Characterizing scale-specific environmental factors affecting soil organic carbon along two landscape transects
Soil organic carbon (SOC) is one of the most important soil properties affecting many other soil and environmental properties and processes. In order to understand and manage SOC effectively, it is important to identify the scale-specific main factors affecting SOC distributions, which in this study occurred in a watershed on the Loess Plateau. Two transects were selected that passed along the upper slopes on each side of the main gully of the Liudaogou watershed. Transect 1 (3411-m length) had 27 sampling sites at 131-m intervals; transect 2 (3597 m length) had 30 sampling sites at 124-m intervals. The two transects were chosen in order to compare landscape patterns of differing complexity that were in close proximity, which reduced the effects of factors that would be caused by different locations. The landscape of transect 1 was more complex due to the greater diversity in cultivation. Multivariate empirical mode decomposition (MEMD) decomposed the total variation in SOC and five selected environmental factors into four intrinsic mode functions (IMFs) and a residual according to the scale of occurrence. Scale-specific correlation analysis was used to identify significant relationships between SOC and the environmental factors. The dominant scales were those that were the largest contributors to the total SOC variance; for transect 1, this was the IMF 1 (scale of 403 m), whereas for transect 2, it was the medium scale of the IMF 2 (scale of 688 m). For both transects, vegetation properties (vegetation cover and aboveground biomass) were the main factors affecting SOC distributions at their respective dominant scales. At each scale, the main effective factors could be identified although at the larger scales, their contributions to the overall variance were almost negligible. The distributions of SOC and the factors affecting it were found to be scale dependent. The results of this study highlighted the suitability of the MEMD method in revealing the main scale-specific factors that affect SOC distributions, which is necessary in understanding and managing this important soil property.
Analysis of scale-specific factors controlling soil erodibility in southeastern China using multivariate empirical mode decomposition
Abstract Soil erodibility (K) is a key factor in predicting the erosion of soil by water. K is spatially influenced by many environmental factors, but studies of the scales of factors influencing K are rare. The objective of this study was to identify the scale-dependent relationships between K and various environmental factors using multivariate empirical mode decomposition (MEMD). K and nine environmental factors were investigated at 101 locations along a 4200-km sinuous transect in southeastern China and then they were decomposed and analyzed using MEMD. Mean K was 0.043 ± 0.008 t ha h MJ−1 mm−1 ha−1 and had a weakly moderate spatial variability. Six intrinsic mode functions (IMFs) and a residue were obtained for K and the environmental factors after decomposition. The mean scales for IMF1 to IMF6 were 123.4, 192.4, 347.0, 598.9, 1268.3 and 1559.2 km, respectively. IMF1 for each variable explained most of the spatial variability for the variable, and IMF1 and IMF2 or IMF1 and IMF3 explained half of the spatial variability of the variable. K was mainly associated with soil-particle composition and soil organic-matter content at small scales (IMF1-IMF2), with soil-particle composition and pH at moderate scales (IMF3-IMF4) and with elevation, saturated hydraulic conductivity and clay content at large scales (IMF5-IMF6). Modeled prediction functions of K at each scale of decomposition were accurate, but the total prediction accuracy at the sampling scale was slightly lower than for multiple linear regression. The MEMD method was nevertheless valuable and provided detailed information about the factors influencing K at different spatial scales.
Soil organic matter and microbiological development of technosols in the South Wales Coalfield
Abstract Degraded land (formerly ‘reclaimed’) after surface-coal-mining is a serious problem in South Wales. This project uses forestation to foster soil development on opencast coal-mine spoil technosols. It compares records of humification and the soil microbiological system (microcoenosis) using paired data from the same plantings in 1998 and 2018. Statistical analysis finds no significant difference between samples collected under trees planted by the pit-planting versus trench planting method or trees planted using organic or mineral fertilizer. However, there are strong significant differences in both soil organic matter and microflora components and significant correlations with time since tree planting. Most components of the soil organic carbon (TOC) and the microflora increase, often significantly. However, compared to 2018, 1998 samples contain significantly greater maximum levels of Insoluble Carbon while the microflora had significantly more Ammonifying bacteria. Decreases in Insoluble Carbon explain the relatively small increase in TOC between 1998 and 2018. The % extracted with 0.1 N H2SO4 is significantly larger in 2018, suggesting active weathering. Similarly, both the maxima and minima of total Humic and Fulvic acids content, extracted with 0.1 M Na4P2O7 + 0.1 M NaOH, are significantly greater in 2018. Total microflora shows significant positive correlations with time-since-tree-planting as do the proportions of bacilli and actinomycetes but the correlation with ammonifying bacteria is negative. In 1998, the microflora was dominated by non-spore-forming bacteria while, in 2018, bacilli and actinomycetes prevail; both are involved in the transformation of complex organic compounds and humification. This indicates active transformation of more complex organic compounds and advancing humification. In sum, forestation of these degraded, formerly reclaimed, opencast coal-mine spoils has resulted in a massive increase in both the size and functioning of the soil organic system.