Guanfang Sun

This laboratory-scale study examined how soil particle-size distribution (PSD), especially the median diameter d₅₀, affects slope runoff and sediment yield, and evaluated d₅₀ as a simplified indicator for erosion prediction. Simulated-rainfall experiments were performed using a rainfall simulator and an adjustable steel flume. Five soils with contrasting PSDs (sandy loam to silty clay; d₅₀ = 0.00524–0.06105 mm) were tested under three rainfall intensities (60, 90, and 120 mm h⁻¹) for 45 min events, with two replicates per treatment (30 events total). Runoff rates increased with clay content: sandy loam < mixed sandy loam < loam < mixed silty clay < silty clay. Partial correlation analysis showed strong associations between runoff rates and d₁₀, d₃₀, d₅₀, d₆₀, and C_c, with a partial correlation coefficient of −0.78 for d₅₀. Sediment yield rates showed the opposite trend, decreasing as clay content increased. Cumulative sediment yield increased with d₅₀ via a positive power-law relationship, with calibration R² values of 0.91–0.95 across rainfall intensities. The proposed d₅₀-based erosion model achieved a calibration R² of 0.97 with two fitted parameters (k₁ and b) and inputs of rainfall erosivity, slope length, and slope steepness. These laboratory-scale results provide a preliminary basis for incorporating d₅₀ into erosion-prediction models for production and construction projects; however, field validation is required before engineering application.

Climate change and human activities have caused a range of impacts on the ecological environment. The Loess Plateau (LP) is critical to the stability and health of ecosystems in central and western China, but there is still a lack of research on spatial and temporal heterogeneity in the effects of climate and human activities on the EEQ of the LP. We quantified the ecological environment quality of the study area from 2001 to 2019 based on the improved remote sensing ecological index (RSEI-2) and studied the spatial and temporal evolution of EEQ and its drivers during this period by trend analysis and multiscale geographic weighted regression (MGWR) model. The EEQ of the LP showed an increasingly slowing trend during 2001–2019, with apparent spatial heterogeneity, the south-central part was the hot spot area of change, and the center of gravity of change shifted 124.56 km to the southwest. The driving effects and ranges of each factor changed over time during the study period, and the positive effects of precipitation (PRE) and temperature (TEM) on the EEQ of the southern LP became more apparent, but the negative effects of TEM on the northwestern part have expanded. The negative effect of the intensity of land utilization (LUI) has increased from north to south and has the most profound impact, while population growth has less impact on the central region. The results of this research indicate that the execution of the Grain to Green Program (GGP) in the LP over the last two decades has been effective, but more attention should be paid to the maintenance of the restoration effect in the central region and the reasonable development of the land in the southern area. This research can enhance the comprehension of alterations in ecological factors that impact the environment of the LP. Additionally, it serves as a foundation for investigating strategies for ecological preservation and sustainable land development.

Soil salinization is a major eco-environmental problem in irrigated agro-ecosystems. Understanding regional soil salinity spatial patterns and seasonal dynamics and their driving factors under changing environments is beneficial to managing soil salinity to maintain agricultural production in arid agricultural areas. To better investigate this topic, soil salinity was measured, ranging from topsoil to the depth of 1.8 m in an irrigation district with 68 sampling sites before and after the crop growing seasons of the dry year of 2017 and wet year of 2018. Soil texture, groundwater table depth, groundwater salinity, and crop type were monitored. The results indicated that an increase in soil salinity in the root zone (0–0.6 m) was accompanied by a decrease in soil salinity in the deep soil (0.6–1.8 m) through the crop growing season due to water movement from the deep layer to shallow layer, whereas the opposite trend was observed during the fallow seasons. During the dry year, the area with soil desalted was measured to be 19.89%, 14.42%, and 2.78% lower at depths of 0–0.6 m, 0.6–1.2 m, and 1.2–1.8 m than that during the wet year. The groundwater table depth in the crop growing season had the least impact on the change in root zone soil salinity (p > 0.05). Interactions between crop types and groundwater table depth had a significant effect on the change of soil salinity in the root zone during the growing season of the dry year, but were insignificant during the wet year. Crop types, groundwater table depth, and climate conditions determined the contribution of shallow groundwater to crop water consumption and, to a greater extent, soil salinity. Regression tree analysis showed that groundwater salinity and soil texture had a greater influence on soil salinity than groundwater table depth and land elevation. The effect of groundwater on soil salinity is strongly related to soil texture, and the salinity of fine-textured soil was 36–54% greater than that of coarse-textured soil due to large capillary action. Therefore, we suggest strengthening groundwater management in areas with fine-textured soil to relieve soil salinization, particularly during dry years.

Irrigated agriculture in arid and semi-arid regions is seriously threatened by water shortage and soil salinization. The well-canal conjunctive irrigation scheme provides a stable groundwater resource for irrigation and can reduce surface salt accumulation by decreasing the groundwater levels, which makes it more suitable to alleviate the problems of irrigated agriculture in arid and semi-arid regions. However, the soil salinization process requires assessment on regional spatial and decadal time scales, as it is a continuous but slow change. Therefore, a water and salt balance model (WSBM) for well-canal conjunctive irrigation is developed herein to obtain long-term predictions of regional root zone salinity dynamics in canal- and well-irrigated areas. In the developed model, the characteristic length of the well-canal conjunctive irrigated area (L_c) is used to couple the canal- and well-irrigated areas. The performance of the WSBM as well as a sensitivity analysis and the value rule of the special parameter L_c are evaluated by comparing the simulation results with those derived from the MODFLOW. The results demonstrate the validity of the developed model, and the special parameter L_c is found to be insensitive, with a value approximately two-thirds of the center distance when the canal and well irrigation districts are regularly adjacent or centrosymmetric. Moreover, when a real-world application is adopted, the water table depth and root-zone soil salinity are simulated in the Longsheng well-canal irrigation area in the Hetao Irrigation District, Inner Mongolia, China. Water table depth and soil salinity collected from 2002–2005 and from 2006–2020 are used to calibrate and validate the model. The calibrated model is subsequently used to predict soil salinity dynamics in the next 100 years under current and future water-saving conditions. The predictions indicate that the soil salinity is basically stable at a relatively low level (<0.2 kg/100 kg) under current irrigation practices. The study could support planning making before implementation of well-canal conjunctive irrigation.