Evolution of the pore structure of Technosols during early pedogenesis quantified by image analysis

Despite Technosols being widely present in environments, their pedogenesis has been studied to a much lesser extent than "natural" soils. As the initial characteristics of constructed Technosols are controlled and well-known, they represent unique experimental models for studying the early stages of soil formation. Focusing on those processes involved in soil structuration, our study proposes an image analysis protocol for the quantification of porosity and the study of pore system architecture evolution. The implications that the architecture of soil pore system evolution could have on the capacity of these constructed soils as well as "natural" soils to carry out their basic functions are also discussed. Soils with porosities of >50 mu m and 0.5-50 mu m were directly quantified by analyzing thin section images prepared from undisturbed soil samples, collected in situ in Kubiena boxes in 2008 and 2010. Pores were classified according to their diameter (five classes: diameter > 2000 mu m, 500-2000 mu m; 50-500 mu m; 25-50 mu m; and 0.5-25 mu m). The >50 mu m porosity decreased significantly between 2008 (20.60% +/- 6.10) and 2010 (14.36% +/- 5.35). Only the number and surface of large pores (packing pores) with equivalent diameters exceeding 2000 mu m decreased. The surface of 0.5-50 mu m porosity increased between 2008 (10.56 +/- 2.64) and 2010 (13.63 +/- 2.55). This means that the soil is compacting. The consequence of this is a reduction of water holding capacity, which has a bearing on the filtering/buffering function of soil. After statistical analysis, the number of pores (N), surface area (A), index of connectivity (Ic) and shape factor (Sf) are proposed as indicators to be monitored in the study of Technosol porosity evolution.