Seasonal temperature changes can bring about appreciable variation of biological
activities in shallow water sediments, and consequently have an influence on the
diagenetic processes, which is mainly biologically catalyzed (BiUen 1982; Holdren
and Armstrong 1986). Jgrgensen and Serensen (1985) reported that the temperature
coefficient (Q I 0, the factor of reaction r~te increase per 10~ temperature increase) is
2.7 for O 2 oxidation and 2.1 for SO4 " reduction in the sediments of Norsminde
Fjord, Denmark. In a laboratory experiment, Sagemann et al. (1994) found a
significant correlation between denitrification rate and temperature within the
sediment from Weser Estuary, Germany.
2.2 Behaviour of heavy metals and nutrients during early diagenesis
In natural waters, heavy metals and nutrients are mainly adsorbed and/or bound to
particles such as Fe/Mn oxides, clay minerals and organic materials. The
mineralization of organic matter leads to a change of the Eh-pH conditions and the
chemical composition of the sediments. This results in a series of new chemical
equilibria between sediments and water. Adsorption/desorption on Fe/Mn oxides,
precipitation/dissolution of minerals, and complexation with organic and inorganic
colloids are the predominant processes. These reactions mainly control the cycling of
elements in aquatic systems.
Previous studies have shown that Fe/Mn oxides provide important adsorbing
surfaces and constitute significant sinks for heavy metals and nutrients in surface
water (Tessier et al. 1985; Sigg 1986; Sigg et al. 1987). In the anoxic sediment layer,
heavy metals and phosphates bound to the oxides can be released ir~to porewat~r,
following the reduction of Fe/Mn oxides. On the other hand, Fe 2+ and Mn 2§
diffusing into the oxic sediment layer will be oxidized to Fe/Mn oxides and
immobilized. The freshly formed Fe/Mn oxides are very efficient scavengers for
heavy metals and phosphate in this layer. Therefore, the cycling of Fe and Mn may
play an important role in transport processes of heavy metals and phosphorus
(Davison et al. 1982; Pedersen and Price I982; Hamilton-Taylor et al. 1984; Gendron
et al 1986; Salomons et al. 1987; Francis and Dodge 1990; McCorkle and
Klinkhammer 1990; Dahmke et al. 1991; Balistrieri et al. 1992; Johnson et al. 1992;
Morse and Arakaki 1993; Williams 1992; Matsunaga et al. 1993).
Another important reaction is the formation of minerals during the early diagenetic
processes. Precipitation/dissolution of calcile, dolomite, siderite, ~hodochrosite may
2-~
2+
2+
2+
influence porewater concentrations of Ca , Mg , Fe , Mn , and alkahnity
(Emerson 1976; Matisoff et al. 1981; Postma 1981; Kuivila and Murray 1984;
Dahrnke et al. 1986, Norton 1989; Wallmann 1990; Vuynovich 1989; Dahmke et al
1991). Numerous studies have attested that the formation of phosphorus minerals
(e.g. vivianite, reddingite) may control phosphate concentrations in anoxic porewater
(Nriagu and Dell 1974; Emerson 1976; Suess 1979; Elderfield et al. 1981; Postma
1981). In the last few years, the role of sediment sulfides in controlling the
distribution of heavy metals between sediments and porewater has been
demonstrated. HS" is produced due to SO42" reduction in anoxic sediments. It can
activities in shallow water sediments, and consequently have an influence on the
diagenetic processes, which is mainly biologically catalyzed (BiUen 1982; Holdren
and Armstrong 1986). Jgrgensen and Serensen (1985) reported that the temperature
coefficient (Q I 0, the factor of reaction r~te increase per 10~ temperature increase) is
2.7 for O 2 oxidation and 2.1 for SO4 " reduction in the sediments of Norsminde
Fjord, Denmark. In a laboratory experiment, Sagemann et al. (1994) found a
significant correlation between denitrification rate and temperature within the
sediment from Weser Estuary, Germany.
2.2 Behaviour of heavy metals and nutrients during early diagenesis
In natural waters, heavy metals and nutrients are mainly adsorbed and/or bound to
particles such as Fe/Mn oxides, clay minerals and organic materials. The
mineralization of organic matter leads to a change of the Eh-pH conditions and the
chemical composition of the sediments. This results in a series of new chemical
equilibria between sediments and water. Adsorption/desorption on Fe/Mn oxides,
precipitation/dissolution of minerals, and complexation with organic and inorganic
colloids are the predominant processes. These reactions mainly control the cycling of
elements in aquatic systems.
Previous studies have shown that Fe/Mn oxides provide important adsorbing
surfaces and constitute significant sinks for heavy metals and nutrients in surface
water (Tessier et al. 1985; Sigg 1986; Sigg et al. 1987). In the anoxic sediment layer,
heavy metals and phosphates bound to the oxides can be released ir~to porewat~r,
following the reduction of Fe/Mn oxides. On the other hand, Fe 2+ and Mn 2§
diffusing into the oxic sediment layer will be oxidized to Fe/Mn oxides and
immobilized. The freshly formed Fe/Mn oxides are very efficient scavengers for
heavy metals and phosphate in this layer. Therefore, the cycling of Fe and Mn may
play an important role in transport processes of heavy metals and phosphorus
(Davison et al. 1982; Pedersen and Price I982; Hamilton-Taylor et al. 1984; Gendron
et al 1986; Salomons et al. 1987; Francis and Dodge 1990; McCorkle and
Klinkhammer 1990; Dahmke et al. 1991; Balistrieri et al. 1992; Johnson et al. 1992;
Morse and Arakaki 1993; Williams 1992; Matsunaga et al. 1993).
Another important reaction is the formation of minerals during the early diagenetic
processes. Precipitation/dissolution of calcile, dolomite, siderite, ~hodochrosite may
2-~
2+
2+
2+
influence porewater concentrations of Ca , Mg , Fe , Mn , and alkahnity
(Emerson 1976; Matisoff et al. 1981; Postma 1981; Kuivila and Murray 1984;
Dahrnke et al. 1986, Norton 1989; Wallmann 1990; Vuynovich 1989; Dahmke et al
1991). Numerous studies have attested that the formation of phosphorus minerals
(e.g. vivianite, reddingite) may control phosphate concentrations in anoxic porewater
(Nriagu and Dell 1974; Emerson 1976; Suess 1979; Elderfield et al. 1981; Postma
1981). In the last few years, the role of sediment sulfides in controlling the
distribution of heavy metals between sediments and porewater has been
demonstrated. HS" is produced due to SO42" reduction in anoxic sediments. It can