Environmental Science Processes & Impacts View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
PAPER
Cite this: Environ. Sci.: Processes Impacts, 2014, 16, 1480
View Journal | View Issue
Effectiveness assessment of soil conservation measures in reducing soil erosion in Baiquan County of Northeastern China by using 137Cs techniques Qing-wen Zhang and Yong Li* Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers. Over the last decade, several soil conservation programs for erosion control have been conducted throughout Northeastern China. Reliable information on soil erosion rates is an essential prerequisite to assess the effectiveness of soil conservation measures. A study was carried out in Baiquan County of Northeastern China to assess the effectiveness of soil conservation measures in reducing soil erosion using the
137
Cs tracer technique and
137
Cs measurements to quantify medium-term soil related techniques. This study reports the use of erosion rates in traditional slope farmland, contour cropping farmland and terrace farmland in the Dingjiagou catchment and the Xingsheng catchment of Baiquan County. The 2
of 2532 670 Bq m
was determined. Based on the principle of the
137
Cs reference inventory
137
Cs tracer technique, soil erosion
rates were estimated. The results showed that severe erosion on traditional slope farmland is the dominant soil erosion process in the area. The terrace measure reduced soil erosion rates by 16% for the entire slope. Typical net soil erosion rates are estimated to be 28.97 Mg per hectare per year for traditional slope farmland and 25.04 Mg per hectare per year for terrace farmland in the Dingjiagou Received 9th October 2013 Accepted 13th March 2014
catchment. In contrast to traditional slope farmland with a soil erosion rate of 34.65 Mg per hectare per year, contour cultivation reduced the soil erosion rate by 53% resulting in a soil erosion rate of 22.58 Mg per hectare per year in the Xingsheng catchment. These results indicated that soil losses can be
DOI: 10.1039/c3em00521f
controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace or
rsc.li/process-impacts
contour cultivation.
Environmental impact Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers. Over the last decade, several soil conservation programs for erosion control have been conducted throughout Northeastern China. Reliable information on soil erosion rates is an essential prerequisite to assess the effectiveness of soil conservation measures. This study reports the use of 137Cs measurements to quantify medium-term soil erosion rates in traditional slope farmland, contour cropping farmland and terrace farmland in two catchments in Northeastern China using the 137Cs tracer technique and related techniques. The results indicated that soil losses can be controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace or contour cultivation.
Introduction Accelerated soil erosion is considered as a major land degradation process resulting in reduced soil quality, increased sediment production and sediment-associated nutrient inputs to rivers.1–3 Various conservation measures are adopted to combat soil erosion around the world.4–9 In view of increasing
Institute of Environment and Sustainable Development in Agriculture, CAAS/Key Laboratory of Agro-Environment, Ministry of Agriculture, No. 12 Zhongguancun South Street, Beijing, China. E-mail: [email protected]; [email protected]; Tel: +86-10-82106031
1480 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
water scarcity and limited land resources to feed an evergrowing world population, there is a need to obtain reliable data to quantify soil erosion rates to guide the selection of effective soil-conservation technologies.10 Northeastern China comprises Heilongjiang, Jilin and Liaoning Province, with a total area of 790 000 km2 and a population of 107 million. Cultivation in Northeastern China dates back thousands of years, while the most extensive cultivation occurred in the later Qing Dynasty (aer 1903), and in two other periods (1958–1960, and 1966–1975 A.D.) aer New China was established.11 Black soil is an important soil resource in the northeast and is ne in texture with a high amount of clay
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Paper
and is typically dark in colour. The cultivated blacksoil land accounts for 18% of the cultivated land, but produces 28% of the food products in the northeast, or 7.8% of the whole country. Northeastern China lies in the semi-arid to sub-humid climate zone, with an average annual precipitation of about 400 mm. The soil in this region has a very low inltration rate and hydraulic conductivity, which are potential causes of severe erosion and degeneration of the soil quality. In places where soil erosion is less severe, the soil is 40 cm to more than 1 m deep, but soil depths have decreased to less than 40 cm in areas with high erosion in the last 60 years and in some locations the loess parent material is already exposed.12 Soil erosion has adversely affected the local ecology, resulting in more frequent droughts, oods and sandstorms. Although different methodologies were used to obtain soil loss values measured in Northeast China for total soil erosion or individual soil erosion processes, they indicated that water erosion can rise from 5 to 60 Mg per hectare per year.12–17 Evidence of serious tillage erosion is given by the fact that the total soil loss on convexities (shoulders) amounted to 60 Mg per hectare per year on a hill slope in the Songhua river basin.14 The wind erosion in Northeastern China was also relatively serious, affecting an area of about 22 448.2 km2, accounting for 11.1% of the total land area.18 Protection of the black soil is an urgent issue. Over the last decade, several soil conservation programs for erosion control through terracing and contour farming on cultivated sloping land have been conducted in Northeastern China. Quantifying soil erosion is essential in implementing appropriate practices to reduce soil and water losses. Currently, plot observations,19,20 rainfall simulators21–23 and modelling approaches based on GIS technology24–27 are the prevalent methods used to evaluate the effects of land use on soil erosion. The existing techniques for measuring soil erosion possess a number of limitations in terms of their spatial resolution, their potential for providing information on long term rates of soil loss and associated spatial patterns over extended areas, and the costs involved.28–31 Plot observations cannot describe how a catchment responds to certain management practices.32 Owing to the relatively high natural variability of most hydrological systems, extrapolating or generalizing the results from simulation models to other systems can be challenging.33 A number of scholars have explored the potential of using fallout radionuclides, and particularly cesium-137 (137Cs), to obtain estimates of the rates of soil erosion.26,34–36 137Cs is an articial radioactive isotope with a half-life of 30.17 years and is a byproduct of the atmospheric testing of nuclear weapons, which commenced in the 1950s. It was globally distributed by the wind before being deposited onto the soil, primarily by wet deposition (rainfall) as well as by dry deposition. In most environments, 137Cs fallout reaching the land surface was rapidly and strongly xed by the surface soil and its subsequent redistribution in the landscape was closely associated with erosion and associated soil redistribution processes.35,37 Thus the 137Cs concentration can be used to estimate soil erosion and redistribution rates in the eroding or depositing soil based on a comparison of the 137Cs inventories (total activity in the soil prole per unit area) at individual sampling points with a
This journal is © The Royal Society of Chemistry 2014
Environmental Science: Processes & Impacts
reference inventory of the local fallout input, representing a site with neither erosion nor deposition.38 The technique, with its important advantages, is well described by Vanden Berghe and Gulinck,39 and Quine and Walling.40 The 137Cs technique was originally used to study soil erosion by water in the United States,37,41 and later in Europe. Nowadays, the approach has been used in numerous studies throughout the world.34,42–45 At the global scale, 137Cs fallout is an order of magnitude greater in the Northern Hemisphere than in the Southern Hemisphere and this imbalance has been attributed to the greater number of atmospheric tests that were conducted in the Northern Hemisphere.35,46 In addition to the hemispherical differences, 137Cs fallout also exhibits latitudinal effects with the greatest 137Cs fallout having occurred in the 40 to 50 latitudinal bands of both hemispheres.35 Qi et al.47 summarized the results of the study on soil erosion in China using the 137Cs technique and found that the 137Cs reference inventory distribution in China decreased from north to south and from east to west, which is consistent with the results from other sites around the globe.48,49 There is still a problem in using 137Cs since some have noted that the assumptions made in the theoretical application of this methodology are dubious and render all rates of soil loss obtained by it inaccurate.50 However, a wide range of environmental studies have shown that the 137 Cs inventory in the soil is still signicant and hence adequate to quantify soil redistribution.51–53 Therefore, the 137Cs technique is still a reliable method to quantify soil erosion and deposition under different soil conservation measures and well used world-wide under different environments54 and possibly for a comparative study within a small area with a similar soil type. The objective of this paper is to assess the effectiveness of soil conservation measures in reducing soil erosion in Northeastern China using the 137Cs technique. Baiquan County of Northeastern China, where different soil and water conservation programs have been conducted, was selected for a case study to calculate erosion and deposition rates of black soil and to assess the effectiveness of soil conservation measures in reducing soil erosion, using fallout radionuclides and related techniques.
Materials and methods Study site The study site was selected in Baiquan County (47 300 N, 125 510 E) in Heilongjiang Province of Northeastern China. The mean annual precipitation of the study site ranges from 550 mm to 600 mm. The precipitation and runoff are seasonally variable: more than 70% of them occur in the rainy season from July to September, normally with a high rainfall intensity during a short period, and thus easily resulting in concentrated runoff and severe soil erosion. Most land of Baiquan County is low hills with slope gradient from 3 to 10 and a slope length of about 500 m. Grown in the ridges, soybean is the major crop in Baiquan. There are no crops in furrows between ridges. The study performed by Yu et al.55 showed that the stable inltration rate was only 0.01 mm min1 due to the machine compacted surface
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1481
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Environmental Science: Processes & Impacts
Paper
soil with a moldboard plough in the sloping farmland. In the rainy season, concentrated runoff is easily produced in furrows and there is a severe loss of soil and water. Water erosion is a serious problem on the eroded hillslopes, resulting in reduction of soil depth from 60 cm to about 20–30 cm from 1903 to 1982, and soil organic matter from 8% to 3.7%.56 The area suffering from water and soil loss was 215 300 hectares, of which the eroded farmland was 170 670 hectares. The amount of water loss was up to 0.1 billion m3 t, soil loss 14 million t, loss of nitrogen fertilizer 36 million t, phosphate fertilizer 310 million t, and potassium fertilizer 60 million t.57 As soil erosion rates increased dramatically, effective measures for soil and water conservation have been taken in Baiquan County. Until the date of sampling, the total area under soil and water control reached more than 149 870 hectares, of which terrace farmland was 23 200 hectares and contour cropping farmland was 43 530 hectares, and 8448 eroding gullies were controlled.58 Field sampling program and soil sampling Occupying 45% of the total area under soil and water control, the terrace and contour cropping farmlands are the effective soil and water controlling measures. To assess the effectiveness of terrace and contour cropping in reducing soil erosion in Baiquan County, soil samples were collected from terrace farmland and sloping farmland in the Dingjiagou catchment (Fig. 1), and also from contour cropping farmland and sloping farmland in the Xingsheng catchment (Fig. 2). Corn and soybean are the major crops grown in the study site, occupying about 88% of the cultivation area.58 The use of 137Cs to identify and quantify rates of soil erosion and deposition requires rstly the determination of the baseline or reference 137Cs inventory which indicates the amount of
Photo and field sampling from terrace farmland and sloping farmland in the Dingjiagou catchment.
Fig. 1
1482 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Field sampling from contour cropping farmland and sloping farmland in the Xingsheng catchment.
Fig. 2
137
Cs fallout deposited in the area.35 Reference sites for determining the 137Cs inventories were established on uncultivated grassland far from human disturbance within the study catchment. Five samples were collected at the reference site for determining the reference inventories of 137Cs. Each sample was collected with depth intervals of 5 cm from the surface down through the soil prole and in a maximum soil depth of 30 cm. In Dingjiagou, the elevation of slope farmland varies from 319.96 m at the hillslope summit to 315.42 m at the lower backslope adjacent to the gully bank. The horizontal distance of slope farmland was about 102 m. Soil cores were collected at 20 m intervals of horizontal distance from the summit, upper backslope to lower backslope for slope farmland. The elevation of terrace farmland varies from 319.96 m at the hillslope summit to 315.42 m at the gully bank adjacent to the hillslope. The horizontal distance of the terrace farmland from the summit position to the lower position was about 49 m. Soil cores were collected at about 20 m intervals of horizontal distance from the summit, middle to lower slope positions at terrace farmland. Five cores were collected at the same position. In Xingsheng, the elevation of slope farmland varies from 301.46 m at the hillslope summit to 280.29 m at the lower backslope adjacent to the gully bank. The horizontal distance of slope farmland was about 436 m. Soil cores were collected at about 50 m intervals of horizontal distance from the summit, upper backslope to lower backslope. As for contour farmland the elevation varies from 301.78 m at the hillslope summit to 296.64 m at the lower backslope adjacent to the gully bank. The horizontal distance of contour farmland was about 78 m. Soil
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Paper
cores were collected at about 20 m intervals of horizontal distance from the summit, upper backslope to lower backslope for contour farmland. A soil sample was also collected at a sediment deposition site of a gully in the Xingsheng catchment, to assess the effects of soil conservation measures on gully evolution. To quantify gully erosion rates as affected by land use change, a RTK-GPS (Real Time Kinematic-Global Position System) was used for detailed topographic surveys of the core locations. Gully development was measured by using RTK-GPS survey data in 2005 and the geographical map in 1998 created by digitizing the relief map in the Xinsheng catchment (Fig. 3). Sediment production by gully erosion was estimated based on RTK-GPS survey data and the 137Cs dating method. Soil cores from different land use sites were all collected using a 6.74 cm diameter hand-operated core sampler. At different land use study sites, soil cores were taken to a depth of 30 cm to ensure that the core had penetrated to the full depth of the 137Cs prole. Three soil core samples were taken at each coring location and combined into one sample. Soil cores were also analyzed for bulk densities. The soil bulk densities (g cm3) were calculated from the volume of bulked soil cores and over-dried soil mass to calculate the cumulative mass depth d (kg m2). Laboratory and data analysis Soil samples were air-dried, weighed, and passed through a 2 mm sieve for the measurement of 137Cs activities. Measurements of 137Cs activities were conducted using a hyper pure coaxial Ge detector coupled to a multi-channel analyzer (Genie-
Environmental Science: Processes & Impacts
2000 spectroscopy system) and other standard nuclear electronics.45 Cesium-137 activity was detected at 662 keV peak using a counting time over 80 000 s, which provided an analytical precision of 5% for 137Cs.45 All statistical analyses were performed using Statistical Analysis System (SAS) general linear model procedures.59 The mass balance model was used to convert 137Cs measurements to quantitative estimates of erosion rates.52,60 In this model, a sampling point with a total 137Cs inventory A (Bq m2) less than the local reference inventory Aref (Bq m2) is assumed to be an eroding site, while a point with a total 137Cs inventory greater than the local reference inventory is assumed to be a depositional site. For an eroding point (A(t) < Aref), the change in the total 137Cs inventory A(t) with time can be represented as dAðtÞ R ¼ ð1 GÞIðtÞ l þ P AðtÞ (1) dt d where, A(t) ¼ cumulative 137Cs activity per unit area (Bq m2); R ¼ erosion rate (kg per m2 per year); d ¼ cumulative mass depth representing the average plough depth (kg m2); l ¼ decay constant for 137Cs (year1); I(t) ¼ annual 137Cs deposition ux (Bq per m2 per year); G ¼ percentage of the freshly deposited 137 Cs fallout removed by erosion before being mixed into the plough layer; P ¼ particle size correction factor. The assumptions of this model are a considerable oversimplication of reality in terms of the accumulation of 137Cs in the soil. However, possibly for a comparative study within a small area with a similar soil type, it can be used to qualitatively assess the conservation measures.
Results Effectiveness of terracing and contour cropping in reducing soil erosion in farmlands of Baiquan County
Fig. 3 Contour map in 1983, created by digitizing the relief map, and the map in 2005 derived from a GPS survey.
This journal is © The Royal Society of Chemistry 2014
The reference value of 137Cs inventories in our study was calculated to be 2532 670 Bq m2 for Baiquan. Yan and Tang61 once found that the reference 137Cs inventory of black soil in Northeast China was 2463.64 Bq m2. The depth proles of fallout 137Cs in reference sites showed a typical exponential decrease with soil depth, and most of the 137Cs concentrated within the surface layers of 0–10 cm of soil in the study area. The spatial patterns of the 137Cs inventories and soil erosion redistribution were documented from soil cores taken on different land use of the study sites, shown in Fig. 4–7. We examined the effectiveness of two typical soil conservation measures, terrace and contouring cropping, in reducing soil erosion using fallout 137 Cs measurements. In the slope farmland of the Dingjiagou catchment, the upper position contained the highest amount of 137Cs whereas the lower position had the lowest 137Cs. The amounts of 137Cs of sampling sites decreased from upper, mid and lower positions in the slope farmland (Fig. 4). The inventories of 137Cs were 1079.03 84.09, 862.37 66.43, and 296.28 26.81 Bq m2 on the upper, middle and lower slope positions, respectively. Using the 137Cs converting model, soil erosion rates are correspondingly calculated to be 23.56, 27.08, and 36.26 Mg per hectare per year on the upper, middle and lower slope positions,
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1483
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Environmental Science: Processes & Impacts
Inventory of 137Cs and erosion rates at the different slope positions on the slope farmland in the Dingjiagou catchment (bars represent uncertainties for inventory and the error of mean for soil erosion rates. The following figures are the same).
Fig. 4
respectively. The sediment budget calculated using 137Cs inventories showed that much soil was lost from the eroded slope farmland. Fig. 5 shows the distribution of 137Cs inventory and soil erosion rates at the different positions on the terrace farmland in the Dingjiagou catchment. In contrast to the slope farmland, the amounts of 137Cs of sampling sites have no signicant difference at different positions on the terrace farmland. The inventories of 137Cs were 1183.47 94.71, 947.83 77.62, and 831.78 65.12 Bq m2 on the upper, middle and lower positions, respectively. Correspondingly, the erosion rates slightly increased in the following order: upper < middle < lower with the rates of 21.87, 25.69, and 27.57 Mg per hectare per year, respectively (Table 1). Compared with the slope farmland, the terrace measure reduced soil erosion by 7.73, 5.41 and 31.52% on the upper, middle and lower slope positions. In total, the terrace measure reduced soil erosion by 15.67% for the entire slope. In the Xingsheng catchment (Fig. 6), the upper and lower positions contained a higher amount of 137Cs whereas the middle position had a less 137Cs inventory for the slope farmland. The inventories of 137Cs were 809.4 71.26, 612.36 52.55, and 929.34 71.59 Bq m2 on the upper, middle and lower slope positions, respectively. Correspondingly, along the downslope positions, erosion rates were calculated to be 32.53,
1484 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Paper
137
Cs inventory and erosion rates at different slope positions on the terrace farmland in the Dingjiagou catchment.
Fig. 5
39.92, and 31.50 Mg per hectare per year on the upper, middle and lower slope positions, respectively (Fig. 6). While on the contour cropping farmland, the amount of 137 Cs and soil erosion rates had no signicant difference among the different slope positions (Fig. 7). The amounts of 137Cs were 1052.7 96.49, 1190.45 116.23, and 1196.56 95.84 Bq m2 on the upper, middle and lower slope positions, respectively. Correspondingly, soil erosion rates on the contour cropping farmland were calculated to be 23.09, 21.75, and 22.89 Mg per hectare per year on the upper, middle and lower slope positions, respectively. Compared with slope farmland, contour cultivation reduced soil erosion by 40.88, 83.54 and 37.61% on the upper, middle and lower slope positions, respectively. In total, the contour cultivation reduced soil erosion by 53.48% for the entire slope (Table 2). Gully development in Baiquan County using GPS survey
137
Cs tracer and
Gullies are extensively distributed in the gentle sloping hillygully regions of Northeastern China. In addition, gullies in the agricultural environment are effective links between upland areas and channels. By establishing a sediment chronology within the gully systems using 137Cs dating we intended to develop a relationship between gully development and the history of gully catchment land use. Comparing the data from the RTK-GPS survey in 2005 with digital data from a contour map in 1983, we studied the gully
This journal is © The Royal Society of Chemistry 2014
View Article Online
Paper Table 1
Environmental Science: Processes & Impacts Effectiveness of the terrace farmland in reducing soil erosion compared with the slope farmland in the Dingjiagou catchment
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
137
Soil erosion rate (Mg per hectare per year)
Cs inventory (Bq m2)
Slope position
Terrace farmland
Uncertainty
Slope farmland
Uncertainty
Terrace farmland
Slope farmland
Soil erosion reduction percent by the terrace farmland (%)
Upper Middle Lower Total
1183.47 947.83 831.78 987.69
94.71 77.62 65.12 79.15
1079.03 862.37 296.28 745.89
84.09 66.43 26.81 59.11
21.87 25.69 27.57 25.04
23.56 27.08 36.26 28.97
7.73 5.41 31.52 15.67
137 Cs inventory and erosion rates at the different slope positions on the slope farmland in the Xingsheng catchment.
Fig. 6
Fig. 7 137Cs inventory and erosion rates at different slope positions on the contour cropping farmland in the Xingsheng catchment.
erosion development as affected by the land use. By comparing gully area morphologies in two years, we found that a new eroding gully developed in 2005 in the place where there was no gully at all in 1983, while the topographical conditions and landscape position are the same except that the cropping ridge directions changed. The slope is gentle in the place where the new gully has initiated a link with the old gully, which cannot be explained by the topography evolution. It can mainly be attributed to agronomic practices such as the growth of soybeans on ridges in Northeastern China, resulting in concentrated ow erosion occurrence in furrows between ridges during the rainfall, as concentrated ow is the main factor for gully development. Severe gully erosion may occur if the run-off is concentrated in furrows between ridges. Furrows between ridges concentrate water during storms and are persistent sources of sediment, as well as effective conduits for transporting eroded soil to gullies and channels. Gully parameters of the Xingsheng gully estimated from 137 Cs dating and the RTK-GPS survey are shown in Table 3.
This journal is © The Royal Society of Chemistry 2014
Based on the data from the RTK-GPS survey, the gully length of 182.5 m was developed from 1983 to 2005. The total erosion amount for the Xingsheng gully was 4093 t. Taking average sediment yields by sheet erosion as 34.65 Mg per hectare per year, derived by the 137Cs tracing method, gully erosion contributed 69% of the total sediment yield in the study catchments. An average bulk density of 1.3 g cm3 from measurements was used for calculation of sediment yields and the gully erosion rate.
Discussion The intensive agricultural cultivation history of Northeastern China is over hundreds of years. In places where soil erosion is less severe, the soil is 40 cm to more than 1 m deep, but soil depths decreased to less than 40 cm in highly eroding places and in some locations the loess parent material is even
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1485
View Article Online
Environmental Science: Processes & Impacts Table 2
Paper
Effectiveness of contour cultivation in reducing soil erosion, compared with the slope farmland in the Xingsheng catchment
137
Soil erosion rate (Mg per hectare per year)
Slope position
Contour cropping
Uncertainty
Slope farmland
Uncertainty
Contour cropping
Slope farmland
Soil erosion reduction percent by the contour cultivation (%)
Upper Middle Lower Total
1150.7 1190.45 1196.56 1179.24
96.49 116.23 95.84 102.85
809.4 612.36 929.34 783.70
71.26 52.55 71.59 65.13
23.09 21.75 22.89 22.58
32.53 39.92 31.5 34.65
40.88 83.54 37.61 53.48
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Cs inventory (Bq m2)
Table 3
Gully parameters of the Xingsheng gully estimated from 137Cs dating and the GPS survey
Gully depth (m)
Gully width (m)
Mean
Maximum
Mean
Maximum
Gully length (m)
Drainage area (m2)
Gully erosion amount (t)
1.2
6.42
13.2
20.7
182.5
11 916
4093
outcropping.12 Results from Baiquan County showed that the upper position contained the highest amount of 137Cs whereas the lower slope position had the lowest 137Cs for the slope farmland. The sediment budget calculated using 137Cs inventories showed that much soil was lost from the eroded slope farmland. Average soil losses derived from 137Cs in this study are comparable to those studies measured with remote sensing or runoff plots in Northeastern China. Water erosion on slope farmland and in the gully is the dominant soil erosion process in Northeastern China.11–14,16,17 Table 4 gives an overview of soil loss values measured in Northeast China for total soil erosion or individual soil erosion processes. This table shows that water erosion can cause soil losses from 5 to 60 Mg per hectare per year. Evidence of serious tillage
Table 4 Soil erosion rates derived from
erosion is given by the fact that the total soil loss on convexities (shoulders) amounted up to 60 Mg per hectare per year on a hill slope in the Songhua river basin (Table 4). Derived from 137Cs in this study, the soil erosion rate in Northeastern China is 31.81 Mg per hectare per year for the slope farmland and 76.47 Mg per hectare per year for gully erosion. This study showed that soil conservation measures such as the terrace and contour cropping in Northeastern China are effective ways for reducing soil erosion. The soil erosion rate, derived from 137Cs techniques, is 25.04 Mg per hectare per year for the terrace farmland and 22.58 Mg per hectare per year for the contour cropping farmland. The widespread terrace in the region is generally believed to be an effective soil conservation measure in low hilly-gully areas
137
Cs in this study and other data in Northeastern China
Erosion process
Soil loss (Mg per hectare per year)
Study sites and remarks
Source
Water erosion
31.81 (a), 25.04 (b), 22.58 (c), 76.47 (d)
This study
Water erosion
30–50
Water erosion
5–25
Water erosion
5.5–13.2 (a), 7.5–31.3 (b), 16.4–60 (c)
Total soil erosion
24 (TS), 60.0 (SS), 26.2 (BS)
Slope farmland (a), terrace farmland (b), contour cropping farmland (c), gully erosion (d), in Baiquan, Northeastern China Water erosion area of North-east China based on the national soil erosion survey, using topographical maps (1 : 100 000), remote sensing, eld survey and plot measurements Jilin Province based on the remote sensing study and eld survey cropland Liaoning Province based on runoff plots on the hilly eld measured during the 1980–1990 period slopes: a, 6 ; b, 10 ; c, 15 TS, top of the slope; SS, the slope shoulder; BS, the backslope. 137Cs study on crop land for a typical slope transecting the Songhua River basin
1486 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Cai et al.13 and Fan et al.12
Zhu and Quan17
Sun et al.16
Fang et al.14
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Paper
of Northeastern China. Compared with the slope farmland, the terrace measure reduced soil erosion rates by 16% for the entire slope. The terrace eld could slow or prevent the rapid surface runoff in the low hilly-gully areas due to interception of runoff water and a short slope length, which reduced runoff and soil erosion rates signicantly. The soybean cultivation in terraces plowing following the natural contours is a classic feature in the low hilly-gully areas of Northeastern China. Terraces are easier for both mechanical and manual sowing and harvesting than steep slopes. Runoff as concentrated ow from the sloping land can be controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace cultivation. Contour cropping, involving sowing crops across the slope in line with contours, is another effective soil conservation measure. The amount of 137Cs and soil erosion rates made no signicant difference in different slope positions on the contour cropping farmland in the Xingsheng catchment. Contour cultivation measures could effectively control soil erosion, especially on the middle position where serious soil erosion occurs. In total, contour cultivation reduced soil erosion losses up to 53.48% for the entire slope. Soil losses can be controlled by changing tillage practices from downslope cultivation to contour cultivation. Contour cropping reduces erosion by reducing the length of the slope. The crops provide a perpendicular barrier to run-off due to stem density. Theoretically this reduces both erosion and run-off by removing natural drainage channels down the slope which occur with conventional cropping. Reducing run-off improves inltration and reduces soil erosion. Whereas if rain falls on sloping land, it tends to run off rapidly as concentrated ow in the furrows. In practice contour cropping is more effective on lands with long, uniform, and gentle slopes. On steeper slopes, if without supplementary practices, the effectiveness of contouring is generally reduced because of possible breakover of rows by runoff water. Our results suggested that gully erosion is the major sediment source and the dominant water erosion process causing considerable soil losses in Baiquan County. Gullies developed in farmlands not only act as sources of sediments but also aggravate ooding and silting of reservoirs. Based on the data from the RTK-GPS survey, gullies with a length of 182.5 m have been developed in the last 20 years. Results showed that gully erosion contributed to 69% of the total sediment yield in the study catchments. The reason for gully initiation and development could be explained by the unreasonable downslope cropping ridge measures in combination with extreme rainfall. Natural gullying processes are accelerated by the intensication of annual cropping. The downslope cropping ridges collected the overland ow, which incised through the plough layer, and then the gully initiated and developed in the cropland. The spaces between ridges act as the runoff way to concentrate the overland ow, and enhance gully development. The main technique to prevent gully development is to convert a downslope cropping ridge to a contour cropping ridge or to establish stiff grass hedges. The contour cropping ridge and grass hedges can retard and spread out surface runoff, cause deposition of eroded sediments, and hence prevent gully incision.
This journal is © The Royal Society of Chemistry 2014
Environmental Science: Processes & Impacts
Conclusions Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers in Baiquan County. In the Dingjiagou catchment, the sediment budget calculated using 137Cs inventories showed that much soil was lost from the eroded slope farmland. The terrace eld reduced soil erosion rates by 16% for the entire slope, compared with the slope farmland. In contrast to the slope farmland, the contour cultivation reduced soil erosion rates by 53% for the entire slope. These results indicated that soil losses can be controlled by changing tillage practices from the slope farmland cultivation to the terrace or contour cultivation.
Acknowledgements This study was supported by the National Nature Science Foundation of China (no. 41371285), the National S&T Major Project (no. 2012ZX07104003), the Special Foundation for Basic Scientic Research of Central Public Welfare Institute and Agricultural Clear Watershed Group, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences (CAAS). We would give thanks to Lu Li and Jun-Jie Li for GPS surveying and data processing.
Notes and references 1 A. Cerd` a, Can. J. Soil Sci., 1998, 78, 321–330. 2 R. Lal, M. Griffin, J. Apt, L. Lave and G. M. Morgan, Science, 2004, 304, 393. 3 G. Zhao, X. Mu, Z. Wen, F. Wang and P. Gao, Land Degradation & Development, 2013, 24, 499–510. 4 Z. M. Feng, Y. Z. Yang, Y. Q. Zhang, P. T. Zhang and Y. Q. Li, Land Use Policy, 2005, 22, 301–312. 5 Q. J. Liu, Z. H. Shi, X. X. Yu and H. Y. Zhang, Soil Tillage Res., 2014, 136, 1–8. 6 C. Y. Miao, L. Yang, X. H. Chen and Y. Gao, Land Degradation & Development, 2012, 23, 62–71. 7 D. C. Reicosky, in Conservation Agriculture: A worldwide challenge, ed. L. Garcia-Torres, J. Benites and A. MartinezVilela, Cordoba, Spain, 2001, pp. 3–12. 8 Y. Q. Wang and M. A. Shao, Land Degradation & Development, 2013, 24, 296–304. 9 Q. X. Xu, T. W. Wang, C. F. Cai, Z. X. Li and Z. H. Shi, Land Degradation & Development, 2012, 23, 34–42. 10 P. Prokop and G. J. Pore ˛ba, Land Degradation & Development, 2012, 23, 310–321. 11 J. M. Sun and T. S. Liu, Quat. Sci., 2001, 21, 72–78. 12 H. M. Fan, Q. G. Cai and H. S. Wang, J. Soil Water Conserv., 2004, 18, 66–70. 13 Q. G. Cai, H. M. Fan and B. Shen, J. Soil Water Conserv., 2003, 17, 21–24. 14 H. J. Fang, X. J. Yang and X. P. Zhang, Chin. J. Appl. Ecol., 2005, 16, 464–468. 15 H. Y. Fang, M. L. Sheng, Z. H. Tang and Q. G. Cai, Soil Tillage Res., 2013, 133, 85–92.
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1487
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Environmental Science: Processes & Impacts
16 J. H. Sun, Y. G. Yang and B. J. Zhang, Research of Soil and Water Conservation, 1997, 4, 63–74. 17 Z. E. Zhu and H. Quan, Bulletin of Soil and Water Conservation, 1992, 12, 33–37. 18 T. J. Liu, D. Shan, J. Y. Guo, T. M. Gao and X. B. Zhao, Agric. Sci. Technol., 2011, 12(12), 1925–1928. 19 C. Fern´ andez, J. A. Vega, E. Jim´ enez, D. C. S. Vieira, A. Merino, A. Ferreiro and T. Fonturbel, Land Degradation & Development, 2012, 23, 150–156. 20 P. Licznar and M. A. Nearing, Catena, 2003, 51, 89–114. 21 T. Iserloh, J. B. Ries, J. Arnaez, C. Boix Fayos, V. Butzen, A. Cerd` a, M. T. Echeverr´ıa, J. Fern´ andez-G´ alvez, W. Fister, C. Geißler, J. A. G´ omez, H. G´ omez-Macpherson, N. J. Kuhn, R. L´ azaro, F. J. Le´ on, M. Mart´ınez-Mena, J. F. Mart´ınez-Murillo, M. Marzen, M. D. Mingorance, L. Ortigosa, P. Peters, D. Reg¨ u´ es, J. D. Ruiz-Sinoga, T. Scholten, M. Seeger, A. Sol´ e-Benet, R. Wengel and S. Wirtz, Catena, 2013, 110, 100–112. 22 I. T. Meerveld and M. Weiler, J. Hydrol., 2008, 361, 24–40. 23 F. M. Ziadat and A. Y. Taimeh, Land Degradation & Development, 2013, 24, 582–590. 24 D. D. Alexakis, D. G. Hadjimitsis and A. Agapiou, Atmos. Res., 2013, 131, 108–124. 25 B. J. Fu, W. W. Zhao, L. D. Chen, Q. J. Zhang, Y. H. L¨ u, H. Gulinck and J. Poesen, Land degradation & development, 2005, 16(1), 73–85. 26 A. Routschek, J. Schmidt, W. Enke and T. Deutschlaender, Geomorphology, 2014, 206, 299–306. 27 Z. H. Shi, L. Ai, N. F. Fang and H. D. Zhu, J. Hydrol., 2012, 438, 156–167. 28 R. J. Loughran, Progr. Phys. Geogr., 1990, 13, 216–233. 29 D. L. Higgitt, Progr. Phys. Geogr., 1991, 15, 91–100. 30 Y. Li, J. Poesen, J. C. Yang, B. Fu and J. H. Zhang, Soil Tillage Res., 2003, 69, 107–115. 31 V. Chaplot and J. Poesen, Catena, 2008, 88, 46–56. 32 R. DeFries and K. N. Eshleman, Hydrol. Processes, 2004, 18, 2183–2186. 33 B. L. Campbell, G. L. Elliott and R. J. Loughran, J. Soil Water Conserv., 1985, 41, 86–89. 34 L. Gaspar and A. Navas, Geoderma, 2013, 207–208, 131–143. 35 R. J. Loughran, Trends in Hydrology, 1994, 1, 149–167. 36 F. Zapata, Soil Tillage Res., 2003, 69, 3–13. 37 A. S. Rogowski and T. Tamura, Health Phys., 1965, 11, 1333– 1340. 38 D. E. Walling and T. A. Quine, J. Soil Sci., 1991, 42, 147– 165. 39 I. Vanden Berghe and H. Gulinck, Pedologie, 1987, 37, 5–20.
1488 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Paper
40 T. A. Quine and D. E. Walling, Soil Use Manage., 1991, 7, 169– 176. 41 J. C. Ritchie, J. R. McHenry, A. C. Gill and P. H. Hawks, Proceedings of the Mississippi Water Resource Conference, Mississippi, 1970. 42 M. S. Al-Masri and A. W. Doubal, Appl. Radiat. Isot., 2013, 75, 50–57. 43 M. L. Montes, L. M. S. Silva, C. S. A. S´ a, J. Runco, M. A. Taylor and J. Desimoni, J. Environ. Radioact., 2013, 116, 133–140. 44 P. J. Wallbrink and A. S. Murray, Hydrol. Processes, 1993, 7, 297–304. 45 Y. Li, Q. W. Zhang, D. C. Reicosky, L. Y. Bai, M. J. Lindstrom and L. Li, Soil Tillage Res., 2006, 86, 176–184. 46 R. A. Sutherland, Land Degrad. Rehabil., 1989, 1, 199–208. 47 Y. Q. Qi, X. B. Zhang, X. B. He, A. B. Wen and J. X. Fu, Nuclear Techniques, 2006, 29, 42–50. 48 J. J. Kiss, E. de Jong and L. W. Martz, J. Environ. Qual., 1988, 17, 445–452. 49 J. C. Lance, S. C. McIntyre, W. Naney and S. S. Rousseva, Soil Sci. Soc. Am. J., 1986, 50, 1303–1309. 50 A. J. Parsons and I. D. Foster, Earth–Sci. Rev., 2011, 108, 101– 113. 51 M. Benmansour, L. Mabit, A. Nouira, R. Moussadek, H. Bouksirate, M. Duchemin and A. Benkdad, J. Environ. Radioact., 2013, 115, 97–106. 52 Q. He and D. E. Walling, Appl. Radiat. Isot., 1997, 48, 677– 690. 53 T. Wells and G. Hancock, Geoderma, 2014, 214–215, 228–238. 54 F. Zapata and Y. Li, Working material, IAEA-311-D1-RC-888, Vienna, Austria, 2007. 55 T. Y. Yu, X. Y. Zhang, S. L. Zhang and X. W. Chen, Bulletin of soil and water conservation, 2007, 27, 71–74. 56 Ministry of Water Resources, Chinese Academy of Sciences, Chinese Academy of Engineering, Soil and water conservation and ecology safety in China, Science publishing press, Beijing, 2010, pp. 270–281. 57 J. R. Zhao, S. L. Sun and L. H. Zhao, Water Resources & Hydropower of Northeast China, 2002, 20, 41–42. 58 China Yearbook Full-text Database(CYFD), http:// number.cnki.net/cyfd, accessed July 2008. 59 SAS Institute, SAS user's guide, Statistics, version 9.3, Statistical Analysis System Institute Inc., Cary, NC, 2011. 60 D. E. Walling, Q. He and P. G. Appleby, in Handbook for the assessment of soil erosion and sedimentation using environmental radionuclides, ed. F. Zapata, Kluwer Academic Publishers, Dordrecht, 1997, pp. 111–164. 61 B. X. Yan and J. Tang, J. Soil Water Conserv., 2004, 18, 33–36.
This journal is © The Royal Society of Chemistry 2014
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
PAPER
Cite this: Environ. Sci.: Processes Impacts, 2014, 16, 1480
View Journal | View Issue
Effectiveness assessment of soil conservation measures in reducing soil erosion in Baiquan County of Northeastern China by using 137Cs techniques Qing-wen Zhang and Yong Li* Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers. Over the last decade, several soil conservation programs for erosion control have been conducted throughout Northeastern China. Reliable information on soil erosion rates is an essential prerequisite to assess the effectiveness of soil conservation measures. A study was carried out in Baiquan County of Northeastern China to assess the effectiveness of soil conservation measures in reducing soil erosion using the
137
Cs tracer technique and
137
Cs measurements to quantify medium-term soil related techniques. This study reports the use of erosion rates in traditional slope farmland, contour cropping farmland and terrace farmland in the Dingjiagou catchment and the Xingsheng catchment of Baiquan County. The 2
of 2532 670 Bq m
was determined. Based on the principle of the
137
Cs reference inventory
137
Cs tracer technique, soil erosion
rates were estimated. The results showed that severe erosion on traditional slope farmland is the dominant soil erosion process in the area. The terrace measure reduced soil erosion rates by 16% for the entire slope. Typical net soil erosion rates are estimated to be 28.97 Mg per hectare per year for traditional slope farmland and 25.04 Mg per hectare per year for terrace farmland in the Dingjiagou Received 9th October 2013 Accepted 13th March 2014
catchment. In contrast to traditional slope farmland with a soil erosion rate of 34.65 Mg per hectare per year, contour cultivation reduced the soil erosion rate by 53% resulting in a soil erosion rate of 22.58 Mg per hectare per year in the Xingsheng catchment. These results indicated that soil losses can be
DOI: 10.1039/c3em00521f
controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace or
rsc.li/process-impacts
contour cultivation.
Environmental impact Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers. Over the last decade, several soil conservation programs for erosion control have been conducted throughout Northeastern China. Reliable information on soil erosion rates is an essential prerequisite to assess the effectiveness of soil conservation measures. This study reports the use of 137Cs measurements to quantify medium-term soil erosion rates in traditional slope farmland, contour cropping farmland and terrace farmland in two catchments in Northeastern China using the 137Cs tracer technique and related techniques. The results indicated that soil losses can be controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace or contour cultivation.
Introduction Accelerated soil erosion is considered as a major land degradation process resulting in reduced soil quality, increased sediment production and sediment-associated nutrient inputs to rivers.1–3 Various conservation measures are adopted to combat soil erosion around the world.4–9 In view of increasing
Institute of Environment and Sustainable Development in Agriculture, CAAS/Key Laboratory of Agro-Environment, Ministry of Agriculture, No. 12 Zhongguancun South Street, Beijing, China. E-mail: [email protected]; [email protected]; Tel: +86-10-82106031
1480 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
water scarcity and limited land resources to feed an evergrowing world population, there is a need to obtain reliable data to quantify soil erosion rates to guide the selection of effective soil-conservation technologies.10 Northeastern China comprises Heilongjiang, Jilin and Liaoning Province, with a total area of 790 000 km2 and a population of 107 million. Cultivation in Northeastern China dates back thousands of years, while the most extensive cultivation occurred in the later Qing Dynasty (aer 1903), and in two other periods (1958–1960, and 1966–1975 A.D.) aer New China was established.11 Black soil is an important soil resource in the northeast and is ne in texture with a high amount of clay
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Paper
and is typically dark in colour. The cultivated blacksoil land accounts for 18% of the cultivated land, but produces 28% of the food products in the northeast, or 7.8% of the whole country. Northeastern China lies in the semi-arid to sub-humid climate zone, with an average annual precipitation of about 400 mm. The soil in this region has a very low inltration rate and hydraulic conductivity, which are potential causes of severe erosion and degeneration of the soil quality. In places where soil erosion is less severe, the soil is 40 cm to more than 1 m deep, but soil depths have decreased to less than 40 cm in areas with high erosion in the last 60 years and in some locations the loess parent material is already exposed.12 Soil erosion has adversely affected the local ecology, resulting in more frequent droughts, oods and sandstorms. Although different methodologies were used to obtain soil loss values measured in Northeast China for total soil erosion or individual soil erosion processes, they indicated that water erosion can rise from 5 to 60 Mg per hectare per year.12–17 Evidence of serious tillage erosion is given by the fact that the total soil loss on convexities (shoulders) amounted to 60 Mg per hectare per year on a hill slope in the Songhua river basin.14 The wind erosion in Northeastern China was also relatively serious, affecting an area of about 22 448.2 km2, accounting for 11.1% of the total land area.18 Protection of the black soil is an urgent issue. Over the last decade, several soil conservation programs for erosion control through terracing and contour farming on cultivated sloping land have been conducted in Northeastern China. Quantifying soil erosion is essential in implementing appropriate practices to reduce soil and water losses. Currently, plot observations,19,20 rainfall simulators21–23 and modelling approaches based on GIS technology24–27 are the prevalent methods used to evaluate the effects of land use on soil erosion. The existing techniques for measuring soil erosion possess a number of limitations in terms of their spatial resolution, their potential for providing information on long term rates of soil loss and associated spatial patterns over extended areas, and the costs involved.28–31 Plot observations cannot describe how a catchment responds to certain management practices.32 Owing to the relatively high natural variability of most hydrological systems, extrapolating or generalizing the results from simulation models to other systems can be challenging.33 A number of scholars have explored the potential of using fallout radionuclides, and particularly cesium-137 (137Cs), to obtain estimates of the rates of soil erosion.26,34–36 137Cs is an articial radioactive isotope with a half-life of 30.17 years and is a byproduct of the atmospheric testing of nuclear weapons, which commenced in the 1950s. It was globally distributed by the wind before being deposited onto the soil, primarily by wet deposition (rainfall) as well as by dry deposition. In most environments, 137Cs fallout reaching the land surface was rapidly and strongly xed by the surface soil and its subsequent redistribution in the landscape was closely associated with erosion and associated soil redistribution processes.35,37 Thus the 137Cs concentration can be used to estimate soil erosion and redistribution rates in the eroding or depositing soil based on a comparison of the 137Cs inventories (total activity in the soil prole per unit area) at individual sampling points with a
This journal is © The Royal Society of Chemistry 2014
Environmental Science: Processes & Impacts
reference inventory of the local fallout input, representing a site with neither erosion nor deposition.38 The technique, with its important advantages, is well described by Vanden Berghe and Gulinck,39 and Quine and Walling.40 The 137Cs technique was originally used to study soil erosion by water in the United States,37,41 and later in Europe. Nowadays, the approach has been used in numerous studies throughout the world.34,42–45 At the global scale, 137Cs fallout is an order of magnitude greater in the Northern Hemisphere than in the Southern Hemisphere and this imbalance has been attributed to the greater number of atmospheric tests that were conducted in the Northern Hemisphere.35,46 In addition to the hemispherical differences, 137Cs fallout also exhibits latitudinal effects with the greatest 137Cs fallout having occurred in the 40 to 50 latitudinal bands of both hemispheres.35 Qi et al.47 summarized the results of the study on soil erosion in China using the 137Cs technique and found that the 137Cs reference inventory distribution in China decreased from north to south and from east to west, which is consistent with the results from other sites around the globe.48,49 There is still a problem in using 137Cs since some have noted that the assumptions made in the theoretical application of this methodology are dubious and render all rates of soil loss obtained by it inaccurate.50 However, a wide range of environmental studies have shown that the 137 Cs inventory in the soil is still signicant and hence adequate to quantify soil redistribution.51–53 Therefore, the 137Cs technique is still a reliable method to quantify soil erosion and deposition under different soil conservation measures and well used world-wide under different environments54 and possibly for a comparative study within a small area with a similar soil type. The objective of this paper is to assess the effectiveness of soil conservation measures in reducing soil erosion in Northeastern China using the 137Cs technique. Baiquan County of Northeastern China, where different soil and water conservation programs have been conducted, was selected for a case study to calculate erosion and deposition rates of black soil and to assess the effectiveness of soil conservation measures in reducing soil erosion, using fallout radionuclides and related techniques.
Materials and methods Study site The study site was selected in Baiquan County (47 300 N, 125 510 E) in Heilongjiang Province of Northeastern China. The mean annual precipitation of the study site ranges from 550 mm to 600 mm. The precipitation and runoff are seasonally variable: more than 70% of them occur in the rainy season from July to September, normally with a high rainfall intensity during a short period, and thus easily resulting in concentrated runoff and severe soil erosion. Most land of Baiquan County is low hills with slope gradient from 3 to 10 and a slope length of about 500 m. Grown in the ridges, soybean is the major crop in Baiquan. There are no crops in furrows between ridges. The study performed by Yu et al.55 showed that the stable inltration rate was only 0.01 mm min1 due to the machine compacted surface
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1481
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Environmental Science: Processes & Impacts
Paper
soil with a moldboard plough in the sloping farmland. In the rainy season, concentrated runoff is easily produced in furrows and there is a severe loss of soil and water. Water erosion is a serious problem on the eroded hillslopes, resulting in reduction of soil depth from 60 cm to about 20–30 cm from 1903 to 1982, and soil organic matter from 8% to 3.7%.56 The area suffering from water and soil loss was 215 300 hectares, of which the eroded farmland was 170 670 hectares. The amount of water loss was up to 0.1 billion m3 t, soil loss 14 million t, loss of nitrogen fertilizer 36 million t, phosphate fertilizer 310 million t, and potassium fertilizer 60 million t.57 As soil erosion rates increased dramatically, effective measures for soil and water conservation have been taken in Baiquan County. Until the date of sampling, the total area under soil and water control reached more than 149 870 hectares, of which terrace farmland was 23 200 hectares and contour cropping farmland was 43 530 hectares, and 8448 eroding gullies were controlled.58 Field sampling program and soil sampling Occupying 45% of the total area under soil and water control, the terrace and contour cropping farmlands are the effective soil and water controlling measures. To assess the effectiveness of terrace and contour cropping in reducing soil erosion in Baiquan County, soil samples were collected from terrace farmland and sloping farmland in the Dingjiagou catchment (Fig. 1), and also from contour cropping farmland and sloping farmland in the Xingsheng catchment (Fig. 2). Corn and soybean are the major crops grown in the study site, occupying about 88% of the cultivation area.58 The use of 137Cs to identify and quantify rates of soil erosion and deposition requires rstly the determination of the baseline or reference 137Cs inventory which indicates the amount of
Photo and field sampling from terrace farmland and sloping farmland in the Dingjiagou catchment.
Fig. 1
1482 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Field sampling from contour cropping farmland and sloping farmland in the Xingsheng catchment.
Fig. 2
137
Cs fallout deposited in the area.35 Reference sites for determining the 137Cs inventories were established on uncultivated grassland far from human disturbance within the study catchment. Five samples were collected at the reference site for determining the reference inventories of 137Cs. Each sample was collected with depth intervals of 5 cm from the surface down through the soil prole and in a maximum soil depth of 30 cm. In Dingjiagou, the elevation of slope farmland varies from 319.96 m at the hillslope summit to 315.42 m at the lower backslope adjacent to the gully bank. The horizontal distance of slope farmland was about 102 m. Soil cores were collected at 20 m intervals of horizontal distance from the summit, upper backslope to lower backslope for slope farmland. The elevation of terrace farmland varies from 319.96 m at the hillslope summit to 315.42 m at the gully bank adjacent to the hillslope. The horizontal distance of the terrace farmland from the summit position to the lower position was about 49 m. Soil cores were collected at about 20 m intervals of horizontal distance from the summit, middle to lower slope positions at terrace farmland. Five cores were collected at the same position. In Xingsheng, the elevation of slope farmland varies from 301.46 m at the hillslope summit to 280.29 m at the lower backslope adjacent to the gully bank. The horizontal distance of slope farmland was about 436 m. Soil cores were collected at about 50 m intervals of horizontal distance from the summit, upper backslope to lower backslope. As for contour farmland the elevation varies from 301.78 m at the hillslope summit to 296.64 m at the lower backslope adjacent to the gully bank. The horizontal distance of contour farmland was about 78 m. Soil
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Paper
cores were collected at about 20 m intervals of horizontal distance from the summit, upper backslope to lower backslope for contour farmland. A soil sample was also collected at a sediment deposition site of a gully in the Xingsheng catchment, to assess the effects of soil conservation measures on gully evolution. To quantify gully erosion rates as affected by land use change, a RTK-GPS (Real Time Kinematic-Global Position System) was used for detailed topographic surveys of the core locations. Gully development was measured by using RTK-GPS survey data in 2005 and the geographical map in 1998 created by digitizing the relief map in the Xinsheng catchment (Fig. 3). Sediment production by gully erosion was estimated based on RTK-GPS survey data and the 137Cs dating method. Soil cores from different land use sites were all collected using a 6.74 cm diameter hand-operated core sampler. At different land use study sites, soil cores were taken to a depth of 30 cm to ensure that the core had penetrated to the full depth of the 137Cs prole. Three soil core samples were taken at each coring location and combined into one sample. Soil cores were also analyzed for bulk densities. The soil bulk densities (g cm3) were calculated from the volume of bulked soil cores and over-dried soil mass to calculate the cumulative mass depth d (kg m2). Laboratory and data analysis Soil samples were air-dried, weighed, and passed through a 2 mm sieve for the measurement of 137Cs activities. Measurements of 137Cs activities were conducted using a hyper pure coaxial Ge detector coupled to a multi-channel analyzer (Genie-
Environmental Science: Processes & Impacts
2000 spectroscopy system) and other standard nuclear electronics.45 Cesium-137 activity was detected at 662 keV peak using a counting time over 80 000 s, which provided an analytical precision of 5% for 137Cs.45 All statistical analyses were performed using Statistical Analysis System (SAS) general linear model procedures.59 The mass balance model was used to convert 137Cs measurements to quantitative estimates of erosion rates.52,60 In this model, a sampling point with a total 137Cs inventory A (Bq m2) less than the local reference inventory Aref (Bq m2) is assumed to be an eroding site, while a point with a total 137Cs inventory greater than the local reference inventory is assumed to be a depositional site. For an eroding point (A(t) < Aref), the change in the total 137Cs inventory A(t) with time can be represented as dAðtÞ R ¼ ð1 GÞIðtÞ l þ P AðtÞ (1) dt d where, A(t) ¼ cumulative 137Cs activity per unit area (Bq m2); R ¼ erosion rate (kg per m2 per year); d ¼ cumulative mass depth representing the average plough depth (kg m2); l ¼ decay constant for 137Cs (year1); I(t) ¼ annual 137Cs deposition ux (Bq per m2 per year); G ¼ percentage of the freshly deposited 137 Cs fallout removed by erosion before being mixed into the plough layer; P ¼ particle size correction factor. The assumptions of this model are a considerable oversimplication of reality in terms of the accumulation of 137Cs in the soil. However, possibly for a comparative study within a small area with a similar soil type, it can be used to qualitatively assess the conservation measures.
Results Effectiveness of terracing and contour cropping in reducing soil erosion in farmlands of Baiquan County
Fig. 3 Contour map in 1983, created by digitizing the relief map, and the map in 2005 derived from a GPS survey.
This journal is © The Royal Society of Chemistry 2014
The reference value of 137Cs inventories in our study was calculated to be 2532 670 Bq m2 for Baiquan. Yan and Tang61 once found that the reference 137Cs inventory of black soil in Northeast China was 2463.64 Bq m2. The depth proles of fallout 137Cs in reference sites showed a typical exponential decrease with soil depth, and most of the 137Cs concentrated within the surface layers of 0–10 cm of soil in the study area. The spatial patterns of the 137Cs inventories and soil erosion redistribution were documented from soil cores taken on different land use of the study sites, shown in Fig. 4–7. We examined the effectiveness of two typical soil conservation measures, terrace and contouring cropping, in reducing soil erosion using fallout 137 Cs measurements. In the slope farmland of the Dingjiagou catchment, the upper position contained the highest amount of 137Cs whereas the lower position had the lowest 137Cs. The amounts of 137Cs of sampling sites decreased from upper, mid and lower positions in the slope farmland (Fig. 4). The inventories of 137Cs were 1079.03 84.09, 862.37 66.43, and 296.28 26.81 Bq m2 on the upper, middle and lower slope positions, respectively. Using the 137Cs converting model, soil erosion rates are correspondingly calculated to be 23.56, 27.08, and 36.26 Mg per hectare per year on the upper, middle and lower slope positions,
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1483
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Environmental Science: Processes & Impacts
Inventory of 137Cs and erosion rates at the different slope positions on the slope farmland in the Dingjiagou catchment (bars represent uncertainties for inventory and the error of mean for soil erosion rates. The following figures are the same).
Fig. 4
respectively. The sediment budget calculated using 137Cs inventories showed that much soil was lost from the eroded slope farmland. Fig. 5 shows the distribution of 137Cs inventory and soil erosion rates at the different positions on the terrace farmland in the Dingjiagou catchment. In contrast to the slope farmland, the amounts of 137Cs of sampling sites have no signicant difference at different positions on the terrace farmland. The inventories of 137Cs were 1183.47 94.71, 947.83 77.62, and 831.78 65.12 Bq m2 on the upper, middle and lower positions, respectively. Correspondingly, the erosion rates slightly increased in the following order: upper < middle < lower with the rates of 21.87, 25.69, and 27.57 Mg per hectare per year, respectively (Table 1). Compared with the slope farmland, the terrace measure reduced soil erosion by 7.73, 5.41 and 31.52% on the upper, middle and lower slope positions. In total, the terrace measure reduced soil erosion by 15.67% for the entire slope. In the Xingsheng catchment (Fig. 6), the upper and lower positions contained a higher amount of 137Cs whereas the middle position had a less 137Cs inventory for the slope farmland. The inventories of 137Cs were 809.4 71.26, 612.36 52.55, and 929.34 71.59 Bq m2 on the upper, middle and lower slope positions, respectively. Correspondingly, along the downslope positions, erosion rates were calculated to be 32.53,
1484 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Paper
137
Cs inventory and erosion rates at different slope positions on the terrace farmland in the Dingjiagou catchment.
Fig. 5
39.92, and 31.50 Mg per hectare per year on the upper, middle and lower slope positions, respectively (Fig. 6). While on the contour cropping farmland, the amount of 137 Cs and soil erosion rates had no signicant difference among the different slope positions (Fig. 7). The amounts of 137Cs were 1052.7 96.49, 1190.45 116.23, and 1196.56 95.84 Bq m2 on the upper, middle and lower slope positions, respectively. Correspondingly, soil erosion rates on the contour cropping farmland were calculated to be 23.09, 21.75, and 22.89 Mg per hectare per year on the upper, middle and lower slope positions, respectively. Compared with slope farmland, contour cultivation reduced soil erosion by 40.88, 83.54 and 37.61% on the upper, middle and lower slope positions, respectively. In total, the contour cultivation reduced soil erosion by 53.48% for the entire slope (Table 2). Gully development in Baiquan County using GPS survey
137
Cs tracer and
Gullies are extensively distributed in the gentle sloping hillygully regions of Northeastern China. In addition, gullies in the agricultural environment are effective links between upland areas and channels. By establishing a sediment chronology within the gully systems using 137Cs dating we intended to develop a relationship between gully development and the history of gully catchment land use. Comparing the data from the RTK-GPS survey in 2005 with digital data from a contour map in 1983, we studied the gully
This journal is © The Royal Society of Chemistry 2014
View Article Online
Paper Table 1
Environmental Science: Processes & Impacts Effectiveness of the terrace farmland in reducing soil erosion compared with the slope farmland in the Dingjiagou catchment
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
137
Soil erosion rate (Mg per hectare per year)
Cs inventory (Bq m2)
Slope position
Terrace farmland
Uncertainty
Slope farmland
Uncertainty
Terrace farmland
Slope farmland
Soil erosion reduction percent by the terrace farmland (%)
Upper Middle Lower Total
1183.47 947.83 831.78 987.69
94.71 77.62 65.12 79.15
1079.03 862.37 296.28 745.89
84.09 66.43 26.81 59.11
21.87 25.69 27.57 25.04
23.56 27.08 36.26 28.97
7.73 5.41 31.52 15.67
137 Cs inventory and erosion rates at the different slope positions on the slope farmland in the Xingsheng catchment.
Fig. 6
Fig. 7 137Cs inventory and erosion rates at different slope positions on the contour cropping farmland in the Xingsheng catchment.
erosion development as affected by the land use. By comparing gully area morphologies in two years, we found that a new eroding gully developed in 2005 in the place where there was no gully at all in 1983, while the topographical conditions and landscape position are the same except that the cropping ridge directions changed. The slope is gentle in the place where the new gully has initiated a link with the old gully, which cannot be explained by the topography evolution. It can mainly be attributed to agronomic practices such as the growth of soybeans on ridges in Northeastern China, resulting in concentrated ow erosion occurrence in furrows between ridges during the rainfall, as concentrated ow is the main factor for gully development. Severe gully erosion may occur if the run-off is concentrated in furrows between ridges. Furrows between ridges concentrate water during storms and are persistent sources of sediment, as well as effective conduits for transporting eroded soil to gullies and channels. Gully parameters of the Xingsheng gully estimated from 137 Cs dating and the RTK-GPS survey are shown in Table 3.
This journal is © The Royal Society of Chemistry 2014
Based on the data from the RTK-GPS survey, the gully length of 182.5 m was developed from 1983 to 2005. The total erosion amount for the Xingsheng gully was 4093 t. Taking average sediment yields by sheet erosion as 34.65 Mg per hectare per year, derived by the 137Cs tracing method, gully erosion contributed 69% of the total sediment yield in the study catchments. An average bulk density of 1.3 g cm3 from measurements was used for calculation of sediment yields and the gully erosion rate.
Discussion The intensive agricultural cultivation history of Northeastern China is over hundreds of years. In places where soil erosion is less severe, the soil is 40 cm to more than 1 m deep, but soil depths decreased to less than 40 cm in highly eroding places and in some locations the loess parent material is even
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1485
View Article Online
Environmental Science: Processes & Impacts Table 2
Paper
Effectiveness of contour cultivation in reducing soil erosion, compared with the slope farmland in the Xingsheng catchment
137
Soil erosion rate (Mg per hectare per year)
Slope position
Contour cropping
Uncertainty
Slope farmland
Uncertainty
Contour cropping
Slope farmland
Soil erosion reduction percent by the contour cultivation (%)
Upper Middle Lower Total
1150.7 1190.45 1196.56 1179.24
96.49 116.23 95.84 102.85
809.4 612.36 929.34 783.70
71.26 52.55 71.59 65.13
23.09 21.75 22.89 22.58
32.53 39.92 31.5 34.65
40.88 83.54 37.61 53.48
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Cs inventory (Bq m2)
Table 3
Gully parameters of the Xingsheng gully estimated from 137Cs dating and the GPS survey
Gully depth (m)
Gully width (m)
Mean
Maximum
Mean
Maximum
Gully length (m)
Drainage area (m2)
Gully erosion amount (t)
1.2
6.42
13.2
20.7
182.5
11 916
4093
outcropping.12 Results from Baiquan County showed that the upper position contained the highest amount of 137Cs whereas the lower slope position had the lowest 137Cs for the slope farmland. The sediment budget calculated using 137Cs inventories showed that much soil was lost from the eroded slope farmland. Average soil losses derived from 137Cs in this study are comparable to those studies measured with remote sensing or runoff plots in Northeastern China. Water erosion on slope farmland and in the gully is the dominant soil erosion process in Northeastern China.11–14,16,17 Table 4 gives an overview of soil loss values measured in Northeast China for total soil erosion or individual soil erosion processes. This table shows that water erosion can cause soil losses from 5 to 60 Mg per hectare per year. Evidence of serious tillage
Table 4 Soil erosion rates derived from
erosion is given by the fact that the total soil loss on convexities (shoulders) amounted up to 60 Mg per hectare per year on a hill slope in the Songhua river basin (Table 4). Derived from 137Cs in this study, the soil erosion rate in Northeastern China is 31.81 Mg per hectare per year for the slope farmland and 76.47 Mg per hectare per year for gully erosion. This study showed that soil conservation measures such as the terrace and contour cropping in Northeastern China are effective ways for reducing soil erosion. The soil erosion rate, derived from 137Cs techniques, is 25.04 Mg per hectare per year for the terrace farmland and 22.58 Mg per hectare per year for the contour cropping farmland. The widespread terrace in the region is generally believed to be an effective soil conservation measure in low hilly-gully areas
137
Cs in this study and other data in Northeastern China
Erosion process
Soil loss (Mg per hectare per year)
Study sites and remarks
Source
Water erosion
31.81 (a), 25.04 (b), 22.58 (c), 76.47 (d)
This study
Water erosion
30–50
Water erosion
5–25
Water erosion
5.5–13.2 (a), 7.5–31.3 (b), 16.4–60 (c)
Total soil erosion
24 (TS), 60.0 (SS), 26.2 (BS)
Slope farmland (a), terrace farmland (b), contour cropping farmland (c), gully erosion (d), in Baiquan, Northeastern China Water erosion area of North-east China based on the national soil erosion survey, using topographical maps (1 : 100 000), remote sensing, eld survey and plot measurements Jilin Province based on the remote sensing study and eld survey cropland Liaoning Province based on runoff plots on the hilly eld measured during the 1980–1990 period slopes: a, 6 ; b, 10 ; c, 15 TS, top of the slope; SS, the slope shoulder; BS, the backslope. 137Cs study on crop land for a typical slope transecting the Songhua River basin
1486 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Cai et al.13 and Fan et al.12
Zhu and Quan17
Sun et al.16
Fang et al.14
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Paper
of Northeastern China. Compared with the slope farmland, the terrace measure reduced soil erosion rates by 16% for the entire slope. The terrace eld could slow or prevent the rapid surface runoff in the low hilly-gully areas due to interception of runoff water and a short slope length, which reduced runoff and soil erosion rates signicantly. The soybean cultivation in terraces plowing following the natural contours is a classic feature in the low hilly-gully areas of Northeastern China. Terraces are easier for both mechanical and manual sowing and harvesting than steep slopes. Runoff as concentrated ow from the sloping land can be controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace cultivation. Contour cropping, involving sowing crops across the slope in line with contours, is another effective soil conservation measure. The amount of 137Cs and soil erosion rates made no signicant difference in different slope positions on the contour cropping farmland in the Xingsheng catchment. Contour cultivation measures could effectively control soil erosion, especially on the middle position where serious soil erosion occurs. In total, contour cultivation reduced soil erosion losses up to 53.48% for the entire slope. Soil losses can be controlled by changing tillage practices from downslope cultivation to contour cultivation. Contour cropping reduces erosion by reducing the length of the slope. The crops provide a perpendicular barrier to run-off due to stem density. Theoretically this reduces both erosion and run-off by removing natural drainage channels down the slope which occur with conventional cropping. Reducing run-off improves inltration and reduces soil erosion. Whereas if rain falls on sloping land, it tends to run off rapidly as concentrated ow in the furrows. In practice contour cropping is more effective on lands with long, uniform, and gentle slopes. On steeper slopes, if without supplementary practices, the effectiveness of contouring is generally reduced because of possible breakover of rows by runoff water. Our results suggested that gully erosion is the major sediment source and the dominant water erosion process causing considerable soil losses in Baiquan County. Gullies developed in farmlands not only act as sources of sediments but also aggravate ooding and silting of reservoirs. Based on the data from the RTK-GPS survey, gullies with a length of 182.5 m have been developed in the last 20 years. Results showed that gully erosion contributed to 69% of the total sediment yield in the study catchments. The reason for gully initiation and development could be explained by the unreasonable downslope cropping ridge measures in combination with extreme rainfall. Natural gullying processes are accelerated by the intensication of annual cropping. The downslope cropping ridges collected the overland ow, which incised through the plough layer, and then the gully initiated and developed in the cropland. The spaces between ridges act as the runoff way to concentrate the overland ow, and enhance gully development. The main technique to prevent gully development is to convert a downslope cropping ridge to a contour cropping ridge or to establish stiff grass hedges. The contour cropping ridge and grass hedges can retard and spread out surface runoff, cause deposition of eroded sediments, and hence prevent gully incision.
This journal is © The Royal Society of Chemistry 2014
Environmental Science: Processes & Impacts
Conclusions Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers in Baiquan County. In the Dingjiagou catchment, the sediment budget calculated using 137Cs inventories showed that much soil was lost from the eroded slope farmland. The terrace eld reduced soil erosion rates by 16% for the entire slope, compared with the slope farmland. In contrast to the slope farmland, the contour cultivation reduced soil erosion rates by 53% for the entire slope. These results indicated that soil losses can be controlled by changing tillage practices from the slope farmland cultivation to the terrace or contour cultivation.
Acknowledgements This study was supported by the National Nature Science Foundation of China (no. 41371285), the National S&T Major Project (no. 2012ZX07104003), the Special Foundation for Basic Scientic Research of Central Public Welfare Institute and Agricultural Clear Watershed Group, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences (CAAS). We would give thanks to Lu Li and Jun-Jie Li for GPS surveying and data processing.
Notes and references 1 A. Cerd` a, Can. J. Soil Sci., 1998, 78, 321–330. 2 R. Lal, M. Griffin, J. Apt, L. Lave and G. M. Morgan, Science, 2004, 304, 393. 3 G. Zhao, X. Mu, Z. Wen, F. Wang and P. Gao, Land Degradation & Development, 2013, 24, 499–510. 4 Z. M. Feng, Y. Z. Yang, Y. Q. Zhang, P. T. Zhang and Y. Q. Li, Land Use Policy, 2005, 22, 301–312. 5 Q. J. Liu, Z. H. Shi, X. X. Yu and H. Y. Zhang, Soil Tillage Res., 2014, 136, 1–8. 6 C. Y. Miao, L. Yang, X. H. Chen and Y. Gao, Land Degradation & Development, 2012, 23, 62–71. 7 D. C. Reicosky, in Conservation Agriculture: A worldwide challenge, ed. L. Garcia-Torres, J. Benites and A. MartinezVilela, Cordoba, Spain, 2001, pp. 3–12. 8 Y. Q. Wang and M. A. Shao, Land Degradation & Development, 2013, 24, 296–304. 9 Q. X. Xu, T. W. Wang, C. F. Cai, Z. X. Li and Z. H. Shi, Land Degradation & Development, 2012, 23, 34–42. 10 P. Prokop and G. J. Pore ˛ba, Land Degradation & Development, 2012, 23, 310–321. 11 J. M. Sun and T. S. Liu, Quat. Sci., 2001, 21, 72–78. 12 H. M. Fan, Q. G. Cai and H. S. Wang, J. Soil Water Conserv., 2004, 18, 66–70. 13 Q. G. Cai, H. M. Fan and B. Shen, J. Soil Water Conserv., 2003, 17, 21–24. 14 H. J. Fang, X. J. Yang and X. P. Zhang, Chin. J. Appl. Ecol., 2005, 16, 464–468. 15 H. Y. Fang, M. L. Sheng, Z. H. Tang and Q. G. Cai, Soil Tillage Res., 2013, 133, 85–92.
Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488 | 1487
View Article Online
Published on 17 March 2014. Downloaded by Brown University on 24/10/2014 22:07:27.
Environmental Science: Processes & Impacts
16 J. H. Sun, Y. G. Yang and B. J. Zhang, Research of Soil and Water Conservation, 1997, 4, 63–74. 17 Z. E. Zhu and H. Quan, Bulletin of Soil and Water Conservation, 1992, 12, 33–37. 18 T. J. Liu, D. Shan, J. Y. Guo, T. M. Gao and X. B. Zhao, Agric. Sci. Technol., 2011, 12(12), 1925–1928. 19 C. Fern´ andez, J. A. Vega, E. Jim´ enez, D. C. S. Vieira, A. Merino, A. Ferreiro and T. Fonturbel, Land Degradation & Development, 2012, 23, 150–156. 20 P. Licznar and M. A. Nearing, Catena, 2003, 51, 89–114. 21 T. Iserloh, J. B. Ries, J. Arnaez, C. Boix Fayos, V. Butzen, A. Cerd` a, M. T. Echeverr´ıa, J. Fern´ andez-G´ alvez, W. Fister, C. Geißler, J. A. G´ omez, H. G´ omez-Macpherson, N. J. Kuhn, R. L´ azaro, F. J. Le´ on, M. Mart´ınez-Mena, J. F. Mart´ınez-Murillo, M. Marzen, M. D. Mingorance, L. Ortigosa, P. Peters, D. Reg¨ u´ es, J. D. Ruiz-Sinoga, T. Scholten, M. Seeger, A. Sol´ e-Benet, R. Wengel and S. Wirtz, Catena, 2013, 110, 100–112. 22 I. T. Meerveld and M. Weiler, J. Hydrol., 2008, 361, 24–40. 23 F. M. Ziadat and A. Y. Taimeh, Land Degradation & Development, 2013, 24, 582–590. 24 D. D. Alexakis, D. G. Hadjimitsis and A. Agapiou, Atmos. Res., 2013, 131, 108–124. 25 B. J. Fu, W. W. Zhao, L. D. Chen, Q. J. Zhang, Y. H. L¨ u, H. Gulinck and J. Poesen, Land degradation & development, 2005, 16(1), 73–85. 26 A. Routschek, J. Schmidt, W. Enke and T. Deutschlaender, Geomorphology, 2014, 206, 299–306. 27 Z. H. Shi, L. Ai, N. F. Fang and H. D. Zhu, J. Hydrol., 2012, 438, 156–167. 28 R. J. Loughran, Progr. Phys. Geogr., 1990, 13, 216–233. 29 D. L. Higgitt, Progr. Phys. Geogr., 1991, 15, 91–100. 30 Y. Li, J. Poesen, J. C. Yang, B. Fu and J. H. Zhang, Soil Tillage Res., 2003, 69, 107–115. 31 V. Chaplot and J. Poesen, Catena, 2008, 88, 46–56. 32 R. DeFries and K. N. Eshleman, Hydrol. Processes, 2004, 18, 2183–2186. 33 B. L. Campbell, G. L. Elliott and R. J. Loughran, J. Soil Water Conserv., 1985, 41, 86–89. 34 L. Gaspar and A. Navas, Geoderma, 2013, 207–208, 131–143. 35 R. J. Loughran, Trends in Hydrology, 1994, 1, 149–167. 36 F. Zapata, Soil Tillage Res., 2003, 69, 3–13. 37 A. S. Rogowski and T. Tamura, Health Phys., 1965, 11, 1333– 1340. 38 D. E. Walling and T. A. Quine, J. Soil Sci., 1991, 42, 147– 165. 39 I. Vanden Berghe and H. Gulinck, Pedologie, 1987, 37, 5–20.
1488 | Environ. Sci.: Processes Impacts, 2014, 16, 1480–1488
Paper
40 T. A. Quine and D. E. Walling, Soil Use Manage., 1991, 7, 169– 176. 41 J. C. Ritchie, J. R. McHenry, A. C. Gill and P. H. Hawks, Proceedings of the Mississippi Water Resource Conference, Mississippi, 1970. 42 M. S. Al-Masri and A. W. Doubal, Appl. Radiat. Isot., 2013, 75, 50–57. 43 M. L. Montes, L. M. S. Silva, C. S. A. S´ a, J. Runco, M. A. Taylor and J. Desimoni, J. Environ. Radioact., 2013, 116, 133–140. 44 P. J. Wallbrink and A. S. Murray, Hydrol. Processes, 1993, 7, 297–304. 45 Y. Li, Q. W. Zhang, D. C. Reicosky, L. Y. Bai, M. J. Lindstrom and L. Li, Soil Tillage Res., 2006, 86, 176–184. 46 R. A. Sutherland, Land Degrad. Rehabil., 1989, 1, 199–208. 47 Y. Q. Qi, X. B. Zhang, X. B. He, A. B. Wen and J. X. Fu, Nuclear Techniques, 2006, 29, 42–50. 48 J. J. Kiss, E. de Jong and L. W. Martz, J. Environ. Qual., 1988, 17, 445–452. 49 J. C. Lance, S. C. McIntyre, W. Naney and S. S. Rousseva, Soil Sci. Soc. Am. J., 1986, 50, 1303–1309. 50 A. J. Parsons and I. D. Foster, Earth–Sci. Rev., 2011, 108, 101– 113. 51 M. Benmansour, L. Mabit, A. Nouira, R. Moussadek, H. Bouksirate, M. Duchemin and A. Benkdad, J. Environ. Radioact., 2013, 115, 97–106. 52 Q. He and D. E. Walling, Appl. Radiat. Isot., 1997, 48, 677– 690. 53 T. Wells and G. Hancock, Geoderma, 2014, 214–215, 228–238. 54 F. Zapata and Y. Li, Working material, IAEA-311-D1-RC-888, Vienna, Austria, 2007. 55 T. Y. Yu, X. Y. Zhang, S. L. Zhang and X. W. Chen, Bulletin of soil and water conservation, 2007, 27, 71–74. 56 Ministry of Water Resources, Chinese Academy of Sciences, Chinese Academy of Engineering, Soil and water conservation and ecology safety in China, Science publishing press, Beijing, 2010, pp. 270–281. 57 J. R. Zhao, S. L. Sun and L. H. Zhao, Water Resources & Hydropower of Northeast China, 2002, 20, 41–42. 58 China Yearbook Full-text Database(CYFD), http:// number.cnki.net/cyfd, accessed July 2008. 59 SAS Institute, SAS user's guide, Statistics, version 9.3, Statistical Analysis System Institute Inc., Cary, NC, 2011. 60 D. E. Walling, Q. He and P. G. Appleby, in Handbook for the assessment of soil erosion and sedimentation using environmental radionuclides, ed. F. Zapata, Kluwer Academic Publishers, Dordrecht, 1997, pp. 111–164. 61 B. X. Yan and J. Tang, J. Soil Water Conserv., 2004, 18, 33–36.
This journal is © The Royal Society of Chemistry 2014
