Friday, 12 April 2019

Coconuts and curry – a geochemical survey programme in Sri Lanka...by Charles Gowing

Steep sided valleys of tea and rubber plantations above
fertile paddy fields
Charles Gowing and Paul Everett have returned from a BGS Global funded trip to the Geological Survey and Mines Bureau (GSMB) in Sri Lanka where they have been working with geologists and chemists on refinement of a national geochemical survey programme. Soil sampling is well underway in the south and north of the country and the GSMB have already produced the first environmental series atlas of top soil in the Rakwana-Tangalla region.


The aim of the visit was to review existing soil sampling procedures and discuss options for sampling stream sediments with field geologists, and to discuss analytical geochemical procedures and sampling handling processes with laboratory chemists, and to learn how their geochemical maps were compiled.

In the laboratories, aqua regia is used to digest top soil samples before analysis using a combination of ICP-OES and AAS for a specified suite of elements. Existing methods were demonstrated with a view to recommending extensions to the range of elements measured and improvements to the quality system. Proposed methods of analysing sub soil and stream sediment samples were explored in detail, together with potential enhancements to sample receipt, preparation and storage processes.

The highlight of the trip was a field visit 2 hours drive south of Colombo to Matugama to see soil sampling in action. A trek past paddy fields in the valley bottoms took us past houses where we were offered rambutan (large lychee) and mangosteen by householders and then up through tea plantations interspersed with pepper and cinnamon, as well as spotting vines lashed to trees to allow easy access to the fruit from which local beverage is fermented.

From L-R: Charles and the laboratory chemists at GSMB debating calibration protocols; Paul walking to field location through tea, pepper and cinnamon plantations.  
Field sampling can be a laborious process especially obtaining samples from as deep as 2 m, so ingenuity is required to assist manual sampling by auger. Sites are selected to be close to the specified sampling coordinate and away from recent fertilizer applications or other sources of potential anthropogenic contamination. Subsoil samples are cone-quartered in the field to reduce the amount of material transported out of the field.
 
In an area washed by monsoon rains, streams can be seasonal, but we located an accessible sandy bank for Paul to be able to demonstrate panning to the GSMB geologists; local schoolchildren were fascinated by such activity from their grandstand view on a nearby bridge.

From L-R: Gravity assisted manual soil sampling; Paul and GSMB geologists panning for heavy minerals.
Working at 35˚C and 100% humidity presented additional challenges, particularly as the field sites were located on steep hillsides above the paddy fields in the valley bottoms. The hot work was rewarded with refreshing drink from king coconuts, although half of the fluid seemed to end up down our shirts, and a delicious curry lunch served on banana leaves in a nearby Buddhist temple, after which we were invited to become monks – a truly tempting offer given their hospitality and the beautiful locations.
       
Charles enjoying the local hospitality.
Dr Charles Gowing is the UKAS Quality Manager for the Inorganic Geochemistry Laboratories in The Centre for Environmental Geochemistry and has analysed samples water, soil and stream sediment samples for the G-Base programme since 1992. Paul Everett is a building stones specialist and has coordinated and managed several BGS geochemical baseline sampling campaigns since 2009.

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