壤中流和土壤解冻深度对黑土坡面融雪侵蚀的影响

融雪侵蚀是东北黑土区土壤流失的一种重要形式,而目前有关壤中流和土壤解冻深度对融雪径流侵蚀的影响研究较少。本研究采用室内模拟试验,设计两个融雪径流量(1和4 L·min^-1)和两个土壤解冻深度(5和10 cm),以及有、无壤中流处理,分析壤中流和土壤解冻深度对黑土区坡面融雪侵蚀的影响。结果表明: 1)壤中流处理下坡面融雪径流深度和侵蚀量分别是无壤中流处理的1.1～1.2倍和1.3～1.9倍。两个融雪径流量下,当土壤解冻深度由5 cm增加到10 cm时,无壤中流处理下坡面融雪径流深度和侵蚀量分别增加10.0%～13.5%和15.4%～37.1%;而有壤中流处理下坡面融雪径流深度增加6.5%～8.5%,融雪侵蚀量则无显著变化。2)坡面细沟发育受壤中流、土壤解冻深度和融雪径流量的综合影响,各处理下细沟侵蚀量占坡面融雪侵蚀量的72%以上。3)壤中流发生使坡面径流流速和径流剪切力分别增加20.3%～23.2%和37.0%～51.3%,Darcy-Weisbach阻力系数减少9.0%～21.4%,从而增加了坡面融雪侵蚀量;且壤中流发生促进了坡面细沟发育,其细沟侵蚀量较无壤中流处理增加43.6%～69.9%,也导致坡面融雪侵蚀量增加。无壤中流条件下,土壤解冻深度加剧坡面融雪侵蚀的主要原因是随着土壤解冻深度的增加,坡面径流侵蚀能力和可蚀性物质来源增加,导致融雪径流侵蚀量增加。此外,土壤解冻深度对壤中流条件下细沟形态发育也有明显的影响,土壤解冻深度为5 cm时,细沟横向加宽作用显著;而土壤解冻深度为10 cm时,细沟下切侵蚀作用更显著。本研究加深了对黑土区融雪侵蚀机理的认识,可为水蚀模型的研发提供理论指导。

Impacts of seepage flow and soil thaw depth on hillslope snowmelt erosion in Chinese Mollisol region

Snowmelt erosion is an important way of soil loss in Chinese Mollisol region. However, little is known about the effects of seepage flow and soil thaw depth on hillslope snowmelt runoff erosion. An indoor simulated experiment was conducted to analyze the impacts of seepage flow and soil thaw depth on hillslope snowmelt erosion. There were two snowmelt flow rates (1 and 4 L·min^-1), two soil thaw depths (5 and 10 cm), and two near-surface hydrological conditions (with and without seepage flow). The results showed that hillslope runoff depth and soil erosion amount in the treatment with seepage flow were 1.1 to 1.2 times and 1.3 to 1.9 times of those in the treatment without seepage flow, respectively. Under two snowmelt flow rates, when soil thaw depth increased from 5 cm to 10 cm, hillslope runoff depth and soil erosion amount increased by 10.0% to 13.5% and 15.4% to 37.1% in the treatment without seepage flow, respectively. In the treatment with seepage flow, when soil thaw depth shifted from 5 cm to 10 cm, hillslope runoff depth increased by 6.5% to 8.5%, and soil erosion amount remained stable. Moreover, hillslope rill development was comprehensively influenced by seepage flow, soil thaw depth, and snowmelt flow rate, with rill erosion amount occupying more than 72% of hillslope snowmelt erosion amount. Compared with the treatment without seepage flow, flow velocity and shear stress under the treatment with seepage flow increased by 20.3% to 23.2% and 37.0% to 51.3%, respectively; but Darcy-Weisbach friction coefficient reduced by 9.0% to 21.4%, which caused an increase of hillslope snowmelt erosion. In addition, seepage flow enhanced rill development, which caused rill erosion amount to increase by 43.6% to 69.9% compared with the treatment without seepage flow, and it further resulted in the increase of hillslope snowmelt erosion amount. The main reason for soil thaw depth enhancing hillslope snowmelt erosion amount under the treatment without seepage flow was that both sloping runoff erosivity and erodible materials increased with increasing soil thaw depth. Furthermore, soil thaw depth had a significant impact on hillslope rill morphology development under the treatment with seepage flow. Rill widening process was dominated when soil thaw depth was 5 cm, whereas rill incision process was dominant when soil thaw depth was 10 cm. This study could improve the understanding of hillslope snowmelt erosion mechanism in Chinese Mollisol region and provide theoretical guidance for the development of water erosion model.