| 其他摘要 | With the progress of human history, the human being has changed the world so widely that
human being has touched every corner of the world. Soil erosion is a natural process, however,
due to human activities, great changes has taken place in erosion forms, the degree of loss, the
spatial distribution and evolution processes. Understanding how human beings influence the
soil erosion and related mechanism and processes and quantifying this influence is of great
importance to readjustment of the human activities and soil and water conservation policy
making.
This paper, took the Yanhe River watershed and Zhifanggou watershed as case study areas,
analyzed surface morphology and vegetation cover using PE-factor (soil and water
conservation engineering measures) and C-factor (vegetation and management factor) and
quantified the impact of human activities on soil erosion environment, and clarified the
variation in the vegetation pattern at the landscape scale. Meanwhile, taking a typical small
watershed of Zhifanggou watershed as an example, reconstructed artificial terrain DEM of
different time series using Hc-DEM method, and analyzed the evolution of the topographic
factors such as slope degree, and slope length and related environmental factors. After that,
a quantitative evaluation of the evolution of soil erosion in Zhifanggou in past 70 years and
the impact of human activities on this evolution was done. The main conclusions are as
follows:
(1) Delineated the surface morphology using the factor value of soil and water conservation
engineering measures, studied the extent of the impact of human activities on topography by
building an index of human activities topographic effects, and quantitatively analyzed the
human impact on the evolution of surface morphology in Zhifanggou watershed and Yanhe
River watershed The values of engineering measures factor value linearly decreased with
time in Zhifanggou watershed and Yanhe River watershed, and the changes in surface
morphology changes could help control soil erosion. The trends of topographic index Ht of human activities in different periods showed that the extent and scope of surface morphology
resulted from human activities continued to increase in Zhifanggou watershed from 1938 to
1987, then to decrease except for a slight increasing during the period from 1999 to 2003. The
extent and scope of changes in surface morphology due to human activities increased first and
then decreased, but the most obvious impact had been observed in in period from 1997 to
2000. The analysis of man-made terrain DEM in Zhifanggou watershed showed that slope,
slope length, slope factor, slope length factor, slope of slope length factor showed a
decreasing trend as to the impact of human activities on terrain continued, which the slope
changes with minimal degree, the slope length changes with largest degree. The change in
slope length was bigger than that in slope. The average annual decreasing rate was 3.58% and
11.94% respectively, and the terrain factor valued decreased with the increase of basic
farmland and residential area.
(2) Described the surface cover(vegetation) using the value of cover-management factor,
analyzed the extent and scope of the impact of human activities on surface cover by building
human activities vegetation effects indexes, and quantitatively analyzed the human impact on
vegetation cover in Zhifanggou watershed and Yanhe River watershed. The
cover-management factor values of Zhifanggou watershed showed a 4 times parabola
relations with time, and increased first then decreased in Yanhe River watershed. The analysis
of the variation of the vegetation index Hc suggested that human activities impacted
vegetation by destruction in Zhifanggou watershed from 1938 to 1958, then by restoring
activities, and this restoring effect was most obvious from 1987 to 1999. The disruptive
impact of vegetation due to human activities decreased, and the restoring impact increased in
Yanhe River watershed from 1986 to 2006. Big changes occurred in the landscape pattern of
various vegetation factors in Zhifanggou watershed and Yanhe River watershed, the area of
woodland and farmland changed significantly in Zhifanggou watershed, and the area of
grassland changed a little, the landscape diversity and evenness index decreased first and then
increased, while the woodland, grassland and farmland changed greatly in Yanhe River
watershed, the landscape diversity index and evenness index increased year by year.
(3) During the studying period from 1938 to 2010, soil erosion experienced a dramatic
increasing period and then a decreasing one. Soil erosion modulus was the largest, and from
then on showed a generally downward trend. In 1938, soil erosion of middle degree was the
mainly erosion type, while severe erosion was the mainly erosion type during period from
1958 to 1978. Nevertheless, soil erosion declined in years from 1978 to 1998. From 1999, the
area associated with slight erosion averaged 3.85km2, while extreme erosion accounted for
8.96% of the total area of the watershed. Erosion was significantly influenced by topography at a watershed-scale and increased dramatically with slope increase. The soil erosion mainly
occurred in slopes above 25°. Noticeably, more soil erosion was from slopes more than 35°
and south facing slopes produced more erosion than north facing ones. Among various land
use types, the slightest erosion was associated with forestland, and the strongest one with
deserted land. Farmland was the major source of erosion during 1958-1998, while in the
following period, the key area for soil conservation switched to grassland. Though the
eco-environment of Zhifanggou watershed has been markedly improved through 30 years of
comprehensive management, severe soil erosion on steep slope of gullies and hills remained a
problem demanding attention.
(4) We took 1938 as a base period with exacerbation of soil erosion by human beings, and
analyzed the role of human activity in the increase of soil erosion by comparing the
differences of soil erosion in 1958 and 1938; we then took 1958 as a base period with the
decrease of soil erosion by human activities, quantitatively analyzed the impact of human
activity on the decease of soil erosion in different periods by comparing the differences of soil
erosion between 1978-2010 and 1958, Compared to 1938, the increased soil erosion was
249111.57t in 1958 due to the human activities, of which the increase of soil erosion due to
vegetation cover changes was 310890.84t while the changes in surface morphology reduced
soil erosion by 61779.27t. Compared to 1958, the soil erosion decreased year by year due to
the human activities from 1978 to 2010.The reduced erosion was about 11870.47-140085.99t,
of which 7078.48-14442.88t was reduced by the increase of vegetation cover, and
4971.98-25301.57t was reduced due to surface morphology change. Compared to the changes
in surface morphology, vegetation cover changes reduced more soil erosion.
Key words: soil erosion environment, GIS, quantitative characterization, human activity,
Loess Plateau |
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