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Isotope Techniques Trace Erosion Source to Sri Lanka’s Terraced Tea Plantations

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(Photo: Champa Dissanayake/Sri Lanka AEB)

The Central Highlands of Sri Lanka present a picture perfect snapshot of green hillsides, with beautifully terraced fields and gardens that produce a considerable amount of world class tea, rubber, spices and vegetables. These fields, cumulatively, are responsible for around 20 percent of national GDP. Yet a closer look at the area reveals problems. The area is highly prone to soil erosion, which at one point reached almost 40 tonnes of soil per hectare lost each year. In a search for solutions, the Joint FAO/IAEA Division, in collaboration with the Sri Lanka Atomic Energy Board and Natural Resources Management Centre, brought in isotopic techniques to help pinpoint the specific areas where appropriate conservation measures should be taken to improve soil management – measures that led to a 42 percent reduction in annual soil losses.

The landscape of the Dolosbage sub-catchment in Sri Lanka’s Central Highlands, which is extremely prone to erosion, is made up of plantations, orchards, crop fields, livestock pastures and even small home gardens. Not only does the area lose soil to erosion, it also loses all of the nutrients in that soil, which the plants and plantations need to thrive.

The problem multiplies when the eroding soil enters water reservoirs and the nutrients, especially nitrogen and phosphorous, become feed for the algae in the water. Known as algal bloom, as the algae grow, they consume the oxygen that fish need to survive. Also, as the sediment load increases in the reservoir, it decreases the amount of water that the reservoir can hold and shortens the lifespan of the dam.

Because the study area was a large catchment with a mixture of land uses, it was obvious that any attempt to help solve the area’s erosion problems had to be done at landscape level. It was equally imperative to identify the main sources of the erosion. Working with its Sri Lankan partners, the Joint Division, in part through the IAEA’s technical cooperation programme, used fallout radionuclides (FRNs) to conduct land degradation assessments and compound-specific stable isotopes to identify its source, a relatively new concept for Sri Lanka.

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