -t<'Gtf loco..t\°"'
0
-
• 5,~
No 1.
<
Figure 3
O'JL-\ \o V ( l(p •
TABLE 3 HOSQUITO BREEDING SURVEY - PINE CREEK AUGUST 1988
Numbers of female mosquitoes in carbon dioxide baited traps per night
SITE TRAP LOCATION An.amictus Cx.annulirostris TOTALS
NO. An.annulipes Cx.quinquefasciatus
1 Adjacent to final 9 3 192 204
evaporation pond
2 Adjacent to open 17 4 169 190
excess effluent drain
3 Adjacent to broken 11 3 159 5 178
sewer main
4 SE end of Hain Tee, 1 4 38 43
at edge of town.
~ ·-
TOTALS 38 10 524 43 615
PERCENTAGE OF TOTAL 6 .179 1.626 85.2 6.992 100
-
.
..
TABLE 4 MOSQUITO BREEDING SURVEY - PINE CREEK, AUGUST 1988 LARVAL COLLECTIONS
LOCATION
Sewage ponds - evaporation pond
Sewage Ponds - open unlined drain receiving excess e·Hl uent.
Roadside culvert - adjacent to sewage pump station.
Depression on flat dowstream from above 1 oc at ion .
DESCRIPTION OF BREEDING SITE
In emergent vegetation at margin of final pond.
No predators.
In animal hoofprints, with some green grass and green algae.
Open, sunlit - no predators.
In 1 odged, dry grass at margin of culvert under road where sewage is leaking from broken main.
Partly shaded, turbid, slow flowing.
Semi-shaded depression, No vegetation or
predators. Green algae.
MOSQUITO SPECIES
Cx. annulirostris An.amictus
ex.annul irostris
Cx.quinquefasciatus ex.annul irostris
ex.annul irostris
V V Y \ O V / ' L