水保所知识产出(1956---)知识库

大气氮沉降的增加可能会通过草地群落进而影响坡面流水动力特性。选取黄土高原典型地带性草本白羊草为研究对
象，通过设置不同施氮处理（0，2.5，5，10 g/(m 2 ·a)，以N 计，下同）模拟氮沉降，采用人工模拟降雨，探究土壤有效氮升高
对白羊草群落季节变化及坡面流水动力特征的影响。结果表明，一定程度的施氮可有效增加白羊草盖度，促进藻结皮的生长，
但会抑制苔藓结皮的发育。施氮使 Darcy-Weisbach 阻力系数和曼宁糙率系数分别降低了 68.6%～71.5%和44.7%～47.4%；平均
流速加快了 32.0%～44.0%，径流深减小了 25.1%～28.7%，同时，使径流剪切力和水流功率显著增加，过水断面单位能减少。
随着季节变化，9 月白羊草群落坡面 Darcy-Weisbach 阻力系数和曼宁糙率系数分别较 6—8 月显著增加了 220.2%～496.9%和
79.5%～139.4%，平均流速减缓了 23.5%～29.7%，径流深增加了 36.4%～66.9%，径流剪切力和水流功率均显著降低，过水断
面单位能增加。降雨强度对坡面流特征也存在显著影响。随着降雨强度的增大，坡面流阻力减小，进而导致流速、径流深及水
流功率增加。草地具有良好的调控坡面流的作用，然而大气氮沉降的增加可能会加剧草地群落坡面土壤侵蚀。

Atmospheric nitrogen deposition is one of the most concerned issues in global changes. Grassland communities
respond significantly to nitrogen deposition and then have influences on soil erosion. In this study, the typical zonal grass
species (Bothriochloa ischaemum (Linn.) Keng) on the Loess Plateau was selected as the research object. The nitrogen
deposition process was simulated through nitrogen additions, and the influences of seasonal changes of vegetation
communities on overland flow hydrodynamics were explored by the artificial simulated rainfall method. This experiment was
conducted at the Institute of Soil and Water Conservation, CAS & MWR (108°04′27.95″ E and 34°16′56.24″ N), Yangling
City, Shaanxi Province, China in 2016. Five treatments with different nitrogen addition levels of 0, 2.5, 5, 10 g/(m 2 ·a) (based
on N) were designed and they were regarded as N 0 , N 2.5 , N 5 and N 10 , respectively. All the treatments were subjected to
simulated rainfall under three rainfall intensities of 60, 90 and 120 mm/h monthly from June to September. In addition, from
May to September, the coverage of Bothriochloa ischaemum (Linn.) Keng and biological soil crusts before the first rainfall test
of each month were monitored. During the rainfall, the mixed samples of runoff and sediment were collected when the flow
velocity became stable, and the surface flow velocity and water temperature were measured at the same time. According to the
formula of open channel flow, the hydrodynamic parameters such as flow discharge, mean flow velocity, water depth,
Reynolds number, Froude number, Darcy-Weisbach resistance coefficient, Manning’s roughness coefficient, flow shear stress,
stream power and unit energy of water-carrying section were calculated. The results showed that nitrogen additions promoted
the coverage of Bothriochloa ischaemum (Linn.) Keng and algal crusts, but inhibited the moss crusts. Compared with no
nitrogen treatment (N 0 ), the overland flow resistances values of treatments of N 2.5 , N 5 and N 10 were significantly decreased by
68.6% to 71.5% (Darcy-Weisbach resistance coefficient) and by 44.7% to 47.4% (Manning’s Roughness coefficient). The
mean flow velocity values were accelerated by 32.0% to 44.0% and water depth values were reduced by 25.1% to 28.7%. The
flow shear stress and stream power values were increased significantly by 228.7% to 327.4% and 313.5% to 543.2%,
respectively. The unit energy of water-carrying section values was reduced by 24.4% to 27.9%. With seasons changing, the
resistance values to overland flow in September were increased significantly by 220.2% to 496.9% (Darcy-Weisbach
resistance coefficient) and 79.5% to 139.4% (Manning’s roughness coefficient), compared with the early-mid period (from
June to August). Furthermore, the mean flow velocity values were decreased by 23.5% to 29.7%, the water depth values
increased by 36.4% to 66.9%. The flow shear stress and stream power values were decreased by 97.7% to 99.4% and 98.1% to
99.7%, respectively, and the unit energy of water-carrying section values was increased by 20.8% to 64.2%. Moreover,
overland flow resistance was decreased with the increase of rainfall intensity, which promoted mean flow velocity, water depth,
and stream power. All in all, with the nitrogen addition increasing, the overland flow resistance was significantly reduced, the
flow velocity was accelerated, the water depth was decreased, the flow shear stress and stream power were significantly
increased, and the unit energy of water-carrying section was reduced. Grassland plays vital roles in regulating overland flow.
However, the increase of atmospheric nitrogen deposition may exacerbate soil erosion on the slope. Overall, the results can
provide a scientific instruction for grassland vegetation construction and soil erosion control in the Loess Plateau.