XIE Yun, GAO Yan, GU Zhijia, LIU Gang, GAO Xiaofei, WEI Xin, CHENG Congcong, REN Xiaoyu, WANG Sichu
Potential hazard assessment of slope farmland soil erosion in black soil region of northeastern China
[Background] Soil depth with rich organic matter provides nutrients for grain production in the black soil region of northeastern China. However, at present, the thickness of the black soil layer in the black soil region of northeastern China is thinner or even lost. A large number of ephemeral gullies and permanent gullies have directly affected the sustainable use of black soil resources and national food security. Classification Standard for Potential Hazard of Soil Erosion (SL718—2015) issued by the Ministry of Water Resources (MWR) focusing on vegetation recovery may not be suitable for assessing slope farmland soil erosion risk. [Methods] Total 196 soil profile samples from slope farmland were collected in Songnen black soil region with area of 200 000 km2, and top soil depth for each sample was identified using quantitative index of mollic epipedon and isohumo features in Chinese soil taxonomy. According to the standard SL718—2015, the erosion risk was assessed for 196 samples using single index of anti-erodibility duration and combined index of vegetation recovery duration and slope degree respectively. Furthermore, they were assessed again by using modified values of anti-erodibility duration for each class based the rate of black soil formation. [Results] The anti-erodibility duration index could be used for assessing the potential hazard of soil depth decreasing caused by soil erosion. However, to maintain the crop growth and farmland productivity, it was better to change the value of threshold soil depth for estimating anti-erodibility duration from 10 cm to 20 cm. According to the standard SL718—2015, only 13.8% of the total 196 samples demonstrated potential hazard by using the index of anti-erodibility duration, and all the samples were classified as light, medium, and heavy potential hazard by using combined index of vegetation recovery duration and slope degree, of which 84.7% was light. The potential hazard degree was underestimated and the standard was not suitable for assessing the soil erosion potential hazard for the slope farmland. [Conclusions] To maintain the sustainable productivity of the black soil, the soil erosion rate should be less than or equal to soil formation rate, which could be used as the critical value for identifying soil erosion risk. The modified threshold values of the anti-erodibility duration for each potential hazard class were suggested as 2 000 years for not potential hazard, >500-2 000 years for light, >100-500 years for medium, >50-100 years for heavy, and ≤50 years for extreme potential hazard. Of total 196 samples, 36.7%, 36.2%, 5.1%, and 14.3% were light, medium, heavy, and extreme potential hazard under modified index class threshold values, i.e., the percentage over light potential hazard was 92.3%.
Improvement and effects of calcium-containing wastes on saline-alkali soil and growth of Lespedeza bicolor Turcz.
[Background] Saline-alkali soil is widely distributed in our country, while desulfurized gypsum, citric acid slag and fly ash are produced and accumulated in large quantities, which cause great pressure on national economy and ecological environment. But all of them can be used to improve saline-alkali soil. Exploring the improvement of saline-alkali soil by these calcium-containing wastes and the effect on plant growth is conducive to reducing environmental pollution and eventually provides scientific basis for the recycling and reuse of calcium-containing wastes and the improvement of saline-alkali soils. [Methods] Conditional control method was used in the research. Three kinds of calcium-containing waste materials (desulfurized gypsum, citric acid slag and fly ash)were applied to pot-planted Lespedeza bicolor Turcz. with saline-alkali soil soils respectively. Indexes of plant biochemical and soil composition such as net photosynthetic rate Pn, stomatal conductance Gs, transpiration rate Tr, intercellular CO2 concentration Ci, stomatal limitation Ls, water use efficiency (WUE), chlorophyll, content of main ion, exchangeable sodium percentage and sodium adsorption ratio were measured accordingly. [Results] 1) The main soil ion content after improved such as Na+, CO32-, and HCO3- reduced significantly, while the content of Ca2+, Mg2+, SO42- and CEC increased. 2) Na+ and alkaline ions were replaced, and the content of exchangeable Na+ even decreased by 84.3% in desulfurized gypsum treatment. 3) The alkali-reducing degree of each treatment soil exceeded 50%, and the soil was transferred from moderate saline to mild saline-alkali,the degree of salinity in each treatment also shifted from moderate to mild, all of the pH after the experiment decreased, and especially the citric acid residue treatment even reached to 7.1, which was basically neutral. 4) Pn, Gs, Tr and WUE of L. bicolor Turcz. were all higher, while Ci and Ls were lower.5) The contents of chlorophyll a, chlorophyll b and total chlorophyll were all over 2.4 mg/g, 1.1 mg/g and 3.5 mg/g in each treatment, that in fly ash treatment was the highest, mainly because the salt resistance was coupled, meanwhile it showed that by changing salt stress, calcium-containing materials changed the external environmental factors, and then affected the synthesis of plant chlorophyll. [Conclusions] Calcium-containing wastes such as desulfurized gypsum, citric acid slag and fly ash may improve the physicochemical properties of the saline-alkaline soil by changing the composition and contents of salt-damaging ions in saline-alkali soil. Normal physiological functions are maintained by adjusting the feedback regulation mechanism of L. bicolor Turcz. under salt stress, and reducing the effect of salt stress on the growth of L. bicolor Turcz. This study may provide scientific basis and reference for the recycling and reuse of calcium-containing wastes and the improvement of saline-alkali soil.
Effects of new polyurethane material (W-OH) on infiltration and runoff and sediment yield of two typical erodible soils in South China
[Background] The new polyurethane material (W-OH) has been widely used in soil and water conservation in our country, but its related theories lag behind its practice. Therefore, the study chose the two typical erosion soils red clay of slope cultivated land and arenosol of collapsing gully as objects and analyzed their infiltration and water-sand characteristics under the spraying of different W-OH concentrations. [Methods] Studying how much the new W-OH material influences the typical southern erosion soil in the infiltration, runoff and sediment was conducted. by indoor infiltration experiments and outdoor artificial simulated rainfall tests. [Results] 1) The nutrient of red clay soil and collapsing gully soil was infertile. The content of sand, powder and clay soil in red clay was almost equal. The content of sand in collapsing gully soil was more than 2/3, and the content of clay was only about 5.4%. 2) The spraying W-OH obviously reduced the infiltration rate of the two kinds of soils. With the increasing concentration (0-7%), the average infiltration rate of the red clay soil decreased from 6.98 to 1.42 mm/min and the collapsing gully soil decreased from 5.26 to 2.01 mm/min. The spraying of W-OH had a better effect on reducing the infiltration rate of red clay soil than that of collapsing gully soil. 3) The red clay soil sprayed with 5% W-OH showed an increase of 190% in the average flow rate and a decrease of 73.9% in the rate of sediment yield. The collapsing gully soil sprayed with W-OH showed similarly an increase of 37.3% in the average flow rate and a decrease of 62.1% in the rate of sediment yield. The spraying of W-OH increased runoff and decreased soil loss obviously. 4) The spraying of W-OH presented an inconspicuous impact on the average moisture content of the two kinds of soils before, after rainfall and 24 h later. [Conculsions] This study may provide a theory basis for W-OH's further application to the control of water loss and soil erosion in arable land of southern slope and collapsing gully.
Spatiotemporal coupling analysis of precipitation field based on REOF and ESMD: A case study on winter precipitation in Shandong province
[Background] The precipitation in winter has an important influence on soil moisture, winter crops,spring plowing and sowing. Shandong is a major agricultural province in China. However the characteristics of spatio-temporal distribution of winter precipitation in Shandong province is still unclear. The purpose of this study is to reveal the spatio-temporal distribution of winter precipitation and its relationship in Shandong province. [Methods] The data required for the paper comes from China National Meteorological Information Center, and the minimum time scale for data monitoring is 12 h. Based on the methods of both Rotated Empirical Orthogonal Function (REOF), Extreme-Point Symmetric Mode Decomposition (ESMD) and precipitation data from China National Meteorological Information Center, the spatial mode and cycle characteristics of winter precipitation field in Shandong province in recent 68 years were analyzed. [Results] 1) According to analysis of EOF reflecting the spatial variability of the whole region, the winter precipitation in Shandong province presents three main distribution modes: overall consistent, northwest-southeast antiphase and northeast-southwest antiphase. And variance contributions of three modes from EOF were 68.7%, 10.39% and 6.38% respectively. Obviously the first mode, overall consistent one of winter precipitation, was the most important distribution pattern. 2) Based on regional characteristics from REOF analyses, winter precipitation in Shandong province has formed a spatial distribution structure with the high-load areas of southeastern Shandong, northern Shandong and western Shandong respectively. The variances of the three modes were 34.17%, 30.20% and 21.10% respectively, indicating that the winter precipitation anomalies in these three regions had relatively obvious regional characteristics. The results of the period analysis based on FFT (fast Fourier transform) indicated that time coefficients (TCs) of southeast mode had the significant periodic characteristics with quasi-2.9-year and quasi-11.6-year, TCs of the north mode with quasi-2.52-year and quasi-8.29-year, TCs of the west mode with quasi-3.63-year, quasi-6.44-year and quasi-14.50-year. Meanwhile, the trend components of each mode decomposed by ESMD showed that the inter-decadal fluctuation was dominant, and there was no obvious trend of linear change, which indicated that the winter precipitation of the three modes in Shandong didn’t show a single trend characteristic during the monitoring period. Further analysis shows that the southeastern type shows a weak fluctuation and non-significant increase trend, while the northern type showed a weak fluctuation and insignificant decrease trend, while the western type shows little overall change. [Conclusions] REOF and ESMD are effective methods to analyze the spatiotemporal coupling relationship of large scale regional meteorological data. Taking winter precipitation of Shandong province as an example with the above two methods, the research results may provide reference for scientific practice for the rational planning and guidance of agricultural production in Shandong province.
LIU Ran, YU Xinxiao, CAI Qiangguo, SUN Liying, FANG Haiyan, JIA Guodong, HE Jijun
Research progressin the effect of slope length on slope erosion, transportation and deposition processes
[Background] Slope length is one of the important geomorphological factors that affect the process of slope runoff erosion and sediment production. It determines the variation of slope water flow energy along the way, and affects sediment carrying capacity of the water flow, thereby affecting the process of soil erosion, transportation and deposition. In recent years, the research on impact of slope length on soil erosion has received considerable attention. Meanwhile, understanding the changing law of critical slope length provides an important theoretical basis for the study of sediment transport and deposition processes on slopes. [Methods] Based on the literature review, we summarized the influence of slope length on runoff erosion and sediment yield, the general law of erosion critical slope length, the calculation method of critical slope length and the influence of slope length on slope deposition. And we discussed the limitations of soil erosion in terms of slope length, and highlighted the focus of future research. The information for the methods comes from 46 core papers out of 2199 papers published in the web of science, CNKI, Baidu Academic and Science Direct in the past few decades with the keywords of "slope length soil erosion" and "slope surface deposition". [Results] 1)The relationship between slope length and soil erosion is very complicated. Due to the difference in experimental conditions, the erosion intensity varying with slope length has three dynamic forms: increasing, decreasing and fluctuating. 2) Through previous studies, we summarized the definition of the critical slope length for erosion, and pointed out that different critical slope lengths are obtained in different studies due to factors such as rainfall conditions, slope, and slope length. Moreover, the established calculation model of critical slope length is based on the experimental data of researchers, which causes certain limitations. 3)During the erosion, transportation, and deposition of the slope, the sediment is characterized by alternating strong and weak spatial changes. The existence of the critical slope length makes the influence of slope length on slope erosion and deposition more complicated. When the slope length does not reach the critical slope length, erosion and sedimentation activities cannot be fully developed.4)The key points of future research are described as follows. First of all, it is necessary to carry out further research and experiments on the sediment deposition process on the slope. Second, research on the critical slope length for erosion changes as well as experimental research on the relationship between slope lengths of different soil textures and soil erosion should be strengthened. Finally, slope length affects the wave form of slope erosion-sedimentation, and the coupling mechanism of slope length and slope erosion and sediment deposition process needs to be studied. [Conclusions] This paper summarizes the research progress and future research directions of slope length on slope erosion, transportation and deposition process, and aims to provide guidance for the research application and decision-making of soil erosion on slope length.
Current status and thoughts on international standardization in the field of mitigating land degradation and combating desertification
[Background] Land degradation and desertification are the major global ecological issues threating the human living environment and development. The study and formulation of relevant international standards and their application will contribute to the efficient and orderly implementation of land degradation and desertification control at the global, national and regional levels. [Methods] The paper briefly reviews the current status and prevailing trend of global land degradation and desertification, analyzes the today’s development of international standardization in land degradation and desertification control, and summarizes the development processes and achievements initiated by the International Standardization Organization (ISO) from sorting out standardizations in land degradation and desertification control by studying a large number of literatures. Based on achieving the global goal of "zero growth in land degradation" and fulfilling international conventions, the necessities to initiate the development of international standardization in the field of land degradation and desertification control were discussed. [Results] 1)There is an urgent need to establish international standards of terminology, methods, techniques and management to further guide action and planning to combat land degradation and desertification on global scale.2)Based on the global requirement and national priority potential in the field of land degradation and desertification control in China, concrete efforts and measures are proposed to promote the development and further initiatives to launch the international standardization in the field of land degradation neutrality and desertification rehabilitation, such as improving the standard system, cultivating standard talents, service One Belt and One Road strategy, proposing international standards, and enhancing international influence. 3)The coming new technical committee on land degradation and desertification control (LDC-TC) will effectively carry out closer consultation and strengthening cooperation with UN Convention to Combat Desertification (UNCCD) and relevant international organizations, perfecting international standard system, improving basic standards, proposing international standards, and providing specific and operable technical guidelines for combating land degradation and desertification. [Conclusions] In order to promote the international standardization process, it is proposed to 1) establish a secretariat in China for launching the efforts and development of the international standardization to mitigate land degradation and combat desertification; 2) set up a technical committee on land degradation and desertification control (LDC-TC) under the leadership of ISO to develop work plan and mobilize resources, including scopes, tasks, working mechanism, and goals.
