| Desert steppe grassland ecosystem was drought-tolerate yet very sensitive to disturbance,and itisunder the double stress of wind erosion and grazing. It is important to study the grassland grazing and wind erosion process in arid area to investigate the effect of different grazing intensity on wind erosion process in desert steppe.Understanding this impact will allow usto formulate reasonable regional grassland protection policies. Our study was conducted in Inner Mongolia stipabrevifloragrassland. In this study, BSNE sand collection instrument was set up in the 11-year continuous random block group site (set 4 grazing intensities for 0.93,1.82,2.71,0 sheep/hm2/year). The quantitative relationship between grazing intensity and flux of windborne sand, and particle size characteristics of wind erosion was investigatedthrough 4 sampling periods during 2 years (April 2013-April 2015). We also took undisturbed soil samples to wind tunnel tests to study the quantitative relationship between grazing intensity and wind erosion rate, and estimate the wind erosion amount in Desert steppe under different grazing intensities. The results show:1. The grazing intensity and season had significant effects on the aeoliansand flux(P< 0.001) in desert steppe. Daily mean sand flux was between 2.38-31.39 g/m/d, and the average was 16 g/m/d(the average of all seasons). The aeoliansand flux increased gradually with the increase of grazing intensity, and the aeoliansand flux in the growing season was lower than that in the non-growing season. The effects of grazing intensity and season on aeolian sand flux wasnot universal. The difference of sand flux between different grazing intensity in the non-growing season was much smaller than that in the growing season.2. The distribution of wind blown sand with height was different in different seasons. In the growing season,aeoliansand flux was in line with the classic aeoliansand flux function, whereasthe fittingwas poor for the non-growing season.The grazing intensity in growing season increased sediment flux particularly near the surface, the sediment concentration at heights more than 50 cm in the non-growing season increased significantly. The aeoliansand fluxat heights greater than 50 cm was mainly controlled by the seasons, and was less affected by the grazing intensity. The difference of the sand fluxstructure between the grazing intensities was mainly reflected in the near surface layer.3. Particle size ofaeoliansediments was generally< 0.25 mmin the desert steppe whichaccounted for more than 85% of all sediment particles. The size of aeolian sediment gradually became finerwith the increase of height. Particles with size of D50 (<50μm) in the topsoil wasmost active under wind erosion, but particles of D50-125 (50-125μm) and D125-250 (125-250μm) aggregated in the severe and moderate grazing area. The particle(<50μm) enrichment ratio increased steadily with increasing height, but the enrichment ratio at 50 cm or more was no longer changing with a high degree of increase in CK and LG, and basically at the same level. It indicated that the grazing can lead to the accumulation of fine particles ata certain height, which have the potential to transport at a long distance and may have a greater impact to the nutrients loss on the grassland.4. The C, N elements and measurement characteristics of aeoliansediments in desert steppe are as follows:Total C and N content in the wind erosion sediment were 30.90 g/kg and 2.87 g/kg, respectively.TC and TNin windblown sediment decreased gradually with the increase of grazing intensity,. In particular,nutrients of windblown sand were higher in CK. TC and TN content were the lowest near the surface, but the other nutrients changed less significantly with the increase of height. Andat the height of 50 cm, sediment nutrients reached 95% of the peak value. The impact of height and stocking rate on the nutrients of the aeolian sediment was not universal.For example, the difference of sediment nutrient level was relatively small with different height in CK and LG, but the difference of sediment nutrient was greaterin MG and HG. The high stocking rate caused significant difference of nutrients in windblown sediment at variousheights, and this trend was particular strong for BSNE trapsnear the ground level. The average C/N of the windblown sediment was 10.88, andthe effect of grazing intensity on C/N stoichiometry was significant. Compared with the surface soil, all elements in the sedimentshowed a higher enrichment concentration, suggesting thatwind erosion have depleted most nutritious from the soil.5. The aeolian sediment nutrient fluxes in desert steppe:Nutrient flux was a comprehensive reflection of nutrient content and the quality of wind erosion particles, The fluxes of total carbon and total nitrogen in non-growth accounted for 68% and 65% of annual fluxes, respectively. The nutrient flux increased gradually with the increase of grazing intensity, and the average nutrient flux in HG was 1.8 times higher thanthat in CK. Even though nutrient content in the windblown sediment of the HG was low, the high wind erosion rate caused the greater loss of soil nutrients in the HG plots.6. Estimation of wind erosion intensity using wind tunnel in desert steppe:wind erosion intensity in CK was 115.24 t/km2.year, and 648.95 t/km2.year in HG. Compared with the heavy grazing used in typical steppe, wind erosion intensity was 10 times higher in desert steppe. The effects of grazing on soil was comprehensive and complex.Different grazing intensities had different trampling effect on soil, and livestock wandering time increased significantly due to the decrease of edible herbage in HG, therefore the relationship between soil trampling and grazing intensity is nonlinear. The mechanism of the effects of grazing and wind erosion on vegetation still needs to further investigation.7. Grazing is one of the primary measures for the grassland management. Compared to the typical steppe and meadow steppe, the coupling of wind erosion and grazing process is likely an important reason for the degradation of desert steppe. Losses of fine grainsand associated nutrients in the windblown sediment, and the more severe erosionsand in the HG were important driving forces for the grassland degradation. In recent years, the implementation of a series of grassland grazing policies and measures have played a positive role onimproving the ecological environment of the grassland, which has inhibited the trend of grassland degradation.These changes illustrated thatgrassland desertification can be effectively controlled through the macro control and policy guidance. In the future, these effective strategy and measures of grassland conservation should continueto further improve the sustainability ofthe steppe grassland in arid and semiarid regions. |
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