Explore the vast range of titles available.

Soil moisture (SM) plays a key role in hydrological processes and the distribution and growth status of vegetation in arid and semi-arid regions. An understanding of SM dynamics can help to better explain runoff and soil erosion processes, enable vegetation restoration, and improve water resources management. This study investigated SM changes under different land cover types on hillslopes using fine-scale (every 10 cm and every hour) SM monitoring data at Dun Mountain in the semi-arid Loess Plateau. It was found that the SM of each soil layer generally followed the order of bare land > grassland > forestland. The mean annual SM of grassland and forestland was 71.8 and 65.4% of that of bare land, respectively. The SM of bare land generally displayed an increasing trend with depth. The SM of grassland and forestland generally increased first and then decreased with increasing depth. The mean SM of all three land cover types in different soil layers was largest in autumn. In grassland and forestland, there was a higher soil water replenishment (653.02 and 608.39 mm) and consumption (576.77 and 555.70 mm) than the corresponding values for bare land during the four seasons. The amount of soil water replenished in grassland and forestland in summer was 1.32 and 1.21 times that of bare land, respectively. The cumulative amounts of frozen soil water in bare land, grassland, and forestland were 495.98, 334.78, and 213.15 mm, respectively. The SM distribution among the different soil layers exhibited a strong temporal stability. The effect of meteorological factors on actual evapotranspiration displayed significant seasonal differences. In conclusion, vegetation cover reduced the SM at the slope scale, but the reduction was discontinuous at the annual scale. The results contribute to clarify the seasonal difference in actual evapotranspiration and provide new insights into soil moisture retention and freeze–thaw process in arid region.

The accurate estimation of sediment flux in naturally confluent rivers remains challenging. In this study, we developed a momentum‐sediment model (MSM) that considers the complex structure of confluent rivers to estimate sediment flux. Trend analyses of annual runoff and sediment flux from 1956 to 2022 were conducted at four hydrological stations in the upper reaches of the Yangtze River Basin: Pingshan, Zhutuo, Cuntan, and Yichang. Runoff change was insignificant, whereas the sediment flux decreased significantly at all four stations. The entire time series was divided into five periods: a reference period (P1: 1956–1984) and four changing periods (P2: 1985–1993; P3: 1994–2002; P4: 2003–2012; and P5: 2013–2022). The hydrological time series of the reference period served as the calibration period for constructing the momentum‐sediment models for Zhutuo, Cuntan, and Yichang stations. The MSM expressions were validated in the four changing periods. The momentum‐sediment models for period P1 at Zhutuo and Cuntan stations could be directly applied in periods P2–P5. The MSM for the Yichang station was improved by incorporating the trapping efficiency of the Three Gorges Reservoir. The simulation results of the MSM for sediment flux outperformed the sediment rating curves and linear relationship, particularly for maximum measured values. The applicability of the MSM was validated in the Jialing River, which is characterized by a small basin area, and the Yellow River, which is known for its scarce water and rich sediments. This confirmed that the MSM was insensitive to watershed scale and hydrological conditions.

There is debating over the question of whether the large-scale 'Grain for Green' program on the Loess Plateau of China threatens regional food security. Self-sufficiency index and cropland pressure index were used to assess food security on the Loess Plateau after the implementation of revegetation program. The results showed that the 'Grain for Green' program initially had a considerable impact on regional food security, where grain yield fell from 1999 to 2001, resulting in a lower grain self-sufficiency and increased farmland stress. Subsequently, grain yield in this region increased due to the elevated agricultural material input and increased construction of terraces and check dams. The grain self-sufficiency index would have increased to 96.55% if there were improvements to the agricultural conditions, such as fertilization and irrigation, which would have resulted in an increase in the crop yield per unit of 20%. However, the grain self-sufficiency increased to 105.25% via the construction of terraces and check dams. Thus, the government should further expand the 'Grain for Green' program in coordination with improvements to the agricultural production conditions and the construction of terraces and check dams on the Loess Plateau.

Heavy metals (HMs), characterized by their non-biodegradable nature, are prone to enrichment in river sediments, thereby severely jeopardizing the equilibrium of ecosystems and human health. Given the critical importance of safeguarding valuable water resources, it is of utmost urgency to initiate research on HMs within the Yellow River Basin (YRB). This study collected river sediment samples from the Yellow River Basin and analyzed the distribution characteristics, health risks, and pollution sources of HMs utilizing the pollution index method, health risk assessment, and positive matrix factorization (PMF) model. The results demonstrate that arsenic (As), zinc (Zn), and cadmium (Cd) are the primary elements contributing to heavy metal (HM) pollution in the sediments of the YRB. The proportions of sediment samples with low HM pollution in the upstream, midstream, and downstream are 36.48%, 71.43%, and 72.73%, respectively, whereas the proportions of samples with moderate pollution are 63.16%, 28.57%, and 27.27%, respectively. The health risk assessment reveals that the non-carcinogenic risks posed by HM pollution in the sediments to adults are negligible, whereas those to children are not. Regarding carcinogenic risks, the carcinogenic risk index of As is significantly higher than that of the other HMs. The primary sources of HM pollution in the sediments are identified as traffic–industrial sources, agricultural–industrial sources, and industrial sources, with respective contribution rates of 32.47%, 44.87%, and 22.66%. As and Zn are prioritized as elements for health risk control, while agricultural–industrial sources are highlighted as the priority sources for pollution control.

Land uses determine water quality within riparian environments to a certain extent and directly affect human health via drinking water. The main objective of this paper is to investigate the influences of land use, both in hydrologic response units (HRUs) and 200-m-wide buffer areas, on surface water quality. The variations and interrelationships between water physicochemical properties and land uses were assessed for better management of water environment. Nitrogen was the dominant nutrient and was significantly correlated with other water quality parameters. In the HRUs and buffer areas, the dominant landscape was grassland and farmland, respectively. Total organic carbon (TOC) and dissolved oxygen (DO) had negative correlation with land use factors; nitrate nitrogen, total nitrogen, total phosphorus, electrical conductivity, and temperature, in contrast, were positively correlated with them. Industrial and residential land was the critical land use for the aquatic environment in the Dan River, indicating that point pollution should receive more attention. Vegetation area had strong regression relationships with TOC and DO. Furthermore, more specific types of land use (subcategory classification) had a greater role in water quality. The land use in buffers can act on the water body more directly and effectively.

Understanding soil moisture’s spatiotemporal variations and the factors influencing it is crucial for the restoration and growth of vegetation across the Loess Plateau, particularly in the Ziwuling region. This study employs soil moisture remote sensing data, complemented by information on soil properties, environmental conditions, and topography, to examine soil moisture variability within the Ziwuling region between 2001 and 2020. Using trend analysis, geographic detectors, and multi-scale geographic weighting techniques, this research aims to elucidate the effects of driving factors on soil moisture’s spatiotemporal patterns. The findings indicate the following: (1) Over the study period, the mean soil moisture in the Ziwuling region exhibited a relatively stable declining trend, with an annual decrease of −0.00047 m3/(m3·a). Spatially, higher soil moisture levels were observed in the south-central area, while lower levels occurred in the northern, western, and eastern peripheries. (2) Geoprobe analysis illustrated that the normalized difference vegetation index (NDVI) had the most notable effect on the spatial distribution of soil moisture in the region. As a direct indicator of vegetation cover, NDVI strongly affects soil moisture distribution through ecological and hydrological processes. Following NDVI, average annual potential evapotranspiration and annual precipitation were identified as the next most influential factors. The combined effect of these factors on soil moisture surpassed that of individual factors, with the interaction between NDVI and annual precipitation being particularly pronounced, predominantly controlling the spatial variability of soil moisture in the Ziwuling region. (3) Different factors exhibited varying effects on soil moisture levels. Notably, slope and elevation consistently had negative impacts, whereas variables such as soil texture (loam and sand), land use, temperature, precipitation, NDVI, and slope aspect showed bidirectional influences. This study offers a comprehensive analysis of the spatiotemporal variability of soil moisture and its controlling factors in the Ziwuling region, ultimately offering a scientific basis to support ecological restoration and sustainable development initiatives on the Loess Plateau.

The capacity of soil and water conservation measures, defined as the maximum quantity of suitable soil and water conservation measures contained in a region, were deter- mined for the Loess Plateau based on zones suitable for establishing terraced fields, forest- land and grassland with the support of geographic information system （GIS） software. The minimum possible soil erosion modulus and actual soil erosion modulus in 2010 were calcu- lated using the revised universal soil loss equation （RUSLE）, and the ratio of the minimum possible soil erosion modulus under the capacity of soil and water conservation measures to the actual soil erosion modulus was defined as the soil erosion control degree. The control potential of soil erosion and water loss in the Loess Plateau was studied using this concept. Results showed that the actual soil erosion modulus was 3355 t-km-2.a-1, the minimum pos- sible soil erosion modulus was 1921 t.km-2.a-1, and the soil erosion control degree was 0.57 （medium level） in the Loess Plateau in 2010. In terms of zoning, the control degree was rela- tively high in the river valley-plain area, soil-rocky mountainous area, and windy-sandy area, but relatively low in the soil-rocky hilly-forested area, hilly-gully area and plateau-gully area. The rate of erosion areas with a soil erosion modulus of less than 1000 t.km-2.a-1 increased from 50.48% to 57.71%, forest and grass coverage rose from 56.74% to 69.15%, rate of ter- raced fields increased from 4.36% to 19.03%, and per capita grain available rose from 418 kg.a-1 to 459 kg.a-1 under the capacity of soil and water conservation measures compared with actual conditions. These research results are of some guiding significance for soil and water loss control in the Loess Plateau.

As an important soil and water conservation engineering measure, check dams have been constructed on a large scale in the Loess Plateau of China. However, their effects on runoff and sediment processes in the basin are still unclear. In this study, the hydrodynamic processes of the Wangmaogou watershed located in the Loess Plateau were simulated, and the influence of check dams on the flood and erosion dynamic processes in this watershed were also evaluated. The results showed that the check dams obviously reduced the flood peak and flood volume and mitigated the flood process. After the dam system was completed, the flood peak and flood volume were reduced by 65.34% and 58.67%, respectively. The erosion dynamic distribution of the main channel in the small watershed was changed to different extents by the different dam type combinations, and the erosion dynamic parameters of the channel decreased most after the dam system was completed, when the velocity and runoff shear stress of the outlet section were reduced by 10.69% and 31.08%, respectively. Additionally, the benefits of sediment reduction were most obvious after the check dam system was completed, with the sediment discharge in the watershed being reduced by 83.92%. The results of this study would provide specific implications for construction and management of check dams in the Loess plateau.

Crop types and tillage measures on slopes have significant impacts on regional water and soil conservation. In this study, we investigated the influences of multiple crop types and tillage measures on water and sediment yields based on plot-scale experiments under artificial rainfall. The objective of the study is to find the best combination of crop type and tillage measure from the perspective of reducing soil erosion. We performed artificial rainfall experiments under eight slope treatments, which are the bare-land (BL, as a reference), peanut monoculture (PL), corn monoculture (CL), bare land (upper slope) mixed with peanut monoculture (lower slope) (BP), corn and peanut intercropping (TCP), corn and soybean intercropping (TCS), downslope ridge cultivation (BS) slope, and straw-mulched (SC), respectively. Under similar rainfall intensity and initial soil moisture conditions, these treatments except for BS efficiently reduced sediment yield compared to the BL slope. In comparison, the most effective slope treatment to reduce soil erosion is TCP, followed by PL and TCS. The amount of sediment yielded from the three treatments accounts for 0.4%, 2.0%, and 3.3% of the sediment yielded from BL. We recommend the three slope treatments as the preferred choices among eight treatments. Also, the lower sediment yield in the three slope treatments benefits from their higher vegetation coverage. Vegetation coverage plays a greater role in regulating sediment yield than the surface runoff at a plot scale.

Microorganisms have a profound impact on the stability and ecological health of aquatic environments. Fungi, as important components of river ecosystems, play critical roles as decomposers and symbionts. A comprehensive understanding of the mechanisms underlying fungal community assembly is essential for the effective conservation and management of river ecosystems. However, the distribution patterns and assembly process of fungal communities along elevation gradients in river sediments remain poorly understood. In this study, ITS amplicon sequencing, a neutral community model, and a null model were employed to analyze the distribution patterns and assembly processes of fungal communities in sediments along the altitudinal gradient of the Yellow River. The results indicated that Ascomycota (47.79%) and Basidiomycota (15.68%) were identified as the dominant phyla in the sediments, collectively accounting for 63.47% of the total relative abundance of the community. In the three different altitudinal gradients, the fungal community diversity (Shannon) showed a gradually decreasing trend with increasing altitude. The co-line networks of fungal communities exhibited positive interactions and had more complex and compact networks in the sediments of the Tibetan Plateau area (YRA). Environmental factors in the sediments played an important role in shaping the structure of fungal communities, with lead (Pb), total nitrogen (TN), silt, and total organic carbon (TOC) being the main factors driving changes in community structure, contributing 15.5%, 12.3%, 10.7%, and 10.2%, respectively. In the community assembly process, deterministic processes were found to dominate, with homogenizing selection contributing the most (69.66%). These research results help us understand the distribution patterns of fungal communities along altitudinal gradients and the mechanisms of community assembly, and also provide a scientific basis for biodiversity conservation and the rational use of biological resources.