Аннотация:River deltas occupy a special interface position in the environment and are characterized by contrasting hydrological
and landscape-geochemical regimes. Small depth of water and weak currents contribute to suspended matter
deposition. Significant spread of aquatic plants provides the enrichment of subaquatic soils in organic matter. All
these factors contribute to the formation of different subaquatic soils. Possibility of including them in the classification
systems is discussed by many authors (Demas and Rabenhorst, 2001; Stolt et al., 2011); there is also a special
subaquatic qualifier for submerged soils in WRB; however, they are still absent in many national classification
systems, as well as in the recent Russian one (2008). The purpose of this research is to reveal the properties of the
subaquatic soils in the Volga, Don and Kuban Rivers deltaic areas and to propose pedogenetic approaches to categorize
AQUAZEMS. Investigations of deltaic areas were performed in 2010-2012 in deltaic lagoons, fresh-water
bays, small channels, oxbow lakes, and also in the part of deltaic near-shore zone. Morphological descriptions of
distinguishable layers (colour, texture, thickness, boundaries, consistence, plant residues and shell debris) were
made in columns obtained by augering as it is done by other researchers (Stolt et al., 2011), and supplemented
with analytical data (pH, Eh, TDS, particle-size composition, and Corg). It is suggested to name the horizons in
aquazems in the same way as in terrestrial soils in the recent Russian soil classification system, and apply symbols
starting with the combination of caps – AQ. Most typical for aquazems is their aquagley AQG horizon that has features
similar to terrestrial gleys – homogeneity in color and consistence, permeation by clay, predominance of dove
grey colour. The AQG horizon gradually merges into parent material – stratified bottom sediments. The “topsoil”
is usually enriched in organic matter and may be different in accordance with plant communities. The highest Corg
content (4-6%) was recorded under lotus (Nelumbo sp.) and reed (Phragmites australis); reed is hard to decompose
and its residues preserve recognizable plant tissues. Hence, two variants of upper horizons may be identified:
aquahumus horizon – AQA and aquapeat horizon – AQT. Floating plants do not create any stable horizon under
active hydrodynamic processes, whereas if they are weak, a discontinuous greyish-bluish horizon, 2-3 cm thick, is
formed with org content not exceeding 1-2%. In active channels, mixing of the upper part of aquazem profiles by
currents results in the formation of a thin yellowish-grey oxidized layer (AQOX) with a very low content of Corg:
less than 1%. Following the rules of the new system of soil classification of Russia (2004, 2008) aquazems may
be tentatively classified in the following way. All aquazems may be referred to the trunk of synlithogenic soils as
a special aquazem order; aquazem types may be specified by the combinations of horizons, hence, typical (AQAAQG-AQC-C),
organogenic (AQT-AQG-AQC-C), and oxidized (AQA-AQOX-AQG-AQC-C). The extension of
studies is sure to find new types.