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Biological soil crusts (biocrusts) are ubiquitous in arid and semi-arid regions and play many critical roles in soil stabilization and erosion prevention, greatly decreasing soil loss. Although sediments may be completely controlled by well-developed biocrusts, runoff loss is observed. Consequently, it is important to study how biocrusts resist runoff erosion in different developmental stages to evaluate and manage water erosion.
Materials and methodsIn the Loess Plateau Region, we sampled 32 biocrust plots representing eight stages of biocrust development and 5 slope cropland soil plots as bare soil control plots. We then used a rectangular open channel hydraulic flume to test the effects of biocrust development on runoff erosion.
Results and discussionAs expected, the establishment of biocrusts enhanced soil stability, and accordingly, soil anti-scourability significantly increased with biocrust development. Biocrusts exhibiting more than 36% or 1.22 g dm?2 of moss coverage or biomass fully protected the soil from runoff erosion. Moreover, soil properties, such as soil organic matter, soil cohesion and soil bulk density, were also important in reducing erosion. The findings indicated that biocrusts inhibited runoff erosion through direct physical protection related to biocrust cover and biomass and through the indirect modification of soil properties. In the early biocrust development stage (when moss cover was less than 36%), cyanobacterial biocrust played a primary role in providing resistance to runoff erosion, with resistance being positively related to cyanobacterial biomass (chlorophyll a) and influenced by soil properties.
ConclusionsThe relationship between soil anti-scourability and moss coverage or biomass can be divided into two stages based on a moss cover or biomass threshold. The capacity of biocrusts to resist runoff erosion was limited when moss cover was below the threshold value. Therefore, the stage corresponding to this level of moss cover should be of concern when estimating, predicting and managing water erosion.
相似文献Based on two consecutive years of field-scale trials, under different water managements, we illustrated the persistence of remediation effect of palygorskite on a Cd-polluted rice field.
Materials and methodsThe Cd uptake by a plant, pH and Cd chemical extractability, available P/K, and extractable Zn/Cu in paddy soils were used to evaluate the influence of palygorskite on Cd immobilization and soil fertility index.
Results and discussionIn contrast to the 1st year, at 0–1.5% palygorskite applied dose in soils, 0.025 M HCl–extractable Cd in continuous flooding reduced by 12.1–19.0%, and that in wetting irrigation increased by 10.9–18.9% in the 2nd year (p?<?0.05). The toxicity characteristic leaching procedure Cd reduction of 3.0–11.4% and increase of 8.9–12.0% were obtained under above-mentioned water managements (p?<?0.05). Compared with the 1st year, at different clay additional concentrations, grain Cd in continuous flooding reduced by 7.0–11.3%, and that in wetting irrigation increased by 6.5–10.8% in the 2nd year (p?<?0.05). Although trace elements in clay treated soils declined, they had no influence on the grain yield due to a minimum value higher than the critical value of 1.5 mg kg?1 for Zn and 2.0 mg kg?1 for Cu. The available P in continuous flooding took on a maximum increase of 8.2% in the 2nd year (p?<?0.05).
ConclusionsTwo consecutive years of field-scale in situ demonstration tests revealed that continuous flooding was a preferable water management regime for Cd immobilization using palygorskite in the rice field. There were no remarkable differences in extractable Zn/Cu between 2 years.
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