Using 137Cs to estimate wind erosion and dust deposition on grassland in Inner Mongolia-selection of a reference site and description of the temporal variability
Using 137Cs to estimate wind erosion and dust deposition on grassland in Inner Mongolia-selection of a reference site and description of the temporal variability
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DOI：
10.1007/s11104-011-0964-y
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发表时间：
2012-02-01
期刊：
影响因子：
4.9
通讯作者：
Sommer, Michael
中科院分区：
文献类型：
--
作者：
Funk, Roger;Li, Yong;Sommer, Michael
本研究的目的是识别风蚀和沙尘沉积的区域，并基于Cs-137技术量化不同放牧强度对草原土壤再分配率的影响。由于该方法使用参考清单作为侵蚀或沉积的阈值，因此任何其他地点作为源或汇的分类取决于该参考站点的准确选择。在不同放牧强度的大针茅和羊草优势种草地上进行了Cs-137清单和深度分布的测量。在耕地、植物覆盖的沙丘和冲积平原上进行了额外的测量。风致土壤侵蚀和粉尘沉积速率由Cs-137清单通过“剖面分布”和“质量平衡II”模型计算，参考点的选择是基于流体动力学和过程决定参数。所选地点应符合以下四个条件：(I)位于沉积速率明显较低的山顶位置；(Ii)有足够的植被覆盖以防止风蚀；(Iii)平面以避免水蚀；及(Iv)在较高海拔的风/沙尘阴影下。测量的Cs-137参考清单为1967年(+/-102)BQM(-2)，位于中度放牧羊草草原的顶端。其他地点的Cs-137库存量从重度放牧地的1330 BQM(-2)到河流沉积物的5119 BQM(-2)不等，分别代表年平均土壤流失量高达130 TKM(-2)和沉降量高达540 TKM(-2)。计算的未放牧羊草样地沙尘沉降量的年平均值与近50年的沙尘暴频率相关，从而描述了年沙尘沉降量的时间变化，从20世纪60年代的约154TKM(-2)到近期的26TKM(-2)。在此基础上，80%的沙尘沉降量可与20世纪60年代至70年代末的沙尘沉积有关，只有20%的沙尘沉降量与1980至2001年的沙尘沉降量有关。Cs-137技术是一种很有前途的方法，可以评估放牧强度和土地利用类型对半干旱草原风生土壤和沙尘再分布过程的空间变异性的影响。然而，需要付出相当大的努力来确定可靠的参照点，因为风引起的侵蚀和沉积可能发生在同一地点。由Cs-137剖面资料得到的沙尘沉降速率与沙尘暴频率相结合，有助于更好地重建该地区沙尘沉降和风蚀的时间变异性。计算的近期沉积速率约为20TKM(-2)，与其他作者的数据符合得很好。
The aims of this study were to identify areas of wind erosion and dust deposition and to quantify the effects of different grazing intensities on soil redistribution rates in grasslands based on the Cs-137 technique. Because the method uses a reference inventory as threshold for erosion or deposition, the classification of any other site as source or sink for dust depends on the accurate selection of this reference site.Measurements of Cs-137 inventories and depth distributions were carried out at pasture sites with predominant species of Stipa grandis and Leymus chinensis which are grazed with different intensities. Additional measurements were made at arable land, plant-covered sand dunes and alluvial plains. Wind-induced soil erosion and dust deposition rates were calculated from Cs-137 inventories by means of the "Profile-Distribution" and the "Mass Balance II" models.The selection of the reference site was based on fluid dynamical and process-determining parameters. The chosen site should meet the following four conditions: (i) located at a summit position with obviously low deposition rates, (ii) sufficient vegetation cover to prevent wind erosion, (iii) plane to exclude water erosion and (iv) in the wind/dust shadow of a higher elevation. The measured reference inventory of Cs-137 was 1967(+/- 102) Bqm(-2) located at a summit position of moderately grazed Leymus chinensis steppe. The Cs-137 inventories at other sites ranged from 1330 Bqm(-2) at heavily grazed sites to 5119 Bqm(-2) at river deposits, representing annual average soil losses of up to 130 tkm(-2) and deposits of up to 540 tkm(-2), respectively. The calculated annual averages of dust depositions at ungrazed Leymus chinensis sites were related to the dust storm frequencies of the last 50 years resulting in a description of the temporal variability of annual dust depositions from about 154 tkm(-2) in the 1960s to 26 tkm(-2) at recent times. Based on this quantification already 80% of the total dust depositions can be related to the 20 years between the 1960s and the end of the 1970s and only 20% to the time between 1980 and 2001.Cs-137 technique is a promising method to assess the effect of grazing intensity and land use types on the spatial variability of wind-induced soil and dust redistribution processes in semi-arid grasslands. However, considerable efforts are needed to identify a reliable reference site, because erosion and deposition induced by wind may occur at the same places. The combination of the dust deposition rates derived from Cs-137 profile data with the dust storm frequencies is helpful for a better reconstruction of the temporal variability of dust deposition and wind erosion in this region. The calculated recent deposition rates of about 20 tkm(-2) are in good agreement with data of other authors.