**3.3 Aeolian sediment flux**

## *3.3.1 Wind rose diagram inside and outside shelterbelt*

During the occurrence of sandstorms, the main wind directions were W, WNW, and NE, but their proportions were different inside and outside shelterbelt (**Figure 5**). Three directions inside shelterbelt accounted for 21.77%, 20.20%, and 18.00%, respectively. However, three directions outside shelterbelt accounted for 40.11%, 22.81%, and 11.69%, respectively. The wind direction inside and outside shelterbelt was similar, but the wind flow near surface ground was changed by shelterbelt. The proportion of sand driving wind in W direction outside shelterbelt was relatively high, while the proportions of other three wind directions inside shelterbelt were relatively even. Moreover, wind speed was decreased significantly by shelterbelt. The frequencies of sand driving wind exceeding 11 m·s−1 were 40.06% and 6.10% outside and inside shelterbelt, respectively, which was reduced by 84.77%. The frequencies of sand driving wind between 9 m·s−1 and 11 m·s−1 were 16.72% and 16.60% outside and inside shelterbelt, respectively. However, the wind speeds of sand driving wind between 5 m·s−1 and 7 m·s−1 together with those between 7 m·s−1 and 9 m·s−1 inside shelterbelt were both higher than outside shelterbelt.

#### *3.3.2 Horizontal aeolian sediment flux*

The horizontal sediment flux outside shelterbelt decreased significantly with the increase of height (**Figure 6**), and the relationship was expressed as *M*H = 1224.8 *h*−0.343 (*R*<sup>2</sup> = 0.93, *P* < 0.01). The horizontal sediment flux inside shelterbelt increased slowly with the increase of height, which ranged from 99.62 g·m−2 to 280.90 g·m−2. The relationship between horizontal sediment flux and height was expressed as *M*H = 130.08e0.023h (*R*<sup>2</sup> = 0.85, *P* < 0.01).

The horizontal sediment flux decreased when sandstorm passed through shelterbelt. The average horizontal sediment flux within 0 ~ 50 m was 592.87 g·m−2 outside shelterbelt during one sandstorm, whereas the average horizontal sediment flux was only 178.43 g·m−2 inside shelterbelt. The concentration of horizontal

**Figure 5.** *Sand driving wind rose inside and outside shelterbelt during occurrence of dust storms.*

*Ecological Effects of Oasis Shelterbelts in Ulan Buh Desert DOI: http://dx.doi.org/10.5772/intechopen.98679*

**Figure 6.** *Horizontal aeolian sediment flux profile inside and outside shelterbelt.*

sediment flux was reduced by 69.90%. As the height increased, the difference between two sites gradually decreased with a trend of gradual overlap.

#### *3.3.3 Aeolian deposition flux*

The aeolian deposition flux decreased significantly with the increase of height inside and outside shelterbelt (**Figure 7**). Their relationship was expressed as *MV* = 6.64 *h*−0.42 (*R*<sup>2</sup> = 0.96, *P* < 0.01) outside shelterbelt and *MV* = 4.42 *h*−0.40

**Figure 7.** *Aeolian deposition flux velocity profile.*

(*R*<sup>2</sup> = 0.89, *P* < 0.01) inside shelterbelt. The aeolian deposition flux below 24 m decreased gradually with height inside and outside shelterbelt. The aeolian deposition flux above 24 m continued to decrease gradually outside shelterbelt. However, the aeolian deposition flux gradually increased above 24 m inside shelterbelt. The average aeolian deposition flux during one sandstorm within 50 m was 2.85 g·m−2 outside shelterbelt, while it was only 2.04 g·m−2 inside shelterbelt. Moreover, the difference between the aeolian deposition flux inside and outside shelterbelt also gradually decreased as the increase of height with a trend of gradual overlap.
