FJ-6

FJ-7

FJ-8

FJ-9

FJ-10

FJ-11

FJ-12

FJ-13

FJ-14

FJ-15

FJ-16

Fig. 1. Topography of Field-1

36

8.4

8.6

8.8

9

9.2

9.4

9.6

Fig. 2. Three dimension topography of field-1

37

FJ-17

FJ-22

FJ-18

FJ-19

FJ-20

Fig. 3. Location of sampling points at Field-2

38

0 200 400 600 800 1000

2-4

6-8

10-12

14-16

18-22

24-26

28-40

Dep

th (c

m)

Activity (Bq/m2)

Fig. 4. Depth profile of Cs-137 of reference site at Fateh Jang

Fig. 5. Inventory of Cs-137 at reference site by bulk cores

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

No. of bulk core

Act

ivity

(Bq/

m2 )

39

Fig. 6. Depth profile of Cs-137 of reference site at Satra Meel

Fig. 7. Depth profile of Cs-137 of reference site at Missa Kaswal

0 200 400 600 800 1000 1200 1400

2-4

6-8

10-12

14-16

18-22

24-26

Dep

th (c

m)

Activity (Bq/m )2

0 100 200 300 400 500 600 700

0-2

2-4

4-6

6-8

8-10

10-12

12-14

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16-18

18-22

22-24

24-26

26-43

Dep

th (c

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Activity (Bq/m2)

40

FJ-6

FJ-7

FJ-8

FJ-9

FJ-10

FJ-11

FJ-12

FJ-13

FJ-14

FJ-15

FJ-16

Fig. 8. Contours of soil loss at Field-1

41

Fig. 9. Three dimensional view of Cs-137 Inventory in Field-1

Fig. 10. Three dimensional map showing soil loss/deposition at Field-1

42

3.4. Philippines

3.4.1. Country Report Partners Institution: Philippines Nuclear Research Institute (PNRI), and Bureau of Soils and Water Management (BSWM). (University of the Philippines-Los Banos and Department of Environment and Natural Resources, future implementation) National Project committee: Philippines Nuclear Research Institute (PNRI), and Bureau of Soils and Water Management (BSWM). (University of the Philippines-Los Banos and Department of Environment and Natural Resources, future implementation) Selection of study area: Two cultivated sites and one uncultivated site Specific Objectives of the study: • To establish soil and sediment sampling methodology • To establish analytical procedures • To establish reference inventories in the study sites and to do 137Cs analysis on core samples

from study sites Application of Cs137 technique: (please refer to the attached technical report) Staff Training: • one staff on sampling, measurements and data analysis (Walling’s lab, 4 months, under PHI

001 Human Resource Development program) • one staff on sampling and data analyis (proposed, being processed) Local training Cs137 analysis 2 staff members Laboratory upgrading • one dedicated gamma analysis system Other project activities • application of Pb210 (through Po210 alpha) in soil erosion studies Recommendations: • Explore the application for other radionuclides in erosion/deposition studies • Work on one site to establish the reference inventory, topographic description (digital

topographic map) and soil redistribution in the area using Cs137 and Pb-210.

43

3.4.2. Technical Report Philippines E.Z.Sombrito, C.Rosales, A.Bulos, R.Balog, F.Rivera & E.Sta.Maria, Philippine Nuclear Research Institute Commonwealth Ave., Diliman 1101 Quezon City, Philippines Z. Reyes & D.Margate Bureau of Soils and Water Management Elliptical Road, Diliman 1101 Quezon City, Philippines (1) Introduction The use of Cesium-137 (137Cs) as tracer in soil erosion management has been demonstrated in many areas of the world, including the tropical areas of Thailand and Africa (1). However, in the Philippines, the technique has not been used yet for the quantification of erosion rate. There is also no quantitative data on long-term erosion rate in the country. A quantitative representation of the erosion problem is often very difficult to obtain because of the problems associated with data collection, and the diversity of analytical methods used. Although several methods have been used for predicting and quantifying soil erosion, the use of isotopes for the reconstruction of the erosional records, including the dating of sediment and studying topsoil movement has not been explored locally yet. Considering its latitudinal position, terrain, climatic conditions and land usage, the soil is expected to contain low level of 137Cs. During the peak of fallout deposition, the deforestation data showed that most areas were forested, further limiting the amount of 137Cs directly accreting in the soil surface. Rainfall would be high, resulting in the removal of 137Cs that may be directly deposited in the surface. Thus, this particular study is being implemented initially to assess the applicability of using the 137Cs technique in cultivated and uncultivated soil in the country. This is being accomplished by collecting data on the level of Cs-137 both in terms of horizontal and vertical distribution in soil in three different study sites. This study is conducted within the framework of the regional cooperation IAEA/ RAS 5/039 Restoration of Soil Fertility and Sustenance of Agricultural Productivity, Part 2. Measuring Soil Erosion/Sedimentation and Associated Pesticide Contamination. The Philippine Situation The Philippines lies SE of Asia, between latitudes 4º23' to 21º25'N, 116º to 127ºE. Its climate is tropical marine with generally rainy season from May to October and dry season from November to April. The average annual rainfall ranges from 914 to 4358 mm.(2). The Philippines has the most number of passage of tropical cyclones, averaging 19 up to 20 tropical cyclones per year, though not all areas of the country are in the path of the cyclones. Associated with tropical cyclones and heavy rainfall are floods and storm surges. Many areas of the Philippines can also suffer from droughts associated with the occurrence of ENSO. The country has a total land area of 300,000 sq. km. It is mostly mountains with narrow to extensive coastal lowlands. Based on a slope of 11%, an estimated 58% of the country’s total land area is on a slope (2) Arable land is about 5.65 M ha (2001, FAO Statistics) with areas affected by moderate to severe erosion estimated at 14 M ha.(1992-1993). The rate of soil erosion on slopelands can be high, with annual soil losses ranging from 23 - 218 mt/ha from bare plots on gradients of 27-29% to 36-200 mt/ha on plots cultivated up and down the slope(3) With deforestation and agricultural intensification, soil erosion is greatly accelerated in the country. At the beginning of the century, forests cover 70%. From 1970 to 1990, forests declined from about one third to one-fifth of land area.

44

(2) Study Sites The study sites (Figure 1) covered by this report are located in the provinces of Bukidnon (Central Mindanao), Nueva Ecija (Central Luzon) and Isabela (Northern Luzon). Study Site 1 - Description The study site is described as follows:

Location Barangay Dalwangan, Malaybalay, Bukidnon

Coordinates 8o12'N , 125o12' E Elevation 900 m ASL Annual rainfall 2663 mm (1989-2002) Classification Ultisols (clay loam) Parent Materials Andesitic and basaltic rocks Soil Erosion History Water and tillage erosion General Description These soils found on plateau with

undulating to rolling landscapes, are reddish brown to yellowish red clay loam and well-drained

Major Land Use Corn is the major land use. The soils are also grown to pineapple and sugarcane. Prior to 1980, the area was planted with fruit trees. Contour lines were established in early 80’s

Type of soil conservation works

Contour lines were established in early 80’s, terracing

Soil sampling for 137Cs analysis. Nine sampling points were established at the cultivated slope transect, corresponding to strategic portions of the slope facet model i.e summit to toeslope. (Figure 2). A soil pit of about 60 cm depth was dug into each sampling points at disturbed site to characterize the depth distribution of 137Cs in the study area. A total of 10 sections at a uniform depth of 5 cm were extracted from the soil pit. Twenty-two bulk samples were also collected using soil auger from these nine sampling points. To establish the reference value for 137Cs inventory in the area, two sets of samples were collected. One set was obtained from a forest area with no visible events of erosion and is presumably an undisturbed area. The second set of five samples were collected on a grassy undisturbed area by bulk sampling using a soil corer. Study Site 2 – Description

Location Baligatan, Ilagan, Isabela. Coordinates 17009’ N and 121053’ E Elevation 86 m Annual rainfall 1473 mm (1990-1999) Soil type sandy loam to clay loam, brown to dark

brown in color and non-sticky. Soil Erosion History Water erosion General Description Rolling to hilly and mostly covered by

45

grass Major Land Use Pasture land during the 70’s, planted with

sweet potatoes in mid 90’s. Presently, the area is planted with banana and rice.

Type of soil conservation works

none

Soil sampling for 137Cs analysis The samples collected correspond to the hill-slope model. For every portion of the slope, 5 soil samples were collected using a steel pipe cylinder, with diameter of about 8.1 cm. Samples were collected down to about 30 cm depth. Reference samples were collected from an adjacent uncultivated (undisturbed) site. One sample was collected using a metal scraper of 990 cm2 area to a depth of 20 cm (BAR1). Sixteen other samples were collected using a steel pipe corer with a diameter of 8.1cm (BAR2). Eight bulk samples were also collected using the same corer from a site 300 m away from the first site (BAR3). Study Site 3 – Description

Location Pantabangan, Nueva Ecija Coordinates 15o46’N, 121o13’ E Elevation 300 m Annual rainfall 1960 mm Soil Type Clay loam General Description Open grassland, slope > 16% Major Land Use Uncultivated.

Soil sampling for 137Cs analysis Soil samples were taken from two erosion plots (100 m2) which are situated in a sloping portion of the study site using soil auger. Erosion plots (Plot N and Plot S) were laid down during a previous study in the site. Four samples from each of the erosion plots were obtained Samples were also collected from an area where deposition could have been occurring. The reference samples were obtained from a flat area on top of the hill. The area is not strictly undisturbed as there are signs that animals and humans trod the area. Relative to the erosion plots, however, the area is relatively undisturbed. Using a metal scraper (area=990 cm2), samples were collected at 2 cm depth increments, up to a depth of 20 cm . Sixteen (16) soil bulk samples were collected using a soil auger at different depths from this reference site. Samples were collected two meters apart from each point running in two straight lines that are also two meters apart from each other. Eight sampling points were collected from each line. Another set of reference samples were collected from Palabuan, Pantabangan, about a kilometer west of the first sampling site. (3) Methods A. Soil Sample Preparation The soil samples were oven-dried at 40oC for at least 24 hours, ground to pass a 2 mm sieve, homogenized and quartered. About 1000 g of soil sample is placed into a one liter Marinelli beaker.

46

Samples that are not enough to fill the one liter Marinelli beaker were placed in a 500 ml Marinelli beaker. B. Gamma Spectrometry of 137Cs 137Cs concentrations were measured by gamma-spectrometry at 662 keV, using a high-resolution coaxial HPGe detector with relative efficiency of about 20%. The counting time ranged from 24 hours to 36 hours depending on the 137Cs content of the samples. A mixed Amersham radionuclide standard was used to measure the efficiency at the counting geometry used. C. 210Pb analysis 210Pb was determined by measurement of its daughter nuclide, 210Po, which decays by alpha particle emission. (Secular equilibrium was assumed) Sample digestion involved acid treatment of dried one-gram samples spiked with a 208Po tracer for chemical yield measurement followed by spontaneous plating onto a silver disc. 210Po and 208Po were detected by counting in an alpha particle spectrometry system using a surface barrier silicon detector for a minimum of 24 hours. (4) Results A. Bukidnon - Reference site A1. Three reference samples were initially collected through incremental soil sampling from this site. These were labeled DaR1, DaR2 and DaR3. The reference samples were collected from a forest area with no visible events of accelerated erosion and is presumably an undisturbed area. Figures 3 a-c show the depth profile of 137Cs inventory in these three samples. The depth at which 137Cs has penetrated the soil layers and the total 137Cs inventory in DaR1 indicate that the site is a depositional site. Indeed, DaR1 was taken at the foot of a sloping area. (Figure 4). The exponential plot of inventory versus depth shown in Figure 5 gave an acceptable linear correlation for DaR2 and DaR3 and therefore these values were included in the reference values for the site. Additional samples were collected by bulk sampling in another visit to the site. Table 1 gives the values obtained for the reference samples.

137Cs Inventory (Bq/m2) DaR 2 210 ± 30 DaR 3 260 ± 40 DaR 4 220 ± 20 DaR 5 200 ± 30 DaR 6 240 ± 20 DaR 7 200 ± 20 Average (6) 220 ± 20

These reference values are considerably lower than the values expected from computed value based on rainfall data in the area (600 Bq/m2). However, there is little dispersion in the values obtained. Some erosional process could have occurred from the period of 137Cs deposition to the present time or the conditions at the time of deposition could have resulted in low deposition because of forest cover in the area. Extrapolation of the linear exponential plot to 600 Bq/m2 would mean that a soil layer of 20 cm could have been eroded from the area. A very simplistic calculation will translate this depth to an erosion rate of 50 t/ha/yr. A.2 Study Site

47

Nine sampling points were established at the cultivated slope transect to a depth of about 50 cm. Figure 6 shows a graphical presentation of the slope and distance of the points relative to each other together with the total Cs inventory in the study points. Figures 7a-i give the horizontal bar chart of each inventory in the area. The total inventory is summarized in Table 2. Table 2. Cs inventory in Dalawangan study site. DAC1 is at the foot of the hill. 137

Sample ID Total Inventory

Bq/m Error Bq/m 2

DaC1 300 70

137

2

DaC2 420 60 DaC3 320 50 DaC4 250 50 DaC5 260 60 DaC6 190 40 DaC7 320 70 DaC8 240 20 DaC9 110 20

Considering the uncertainties in the measurements for the reference and the sample inventories, DaC2 and DaC3 at the foot slope are depositional sites including DaC7 while DaC9 at the summit is an erosion site. DaC6 may be an erosion site while the rests of the sites do not differ significantly from the reference values. More soil samples along the slope have been collected to take note of the variability within the same slope point. An attempt to convert the 37Cs loss and gain to soil loss was made using the proportional model of Walling and Que (5). The conversion gave an estimated deposition rates of 17 t/ha/yr (DaC3) to 24 t/Ha/yr (DaC2) and erosion rate in the summit (DaC9) of 22 t/ha/yr. Erosion plots of a cultivated area estimated recent erosion processes in the area at 7-14 t/ha/yr Particle size analysis showed that soils taken from the summit have higher sand content than the other part of the slope. B. Isabela B1. Reference Site Three areas were sampled for the measurement of local 137Cs inventory. The data are shown in Table 3. Table 3. 137Cs activity concentrations in Reference sites in Ilagan, Isabela 3a.Reference Sample 1 : Location -Baligatan Area; Method of Sampling Scraper Plate, 989.8 cm2

Sample Code

Depth (cm) General Soil Appearance 137Cs Activity mBq/kg

137Cs Inventory Bq/m2

BaR1-1 0 - 3.8 Light brown, Clay loam 1200 ± 80 70 ± 4.52 BaR1-2 3.8 - 5.8 Light brown, Clay loam ND BaR1-3 5.8 - 7.8 Light brown, Clay loam 60 ± 8 ND BaR1-4 7.8 - 9.8 Light brown, Clay loam ND ND BaR1-5 9.8 – 11.8 Yellowish brown, Clay loam ND ND BaR1-6 11.8 – 13.8 Yellowish brown, Clay loam ND ND BaR1-7 13.8 – 15.8 Yellowish brown, Clay loam ND ND BaR1-8 15.8 – 17.8 Yellowish brown, Clay loam ND ND BaR1-9 17.8 – 19.8 Yellowish brown, Clay loam ND ND

48

BaR1-10 19.8 – 39.8 soil auger

Yellowish brown, Clay loam ND ND

• ND – Not Detected 3.b Reference Sample 2 : Location Baligatan Area; Method of Sampling- Steel pipe Corer, 8.1cm Sample Code

Depth General Soil Appearance 137Cs Activity mBq/kg

137Cs Inventory Bq/m2

BaR2-1 42 Light brown, Clay loam ND ND BaR2-2 32 Light brown, Clay loam 150 ± 25 63±11 BaR2-3 32 Yellowish brown, Clay loam ND ND BaR2-4 34 Yellowish brown, Clay loam ND ND BaR2-5 30 Light brown, Clay loam 880 ± 60 340 ± 23 BaR2-6 32 Light brown, Clay loam ND ND BaR2-7 34 Brown, Clay loam ND ND BaR2-8 31 Brown, Clay loam 250 ± 36 100 ± 14 BaR2-9 34 Brown, Clay loam 210 ± 16 94 ± 8.1 BaR2-10 32 Brown, Clay loam 44 ± 6 17 ± 1.5 BaR2-11 30 Brown, Clay loam 260 ±23 93 ± 8.1 BaR2-12 30 Brown, Clay loam 100±14 39 ± 5.2 BaR2-13 34 Yellowish brown, Clay loam 300±35 140 ±16 BaR2-14 30 Yellowish brown, Clay loam 200±21 76±8.1 BaR2-15 36 Yellowish brown, Clay loam ND ND BaR2-16 31 Yellowish brown, Clay loam ND ND * ND – Not Detected 3.c Reference Sample 3 Location - Baligatan Area; Method of sampling: Steel Pipe Corer, 8.1 cm Sample Code

Depth (cm) General Soil Appearance 137Cs Activity mBq/kg

137Cs Inventory Bq/m2

BaR3-1 33 Light brown, Clay loam 510 ± 45 200 ± 18 BaR3-2 33 Light brown, Clay loam 570 ± 56 240 ± 24 BaR3-3 34 Light brown, Clay loam 460 ± 43 210 ± 19 BaR3-4 31 Light brown, Clay loam 600 ± 50 220 ± 18 BaR3-5 34 Light brown, Clay loam 310 ± 40 150 ±19 BaR3-6 34 Light brown, Clay loam 390 ± 44 160 ±18 BaR3-7 33 Light brown, Clay loam 170 ± 21 70 ± 8.7 BaR3-8 33 Light brown, Clay loam 220 ± 29 96 ± 12 For the first reference site, the 137Cs activity is present mostly in the upper 4 cm portion of the soil profile. The total 137Cs reference inventory for this site is only 73 Bq/m2. The second reference inventory site (BAR-2) is located adjacent to the first reference site. Sampling was done by a steel pipe cylinder corer. The 137Cs reference inventory obtained ranges from 40 to 340 Bq/m2. The 137Cs activity exhibits wide variability from one sampling point to the other. Interview with the farmers revealed that the area has been run over by machinery to create a foot path, although at the time of sampling there were tall cogon grasses. The third reference site in the area (BAR-3) is located about 300 meters away from the first two sites. Bulk sampling gave 137Cs inventories ranging from 70-240 Bq/m2 as presented in Figure 8. Compared to the values derived from the first sampling site, the 137Cs inventories are in closer agreement with each other, although there is still some degree of variability. The average reference inventory is about 170 ± 60 Bq/m2. More samples would have to be taken from the site to improve the precision. If the two lower values are excluded, the average inventory is 200 ± 30 Bq/m2, a value comparable to the Bukidnon value.

49

B2. The data for the cultivated areas show similar trend in the 137Cs inventory as in Bukidnon, where the summit displays soil loss and the bottom showing soil accretion. This is graphically presented in Figure 9. C. Nueva Ecija C.1 Reference site Two reference inventory sites were collected from Cadaclan area in the province of Nueva Ecija. The first reference site used the scraper method of sampling. The total inventory obtained for the first reference site was 140 Bq/m2 (Figure 10). This value is lower compared to the reference inventory value obtained from Bukidnon. 210Pb analysis was performed in the same sample obtained by the scraper method. This isotope is continuously produced in the atmosphere and deposited with air particulates to the ground. It has been found to associate with very fine soil and sediment. Since the soil in the area is mostly clay, it was thought that unsupported 210Pb can be detected in the soil. Figure 10 shows the 210Pb in the same samples collected by the scraper method. The activity is ten times as much. However, the correlation between the loss in 210Pb activity with soil loss needs interpretation. Bulk sampling in the same location gave inventory values from 90 Bq/m2 to 1100 Bq/m2, graphically presented in Figure 12. The variability is quite high at 60% (450 ± 280 Bq/m2). C.2 Study sites Two erosion plots were sampled. The inventories obtained are illustrated in Figure 12. The low inventory values indicate erosion in these 2 areas. The data are quite difficult to interpret and conversion to soil loss is not possible until the reference value has been established. (5) Summary 1. The reference values obtained from the three sites are as follows: • Study Site 1 (6) 220 ± 20 Bq/m2 • Study Site 2 (8) 170 ± 60 Bq/m2, (6) 200 ± 30 Bq/m2 • Study Site 3 (16) 450 ± 280 Bq/m2 2. The hill slope model in study sites 1 and 2 (both are cultivated) showed that the summit experiences 137Cs loss with corresponding deposition at the foot slope with generally no net 137Cs loss along the slope. 3. Converting 137Cs loss to soil loss using the proportional model gave an estimated ~20 t/ha/yr loss in the summit. 4. The 137Cs reference inventory exhibited large spatial variability. 5. 137Cs is generally detected to 20 cm depth. (6) Conclusion and recommendations Soil erosion is a major constraint in the agricultural development of the Philippines. The increasing population, and with it, the pressure for increased food production, results in the expansion of agriculture to marginal lands, usually leading to accelerated soil erosion. Appropriate soil erosion control techniques that could be employed to combat erosion in specific circumstances are available but generally not implemented. One aspect for non-implementation could be the absence of a quantitative estimate of the erosion and its impact on which policy makers can base their recommendations on (admittedly, among many other factors).

50

No quantitative data are available on how much soil loss have occurred in the last forty years, although estimates are often quoted to be 200 t/ha/yr on the high end of the scale. This gap can be addressed by using 137Cs as tracer for long-term erosion rate values. This study is the first attempt to measure 137Cs in agricultural soil samples. Measurements reported here were taken in cultivated slope lands. Erosion could be high during the past forty years because of rapid deforestation in the country coupled with high amount of rainfall and agricultural activities with no soil conservation measures. High erosion rate would result in low 137Cs values, as seen in the samples analyzed so far. Very low level 137Cs observed in most samples resulted in a measurement error as high as 30%. To improve the measurement statistics, long counting time is needed. The use of high efficiency Ge detector, low background shielding material and stable power supply should be considered. Furthermore, 137Cs in the study areas have patchy concentrations. This would mean taking more samples from an area translating to increased detector time for processing the samples. This problem can be addressed by adding a dedicated counting system in use. More training is needed in designing sample collection scheme to optimize the use of the detector time, considering that the detector time limits the number of samples that can be collected. The conversion of 137Cs loss to soil loss needs the choice of a model suitable for the study site. Guidance in this area is also needed. (7) Acknowledgement The funding assistance from the IAEA and the Bureau of Agricultural Researches are gratefully acknowledged. The laboratory facilities of the Bureau of Soils and Water Management and the Philippine Nuclear Research Institute were used in this study. The expert assistance of Dr. Robert Loughran and the support of Dr. Felipe Zapata, technical officer for this project, are deeply appreciated. (8) References • Walling, D.E., Use of 137Cs and other fallout Radionuclides in Soil erosion Investigations:

progress, problems and prospects in Use of 137Cs in the study of Soil erosion and sedimentation, Proc. of a consultant’s meeting, Joint FAO/IAEA, Vienna, 13-16 November 1995)

• Acebes, T.B. Country Report, 2000 http://www.cossa.csiro.au/reports/campbells/bkk/philrp.html

• Manguerra, J.D.,”Evaluation of various management practices for watershed erosion control” Master’s Thesis submitted to the Environmental Science Program, University of the Philippines, 1999.

• Paningbatan 1993 and Sajise 1983 in Crisanto R. Escaño and Sonny P. Tababa, Fruit Production and the Management of Slopelands in the Philippines, http://www.agnet.org/library/article/eb450.html, September 01, 1998.

• Walling, D.E & Q. He , Models for Converting 137Cs Measurements to Estimates of SoilRedistribution Rates on Cultivated and Uncultivated Soils, and Estimating Bomb-Derived 137Cs Refernce Inventories, IAEA. 2001.

51

Fig. 1. Three areas were sampled for 137Cs measurements: Malaybalaya, Bukidnon (Study Site 1), Ilagan, Isabela (Study Site 2) and Pantabangan, N. Ecija (Study Site 3)

Fig. 2. Nine samples were collected from study site 1,

located in Dalwangan, Malaybalay, Bukidnon, in Southern Philippines. The area is presently planted with corn.

52

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Dep

th, c

m

0

10

20

30

40

50

60

DaR-Activity, m

Total Inventory= 690 Bq/m2

Activity, mBq/kg

b

Total Inventory= 690 Bq/m2

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

-10

0

10

20

30

40

50

60

DaR2

Dep

th, c

m

Activity, mBq/kg

Total Inventory = 210 Bq/m2

DaR3

Activity, mBq/kg

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Dep

th, c

m

-10

0

10

20

30

40

50

60

DaR3

Total Inventory=260 Bq/m2

Figure 3. The depth at which 137Cs has penetrated the soil layers and the total 137Cs inventory in DaR1(topmost) indicate that the site is a depositional site. The inventory values for DaR2 (middle) and DaR3 (bottom) are considered reference values for the site.

53

Activity profile, log scale

Activity, mBq/kg

1 10 100 1000

Dep

th

0

10

20

30

40

50

DaR3 vs Col 1 Plot 1 Regr

r2 = 0.8261

Activity profile, log scale

Total Inventory=260 Bq/m2

Activity profile, log scale

Activity, mBq/kg

1 10 100 1000

Dep

th

0

10

20

30

40

50

DaR2 vs Col 1 Plot 2 Regr

r2 = 0.8261

r ² = 0.5271

Total Inventory = 210 Bq/m2

Figure 5. The exponential plot of inventory versus depth gave an acceptable linear correlation for DaR2 and DaR3 and therefore these values were included in the reference values for the site.

DaR3 260 Bq/m2 DaR2 DaR1 210 Bq/m2 690 Bq/m2 0 30 60 Distance (m)

Figure 4. The shape of the 137Cs profiles and the inventory values can further be explained by the relative position of the reference samples. DaR1 is a depositional site relative to the other two sites.

54

420

110 240 320 190 260

250

320 300

Figure 6. The 137Cs inventory in the nine samples showed that area 2 is a deposition site. The summit is an erosion site and soil loss is estimated at about 20 t/ha/yr.

55

c

m

Dep

t

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

1 3 7 C s I n v e n t o r y p r o f i l e

1 3 7 C s I n v e n t o r y , B q / m 2

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

h,

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

D a C 1

T o t a l I n v e n t o r y : 3 0 0 B q / m 2

1 3 7 C s I n v e n t o r y p r o f i le

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

D a C 2 Dep

th, c

m

T o t a l I n v e n t o r y : 4 2 0 B q / m 2

1 3 7 C s I n v e n t o r y , B q / m 2

0 20 40 60 80 100 120 140 160 180 200

0

5

10

15

20

25

30

35

40

45

50

55

60

DaC3

Dep

th, c

m

Total Inventory: 320 Bq/m2

137Cs Inventory, Bq/m2

137Cs Inventory, Bq/m2

0 20 40 60 80 100 120 140 160 180 200

0

5

10

15

20

25

30

35

40

45

50

55

60

DaC4

Total Inventory: 250 Bq/m2

Dep

th, c

m

137Cs Inventory, Bq/m2

1 3 7 C s I n v e n t o r y P r o f i l e

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

Dep

th

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

D a C 5

1 3 7 C s I n v e n t o r y , B q / m 2

T o t a l I n v e n t o r y : 2 6 0 B q / m 2

1 3 7 C s I n v e n t o r y , B q / m 2

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

Dep

th, c

m

D a C 7

T o t a l I n v e n t o r y : 3 2 0 B q / m 2

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

D e p t h , c m D a C 9

T o t a l I n v e n t o r y : 1 1 0 B q / m 2

1 3 7 C s I n v e n t o r y , B q / m 2

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

Y D

ata

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

D a C 6

T o t a l I n v e n t o r y : 1 9 0 B q / m 2

1 3 7 C s I n v e n t o r y , B q / m 2

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

Dep

th, c

m

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

D a C 8

T o t a l I n v e n t o r y : 2 4 0 B q / m 2

Figures 7 a-i. DaC2 and DaC3 at the foot slope are depositional sites including DaC7 while DaC9 at the summit is an erosion site. DaC6 may be an erosion site while the rests of the sites do not differ significantly from the reference values.

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170 ± 60 Bq/m2

Figure 8. The spread and magnitude of 137Cs inventory in study site 2 (Isabela) isshown here. The average inventory at the reference site is 160 ± 60 Bq/m2. 170

050

100150200250300350400450500

1 2 3 4 5 6

Figure 9. 137Cs inventory in 1-Summit, 2-shoulder 3-back 4-toe 5-foot 6-deposition site in the hill model in study site 2: a. Balicatan b. Rugao

0.0

50.0

100.0

150.0

200.0

250.0

1 2 3 4 5 6 7 8

Reference inventories

9a

9b

050

100150200250300350400450500

1 2 3 4 5 6

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Total Inventory=260 Bq/m2

Activity, mBq/kg

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Dep

th, c

m

-10

0

10

20

30

40

50

60

Total Inventory=130 Bq/m2

CaR1

Figure 10. 137Cs activity profile of a scraper plate sample taken from an assumed undisturbed area

Activity profile, log scale

Activity, mBq/kg

1 10 100 1000

Dep

th

0

10

20

30

40

50

Figure 11. Unsupported 210Pb activity profile of a scraper plate sample in study site 3 shows evidence of erosion in the reference area. (activity in the scale is 1/10 of the actual value)

58

0

200

400

600

800

1000

1200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Series1

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10 11

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12

Figure 12. 137Cs inventory values from the reference site (top) and from the two erosion plots (middle and bottom)

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3.5. Sri Lanka

3.5.1. Country Report Participating Institutes: The Land Use Division (LUD), Department of Irrigation, Colombo 7, Sri Lanka. National Project Coordinator: Dr.T.S.B.Weerasekera Collaborating Institutes: The Atomic Energy Agency (AEA) of Sri Lanka. Department of Agriculture, Natural Resource Management Center (NRMC) University of Sri Lanka, Faculty of Agriculture Expert Staff and Supervision: The International Atomic Energy Agency (IAEA) Collaboration between the AEA had been very successful so that all the results are being discussed and reviewed by LUD and AEA regularly. The facilities of the AEA have been strengthened as a result of this. This collaborative functioning will continue. The collaboration with Faculty of Agriculture will commence when pesticide studies are taken up in 2004. National Project Committee: Dr. T.S.B.Weerasekera (Head, LUD) Prof. Mrs. Rohini Hewamanne (The Chairperson, AEA) Dr. Mrs. Darshanee Kumaragamage (Lecturer, University of Sri Lanka, Peradeniya) The project progress is reviewed by the committee regularly. Specific Objectives of the Study: • To collect base line information on soils, land use, geomorphology, and hydrology of the area. • To develop the computerised information system of the above. • To determine the type of erosion, spatial origin of erosion material, and redistribution of

eroded material using 137Cs, nutrient movement using non-radioactive isotopes of C and N. • To disseminate information to farmer community and scientists. • To strengthen the capability of participating institutes to continue and to promote using these

techniques. Table 1 shows the work plan for year 2002. The progress achieved under each item is given in parenthesis and also described under the sections / sub sections. Table 1 - Work Plan and Progress Achieved for Year 2002 Description of Work First

Quarter Second Quarter

Third Quarter

Fourth Quarter

1. Project formulation meeting X(C) 2. Selection of field site X(C) 3. Send TSC to IAEA X(C) X(C) 4. Collect base maps of the selected area X(C) X(C) 5. Workshop on 137Cs X(C) 6. Determine sampling sites for erosion, X(C) X(C)

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nutrient and pesticide studies 7. IAEA expert visit X(C) 8. Prepare digital database for the site X(C) 9. Sediment and soil sampling X(PC) X(PC) 10. Processing and detection of 137Cs in soil / sediment samples

X(C) X(C)

11. Pesticide and nutrient sampling X(N) X(N) 12. Processing and analysis of pesticide and nutrient samples

X(N) X(N)

13. Two weeks scientific visit X(A) C – Completed, PC – Partly completed, A – Being completed, N – Not completed. Selection of the Study Area (Item No. 2): After the project formulation meeting (item 1) in Beijing, China, a watershed (Uma Oya) in the intermediate climatic zone of Sri Lanka was selected for the study. This watershed has many kinds of land use that are economically important. It also represents an area in which erosion is a severe problem. The watershed presents an optimal combination of soils, topography, and land use so that interpretation of the data will be meaningful. The watershed contains a number of areas under forest reserves that have not been affected by human activity leading to erosion in the last 50 – 60 years. These areas are identified for establishing the reference sampling sites. There are areas that have been cultivated throughout in the last 50 years. The cultivations include tea, vegetables, and some perennial fruit crops mainly associated with homesteads. In some of these areas the soils have been derived from the erosional material originated from the upper slopes of the landscape. In the downstream there is a reservoir that has been built for irrigation and for generating hydropower. Siltation of this reservoir has been a severe problem. It is expected that core samples from the reservoir is obtained in order to determine the history of the siltation so that specific sources of erosion may be identified and then the problem be alleviated. Application of the 137Cs Technique: (a) General information Workshop on 137Cs (Item 5) Mr. A.R. Dassanayake of the Land Use Division, a scientist participating in this project attended this workshop that was held in China from 3rd to 9th June, 2002. Apart from a field visit to a reservoir watershed he studied soil erosion and redistribution, sampling strategies, sample preparation, and use of conversion models. The interaction he had with other scientists participated in the workshop, and the knowledge he gained are of much relevance to the project, and have increased his contribution to the project. IAEA Expert visit (Item 7) The IAEA expert Dr. Robert Loughran visited Sri Lanka. During the period 28th July -5th August 2002 he reviewed the progress of the project, visited the watershed area, and gave the project staff the guidelines on selecting sampling sites and sampling methodology. He also visited the Sri Lanka Atomic Energy Authority (AEA) and discussed the 137Cs detection methodology with the project staff. In these discussions, the areas of improvement to the AEA detection facility were

61

highlighted. It was recommended that the necessary attention is given to background radiation, sample characteristics, and the usage of standard material. Preparation of the digital database for the site (Item 8) A digital map of the watershed was prepared using ARC /INFO software. The sampling sites selected so far have been included in this map. The geomorphology of the sites obtained from the survey is digitized separately. The current land use and the distribution of the soils in the watershed have been included in the digital map of the area. The 137Cs profiles of the sites are to be included when the results of the detection are available. Erosion studies by other institutes The studies date back to 1950 s when the Dept. of agriculture established a unit that dealt with erosion. As a result of the early work of this unit the land conservation act was passed by the parliament. The act prevented cultivation of lands in steep slopes and high altitudes. Subsequent studies were mainly taken up by the Department of Agriculture, Tea Research Institute, and Mahaweli Ministry for project level assessments and recommendations. The work on erosion had mainly been base on conventional technology such as usage of USLE, direct field measurements, and derivation of erosion hazard by interpreting available soil, topographic, hydrological, and geological information. (b) Field reconnaissance survey Collecting base maps of the selected area (Item 4) The base maps at a scale of 1 inch to 1 mile and the air photos at a scale of 1:20000 were obtained from the Survey Department of Sri Lanka. These were sufficient to demarcate the watershed and identify broadly the sampling sites. More detailed maps that show the exact landform of the sampling locations were not available and it was decided to obtain the service of a survey facility for that purpose. Soil maps and land use maps were available at a scale of 1 inch to 1 mile. These were used in identifying the broader categories of soils and land use respectively. The Land Use Division staff obtained the detailed information on these by direct field investigations. The exact locations of the sampling sites were also determined by the survey facility using GPS equipment. Because the sites are away from the known land marks it was necessary that the sites are located on the ground and accurately transfer their coordinates to the base maps. In the data interpretation phase, the local geomorphology of the sites will have to be used extensively and therefore obtaining the geomorphological information will be continued. Survey on current land use: At the scale of the available base maps it is not possible to prepare a sufficiently detailed current land use database. Therefore, ground observations are used for obtaining information on current land use, particularly in the areas where sampling sites are located. (c) Field sampling design The field sampling design has taken into consideration the geomorphology and the land use of the watershed as the primary criteria. Hydrology and soils are the secondary criteria. To facilitate the interpretation, first to fifth order sub watersheds were identified. The first order watershed is the sub watershed that cannot be subdivided further into smaller watersheds. These are associated with first order streams that are identified as the primary collectors of runoff.

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As the order increases, larger sub watersheds consisting of several lower order sub watersheds are identified. Corresponding higher order streams are associated with them. Finally, the fifth order stream is the river that has a reservoir in the downstream. Erosion and deposition of eroded material can take place in any of the sub watersheds. The sampling design is kept flexible to a certain extent so that with preliminary interpretations it will be possible to reassess the design. (d) Selection of sampling sites (Item 6) Reference sites – Undisturbed sites In the undisturbed forest areas 24 sampling sites were identified, located on the ground, and were surveyed. These sites are in Kande Ela forest reserve, Meepilimana forest reserve, Pidurutalagala forest reserve and Hakgala forest reserve in Nuwara Eliya District. The sampling sites in the undisturbed land were selected in such a way that apart from the absence of recent human activity, there has not been a significant loss of soil by erosion at the sites. Existence of a layer of 2-3 cm of organic material or mulch was a condition observed in selecting the sampling sites as an indication that the sites are undisturbed, and also that erosion has been negligible. In order to confirm the fact that the sites are undisturbed, the carbon, nitrogen, and clay distribution in the profile are compared with the 137Cs distribution. Sites in the cultivated areas and homesteads – Disturbed sites The sampling sites in the cultivated areas are being identified taking into consideration the geomorphology, soils, and land use of the area. They include sites with local deposits of the erosion material, as well as the foot slopes and flat lands where permanent deposits are found. Regular mixing of the first 20cm of soil in the areas where vegetable is cultivated has been of much concern in selecting the sampling sites in such areas. Meaningful interpretation of 137Cs may be difficult in these areas. In order to assess the extent of the removal of soil from these areas, the total 137Cs in the 0-20cm depth will be compared with that of the mixed soil of 0-20cm depth in the reference sites. Sediment and soil sampling (Item 9) Thirty soil samples have been sent to the AEA for detection. Another set of 40 samples have been collected and prepared for detection. So far only the samples from undisturbed sites have been collected. The sediment sampling was postponed until the data for undisturbed sites are available. (e) Sample preparation Processing and detection of 137Cs in soil / sediment samples (Item 10) Only the very large objects such as large roots and stones were removed from the samples. The samples were air-dried and then oven dried at a temperature of 150oC for 24hrs. Then the samples were crushed so that a fairly uniform mixture was obtained. These samples are detected using HPGe detector. The facility AEA has for low level gamma detection is being improved so that reliable results are obtained. The IAEA expert has reviewed some data obtained at AEA, and has suggested that mainly because of the background radiation a shield has to be installed. This has been purchased by IAEA and it will be installed. Once the detector is ready with all the necessary features, the IAEA expert will visit AEA and make further recommendations before the samples are detected. (f) 137Cs analysis by HPGe

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Detection Cs-137 radioactivity was measured by Counting the 661.5 keV gamma range (Gamma spectrometry) with a high Pure Germanium detector. The Gamma spectrometry system used consist of • HPGe: model: Canberra GC 3021 • Nuclear spectroscopy electronics: Genie 2000 MCA card • Genie 2000 software for data acquisition A 1-kg sample sieved (2mm mesh) was placed over the detector in a Marineli beaker and counted for 20 hrs. A 1-kg Soil –6 IAEA reference materials was used to calibrate the efficiency of Cs-137 peak. Radioactivity levels were reported on of the date of Counting. Quality Control: Analyzing the reference material IAEA soil –375 in different counting geometry (138 g –cup) - checked performance of analytical procedure. The result of 4347 ± 285 Bq/kg Cs- 137 Concentration was obtained for 31.07.03. The reference value (from certificate) equals to 4642 Bq/kg and the confidence interval quoted is 4546 – 4721 Bq/kg. Control Charts: Analytical laboratory is maintaining the control Charts for Instrumental parameters (FWHM: count rates) to check the instrumental Analytical performance. Staff training: The scientific visits /fellowships (Item 13)

• Training workshop IAEA / RCA Regional Training Workshop on the use of 137Cs in the assessment of soil erosion and redistribution was held in China from 3rd to 10th June 2002. A scientist from LUD participated in this workshop. He also visited the soil conservation project site in the Yellow River watershed, and also the 137Cs detection facility at the Institute for Application of Atomic Energy.

• Pesticide workshop This workshop was held in China, March 2003. A pesticide scientist attached to the RAS / 05 / 039 group participated.

• Training at the detection laboratory at CSIRO, Canberra A technician from AEA was trained at CSIRO, Canberra in July/August 2003. The fellowship was mainly for;

• Soil and sediment sample collection, • Preparation of samples for detection, • Preliminary assessment of results, • Training in use of Gamma spectrometers to analyse soil and sediment samples, • Training in maintenance of Gamma spectrometers. • Training in the operation of Gamma spectrometry software.

64

• Training in calibration of Gamma spectrometers, • Training in application of software to analyse Gamma spectra.

Scientific visit: A scientific visit to China and Australia has been planned for the senior scientist in October / November 2003. Laboratory Upgrading: On the recommendation of the IAEA visiting expert Dr. R. Loughran, it was decided to upgrade the low level gamma detection facility at the AEA so that it is suitable for the determination of 137Cs content in soil samples. The IAEA supplied an uninterruptible power supply unit (UPS) that has improved significantly the efficiency of the facility. The reading obtained from the detector was sent to IAEA expert Dr. Marek Makarevicz for further recommendations. He observed that there is a high level of back ground radiation. As a result the IAEA supplied a shield, suitable for the present detector configuration. The IAEA has supplied the Soil –6 IAEA reference material to be used for gamma level determination of the soil samples, and also a set of suitable Marinelli beakers. With all the equipment in place, Dr. Makarevicz will visit the AEA in November 2003 to examine the detection facility and to make any necessary recommendations while providing the AEA detection staff the necessary advice. Other Project Activities: Pesticide and nutrient sampling and detection (Items 11 and 12) The pesticide sampling was temporarily halted because of the TC project on pesticide that is being implemented by another group of scientists. On the recommendations of IAEA, the pesticide scientist selected for RAS / 05 / 039 is expected to collaborate with the TC project SRL/5/037. The mode of collaboration is being discussed and further action will follow after the review by IAEA visiting experts. Nutrients such as Carbon, Nitrogen and Phosphorous in the samples are determined at LUD laboratory. The earlier programme of using labeled nutrients will not be implemented because of the limited detection facilities. Achievements: • Introduction of 137Cs technology as a method complementary to conventional methods in

assessing soil erosion and redistribution (Section 6). • Improvements to the gamma detection facility at AEA with the support of equipment and

expertise provided by IAEA (Section 8). • Human resource development by training of staff with IAEA fellowships / scientific visits

(Section 7). Recommendations: • Further training in sample preparation, detection and interpretation of information.

Fellowships for a technician and a scientist (1-2 weeks each), and scientific visits for two senior scientists (1-2 weeks each) are recommended.

• IAEA expert visit for detection and quality control. • Introducing the Genie’s Interactive peak fitting approach for Bi – 214 correction using Genie

– 2000, S506 Version. • Introducing the Mixed Radio nuclide standard in similar Counting Geometry for efficiency

calibration.

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3.5.2. Technical Report Sri Lanka T.S.B. Weerasekera, M.C.S. Seneviratne, A.R.Dassanayake (1) Introduction This report presents an account on the initiation of the assessment of soil erosion and redistribution of soil material in a watershed using 137Cs profiles of the soils. It also presents examples of such profiles in the sites of the selected watershed that have not been the disturbed by the human activity or otherwise, and the some interpretation of the observations. (2) The Watershed A watershed (Uma Oya) in the intermediate climatic zone of Sri Lanka was selected for the study. This watershed has many kinds of land use that are economically important. It also represents an area in which erosion is a severe problem. The watershed presents an optimal combination of soils, topography, and land use so that interpretation of the data will be meaningful. The watershed contains a number of areas under forest reserves that have not been affected by human activity leading to erosion in the last 50 – 60 years. These areas are identified for establishing the reference sampling sites. There are areas that have been cultivated throughout in the last 50 years. The cultivations include tea, vegetables, and some perennial fruit crops mainly associated with homesteads. In some of these areas the soils have been derived from the erosional material originated from the upper slopes of the landscape. In the downstream there is a reservoir that has been built for irrigation and for generating hydropower. Siltation of this reservoir has been a severe problem. It is expected that core samples from the reservoir is obtained in order to determine the history of the siltation so that specific sources of erosion may be identified and then the problem be alleviated. (3) The Reference Sites These are forests in the watershed conservation areas. The forests are 60 – 80 years old. Some sites have the native plant species while some have pine and gum-tree stands. The reference sites within the same land use (kind of tree stand) have been selected according to the geomorphology and soils. At this stage of the research, all the reference sites are at the primary (1st order) sub watersheds because they are the main contributors to surface run off. A thorough understanding of the distribution of 137Cs in the soil profiles at these sites is necessary for the interpretation of information in terms of erosion. Altogether 36 reference sites have been identified for sampling. These sites occupy the crests, upper / lower convex slopes, and upper / lower concave slopes. Such a sampling design was formulated anticipating any possible indications of naturally occurring erosion and deposition of the soils in the reference sites. The reference sampling sites in the secondary sub watersheds and other higher order watersheds will be identified depending on the necessity. (4) Sampling and Sample Preparation An adjustable scraper was used in collecting the samples. This can scrape at 1 cm. intervals. The mulch was scraped as separate samples, and then the soil was sampled to a depth of > 20cm. The whole samples (i.e., without the removal of stones, gravel, or roots) were collected for analysis.

66

At the laboratory the soils were air- dried and crushed. Then large roots and stones were removed to make the sample a uniform mixture. The samples were oven-dried at 150o for 48 hours before being sent for detection. (5) Detection 5.1 Detection methodology Twenty three soil samples collected from different sites were detected for 137Cs radioactivity analysis. 137C radioactivity was measured by counting the 661.5 keV gamma line (Gamma spectrometry) with a Hyperpure Germanium detector. The Gamma spectrometry system used consists of the following: • HPGe model: Canberra GC 3021 • Nuclear spectroscopy electronics: Genie 2000 MCA card • Software: Genie 2000 software for data acquisition One Kg of prepared sample was placed over the detector in a Marinelli beaker and counted for 20 hrs. One Kg of Soil –6 IAEA reference materials was used to calibrate the efficiency of 137Cs peak. Radioactivity levels were reported on of the date of counting. 5.2 Results The results of samples analyzed are given in table 01, table 02, and table 03. Detection limit (DL) for soil is taken as 1.65 Bq / kg. Table 01. 137Cs radioactivity in soil samples of site R1

Site Code Sample Depth (cm)

Activity Bq / kg

UNC. Bq / kg

R1 R101 0-2 6.19 1.26

R102 2-6 6.52 1.09 R103 >6 5.59 0.93

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Table 02. 137Cs radioactivity in soil samples of site R2

Site Code Sample Depth (cm)

Activity Bq / kg

UNC. Bq / kg

R2 R201 0-2 <DL

R202 2-4 11.85 1.81 R203 4-6 10.99 1.57 R204 6-8 10.90 1.56 R205 8-10 8.99 1.33 R206 10-12 7.44 1.16 R207 12-14 7.00 1.09 R208 14-16 5.52 0.92 R209 16-18 4.30 0.80 R210 18-20 3.61 0.73

Table 03. 137Cs radioactivity in soil samples of site R3

Site Code Sample Depth (cm)

Activity Bq / kg

UNC. Bq / kg

R3 R303 2-3 7.12 1.24

R304 3-4 5.40 1.10 R305 4-5 6.34 1.24 R306 5-6 5.92 1.03 R307 6-7 6.09 1.15 R308 7-8 6.45 1.04 R309 8-9 5.36 0.92 R310 9- 10 6.11 1.06 R311 10-11 3.28 0.78 R312 11-12 4.50 0.85

* Values are not reported due to insufficient sample.

Figures 1 and 2 show the 137Cs profiles of sites R1 and R2.

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

0-2

2-4

4-6

6-8

8-10

10-12

12-14

14-16

16-18

18-20

Dep

th (c

m)

Cs-137 Profile1 (Bq/kg)

Fig.1. 137Cs activity distribution with depth at site R2

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0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

0-1

2-3

4-5

6-7

8-9

10-11

Dep

th(c

m)

Cs-137 Profile 2(Bq/kg) Fig. 2. 137Cs activity distribution with depth at site R3

5.3 214Bi correction

The main 137Cs peak is located at an energy of 661,5 keV, but there is some interference from an overlapping 214Bi peak on the high energy side at 665.8 keV. These results are not corrected for 214Bi interference.

5.4 Uncertainty Budget

The following components were considered to calculate the uncertainty of the results given for 137Cs in soil samples. Table 04. The Uncertainty budget for determination of 137Cs in Soil Samples

Variable Names Symbol of the variable

Value Uncertainty Component Symbol

Uncertainty value

Relative standard uncertainty (u)c %

Percent contribution to combined uncertainty (U) %

1. Mass of the sample M (g) 586.7 U(m) 0.586 0.10 0.0096

2. Detector efficiency E 0.0035 u (E) 0.00022 6.29 38.24

3. Background corrected net area of the sample peak

N

778

U(N)

62

7.99

61.68

4. Emission probability Y 0.85 U(Y) .003 0.35 0.125

Value of the measured (activity concentration) A = 4.47 Bq/kg Relative combined standard uncertainty Uc (A) = 10.16% Relative expanded uncertainty U (A) = 20.32 % (coverage factor = 2) Value of the measured + expanded uncertainty = 4.47 + 0.9 Bq/kg. (Source : SOP for Uncertainly Budget for Gamma Spectrometry – AEA/NAT/Sop 08) (6) Interpretations The 137Cs profiles of R1 and R2 differ significantly when the distribution of 137Cs is considered, although the activity levels are in general agreement, particularly in the lower depths. These two sites are in similar primary watersheds that are under natural forests. They occur in the same altitude and on the similar slopes. A detailed geodetic survey reveals however, that the geomorphology of the two sites differs. This difference is attributed to the 137Cs activity differences

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in these two profiles. In the site R3 there has been deposition of the material resulting from vary slow natural erosion process in the surrounding area. The total carbon and total nitrogen profiles of the two sites confirm this fact. The geomorphology of the site R3 allows such accumulation whereas that of site R2 does not support accumulation. These observations suggest that the reference sites should be thoroughly studied before the 137Cs profiles are interpreted in terms of erosion and deposition.

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3.6. Vietnam

3.6.1 Country Report Partners Institutions: Vietnam Atomic Energy Commission (Ministry for Science & Technology), Institute of Soil and Fertilizer, Ministry of Forestry (Ministry of Agriculture and Rural Development). National project committee Informal, comprising specialists from the above institutions Selection of study area (s):

3 study areas, 8 run-off plots

Objectives of the study: • To establish and investigate 137Cs reference inventories and their variability, • To check the existing conversion models and occasionally to establish models most suitable

for the conditions of Vietnam. Application of the Cs-137 technique: a) General information • 137Cs in soil samples have been measured for many years. The distribution of 137Cs reference

inventories across the territory was established. The reference inventories were found to be governed by latitude and annual rainfall at sampling sites (J. Environmental Radioactivity, 62, 295, 2002).

• In 2002 the inventories of 239+240Pu and 90Sr were also measured and compared with 137Cs (submitted to J of Environmental radioactivity).

• The 137Cs tracer technique was applied to estimate soil erosion/deposition rates at Song Da afforestation field in northern Vietnam where a big reservoir was constructed in 1982 for a 1800 MW hydropower plant (2000).

• For the current Project RAS/5/039, Part 2, the mission of expert (Mr. Loughran) was not implemented and an IAEA research project is still pending.

b) Field reconnaissance survey

8 run-off plots in Cental Plateau and North Vietnam.

c) Field sampling design done for 8 run-off plots

d) Selection of reference site (s) Three areas were selected for reference inventories

e) Sample preparation about 100 samples

f) Cs-137 analyses by HPGe about 100 samples

Staff training:

one person participating in the workshop in China 2002, Mr. Tu

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Laboratory upgrading not significant Other project activities Vietnam participate in the IAEA CRP on “Using fallout radionuclides to evaluate the effectiveness of soil conservation measures for sustainable crop production”. Chief investigator: Mr. Phan Son Hai, Dalat Nuclear Research Institute. Achievements: • One paper was sent to J. of Environmental Radioactivity (see Abstract in the attachment). • The preparation of a second paper on the variability of 137Cs reference inventories is

completing (see attached document). • Verifying conversion models for converting from 137Cs loss to soil loss is underway. Recommendations: A topography survey equipment is needed for further works 3.6.2. Technical Report Vietnam Pham Duy Hien: Vietnam Atomic Energy Commission, 59 Ly thuong Kiet Hanoi, Vietnam (1) Abstract Seventy four reference sites were selected for the study of 137Cs inventory variability in the Red River (33) and Mekong (16) deltas and a 75 m x 75 m flat hill top terrain in the Central Plateau of Vietnam (25). The coefficient of variation of 137Cs reference inventories varies from 17% in the third case to 33% in the firt case, that is generally similar to the CVs of soil parameters (21% -69%). Experimental errors take up about 10% of the 137Cs CVs. The remaining part could be attributed to the effect of 137Cs redistribution after deposition from the atmosphere. (2) Introduction The use of bomb-derived 137Cs as a marker to estimate rates of erosion and deposition (Ritchie and McHenry, 1975; Walling and Quine, 1991) is based on comparison of the 137Cs inventories at individual sampling points with a reference inventory (RI), which should be expected at a site that experiences neither soil erosion nor deposition. In practice the 137Cs inventories at sites selected as reference in soil erosion studies vary considerably even within a small catchment area. In reviewing literature data from over 70 published studies, Sutherland (1996) found that the coefficient of variation (CV) of inventories at such “potential” reference sites ranged from 1.5 to 86.4% with the median CV of 19.3%. (CV is defined as the ratio of the sample standard deviation to sample mean). If CV is large, a great number of samples should be taken in order to obtain an appropriate error of the mean inventory, which will be ultimately regarded as the RI at the study area. In studying soil erosion in New Zealand, for example, Basher (2000) found that on average 16 samples must be taken at each site for the mean inventory being within ± 10% at 90% confidence interval. The above situation demonstrates the difficulty in identifying sites suitable for estimating RI in soil erosion studies. The task becomes more difficult for tropical regions, where non-eroded virgin lands are usually scarce under the pressure of population growth, industrialization and urbanization. To overcome this difficulty, Walling and He (2001) developed a global-scale model for estimating RI based on geographical coordinates and annual precipitation, which are the dominant parameters influencing the deposition of fallout 137Cs from the atmosphere. Hien et al.

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(2002) measured the inventories at 292 undisturbed sites across Vietnam - a 320,000 km2 territory extending from 9oN to 23oN along the West coast of the Pacific – and found a regression model for the logarithm of RI: Ln(RI) - ε = (3.53 ± 0.09) + (0.092 ± 0.004)L + (0.62 ± 0.03)AR (1) Latitude (L) and annual rainfall (AR) of the reference sites are the two predictors of RI, which could explain 76% of the total variance of Ln(RI), leaving the 24% remaining variance to the residual ε. The latter is partly associated with random experimental errors and uncertainties in estimating ARs when nearby weather stations are not available. But the main source of the residual ε is associated with the redistribution processes taking place at the sampling area with dissolved 137Cs just after its deposition by rain via overland flows, as well as with 137Cs adsorbed in soil particles via erosion transport (VandenBygaart et al., 1999; Pennock, 2000). These redistribution processes lead also to the changes in other soil quality indicators (Pennock, 2000). As a result, some association between 137Cs and soil parameters should be expected. The relationships between 137Cs and soil parameters can be revealed considering medium or small-scale areas in which the variations in L and AR are insignificant (Hien et al., 2002). Red River Delta The Red River Delta is located in the coastal region of northern Vietnam, just to the south of the Tropic of Cancer between latitudes 20oN and 21oN and longitudes 105o30’E and 106o40’E. The central part of the delta of approximately 12,000 km2 is very flat (Fig. 1). Annual rainfalls recorded at 12 weather stations within the area vary mainly from 1600 mm to 1800 mm. Due to such a slight variation, the annual rainfall at any sampling site within the area could be accurately estimated from the records at the nearby weather stations. Agricultural lands are dominated by alluvial soils and are used for paddy and annual crops. Main characteristics of the soil at 33 reference sites and their correlations are shown in Table 1 and Table 2, respectively. The RIs vary from 330 to 1176 Bq m-2 with a CV of 31%, generally similar to those of soil parameters. A multiple regression analysis was applied to reveal site characteristics, which control the variations in RI across the delta region. To obtain a physically reasonable regression model the logarithms of RIs were used as a dependent variable (Hien et al., 2002). A stepwise multi-linear regression method was applied with the significance level of the regression coefficients set at 0.05. AR and pH appeared as determinants of Ln(RI) according to the following model: Ln(RI) = (3.06 ± 1.06) + (1.67 ± 0.65)AR + (0.11 ± 0.04) pH, (2) R2 = 0.43 Table 1. Relevant characteristics of 33 reference sites in the Red River Delta of northern Vietnam

Range Mean Coefficient of variation (CV)

ph 3.8 - 7.8 6.1 0.21Organic matter (OM), % 0.46 - 2.6 1.5 0.34Total cation exchange capacity (CEC), cmol kg-1 1.4 - 37. 13.7 0.59Clay, % 1.4 - 34.4 12.8 0.69Annual rainfall (AR), m 1.53 - 1.80 1.68 0.05

Measured reference inventory (RI), Bq m-2 403 - 1176 735 0.31

Predicted RI, Bq m-2 439 - 990 699 0.20

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Table 2. Correlations of site characteristics. Red River Delta.

pH OM CEC clay latitude longitude pH 1 OM -0.14 1 CEC 0.71 0.16 1 clay -0.34 0.48 -0.21 1

latitude -0.19 0.15 -0.31 0.03 1 longitude 0.03 -0.16 -0.16 -0.35 -0.26 1

The values of Ln(RI) measured in the experiment and predicted by model (1) are plotted in Fig. 2. Returning to the ordinary scale of RI, it was found that the variations in AR and pH across the delta region could explain 20% of the variations in RIs (Table 1). As the relative experimental error is about 10%, it is clear that model (2) could explain the 31% CV of the RIs across the Red River delta. pH is a unique soil parameter appearing in model (2) as a determinant of RI. The weak correlation of pH with geographical coordinates indicates that model (2) has nothing to do with the spatial distribution of atmospheric fallout over the delta as model (1). On the other hand, as pH correlates with other soil parameters, especially with CEC, model (2) does reflect the effect of 137Cs redistribution processes that result also in the change in soil parameters. Mekong Delta Sixteen locations were selected for measuring RIs in the Mekong delta of southern Vietnam (Fig. 3). The area is dominated by alluvial soils. In the coastal regions alluvial soils are slightly or moderately sulphate acidic. The annual rainfall increases westward ranging from 1.5 to 1.8 m. Site characteristics and their correlations are shown in Tables 3 and 4. The stepwise multiple regression of Ln(RI) against site characteristics had revealed pH as a determinant, i.e.

Ln(RV) = (4.74 ± 0.24) + (0.15 ± 0.05)pH, (2) R2 = 0.42

The measured vs predicted by model (2) Ln(RI) are plotted in Fig. 2. Returning to the ordinary scale of RI, it was found that the model (2) could explain 17% of the CV of the measured RIs, leaving the remaining 7% to the experimental errors. Table 3 Relevant characteristics of 16 reference sites in the Mekong Delta of southern Vietnam

Range Mean Coefficient of variation (CV)

ph 3.7 - 7.2 5.1 0.22 OM, % 0.6 - 4.0 2.1 0.56 CEC, cmol kg-1 2.7 - 31.5 14.5 0.55 Clay, % 6.6 - 53.8 27.1 0.54 AR, m 1.45 - 1.86 1.64 0.04 137Cs RV, Bq m-2 165 - 387 249 0.24 Predicted 137Cs RV, Bq m-2 201 - 344 245 0.17

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Table 4. Correlations between site characteristics. Mekong Delta

pH OM CEC clay AR latitude longitude pH 1 OM 0.04 1 CEC 0.38 0.78 1 clay -0.13 0.77 0.53 1 AR -0.09 0.42 0.46 0.24 1 latitude 0.28 -0.65 -0.42 -0.47 -0.66 1 longitude -0.23 -0.68 -0.63 -0.57 -0.39 0.10 1 The Central plateau The sampling site is a flat hill top terrain located in the Central Plateau of Vietnam (11.95oN, 108.43oE, 1513 m asl)), about 300 km north of Hochiminh City. Twenty-five soil samples were collected in a 15m x 15m square grid. The mean inventory, which can be regarded as the reference value at this site, was (339 ± 22) Bq/m2. The 137Cs inventory values at 25 sampling points given in Table 5 have a CV of 15%, which is somewhat larger than the 1σ error of activity measurements (about 10%). The inventory map in Fig. 5 obviously reflects a spatial redistribution pattern of eroded and deposited soils rather than a random pattern of measurement errors. Unfortunately, advanced survey techniques were not available for topography mapping of the terrain in order to confirm this conclusion. Table 5. 137Cs inventory values at 25 grid points on a 75 m x 75 m hill top terrain in the Central Plateau 15m 30m 45m 60m 75m

15m 390 420 319 410 373 30m 262 259 323 289 389 45m 281 357 376 297 367 60m 415 386 352 278 287 75m 267 367 390 341 316

(3) Conclusion 137Cs RIs were measured in 33, 16 and 25 soil samples taken from the Red River and Mekong deltas and a 15 m x 15 m square grid on a flat hill top terrain in the Central Plateau of Vietnam. The CVs of the measured RIs range from 17% to 31%, that are generally similar to the CVs for soil parameters (21% - 69%). AR and pH appear as determinants of the RI variability in the Red River delta, while for the Mekong delta pH is a unique determinant of RI. Regression relationships could explain two-thirds of the CVs leaving the remaining one-third for experimental errors. Thus, the variability of RIs is natural, reflecting the effect of 137Cs redistribution after deposition from the atmosphere. In the case of a small reference site of 75 m x 75 m in the Central Plateau the CV is much smaller (17%) and the effect of redistribution processes is also clearly shown. (4) References • Basher, L. R., 2000. Surface erosion assessment using 137Cs: examples from New Zealand. Acta

Geologica Hispanica, 35, 219-228.

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• Hien, P. D., Hiep, H. T., Quang, N. H., Huy, N. Q., Binh, N. T., Hai, P. S., Long, N. Q., (2002). Derivation of 137Cs deposition density from measurements of 137Cs inventories in undisturbed soils. Journal of Environ. Radioactivity, 62, 295-303.

• Pennock, D. J., (2000). Suitability of 137Cs redistribution as an indicator of soil quality. Acta Geologica Hispanica, 35, 213-217

• Ritchie, J. C. & McHenry, J. R. (1975). Fallout 137Cs: A tool in conservation research. J. Soil and Water Cons. 30, 283-286.

• Sutherland, R. A.,1996. Caesium-137 soil sampling and inventory variability in reference locations. Hydrological Processes, 10, 33-50.

• Walling, D. E. & Quine, T. A. (1991). The use of 137Cs measurements to investigate soil erosion on arable fields in the UK: potential applications and limitations. J of Soil Science 42, 147-165.

• Walling, D. E., He, Q., (2001). Models for converting 137Cs measurements to estimates of soil redistribution rates on cultivated and uncultivated soils, and estimating bomb-derived 137Cs reference inventories. A contribution to the IAEA Coordinated Research Programme on Soil Erosion (D1.50.05) and Sedimentation (F3.10.01).

Figure 1. Sampling points on the Red river delta

Ln(RI), Red River Delta

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Figure 3: Sampling sites at the Mekong delta

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Figure 5: The spatial distribution of RI on a 75m x 75m hill top terrain in the Central Plateau of Vietnam.

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3.7. People’s Republic of China

3.7.1. Country Report CHINA (PART –I) Partners Institutions and National Project Committee: Prof.Y.Li, National Co-ordinator, Institute of Agricultural Environment and Sustainable Development, CAAS Prof.L.Bai, Institute of Agricultural Environment and Sustainable Development,CAAS Prof. X.Zhang, Institute of Agricultural Environment and Sustainable Development,CAAS Prof. Juncheng Yang, Institute of Soils and Fertilizers, CAAS, Beijing Prof. Bujin Xu, Zhejiang University, Hangzhou Prof. Mingan Shao, Institute of Soil and Water Conservation, CAS, Yangling Prof. Xiejing Zhao, Institute of Soil and Fertilizer, SAAS, Chengdu

Study areas: • Two major areas: Loess Plateau and Upper Yangtze River Basin • Case study area, Nianzhuang watershed in Loess Plateau • Area: 54 km2 198 check-dams, constructed during 1956-2002 • Major crops: maize, potato, soybean, no natural vegetation Initial Problems: • Water erosion and sedimentation in the western China are the highest in the world • Intensive tillage and grazing on steep slopes are responsible for this accelerated soil erosion

Land use change events: • 1942 deforestation • 1958-1966 intensive cultivation • Since 1970 planting vegetation • Since 2002, completely stop farming and grazing on sloping land Specific Objectives of this study: • Identify the key erosion processes affecting soil quality parameters under different land use

structures and land management practices; • Evaluating soil redistribution–soil quality relationship on hillslope scales. • Increase the national ability to conduct proper field-sampling, analysis on soil redistribution and

soil quality by using measurements of Cs-137 Application of the Cs-137 technique Field Sampling Design-Grid sampling (Grid: 5*5-10 m) Total number of samples: 201 Measurements: 137Cs, 210Pbex and SOM, BD, and Available N, P, particle size distribution Field Sampling Design-Multiple transect sampling: 18 soil profiles sampled along the downslope of 50 m

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Check-dam reservoir sediment survey by RTK-GPS: 12 check-dam reservoirs were investigated Core sampling for measuring SOC, and sediment sources Sediment sampling till 4-m depth for 12 check-dam reservoirs. Profile sampling for assess gully development using 137Cs and 210Pb: 3 profiles on the gully bottoms Large profile (80-m wide and 8 m high) sampling for reconstructing past soil erosion by using 14C, 137Cs and 210Pb Field Sampling Design-Tillage experiment on slope land 50-plowing operations conducted, SOC, available nutrients were measured before and after tillage Sampling at Reference Sites: grassland, forestland, terraces at summit of the hillslopes: Sampling numbers of points: 25 Sample preparation and measurements of Radionuclides Sample Preparation – air-dried samples passed through a 2-mm mesh sieve, weighed, stored for measurement 137Cs and 210Pbex analyses by HPGe Gamma Spectrometry Measurements of 137Cs and 210Pbex LABOCS Measuring time: 5-24 hrs Analytical precision: < 8%

To date: 180 samples have been measured, other 120 samples are under process. Reference Inventory of 137Cs and 210Pbex Numbers of points: 25 Cs-137 Inventory, range: 1100-2980 Bq/m2, SD: 617, CV: 28% 210Pbex Inventory: Range: 7182-11633 Bq/m2

Staff training One staff, and other two students participated RTW in Yan’an, 2002 One staff participated RTW, March 2003, Hangzhou Three staff has been trained and can work with Gamma Spectrometry Three staff participated in RTK-GPS training in Sep. 2003. One staff will have a scientific visit to Australia in Nov. 2003

We will accept two scientific visit from Pakistan and Sri Lanka, 2003 Laboratory upgrading since August 2002 • Rtk-Gps • Soil Quality Lab • Isocs Be5030, Gamma Spectrometry • Field car • Auto Total organic Carbon /Total nitrogen Analyzer • 8 desk computers and 3 Note-book computers Other on-going Projects:

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IAEA Research contract under CRP on Soil Conservation, TWO NSFC Projects, and one CAAS Project. Achievements: Publications related to RAS/5/039, Part 2 • Y. Li, G. Tian, M. Lindstrom, and H.-R. Bork. Variation of surface soil quality parameters by

intensive donkey-drawn tillage on steep slope (accepted by SSSAJ) • Y. Li and Lingyu Bai. 2003. Variations of sediment and organic carbon storage by check-dams

of the Chinese loess plateau. Journal of Soil and Water Conservation 17(2): 1-4. (in Chinese)Y. Li and Lingyu Bai., Xingchang Zhang, H.-R. Bork, and M. Lindstrom. 2003. Profile variations of 137Cs, 210Pbex and SOM as affected by intensive tillage on slope land. Journal of Soil and Water Conservation 17(3): 1-6. (in Chinese)

• Y. Li, J. Poesen, and C. Valentin (eds.). Gully Erosion under Global Change. Sichuan Science and Technology Publishing House. Chengdu, China. 2003. 334 pp.D. Liu, and Yong Li. 2003. The effects of roots of different vegetation species on soil resistance of soil to concentrated flow erosion. Journal of Soil and Water Conservation 17(3): 80-86. (in Chinese)

• H.-R. Bork, H.R. Beckedahl, C. Dahlke, K. Geldmacher, A. Mieth, and Y. Li. 2003. The world-wide explosion of soil erosion rates in the 20th century: The global soil erosion drama are losing our food production base? Pertermanns Geographische Mitteilungen 147(3): 16-25.

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CHINA (PART –II) Title of Project:

EVALUATION SOIL REDISTRIBUTION-SOIL QUALITY RELATIONSHIP IN CHINESE LOESS PLATEAU BY USING CESIUM-137 MEASUREMENTS

Part of IAEA Technical Co-peration Project on: Restoration of Soil Fertility and Sustenance of Agricultural Productivity (RAS/5/039); part 2: Measuring Soil Erosion/Sedimentation and Pesticide Contamination Institute where research is being carried out: Institute of Agricultural Environment and Sustainable Development, and Institute for Application of Atomic Energy, Chinese Academy of Agricultural Sciences (CAAS), No.12 Zhongguancun South Street, Beijing 100081, PR China

National Coordinator: Prof. Dr. Yong LI Time period covered: May 2002 – Oct 2003

LI Yong, BAI Lingyu, ZHANG Xingchang, and YANG Juncheng, 1. GENERAL DESCRIPTION OF THE WORK CONDUCTED DURING MAY 2002 –APRIL 2003 As the part of China Country Project “Quantifying soil erosion/sedimentation and its impacts on pesticide fate processes at the lager scale in west China” (RAS/5/039, Part 2: Measuring Soil Erosion/Sedimentation and Pesticide Contamination), the objectives for the first year (2002) are to: • Identify the key erosion processes affecting soil quality parameters under different land use

structures and land management practices; • Evaluating soil redistribution–soil quality relationship on hillslope scales. • Increase the national ability to conduct proper field-sampling, analysis on soil redistribution and

soil quality by using measurements of Cs-137. In 2002, we collected the background information within the Nianzhuang Watershed (with area of 54.4 km2). This information includes: land use history, land use and management practices, topography, precipitation, soil types, erosion types, etc. Based on the detailed survey and our past experience, we set up 4 reference sites in the watershed: 1 reference sites in the terraces constructed before 1958, 3 reference sites in grassland located on the level hill top in the dividing line of the catchment. Core and depth sampling on cultivated and uncultivated hillslope transect at 5 to 10 m intervals, total soil samples of 300 for measuring 137Cs, 210Pbex and soil organic matter, silt and clay contents, available nutrients, and bulk density. So far, we have completed the measurements of 180 soil samples collected. In order to link the soil redistribution pattern on the slope to soil quality patterns by intensive tillage, we conducted 50-plowing operations over a 5-days period using a donkey-drawn moldboard-plow on s steep backslope of the Chinese Loess Plateau. A detailed comparison between 50-plowing slope and adjacent control slope was made in the profile variations of 137Cs, 210Pbex and SOM contents. Both selected experimental slope and control slope had a similar land use history, complete topography, and soil type. To identify the key erosion processes affecting soil quality parameters under different land use structures and land management practices, we investigated deposition rates and soil organic

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matter contents of the slopes basis over the past 3000 years by using 137Cs, 210Pbex, and 14C dating techniques. 2. MAIN RESULTS OF THE WORK CONDUCTED Accelerated soil erosion by intensive tillage on steep slopes is the major threat for the sustainable agricultural production in the western China as well as environmental problem. This accelerated erosion results in preferable progressing removal of surface soils and has an adversely effects on the quality of soil on-site. Organic matter content, mainly concentrated in soil surface horizon, is an important determinant of the soil quality. SOM is preferably removed by flowing water and tillage erosion. Few direct measurements, however, have conducted to investigate this dynamic process occurred at the field level only caused by intensive tillage. Moreover, a historic reconstruction of long-term soil redistribution by tillage and water erosion on soil quality variations is urgently needed for establishing the cause-effect relationship. The key problem is how to link the soil redistribution pattern on the slope to soil organic matter patterns. Against this background, we conducted the following two investigations. 2.1. Profile variations of 137Cs, 210Pbex and SOM as affected by intensive tillage on slope land We assumed that fallout radionuclides could be used directly for assessing the tillage erosion effects on soil organic matter pattern if 137Cs, 210Pbex and SOM move on the slope land by the same physical mechanism during tillage operations. To confirm this hypothesis, we measured the profile variations of 137Cs, 210Pbex and SOM contents along downslope before and after tillage series. We conducted 50 plowing operations over a 5-days period using a donkey-drawn moldbord-plow on s steep backslope of the Chinese Loess Plateau. Profile variations of 137Cs, 210Pbex and SOM contents are measured at upper, mid, and lower portion in a slope land after 50-plowing operations. Intensive tillage effects on 137Cs, 210Pbex and SOM contents were determined from a control slope adjacent to experimental slope. Our results indicated that 137Cs concentration was uniformly distributed in the top 0-30 cm of soil whereas 210Pbex showed a linear decrease at upper and mid portion, and an exponential decrease with depth on the lower portion of the control slope (Table 1). SOM contents of 0-30 cm layers were much higher than the soil layers below 30 cm of soil on the control slope, and showed a similar decrease pattern with soil depth to profile pattern of 210Pbex on the mid and lower portion of the control slope. Mean values of SOM, 137Cs, and 210Pbex of sampling soil profiles are spatially increased in the following order: lower > mid > upper for both the control slope (Table 1). Intensive tillage operations resulted in a dramatic decline of 137Cs and SOM concentration at upper portions of the slope while a temporal increase at the lower boundary of the slope. But the all of the positions of the plowing-slope showed a significant decline of 210Pbex concentrations compared to the control slope (Table 1 and Fig.1a, b, c). On the basis of the calculations of changes in 137Cs, 210Pbex and SOM between control slope and 50-plowing slope, intensive tillage operations resulted in a decrease of SOM content (g kg-1) by 37% and by 45% for the soil layers of 0-45 cm at upper portion and mid portion, respectively (Table 2). However, the lower position showed an increase of SOM content by 34% in the soil layers of 0-100 cm after 50 plowing operations. Weighed mean values of 137Cs concentrations decreased from 2.2 to 0.32 Bq kg-1 at upper position, from 3.79 to 0.33 Bq kg-1at mid position, and increased from 1.48 to 2.63 Bq kg-1 at lower position. Weighed mean values of 210Pbex concentrations decreased from 27.71 to 6.45 Bq kg-1 at upper position, from 35.46 to 1.57 Bq kg-1at mid position, and from 25.53 to 19.40 Bq kg-1 at lower position (Fig.1a, b, c). Our results (Table 2) supported conclusion by other researchers that tillage operation tends to reduce the profile variations of soil properties. After 50-plowing operations, the profile coefficients of variations (PCV) in SOM decreased from 19.87 to 1.77% at upper, from 30.42 to 17.64% at middle, from 38.45 to 7.61% at lower position. PCV of 137Cs and 210Pbex decreased

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from 86.66, 58.78 to 21.53 and 27.06% at upper position, from 88.18, 39.90 to 14.14 and 3.69% at middle, and from 155.56, 63.68 to 28.80 and 31.97% at lower position, respectively. Profile concentrations of 137Cs and 210Pbex are significantly correlated with SOM contents with R2 values of 0.82-0.86 for control slope (Fig.2a, b), and 0.86-0.90 for 50-plowing slope (Fig.3a, b). These results also provided the new evidence that fallout 137Cs and 210Pbex 137Cs, 210Pbex and SOM are moving on the slope land by the same physical mechanism and the same pathway during tillage operations. Therefore, fallout 137Cs and 210Pbex could be used directly for quantifying dynamic soil organic matter-soil redistribution relationship as affected by tillage erosion. A Historic reconstruction of the key erosion processes affecting soil redistribution and soil quality degradation in the Chinese Loess Plateau In many cases management of soil quality has failed to produce sustainable solutions due to lack of long-term quantitative records of erosion data. To obtain a realistic reconstruction of long-term erosion data, alternative sources could be used. One possible source for such reconstruction is sediments from lakes and reservoirs. But no lakes exist in the Chinese Loess Plateau. Although check-dam reservoirs are extensively distributed in the loess plateau, none lasted for more than 20 years. In the absence of long-term records of soil redistribution, we assumed that the deposits of natural terrace slope offer considerable potential for reconstructing the changing soil erosion rates at hill slope scale in response to the environmental change. In order to confirm this hypothesis, we reconstructed the soil accumulation rates of two natural terraced slope basis by using of fallout 137Cs, and 210Pbex, and 14C dating techniques. The investigated slopes are located in Yangjuangou catchment, 14 km east of Yan’an city, Northern Shaanxin Province. Two slope bases of natural terraces (Slope II and slope III) were selected to carry out this study. One (Slope III) is at the top position and the other (Slope II) is at the lower position of the hillslope. Plowing depth is 15 cm in the study area. In the deposition profile from slope III, maximum depth of significant caesium-137 activity was found to a depth of 40 cm and the peak value at the depth of 20-30 cm whereas maximum depth of significant 210Pbex concentration was found at a depth of 140-180 cm and two peak values at the depth of 100 and 160 cm, respectively (Figure 4a). Slope II showed the deeper 137Cs distribution than that in slope III (Figure 4b). Two peak values of 210Pbex concentration were found at the depth of 120 and 180 cm, respectively. Maximum depth represents the time when a significant level of caesium-137 was first recorded in 1954 and significant profile range of 210Pbex could be recorded in 1901 at slope II and III. The highest caesium-137 activity at 20-30 cm be equated with the period of maximum atmospheric fallout in 1963 (Slope III). Two peak values of 210Pbex concentration in both two slopes are because the dramatic destruction of natural vegetation for crop production in 1942. According to the dating of 14C, the original surface level of terrace slope III has increased about 800 cm over the past 3200 years. Using these five dated levels it was possible to provide an absolute chronology for reconstructing the temporal patterns of the sediment accumulation sequence on study slopes (Figures 5a and 5b). On the basis of these five-dated levels we divided the phase into five time periods. These are respectively: Phase I before 1901-BC 1200 (3100 years with sedimentation rate of 0.23 cm/yr.), Phase II between 1941-1901 (41 years with the rate of 0.49 cm /yr.), Phase III between 1953-1942 (11 years with the rates from 5.83 to 6.67 cm/yr.), Phase IV between 1962-1954 (12 years with the rate of 1.11-2.22 cm/yr.) and Phase V between 2001-1963 (39 years with accumulation rate of 0.77-1.28 per year). The deposited depth of sediments during the period of 2001-1901 was two to twenty-nine times higher than the period before 1901, with values increasing from ca. 0.23- 6.67 cm per year. This can be explained by increasing population and land use intensity. Maximum deposited depth was found in the years from 1953-1942, mainly caused by first dramatic destruction of natural vegetation for crop production in the study area. A clear increasing trend of sedimentation rates at slope basis in the years from 1901 to 1953 whereas a clear decrease of sedimentation rates in the years after 1953. These suggest the different erosion processes in controlling soil redistribution on the steep slopes in the two periods before 1953 and after 1953. Over the period from 1901 to 1953

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tillage translocation and tillage erosion should be the dominant soil redistribution processes whereas water erosion should be dominant process since 1953. These two different soil erosion processes will have different effects on the quality of soils on-site (Fig. 4a and 4b).

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g-1)

TaSOM线性 ( TaSOM)

Fi g. 3b. 210Pbex vs SOM on 50- pl owi ng sl ope

y = 0. 18x + 3. 18R2 = 0. 86

0

3

6

9

0 10 20 30210Pbex ( Bq/ kg)

SOM

(g k

g-1)

TaSOM线性 ( TaSOM)

Fig. 4a Measured depth distribution of 137Cs, 210Pbex, and SOM from the lowerboundary of natural terraced slope

0

15

30

45

0-10

10-2

0

20-3

0

30-4

0

40-5

0

50-6

0

60-7

0

70-8

0

80-1

00

100-

120

120-

140

140-

160

160-

180

180-

200

200-

220

220-

240

240-

260

Soil depth (cm)

210P

bex

(Bq/

kg)

0

2

4

6

813

7Cs (

Bq/

kg)/

SOM

(g/k

g)III-210Pbex(Bq/kg)III-137Cs(Bq/kg)OM (g/kg))

87

Fig. 4b Measured depth distribution of 137Cs, 210Pbex, and SOM from the lower boundaryof natural terraced slope

0

10

20

30

40

0-10

10-2

0

20-3

0

30-4

0

40-5

0

50-6

0

60-7

0

70-8

0

80-9

0

90-1

00

100-

110

110-

120

120-

140

140-

160

160-

180

180-

200

200-

220

220-

240

Soil depth (cm)

210P

bex

(Bq/

kg)

0

3

6

9

137C

s (B

q/kg

)/SO

M (g

/kg)

II-210PbexII-137CsSOM (g/kg))

Fig.5a Reconstructed soil deposition rates at a slope basis of natural terraced slope III

0,77 1,11

6,67

0,49 0,230

2

4

6

8

2001-1963 1962-1954 1953-1942 1941-1901 1901- BC.1200

Time periods (Year)

Sedi

men

tatio

n ra

te (c

m/y

ear

Fi g. 5b Reconstructed soil deposition rates at a slope basis of natural terraced slope I I

1, 282, 22

5, 83

0, 49

0

2

4

6

2001- 1963 1962- 1954 1953- 1942 1941- 1901Ti me per i ods ( Year )

Sedi

ment

atio

n ra

te

(cm/

year

)

88

Table 1. Profile variation of SOM content (mean ± SD), 137Cs, and 210Pbex activity between 50 plowing slope and control slope Control slope 50-plowing slope

Depth (cm)SOM(g kg )-1 137Cs (Bq/kg) 210Pbex(Bq/kg) SOM(g kg )-1 137Cs (Bq/kg) 210Pbex(Bq/kg)

Lacation

Upper 0-15 6.17±0.63 2.17 42.29 3.64±0.13 0.36 4.36

15-30 6.72±0.38 2.26 30.71 3.59±0.03 0.27 7.6530-45 4.51±0.11 0.00 10.13 0.24 6.45

Mid 0-15 8.55±0.44 3.37 50.94 0.30 1.5015-30 7.05±0.39 4.21 32.23 0.30 1.6030-45 4.52±0.21 0.00 23.20 0.38 1.60

Lower 0-15 9.62±0.23 4.77 55.93 2.54 11.0115-30 6.98±0.01 4.11 29.50 1.98 16.7430-45 5.63±0.22 0.00 22.12 2.11 16.3345-60 4.78±0.20 0.00 21.01 2.66 19.1060-80 3.92±0.25 0.00 12.32 3.50 25.7580-100 3.76±0.03 0.00 12.30 4.04 27.46

Table 2. Summary statistics of SOM, 137Cs, and 210Pbex of sampling profiles

3.52±0.074.07±0.413.81±0.572.87±0.476.17±0.316.59±0.386.46±0.317.10±0.297.51±0.447.26±0.20

Control slope 50-plowing slope

Lacation SOM (g kg-1)

137Cs (Bq/kg)

210Pbex (Bq/kg)

SOM (g kg-1)

137Cs (Bq/kg)

210Pbex (Bq/kg) Upper Mean 5.80 1.48 27.71 3.58 0.29 6.15

SD 1.15 1.28 16.29 0.06 0.06 1.66 CV 19.87 86.66 58.78 1.77 21.53 27.06

Mid Mean 6.71 2.53 35.46 3.58 0.33 1.57

SD 2.04 2.23 14.15 0.63 0.05 0.06

CV 30.42 88.18 39.90 17.64 14.14 3.69Lower Mean 5.78 1.48 25.53 6.85 2.81 19.40

SD 2.22 2.30 16.26 0.52 0.81 6.20 CV 38.45 155.56 63.68 7.61 28.80 31.97

89