| 其他摘要 | The fertile black soil in Northeast China is famous for the "granary." However, the
long excessive reclamation had led to increasingly serious soil erosion, and cultivated
slope had become a major sediment sources. So the serious degradation of quality of
cultivated black soil had posed a serious threat to the food security in China. Therefore, an
understanding of erosion rules is important for designing conservation programs and
deepening the erosion mechanism.
In this paper, a straight cultivated for nearly 100 years slope with 500 meters long, 3°
slope gradient, southward and a convex cultivated for more than 50 years slope with 350
meters long，northward were selected in Keshan county in Hei Long Jiang Province to
study the 50-100 years erosion rates of cultivated black soil, and analysis the soil physical
and chemical properties as well as nutrient content, in order to discuss the erosion rules and
the degradation process of the cultivated black soil. Major methods contain field sampling
and laboratory analysis, 137Cs and 210Pbex composite tracer technology, USLE model,
wavelet analysis, SPSS, and so on. The main results as follow:
(1) The spatial distribution of soil erosion intensity on the long and straight cultivated
slope was studied using 137Cs measurement and wavelet analysis. The results showed that
there was a fluctuant period of soil erosion intensity with 142m along 4 transects
downslope, which suggested that the downslope intensity of soil transporting alternately
changed between weak and strong due to the impact of long-term erosive rainfall.
Moreover, the best fitting result (R2>0.96) of the soil erosion rates along the four transects
was the sum of sine function. It was further convinced the correctness of the fluctuant of
the erosion intensity on the study slope; the same study of the convex slope showed the
downslope erosion intensity was not periodic fluctuated, so the wavelet analysis was not applicable for the erosion study of other shapes of slope.
(2) The 137Cs contents in soil samples collected on the slope flat were analyzed and the
results showed that 137Cs inventory of all samples were less than the 137Cs reference
inventory, and the primary reason was there existed some wind erosion. Because 137Cs
measurement could get the total erosion rates and USLE model could measure the water
erosion rate, the contributions of water and wind erosion rates were partitioned and the
results showed that the annual mean erosion rate on the straight slope and convex slope
was 3054 t km2 a-1 and 3548 t km2 a-1 respectively. Meanwhile, the wind erosion rate was
631 t km2 a-1 and 1155 t km2 a-1, 20.7% and 32.6% respectively because of the different
slope aspect, which means that nearly 0.5~1mm soil was blew off in the study area every
year. The water erosion rate proportion of the two slope was 79.3% and 67.4%, thus water
erosion was still the dominant erosion style in the study area. Accordingly, the prevention
needs to be considered adequately about the different influence by water and wind and
comprehensively designed.
(3) By comparing the profile distributing of the SOM content of the two slope, it was
found that the SOM content in straight slope cultivated for 100 years and convex slope
cultivated for 54 years were 4.3% and 5.6% respectively, soil degradation was more
serious in straight longer reclaimed slope obviously. By stepwise regression of the erosion
rate and nutrient content on two slopes, it was found that erosion rate Y can be represented
by function of nutrient content, for the straight slope, that was:
Y=189082.80X-14503.31(R=0.506), X was TP content. And, for the convex slope, Y=
2282.516X-16762.25(R=0.646), X was SOM content. These functions may show the
intensive relations between soil nutrient loss and soil erosion. By estimating the nutrient
loss of study area, the results indicated that the soil loss amount in straight slope were
241.87、10.94、6.14 t km2 a-1 of SOM, TN and TP respectively, but the nutrient loss on
convex slope were more 367.76、14.22、9.14 t km2 a-1 respective of SOM, TN and TP.
(4) The soil erosion rate of the two cultivated slope was studied using 137Cs and
210Pbex tracer measurement, the results showed that on the straight cutivated for nearly
100 years slope, due to the little difference of rainfall during the last 100 years in
this region, the erosion rate derived from 137Cs and 210Pbex should be similar, and the
results showed the erosion rate were 2812 t km2 a-1 and 2575 t km2 a-1 respectively by 137Cs and 210Pbex, though 137Cs traced soil erosion rate of more than 50 years while
210Pbex nearly 100 years, so it can be concluded that the two tracer measurement
were both correct in this area. However, on the convex cultivated for 54 years slope,
cause the little erosion before reclaimed, the erosion rate in the last 100 years by
210Pbex was 1890 t km2 a-1, which was significantly less than after reclaimed: 3771 t km2
a-1 derived from 137Cs measurement. Using the weighed average method, the erosion rate
of the convex slope before reclaimed can be got, it was 319 t km2 a-1 and nearly 12 times
less than that of after reclaimed. It could be concluded, because of the excessive
reclamation and other unreasonable utilizations by human, the soil erosion had been
accelerated seriously. Therefore, the fertile land in black soil region needs to be
protected scientifically and quickly. |
修改评论