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Water Research 39 (2005) 2291–2300

www.elsevier.com/locate/watres

Phytoremediation of effluents from aluminum smelters: Astudy of Al retention in mesocosms containing aquatic plants

Richard R. Gouleta,�, Janick D. Lalondeb, Catherine Mungerc, Suzanne Dupuisc,Genevieve Dumont-Frenettec, Stefane Premontb, Peter G.C. Campbellb

aEnvironment Canada, Assessment Division, Existing Substances Branch, Place Vincent Massey, 20th floor, 351 St. Joseph, Gatineau,

Quebec, Canada K1A 0H3bINRS-Eau, Terre et Environnement, Universite du Quebec, 490 de la Couronne, Quebec (QC), Canada G1K 9A9

cCentre de recherche et de developpement Arvida, ALCAN International Ltee, Edifice 110, 1955 Boul. Mellon, C.P. 1250, Jonquiere,

Quebec, Canada G7S 4K8

Received 7 August 2003; received in revised form 17 December 2004; accepted 5 April 2005

Abstract

Four mesocosms were exposed to circumneutral and aluminum (Al)-rich wastewater during two successive summers

(2000, 2001). The goals of the study were to measure the bioaccumulation of dissolved Al by the aquatic plants Typha

latifolia, Lemna minor, Nuphar variegatum and Potamogeton epihydrus, and to evaluate their importance in the retention

of Al by the mesocosms. In 2000, inlet concentrations of total monomeric Al were reduced by 56% and 29% at the

Arvida and Laterriere mesocosms, respectively, whereas in 2001 inlet dissolved Al concentrations in the inlet decreased

by 40% and 33%. L. minor had the highest Al uptake rate (0.8–17mg Al g�1 d�1). However, because T. latifolia

(cattails) yielded the highest biomass, it was responsible for 99% of the Al uptake, largely in its root tissue. In 2001, Al

uptake by macrophytes accounted for 2–4% and 15–54% of the total Al retained by the Laterriere and Arvida

mesocosms, respectively. In the Laterriere mesocosms, Al uptake by cattails could account for 12% and 18% of the

dissolved Al retained by both mesocosms. In contrast, dissolved Al was not significantly reduced in the Arvida

enclosures, yet cattails did accumulate Al in their roots. Further research is needed to identify the species community

composition that would optimize dissolved Al retention.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Metal removal; Macrophyte; Mass balance; Wastewater treatment; Industrial runoff

1. Introduction

Aluminum (Al) smelters, as well as other type of

industries (Droste, 1997), commonly use water manage-

ment ponds as secondary treatment systems. These

ponds are particularly efficient in removing particulate

e front matter r 2005 Elsevier Ltd. All rights reserve

atres.2005.04.029

ing author. Tel.: +1819 994 9556;

4936.

ess: richard.goulet@ec.gc.ca (R.R. Goulet).

metals, but less efficient in removing dissolved elements.

Improved treatment performance by these ponds could

possibly be achieved by phytoremediation, since aquatic

plants are known to take up and bioaccumulate

dissolved metals, this uptake normally being related to

the dissolved free metal ion concentration (Parker and

Pedler, 1997). Aquatic plants can also influence metal

retention indirectly by acting as traps for particulate

material, by slowing the water current and favoring

sedimentation of suspended particles (Hokosawa and

d.

ARTICLE IN PRESSR.R. Goulet et al. / Water Research 39 (2005) 2291–23002292

Horie, 1992; Kadlec, 2000). Aquatic plants also

reduce sediment resuspension by offering wind protec-

tion (Brix, 1994, 1997), and they act as a substrate for

growth of epiphytes, which can bioaccumulate metals

directly from the water column (Khatiwada and

Polprasert, 1999).

Phytoremediation has been used extensively to reduce

metal loadings to the environment (Williams, 2002). For

example, 54% removal of Al from acid mine drainage

was achieved by wetland treatment systems (Wieder,

1993). The effectiveness of such systems for treatment of

Al-rich but circumneutral effluents is however unknown.

Possible improvements to Al removal through phyto-

remediation in such ponds would be of interest to the Al

refining industry, but present scientific knowledge in

this area is very scant (Wieder, 1993; Gensemer and

Playle, 1999).

In a preliminary experiment, we exposed aquatic

macrophytes hydroponically to synthetic Al effluents

and observed that the species studied removed from

59% to 85% of the dissolved Al present in the water at

the beginning of the experiment (Gallon et al., 2004).

This experiment allowed us to estimate the potential

contribution of aquatic macrophytes to the overall

retention of Al, if aquatic plants were to be introduced

into water management ponds. These results led us

to conduct a second experiment in which aquatic

plants were exposed in mesocosms to real effluents from

two Al smelters located in the Saguenay/Lac St-Jean

area, Quebec, Canada. The primary objective of this

second study was to estimate the efficiency of

Al removal by the mesocosms and to evaluate the

relative contribution of plants to the removal of

dissolved Al. For this purpose, we studied the bioaccu-

mulation of Al in four types of macrophytes that

are endemic in wetlands in the Saguenay: an emergent

macrophyte, cattails (Typha latifolia L.); a floating

macrophyte, duckweed (Lemna minor); a rooted

floating leaf macrophyte, variegated pond-lily (Nuphar

variegatum); and a rooted macrophyte, pondweed

(Potamogeton epihydrus).

2. Methods

2.1. Experimental design

The experiments were conducted at the Arvida and

Laterriere plants, located in the greater Saguenay area.

In summer 2000, we conducted a bioaccumulation

experiment, in which mesocosms were used to determine

Al accumulation in different species of macrophytes that

were exposed to two types of Al wastewater. In summer

2001, the mesocosms and macrophytes therein were used

to carry out Al mass budget experiments.

2.2. Mesocosm description

Two pools (1.25m high by 3.7m diameter) were

assembled as mesocosms at the Arvida and at the

Laterriere plants, respectively. A synthetic sheet was

installed inside the mesocosms to prevent water infiltra-

tion. Approximately 420L of natural sediments were

introduced on the synthetic sheet at the bottom of the

mesocosm. On top of these sediments, we added 120L of

pre-acclimated sediments, previously exposed for 9

months to Al-rich industrial effluent. In each mesocosm,

we introduced floating macrophytes species originating

from a nearby site (L. minor and Spirodela polyrhiza),

rooted macrophytes (P. epihydrus and N. variegatum)

and emergent macrophytes (T. latifolia). T. latifolia

(cattails) were planted on the perimeter area of each

mesocosm and rooted macrophytes were planted in the

middle area. Water pond lilies (N. variegatum) were

spread across the surface of the water.

2.3. Mass balances

Wastewater was pumped into the mesocosms and flow

rates were measured daily at the inlet and outlet of the

mesocosms, based on triplicate measurements of the

time required to fill a 1-L bottle. The volume storage of

water was kept as constant as possible over the time of

the experiment. The daily evapotranspiration rates were

calculated using the Penman estimate (Kadlec and

Knight, 1996) with meteorological data obtained from

the Bagotville meteorological station, located 20 km

from the experimental sites.

During the year 2000 bioaccumulation experiment,

duplicate water samples were collected daily at the inlet

and outlet of the mesocosms from 27 July to 10 August.

In 2001, the Al budget experiments started on 11 June

and ended on 27 August, during which time duplicate

water samples were taken every two weeks at the inlet

and outlet of the mesocosms. All water samples were

stored in 1-L high-density polyethylene (HDPE) bottles

and sent to the INRS-ETE laboratory for analysis.

Sediment traps were used to estimate deposition rates

during the Al budget experiment. The traps were similar

to the ones described by Fenessy et al. (1994). Before the

beginning of the experiment, sediment traps were gently

deposited at the bottom of the mesocosms from an

inflated boat. Once in place, the lids of the sediment

traps were removed, and the traps were left in the

mesocosms until the end of the experiment. Two

sediment traps were placed in the middle of the

mesocosms and one in the littoral area. Each trap was

retrieved and sent to the INRS-ETE laboratory for

determination of total Al and sediment mass.

For the Al budget experiments, we used an in situ

dialysis technique (detailed procedure described in

Carignan et al., 1985, 1994) to determine the quality of

ARTICLE IN PRESSR.R. Goulet et al. / Water Research 39 (2005) 2291–2300 2293

the sediment pore water and to establish the concentra-

tion gradients at the sediment–water interface. In each

mesocosm, three dialysers were deployed towards the

outer perimeter of the mesocosms and left to equilibrate

with the surrounding water for 2 weeks. Overlying and

pore water were sampled within the dialyser cells for

dissolved Al and pH.

During the bioaccumulation experiment, plant mate-

rial was collected after 0, 16, 31, 37, 44, 51 and 58 d of

exposure in each mesocosm; on each sampling date,

several individual specimens of L. minor and three

individual plants of the other macrophyte species were

collected. In 2001, plant material was collected at the

beginning and at the end of the experiment. Half of

the harvested plant material was frozen and sent to the

INRS-ETE laboratory while the other half was retained

for biomass measurement. Total plant as well as root,

shoot and leaf biomass was measured by drying at 60 1C

for 72 h and weighing the dried plant material with a

microbalance. The total biomass of aquatic plants, ‘‘B’’,

in each mesocosm was calculated as follows:

B ¼ dAmesPareaPdw, (1)

where ‘‘d’’ is plant density (number of plantsm�2),

‘‘Ames’’ is the surface area of the mesocosm (m2), ‘‘Parea’’

is the percent of the mesocosm surface covered by plants

and ‘‘Pdw’’ is the mean macrophyte dry weight (g). Every

3 weeks, the percent coverage was estimated by visual

inspection and the density of each macrophytes species

was estimated within a 1m2 quadrat that was randomly

placed into the mesocosm at the beginning of the

experiment.

2.4. Sample preparation

Water samples (50mL) were filtered through 0.4mmpore size polycarbonate filters (Osmonics, Minnetonka,

MN) to determine particulate and dissolved Al in 2001.

Filtered water used for measurement of dissolved Al was

kept in 60mL HDPE bottles and acidified with concen-

trated nitric acid (0.5% v/v). Filters were dried at 60 1C for

24h, weighed and digested in concentrated HNO3 and HF

(50:1 v/v) for measurement of particulate Al.

To prepare the sediment traps for measurements of

total Al content, the overlying water in the traps was

siphoned down to 2 cm above the sediments. The trap

walls were then cut above the sediments to prevent

periphyton from falling into the sample and the sediment

was dried at 60 1C for 3d. Dried sediments were

homogenized and weighed. Sub-samples from each trap

were digested on a hot plate using concentrated HNO3,

HClO4 and HF (1:1 v/v), HF, and HNO3, successively.

Plant material was washed with tap water, and

distilled acidified water (pH 4.5) to remove attached

algae, Al co-precipitated with iron plaque, and adsorbed

Al. For each plant, leaves, stems and roots were

separated and stored in Whirl-pak bags. Samples were

dried in an oven at 60 1C for 72 h and 0.05 g sub-samples

of the dried material were digested for 48 h with

concentrated HNO3 and HF acids (50:1 v/v) at 60 1C

in a closed HDPE bottle.

2.5. Chemical analysis

Monomeric Al was determined on filtered surface water

with a spectrophotometric technique based on the

reaction with pyrocatechol violet (Dougan and Wilson,

1974). The analyses were carried out on an automated

Technicon spectrophotometer (model AA-II), with a

detection limit of 10mgL�1. Major cations concentrations

in surface water and Al concentrations of surface and pore

water, sediment extracts, and plant extracts were mea-

sured by ICP-AES (Varian, model Vista AX-with an axial

torch). Concentrations of dissolved F were determined by

ion chromatography (Dionex DX-300, equipped with an

ionic suppressor and a conductivity detector). The pH of

filtered surface and pore water samples was measured with

a portable pH meter (Hanna Instrument Inc.).

Quality control was ensured for water and sediments

samples by appropriate use of certified standards,

method and field blanks and blind duplicate samples.

Overall, measured metal concentrations compared well

with the certified values for Al in water (9777 mgL�1

versus 96719 mgL�1 for the certified material 1643D,

NIST, Gaithersburg, MD), sediment (66.1 versus

66.273.2mg g�1 dry weight for the certified material,

Buffalo river sediment (SRM2704a, NIST) and plant

material (581714 versus 598712mg g�1 dry weight for

the certified material, tomato leaves (SRM1573a, NIST).

The duplicates varied by 2.471.6% (n ¼ 7) for water

samples, 5% (n ¼ 1) for sediment samples, and

13726% (n ¼ 13) for the plant material while the

digestion blanks were consistently low (less than 10% of

the lowest measurements).

2.6. Statistical analysis

In 2001, as the inlet and outlet data were few, and

independent of each other because of the lag time

associated with the passage of Al through the mesocosm,

we used the non-parametric Mann–Whitney U-test to

discriminate among statistically significant differences.

3. Results and discussion

3.1. Concentration reduction in dissolved Al by

mesocosms

In 2000 and 2001, inlet and outlet water quality was

monitored. At each site (Arvida, Laterriere), the inlet

water chemistry characteristics were combined for both

ARTICLE IN PRESSR.R. Goulet et al. / Water Research 39 (2005) 2291–23002294

mesocosms since they received wastewater from the

same source (Table 1). Fig. 1 depicts trends in dissolved

Al at the inlet and outlet of the Arvida and Laterriere

mesocosms. In general, Al concentrations were reduced

as the effluent passed through the mesocosms (Fig. 1).

Since Al comes from fugitive emissions and fallout on

the plant site, variations in total monomeric Al (2000)

and dissolved Al concentrations (2001) are likely the

result of rain events, which increased the amount of Al

discharged into the drainage system (Arvida) or water

detention pond (Laterriere). At the Arvida site, meso-

cosms were also partially fed with nitrate- and phos-

phate-rich waste water originating from a nearby

sanitary building.

3.2. Al accumulation by macrophytes

Macrophyte species in all four mesocosms survived

transplantation and there was evidence of plant repro-

duction and spreading in 2000 and 2001. During the

bioaccumulation experiment in 2000, we compared Al

uptake between the two sites and among different

macrophyte species, by calculating Al uptake rates

(quantity of Al accumulated per unit time) during the

initial accumulation phase, which spanned the first 16 d

(Table 2). Among the different macrophytes, the uptake

rate of Al by L. minor was the highest followed by

Potamogeton sp., Typha sp. and Nuphar sp. (Table 2).

Sprenger and McIntosh (1989) also observed higher Al

contents in rooted species as compared to floating-

leaved and emergent taxa. Initial Al uptake rates for

macrophytes were greater in the Arvida mesocosms than

for the macrophytes at Laterriere (Table 2). Al uptake

by macrophytes would be expected to increase with

increasing dissolved Al concentrations, i.e., Laterriere4Arvida, with due consideration of possible attenuating

effects by the H+-ion and Ca2+ (Parker and Pedler,

Table 1

Water chemistry as measured at the inlet and outlet of the Laterriere an

2000 and during the budget experiment in 2001

Arvida

2000 2001

Inlet Outlet Inlet Outlet

Total Al n/aa 1.05 (0.88) 0.48 (0

Monomeric Al 0.32 (0.30) 0.14 (0.02)

Dissolved Al 0.53 (0.60) 0.14 (0.03) 0.24 (0.10) 0.14 (0

pH 6.6 (2.0) 8.2 (0

F 12.6 (12.0) 6.5 (0.2) 6.5 (1.9) 7.8 (1

Ca 14.6 (4.1) 21.5 (1.6)

Results are expressed as mean concentrations of elements at the inlet a

(mgL�1; SD in parentheses, n ¼ 327).an/a ¼ data not available.

1997; Parker et al., 1987; Maessen et al., 1992; Camp-

bell, 1995). We suggest that Al uptake rates in the

Arvida mesocosms were higher than at Laterriere

because of lower Ca concentrations and less Ca

competition for uptake sites.

Macrophyte Al concentrations (Fig. 2) were in a

similar range to those reported for other studies

(Gensemer and Playle, 1999; Havas, 1986). Havas

(1986) tabulated Al bioaccumulation data for US and

Canadian lakes and observed that macrophytes accu-

mulated from less than 40 to 32,000 mg Al g�1 dry

weight. This wide range of Al levels was a function of

season, location, species tested and portion of the plant

analyzed. Overall, aquatic plants in our mesocosms had

higher concentrations at the end of the growing season

in 2001 than in 2000 (Fig. 2).

The relative distribution of Al among various plant

organs varied from one species to another (Fig. 2). Al was

mainly measured in the roots for Typha sp. and Lemna

sp., whereas no clear pattern was observed for Potamo-

geton sp. in which we observed higher Al concentrations

in either the leaves or the roots and Nuphar sp. in which

we observed higher Al concentrations in either the stem or

the roots. During the year 2001 budget experiments,

Utricularia sp. and Myriophyllum spicatum accumulated

Al mainly in their stems and leaves, respectively. Such a

trend is in agreement with the observations of Denny

(1972), who noted an increase in shoot versus root

absorption of nutrients with progression towards sub-

mergence and simplicity of structure.

During the budget experiment in 2001, we measured

macrophyte biomass at the end of the experiment and

found that most of the aquatic plant biomass was present

as cattails (T. latifolia). Cattails were in effect responsible

for 99% of the plant Al uptake, largely in their roots.

Cattails stored more Al at the Arvida site than in the

Laterriere mesocosms, as noted earlier (Fig. 2).

d Arvida mesocosms during the bioaccumulation experiment in

Laterriere

2000 2001

Inlet Outlet Inlet Outlet

.25) 1.44 (0.35) n/aa 1.66 (0.35) 0.55 (0.10)

0.41 (0.02) 0.29 (0.10)

.07) 1.07 (0.05) 0.43 (0.03) 0.64 (0.05) 0.40 (0.11)

.8) 7.4 (0.4) 7.2 (0.3)

.6) 13.5 (0.1) 12.8 (0.1) 12.8 (0.5) 12.7 (0.7)

36.4 (0.4) 34.1 (0.9)

nd two outlets of both sites over the duration of each experiment

ARTICLE IN PRESS

Table 2

Initial Al uptake (mean over the first 16 days; 7SD) by the different organs of macrophytes averaged for both mesocosms at the

Arvida plant site and both mesocosms at the Laterriere plant site for the 2000 exposure experiment

Species Organ Arvida Laterriere

n mg Al g�1 d�1 n mg Al g�1 d�1

Typha latifolia Leaf 6 0.4570.40 6 0.1870.26

Root 6 3.6572.87 4 3.0072.14

Lemna minor Leaf 3 6.2574.12 3 0.8070.47

Root 3 17.20714.19 3 5.0071.04

Nuphar variegatum Leaf 6 0.9070.49 6 0.5770.25

Stem 6 0.3470.46 6 1.4470.65

Root 6 3.6473.54 4 �0.2970.40

Potamogeton epihydrus Leaf 6 1.6872.42 6 2.1871.19

Stem 6 1.0470.99 6 1.0371.27

Root 5 0.0872.75 6 4.4075.82

27 July

2 August

3 August

4 August

9 August

10 August

0

100

200

300

400

500

27 July

2 August

3 August

4 August

9 August

10 August

Al t

otal

mon

omer

(µ g

L-1

)

0

100

200

300

400

500

Sampling period

12 June

19 June

5 July

17 July

30 July

15 August

30 August

Dis

solv

ed A

l (µ g

L-1

)

0

100

200

300

400

500

Inletmesocosm 1 outletmesocosm 2 outlet

12 June

19 June

5 July

17 July

30 July

15 August

30 August

0

200

400

600

800

1000

Arvida Laterriere

Fig. 1. Concentration of total monomeric Al during the 2000 bioaccumulation experiment (upper panel) and of total dissolved Al

during the 2001 budget experiment (lower panel) at the inlet and outlet of the Arvida and Laterriere mesocosms.

R.R. Goulet et al. / Water Research 39 (2005) 2291–2300 2295

3.3. 2001 budget experiment

The duration of the Al budget study, from the initial

exposure of the mesocosms to the Al wastewater to

the final macrophyte sampling date, was 73 d for the

Arvida mesocosms and 76 d for the Laterriere meso-

cosms. The Al mass budget can be described as

follows:

AlinAlout ¼ Almacrophyte þAlsed, (2)

ARTICLE IN PRESS

Typha

Nuphar

Lemna

Potam

ogeton

Myriophyllum

Gender

Typha

Nuphar

Lemna

Potam

ogeton

Myriophyllum

Utricularia

Al (

mg

g-1)

0

10

20

30

40

50

Typha

Nuphar

Lemna

Potam

ogeton

0

10

20

30

40

50

RootStemLeaf

Typha

Nuphar

Lemna

Potam

ogeton

2000

LaterriereArvida

2001

Fig. 2. Mean metal concentrations in organs of aquatic macrophyte species at the end of the 2000 (upper panel) and 2001 (lower panel)

experiments at the Arvida and Laterriere mesocosms.

R.R. Goulet et al. / Water Research 39 (2005) 2291–23002296

where ‘‘Alin’’ is the Al mass rate entering the mesocosms

(g d�1), ‘‘Alout’’ is the Al mass rate leaving the mesocosm

(g d�1), ‘‘Almacrophyte’’ is the accumulation rate of Al by

macrophytes (g d�1), and ‘‘Alsed’’ is the accumulation

rate of Al in sediments (g d�1). The results of the mass

balance for each mesocosm are given in Table 3.

Alin and Alout were obtained by multiplying the mean

water flow rate (7standard deviation) by the mean Al

concentration (7standard deviation) measured at the

inlet and outlet of the mesocosm over the time of the

experiment where flow rates were stable. Influent and

effluent water samples collected during the first 29 d of

the experiment for chemical analysis were not included

in the Al budget. During this period, surface flow could

not be controlled adequately, due to clogging and

pressure problems within the tubing system. Reliable

and stable water retention times of 10 d and hydrological

fluxes of 512Ld�1 into and 455Ld�1 out of the four

mesocosms were obtained for the remainder of the

study. Differences between the inflow and outflow

rates could be accounted for by evapotranspirational

water losses estimated at 57Ld�1 using the Penman

equation based on local meteorological data (Kadlec

and Knight, 1996).

Retention of dissolved, particulate and total Al was

statistically significant for the two Laterriere mesocosms

but not at the two Arvida mesocosms, the only

exception being a significant dissolved Al retention in

the Arvida II mesocosm (Table 3). Both Laterriere

mesocosms behaved similarly and retained an average of

�40% of particulate Al and �10% of dissolved Al

entering the mesocosms (Table 3). The statistically non-

significant Al retention within the Arvida mesocosms

reflects the high variability in Al loadings coming into

these mesocosms, which decreased the robustness of the

statistical tests.

The Alsed term of Eq. (2) considered both fluxes of

dissolved and particulate Al. The in situ dialysis

ARTICLE IN PRESS

Table 3

Mass balance of Al in the Arvida and Laterriere mesocosms

Site/Al fraction Al at inlet

(g d�1)

Al at outlet

(g d�1)

Al retention

(g d�1)

Plant uptake

(g d�1)

Plant contrib.

retentiona (%)

Flux of Al (g d�1)

Arvida I

Dissolved 0.1170.05 0.0870.04 0.0370.05 163 0.00370.002b

Particulate 0.4370.47 0.1470.09 0.297 0.47 17 �7.5473.23c

Total 0.5470.45 0.2270.13 0.3270.45 0.04970.040 15

Arvida II

Dissolved 0.1170.05 0.0570.02 0.0670.05 290 0.00370.001b

Particulate 0.4370.47 0.1770.08 0.2670.47 67 �5.7870.85c

Total 0.5470.45 0.2270.09 0.3270.45 0.17470.103 54

Laterriere I

Dissolved 0.3370.08 0.1970.02* 0.1470.08 18 0.00270.012b

Particulate 0.5370.64 0.0770.03* 0.4670.64 5 �1.5870.17c

Total 0.8670.72 0.2570.02* 0.6170.72 0.02570.011 4

Laterriere II

Dissolved 0.3370.08 0.2170.02* 0.127 0.08 11 0.00170.015b

Particulate 0.5370.64 0.0470.01* 0.497 0.64 3 �1.3270.58c

Total 0.8670.72 0.2570.01* 0.617 0.72 0.01470.002 2

The ‘‘�’’ sign indicates a flux from the water column to the sediments.

*Indicates a statistical difference between the Al load at the inflow and the outflow (Mann–Whitney U-test).aContribution of plant uptake rate to the retention of the different Al fractions. The values are the percentage of the uptake rate by

plants relative to the retention of the Al fraction.bCalculated from [Al] profile measured in dialysers. A positive value represents a flux out of the sediments and a negative value a flux

to the sediments.cCalculated from [Al] measured in the sediment traps. A positive value represents a flux out of the sediments and a negative value a

flux to the sediments.

R.R. Goulet et al. / Water Research 39 (2005) 2291–2300 2297

technique allowed us to estimate fluxes of dissolved Al at

the sediment–water interface of the mesocosms (Tessier

et al., 1994). These fluxes were estimated using Fick’s

first law of diffusion:

FAl ¼ FDAlDC

Dx, (3)

where ‘‘F’’ is the sediment porosity, ‘‘DAl’’ is the

diffusion coefficient of Al in water obtained from Li

and Gregory (1974), ‘‘DC’’ is the difference between the

dissolved Al concentration in pore water and the

dissolved Al concentration in the overlying water, and

‘‘Dx’’ is the distance between the cells above and under

the sediment–water interface. Fluxes of dissolved Al,

either out of or into the sediments, were not significant

in the four mesocosms (Table 3 and Fig. 3), i.e., the

sediments do not seem to be an important sink/source of

dissolved Al. In contrast, in 15 wetlands in south-eastern

Ontario (Bendell-Young and Pick, 1995) and in three

Canadian Shield lakes (Nriagu et al., 1987), sediments

were an important source of Al to the overlying water.

In both studies, the overlying water column contained

5–20 times less Al than the interstitial waters, whereas in

our mesocosms there was no appreciable concentration

gradient between the sediment interstitial water and the

overlying water.

Sediment deposition rates, represented as ‘‘s’’ in

Eq. (2), were calculated with the following equation:

S ¼CsedSeddw

AttAmes, (4)

where ‘‘Csed’’ is the concentration of Al in the sediment

collected by the sediment traps, ‘‘Seddw’’ is the mass of

dried sediment collected by the traps, ‘‘At’’ is the area of

the sediment trap opening, ‘‘t’’ is the deployment time of

the sediment traps and ‘‘Ames’’ is the surface area of the

mesocosms. Retention of suspended particles is recog-

nized as a primary mode of pollutant removal by

wetlands (Kadlec and Knight, 1996) and indeed the

deposition of particulate Al in mesocosms was impor-

tant. However, the measured deposition accounted for

more than the actual calculated total Al retention in

mesocosms (Table 3). Part of the observed high particle

deposition could be due to resuspension of nearby

sediments into the sediment traps. The deposition rates

of fresh sediments as measured by our sediment traps

were of 7.7 g dry weightm�2 d�1 at Arvida and 2.7 g dry

weightm�2 d�1 at Laterriere. These values are in the

ARTICLE IN PRESS

Mesocosms

Arvida 1 Arvida 2 Laterriere 1 Laterriere 2

Mas

s of

Al (

g)

0

3000

6000

9000

12000

15000

rootleaf

Fig. 4. Quantity of Al contained in organs of the emergent

macrophyte Typha latifolia in each mesocosm during the 2001

budget experiment.

0 10 20 30 40 50 60

Dep

th (

cm)

-4

-2

0

2

4

0 10 20 30 40 50 60

Peeper #1Peeper #2Peeper #3

[Total dissolved Al] (µg L-1)

-4

-2

0

2

4

Water

Sediment

(a) (b)

(c) (d)

Arvida 1 Arvida 2

Laterrière 1 Laterrière 2

Fig. 3. Total dissolved Al concentrations in overlying waters and sediment pore waters measured by in situ dialysis in the Arvida and

Laterriere mesocosms during the Al mass budget experiment in 2001. The three profiles correspond to three separate dialysers or

‘‘peepers’’.

R.R. Goulet et al. / Water Research 39 (2005) 2291–23002298

lower range of those reported by Fennessy et al. (1994)

(1–103 g dry weightm�2 d�1) for treatment wetlands.

Aquatic plants take up and bioaccumulate dissolved

metals, this uptake normally being related to the

dissolved free metal ion concentration (Parker and

Pedler, 1997). We first calculated the contribution of

plant uptake to the removal of the dissolved, particulate

and total Al fractions (Table 3). This was done by

comparing the uptake rate by plants on a daily basis

(Table 3) to the retention of each Al fraction by the

mesocosms (Table 3). The quantity of Al retained by

plants on a daily basis (Table 3) was obtained by

multiplying the mean uptake rate of Al by macrophytes

(fourth column in Table 3) by the total biomass of

macrophytes for each mesocosm. As noted earlier, 99%

of the plant-associated Al was found in T. latifolia roots

(Fig. 4). Therefore, uptake rates by plants presented in

Table 3 are mainly Al uptake rates for T. latifolia. These

values ranged between 0.014 and 0.025 g d�1 at Later-

riere and between 0.049 and 0.174 g d�1 at Arvida.

In the present study, we wanted to evaluate to what

extent Al uptake by macrophytes contributed to the

retention of dissolved Al by the mesocosms. At the

Laterriere mesocosms, Al uptake by cattails could

account for 11–18% of the dissolved Al retained by

both mesocosms (Table 3). In contrast, retention of

dissolved Al was not statistically significant in the

Arvida mesocosms, and yet, cattails accumulated Al;

the amount of Al accumulated by cattails corresponded

to 163% and 290% of the dissolved Al removed by the

Arvida mesocosm (Table 3). This observation suggests

that the Al uptake by cattails was from the sediments

and not from the overlying water. Indeed, most of the Al

taken up by cattails was measured in the roots. It is not

clear if the dissolved Al pool in the sediment interstitial

water is replenished by exchange with Al bound to the

sediments or by a diffusive flux of dissolved Al moving

from the overlying water to the sediment pore water.

Considering the Al flux estimates obtained from the in

situ dialysis measurements in the four mesocosms, the

overlying water does not seem to be a major source of

ARTICLE IN PRESSR.R. Goulet et al. / Water Research 39 (2005) 2291–2300 2299

dissolved Al to the sediments (Fig. 3). Hence, the

retention of total Al in the mesocosms, and by extension

in treatment wetlands, is mainly affected by particulate

Al deposition and less by direct uptake by macrophytes.

4. Conclusion

Dissolved Al is less efficiently retained by water

management ponds than is particulate Al. Phytoreme-

diation could potentially improve the retention of

dissolved Al, but there is limited information on the

capacity of aquatic macrophytes to accumulate dissolved

Al. In the present study, where mesocosms containing

various aquatic plants were used to treat an Al-rich

smelter effluent, deposition of particulate Al was the

dominant contribution to Al retention but significant

decreases in dissolved Al were also noted. The macro-

phytes accumulated Al to non-toxic levels, with cattails

(an emergent plant) accounting for 99% of the plant-

bound Al at the end of the growing season. However,

because cattails accumulated Al mainly in root tissue,

their role in removing dissolved Al from the effluent is

unclear. The relative importance of dissolved Al uptake

by aquatic macrophytes would be higher if plant biomass

were increased, e.g., by choosing species that accumulate

Al directly from the water column such as L. minor and

Ceratophyllum demersum (Jackson, 1998). Further re-

search is needed to identify the species community

composition that would optimize dissolved Al retention.

Acknowledgments

The authors would like to thank Alcan International

Ltee for their logistical help on site. The technical

assistance provided by G. Cote, L. Rancourt, R.

Rodrigue, S. Duval, P. Fournier and M. Bordeleau is

gratefully acknowledged. Funding was provided by

Alcan International Ltee, by a Natural Science and

Engineering Research Council industrial postdoctoral

fellowship to C. Munger, and by a Fonds de Recherche

sur la Nature et les Technologies du Quebec postdoctor-

al scholarship to R. Goulet. P.G.C. Campbell is

supported by the Canada Research Chair Program.

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