分类： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： The existing 210Pbex mass balance models for the assessment of cultivated soil erosion are based on an assumption that 210Pbex is quite evenly mixed within the plough layer. However, the amount of 210Pbex distributed in the soils below the plough depth, like a downward tail in the lower part of the 210Pbex profile, has been largely ignored. In fact, after the initial cultivation of undisturbed soils, 210Pbex will diffuse downward from plough layer to the plough pan layer due to the concentration gradient. Assuming 210Pbex inventory is constant, the depth distribution in the two layers of the cultivated soils will achieve a steady state after continuous cultivation for 10.37 years, when 210Pbex is evenly distributed in the soils of the plough layer with an exponential concentration decline with depth in the soils of the plough pan layer, and the 210Pbex concentration at any depth will be invariable with time. The work reported in this paper attempts to explain the formation of the 210Pbex tail in the soil profile below the plough depth by theoretical derivation of the 210Pbex depth distribution process in the two layers of the cultivated soils, propose a 210Pbex mass balance model considering 210Pbex diffusion based on the existing model, and discuss the influence of the 210Pbex tail to the existing model.
分类： 地球科学 >> 地理学 提交时间： 2023-03-19 合作期刊: 《干旱区科学》
摘要：Eco-environmental quality is a measure of the suitability of the ecological environment for human survival and socioeconomic development. Understanding the spatial-temporal distribution and variation trend of eco-environmental quality is essential for environmental protection and ecological balance. The remote sensing ecological index (RSEI) can quickly and objectively quantify eco-environmental quality and has been extensively utilized in regional ecological environment assessment. In this paper, Moderate Resolution Imaging Spectroradiometer (MODIS) images during the growing period (July–September) from 2000 to 2020 were obtained from the Google Earth Engine (GEE) platform to calculate the RSEI in the three northern regions of China (the Three-North region). The Theil-Sen median trend method combined with the Mann-Kendall test was used to analyze the spatial-temporal variation trend of eco-environmental quality, and the Hurst exponent and the Theil-Sen median trend were superimposed to predict the future evolution trend of eco-environmental quality. In addition, ten variables from two categories of natural and anthropogenic factors were analyzed to determine the drivers of the spatial differentiation of eco-environmental quality by the geographical detector. The results showed that from 2000 to 2020, the RSEI in the Three-North region exhibited obvious regional characteristics: the RSEI values in Northwest China were generally between 0.2 and 0.4; the RSEI values in North China gradually increased from north to south, ranging from 0.2 to 0.8; and the RSEI values in Northeast China were mostly above 0.6. The average RSEI value in the Three-North region increased at an average growth rate of 0.0016/a, showing the spatial distribution characteristics of overall improvement and local degradation in eco-environmental quality, of which the areas with improved, basically stable and degraded eco-environmental quality accounted for 65.39%, 26.82% and 7.79% of the total study area, respectively. The Hurst exponent of the RSEI ranged from 0.20 to 0.76 and the future trend of eco-environmental quality was generally consistent with the trend over the past 21 years. However, the areas exhibiting an improvement trend in eco-environmental quality mainly had weak persistence, and there was a possibility of degradation in eco-environmental quality without strengthening ecological protection. Average relative humidity, accumulated precipitation and land use type were the dominant factors driving the spatial distribution of eco-environmental quality in the Three-North region, and two-factor interaction also had a greater influence on eco-environmental quality than single factors. The explanatory power of meteorological factors on the spatial distribution of eco-environmental quality was stronger than that of topographic factors. The effect of anthropogenic factors (such as population density and land use type) on eco-environmental quality gradually increased over time. This study can serve as a reference to protect the ecological environment in arid and semi-arid regions.
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