2 Introduction
Pollutants discharged into aquatic systems are mostly adsorbed on suspended
particles and t-really accumulate in sediments. As many aquatic organisms spend a
major portion of their life in or on sediments, polluted sediments provide a pathway
for the chemicals to food chain organisms, and f'mally to humans.
Numerous studies have shown that sediment-water interactions in natural aquatic
systems play an important role in controlling transport processes of pollutants (Eck
and Smits 1986; Gobeil et al. 1987; Morfert et al. 1988; Jahnke et al. 1989; Gerringa
1990; Ivert 1990; Carignan and Lean 1991; Dahmke et ai. 1991; Barbanti et al.
1992a; Williams 1992).
The aun of this work is to understand the relationships between mineralization of
organic matter and the mobility of heavy metals and nutrients in the heavily polluted
sediments. The study includes two parts: the first focuses on describing the diagenetic
processes, involving decomposition of organic matter and recycling of nutrients
(NO3", NH4 +, PO43-, and alkalinity); the second emphasizes the associated chemical
behavior of heavy metals in the contaminated sediments, and their mobility during the
early diagenetic processes.
The results should enable us to know whether heavy metals and nutrients are
released into the overlying water under changes of physicochemical conditions. This
is important to water management and sediment cleanup plans.
2.1 Early diagenesis
In natural water, sediment-water interaction plays a fundamental role in
biogeochemical cycling of elements. One of the important reactions is the
mineralization of organic matter during early diagenesis, which is mainly biologically
catalyzed. This process leads to a change in concentration, temporal and spatial
distribution, and speciation of elements in water, suspended particles, and sediments.
Therefore, the knowledge about this process is important to evaluate the chemical
behavior of heavy metals in sediments.
Organic matter in sediments mainly derives from phytoplankton, zooplankton, and
other organic materials. The commonly accepted model for decomposition of organic
matter is illustrated in Fig. 2.1. Organic matter is oxidized by the oxidant yielding the
greatest free energy change per mole of organic carbon oxidized. When this oxidant
is depleted, oxidation will proceed utilizing the next most efficient oxidant (Froelich
et al. 1979; Berner 1980):
1. (CH20)I06(NH3)16(H3PO4) + 138 02
--~ 106 CO2 + 16 HNO3 + H3PO4 + 122 H20
AG ~ = -3190 k J/mole
Pollutants discharged into aquatic systems are mostly adsorbed on suspended
particles and t-really accumulate in sediments. As many aquatic organisms spend a
major portion of their life in or on sediments, polluted sediments provide a pathway
for the chemicals to food chain organisms, and f'mally to humans.
Numerous studies have shown that sediment-water interactions in natural aquatic
systems play an important role in controlling transport processes of pollutants (Eck
and Smits 1986; Gobeil et al. 1987; Morfert et al. 1988; Jahnke et al. 1989; Gerringa
1990; Ivert 1990; Carignan and Lean 1991; Dahmke et ai. 1991; Barbanti et al.
1992a; Williams 1992).
The aun of this work is to understand the relationships between mineralization of
organic matter and the mobility of heavy metals and nutrients in the heavily polluted
sediments. The study includes two parts: the first focuses on describing the diagenetic
processes, involving decomposition of organic matter and recycling of nutrients
(NO3", NH4 +, PO43-, and alkalinity); the second emphasizes the associated chemical
behavior of heavy metals in the contaminated sediments, and their mobility during the
early diagenetic processes.
The results should enable us to know whether heavy metals and nutrients are
released into the overlying water under changes of physicochemical conditions. This
is important to water management and sediment cleanup plans.
2.1 Early diagenesis
In natural water, sediment-water interaction plays a fundamental role in
biogeochemical cycling of elements. One of the important reactions is the
mineralization of organic matter during early diagenesis, which is mainly biologically
catalyzed. This process leads to a change in concentration, temporal and spatial
distribution, and speciation of elements in water, suspended particles, and sediments.
Therefore, the knowledge about this process is important to evaluate the chemical
behavior of heavy metals in sediments.
Organic matter in sediments mainly derives from phytoplankton, zooplankton, and
other organic materials. The commonly accepted model for decomposition of organic
matter is illustrated in Fig. 2.1. Organic matter is oxidized by the oxidant yielding the
greatest free energy change per mole of organic carbon oxidized. When this oxidant
is depleted, oxidation will proceed utilizing the next most efficient oxidant (Froelich
et al. 1979; Berner 1980):
1. (CH20)I06(NH3)16(H3PO4) + 138 02
--~ 106 CO2 + 16 HNO3 + H3PO4 + 122 H20
AG ~ = -3190 k J/mole