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Journal ArticleDOI

Geochemistry of trace metals in a fresh water sediment : Field results and diagenetic modeling

01 Aug 2007-Science of The Total Environment (Elsevier)-Vol. 381, Iss: 1, pp 263-279

TL;DR: Pore water and sediment analyses indicate a shift in trace metal speciation from oxide-bound to sulfide-bound over the upper 20 cm of the sediment, and sensitivity analyses show that increased bioturbation and sulfate availability, expected upon restoration of estuarine conditions in the lake, should increase the sulfide bound fractions of Zn and Ni in the sediments.

AbstractConcentrations of Fe, Mn, Cd, Co, Ni, Pb, and Zn were determined in pore water and sediment of a coastal fresh water lake (Haringvliet Lake, The Netherlands). Elevated sediment trace metal concentrations reflect anthropogenic inputs from the Rhine and Meuse Rivers. Pore water and sediment analyses, together with thermodynamic calculations, indicate a shift in trace metal speciation from oxide-bound to sulfide-bound over the upper 20 cm of the sediment. Concentrations of reducible Fe and Mn decline with increasing depth, but do not reach zero values at 20 cm depth. The reducible phases are relatively more important for the binding of Co, Ni, and Zn than for Pb and Cd. Pore waters exhibit supersaturation with respect to Zn, Pb, Co, and Cd monosulfides, while significant fractions of Ni and Co are bound to pyrite. A multi-component, diagenetic model developed for organic matter degradation was expanded to include Zn and Ni dynamics. Pore water transport of trace metals is primarily diffusive, with a lesser contribution of bioirrigation. Reactions affecting trace metal mobility near the sediment-water interface, especially sulfide oxidation and sorption to newly formed oxides, strongly influence the modeled estimates of the diffusive effluxes to the overlying water. Model results imply less efficient sediment retention of Ni than Zn. Sensitivity analyses show that increased bioturbation and sulfate availability, which are expected upon restoration of estuarine conditions in the lake, should increase the sulfide bound fractions of Zn and Ni in the sediments.

Topics: Trace metal (57%), Bioirrigation (54%), Trace element (54%), Sediment (53%), Pore water pressure (51%)

Summary (4 min read)

1. Introduction

  • In freshwater sediments, sulfide mineral phases may also immobilize trace metals, despite the lower sulfate concentrations relative to marine systems (Huerta-Diaz et al., 1998; Motelica-Heino et al., 2003).
  • Others have applied multi-component RTMs to assess metal sulfide oxidation (Carbonaro et al., 2005; Di Toro et al., 1996) and the controls on arsenic mobility in sediments (Smith and Jaffe, 1998).
  • A better understanding of trace metal behavior in sediments is needed to guide management efforts to improve water quality and ecosystem health of the lake.

2. Study site

  • In 1970, the Haringvliet estuary was converted to a freshwater lake by building a dam at the outlet to the North Sea (Fig. 1).
  • A partial restoration of estuarine conditions is proposed for Haringvliet Lake, beginning in 2008.
  • Changes in management of the dam will allow water from the adjacent North Sea to enter the lake at high tide.
  • Trace metal contamination has adversely affected benthic communities in sediments of the Rhine–Meuse Delta where low species diversity has been correlated with sediment toxicity including elevated trace metal Netherlands with a box denoting the location of the detail section.
  • Concentrations (Reinhold-Dudok van Heel and den Besten, 1999).

3.1. Sample collection

  • Sediment and pore water samples were collected in September 2002, and April–May 2003.
  • The sampling periods are referred to as late-summer, and spring, respectively.
  • Sediment was collected using a cylindrical box corer, with a 31 cm inner diameter, deployed from RV Navicula.
  • Subcores were taken with polycarbonate tubes (10 cm i.d.).
  • Sub-cores for pore water and solid phase analysis were taken from a single box core and immediately sectioned in a N2 purged glove box on board the ship.

3.2. Pore water analyses

  • Sediment sub-samples for pore water collection were placed in polyethylene centrifuge tubes in a N2 purged glove box during core sectioning.
  • Sulfide was measured colorimeterically (Cline, 1969) using filtered pore water fixed with NaOH (10 μl 1 M NaOH per ml).
  • The pore water concentration was then derived from the estimated diffusive flux through the gel following the established procedure (e.g. Zhang et al., 1995; Naylor et al., 2004).
  • The probes were inserted into sediment cores and incubated for 24 h in the temperature controlled shipboard laboratory.
  • Following incubation, the agarose gel was removed from each individual compartment and eluted in 1 ml 1MHNO3.

3.3. Solid phase analyses

  • Sediment water content and density were determined from the weight loss upon freeze drying, allowing for the determination of sediment porosity.
  • Total carbon, total sulfur, and organic carbon (Corg; following carbonate removal with 1 M HCl) were determined on freeze-dried sediment using an elemental analyzer (LECO SC-1440H).
  • Analysis ofmetals in all extractants was carried out with ICP-MS unless otherwise noted.
  • It is important to note that AVS includes a range of sulfide containing compounds (Rickard and Morse, 2005).
  • The reactive pool extraction in the HuertaDiaz and Morse (1990) method (1 M HCl) is less specific, as it also mobilizes reactive Fe(II) phases (Kostka and Luther, 1994).

3.4. Modeling

  • Reaction-transport model calculationswere carried out with the Biogeochemical Reaction Network Simulator (BRNS; Aguilera et al., 2005; Jourabchi et al., 2005).
  • The discussion of reaction and transport processes in this paper is limited to those that directly involve the trace metals.
  • The model describes 1-D sediment profiles at steady-state.
  • The ability of thermodynamic modeling to predict the speciation of dissolved metals is limited by the use of pure, end-member solid phases and, the limited knowledge of metal–sulfide stability constants.

4.1. Porewater

  • Pore water DOC displayed a gradual increase with depth in late-summer, while a subsurface maximum was observed in spring (Fig. 2).
  • Pore water analyses based on the DGT method indicated the presences of free sulfide in the upper 10 cm of sediment.
  • The pore water concentrations of Zn, Pb, and Cd were similar for the two sampling times.
  • Pore water profiles of Co and Ni resembled those of Mn, for both sampling periods.

4.2. SPM metal content

  • Trace metals in the water column of the Haringvliet Lake are mainly associated with the SPM.
  • Concentrations of solid-phase Zn, Ni, Pb, and Cd in the upper 2 cm of sediment exhibit the same order of abundance and the same magnitudes as in the lake SPM (Fig. 4).
  • Concentrations of Fe and Mn in the SPM varied independently from one another (Fig. 5), as previously observed at other sites in the Rhine–Meuse Delta (Paalman and van der Weijden, 1992).
  • The SPM trace metal concentrations varied substantially in the period 2000–2004, with coefficients of variation ranging from 17% for Zn to 55% for Cd (see error bars on Fig. 4).
  • The trace metal SPM concentrations displayed negative correlations with SPMorganicmatter content; indicating that organicmatter produced in the lake during algae blooms had a lower trace metal content than the terrestrially derived SPM.

4.3. Sediment solid phase

  • The sediment is highly porous, fined grained and organic rich (Table 1).
  • The total sediment profiles of Corg, Fe, Mn, Zn, Pb, Co, and Cd displayed little variation with depth, particularly in the upper 10 cm of sediment (Fig. 6).
  • As expected, the AVS-SEMconcentrationswere lower than the respective total concentrations (Fig. 6).
  • The concentrations of CDB extractable Fe, Ni, and Co declined more sharply with depth than the ascorbate extractable concentrations.

5.1. Pore water profiles

  • The build up of alkalinity in the pore waters reflects Corg mineralization (Fig. 2).
  • The authors previous work has shown that sulfate reduction is an important mineralization pathway (Canavan et al., 2006), which explains the rapid depletion of pore water SO4 2− and the presence of measurable free sulfide.
  • The pore water profiles of Zn, Pb, and Cd show a near-surface enrichment in spring (Fig. 2).
  • For Zn and Pb, the reductive extraction results imply that the near-surface pore water enrichments can, in part, be explained by reductive dissolution of reactive Fe and Mn oxide phases close to the sediment–water interface.
  • The concentration ratios of Mn to Co and Ni in the pore waters (approximately 2000 and 700, respectively) are much higher than those measured in the reductive extractions (Mn:Co=100–450 and Mn:Ni=50–155).

5.2. Sediment solid phase

  • The correlations of sediment Corg, Al, and Fe concentrations with grain size b63 μm (Table 1) indicate a close association of OM, metal oxides and clay minerals (Tessier et al., 1996).
  • The concentrations of target values for of the Dutch Soil Protection Although pore water profiles suggest diagenetic remobilization may occur in the sediment (Fig. 2), those processes to not result in a redistribution of the total sediment concentration profiles, with the exceptions of S and possibly Ni (Fig. 6).
  • The decreasing concentrations with increasing depth of the ascorbate and CDB extractable Fe pools are consistent with reductive dissolution of Fe(III) in the sediment (Fig. 7).
  • The progressive decrease with depth of the ascorbate and CDB extractable concentrations of Mn, Zn, Ni, and Co also indicate release from reducible mineral phases (Fig. 7).

5.3. Diagenetic modeling

  • The second fractio to both oxide pools 3 Oxide formation Mn2+ and Fe2+ can oxidatively precipita trace metal with the same oxideQtrace m 4 Bioirrigation ZnS concentrations rresponds with that given in Fig. 10 f Fe-oxides (Zn), Mn-oxides (Ni), or FeS2 (Ni) by a ratio derived from eductive dissolution.
  • In a simulation run without ZnS oxidation the flux of dissolved Zn2+ across the SWI changed from an efflux of 24 nmol cm−2 yr−1 to an influx of 9 nmol cm−2 yr−1 into the sediment.
  • Ni is estimated at 833 through model fitting of the pore water Ni2+ profile, also known as The ratio of FeS.
  • The simulated changes to sediment processes resulting from estuarine restoration are shown to have a greater effect on the solid phase speciation than on metal efflux.

6. Conclusions

  • The Haringvliet Lake sediment exhibits elevated concentrations of trace metals (Cd, Co, Ni, Pb, and Zn) derived from riverine suspended particles.
  • Results of extractions show declining concentrations of reducible phases and an increase in sulfide species with depth.
  • Pore waters are supersaturated with respect to Zn, Pb, Co, and Cd monosulfides, while Ni and Co are found to be associated with pyrite.
  • These results illustrate a transition from oxide-bound to sulfide-bound trace metals with depth in the sediment.
  • Total metal sediment profiles suggest that little metal release from the sediment is occurring with the possible exception of Ni. Diagenetic model simulations predict a greater mobility of Ni than Zn, as Ni does not form stable metal-sulfides, and is more slowly removed by oxidative precipitation at the sediment surface.

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Geochemistry of trace metals in a fresh water sediment:
Field results and diagenetic modeling
R.W. Canavan
a,
, P. Van Cappellen
a
, J.J.G. Zwolsman
b
,
G.A. van den Berg
b
, C.P. Slomp
a
a
Utrecht University, Faculty of Geosciences, PO Box 80021, 3508 TA Utrecht, The Netherlands
b
Kiwa Water Research, PO Box 1072, 3430 BB Nieuwegein, The Netherlands
Received 6 October 2006; received in revised form 27 February 2007; accepted 1 April 2007
Available online 4 May 2007
Abstract
Concentrations of Fe, Mn, Cd, Co, Ni, Pb, and Zn were determined in pore water and sediment of a coastal fresh water lake
(Haringvliet Lake, The Netherlands). Elevated sediment trace metal concentrations reflect anthropogenic inputs from the Rhine and
Meuse Rivers. Pore water and sediment analyses, together with thermodynamic calculations, indicate a shift in trace metal
speciation from oxide-bound to sulfide-bound over the upper 20 cm of the sediment. Concentrations of reducible Fe and Mn
decline with increasing depth, but do not reach zero values at 20 cm depth. The reducible phases are relatively more important for
the binding of Co, Ni, and Zn than for Pb and Cd. Pore waters exhibit supersaturation with respect to Zn, Pb, Co, and Cd
monosulfides, while significant fractions of Ni and Co are bound to pyrite. A multi-component, diagenetic model developed for
organic matter degradation was expanded to include Zn and Ni dynamics. Pore water transport of trace metals is primarily
diffusive, with a lesser contribution of bioirrigation. Reactions affecting trace metal mobility near the sedimentwater interface,
especially sulfide oxidation and sorption to newly formed oxides, strongly influence the modeled estimates of the diffusive effluxes
to the overlying water. Model results imply less efficient sediment retention of Ni than Zn. Sensitivity analyses show that increased
bioturbation and sulfate availability, which are expected upon restoration of estuarine conditions in the lake, should increase the
sulfide bound fractions of Zn and Ni in the sediments.
© 2007 Elsevier B.V. All rights reserved.
Keywords: RhineMeuse River Delta; Sulfide; Trace metals; Diagenetic modeling; Sediment
1. Introduction
Elevated concentrations of trace metals in sediments
pose toxicological risks to biota and may impair water
quality (Baird and Cann, 2005). Under oxidizing con-
ditions, trace metals bind to organic matter (OM), clays,
and Fe plus Mn-oxides (Turner et al., 2004). These phases
are frequently intimately associated with one another
(Perret et al., 2000; Taillefert et al., 2002), making it
difficult to separate them by physical and chemical
techniques. Decomposition of OM and reductive disso-
lution of Fe and Mn-oxides, which tend to be highest near
the sediment water interface (SWI; Canavan et al., 2006;
Douglas and Adeney, 2000), may lead to release of trace
metals to the pore waters (Zhang et al., 1995).
In reducing sediments, trace metals often associate
with insoluble sulfide precipitates (e.g. Huerta-Diaz et al.,
1998). Sulfide is produced by bacterial sulfate reduction
coupled to OM decomposition (Holmer and Storkholm,
Science of the Total Environment 381 (2007) 263 279
www.elsevier.com/locate/scitotenv
Corresponding author. Tel.: +31 302535016; fax: +31 302535302.
E-mail address: r.canavan@geo.uu.nl (R.W. Canavan).
0048-9697/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.scitotenv.2007.04.001

2001). In coastal marine sediments and salt marsh soils,
abundant sulfate and OM cause high rates of sulfide pro-
duction, with pyrite (FeS
2
) being the most common end-
product (Huerta-Diaz and Morse, 1990; Kostka and
Luther, 1994). In freshwater sediments, sulfide mineral
phases may also immobilize trace metals, despite the
lower sulfate concentrations relative to marine systems
(Huerta-Diaz et al., 1998; Motelica-Heino et al., 2003).
The metals are then buried in the sediment, unless oxi-
dative dissolution of the sulfide mineral phases occurs,
upon sediment mixing by resuspension and bioturbation
(Carroll et al., 2002).
Reactive transport models (RTMs) are often used to
simulate the complex interplay of reaction and transport
processes in sediments (Boudreau, 1999). However,
only few studies have used this approach to quantita-
tively describe trace metal cycling in freshwater
sediments. Recently, Gallon et al. (2004) used an
inverse, steady state model to describe Pb diagenesis
in sediments of a Canadian shield lake. Others have
applied multi-component RTMs to assess metal sulfide
oxidation (Carbonaro et al., 2005; Di Toro et al., 1996)
and the controls on arsenic mobility in sediments (Smith
and Jaffe, 1998).
In this study, we present results of pore water analyses
and sediment extractions for Fe, Mn, Cd, Co, Ni, Pb and
Zn in sediment of a coastal fresh water lake, Haringvliet
Lake, which is part of the RhineMeuse River Delta and
has experienced elevated trace metal inputs from anthro-
pogenic sources. We also include Zn and Ni in an ex-
isting multi-component RTM, which accounts for
organic matter degradation, secondary redox reactions,
mineral precipitation and dissolution, and transport by
bioirrigation and bioturbation (Canavan et al., 2006).
The analytical results, thermodynamic calcul ations, and
reactive transport modeling are used to examine how
trace metal speciation changes with depth in the sedi-
ment. A better understanding of trace metal behavior in
sediments is needed to guide management efforts to im-
prove water quality and ecosystem health of the lake.
2. Study site
In 1970, the Haringvliet estuary was converted to a
freshwater lake by building a dam at the outlet to the
North Sea (Fig. 1). This alteration caused the accumu-
lation of metal-polluted sediments in the lake and habitat
loss (Smit et al., 1997). A partial restoration of estuarine
conditions is proposed for Haringvliet Lake, beginning
in 2008. Changes in management of the dam will allow
water from the adjacent North Sea to enter the lake at
high tide. The sampling site lies within the area that will
be affected by the estuarine restoration (Fig. 1; 51.50.080
N, 04.04.328 E).
Trace metal contamination has adversely affected
benthic communities in sediments of the RhineMeuse
Delta where low species diversity has been correlated
with sediment toxicity including elevated trace metal
Fig. 1. The sampling location in Haringvliet Lake. The inset map shows the Netherlands with a box denoting the location of the detail section. The
RhineMeuse river complex flows into the lake from the east, and the lake discharges through the dam at the western limit of the lake.
264 R.W. Canavan et al. / Science of the Total Environment 381 (2007) 263279

concentratio ns (Reinhold-Dudok van Heel and den
Besten, 1999). Studies of sediment trace metal biogeo-
chemistry, including pore water analysis, have been
conducted at other locations within the delta with the aim
of describing possible release of trace metals from the
sediment to the overlying water (van den Berg et al.,
1999). The present work is part of a study of biogeo-
chemical processes and their response to salinization in
Haringvliet Lake.
3. Methods
3.1. Sample collection
Sediment and pore water samples were collected in
September 2002, and AprilMay 2003. The sampling
periods are referred to as late-summer, and spring, re-
spectively. Sediment was collected using a cylindrical box
corer, with a 31 cm inner diameter, deployed from RV
Navicula. Each box core contained approximately 40 cm
of surface sediment and 30 cm of overlying water. Sub-
cores were taken with polycarbonate tubes (10 cm i.d.).
Sub-cores for pore water and solid phase analysis were
taken from a single box core and immediately sectioned in
aN
2
purged glove box on board the ship.
3.2. Pore water analyses
Sediment sub-samples for pore water collection were
placed in polyethylene centrifuge tubes in a N
2
purged
glove box during core sectioning. The tubes were sub-
sequently removed from the glove box and centrifuged at
2500 g for 10 to 30 min. Core sectioning and cen-
trifugation were conducted in the temperature controlled
laboratory on board with the temperature set to the bottom
water temperature during sampling (18 °C late-summer,
12 °C spring). Following centrifugation, tubes were trans-
ferred to a N
2
filled glove bag where pore water was
filtered (late-summer: 0.2 μm pore size polypropylene
PALL filters; spring: 0.45 μm pore size polyethersulfone
Orange Scientific filters). Pore water pH was determined
directly on the filtrate. Filtrate aliquots for trace metal
analysis were acidified with HNO
3
(50 μl conc. trace
metal grade HNO
3
per ml) and stored in high density
polyethylene bottles at 4 °C until analysis by inductively
coupled plasma mass spectroscopy (ICP-MS; Agilent
7500 series). Pore water blanks were determined by pro-
cessing ultra-pure water from the laboratory in parallel
with pore water samples in the field.
Sulfate and chloride were determined by Ion Chroma-
tography (Dionex DX-120) on frozen filtrate, and dis-
solved organic carbon (DOC) with a Shimadzu TOC-
50550A analyzer on filtrate samples stored at 4 °C.
Alkalinity was determined colorimeterically in the field
(Sarazin et al., 1999). Sulfide was measured color-
imeterically (Cline, 1969) using filtered pore water fixed
with NaOH (10 μl 1 M NaOH per ml). Sulfide pore water
profiles were also measured using the Diffusive Gradient
in Thin Films (DGT) method (Motelica-Heino et al., 2003;
Naylor et al., 2004). Briefly, a gel containing AgI was
covered with a diffusive gel and a 0.45 μm cellulose nitrate
filter, mounted on a plastic assembly (DGT Research), and
inserted into a sediment core and incubated for approx-
imately 24 h in the temperature controlled laboratory.
Sulfide in the pore water diffusing into the gel reacts with
AgI to form AgS
2
, which results in a color change from
yellow to black. Following incubation, the color was re-
corded using a conventional flat bed scanner. The sulfide
concentration in the gel was determined using the cali-
bration of Naylor et al. (2004). The pore water concen-
tration was then derived from the estimated diffusive flux
through the gel following the established procedure (e.g.
Zhang et al., 1995; Naylor et al., 2004).
Additional pore water profiles were obtained using
constrained Diffusive Equilibration in Thin Films (DET;
Davison et al., 2000). Each probe consisted of a plastic
plate containing 75 sequential isolated compartments that
were 1.8 cm wide, 0.1 cm deep, and 0.1 cm across. These
compartments were filled with a 1.5% agarose gel and
covered with a 0.45 μm cellulose nitrate filter, creating a
small scale peeper device. The probes were inserted into
sediment cores and incubated for 24 h in the temperature
controlled shipboard laboratory. Following incubation,
the agarose gel was removed from each individual com-
partment and eluted in 1 ml 1 M HNO
3
. The elutents were
analyzed by ICP-MS. However, the small sample vol-
umes proved too small to obtain reproducible trace metal
pore water profiles, except for manganese.
3.3. Solid phase analyses
Sediment water content and density were determined
from the weight loss upon freeze drying, allowing for
the determination of sediment porosity. Grain size analy-
sis was conducted using a laser diffraction technique
(Malvern Mastersizer S) on freeze dried s ediment
following a HCl and H
2
O
2
pre-treatment. Total carbon,
total sulfur, and organic carbon (C
org
; following carbonate
removal with 1 M HCl) were determined on freeze-dried
sediment using an elemental analyzer (LECO SC-1440H).
A total digestion with HFHClO
4
HNO
3
was con-
ducted on freeze dried sediment samples as described
in Hyacinthe and Van Cappellen (2004). Determination
of major elements (Ca and Al) in the extractant was
265R.W. Canavan et al. / Science of the Total Environment 381 (2007) 263279

performed with inductively coupled plasma optical
emission spectroscopy (ICP-OES; Perkin-Elmer Optima
3000). Analysis of metals in all extractants was carried out
with ICP-MS unless otherwise noted. Acid Volatile
Sulfide-Simultaneously Extractible Metal (AVS-SEM)
extractions were conducted to determine concentrations
of non-pyritic reduced sulfur, and metals bound to non-
pyritic sulfides and other extractible phases (carbonates
and amorphous oxides). AVS-SEM was performed on
approximately1gwetsedimentinanAr-purgedanalysis
train with room-temperature 6 M HCl for 1 h. The re-
leased H
2
S was trapped in a 1 M NaOH solution from
which sulfide concentrations were determined colorimet-
rically (Cline, 1969). It is important to note that AVS
includes a range of sulfide containing compounds (Rickard
and Morse, 2005). For simplicity, however , AVS is
represented as iron monosulfide, FeS, in the model
reaction network.
The sequential extraction method of Huerta-Diaz and
Morse (1990) was performed on freeze dried samples.
The method includes three operationally defined Fe and
trace metal pools: reactive (1 M HCl, 16 h); silicate
(10 M HF,16 h); and pyrite (conc. HNO
3
, 2 h). The
degree of pyritization (DOP) and degree of trace metal
pyritization (DTMP) can then be calculated as follows
(Boesen and Postma, 1988):
DOP kðÞ¼
pyrite FeðÞ
pyrite FeðÞþreactive FeðÞ

100
ð1Þ
DTMP kðÞ
¼
pyrite MeðÞ
pyrite MeðÞþreactive MeðÞ

100 ð2Þ
where the concentrations of Fe or trace metal (Me) mea-
sured in the reactive and pyrite pools of the extraction are
used. DOP represents the percent of reactive Fe that is
present as pyrite and DTMP is the percent of reactive trace
metal bound in the pyrite phase. The degree of sul-
fidization (DOS), that is, the percent of reactive Fe that is
bound to sulfide, is calculated as follows:
DOS kðÞ¼
pyrite FeðÞþAVS FeðÞ
pyrite FeðÞþreactive FeðÞ

100
ð3Þ
where (AVSFe) is the concentration of AVS, and
reactiveFe and pyriteFe are the Fe concentrations in
the respective pools.
Additional extractions with citratedithionite bicar-
bonate (CDB, extraction solution analysis by ICP-OES;
Slomp et al., 1996) and pH 7.5 ascorbate (Hyacinthe and
Van Cappellen, 2004; Kostka and Luther, 1994) were
performed on wet sediment to further characterize the
reactive Fe(III) pool. The CDB extractant extracts all
Fe-oxides while the near-neutral ascorbate extraction is
limited to poorly crystalline and amorphous reducible Fe
(III) phases. The reactive pool extraction in the Huerta-
Diaz and Morse (1990) method (1 M HCl) is less spe-
cific, as it also mobilizes reactive Fe(II) phases (Kostka
and Luther, 1994). The dissolution kinetics in pH 7.5
ascorbate of a freeze-dried surface sediment sample
(00.5 cm late-summer) were followed by periodically
sampling the sediment suspensions over the course of a
25-hour extraction period, following the procedure of
Hyacinthe and Van Cappellen (2004).
Concentrations of Zn, Ni, Pb, and Cd, and grain size
determinations for suspended matter (SPM), determined
during monthly water quality monitoring performed by
the Netherlands Institute for Inland Water Management
and Waste Water Treatment (RIZA), were obtained from
the publicly available database, www.waterbase.nl,and
are reproduced here with permission. Metal concentra-
tions in SPM reported in the data base were measured by
ICP-OES after a HClHNO
3
extraction on freeze-dried
samples. The RIZA provided SPM samples collected in
2001, on which we measured the concentrations of Fe and
Mn, as these elements are not reported in the database.
3.4. Modeling
Reaction-transport model calculations were carried out
with the Biogeochemical Reaction Network Simulator
(BRNS; Aguilera et al., 2005; Jourabchi et al., 2005). The
development and calibration of the model used to describe
the sediment in Haringvliet Lake is presented in Canavan
et al. (2006). The existing model, which includes a
reaction network of 24 chemical species and 32 reactions,
was expanded to include trace metal reactions. The dis-
cussion of reaction and transport processes in this paper is
limited to those that directly involve the trace metals.
Changes to model boundary conditions and rate constants
for Fe, Mn, and S reactions were made to account for
CDB fractions and the depositional input of a pyrite pool
that were not included in the original model (Canavan
et al., 2006). These changes are listed in Appendix A.
Trace metals in the model were subjected to the same
transport processes as other constituents, namely molec-
ular diffusion, bioirrigation, bioturbation, and burial for
solutes, and bioturbation and burial for solids. The model
describes 1-D sediment profiles at steady-state. This
steady-state approach was necessary as insufficient infor-
mation was available to constrain time-resolved variations
266 R.W. Canavan et al. / Science of the Total Environment 381 (2007) 263279

Fig. 2. Porewater profiles of DOC, alkalinity, pH, Fe, SO
4
2
, sulfide, Zn, Pb, Cd, Mn Ni, and Co for the late-summer () and spring () sampling
times. The sediment water interface (SWI) is indicated as a broken horizontal line. Mean values of field blanks for Zn, Pb, Cd, Mn, Co, and Ni are
given at the SWI (). Model fits for alkalinity, pH, Fe
2+
,SO
4
2
, sulfide, Zn
2+
,Mn
2+
, and Ni
2+
are plotted as continuous lines in the plots. Pore water
sulfide profiles measured with the AgI DGT probe (see Section 3.2), are also shown as continuous lines. The sulfide results from late-summer, spring,
and the model are labeled L-S, spring, and RTM respectively. For Mn, the concentrations measured with constrained DET (see Section 3.2) are
presented for the late-summer () and spring ().
267R.W. Canavan et al. / Science of the Total Environment 381 (2007) 263279

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Journal ArticleDOI
Abstract: Three sediment cores were collected in the Scheldt, Lys and Spiere canals, which drain a highly populated and industrialized area in Western Europe. The speciation and the distribution of trace metals in pore waters and sediment particles were assessed through a combination of computational and experimental techniques. The concentrations of dissolved major and trace elements (anions, cations, sulfides, dissolved organic C, Cd, Co, Fe, Mn, Ni, Pb and Zn) were used to calculate the thermodynamic equilibrium speciation in pore waters and to evaluate the saturation of minerals (Visual Minteq software). A sequential extraction procedure was applied on anoxic sediment particles in order to assess the main host phases of trace elements. Manganese was the most labile metal in pore waters and was mainly associated with carbonates in particles. In contrast, a weak affinity of Cd, Co, Ni, Pb and Zn with carbonates was established because: (1) a systematic under-saturation was noticed in pore waters and (2) less than 10% of these elements were extracted in the exchangeable and carbonate sedimentary fraction. In the studied anoxic sediments, the mobility and the lability of trace metals, apart from Mn, seemed to be controlled through the competition between sulfidic and organic ligands. In particular, the necessity of taking into account organic matter in the modelling of thermodynamic equilibrium was demonstrated for Cd, Ni, Zn and Pb, the latter element exhibiting the strongest affinity with humic substances. Consequently, dissolved organic matter could favour the stabilization of trace metals in the liquid phase. Conversely, sulfide minerals played a key role in the scavenging of trace metals in sediment particles. Finally, similar trace metal lability rankings were obtained for the liquid and solid phases.

96 citations


Cites background from "Geochemistry of trace metals in a f..."

  • ...Another sediment core was cut every 2 cm under nitrogen in a glove bag to prevent any oxidation of the reduced species present in the anoxic sediments....

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  • ...As a result, strong vertical gradients are evidenced for dissolved species concentrations in the vicinity of the water-sediment interface, resulting in the release or the trapping of trace metals in sediments (Audry et al., 2010; Canavan et al., 2007, Miller and Orbock Miller, 2007)....

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  • ...…make thermodynamic calculations a promising approach for the evaluation of trace ha l-0 09 22 20 0, v er si on 1 - 24 D ec 2 01 3 metal speciation (Billon et al., 2003; Canavan et al., 2007; Huerta-Diaz et al., 1998; LourinoCabana et al., 2010; Mayer et al., 2008; van den Berg et al., 1999)....

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  • ...Sediments were collected in November and December 2005 in the Scheldt River (at Helkijn) and two of its tributaries (the Lys River at Wervik and the Spiere Canal) (Figure 1)....

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Journal ArticleDOI
Abstract: High resolution profiles of trace elements (Fe, Mn, Co, As, Cu, Cr, Ni and Pb) were assessed using the DET (Diffusive Equilibrium in Thin films) and DGT (Diffusive Gradients in Thin films) techniques in silty, organically enriched, sub-tidal sediments of the Belgian coast during late winter and spring 2008. The general chemical properties of the sediments such as dissolved oxygen, pH, Eh and sulfide profiles, controlling precipitation/mobilization reactions, were determined with electrodes (pH and Eh) and microelectrodes (oxygen) and AgI-DGT probes (sulfide). Most trace elements show subsurface maxima and low concentrations beneath 8 cm of depth. The main physicochemical parameters controlling the vertical concentration profiles are dissolved oxygen and redox potential in the surface sediment and sulfide in the deeper sediment layers. Thermodynamic equilibrium calculations have been carried out verifying which solid phases can explain the dissolved trace metal concentrations. Seasonal variations of trace elements have been observed during the sampling period and sedimentation of fresh particulate organic matter (POM) derived from phytoplankton blooms appear to be the main cause of this temporal variability. Flux calculations based on DGT profiles (these fluxes are minimum ones) show that exchange fluxes of trace metals in February are slightly higher than in April. In addition, “DGT pistons” were deployed at the sediment water interface (SWI) to accumulate labile ions from below. This way all labile ions, binding onto the DGT Chelex resin, are pumped out of the pore waters and the solid sediment phase (only the mobile fraction). These results are a direct estimation of the amount of trace elements that can be released from the upper sediment to the water column (in the range of 4.4·10 − 5 to 0.10 mmol·m − 2 ·d − 1 for Co, Pb, Cr, As, Cu, Ni, Fe and Mn).

87 citations


Cites background from "Geochemistry of trace metals in a f..."

  • ...Several publications have indeed shown MnS is not a solute observed in most pore waters (Canavan et al., 2007; Huerta-Diaz et al., 1998; Morse and Luther, 1999; Billon et al., 2001)....

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Journal ArticleDOI
Abstract: [1] The global-scale quantification of organic carbon (Corg) degradation pathways in marine sediments is difficult to achieve experimentally due to the limited availability of field data. In the present study, a numerical modeling approach is used as an alternative to quantify the major metabolic pathways of Corg oxidation (Cox) and associated fluxes of redox-sensitive species fluxes along a global ocean hypsometry, using the seafloor depth (SFD) as the master variable. The SFD dependency of the model parameters and forcing functions is extracted from existing empirical relationships or from the NOAA World Ocean Atlas. Results are in general agreement with estimates from the literature showing that the relative contribution of aerobic respiration to Cox increases from 80% in deep-sea sediments. Sulfate reduction essentially follows an inversed SFD dependency, the other metabolic pathways (denitrification, Mn and Fe reduction) only adding minor contributions to the global-scale mineralization of Corg. The hypsometric analysis allows the establishment of relationships between the individual terminal electron acceptor (TEA) fluxes across the sediment-water interface and their respective contributions to the Corg decomposition process. On a global average, simulation results indicate that sulfate reduction is the dominant metabolic pathway and accounts for approximately 76% of the total Cox, which is higher than reported so far by other authors. The results also demonstrate the importance of bioirrigation for the assessment of global species fluxes. Especially at shallow SFD most of the TEAs enter the sediments via bioirrigation, which complicates the use of concentration profiles for the determination of total TEA fluxes by molecular diffusion. Furthermore, bioirrigation accounts for major losses of reduced species from the sediment to the water column prohibiting their reoxidation inside the sediment. As a result, the total carbon mineralization rate exceeds the total flux of oxygen into the sediment by a factor of 2 globally.

83 citations


Journal ArticleDOI
Abstract: Editorial handling by M. Kersten a b s t r a c t The early diagenesis of the major carrier phases (Fe and Mn minerals), trace elements (As, Co, Cr, Hg, MeHg, Ni) and nutrients (RNO 3 , NH þ 4 , RPO 4) and their exchange at the sediment water/interface were studied in the Berre Lagoon, a Mediterranean lagoon in France, at one site under two contrasting oxygen-ation conditions (strictly anoxic and slightly oxic) and at an adjacent site with perennially well-oxygen-ated water. From the concentration profiles of the primary biogeochemical constituents and trace elements of the pore and bottom waters, as well as the total and reactive particulate phases, it was pos-sible to locate and identify the diagenetic reactions controlling the mobility of trace elements in the sed-iments and quantify their rates by coupling one-dimensional steady-state transport-reaction modelling and thermodynamic speciation calculations. Under oxic conditions and in the absence of benthic organisms, the main redox reactions were well identified vertically in the surface sediments and followed the theoretical sequence of oxidant consump-tion: O 2 > RNO 3 =MnO 2 > FeðOHÞ 3 > SO 2A 4 . However, under anoxic conditions, only MnO 2 , Fe(OH) 3 and SO 2A 4 reduction were present, and they all occurred at the interface. The main biogeochemical controls on the mobility of As, Cr, Hg, MeHg and Ni in the surface sediments were identified as the adsorption/ desorption on and/or coprecipitation/codissolution with Fe oxy-hydroxides. In contrast, Co mobility was primarily controlled by its reactivity towards Mn oxy-hydroxides. In sulphidic sediments, As, Hg and MeHg were sequestered along with Fe sulphides, whereas Co and Ni precipitated directly as metallic sulphides and Cr mobility was enhanced by complexation with dissolved organic ligands. The fluxes of trace elements at the sediment–water interface are essentially dependent on the localisation of their remobilisation and immobilisation reactions under the interface, which in turn is governed by the ben-thic water oxygenation conditions and kinetic competition among those reaction and diffusion processes. Under oxic conditions, the precipitation of Fe or Mn oxy-hydroxides in the surface sediments constitutes the most efficient mechanism to sequester most of the trace elements studied, thus preventing their dif-fusion to the water column. Under anoxic conditions the export of trace elements to the water column is dependent on the kinetic competition during the reductive dissolution of Fe and/or Mn oxy-hydroxides, diffusion and immobilisation with sulphides. It is also shown that benthic organisms in the perennially oxygenated site have a clear impact on this general pattern. Based on the extensive dataset and geochem-ical modelling, it is predicted that the planned re-oxygenation of the entire lagoon basin, if complete, will most likely limit or reduce the export of the trace elements from the sediments to the water column and therefore, limit the impact of the contaminated sediment.

69 citations


Cites background from "Geochemistry of trace metals in a f..."

  • ...Among the trace elements studied, only Co demonstrates a clear link with the Mn cycle, as previously reported in other aquatic environments (Canavan et al., 2007, Stockdale et al., 2010)....

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Book ChapterDOI
01 Jan 2009
Abstract: Tidal freshwater wetlands link terrestrial and estuarine habitats. They occur in coastal systems around the world, primarily rivers, where the amount of freshwater flow from upstream watersheds is of sufficient volume to create a dynamic tidal zone in which there are tides but the water is almost completely fresh. Tidal freshwater wetlands are characterized by high biodiversity, high productivity, and high rates of decomposition. The animal community is characterized by species that occur in freshwater and estuarine and marine species that spend important life history stage in freshwater environments. Given their location near urban areas in coastal rivers, many tidal freshwater wetlands have been destroyed and the wetlands that remain are threatened by sea level rise, salt water intrusion, and invasive species. Effective conservation, restoration, and management of tidal freshwater wetlands will require vigilance and commitment by governmental and nongovernmental organizations.

64 citations


References
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Abstract: This introduction to modern soil chemistry describes chemical processes in soils in terms of established principles of inorganic, organic, and physical chemistry. The text provides an understanding of the structure of the solid mineral and organic materials from which soils are formed, and explains such important processes as cation exchange, chemisorption and physical absorption of organic and inorganic ions and molecules, soil acidification and weathering, oxidation-reduction reactions, and development of soil alkalinity and swelling properties. Environmental rather than agricultural topics are emphasized, with individual chapters on such pollutants as heavy metals, trace elements, and inorganic chemicals.

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"Geochemistry of trace metals in a f..." refers methods in this paper

  • ...Sulfide was measured colorimeterically (Cline, 1969) using filtered pore water fixed with NaOH (10 μl 1 M NaOH per ml)....

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  • ...The released H2S was trapped in a 1 M NaOH solution from which sulfide concentrations were determined colorimetrically (Cline, 1969)....

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01 Mar 1991
TL;DR: The report describes how to use the MINTEQA2 model, a geochemical speciation model capable of computing equilibria among the dissolved, adsorbed, solid, and gas phases in an environmental setting, which includes an extensive database of reliable thermodynamic data.
Abstract: The attention of environmental decision makers is increasingly being focused on the movement of pollutants into ground water. Of particular importance is the transport and speciation of metals. The MINTEQA2 model is a versatile, quantitative tool for predicting the equilibrium behavior of metals in a variety of chemical environments. MINTEQA2 is a geochemical speciation model capable of computing equilibria among the dissolved, adsorbed, solid, and gas phases in an environmental setting. MINTEQA2 includes an extensive database of reliable thermodynamic data that is also accessible to PRODEFA2, an interactive program designed to be executed prior to MINTEQA2 for the purpose of creating the required MINTEQA2 input file. The report describes how to use the MINTEQA2 model. The chemical and mathematical structure of MINTEQA2 and the structure of the database files also are described. The use of both PRODEFA2 and MINTEQA2 are illustrated through the presentation of an example PRODEFA2 dialogue reproduced from interactive sessions and the presentation of MINTEQA2 output files and error diagnostics. The content and format of database files also are explained.

1,819 citations


"Geochemistry of trace metals in a f..." refers methods in this paper

  • ...Thermodynamic speciation calculations were conducted using Visual MINTEQ (Version 2.4, this program is an adaptation of MINTEQA2; Allison et al., 1991)....

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Journal ArticleDOI
Abstract: The toxicity of chemicals in sediments is influenced by the extent that chemicals bind to the sediment. It is shown that acid volatile sulfide (AVS) is the sediment phase that determines the LC50 for cadmium in the marine sediments tested. Although it is well known that metals can form insoluble sulfides, it apparently has not been recognized that AVS is a reactive pool of solid phase sulfide that is available to bind with metals. Amphipod sediment toxicity tests were conducted in the laboratory and the observed amphipod LC50s on a normalized cadmium concentration basis, [Cd]/[AVS], is the same for sediments with over an order of magnitude difference in dry weight normalized cadmium LC50s. Because other toxic metals also form insoluble sulfides, it is likely that AVS is important in determining their toxicity in sediments as well. Most freshwater and marine sediments contain sufficient acid volatile sulfide for this phase to be the predominant determinant of toxicity. The other sorption phases are expected to be important only for low AVS sediments, for example, fully oxidized sediments. From the point of view of sediment quality criteria the other sorption phases would be important for metals with large partition coefficients and large chronic water quality criteria.

777 citations


"Geochemistry of trace metals in a f..." refers background in this paper

  • ...Additionally, FeS may also bind Ni and Co (Huerta-Diaz et al., 1998; Morse and Arakaki, 1993), while Zn, Pb, and Cd may substitute for Fe resulting in trace metal monosulfides (Di Toro et al., 1990)....

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Journal ArticleDOI
Abstract: Interactions of trace metals with sulfide in anoxic environments are important in determining their chemical form and potential toxicity to organisms. In recent years, a considerable body of observational data has accumulated that indicates very different behavior for various trace metals in sulfidic sediments. These differences in behavior cannot be entirely attributed to thermodynamic relationships, but also reflect differences in ligand exchange reaction kinetics, and redox reaction pathways. Pb, Zn, and Cd, which are generally pyritized to only a few percent of the “reactive” fraction, have faster water exchange reaction kinetics than Fe 2+ , resulting in MeS phases precipitating prior to FeS formation and subsequent pyrite formation, whereas, Co and Ni, which have slower H 2 O exchange kinetics than Fe 2+ , are incorporated into pyrite. Although Hg and Cu have faster reaction kinetics than Fe 2+ , both are incorporated into pyrite or leached from the pyrite fraction with nitric acid. Hg undergoes significant chloride complexation, which can retard reaction with sulfide, but can also replace Fe in FeS to form HgS, which can only be dissolved in the pyrite fraction. Cu 2+ is reduced by sulfide and forms a variety of sulfides with and without Fe that can only be dissolved with nitric acid. Mn 2+ does not form a MnS phase easily and is incorporated into pyrite at high iron degrees of pyritization (DOP). Oxyanions of Mo and As are first reduced by sulfide. These reduced forms may then react with sulfides resulting in incorporation into pyrite. However, the oxyanion of Cr is reduced to Cr 3+ , which is kinetically inert to reaction with sulfide and, therefore, not incorporated into pyrite.

652 citations


"Geochemistry of trace metals in a f..." refers background in this paper

  • ...The low DTMP values found for Mn (Table 2) are characteristic for sediments with DOP values less than 35% (Morse and Luther, 1999)....

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Frequently Asked Questions (1)
Q1. What have the authors contributed in "Geochemistry of trace metals in a fresh water sediment: field results and diagenetic modeling" ?

Canavan et al. this paper measured trace metal concentrations in pore water and sediment of a coastal fresh water lake ( Haringvliet Lake, The Netherlands ).