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    Global fallout Pu isotopes, Cs-137 and( 237)Np records in the sediments of Lake Xingkai and their response to environmental changes in the catchment

    Zhang, ShuaiYang, GuoshengZheng, JianPan, Shaoming...
    9页
    查看更多>>摘要：Plutonium (Pu) isotopes, neptunium-237 (Np-237) and cesium-137 (Cs-137) in the environment have emerged as important tools for promoting geochemical studies. To elucidate their source terms, deposition process, and the geochemical behavior, as well as their response to catchment environmental changes in lacustrine environment, Pu-239,Pu- 240, Cs-137 and( 237)Np were determined for the first time in a sediment core collected from the Lake Xingkai. The 240Pu/239Pu atom ratios (0.163-0.178) in all sediment samples corresponded well with the typical global fallout value of ~0.18, indicating that there were no other significant radioactive source inputs. The activity concentrations of Pu239+240,Cs- 137, and Np-237 were 0.010-1.030 Bq kg( -1), 6.4-30.1 Bq kg -1, and (0.020-2.195) x 10-3 Bq kg(-1), respectively. They presented similar vertical distribution patterns, with a typical global fallout peak (15-16 cm) corresponding to the year of 1964. On the other hand, the 237Np/239Pu atom ratios exhibited a wide range (0.207-1.306), and showed a trend of increasing values with depth, implying different geochemical behaviors of these two elements. Using the advection-dispersion equation model (ADE), the obtained apparent dispersion coefficient of 237Np (0.58 +/- 0.09 cm2 yr(-1)) was higher than that of 239+240Pu (0.38 +/- 0.07 cm2 yr(-1)), indicating that Np has greater mobility than Pu. The total global fallout inventories of 239+240Pu, Cs-137, and 237Np were 145, 4592, and 0.291 Bq m- 2, respectively. Approximately 46% of the total global fallout was derived from riverine input, indicating that severe soil erosion occurred in the catchment of Lake Xingkai in the past decades.
      原文链接:
    • NSTL
    • Elsevier

    Scaling properties of particle-size distributions of purple soils in a small agricultural watershed: A multifractal analysis

    Li, JinlinBao, YuhaiWei, JieHe, Xiubin...
    10页
    查看更多>>摘要：The particle-size distribution (PSD) of soils is a basic physical attribute that affects edaphic hydrological, chemical, and biological properties as well as soil quality and land productivity. Purple soil, as an early weathering product of purple mudstone, is a valuable resource for agricultural development in southwestern China. However, little is known regarding PSDs of purple soil, especially in small agricultural watersheds with diverse land-use types. The present study aimed to elucidate the scaling properties of purple soil PSDs by applying multifractal characterization. Results indicate that the PSDs of purple soils demonstrate clear multifractal behaviour, with generalised dimension and multifractal singularity spectra showing sigma and left deviating unimodal convex-up curves, respectively. By comparing with soils under other land-use types, the present study found that forestland purple soil is characterised by coarser granularity and more complex PSD, and has the minimum volumetric fractal dimension and the maximum generalised dimensions. No statistically significant correlation was observed between multifractal parameters and soil texture separates, except for that between the Ho spacing diaeresis lder exponent of order zero and the clay fraction (p < 0.05). In addition, most of the multifractal parameters do not exhibit statistically significant differences among soils under different land-use types (p < 0.05). The findings of the present study highlight that the effect of current land use on purple soil PSDs is limited and complex at a small watershed scale, and that the legacy effect of historical land use also plays a role in the evolution of purple soil PSDs. Overall, our findings can provide a reference for comprehensive understanding the influence of land use on purple soil quality.
      原文链接:
    • NSTL
    • Elsevier

    Implications of geomorphometric parameters on the occurrence of landslides in the Kali Valley, Kumaun Himalaya, India

    Solanki, AmbarGupta, Vikram
    17页
    查看更多>>摘要：The Kumaun Himalaya registers frequent seismicity, neotectonic behaviour and incessant rainfall which accel-erate hillslope processes governing landsliding phenomenon. Within the Kali Basin between Jauljibi and Gar-byang, morphometric analysis of 45 fourth order sub-basins were carried out to prepare an erosion potential map of the region. The spatial distribution of 376 landslides including 158 debris slide and 97 rockfalls correlates well with the erosion map depicting 40% landslides in very high zone, 15% in high zone, 33% in moderate zone, 12% in low zone across the Kali Basin. The dominant parameters responsible for the erosion were evaluated using statistical methods such as Principal Component Analysis (PCA) and Agglomerative Hierarchal clustering (AHC). The comparison of PC1, PC2 and PC3 illustrates high erosion activity around the Main Central Thrust (MCT) and within the Vaikrita and Chipplakote formations which strongly reflect the function of basin dimension, bifur-cation ratio, drainage density, relief and shape parameters for sub-basins exhibiting high proneness to flooding and typical surface runoff. The PCA results are consistent with AHC, where AHC clusters correspond with PCA factor loadings. Morphotectonic analysis using steepness index (Ksn) and valley floor width to height ratio (Vf) for the Kali and Dhauli rivers were integrated with landslide inventory that indicate the highest landslide density across the active Seraghat-Tintola Fault (STF) near Tawaghat and moderate to high density near topographic fronts of closely spaced active Lasku Fault (LF), Ghatibagar Kalika Fault (GKF) Rauntis Fault (RF) that outcrop within the Lesser Himalayan Sequences(LHS) exposed between Dharchula and Jauljibi.& nbsp;The study provides an understanding of quantitative geomorphometry as an useful approach to identify potentially active zones for slope failures and provide a guide to decision-makers in regional planning and mitigating the landslide hazard in the Kali valley which is developing hub for large scale infrastructural and tourist activities.
      原文链接:
    • NSTL
    • Elsevier

    Site and landscape position-dependent effects of vegetation removal on soil nitrogen mineralization across five sites on China?s Loess Plateau

    Kong, WeiboYao, YufeiHou, LingcaoWang, Xiang...
    12页
    查看更多>>摘要：The soil nitrogen (N) availability is a key limiting element of terrestrial ecosystem productivity and functioning, especially in fragile ecosystems (e.g., eroding environments). However, to date, little is known about how vegetation and erosion individually or jointly affect soil N mineralization under field conditions across a range of sites varying in soil and climate properties on a long-term observational scale. In this study, we elucidated how soil net N mineralization responds to vegetation removal (plots with vs. without vegetation) and landscape position (eroding vs. depositional zones) during a two-year manipulation experiment using an in situ incubation method on the China's Loess Plateau. The results indicated that the nitrate and total mineral N concentrations and net nitrification and mineralization rates were higher in the eroding zone (2.74 +/- 0.12 mg kg-1, 4.47 +/- 0.13 mg kg- 1, 0.046 +/- 0.005 mg kg- 1 d-1 and 0.046 +/- 0.006 mg kg- 1 d-1) than those in the depositional zone (2.01 +/- 0.10 mg kg- 1, 3.80 +/- 0.12 mg kg- 1, 0.030 +/- 0.005 mg kg- 1 d-1 and 0.032 +/- 0.006 mg kg- 1 d-1) on the China's Loess Plateau. Vegetation removal resulted in an increase in the nitrate (2.88 +/- 0.13 vs. 1.87 +/- 0.09 mg kg- 1) and total mineral N concentrations (4.56 +/- 0.14 vs. 3.71 +/- 0.11 mg kg- 1), but did not affect the soil net N mineralization rates on the China's Loess Plateau. The effects of vegetation removal on soil mineral N pools depended on the site, season and landscape position, with stronger effects in the eroding zone than those in the depositional zone. However, the responses of the net N mineralization rates to vegetation removal were consistent across the various landscape positions and sites, but varied with the season. Variance partitioning revealed that soil properties rather than climate and vegetation conditions were the most dominant contributors to the variations of soil N mineralization in both the eroding and depositional zones, explaining 37.6-64.6% of the variation. These results emphasized the substantial spatial (landscape position and site) and temporal (seasonal) dependence of the effects of vegetation removal on soil N mineralization at large scale.
      原文链接:
    • NSTL
    • Elsevier

    Insight into the environmental significance of grain-size fractal and pedogenesis of a typical loess and paleosol sequence

    Hou, KaiZhang, YutingQian, HuiZhang, Qiying...
    16页
    查看更多>>摘要：The loess-paleosol sequence contains rich climate change information during formation process. A typical loess-paleosol sequence was selected to analyze the grain-size, magnetic susceptibility and element intensity of samples. Fractal method was used to describe the characteristics of grain-size distribution and evaluate the relationship between fractal dimension and pedogenesis process. Based on the results of the mass balance and soil reconstruction model, the relationship between loess deposition and pedogenesis was studied. Change of unary fractal dimensions was consistent with the changing trend of climate indicators, and average fractal di-mensions of paleosol (2.246) was greater than that of loess (2.201). The fractal dimension can evaluate the fragmentation degree of particles and magnitude of energy events. Results of piecewise linear regression analysis showed that there were two different fragmentation mechanisms in the process of particle fragmentation. D-F1 was close to 3, and the energy dissipation in the process of coarse particles breaking into fine particles was mainly manifested in volume; D-F2 was close to 2, and the energy in the process of breaking fine particles into clay particles mainly proceeded along a two-dimensional plane. The volume changes of loess and paleosol were simultaneously affected by pedogenesis, formation pressure and global climate. The mass loss or gain shown by the different size-fraction components and element intensity indicated that the loess deposition and pedogenesis were simultaneous. During the prevailing summer monsoon, strong pedogenesis was dominant and formed paleosol. While the cold-dry climate during the prevailing winter monsoon promoted the loess deposition. The fractal and reconstruction model respectively quantitatively calculated the degree of particle fragmentation and the amount and process of material change during the formation process of loess-paleosol. Their combined application can enrich the theory of soil genesis and help to understand the origin of loess-paleosol sequence and its relationship with climate change.
      原文链接:
    • NSTL
    • Elsevier

    Responses of ecosystem respiration and methane fluxes to warming and nitrogen addition in a subtropical littoral wetland

    Xu, LigangWu, JianghuaXu, JiaxingJiang, Mingliang...
    12页
    查看更多>>摘要：Subtropical wetlands sequester vast carbon (C) and their C cycles are sensitive to global changes, such as climate warming and increased nitrogen (N) deposition. However, little is known about the effects of warming and increased N deposition on ecosystem respiration (Re) and methane (CH4) emission from subtropical wetland ecosystems. In this study, a manipulated warming and N addition experiment was conducted at a subtropical wetland in the littoral zone of Poyang Lake, China. Both Re and CH4 fluxes presented clear seasonal variations under all treatments. Warming significantly decreased Re by 20% compared with no warming and warming effect varied with growing season. Nevertheless, effects of N addition and the interaction of two treatments on Re were not detectable throughout the experimental period. Regardless of growing seasons, no treatments affected the temperature sensitivity of Re compared with the control. Contrary to the Re, CH4 flux was not affected by warming, but significantly affected by N addition and its interaction with warming in the whole and spring growing seasons. N addition decreased CH4 emission by 60% and 52% in the whole and spring growing seasons regardless of warming. Soil temperature was the primary driver for Re and explained about 60% of Re variation, while its explanation on CH4 flux was 13%. Soil moisture was not a limiting factor for Re and CH4 flux in this region. Our results imply that effects of warming and N addition on Re and CH4 flux varied with seasons, and these global changes tend to suppress carbon dioxide (CO2) and CH4 emission from this subtropical littoral wetland based on a short-term experiment. However, longer-term experiments are needed to see if this trend would persist and these effects should be included to project how the C sink function of subtropical littoral wetlands would respond to global changes.
      原文链接:
    • NSTL
    • Elsevier

    Spatial distribution characteristics of discontinuous hillslope gullies on the Loess Plateau of China: A special focus on spoon gullies

    Li, ChenruiYang, XinLiu, HailongZhu, Hui...
    17页
    查看更多>>摘要：Gullies characterized by frequent material exchanges and dramatic morphological changes sculpt fragmented surface landscapes and generate severe soil erosion, yet research on discontinuous gullies is currently lacking on the Loess Plateau of China. A special kind of discontinuous gully isolated on a hillslope, termed a spoon gully, was observed during a field investigation on the Loess Plateau. Spoon gullies are permanent gullies that are basically spoon-shaped with fat heads and thin tails. The confluences between spoon gullies and other gullies mainly occur in the subsurface. According to image interpretations and field verifications, 4077 spoon gullies were recognized on the Loess Plateau. These gullies were mainly distributed in the western part and northern fringes of the Loess Plateau with an obvious spatial clustering tendency, forming four concentrated areas with high gully densities. The topography distinctly affects the spatial distribution of spoon gullies. A total of 81.92% of the spoon gullies were located on slopes of 10-30 degrees, and 73.29% of these gullies were located on semi-sunny or semi-shady slopes. Furthermore, the spatial distribution of spoon gullies was associated with loess landforms and soil erosion intensities. A total of 66.37% of the spoon gullies occurred in loess ridge, loess tableland, or loess hill regions, and more than 50% of them arose in areas of strong or moderate water erosion. Overall, spoon gullies were mainly distributed in areas where continuous gullies developed insufficiently, and this finding can be regarded as the integrated result of precipitation, loess thickness and texture, vegetation coverage, and agricultural activities, suggesting that spoon gullies may represent an early stage in the development of continuous loess gully systems. These results not only provide new insights for understanding the formation and evolution of gully landforms but also have significant implications for soil erosion management on the Loess Plateau.
      原文链接:
    • NSTL
    • Elsevier