Fingerprinting Sources of the Sediments Deposited in the Riparian Zone of the Ruxi Tributary Channel of the Three Gorges Reservoir (China)

The riparian zone of the Three Gorges Reservoir serves as a critical transitional zone located between the aquatic and surrounding terrestrial environments. The periodic anti-seasonal alternation of wet and dry periods results in an intensive exchange of substance within the riparian zone. The discrimination of the sources of the sediments deposited within the riparian zone is of fundamental importance for the evaluation of the soil pollution and associated environmental impacts and for the protection of the water quality in the reservoir. In this study, a composite fingerprinting technique has been applied to apportion the sediment sources for the riparian zone with different elevations, ranging between 145—155, 155–165, and 165–175 m in a typical tributary channel. From a sediment perspective, the sediments suspended from the Yangtze mainstream represent the primary sources of the riparian deposits. From a contamination perspective, the sediment input from the Ruxi tributary channel represents an important source of pollution for the riparian environment. More effective sediment and sediment-associated contaminant control plans are needed to reduce the potential environmental problems of the riparian zone

Recent Changes of Suspended Sediment Yields in the Upper Yangtze River and Its Headwater Tributaries

Abstract: Suspended sediment yields in the Upper Yangtze River and its four headwater tributaries (i.e., Jinsha, Min, Jialing and Wu) have declined significantly during the recent decades. Compared with 1956Compared with -1970, mean annual suspended sediment yield during 2001-2011wasreduced by 84% in the Upper Yangtze River at Yichang, by 34% in the Jinsha at Pingshan, by 84% in the Jialing at Beibei, by 75% in the Wu at Wulong, and by 48% in the Min at Gaochang. Linking the observed decadal changes of runoff discharge and suspended sediment load to dam construction and multiple environmental rehabilitation projects (e.g., soil-water conservation, reforestation) during the past decades, it can be concluded that the construction of large dams on the main stem and major tributaries of the Upper Yangtze River has played a principal role in the reduction of fluvial suspended sediment yields, while the environment rehabilitation projects may make limited contributions to the changes in suspended sediment yields except for the Jialing River

Concentrations and Stoichiometric Characteristics of C, N, and P in Purple Soil of Agricultural Land in the Three Gorges Reservoir Region, China

Soil stoichiometry is an essential tool for understanding soil nutrient balance and cycling. Previous studies have recognized that some relationships were observed between particle size and carbon and nitrogen parameters. This study attempted to evaluate nutrient element concentrations and their stoichiometric ratios of surface soil (0–10 cm) under different land use types (forest, sloping arable land, paddy fields, and orchards). and different particle sizes (<32 µm, <63 µm, and <125 µm) from a small typical hilly catchment (0.35 km2) in the Three Gorges Reservoir Region of China. The contents of soil organic carbon (SOC), total nitrogen (TN). and total phosphorus (TP) were measured, and the ratios of C:N, C:P, N:P were calculated. The results indicated that land use type and soil particle size have diverse impacts on the studied indexes (SOC, TN, TP, C:N, C:P, and N:P). Six indexes were significantly affected by land use type (p < 0.01), while only C:N ratio was statistically influenced by soil particle size (p < 0.05). Furthermore, several significant differences of studied parameters of four land use types grouped within three particle sizes were found. The concentrations of SOC (12.34~13.46 g kg−1), TN (1.27~1.59 g kg−1), and TP (0.71~0.92 g kg−1) in the study site were lower than the national average values of China. Moreover, the productivity in the study area was mainly limited by TN concentration. Additionally, the concentration of TP decreased obviously with the increase in particle size. Furthermore, various coupling relationships were validated by linear and nonlinear fitting among different indexes. At the small catchment scale, take forest as a reference, human activities have significant impact on C-N-P stoichiometry (p < 0.05). Especially, tillage may reduce SOC and TN contents, leading to a decline in soil quality. Overall, our findings can provide a basis for rational utilization and sustainable development of land resources

Influence of Precipitation Characteristics and Vegetation on Runoff and Sediment: A Case on the Basin in the Three Gorges Reservoir Region

Sediment is the main carrier of pollutants in river channels. This study analyzed the distribution characteristics of precipitation, runoff, and sediment and their response characteristics in the Daning River basin. Based on daily precipitation (1979–2017), runoff (1989–2017), and sediment (1997–2017) time series, the Gini concentration index, precipitation concentration index (PCI), precipitation concentration degree (PCD), and precipitation concentration period were applied to assess the concentration characteristics of precipitation, runoff, and sediment on the daily, monthly, and seasonal scales. At each intensity level, precipitation was negatively correlated to the PCI and PCD. The normalized difference vegetation index (NDVI) values had strong negative correlations with rainy days with light precipitation (0.1–9.9 mm). The degrees of concentration were in the same order for the multiscale analysis: runoff < precipitation < sediment. Although the amount of daily precipitation of more than 25 mm displayed a significant increasing trend, suggesting an increased risk of flood and soil erosion, the significantly improved vegetation cover reduced the sediment-carrying capacity of the surface runoff, with significant decreases in the total amount and multiscale concentration degrees of sediment being observed. The results of the study provide a reference for the improvement of the potable water safety and ecological environment in the Three Gorges Reservoir region

The Role of Paddy Fields in the Sediment of a Small Agricultural Catchment in the Three Gorges Reservoir Region by the Sediment Fingerprinting Method

Identifying sediment sources is a prerequisite for developing sediment management strategies. Erosion sediment derived from a small agriculture catchment is an important component of sediment inflow in the Three Gorges Reservoir Area. Paddy fields are one of the major land-use types in this region and can have both positive and negative effects on sediment. In this study, two different source group classification schemes were used to analyze the effect of paddy fields on the sediment in a typical small agriculture catchment in the Three Gorges Reservoir Region. A total of 32 soil source samples were collected from four kinds of land-use types (13 from dry land, 5 from orchards, 8 from paddy fields, and 6 from forest) in the Shipanqiu catchment. Moreover, the properties consisted of 41 elements and 12 element ratios were analyzed. Composite fingerprinting methodology was applied to discriminate and quantify the sediment source contributions. Additionally, element ratio was used as the fingerprint property in the fingerprinting application. The results showed that the element ratio was verified as an effective fingerprint property. Additionally, the relative sediment contributions of the potential land-use sources were 55.25% of dry land, 32.69% of orchards, and 12.06% of forest. Paddy fields played a role of sink rather than of source in this study. Accordingly, both forest and paddy fields are effective sediment management strategies. Particularly, paddy fields are a preferred choice for soil erosion control in mountainous and hilly areas. Furthermore, the proper management of paddy fields can help promote sediment retention and reduce soil erosion, which have positive effects on both the environment and agricultural productivity

¹³⁷Cs-Based Variation of Soil Erosion in Vertical Zones of a Small Catchment in Southwestern China

The study of the variability of soil erosion in mountainous areas provides the basis for soil and water conservation work and forest ecological construction in a targeted way. In this study, Liangshan Town catchment, a typical catchment in the Hengduan Mountains region, southwest China, was selected to investigate the variation of soil erosion in different vertical zones using the 137Cs tracing technique. The mean 137Cs reference inventories varied between 573.51 and 705.54 Bq/m2, with the elevation increasing from 1600 to 2600 m. The rates of soil erosion exhibited a significant variation. Under the same land cover condition, the average annual soil erosion modulus of high-elevation forest (elevation &gt; 2200 m) was 400.3 t/(km2&#183;a). However, the average annual soil erosion modulus of a low-elevation sparse forest (elevation &lt; 1600 m) was as high as 1756 t/(km2&#183;a). The average annual soil erosion modulus of the sloping farmland, mainly distributed at elevations of 1600&#8211;2200 m, was estimated to be 2771 t/(km2&#183;a). These results indicate that effective soil management measures need to be implemented on the cultivated sloping land in the future

Relationship between Precipitation Characteristics at Different Scales and Drought/Flood during the Past 40 Years in Longchuan River, Southwestern China

In this study, the temporal and spatial patterns of rainfall in the Longchuan River basin from 1977 to 2017 were analyzed, to assess the feature of precipitation. Based on the daily precipitation time series, the Lorenz curve, precipitation concentration index (PCI), precipitation concentration degree (PCD), and the precipitation concentration period (PCP) were used to evaluate the precipitation distribution characteristics. The PCI, PCD and PCP in five categories, defined by the fixed thresholds, were proposed to investigate the concentrations, and the average values indicated the higher concentrations in the higher intensities. The indices showed strong irregularity of daily and monthly precipitation distributions in this basin. The decrease in the PCD revealed an increase in the proportion of precipitation in the dry season. The rainy days of slight precipitation in the upper and lower basins with significant downward trends (−13.13 d/10 a, −7.78 d/10 a) led to longer dry spells and an increase in the risk of drought, even severe in the lower area. In the upper basin, the increase in rainfall erosivity was supported by the upward trend in the PCIw of heavy precipitation and the simple daily intensity index (SDII) of extreme precipitation. Moreover, the PCP of light precipitation, moderate precipitation, and heavy precipitation concentrated earlier at the end of July. The results of this study can provide beneficial reference information to water resource planning, reservoir operation, and agricultural production in the basin

Preparation and application of yttrium oxide with a large specific surface area through moderate carbonation in the presence of carbon dioxide

Yttrium oxide with a large specific surface area (SSA) (hereafter called LSSA Y2O3) has high-porosity structure, relatively large interface, and relatively abundant active surface sites, and its optical, chemical and thermal stability properties are greatly improved compared with ordinary yttrium oxide. As a result, LSSA Y2O3 has been applied in various fields as a luminescent, catalytic, and adsorbent material, showing enormous market potential. This study creatively presents a process designed to prepare LSSA Y2O3 powders through moderate carbonation in the presence of CO2. Experimentally, CO2 was used to carbonate a yttrium hydroxide [Y(OH)3] slurry. During the initial stage of carbonation, crystalline yttrium carbonate encapsulated Y(OH)3 through heterogeneous nucleation on its surface. This encapsulation considerably improved the filterability of the carbonation product while allowing it to retain the phase structure and high-porosity morphology of Y(OH)3. Further calcination of the carbonation product produced LSSA Y2O3 with an SSA of approximately 84 m2/g. This Y2O3 powder exhibited a relatively high adsorption capacity for methyl orange and was easy to recycle and reuse, thus showing potential for use as an adsorbent. The process developed in this study for preparing LSSA Y2O3 powders through carbonation in the presence of CO2 is advantageous because it requires only moderate conditions, causes no pollution, produces products with a uniform granularity and morphology, and is easy to scale up to meet industrial demands. Therefore, this process can effectively increase the added value and market competitiveness of Y2O3 powders and provide an experimental basis and theoretical guidance for the synthesis of other rare earth (RE) compounds with large SSAs through carbonation

Farmers’ Sustainable Strategies for Soil Conservation on Sloping Arable Lands in the Upper Yangtze River Basin, China

The Upper Yangtze River Basin comprises a densely-populated agricultural region with mountainous and hilly landforms. Intensive cultivation has been extended onto steep hillslopes, which constitute the principal source area for sediment production. Soil conservation on sloping arable lands is thus of utmost priority for persisting sustainable agricultural production and maintaining sound ecosystem services. Although there have been many soil conservation techniques, either promoted by the government or adopted by local farmers, the practiced area was very limited relative to the total area affected by soil erosion. This paper attempts to introduce four popular soil conservation measures on sloping arable lands in this region to enhance a broader scale of implementation, including hedgerow buffers, level trenches, sloping terraces and limited downslope tillage. These practices, although developed from local farmers’ indigenous knowledge for productive purposes, have well conformed to our contemporary understanding of soil erosion processes on sloping landscape affected by human disturbances, were of sound suitability to regional manual tillage agriculture and more trade-off-efficient on rill prevention, runoff harvest and nutrient management