The Matuyama—Brunhes boundary in the loess-palaeosol sequence of Dolynske, southern Ukraine

We present the results of a palaeomagnetic study of the Early—Middle Pleistocene deposits exposed on the left bank of the River Danube at Dolynske, southern Ukraine. A thick succession of water-lain facies is succeeded by stratigraphically complete loess-palaeosol sequence; these constitute a unique palaeoclimate archive in the southern margin of the East European loess province. The Matuyama—Brunhes boundary (MBB) has been detected at the bottom of the Lower Shyrokyne (S7S3) subunit and not in the Martonosha (S6) unit as previously thought. New data align with previous results from the Roksolany and Vyazivok sections, where the MBB was determined at the same stratigraphical level in the S7S3 soil. In contrast to terrestrial Pleistocene records in China and сentral Europe, where the MBB was regularly determined in a loess layer (representing a cold period), the MBB in the Ukrainian subaerial succession is located in the soil unit (representing a warm period). Furthermore, eight, and not seven, glacial-interglacial cycles are recorded in the Brunhes chron. This may indicate the stratigraphic completeness of the loess-soil succession of Ukraine, which can be compared with the reference global marine and terrestrial palaeoclimatic archives. Further palaeomagnetic studies of loess-palaeosol sequences of other regions of Ukraine will allow revision and correlation of still inconsistent stratigraphic and magnetostratigraphic schemes of the Pleistocene deposits.

Experimental Study on Planting Soil Preparation by Improving River & Lake Silt with Plant Wastes

The physicochemical properties of river & lake silt are complex, and whether it can be directly used as planting soil is worth studying. The calliopsis pot experiment is carried out with planting soil prepared by amendment material, i.e. the organic matrix which is made by fermentation of high-nutrient sludge of a river in Nanjing, the dry excavating sludge in a lake and its flocculated and dewatered sludge together with plant wastes such as wood chips, to study the effects of different types of amendment materials and compounding ratio on plant growth. The results showed that the basic properties and fertility index of the planting soil could be adjusted directionally by adding wood chips or matrix. The overall growth of calliopsis in the planting soil formed by the high-nutrient silt in a river and its compound is the best, but some of the fertility indexes of the planting soil are too high and need to be further adjusted before use; the growth of calliopsis in the improved soil made of dry-excavation silt in a lake is better than that in the original silt, such situation is positively correlated with the amount of improved materials mixed; the difference between the growth of calliopsis in the flocculated silt in a lake and that in its improved planting soil is not significant, but some of the fertility indexes are higher than the standard indexes, and such silt can be slightly adjusted and improved into the planting soil. The field cultivation experiment study of calliopsis is carried out with the dry-excavation silt in a lake mixed with 4% wood chips and the original loess soil in the experimental field, and the growth of calliopsis planted in the dry-excavation silt in a lake is better compared with that of calliopsis planted in original loess soil. The research results can provide ideas and basis for the study on improving river & lake silt into planting soil with plant wastes.

Quantitative and Qualitative Responses of Soil Water-Extractable Organic Matter to Carbon and Nitrogen Management Practices in Loess Soil

Soil-dissolved organic matter (DOM) drives the carbon (C) and nitrogen (N) cycles in agroecosystems. Despite many studies on DOM dynamics, hardly any attention has been directed toward DOM quality, particularly DOM composition. The aim of this study was to elucidate how C and N management practices alter soil water-extractable organic matter (WEOM) in a loess soil agroecosystem. Field experiments were conducted with a winter wheat monoculture. Three N fertilization rates (0, 120, and 240 kg ha−1 year−1) were applied for 17 years (2002–2019), combined with five C practices (zero, low, and high rates of sheep manure or wheat straw) for three years (2016–2019). The results reveal that soil organic carbon (SOC) and water-extractable organic carbon (WEOC) concentrations in the topsoil (0–20 cm) were increased by organic amendments considerably but were not affected by N fertilization. The fluorescence excitation–emission matrix spectra (EEM) of WEOM were resolved to two humic-like components (C1 and C2) and two soluble microbial byproduct-like components (C3 and C4). The proportions of C1 and C2 were increased, while the proportion of C3 was decreased by both C and N management practices. In conclusion, organic amendments increased both WEOM quality and its proportion of humic-like components, whereas N fertilization increased the proportion of humic-like components without variations of WEOM quality in the topsoil of loess soil.

Improved Runoff Simulations for a Highly Varying Soil Depth and Complex Terrain Watershed in the Loess Plateau with the Community Land Model

This study aimed to improve runoff simulations and explore deep soil hydrological processes for a watershed in the center of the Loess Plateau (LP), China. This watershed, the Wuding River Basin (WRB), has very complex topography, with soil depths ranging from 0 to 197 m. The hydrological model used for our simulations was the Community Land Model (CLM) version 5 developed by the National Center for Atmospheric Research. Actual soil depths and river channels were incorporated into CLM to realistically represent the physical features of the WRB. Through sensitivity tests, CLM with 150 soil layers produced the most reasonable results and was adopted for this study. Our results showed that CLM with actual soil depths significantly suppressed unrealistic variations of the simulated sub-surface runoff when compared to the default simulations with a fixed soil depth of 8 m. In addition, CLM with higher-resolution soil layering slightly improved runoff simulations, but generated simulations with much smoother vertical water flows that were consistent with the uniform distribution of soil textures in our study watershed. The runoff simulations were further improved by the addition of river channels to CLM, where the seasonal variability of the simulated runoff was reasonably captured. Moreover, the magnitude of the simulated runoff remarkably decreased with increased soil evaporation by lowering the soil water content threshold, which triggers surface resistance. The lowered threshold was consistent with the loess soil, which has a high sand component. Such soils often generate stronger soil evaporation than soils dominated by clay. Finally, with the above changes in CLM, the simulated total runoff matched very closely with observations. When compared with those for the default runoff simulations, the correlation coefficient, root-mean-square error, and Nash Sutcliffe coefficient for the improved simulations changed dramatically from 0.02, 10.37 mm, and −12.34 to 0.62, 1.8 mm, and 0.61. The results in this study provide strong physical insight for further investigation of hydrological processes in complex terrain with deep soils.

Experimental and Numerical Analysis Study on Loess-Lime Structures Used for Lateral Antiseepage in Deep Collapsible Ground Embankment

The focus of this study was to investigate the effect of loess soil treated with lime on the lateral-seepage response. Three groups of box experiments were carried out to study the lateral-seepage effect under different types of loess-lime structures. Automated testing systems were designed to perform experiments and collect data. Additionally, numerical analysis of lateral-seepage impact and embankment settlement was performed. Finally, moisture content and settlement were monitored to quantify lateral-seepage effect results under corresponding loess-lime treatment. Results showed that loess-lime compaction piles and diaphragm wall structures could effectively prevent lateral seepage, and the latter was better. The simulated results are similar to the measured values of the box experiment, which indicates the accuracy of the simulation analysis and further supports the experimental results of this study.