41
The content of exchangeable and mobile (conventionally biologically available)
uranium in soils was established by selective extraction using solutions of 1M
ammonium acetate (NH 4 Ac, pH 7) and 1M HCl or acetate-ammonium buffer solution (рН 4.8). Soil samples were treated with an extracting solution at a ratio of
“soil/solution” of 1:10 for 24 h, followed by the determination of uranium in the
extracts obtained by radiochemical analysis. The acetate-ammonium soil extract
simulates a soil solution with a neutral medium reaction, and the 1M HCl or acetateammonium buffer extract simulates an acidic soil solution at the boundary with the
root system of plants (Frid 1996; Fedorov 2002). The sorption capacity of the soil
with respect to uranium was estimated from the value of the coefficient K d , which is
the ratio between the activity concentrations of the solid phase and the interstitial
solution of the soil in the state of interphase equilibrium in the system or close to it
(Ovsiannikova et al. 2000).
4 Vertical Distribution of Uranium in Soils
The objects of investigation were the mineral and organic soils sampled in August
2008–2010. The location of the sites, their geomorphological position, and the type
of soil cover are given in Table 2.
The sampling sites differed in geomorphological position in the relief, humidification conditions, and soil cover type. The plots SP S 1 and SP S 2 are located within
the floodplain of the river Pripyat. Plot SP S 1 is far from the main riverbed, and SP S 2
is near old riverbed that has lost connection with the basic riverbed. Plot P1 is within
the bogged meadow in depression of above the floodplain terrace. During the spring
and autumn floods, the areas are flooded. In this case, the SP S 2 site for a longer
period is in excess of waterlogging conditions compared to the SP S 1 site.
The soil cover of SP S 1 and SP S 2 sites is formed on ancient alluvial and fluvioglacial sandy alluvium in conditions of temporary excessive moistening and dynamic
water regime. The soil-forming rocks are characterized by high water permeability.
During the spring and autumn floods, the water penetrates to a considerable depth.
In periods between floods, groundwater in the SP S 2 site is at a shallow depth from
the soil surface
In P1 and P2 plots under conditions of constant excess moisture, the marsh process of soil formation develops, which proceeds under anaerobic conditions. Under
such conditions, with a general decrease in the activity of oxidation-reduction processes, the reduction processes prevail over the oxidative processes, and it leads to
a weakening of the processes of mineralization of the organic matter of the soils. As
a result, partly decomposed organic residues accumulate on the soil surface in the
form of peat of different thickness. Under conditions of excessive moisture in the
soils, gleying of the mineral rock takes place. Its characteristic feature is the conversion of ferric iron (III) to ferrous iron (II). The iron (II) compounds give the soil a
bluish tinge. They are better soluble and more mobile than iron (III) compounds.
Under conditions of temporary excessive moistening, the iron compounds in the
soils can be either in the ferric or in the ferrous form. In dry periods of the year, the
Uranium and Its Distribution in Typical Belarusian Soils
The content of exchangeable and mobile (conventionally biologically available)
uranium in soils was established by selective extraction using solutions of 1M
ammonium acetate (NH 4 Ac, pH 7) and 1M HCl or acetate-ammonium buffer solution (рН 4.8). Soil samples were treated with an extracting solution at a ratio of
“soil/solution” of 1:10 for 24 h, followed by the determination of uranium in the
extracts obtained by radiochemical analysis. The acetate-ammonium soil extract
simulates a soil solution with a neutral medium reaction, and the 1M HCl or acetateammonium buffer extract simulates an acidic soil solution at the boundary with the
root system of plants (Frid 1996; Fedorov 2002). The sorption capacity of the soil
with respect to uranium was estimated from the value of the coefficient K d , which is
the ratio between the activity concentrations of the solid phase and the interstitial
solution of the soil in the state of interphase equilibrium in the system or close to it
(Ovsiannikova et al. 2000).
4 Vertical Distribution of Uranium in Soils
The objects of investigation were the mineral and organic soils sampled in August
2008–2010. The location of the sites, their geomorphological position, and the type
of soil cover are given in Table 2.
The sampling sites differed in geomorphological position in the relief, humidification conditions, and soil cover type. The plots SP S 1 and SP S 2 are located within
the floodplain of the river Pripyat. Plot SP S 1 is far from the main riverbed, and SP S 2
is near old riverbed that has lost connection with the basic riverbed. Plot P1 is within
the bogged meadow in depression of above the floodplain terrace. During the spring
and autumn floods, the areas are flooded. In this case, the SP S 2 site for a longer
period is in excess of waterlogging conditions compared to the SP S 1 site.
The soil cover of SP S 1 and SP S 2 sites is formed on ancient alluvial and fluvioglacial sandy alluvium in conditions of temporary excessive moistening and dynamic
water regime. The soil-forming rocks are characterized by high water permeability.
During the spring and autumn floods, the water penetrates to a considerable depth.
In periods between floods, groundwater in the SP S 2 site is at a shallow depth from
the soil surface
In P1 and P2 plots under conditions of constant excess moisture, the marsh process of soil formation develops, which proceeds under anaerobic conditions. Under
such conditions, with a general decrease in the activity of oxidation-reduction processes, the reduction processes prevail over the oxidative processes, and it leads to
a weakening of the processes of mineralization of the organic matter of the soils. As
a result, partly decomposed organic residues accumulate on the soil surface in the
form of peat of different thickness. Under conditions of excessive moisture in the
soils, gleying of the mineral rock takes place. Its characteristic feature is the conversion of ferric iron (III) to ferrous iron (II). The iron (II) compounds give the soil a
bluish tinge. They are better soluble and more mobile than iron (III) compounds.
Under conditions of temporary excessive moistening, the iron compounds in the
soils can be either in the ferric or in the ferrous form. In dry periods of the year, the
Uranium and Its Distribution in Typical Belarusian Soils