Evolution of a spatially heterogeneous paleocryogenic soilscape and its impact upon formation of coupled moisture and thermal regimes.
Evgeny Shein, Moscow State University, Leninskie Gory, Moscow, 119992, Russia
Evolution of a spatially heterogeneous paleocryogenic soilscape and its impact upon formation of coupled moisture and thermal regimes Shein E.V., T.A. Arhangel'skaya, M.A. Butylkina, V.G. Tymbaev Moscow State University, Faculty of Soil Science, Moscow 119992. Russia. Many of the landscapes of Russian Plain have passed through the periglacial stage of evolution. During this stage the wide cryogenic fissures were formed which subsequently were broken down, eroded and filled with plant organic matter. The specific water and thermal regimes were developed in zones of these cryogenic fissures. These processes resulted in formation of a very complex soil cover in which regular alternations of soils with the second humus horizon to podzolic and to carbonated grey forest soils are observed. In this case the 1st task of hydropedology is to investigate pedogenic evolution of soilscape which determines the spatial regularity of the soil cover. 2nd – basing on the features of pedogenic evolution to define the pedotransfer functions and 3rd - to specify spatial distribution of water and thermal regimes of this complex soil cover. These tasks were accomplished for the case study of agricultural field situated in Vladimir opol'e region about 200 km east from Moscow. The special features of paleocryogenic soilscape evolution form the complex soil cover in which the limits of lateral variation of soil density in arable layer are from 0.73 to 1.54 g/cm3 and for the depth 35-40 cm – 1.0-1.68 g/cm3, and limits for organic carbon content are from 1.36 to 2.98 and 0.23-4.65 g/100g, respectively. This high variability is related to the low density and the high organic carbon content of zones where soils with 2nd humus horizon are located. The transport and retention physical properties such as hydraulic conductivity, water retention, thermal conductivity for 2nd humus horizon are also quite different from those of other soils in this paleocryogenic soilscape. These distinctive properties of the 2nd humus horizon result in formation of the special hydrothermal regime in zones of 2nd humus horizon distribution. Water and thermal regime observations were carried out for 5 years for different time and spatial scales. The series of temperature measurements proved that owing to low thermal diffusivity the soils with 2nd humus horizons are slowly warmed up in spring and summer and become cool later in winter. The water regimes of soilscape components also differ: during wet periods with high quantity of precipitation the zones of soils with 2nd humus horizon accumulate and conserve the soil water, but during the periods of drought these zones become dryer than the surroundings. These data illustrate spatial variability of hydrothermal field on this territory and provide understanding of the role of zones with 2nd humus horizon in the variability of water and thermal regimes. For the quantitative estimation of the regimes the pedotransfer functions were defined in the form of dependencies of water retention curve, hydraulic conductivity, thermal diffusivity upon soil density and soil organic carbon content. The specific evolution of paleocryogenic soilscape formed on the base of a spatially homogeneous parent material made possible not to include the clay content and mineralogical characteristics into these pedotransfer equations as the arguments. This way of pedotransfer construction was supported by statistical computations in which the set of arguments was varied. The model assessments of space distributions of water and thermal regimes were quite fit with experimental observations. Thus, for the precise quantitative description of soil water and thermal regimes of a complex soilscape it is necessary: (1) to investigate the peculiarities of pedogenic evolution of the landscape, (2) to select the basic physical properties to be the arguments of pedotransfer functions and to define the pedotransfer functions in accordance with these pedogenic evolution peculiarities and (3) to specify the zones with different water and thermal regimes by means of forecasting models for wide range of upper boundary conditions.