By Eleonora Colzani, IAEA Office of Public Information and Communication

Farmers and nearby residents have noticed increasing algae growth in Viet Nam’s Nhue River, threatening their water and livelihoods. Thanks to the use of nuclear techniques, scientists have now identified the source of the excessive nitrogen and phosphorous pollution and are taking steps to improve the 70-mile-long river’s water quality. Here is their story.

The Nhue is a small river in northern Viet Nam, a tributary of the Red River crossing the capital Hanoi. It has seen excessive plant and algae growth – a result of the high concentration of nutrients known as eutrophication – to the extent that it could no longer be used for fishing, tourism or even irrigation, leading to crop losses, threatening the wellbeing and in some cases the livelihoods of the over 200 000 people who depend on it.

Scientists from the Institute for Nuclear Sciences and Technology (INST) of the Vietnam Atomic Energy Institute (VINATOM) and the Soil and Fertilizers Research Institute (SFRI) have been able to identify the culprit: excessive use of fertilizers on nearby farms. Vietnamese experts were supported by the IAEA in cooperation with the Food and Agriculture Organization of the United Nations (FAO).

As Integrated Soil Fertility Management Specialist at the Joint FAO/IAEA Centre of Nuclear Techniques for Food and Agriculture, Joseph Adu-Gyamfi explains: “Isotopes can be used to trace phosphorous and nitrogen pollutants and therefore help identify the sources of the pollutants, their apportionment and their translocation.”

N-P-K fertilizer when applied in large quantity to rice a month after planting could cause eutrophication in receiving water bodies. (Photo: Institute for Nuclear Sciences and Technology, Hanoi)

By sampling water in the creeks and ponds upstream of the Nhue River where different vegetables and crops are grown and determining the isotopic composition of the water and nutrients, scientists could trace the pollution flow (see Using stable isotopes to trace agro-pollutants in the water) and could make recommendations to farmers who used more fertilizer than their crop could absorb, with the excess chemicals making its way into creeks and ponds feeding the Nhue.

Based on the nitrogen isotopic results, soil scientists can determine when to apply fertilizer and in what amounts, in line with the plants’ needs through their life cycle. By following this practice, fertilizer runoff was decreased and, in some cases, reduced pollution and eutrophication altogether.

Since 2011, SFRI has organized trainings on synchronization and appropriate fertilization techniques to 500 farmers as part of a pilot project. Farmer Do Trong Thang, one of the participants, said: “Now I know that we used to waste a lot of our money, as fertilizer application was not done in the right way, with up to 70 per cent of the fertilizer escaping from the fields due to volatilization, leaching or runoff.” Farmers could reduce the amount of urea (N-fertilizer) applied to crops in the area by more than half, from 75 130 tonnes to 34 560 tonnes a year.

“Water degradation is not fully solved though, as industrial pollution and wastewater from households also ends up in the river. But in the meantime, water quality has somewhat improved already, and the impact will grow as more farmers participate in the programme,” said the project counterpart from the Institute for Nuclear Sciences and Technology in Hanoi, Dr Duc Nhan Dang.

The Science

Using stable isotopes to trace agro-pollutants in the water

When pollution from multiple sources to rivers, creeks or ponds occurs, conventional monitoring is unable to trace where the pollutants originate. Stable isotopes, which are non-radioactive forms of atoms, can be used as tracers thanks to their unique characteristics: the isotopic signature of each nutrient can be a fingerprint of the source. They have the same chemical properties as “regular” atoms but have a heavier nucleus and therefore can be distinguished. Scientists deliberately add stable isotope-labelled fertilizers of nitrogen (N) to the soil to determine the percentage of the added fertilizer taken up by the plant and the excess that escapes to the rivers and ponds through runoff, causing eutrophication.