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Filling Gullies to Create Farmland on the Loess Plateau Qiang Liu, Yunqiang Wang, Jing Zhang, and Yiping Chen* State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, 710075, China land area of the Plateau. Desertification in the Loess Plateau region does not entirely result from low amounts of precipitation but rather to the poor absorbing capacity of the soils, which is exacerbated when poorly managed. Intense summer rainstorms over steep slopes induce large amounts of runoff. Filling gullies could drastically change the ravinelike landforms and consequently would eliminate the “potential energy difference”, which is the primary factor in soil water erosion. Assuming good land management practices were put in place after the gullies were filled, runoff amounts and flow velocities would be considerably reduced from the leveled land with accompanying reductions in soil and water losses. Increased rainwater infiltration would ameliorate or eliminate desertification on the Plateau. The situation can be likened to that in other countries such as Iran and South Israel (Figure 1). Israel achieves
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he Loess Plateau region of China covers an area of about 648 700 km2 and supplies a large proportion of the nation’s food. The soils derived from loessial deposits are poorly structured and are highly susceptible to erosion by water in an area that covers about 70% of the Plateau.1 In its most severe form, water erosion has resulted in gully formation so that the Loess Plateau now has a unique landscape that is incised by numerous gullies, of which 270 000 are longer than 500 m, which hinder agricultural and industrial development. Therefore, the further restoration of this large area of the Loess Plateau is a serious problem confronting China. Currently, the typical approach is to continue to build more check-dams to trap the sediment transported in the gully system. However, during the 400 year history of using check dams to intercept sediments from the Loess Plateau, the sediments in the Yellow River did not necessarily decrease, but even increased at times.2 Therefore, we deem that filling gullies to create farmland on the Loess Plateau should be considered. The suggested approach would be to remove soil from the higher hills, the ridges of which would be flattened in the process, and to push the soil into the gullies, compacting it to make it less susceptible to tunneling and subsidence, and ultimately to level the surface to create flat or gently sloping fields. Afterward, the new topsoil should be cultivated to make it suitable for crop growth. This measure of filling gullies would have the following advantages:
Figure 1. Comparison of precipitation and evaporation among Iran, South Israel (SI) and the Loess Plateau of China (LPC).
sustainable development by increasing water use efficiency, including the reuse of water, control of soil and water losses, and ecological environmental engineering. In comparison, the mean annual precipitation on the Loess Plateau is about 400 mm and the mean annual evaporation is 1500 mm, which means that the situation is better than that in Israel (Figure 1). Eliminating water losses via gullies by filling them would allow the Plateau to take advantage of the water resource potential since the precipitation can satisfy the requirements of both agriculture and the natural ecosystems.
(1) Filling gullies saves water The total area of land that is undergoing desertification in the Loess Plateau region covers about 55% of the total © 2013 American Chemical Society
Received: April 3, 2013 Accepted: June 14, 2013 Published: July 1, 2013 7589
dx.doi.org/10.1021/es402460r | Environ. Sci. Technol. 2013, 47, 7589−7590
Environmental Science & Technology
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Notes
(2) Filling gullies to create farmland for food security The area of cultivable land per capita has continued to decrease since the 1950s in China.3 The reason for this decline is not only due to the population increase but also to the increased industrialization and urbanization, especially over the past 10 years, the abandonment of unsuitable farmland under government environmental protection measures, and to land degradation that includes gully formation. Currently, the total amount of farmland approaches 0.7 billion hectares, which is the lower limit set by the Chinese government that would ensure food security for the Chinese people. However, the population continues to grow and it is estimated that it will reach 1.6 billion by 2030. Should this occur, there would be a food deficit of about 200 million tons,4 which presents a major challenge for the Chinese. Filling the gullies or reducing their slopes would increase the area of cultivable land while at the same time conserving water for agriculture. In this way, food security could be alleviated while achieving the double benefits of ecological restoration and efficient use of land resources. (3) Filling gullies to reduce disasters The loess deposits of the Plateau are loose and have vertical joints. The shear strength and the capacity to resist erosion are relatively weak. The gullies resulting from erosion have steep slopes. These characteristics lead to disasters such as landslides and mud flows, which occur under intense rainfall and erosion conditions or due to gravity after rainfall events. These represent a threat to life and property. In Wuqi County, Shaanxi Province, there have been 784 such disasters of which 92% were landslides.5 Therefore, filling the gullies, which reduces the occurrence of steep slopes and concentrated flow, should reduce costly disasters and save lives. While the cost of filling gullies may be considered to be large, this cost should be compared with that of other large projects on the Loess Plateau. For example, Yuzhong County in Gansu Province recently spent 19 million Chinese Yuan (CNY) in order to create 42 ha of irrigated farmland (including the cost of irrigation equipment). Based on the costs calculated by Yuzhong County, 83.06 billion CNY would be the cost of building check dams on the Loess Plateau in order to create about 18.4 thousand hectares of irrigated farmland. Although the financial costs of such a large scale project that fills the gullies would be 2.7−3 times higher than this, the sustainability of these measures should be considered alongside a comparison with the present costs of not only building check dams but maintaining them and dredging excess sediments from reservoirs (or dam abandonment) as well as the financial benefits of increased agricultural productivity, which would address the looming food security problem due to food deficits, and reductions in disasters, etc. Based on these reasons, we propose to reclaim cropland by filling gullies to sustainably control and make full use of the resources on the Loess Plateau.
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (No. 31070364). We sincerely thank Richard Stone for giving us good suggestions.
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REFERENCES
(1) National Development and Reform Commission, P.R. China; Ministry of Water Resources, P.R. China; Ministry of Agriculture, P.R. China; and State Forestry Administration, P.R. China. Programming for Comprehensive Management of the Loess Plateau (2010−2030), 2010; pp 30-34. (2) Ren, M. E. Sediment discharge of the Yellow River, China: past, present and futureA synthesis. Adv. Earth. Sci. 2006, 21 (6), 551− 563. (3) Feng, Z. M.; Liu, B. Q.; Yang, Y. Z. A study of the changing trend of Chinese cultivated land amount and data reconstructing: 1949− 2003. J. Nat. Resour. 2005, 20 (1), 35−43. (4) Zhan, Q. W. On crop yield breeding and agro-science revolution. Chin. Agric. Sci. Bull. 2006, 22 (1), 136−139. (5) Chen, R. B. Study on the survey method and laws of Geological Disaster in Loess Plateau. Master degree Dissertation, Chang’an University, Xi’an, CN, 2009.
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dx.doi.org/10.1021/es402460r | Environ. Sci. Technol. 2013, 47, 7589−7590
