1. Introduction
Wind erosion and particulate matter emissions are important and
non-negligible reasons that cause landscape degradation and threaten
human production and life (Borrelli et al., 2016; Deetz et al., 2016).
Wind erosion causes a large amount of soil loss in farmland or forest
land. Additionally, the emission of particulate matter caused by wind
erosion carries a large amount of pesticides, microorganisms and heavy
metal elements for migration (Van Pelt and Zobeck, 2007; Tatarko et al.,
2020; Whicker et al., 2006). In recent years, large-scale accidents
caused by wind erosion and particulate matter are no longer unusual (Li
et al., 2018; Middleton, 2017). Effects of wind erosion and particulate
matter emissions range from human health issues to global climate change
(Goudie, 2014; Lambert et al., 2008). Influenced by the source of
particulate matter emissions, previous studies focused on densely
populated urban areas (Currie and Bass, 2008; Jiakai et al., 2016).
However, farmland areas are also an important contribution area of
particulate matter emissions (Korcz et al., 2009). Therefore, land
degradation caused by wind erosion and particulate matter emissions
should be analyzed in detail (Schmidt et al., 2017; Tatarko et al.,
2020).
The factors influencing the natural wind erosion and particulate matter
emission processes can be divided into physical and chemical factors,
including: soil stability, soil properties, soil texture, soil density,
soil water content, land cover, soil nutrients, etc. (Gillies et al.,
2017; Hagen et al., 2010; Kohake et al., 2010; Zou et al., 2018). The
soil particle size distribution is highly sensitive to the wind erosion
process (Larney and Bullock, 1994). Previous studies have shown that
wind erosion is prone to occur when the soil particle size ranges from
0.02 mm to 0.84 mm. Particles with size between 0.05 mm and 0.5 mm are
the most easily eroded particles (Chepil, 1955; Skidmore and Powers,
1982; Zou et al., 2018), sometimes even if the surface sand content is
low, it may become a high PM10 emitter (Feng et al., 2011; Sweeney et
al., 2011). When other factors remain constant, the material with large
particle size and low density is more easily transported by wind (Zobeck
et al., 2013), and soil density has less variability than soil texture
(Kohake et al., 2010; Menut et al., 2013; Shahabinejad et al., 2019).
Previous studies have shown that as soil density increases, soil
erodibility under wind conditions will decrease gradually (Campbell et
al., 2002). Tillage and watering are main ways that rapidly change soil
density and soil properties, affecting wind erosion and dust emission
(Larney and Bullock, 1994). The surface aerodynamic parameters of
different soil properties are variable, especially in arid and semi-arid
areas. This difference has a profound impact on the wind erosion process
(Campbell et al., 2002; Cheng et al., 2017; Zou et al., 2018).
The influence of soil nutrients is mainly reflected in the organic
matter content. Non-agricultural soils increase soil organic matter
through various methods, such as litter decomposition. Thus, as the
organic matter increases, soil particles are aggregated and not easily
dispersed (Mendez et al., 2006; Panebianco et al., 2016). Although
agricultural soils have regular fertilization operations, the continuous
cultivation process will inevitably continuously degrade the organic
matter content in the soil, resulting in poor aggregation of soil
particles and tendency to erosion (Acikgoz et al., 2017).
Irrigation can keep the soil surface moist and minimize wind erosion,
but wind can use the evaporation process to continuously take away the
water in the soil and reduce the cohesion of soil particles (Larney and
Bullock, 1994). Therefore, the influence of soil water content changes
is highly correlated with time.
The emission of particulate matter in wind erosion is directly related
to the amount of wind erosion itself. The reduction of particulate
pollution is a complex and non-linear process (Chang et al., 2019).
Therefore, treatment from the source (such as vegetation or soil crust
coverage) is a relatively efficient method. Biological soil crusts
(BSCs), as one of the means of ground cover, can effectively inhibit
wind erosion and impact significantly on the separation and
transportation of particles of different sizes (Miralles-Mellado et al.,
2011; Neuman et al., 1996). However, BSCs are also one of the sources of
particulate matter emissions, which may have a higher level of microbial
diversity, thereby endangering human health (Abed et al., 2012).
Overall, it is relevant to study wind erosion and particulate matter
emission under the BSC cover.
In order to prevent and control wind erosion and particulate matter
emissions, physical, chemical and biological methods have been adopted.
For instance, Schmidt et al. (2017) used the Index of Land
Susceptibility to Wind Erosion (ILSWE) to quantify the elements of wind
erosion, and assessed the wind erosion potential in Europe. In addition,
Tian et al. (2018) used chemical solutions to consolidate the surface of
the soil, which significantly increased the anti-erosion strength of the
surface. Chang et al. (2021) suggested that windbreak forest belts
effectively reduced wind erosion by 20% and significantly weakened PM10
emission concentration. Among all the prevention and control measures,
biological measures are effective and nearly natural. However, most
biological methods require a long growth period and have inherent
limitations (Diouf et al., 1990; Maleki et al., 2016; McClure, 1998).
Therefore, the use of BSCs for rapid growth and mulching is not only a
more efficient wind erosion and particulate emission prevention and
control method, but also provides a better growth basis for future
vegetation succession. BSCs can effectively combine fine particles with
each other and increase their threshold wind speed (Belnap and Gillette,
1998; Reynolds et al., 2001; Zhang et al., 2014). Previous studies have
shown that mycorrhiza can significantly increase the degree of root
colonization of plants during sowing, thereby decreasing the erodibility
(Burri et al., 2013). Therefore, the use of BSCs to prevent wind erosion
and particulate matter emission has good long-term benefits. Zhang et
al. (2014) used dust fall and soil crust distribution to describe the
stability of the wind and sand environment on a typical desert railway
protection system, proving that it is beneficial to use soil crust to
artificially improve the wind and sand environments.
In order to understand the process of wind erosion and particulate
matter emission, researchers more often use wind tunnel methods. Under
natural conditions, changes in wind erosion and particulate emissions
are more sensitive to height. Zobeck and Van Pelt (2006) suggested that
the emission concentration of particulate matter in the height range of
2-5 m is 2-5 times that in the height range of 5-10 m.
Generally speaking, bryophytes
have a pseudo-leaf and pseudo-stem structure, and the formed moss crust
is also relatively thick. Algae plants do not differentiate into leaves
and stems. Thus, the algae crust is relatively flat (Belnap et al.,
2013). Although the aerodynamic roughness length provided by the two
types of biological soil crusts only measures millimeters or
micrometers, their ability to prevent and control wind erosion and
particulate matter emissions is still significant. The wind erosion
material in the wind tunnel mainly moves horizontally, so the amount of
wind erosion and the emission of particulate matter can be expressed by
the horizontal flux (Panebianco et al., 2016), which has higher research
efficiency. Bu et al. (2015) optimized the combination of soil water
content, crust coverage, and vegetation coverage through experiments,
and gave the most effective combination to reduce wind erosion. However,
the soil water content is a constantly changing instantaneous value
under the action of wind. Therefore, this combination method cannot be
effectively used in practice. Copeland et al. (2009) used a wood-based
long-strand material and agricultural straw to test wind erosion and
particulate matter emissions. Their results show that wood materials
have higher wind speed adaptability than agricultural straws, and wood
materials have reduced wind erosion and particulate matter emissions by
90%, under a wind speed of 11 m/s. Although straw cannot significantly
reduce the total wind erosion, PM10 emissions have dropped by 75%. In
addition, Tatarko et al. (2020) conducted wind tunnel tests on 15
typical soils in the United States and concluded that abrasion
coefficients and particulate matter emissions are more sensitive to soil
types, soil textures and farming methods.
For the prevention and control of suspended dust generated by wind
erosion, it is not only necessary to understand its source (Mirzamostafa
et al., 1998; Hui et al., 2019), but also to clarify the content and
proportion of particles of different sizes. Currently, studies have
focused on the ratio of particles with different particle sizes
(Cowherd, 2006; Feng et al., 2011; Li et al., 2015; Tatarko et al.,
2020). Scholars have developed formulas for predicting particulate
matter emissions (Tatarko et al., 2020), although some researchers
believe that this empirical formula may lack universality (Sullivan and
Ajwa, 2011).
Traditionally, in the research of farmland wind erosion and particulate
matter emission control, BSCs have been studied as a prevention and
control method. However, studies that can clarify the quantitative
relationship between particulate matter emissions and wind erosion
processes are not present in the literature (Li et al., 2015; Tatarko et
al., 2020). This study will take two common BSCs and explore the
thresholds of the proportion of particulate matter emissions during wind
erosion, in order to provide an effective reference for the targeted
management of wind erosion and particulate matter emissions.