A convex distribution of vegetation along a stony soil slope due to subsurface flow in the semiarid Loess Plateau, northwest China

Abstract. The impacts of clouds and atmospheric aerosols on the terrestrial carbon cycle at semi-arid Loess Plateau in Northwest China are investigated, by using the observation data obtained at the SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) site. Daytime (solar elevation angles of larger than 50°) NEE of CO2 obtained during the midgrowing season (July–August) are analyzed with respect to variations in the diffuse radiation, cloud cover and aerosol optical depth (AOD). Results show a significant impact by clouds and aerosols on the CO2 uptake by the grassland (with smaller LAI values) located in a semi-arid region, quite different from areas covered by forests and crops. The light saturation levels in canopy are lower, with a value of about 434.8 W m−2. Thus, under overcast conditions of optically thick clouds, the CO2 uptake increases with increasing clearness index, and a maximum CO2 uptake and light use efficiency of vegetation occur with the clearness index of about 0.37 and lower air temperature. Under other sky conditions the CO2 uptake decreases with the cloudiness but the light use efficiency is enhanced, due to increase in the fraction of diffuse PAR. Additionally, under cloudy conditions, changes in the NEE of CO2 also result from the interactions of many environmental factors, especially the air temperature. In contrast to its response to changes in solar radiation, the carbon uptake shows a negative response to increased AOD. The reason for the difference in the response of the semi-arid grassland from that of the forest and crop lands may be due to the difference in the canopy's architectural structure.

Download Full-text

Characteristic analysis of large-scale loess landslides: a case study in Baoji City of Loess Plateau of Northwest China

Natural Hazards and Earth System Science ◽

10.5194/nhess-11-1829-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 1829-1837 ◽

Cited By ~ 26

Author(s):

H. B. Wang ◽

B. Zhou ◽

S. R. Wu ◽

J. S. Shi ◽

B. Li

Keyword(s):

Loess Plateau ◽

Large Scale ◽

Northwest China ◽

Landslide Inventory ◽

Small Scale ◽

Land Utilization ◽

Characteristic Analysis ◽

Landslide Inventory Map ◽

Loess Landslides ◽

Inventory Map

Abstract. Landslides are one of the most common geologic hazards in the Loess Plateau of northwest China, especially with some of the highest landslide densities found in Shaanxi and adjacent provinces. Prior to assessing the landslide hazard, a detailed landslide inventory map is fundamental. This study documents the landslides on the northwest Loess Plateau with high accuracy using high-resolution Quickbird imagery for landslide inventory mapping in the Changshou valley of Baoji city. By far the majority of landslides are in loess, representing small-scale planar sliding. Most of the large-scale landslides involve loess and bedrock, and the failure planes occurred either along the contacts between fluvial deposits and Neogene argillites, or partially within the bedrock. In the sliding zones of a large scale landslide, linear striations and fractures of the soils were clearly developed, clay minerals were oriented in the same direction and microorganism growths were present. From the analysis of microstructure of sliding soils, it is concluded that the Zhuyuan landslide can be reactivated if either new or recurring water seepage is caused in the sliding surface. It can be concluded that most landslides are attributed to the undercutting of the slope associated with gullying, and numerous ancillary factors including bedrock-loess interface, slope steepness, vegetation cover and land utilization.

Download Full-text

The effect of irrigation and urine application on phosphorus losses to subsurface flow from a stony soil

Agriculture Ecosystems & Environment ◽

10.1016/j.agee.2016.09.040 ◽

2016 ◽

Vol 233 ◽

pp. 425-431 ◽

Cited By ~ 5

Author(s):

C.W. Gray ◽

R.W. McDowell ◽

S. Carrick ◽

S. Thomas

Keyword(s):

Subsurface Flow ◽

Stony Soil ◽

Phosphorus Losses

Download Full-text

Culturable autotrophic ammonia-oxidizing bacteria population and nitrification potential in a sheep grazing intensity gradient in a grassland on the Loess Plateau of Northwest China

Canadian Journal of Soil Science ◽

10.4141/cjss2010-003 ◽

2011 ◽

Vol 91 (6) ◽

pp. 925-934 ◽

Cited By ~ 5

Author(s):

Tianzeng Liu ◽

Zhibiao Nan ◽

Fujiang Hou

Keyword(s):

Loess Plateau ◽

Soil Depth ◽

Grazing Intensity ◽

Northwest China ◽

Ammonia Oxidizing Bacteria ◽

Stocking Rate ◽

The Loess Plateau ◽

Soil Microbial ◽

Nitrification Potential ◽

Dry Soil

Liu, T., Nan, Z. and Hou, F. 2011. Culturable autotrophic ammonia-oxidizing bacteria population and nitrification potential in a sheep grazing intensity gradient in a grassland on the Loess Plateau of Northwest China. Can. J. Soil Sci. 91: 925–934. Grazing is known to enhance the activity of soil microbial communities in many types of grasslands; however, the potential impacts of rotational grazing activity on soil microbial functional groups remain poorly understood. We investigated the effects of 9 yr of rotational grazing by livestock on culturable autotrophic ammonia-oxidizing bacteria (AOB) population size, nitrification potential and soil properties in a semi-arid grassland of the Loess Plateau in Northwest China. Three stocking rate treatments of 2.7, 5.3 and 8.7 wether lambs ha−1were evaluated in geographically separated paddocks. Grazing increased nitrification potential and culturable AOB populations compared with ungrazed treatments. Ammonia-oxidizing bacteria populations increased from 155 bacteria g−1dry soil with 0 sheep ha−1to 16 218 bacteria g−1dry soil with 8.7 sheep ha−1. Grazing led to an increase in population of AOB at 0–10 cm soil depth, but had no effect on AOB at 10–20 cm soil depth. Nitrification potential increased from 1.21 mg NO3-N kg−1soil d−1in ungrazed treatments to 2.86 mg NO3-N kg−1soil d−1at the highest stocking rate. Soil ammonium and nitrate concentrations increased; however, total soil nitrogen and soil moisture content decreased with increased stocking rate for both sampling depths (0–10 cm and 10–20 cm). Soil organic matter was not affected by grazing treatments. Soil nitrification potential and the size of culturable AOB populations were dependent on grazing intensity, soil depth and season. This information is potentially important for the optimal selection of stocking rate for grazed ecosystems.

Download Full-text

On the factors influencing surface-layer energy closure and their seasonal variability over the semi-arid Loess Plateau of Northwest China

Hydrology and Earth System Sciences ◽

10.5194/hess-16-893-2012 ◽

2012 ◽

Vol 16 (3) ◽

pp. 893-910

Author(s):

X. Xiao ◽

H. C. Zuo ◽

Q. D. Yang ◽

S. J. Wang ◽

L. J. Wang ◽

...

Keyword(s):

Surface Layer ◽

Energy Balance ◽

Atmospheric Turbulence ◽

Loess Plateau ◽

Turbulence Intensity ◽

Source Area ◽

Northwest China ◽

The Impact ◽

Semi Arid

Abstract. The energy observed in the surface layer, when using eddy-covariance techniques to measure turbulent fluxes, is not balanced. Important progress has been made in recent years in identifying potential reasons for this lack of closure in the energy balance, but the problem is not yet resolved. In this paper, long-term data that include output of tower, radiation, surface turbulence flux and soil measurement collected from September 2006 to August 2010 in the Semi-Arid Climate Change and Environment Observatory, Lanzhou University, in the semi-arid Loess Plateau of Northwest China, were analysed, focusing on the seasonal characteristics of the surface energy and the factors that have impact on the energy balance closure (EBC). The analysis shows that (1) the long-term observations are successful; the interaction between the land and the atmosphere in semi-arid climates can be represented by the turbulent transport of energy. In addition, even though the residual is obvious, this suggests that the factors that impact the EBC are stable, and their seasonal variations are identical. The analysis also shows that (2) four factors have obvious impact on the EBC: the diverse schemes for surface soil heat flux, the flux contribution from the target source area, the low-frequency part of the turbulence spectra, and the strength of atmospheric turbulence motion. The impact of these four factors on the EBC are similar in all seasons. Lastly, the results indicate that (3) atmospheric turbulence intensity is a very important factor in terms of its impact on the EBC. The relative turbulence intensity, RIw, characterises the strength of atmospheric turbulence motion, and is found to exert a noticeable impact on the EBC; in all seasons, the EBC is increased when the relative turbulence intensity is enlarged.

Download Full-text