Ecological Engineering 17 (2001) 373 – 384
Changes in dissolved and total Fe and Mn in a young
constructed wetland: Implications for retention performance
Richard R. Goulet *, Frances R. Pick
Ottawa -Carleton Institute of Biology, Uniersity of Ottawa, 30 Marie -Curie, Ottawa, Ont., Canada K1N 6N5
Received 1 December 1999; received in revised form 6 September 2000; accepted 13 September 2000
Abstract
Surface-flow wetlands are generally considered sinks for Fe and Mn but they may also export and affect the
partitioning of these metals. This study was undertaken to evaluate the effect of a young constructed wetland on the
retention and transformation of both dissolved and particulate Fe and Mn. Duplicate water samples were collected
every three days at the inlet and outlet structures of the Monahan Wetland, Kanata, Ontario, from spring of 1997
to 1999. While on a yearly basis the wetland showed significant retention of the dissolved phase, the retention of total
Fe and Mn was poor. There were strong seasonal differences in retention and, during the winter, the wetland was a
source. The wetland transformed dissolved into particulate Fe and Mn from spring to fall whereas during the winter,
dissolved Fe and Mn were released. Changes in pH, alkalinity and temperature could explain 11% and 40% of the
outlet variation in the ratio of dissolved to total Fe and Mn respectively. Furthermore, from spring to late summer,
planktonic algal biomass was negatively related to the ratio of dissolved to total Fe and Mn implying a role in Fe
and Mn transformations in young wetlands where emergent and submerged vegetation have yet to dominate the
system. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Dissolved, Fe, Mn; Metal retention; Surface-flow wetlands; Partitioning; Transformation; Vegetation
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1. Introduction
The behaviour of Fe and Mn in wetlands is
governed by a complex and dynamic exchange at
the sediment-water interface (Faulkner and
Richardson, 1989). Fe and Mn are removed from
the water column because Fe
2 +
and Mn
2 +
are
oxidised to Fe
3 +
and Mn
4 +
oxides, which precip-
itate on the surface of sediments (Tarutis and
Unz, 1996). Other trace elements can also be
removed from the water because Fe and Mn
oxides are important adsorption sites (Benjamin
and Leckie, 1981; Tessier et al., 1996; Bendell-
Young and Harvey, 1992). Under anoxic condi-
tions, Fe and Mn are released into the water
column in the dissolved form (Carignan and
Lean, 1991; De Vitre et al., 1994). As a result, the
retention capacity of wetlands depends on the
relative importance of Fe and Mn precipitation
on the surface of sediments over the release of
* Corresponding author. Tel.: +1-613-5625800, ext.: 6365;
fax: +1-613-5625486.
E-mail address: rgoulet@science.uottawa.ca (R.R. Goulet).
0925-8574/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
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