Dac Dung Bui - Vietnam

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					             COUNTRY REPORT (VIETNAM)

                              for
   IAEA/RCA Meeting on “Exchanging of Experiences using
the Cs-137 Technique for Measuring Soil Erosion/Sedimentation
           and Associated Pesticide Contamination”
                     (RAS/5/039 Part II )
                  Kuala Lumpur, Malaysia
                         5-9 July 2004

                          by
          Pham Duy HIEN - Project Co-ordinator,
        Bui Dac DUNG- National project manager,
      Nguyen Hao QUANG, and Nguyen Quang LONG
 THE USE OF Cs-137 AND Pb-210 TECHNIQUES
FOR ASSESSING SOIL REDISTRIBUTION RATES
  AND PATTERNS: A REVIEW OF STUDIES
        CONDUCTED IN VIETNAM
                   1. INTRODUCTION


• Vietnam territory is about 350 000 km2, 3/4 of the land are
  in the hilly and mountainous areas.
• The population (about 80 mil.) has nearly doubled from
  1940s’ to 1980s’.
• Natural forests have been cleared for agricultural purposes.
• The per-capita arable land has reduced from 1320 to 950
  m2 and deforestation occurs with a rate of about 1 Mha/yr.
• Unsustainable use of the high slope lands has lead to soil
  quality degradation.
                      1. INTRODUCTION

• Soil erosion rates are being estimated and soil conservation
  techniques have been implemented through the government
  agricultural projects (Ministry of Agriculture and Rural
  Development)
• Most of the projects on soil erosion estimation have been carried
  out by conventional techniques at the National Institute for Soil
  and Fertilizer (NISF)
• Advanced nuclear techniques such as Cs-137 and Pb-210
  techniques for assessing soil erosion have been tried at Vietnam
  Atomic Energy Commission (VAEC) in some areas with
  promising results.
• Collaboration with soil scientists as the end users needs to be
  improved in order to fasten the application of these techniques.
     2. RECENT APPLICATIONS OF Cs-137 AND Pb-210
                 TECHNIQUES IN VIETNAM
     2.1. Determination of Cs-137 deposition density across the
                        territory of Vietnam

• National Project on determination of Cs-137 deposition density in
  soil was carried out in 1997-2000 period. The Cs-137 inventory
  across the territory of Vietnam was determined.
• The measured Cs-137 inventory varies from 129 (South) to 3294
  (North) Bq m-2.
• The regression model describing the Cs-137 deposition density D
  (Bq m-2) distribution across the territory has been found as:
       Ln(D)=(3.640.11)+(0.0940.004)L + (0.54  0.04)AR
       Where: L-latitude (oN), AR-Annual rainfall (in m) at the
       sampling site.
                                 LATITUDINAL DISTRIBUTION OF 137CS DEPOSITION
                                  DENSITY ACROSS THE TERRITORY OF VIETNAM



                                                      inventory, Bq m-2                 deposition density, Bq m-2

                                1200
Inventory/deposition, Bq m -2




                                 900


                                 600


                                 300


                                   0
                                       9.25

                                              10.25

                                                       11.25

                                                               12.25

                                                                       13.25

                                                                               14.25

                                                                                        15.25

                                                                                                16.25

                                                                                                        17.25

                                                                                                                18.25

                                                                                                                        19.25

                                                                                                                                20.25

                                                                                                                                        21.25

                                                                                                                                                22.25
                                                                                       Latitude, o N
 2.2. Cs-137 technique in estimating soil erosion at Song Da
                     afforestation field

• The Song Da afforestation field lies on a mountainous area
  in North Vietnam where a big reservoir was constructed in
  1982 for an 1800 MW hydropower plant.
• Reference value for Cs-137 is 918.5 Bq m-2.
• Soil samples were taken from three transects of 8 samples,
  in areas with bamboo, acacia and brush plant covers.
• Average soil loss rates were calculated as 3.2, 4.4 and 9.8
  t/ha/yr for acacia, bamboo and brush covers, respectively.
    2.3. Assessing soil erosion and nutrition loss by Cs-137 and
                          Pb-210 techniques

• Aimed at combining techniques for evaluating soil erosion and
  nutrition loss.
• The experimental area, of 200 m2 (10x20 m) on a 100 slope of a
  hill, lies in Doan Hung district, Phu Tho province (about 200 Km
  northwest of Hanoi).
• Erosion rate calculated by Cs-137 technique was 5.2 t/ha/yr, by
  Pb-210 technique was 7.08 t/ha/yr where as the erosion rate
  calculated by direct weighing was 6.09 t/ha/yr.
• Unfortunately, the nutrition loss has not been able to evaluate by
  Cs-137 and Pb-210 results due to limited number of analyzed
  samples.
      3. ONGOING NEW NATIONAL PROJECT
                          3.1. Background

• Although nuclear scientists have been active in the use of Cs-137
  technique for soil erosion, and good laboratory facilities have
  been established for analyzing Cs-137 and Pb-210, our soil
  scientists still know little about these nuclear techniques.
• Joint project (between the Institute for Nuclear Science &
  Technique – INST (VEAC) and the National Institute for Soil &
  Fertilizer - NISF) has two main objectives: One is to validate and
  confirm the many advantages of nuclear techniques in assessing
  soil degradation; The other objective is to get soil scientists
  involved actively in the sampling design, measurement,
  interpretation, and comparing nuclear techniques with
  conventional techniques.
                           3.2. Methods

• Multidisciplinary team was formed with scientists from INST
  and NISF.
• A place where plots for erosion measurements designed by the
  NISF has been chosen. This place is located about 100 Km from
  Hanoi.
• The Cs-137 reference inventory value were estimated first by the
  regression model based on the latitude and the annual rainfall
  values, and found to be around 900 Bq m-2.
• Research for the reference site was a very difficult task because
  of the dense population and unclear history of the cultivation
  practice in the area. After many interviews with local people we
  have found that there are two hilltops that have never been
  cultivated
                3.2. Methods (Reference site)


• A square of 3x3 m where five sample points were taken.
• At each point, four samples from depth interval of 0-10
  cm, 10-20 cm, 20-30 cm, and 30-40 cm were taken for
  investigating depth distribution of Cs-137 and Pb-210.
• Because of the uncertainty in choosing the place, we have
  decided to take samples on work-and-try basic: For the
  first visit we took only samples from 3 points at each site.
Investigated site
                    Reference site
               3.2. Methods (Reference site)

• The “reference” samples were analyzed for Cs-137 and Pb-
  210 by ORTEC HPGe detector at the Environmental
  Radioactive Monitoring Laboratory (INST).
• Total Cs-137 inventory value from each point at one of the
  hills was around 205 Bq m-2, clearly lower than the
  estimated value of 900 Bq m-2.
• At the other site, the Cs-137 values were 713, 937, and
  1006 Bq m-2 for three first points, and are in good match
  with the estimated value. This hilltop, a place where the
  pole of the electric power transmit line is located, is
  considered a good choice for reference site.
Reference site
                  3.2. Methods (Research plots)

• Each research plot has been designed from the top down the hill,
  with observation pond at the toe to collect runoff sediments.
  Every plot has dimension of 7.5 m wide and more than 30 m
  long. There are seven plots for three different types of erosion
  research:
• One plot for observation of bare land erosion.
• One plot for observation of corn cultivated land erosion without
  hedgerows.
• One plot for observation of tea cultivated land erosion without
  hedgerows.
• Four plots for observation of cultivated land erosion with
  different hedgerows.
                  3.2. Methods (Research plots)



• Two transects for a plot, each goes along the length of the plot
  and consists of 12 sample points.
• One soil sample from each point is taken to be analyzed for soil
  property and nutrition contents at the NISF’s laboratories.
• every plot has 24 samples for analyzing Cs-137 and Pb-210 and
  24 samples for analyzing soil property and nutrition contents.
• It is our plan to conduct all sample collection by the end of this
  July and have all samples analyzed by the end of October. To
  date, only one transect has been completed.
Plot No 6
                          3.3. Results



• 10 reference points with 40




                                     Bq.m-2
  samples have been completed.                600
• Average Cs-137 reference                    400
  value is 885 Bq.m-2                         200
• The variation of the reference                0
  inventories is about 16%.
                                                     1        2   3   4
• Depth profiles show that the
                                                    Point B           Depth
  Cs-137 distribution is typical
  one for an undisturbed site
Cs-137 inventories at reference site
        (topomap unit: cm)
         Cs-137 inventories and conversion results
                     for transect 1 on plot 6
        Sample
                  M1      M2       M3      M4      M5      M6
Results
    Cs-137
                  108     444     1359     300     533     983
    (Bqm-2)
      Soil
 Redistribution   -58.7   -33.2   36.3     -44.1   -26.3   7.8
   (t/ha/yr)
         Sample
                  M7      M8       M9      M10     M11     M12
Results
    Cs-137
                  237     407     1216     314     481     1146
    (Bqm-2)
      Soil
 Redistribution   -48.9   -35.9   25.5     -43.0   -30.3   20.2
   (t/ha/yr)
Cs-137 distribution along transect 1 on plot 6
            Reference value: 885 Bq/m2
                     4. CONCLUSIONS


• The Cs-137 deposition in Vietnam is rather high, particularly in
  the central and northern parts. The regression model established
  for calculating the Cs-137 deposition density in Vietnam
  territory is the good guide to estimate reference value in any soil
  erosion/sedimentation study.
• Results of soil erosion studies showed promising future for the
  application of Cs-137 and Pb-210 techniques. A close
  collaboration with soil scientists is the better way to fasten the
  process of transfer these techniques to the end users.

				
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