3.1 Land degradation
The
land can undertake a variety of functions such as offering economic
benefits, maintaining social stability, ensuring food security, and
protecting
ecological environment (Xiao et al.,
2018).
However, productive and constructive engineering always causes land
destruction,
which
is mainly manifested in the
excavation, and cover and occupation of the land.
In
the process of productive and constructive engineering, serious soil
erosion always occurs in the construction area due to a lack of
awareness of soil erosion protection and the weakness of protection
measures. Especially in the ecological environment fragile areas,
productive and constructive projects cause serious soil erosion, even
soil desertification. As shown in Figures 2 and 3, soil desertification
has been caused by the photovoltaic power generation project located in
Zhongning
County, Loess Plateau, Ningxia Province. This area is one of
the
ecologically fragile areas in China because the area is characterized by
the low vegetation cover and highly erodible loess soil, and it is
significantly impacted by climate change and human activity.
The
land-use type in the project construction area is grassland before the
photovoltaic power project is constructed. However, land leveling of
project construction area destroyed surface vegetation,
resulting
in that soil lost fine particle
(silt
and clay particle) and gradually became sandy, and eventually forming
mobile dunes after the construction of the project (Figure 3). Zhang et
al. (2006) found that desertification of the grassland and cultivated
land were the most serious for all kinds of desertification of land,
accounting for about 79.2% of the total. Besides, water erosion also
occurred in the process of construction
(Figure 4). If the constructive
area is not treated promptly after excavation, rainfall directly causes
water erosion and soil nutrients loss of exposed surface. The soil
erosion and land desertification mentioned above are the most typical
forms of land degradation. The land cover and occupation also occurred
in productive and constructive projects (Figure 5). Cover and occupation
of farmland not only narrow the area of farmland but also influence the
growth and yield of the
crop.
Rapid industrialization has encroached a huge quantity of agricultural
land and has caused a continuous reduction of farmland by an
unprecedented degree, in which 60% of non-agricultural occupied land
originates from farmland (Zhang et al., 2006; Liu et al., 2010).
Although non-agricultural land use seems not to be land degradation, the
destructive land-use change could lead to the loss of farmland. Also,
non-agricultural land use may inevitably indirectly increase the input
of chemical energy per unit area to guarantee food security due to the
loss of farmland, ultimately resulting in land degradation and
environmental pollution.