(1999)Constructed Wetlands in Queensland_Ecol_Engin

Ecological Engineering 12 (1999) 39–55

Constructed wetlands in Queensland: Performanceefficiency and nutrient bioaccumulation

Margaret Greenway a,*, Anne Woolley b

a Faculty of En6ironmental Sciences, Griffith Uni6ersity, Nathan, Qld 4111, Australiab Department of Natural Resources, GPO Box 2454, Brisbane, Qld 4001, Australia

Accepted 22 May 1998

Abstract

Nine pilot wetlands (eight free water surface and one subsurface flow) have beenconstructed in Queensland as joint projects between the State and Local Governments, totreat municipal wastewater. The wetlands are in several geographical locations which includetropical, subtropical and arid climates. Each wetland is a different configuration andcontains a variety of macrophyte types and species. Most species are native and werecollected in the locality or self colonised. This paper examines the performance efficiency ofthe wetlands and nutrient bioaccumulation in wetland plants. Biochemical oxygen demandconcentrations were reduced by 17–89% and suspended solids concentrations by 14–77% toproduce wetland effluent with BOD less than 12 mg l−1 and suspended solids less than 22mg l−1. Reduction in total nitrogen concentrations ranged from 18 to 86%, ammonianitrogen from 8 to 95% and oxidised nitrogen from 55 to 98%, producing effluent with totalnitrogen between 1.6 and 18 mg l−1. Reduction in reactive phosphorus concentration wasless than 13% in the free water surface systems with concentration in the effluent exceedingthe influent in many of the systems over long term operation. In contrast reduction throughthe single household subsurface system was 65%. Nutrient bioaccumulation was investigatedin 60 species. Submerged (Ceratophyllum) and free floating species (duckweed) had thehighest tissue nutrient concentrations, followed by the waterlily (Nymphoides indica), aquaticvines (Ipomoea spp., Ludwigia peploides), and waterferns (Ceratopteris, Marsilea). All thesespecies remove nutrients from the water column. Emergent species had lower nutrientconcentrations with the highest nutrients occurring in the exotic sedge Cyperus in6olucratus.Aquatic grasses including Phragmites had higher nutrient content than the sedges. Nitrogen

* Corresponding author.

0925-8574/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved.

PII S0925-8574(98)00053-6

M. Greenway, A. Woolley / Ecological Engineering 12 (1999) 39–5540

concentrations were higher in leaf/stem tissue compared to the root/rhizome, whereasphosphorus was higher in root/rhizome tissue. Emergent species had a greater biomass thansubmerged or free floating species and were therefore able to store more nutrients per unitarea of wetland. Cropping the shoots of emergent species increased nutrient content in newshoot growth. © 1999 Elsevier Science B.V. All rights reserved.

Keywords: Australia; Aquatic plants; Bioaccumulation; Biomass; Constructed wetlands;Municipal effluent; Nutrients; Performance efficiency

1. Introduction

In Queensland, Australia, there is a growing interest by the State government,local authorities, land developers and municipal engineers, in the use of constructedwetlands as low cost, environmentally friendly alternatives to conventional wastew-ater treatment processes. Constructed wetland systems are particularly attractivealternatives for small communities where land is available and the costs of installingtertiary treatment or Biological Nutrient Removal plants is prohibitive.

In 1992, the Queensland Government established an Artificial Wetlands forWater Pollution Control Research Program and received a grant under the Na-tional Landcare Scheme to fund research projects which would provide informationon design suitability and management options for constructed wetlands in Queens-land (McCourt and Woolley, 1997). The potential to reuse water discharged fromthese wetlands was also recognised and applications include irrigating crops,pastures, tree lots, golf courses, parks and the restoration of natural wetlands(Greenway and Simpson, 1996).

The Research Program recognised that information was needed on native plantspecies that could potentially be used in Queensland constructed wetlands. Re-search overseas has focussed on either non-native species, e.g. Eichhornia crassipes(water hyacinth) a noxious aquatic weed in Queensland; Sal6inia molesta (waterfern) and Pistia stratiotes (water lettuce) (Reddy and De Busk, 1987; Tripathi et al.,1991), also aquatic weeds; or cosmopolitan species such as Typha spp. andPhragmites australis (Reddy and De Busk, 1987; Gumbricht, 1993) which, due totheir aggressive growth in Queensland’s subtropical/tropical climate, can alsobecome potential weed species, dominating a wetland by forming dense monospe-cific stands.

Between October 1992 and July 1994, nine pilot wetlands were constructed asState Government joint projects. Eight wetlands are free water surface and treatsecondary sewage effluent, one wetland is subsurface flow and treats all domestichousehold effluent from a private landholder at Wamuran. Two University-LocalGovernment constructed wetlands have also been established (Bolton and Green-way, 1997; King et al., 1997). Each pilot wetlands has a different design configura-tion (Table 1). Retention times and loading rates also vary between wetlands (Table1). Plant species were collected from local stock growing in natural wetlands and/or

M. Greenway, A. Woolley / Ecological Engineering 12 (1999) 39–55 41

Tab

le1

Sum

mar

yin

form

atio

n:de

sign

char

acte

rist

ics

ofQ

ueen

slan

d’s

pilo

tco

nstr

ucte

dw

etla

nds

Bla

ckal

lC

hara

cter

isti

csG

oond

iwin

diC

airn

sW

amur

anIn

gham

Tow

nsvi

lleM

acka

yE

mu

Par

k

Ari

dA

rid

Sub

trop

ical

Tro

pica

l-dr

ySu

btr

opic

alT

ropi

cal-

dry

Tro

pica

l-w

etT

ropi

cal-

wet

Clim

ate

May

1994

Janu

ary

1994

Feb

ruar

y19

93Ju

ne19

94O

ctob

er19

cF

ebru

ary

1993

Con

stru

ctio

nM

arch

1993

Apr

il94

5lin

ear

4lin

ear

5lin

ear

5ci

rcul

ar4

linea

r,1

U-

2U

-sha

ped

3U

-sha

ped

Cha

nnel

s3

linea

rpi

ts+

pond

shap

ed13

:1(1

),4.

2:1

16:1

16:1

20:1

12:1

2m

diam

eter

8:1

Len

gth:

wid

th15

:1(2

)60

050

0D

epth

(mm

)su

bsur

face

450

050

040

030

040

0(a

)3

74

7(a

)12

17(1

)3

7–10

HR

T(d

ays)

10(2

)(b

)5

(b)

2(a

)135

520

(a)

736

230

HL

R(m

3ha

−1

(a)

269

(1)

(a)

391

d−1)

(b)

1215

458

(2)

(b)

1210

(b)1

119

(b)

320

(1)

488

(2)

a,b

deno

tes

diff

eren

ttr

ial

peri

ods/

cond

itio

nsfo

rsa

me

wet

land

s.c

Oct

ober

1992

toJa

nuar

y19

94,

sepa

rate

trea

tmen

tgr

eyan

dbl

ack

wat

er;

sinc

eJa

nuar

y19

94co

-tre

atm

ent

blac

kan

dgr

eyw

ater

.(1

)or

(2),

spec

ifies

num

ber

ofch

anne

ls.


waterways. The species were band planted, i.e. sections of the wetland channel wereplanted with a different species. Open water sections were colonised by duckweed.

This paper presents data on water quality monitoring and phosphorus andnitrogen accumulation in macrophytes in wetlands from eight geographical loca-tions (Fig. 1).

2. Material and methods

2.1. Water quality monitoring

Monitoring of influent and effluent has been conducted by each Local Authorityfor a range of parameters including biochemical oxygen demand (BOD), suspendedsolids (SS), total nitrogen, ammonia, oxides of nitrogen, total phosphorus and

Fig. 1. Location map of constructed wetlands in Queensland, Australia.


reactive phosphorus. The parameters measured vary with each wetland dependingon the project objectives. The frequency of sampling is highly variable betweenLocal Authorities. Hach DR2000 procedures (Hach, 1992) were used to measurereactive phosphorus and oxidised nitrogen for the Mackay, Ingham and Emu Parksystems. Standard laboratory procedures were used for all other tests (Apha, 1992).

2.2. Plant tissue nutrient accumulation

Wetland plants were collected in 1994, 1995 and 1996. At least three replicates ofeach species were sampled from each wetland each year. For some species, plantswere sampled at inlet and outlet sections of the channels. Roots and rhizomes werethoroughly washed to remove any adhering sediment. Plants were oven dried at60°C for 48 h. Emergent macrophyte species were divided into plant components—leaves, stems, roots and rhizomes. All samples were ground in a Rocklab ringgrinder to a fine powder.

Total phosphorus was determined using a mixed acid digestion technique fol-lowed by the ascorbic acid method for colourmetric determination. Total nitrogenand carbon were determined with a Europa ScientificTracer Mass Stable IsotopeAnalyser. The Roboprep-CN Biological Sampler Converter burns the sample andthe resultant nitrogen and carbon dioxide piped into the Analyser.

2.3. Plant biomass

In February 1997 plant biomass was estimated for the plants growing in theCairns wetland. Quadrants 1 and 0.25 m2 were used as the sampling units and foreach plant species there were five replicates. All plant components (shoots, roots,rhizones) were removed from the sampling units. Roots and rhizomes were washedto remove any adhering sediment. Plants were separated into components, ovendried at 75°C for 48 h and weighed. The emergent leafy shoots of all plants withinthe wetland were then harvested 5–10 cm above the water level. The harvestedshoots were removed for composting. In June 1997, after 4 months of regrowth,plant biomass was estimated again.

3. Results and discussion

3.1. Water quality and performance efficiency

Table 2 is a summary of performance data for each wetland system based onresults provided by the Local Governments. These systems had a wide range ofoperating conditions with hydraulic retention times (HRT) from 2 to 17 days andhydraulic loading rates (HLR) of 20–1736 m3 ha−1 d−1 (Table 1). Monitoringperiods reported on are of the order of 2.5–3 years at Cairns, Townsville, Ingham,Blackall and Mackay, and 12–18 months at Goondiwindi, Wamuran and EmuPark.


Tab

le2

Sum

mar

ype

rfor

man

ceda

ta(m

edia

nva

lues

)fo

rQ

ueen

slan

d’s

pilo

tco

nstr

ucte

dw

etla

nds

Tow

nsvi

lleM

acka

yE

mu

Par

kB

lack

alld

Goo

ndiw

indi

Wam

uran

cP

aram

eter

Ingh

amC

airn

s65

(a)

606

(a)

617

tota

l9

sets

(a):

70N

umbe

r(a

)8

(b)

16(b

)7

(b)

70sa

mpl

es/

(b)

30ch

anne

lM

ay19

93–

Oct

ober

1994

May

1994

–F

ebru

ary

1993

–Ju

ne19

93–

Nov

embe

r19

94–

Mon

itor

ing

Feb

ruar

y19

95F

ebru

ary

1995

–Ju

ne19

96M

arch

1996

–F

ebru

ary

1996

Dec

embe

r19

95Ja

nuar

y19

96–

Dec

embe

r19

96Ju

ne19

97D

ecem

ber

1996

peri

od

(a)

BO

D(b

)(a

)(a

)(b

)(b

)(a

)(b

)18

Inm

gl−

118

915

1213

4611

04

2219

1819

1112

108

98

12O

utm

gl−

111

119

739

2317

3880

%re

dnco

nc89

4942

5661

7033

61–1

11%

redn

mas

s56

543.

025

187.

523

1525

1.8

8.4

22L

Rkg

ha−

1d−

1

(a)

(a)

(b)

(a)

(b)

(b)

(a)

SS

(b)

2321

2432

7425

26In

mg

l−1

242

57

476

1822

2217

135

16O

utm

gl−

1

−23

014

3177

7250

33%

redn

conc

−74

5411

58%

redn

mas

s39

−13

548

3022

4738

6.0

LR

kgha

−1

d−1

1.6

290.

9

(a)

Tot

alP

(b)

(a)

(b)

(a)

(b)

33.

38.

96.

88.

96.

8In

mg

l−1

18.

37.

12

44.

27.

52.

77.

26.

2O

utm

gl−

1

−4

18−

36−

2716

7013

9%

redn

conc

−27

12%

redn

mas

s14

27 3.6

−8

4.0

2.1

3.6

2.7

LR

kgha

−1

d−1

(a)

(b)

(a)

(b)

(b)

(a)

Rea

cti6

eP

(a)

(b)

5.5

6.0

6.2

2.1

3.2

Inm

gl−

15

8.1

7.9

6.1

8.3

6.2

5.6

6.9

5.5

3.1

4.2

6.5

2.8

Out

mg

l−1

7.9

5.4

6.8

69

−15

11−

48−

31%

redn

conc

1365

1311

5−

451

3311

16%

redn

mas

s22

263.

07.

26.

43.

23.

81.

93.

42.

410

LR

kgha

−1

d−1

(a)

(a)

(b)

(a)

(b)

(b)

(a)

Tot

alN

(b)

35.9

16.6

17.8

3731

.562

Inm

gl−

119

.55.

99.

21.

66.

918

.013

.611

.018

8.4

1.7

9.7

Out

mg

l−1

5018

3852

7886

%re

dnco

nc83

7350

7235

58%

redn

mas

s86

7039

3322

LR

kgha

−1

d−1

147.

62.

63.

7


Tab

le2

(Con

tinu

ed)

Tow

nsvi

lleM

acka

yE

mu

Par

kB

lack

alld

Goo

ndiw

indi

Wam

uran

cP

aram

eter

Ingh

amC

airn

s65

(a)

606

(a)

617

tota

l9

sets

(a):

70N

umbe

r(a

)8

(b)

16(b

)7

(b)

70sa

mpl

es/

(b)

30ch

anne

lM

ay19

93–

Oct

ober

1994

Mon

itor

ing

May

1994

–Ju

ne19

93–

Feb

ruar

y19

95F

ebru

ary

1993

–F

ebru

ary

1995

–N

ovem

ber

1994

––

Dec

embe

r19

96D

ecem

ber

1995

June

1996

peri

odJa

nuar

y19

96Ju

ne19

97–

Feb

ruar

y19

96D

ecem

ber

1996

Mar

ch19

96

(a)

Am

mon

iaN

(b)

(a)

(a)

(b)

(b)

(a)

(b)

11.5

20.7

23.5

2.0

9.5

8.6

18.6

50In

mg

l−1

0.3

0.2

7.7

2.2

6.2

14.0

0.15

8.7

7.8

7.5

2.6

Out

mg

l−1

0.2

0.2

5.4

7040

938

960

8195

%re

dnco

nc29

7328

37%

redn

mas

s28

261.

019

110.

20.

1L

Rkg

ha−

1d−

13.

0

(a)

(a)

(b)

(a)

(b)

(b)

(a)

Oxi

dN

(b)

5.7

15.8

6.6

6.3

14.5

3.4

5.0

1.5

04.

29.

7In

mg

l−1

2.2

1.1

1.0

0.85

0.2

0.1

1.5

0.3

1.2

Out

mg

l−1

1.0

2.9

B0.

1B

0.1

5598

8384

9494

980

%re

dnco

nc\

98\

9870

8191

9799

64%

redn

mas

s93

988.

06.

2L

Rkg

ha−

1d−

17.

32.

26.

76.

10

1.8

3.8

2.7

(a)

and

(b)

deno

tedi

ffer

ent

tria

lpe

riod

s/co

ndit

ions

for

sam

ew

etla

nd.

cC

ombi

ned

grey

+bl

ack

wat

ertr

eatm

ent

bySS

Fw

etla

nd+

pond

.d

Onl

yla

bora

tory

resu

lts

repo

rted

;m

onit

orin

gsu

ppor

ted

byw

eekl

yH

AC

Hte

sts

whi

chco

nfirm

perf

orm

ance

tren

ds.


3.2. BOD and SS

In wetland systems, BOD is principally removed by microbiological activity withplants and litter providing surfaces for biofilm growth. Wetlands also providequiescent conditions for settling of SS and particulate BOD for subsequent anaero-bic or aerobic digestion of organic settleable matter depending on the oxygen statusat the point of deposition (Reed et al., 1995; McCourt and Woolley, 1997).

Except for some periods at Cairns and Mackay, reduction in the mass of BODranged from 33 to 70% for loadings ranging from 3 to 25 kg ha−1 d−1. Reductionin BOD concentration ranged from 23 to 89% to produce effluent with concentra-tions in the range of 7–12 mg l−1. Likewise the reduction in the mass of SS rangedfrom 11 to 58% for loadings of the order of 1.6 to 47 kg ha−1 d−1. Reduction inSS concentration ranged from 14 to 77% producing effluent with concentrationsfrom 4 to 22 mg l−1. This performance is consistent with that of wetland systemsin North America which consistently produced BOD and SS of less than 20 mg l−1

for inputs of up to 80 mg l−1 for BOD and up to 160 mg l−1 for SS (Reed et al.,1995).

At Cairns, where exceptionally low BOD and SS levels occurred in the influent,BOD and SS in the effluent frequently exceeded that in the influent on both a massand concentration basis. These results are in agreement with the general consensusthat reduction of BOD and SS below about 5 mg l−1 is unlikely because ofbackground levels generated within the wetland (Reed et al., 1995; Kadlec andKnight, 1996).

In the Mackay system, plant establishment was poor. Extensive algal growth inthe large areas of open water together with the dispersion of clay from the barebanks by wind action, high flow rates and a lack of vegetation at the outletcontributed to an initial increase in SS in particular and BOD. This system tookmore than 12 months to stabilise and reduce BOD and SS (Table 2).

3.3. Nitrogen

The nitrogen cycle in wetlands is complex and is discussed in detail by Kadlecand Knight (1996) and Reed et al. (1995). Nitrogen transformation in wetlandsoccurs by five principal biological processes: ammonification, nitrification, denitrifi-cation, nitrogen fixation and nitrogen assimilation. For secondary treated sewage inwhich the predominant forms of nitrogen are ammonia and nitrate, nitrificationand denitrification are generally indicated as the principal processes for nitrogenreduction together with some assimilation by biota. The magnitude of the reductiondepends on factors such as temperature, pH, alkalinity, organic carbon, dissolvedoxygen and biota (Reed et al., 1995; Kadlec and Knight, 1996). Plants and litterprovided surfaces for growth of many of the micro-organisms which mediate theseprocesses.

Reduction in total nitrogen occurred in all of the pilot systems ranging from 35to 86% on a mass basis and from 18 to 86% on a concentration basis for loadingrates between 2.6 and 39 kg ha−1 d−1. Extended aeration (activated sludge)


treatment at Cairns produces sewage effluent in which oxidised nitrogen is thedominant form. This was readily removed through the wetland to produceeffluent with total nitrogen less than 2.0 mg l−1. At Emu Park the wetland ispreceded by lagoon treatment (approximately 28 d HRT) of the sewage effluent(activated sludge treatment) during which almost complete nitrification occurred.Nitrate concentrations in the wetland influent were highly variable ranging from1.2 to 25 mg l−1 in the six samples tested, but removal through the wetland wasalmost complete. Townsville, Blackall, Ingham and Goondiwindi all receiveeffluent from biofilter plants containing both ammonia and oxidised nitrogen invarying amounts. Some reduction in both forms has occurred in Townsville andIngham with HRTs of 7–12 days. Ammonia reduction was the main processthrough the Goondiwindi system where organic nitrogen was a major componentof both influent and effluent. The Blackall system, with shortest HRTs (3–5days) was least efficient in reducing nitrogen, with nitrification appearing to bethe limiting factor. This correlation between nitrogen removal and HRT is con-sistent with the findings of Sakadevan et al. (1995).

The nitrogen levels in the effluent at Cairns (total N 1.7 mg l−1, ammonia N0.2 mg l−1, oxidised NB0.1 mg l−1) are consistent with background levels ofapproximately 1.5 mg l−1 organic nitrogen generated in FWS wetlands as re-ported by Kadlec and Knight (1996).

3.4. Phosphorus

The utilisation of phosphorus in a wetland involves many pathways in acomplex biogeochemical cycle which is discussed in detail by Kadlec and Knight(1996). Principal mechanisims of reduction include sedimentation of particulatephosphorus, adsorption of soluble phosphorus on to clay particles, precipitation,complexation and uptake by biota. Phosphorus in secondary sewage effluent isnormally well in excess of biota requirements. The absorption capacity of wet-land soils and sediments is variable and may be rapidly exhausted.

The pilot FWS systems have not proved to be an effective method for reduc-ing the concentration of phosphorus in secondary treated sewage effluent (con-centrations of the order of 2–8 mg l−1) in the long term. For reactivephosphorus loadings in the range of 2.4–10 kg ha−1 d, long term reductions inmass ranged from −15 to 51% with corresponding reductions in concentrationranging from −48 to 13%. As has been reported elsewhere (Reed et al., 1995)there were indications of reductions during the early stages of operation but overtime export of phosphorus, particularly on a concentration basis. occurred. Thisis illustrated in Fig. 2 for the Mackay wetland (McCourt and Woolley, 1997)where there was an initial average reduction in concentration of 55% during thefirst 6 months, reducing to 8% for the next 10 months after which concentrationin the effluent always exceed the influent. In contrast, a reduction of 70% intotal phosphorus occurred through the Wamuran single household system ofSSF beds plus pond.


Fig. 2. Change in reduction in reactive phosphorus over time in the Mackay wetland.

3.5. Nutrient bioaccumulation

A total of 60 wetland plant species from 25 families were identified (Greenway,1997). Tables 3–5 provide a comparison of the phosphorus, nitrogen and carboncontent of some of the more commonly occuring wetland species growing inQueensland’s constructed wetlands.

3.6. Comparison between plant types and components

3.6.1. Emergent macrophytesIn the emergent macrophytes, phosphorus tended to be slightly higher in the

below ground components (root/rhizome) whereas nitrogen and carbon weregenerally higher in the above ground (leaf/stem) components. Of the sedges(Cyperaceae), Cyperus exaltatus had the highest phosphorus content; C. in6olucra-tus had the highest nitrogen content. Leaf/stem values were not significantlydifferent between species. Values for C. in6olucratus are comparable to those ofHocking (1985) in temperate Australia. Studies by Tanner (1996) in New Zealandfound lower phosphorus in Bolbosoloenus and higher nitrogen in Schoenoplectus.

The aquatic grasses (Gramineae) generally had higher nitrogen and carboncontent than the sedges; however Phragmites, a species widely used in constructedwetlands had the lowest phosphorus content. There was no differences in thenutrient content of the two species of Typha. Phosphorus in the leaves wassignificantly lower than in the root/rhizomes.

Melaleuca trees had the lowest phosphorus and nitrogen content but the highestcarbon content.


The phosphorus content of Phragmites was comparable to that recorded byHocking (1985), Reddy and De Busk (1987) and Gumbricht (1993). The nutrientcontent of Typha was comparable to other studies for leaf tissue but higher forroot/rhizome (Reddy and De Busk, 1987; Gumbricht, 1993; Adcocok and Ganf,1994).

3.6.2. Submerged and free-floating macrophytes and aquatic 6inesSubmerged and floating macrophytes (Table 4) had higher phosphorus and

nitrogen content than emergent species with Ceratophyllum and duckweed(Spirodela spp.) yielding the highest phosphorus content. Duckweed also had thehighest nitrogen content. Values for duckweed, Pistia and Sal6ina were comparableto other studies using these species for wastewater treatment (Reddy and De Busk,1987; Tripathi et al., 1991). Of the aquatic vines Ipomoea had the highest phospho-rus content. With the exception of Paspalum distichum (water couch), which hadsimilar phosphorus and nitrogen content to the emergent grasses (Gramineae, Table3), the other vines/creepers all had higher nitrogen content than the emergents.

Table 3Phosphorus, nitrogen and carbon content (mg g−1) for below ground (root/rhizome) and aboveground (leaf/stem) components of emergent macrophytes and Melaleuca trees (mean9S.D.)

Leaf/stemEmergent macrophytes Root/rhizome

C P N CP N

Cyperaceae13.595.04.391.5 370960 3.091.4 14.395.4 390931Bolbosoloenus caldwellii

Cyperus eragrostis 39093516.594.23.791.735296020.099.63.791.816.796.83.891.8360960 40593015.097.05.094.0Cyperus exaltatus

26.99133.892.2 445998 2.691.0 22.397.8 420918Cyperus in6olucratusa

4.092.7 14.095.0 320980Eleocharis acuta 3.491.5 18.895.4 395928Eleocharis phillipensis 14.094.84.492.0 39392517.294.93.591.2365950Eleocharis sphacelata 39292615.894.02.791.03509654.392.5 13.595.7

2.591.9Rhynochosporus corymbosa 3959313.990.6 2.590.6 16.992.4 391910356950 2.691.2 14.695.0Schoenoplectus 6alidus 3969504.091.9 14.597.0

12.392.52.890.8 373934 2.691.0 16.094.0 415924Scleria poiformisGramineae

4.091.2 387910Echinochloa crus-galia 16.397.018.594.6 3.691.2385916Echinochloa polystachyaa 41093023.79125.791.84159274.391.7 18.096.5

4.290.9Hymenachne acutigluma 39592821.098.0 4.091.3 21.499.0 400925395980 2.090.6 20.498.0Phragmites australis 4209253.291.4 17.397.0

Typhaceae41292715.896.02.090.8365954Typha domingensis 16.89104.091.7

366945 2.391.0Typha orientalis 15.696.74.291.7 42093114.793.4Myrtaceae

11.092.22.790.6Melaleuca quinquener6iab 50093012.095.01.590.5

a Exoticb Tree


Table 4Phosphorus, nitrogen and carbon content (mg g−1) of submerged and free floating macrophytes andaquatic vines/creepers (mean9S.D.)

Whole plantMacrophyte type

P N C

Submerged macrophytesCeratophyllum demersum-hornwort 27.096.3 38492410.392.5

4 (n=1) 29.3 (n=1) 385 (n=1)Potamogeton pectinalis

Free floating macrophytesAzolla spp. Water fern 40.094.0 421937.490.6

389934Duckweed (Spirodela; Wolffia) 10.592.9 39.6910.334592120.999.07.793.1Monocharia cyaneab

30.097.47.592.0 320932Pistia stratiotes-water lettucea

Sal6inia molesta-water ferna 3669526.291.8 29.097.4

Vines/creepers400914Alternanthea philoxeroides-alligator weeda 6.091.1 33.4911.438193530.0911.2Bacopa monniera 4.891.1

Ipomoea aquatica 30.7912.4 3929296.491.234296837.3911.97.592.1Ipomoea diamentinensis

32.7912.35.392.3 395949Ludwidgia peploides-water primrosePaspalum distichum-water couch 4159504.192.0 18.6911.0

41693424.9911.4Persicaria orientalisa 4.291.7

a Exotic species.b Also grow as attached plants.

3.6.3. Floating lea6ed-attached macrophytesThe phosphorus and nitrogen content of the water lilies and water ferns (Table

5) was higher than in the emergent macrophytes. Nymphoides indica had particu-larly high phosphorus bioaccumulation in the roots. The aquatic ferns had similarphosphorus and nitrogen content to the free floating macrophytes. Nymphoides,Ceratopteris and Marsilea produce roots enabling them to remove nutrients fromthe water column as well as the sediment.

3.7. Comparison of species bioaccumulation between inlet and outlet sections ofchannels

A total of 34 pairs of data were examined and the only significant differenceswere at Cairns for duckweed-inlet (14.590.7 mg P g−1, 42.692.7 mg N g−1);outlet (10.190.8 mg P g−1, 28.390.9 mg N g−1). At Cairns low nitrogen oxidesin the wetland outflow (0.1 mg l−1) may have limited nitrogen bioaccumulation induckweed growing at the outlet. The lack of any other differences between inlet andoutlet sections suggest that nutrients are not limiting for other wetland species.


3.8. Comparison of species bioaccumulation between wetlands

A comparison of six species (Table 6) which occurred in nearly all wetlandsshowed the lowest leaf nitrogen and phosphorus content at Emu Park, followed byCairns (for low nitrogen). Pooled data for all species at each wetland (Greenway,1997) similarly showed the plants at Emu Park had the lowest nutrient bioaccumu-lation. The lower values at Emu Park suggest less available nitrogen and phospho-rus for plant growth, however this is not supported by the water quality data (Table2). Low loading rate for oxides of nitrogen and effluent concentrations at theCairns wetland (Table 2) may have limited nitrogen bioaccumulation in comparisonto the other wetlands.

3.9. Biomass of plant species at Cairns

Table 7 provides a comparison of plant total biomass (g m−2 DW) of aquaticmacrophytes at the Cairns wetland in February 1997 at the time of harvesting, andin June 1997 following 4 months of regrowth; and the harvested biomass (g m−2,g P m−2, g N m−2).

Typha had the highest initial total biomass (shoots/rhizomes/roots) of which 64%(1120 g m−2) was harvested i.e. shoots 10 cm above the water level. The har-vestable yield of Schoenoplectus and Eleocharis shoots were only 20–25% of theTypha shoot biomass. Floating mats of Paspalum (water couch) were totallyremoved and gave a yield of 860 g m−2, there was no recolonisation of Paspalum.The initial harvest of duckweed (predominantly Spirodela spp.) yielded twice thebiomass when growing in open water compared to among the Typha.

Total biomass of the emergent species 4 months after the initial harvest waslower in Typha and Schoenoplectus but had a 100% increase in Eleocharis. New

Table 5Phosphorus, nitrogen and carbon content (mg g−1) of floating leaved-attached macrophytes (mean9S.D.)

Leaf/StemFloating leaved- attached Root/Rhizomemacrophytes

P N CP N C

Water lilies7.190.7 300947 4.091.0 36.096.0 367926Nymphea capensisa 30.391.7

36494824.098.64.292.0Nymphea gigantea6.692.0 25.8911Nymphoides indica 36692412.193.7 19.896.3 346912

Aquatic fernsCeratopteris thalicoides- Whole plant 39092030.099.08.391.0

aquatic fernMarsilea spp. (nardoo)b 8.192.5 29.4f99.0 378956Whole plant

a Exotic species.b Also grows as free floating once established.


Tab

le6

Aco

mpa

riso

nof

nutr

ient

cont

ent

(mg

P,

mg

N)

inle

afti

ssue

ofse

lect

edsp

ecie

sfr

omal

lw

etla

nds

Bla

ckal

lG

oond

iwin

diSp

ecie

sW

amur

anC

airn

sIn

gham

Tow

nsvi

lleM

acka

yE

mu

Par

k

1.249

0.90

2.289

0.67

1.839

0.1

2.369

0.84

1.849

0.90

2.429

0.43

3.829

0.86

2.499

0.74

NT

ypha

9.09

2.5

18.29

6.6

19.09

0.7

P20

.89

4.7

13.89

4.8

22.09

7.5

16.09

3.6

18.49

5.3

1.639

0.78

—2.

319

0.1

1.779

0.48

—2.

119

0.52

Phr

agm

ites

N—

2.439

0.22

23.69

4.0

—30

.39

1.2

27.89

5.7

P—

33.19

5.4

26.09

6.2

—3.

869

0.97

—2.

549

1.6

—2.

919

0.50

Sch

oeno

plec

tus

2.829

0.81

—2.

829

1.44

N P19

.89

3.4

6.59

0.83

—19

.49

3.8

—14

.29

4.6

—16

.019

1.6

2.719

0.74

—4.

73n=

1—

—E

leoc

hari

s2.

839

1.0

2.319

0.65

2.939

1.22

N12

.09

2.1

—24

.6n=

1—

P16

.69

3.20

16.79

3.6

17.7

49

3.7

—3.

849

1.17

5.009

1.22

——

5.009

1.93

Pas

palu

m3.

259

1.35

3.36

n−1

3.59

1.5

N15

.99

7.0

P23

.09

11.0

——

16.09

8.0

17.1

3n=

126

.59

11.5

23.09

12.0

9.059

0.78

9.939

2.6

——

11.49

0.82

10.6

59

1.62

Duc

kwee

dN

11.7

49

2.52

11.2

09

6.67

32.89

3.7

P44

.19

12.2

——

36.69

7.3

47.59

7.2

46.39

16.8

48.69

12.1


Tab

le7

Bio

mas

s,ha

rves

ted

biom

ass

and

nutr

ient

cont

ent

ofin

itia

lst

andi

ngst

ock

(Feb

ruar

y19

97)

and

regr

owth

(Jun

e19

97)

atC

airn

s

Tot

albi

omas

sH

arve

sted

biom

ass

(gm

−2,

gN

m−

2,

Tot

albi

omas

sSp

ecie

sH

arve

sted

biom

ass

(gm

−2,

gN

m−

2,

(gm

−2

regr

owth

)g

Pm

−2

init

ial)

gP

m−

2re

grow

th)

(gm

−2

init

ial)

7409

125

Typ

hado

min

gens

is17

509

500

11209

320

13009

700

129

2g

N129

35g

N2.

249

0.6

gP

2.29

0.4

gP

1909

136

Sch

oeno

plec

tus6a

lidus

9009

525

3009

170

3309

200

1.99

1.4

gN

2.19

1.2

gN

0.69

0.3

gP

0.59

0.3

gP

3009

70E

leoc

hari

ssp

hace

olat

a23

09

5030

09

140

10209

230

5.79

1.3

gN

1.49

1.3

gN

0.69

0.1

gP

0.69

0.1

gP

Pas

palu

mdi

stic

hum

8609

110

8609

110

nore

grow

th10

.39

1.3

gN

2.69

0.3

gP

229

5.0

229

5.0

189

2.4

Duc

kwee

d189

2.4

(am

ong

Typ

ha)

0.79

0.09

gN

0.889

0.2

gN

0.339

0.1

gP

0.39

0.04

gP

309

2.3

409

10409

10309

2.3

Duc

kwee

d(o

pen

wat

er)

1.29

0.1

gN

1.59

0.37

gN

0.59

0.03

gP

0.69

0.15

gP

909

30909

3021

09

7021

09

70C

erat

ophy

llum

6.39

2.1

gN

2.79

0.9

gN

4.69

1.5

gP

1.59

0.5

gP


harvestable shoot biomass in Typha and Schoenoplectus was only 65% of theinitial harvest, but 130% for Eleocharis. Duckweed biomass had increasedamongst the Typha but decreased in open water. Ceratophyllum had increased toform a dense underwater mat. The rate of new shoot growth was 6 g m−2 d−1

for Typha, 1.6 g m−2 d−1 for Schoenoplectus and 2.5 g m−2 d−1 for Eleocharis.The nutrient content of the new shoot growth was higher than pre-harvest,

indicating that cropping the shoots increases nutrient uptake and bioaccumula-tion.

3.10. Mass balance—cairns wetland

From the water quality data-the total amount of N and P entering and leavingthe wetland for each 6-month period was calculated. Between August 1996 andFebruary 1997, 6.84 kg P (83% reactive P) and 64.3 kg N (60% NOx) wereretained within the wetland. In February 1997 total plant biomass contained 7.33kg P and 20 kg N. Assuming a 6-month turnover of plant biomass (which is agross overestimate for species like duckweed), the data indicate that potentially allof the reactive phosphorus and 52% of the nitrogen oxides could have beenincorporated into plant biomass.

4. Conclusion

These trials in Queensland have demonstrated that constructed free water sur-face wetlands are a viable option for further improving the quality of secondarysewage effluent by reducing BOD and SS, and with careful design, nitrogen. Ingeneral the studies have shown that a wetland with low HLR and long HRTfavours effluent polishing. Effective long term phosphorus removal was notachieved. Performance was consistent with that reported for constructed wetlandselsewhere (Reed et al., 1995; Kadlec and Knight, 1996). The quality of effluentfrom a constructed wetland is limited by the background levels of organic matter,solids and nutrients generated within the wetland.

A dual subsurface flow and pond system has been particularly effective attreating wastewater from a single household producing effluent of a quality on apar with secondary sewage treatment.

Which ever system is selected, the Queensland experience shows that a widerange of native species can live and thrive in sewage-effluent enriched consructedwetlands. Although emergent species had lower phosphorus and nitrogen tissuecontent than the free floating, submerged and aquatic creepers, biomass (i.e.nutrient storage capacity in plant tissue) was greater in the emergents. Harvestingshoot biomass in the emergents therefore removes more nitrogen and phosphorusper unit area of wetland.

Eleocharis sphacelata responded well to harvesting of the shoots. Schoenoplectusdid not produce dense stands of shoots-however this allowed both duckweed andCeratophyllum to coexist, due to the lack of substantial shading. Such a combina-


tion of emergent, free floating and submerged species maximises nutrient removal infree water surface systems and should therefore be encouraged.

Acknowledgements

Funding for this work was provided through a joint Griffith University andQueensland Department of Natural Resources Collaborative Grant. John Howdle,Steve Marston, Dave Arbuckle and Alex Watt, Environmental Engineering,Griffith University, analysed the plant samples and provided data for this paper.The comments of two anonomous referees are also acknowledged.

References

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Sakadevan, K., Ryan, G., Roser, D., Starrett, J., Bavor, J., Osborne, P., 1995. Phosphorus and nitrogenbudgets for 5 experimental constructed wetland systems. Proc. National Conference on Wetlands forWater Quality Control, Townsville, September, pp. 103–109.

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