ALBERT

Description: Mercury intrusion porosimetry (MIP) is commonly used to determine soil pore size distributions (PSDs) in a wide, but incomplete, range of equivalent pore diameters. Mono- and multifractal analyses of soil PSDs are useful for analyzing the soil porous system. The main objective of this work was to characterize PSDs from tropical soils using the multifractal approach. Duplicate PSDs were measured by MIP for 54 horizons collected from 19 soil profiles in Minas Gerais, Brazil. Although 10 of the studied soils were Ferralsols (Oxisols or Latosols), other soil groups such as Nitisols, Acrisols, Alisols, Luvisols, Planosols, Cambisols, Andisols, and Leptosols also were sampled. Different patterns of PSDs were observed, depending on soil type, texture, and weathering intensity. Textural porosity (0.005–0.2 μm) was positively and significantly correlated to clay and Al 2 O 3 contents and soil specific surface area. Comparison of multifractal analysis from Hg intrusion curves and N 2 adsorption isotherms (NAIs) showed entropy dimension values and width of the singularity spectra smaller for the former than for the latter. Multifractal analysis of MIPs and NAIs allowed a thorough characterization of the complexity and heterogeneity of the soil pore space at different scales and was useful to provide new insights for portraying the soil pore system.

Description: The spatial variability of soil properties can be best characterized through concepts of scale invariance, fractals, and multifractals. The objectives of this study were to analyze and to compare the scaling patterns and structural heterogeneity of soil properties across two transects in Campinas, SP, Brazil, using the multifractal formalism. Two transects were marked parallel and perpendicular to land slope, with a length of 2.28 and 1.98 km, respectively. Soil samples were collected at the 0 to 20 cm depth every 30 m. The soil properties analyzed were: texture (sand, silt, clay), pH (H 2 O and KCl), organic carbon (OC) content, exchangeable Ca, H, and Al, exchangeable bases (SB), cation exchange capacity (CEC), and percent base saturation (V). Spatial variability of soil properties was controlled by natural causes, including parent material and topography, and by soil use and management. The variability of pH across the two transects was characterized by either quasi-monofractal behavior or by a relatively low degree of multifractality. The other soil properties studied showed stronger degrees of multifractality. Hence, the multifractality for OC and silt content was much higher at the transect perpendicular to land slope. Variables from the soil exchange complex, particularly exchangeable Al, Ca, and SB, were characterized by higher multifractal indices in the two transects. Patterns of spatial distribution assessed by multifractal analysis were linked to soil forming factors and processes. Our results suggest that scale heterogeneity in the spatial distribution of soil properties was enhanced by the interaction of various natural or anthropogenic sources of variability.

Description: Weathering of stone materials in urban settings causes significant damage to heritage buildings due to the effects of air pollution and other factors related to the building environment (water transfer, interaction with binders, etc.). The assessment of weathering of rock surfaces requires the use of high resolution techniques, and this task is even more difficult if relatively short periods of time are considered. We explored the joint use of elemental chemical analysis, mercury intrusion porosimetry, and multifractal analysis of pore size distributions (PSDs) to assess the surface weathering of a granite rock widely used in the built heritage in NW Spain. The scaling properties of all PSDs obtained by mercury injection porosimetry could be fitted reasonably well with multifractal models. Generalized dimension spectrum, D q , lead to a better definition of multifractal scaling than singularity spectrum, f (α) versus α. Statistical analysis shows a weak association of weathering with building age considering some chemical elements and several multifractal parameters. Building age has a tendency to decrease Al 2 O 3 , P 2 O 3 , D –10 , ( D –10 – D 10 ), and α 0 , while it suggest building age has a tendency to increase MnO, Cl, SO 3 , D 1 , D 2 , and D 10 . Our results show that multifractal analysis of PSDs may be an appropriate tool for rock pore size distribution and also a suitable indicator for assessing weathering.

Description: Nitrogen adsorption isotherms (NAI) and Nitrogen desorption isotherms (NDI) are commonly used to evaluate specific surface area (SSA) of soils and other materials. Scaling analysis of N 2 isotherms yield complementary information about the complexity of the soil surface. We evaluated the specific surface area (SSA) and examined the scaling properties of NAIs and associated NDIs from clayey soils, rich in organic matter sampled in Santa Catarina State, Brazil. Sixty six soil horizons were sampled in 13 profiles. Ten of these profiles were developed over volcanic rocks with a wide range of mineralogical composition. Clay content and cation exchange capacity (CEC) showed a weak positive correlation to SSA, which was attributed to variable clay mineralogy. Organic carbon content showed a weak negative correlation to SSA. Both NAIs and NDIs exhibited multifractal behavior, but its scaling properties were different so that adsorption isotherms showed higher scaling heterogeneity and were less evenly distributed measures than desorption isotherm. Also, parameterization by the Hurst exponent indicates NAIs were less persistent than NDIs. Differences in multifractality between NAIs and NDIs were attributed to contrasting physical processes during adsorption and desorption. Both, SSA and various multifractal parameters estimated from NAIs and NDIs differentiated between soils developed over either acid or basic parent material. Linear regression and principal component analysis (PCA) showed increasing carbon content decreased scaling heterogeneity and increased persistence of both, NAIs and NDIs. On the other hand, increasing clay content showed a trend to increase scaling heterogeneity and to decrease persistence during the adsorption and desorption phases.