COUNTRY REPORT VIETNAM for IAEARCA Meeting on Exchanging of Experiences using the Cs137 Technique fo

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COUNTRY REPORT (VIETNAM)for IAEA/RCA Meeting
on Exchanging of Experiences usingthe Cs-137
Technique for Measuring Soil Erosion/Sedimentation
and Associated Pesticide Contamination(RAS/5/03
9 Part II ) Kuala Lumpur, Malaysia5-9 July
2004by Pham Duy HIEN - Project
Co-ordinator,Bui Dac DUNG- National project
manager,Nguyen Hao QUANG, and Nguyen Quang LONG
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THE USE OF Cs-137 AND Pb-210 TECHNIQUES FOR
ASSESSING SOIL REDISTRIBUTION RATES AND PATTERNS
A REVIEW OF STUDIES CONDUCTED IN VIETNAM
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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.

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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.

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2. RECENT APPLICATIONS OF Cs-137 AND Pb-210
TECHNIQUES IN VIETNAM2.1. 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.

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LATITUDINAL DISTRIBUTION OF 137CS DEPOSITION
DENSITY ACROSS THE TERRITORY OF VIETNAM
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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.

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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.

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3. ONGOING NEW NATIONAL PROJECT3.1. 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.

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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

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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.

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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.

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Reference site
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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.

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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 NISFs 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.

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Plot No 6
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3.3. Results

• 10 reference points with 40 samples have been
  completed.
• Average Cs-137 reference value is 885 Bq.m-2
• The variation of the reference inventories is
  about 16.
• Depth profiles show that the Cs-137 distribution
  is typical one for an undisturbed site

Point B
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Cs-137 inventories at reference site (topomap
unit cm)
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Cs-137 inventories and conversion results for
transect 1 on plot 6
 
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Cs-137 distribution along transect 1 on plot
6Reference value 885 Bq/m2
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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.