The Water Resources Authority (WRA), in partnership with the International Atomic Energy Agency (IAEA), has completed an isotope hydrology study into the Rio Bueno Sub-Watershed Management Unit (WMU).

This project aims to evaluate how sinking rivers, rising rivers, springs, and groundwater contribute to basin flow.

By clarifying the impact of rainfall and other hydrological factors, the study will help improve source-water-quality protection for Jamaica.

Speaking at a Jamaica Information Service (JIS) Think Tank on September 8, Deputy Managing Director at the WRA, Geoffrey Marshall, said that, as a branch of hydrology, isotope hydrology uses the molecular structure of isotopes as a tracer for where water moves and goes in the Sub-WMU.

“Isotope hydrology is a branch of hydrology that uses nuclear physics or the molecular structure of isotopes in water as a tracer for where water moves and goes. An isotope is a different form of an element. Isotope hydrology is using these different isotopes as a fingerprint of the water, fingerprint of the water molecules, fingerprint of different contaminants or substances within the water molecules, such as carbon or sulphur, or nitrates, or other things, and using these steps you can see where water was coming from and where it was going,” he said.

He added that the assessment of the Rio Bueno Sub-WMU builds on work previously done by the WRA using dye tracing methods.

“Dye tracing is the use of artificial tracers. It has been used historically across the world… you take an artificial dye that’s non-toxic to the environment and you will see a sinking area, and you pour the dye in there and [as] the water travels, the dye will travel also and then you’ll have receptors at expected points,” Mr. Marshall said.

“So, where we had known that some of these rivers in the upper part of St Ann sank and appear, we weren’t sure if those were the only places that came out and we saw that some places where we expect that to come out in springs, it didn’t come out. So, we use isotope hydrology to move from artificial tracing to natural tracing,” he added.

To undertake the study, water samples were collected from rivers, springs, sinks (ponors) and deep wells over the period March 2021 to July 2023.

“We established a network of collection points at 46 sites. We had about three rainfall sites across the basin and rainwater collectors. We had five sinking stream sources, about seven major rising stream sources and 15 springs and 16 wells for groundwater samples. We collected samples from those sites on a monthly basis and collected the data, analysed the data for stable isotopes or hydrogen and oxygen, along with some water-quality testing,” Marshall pointed out.

The study revealed a clear distinction between all the water sources and further proved connections that were previously noted using dye tracing.

“We also saw where there seemed to be distinct water sources for some of the spring sources, as well as the groundwater was very stabilised from the wells, and then there wasn’t much movement there. We also saw the impact of extreme weather events in that time, because during that collection, we saw the impact of Tropical Storm Grace, which happened in August 2021, and we saw the isotopic signature of that storm in the rainfall and we also saw it reflected in the stream flows,” Mr. Marshall said.

Analysis of 60 per cent of the data obtained from the assessment has been done, with a further 40 per cent to be analysed.

“While we have a draft report completed, we’re expecting to have even more clarity once we get all of the data presented. This just goes to show the importance and practicality and application that histopathology can have for water resources in Jamaica and the Caribbean. The IAEA has made much investment in having regional projects dealing with isotope hydrology,” said Marshall.