Finnish Forest Research Institute  Metla

Press release 16.03.2006

Carbon accumulation rate on peat bogs exposed to heavy metal load

Isotopic age-dating methods shown to work well and accurately for determining carbon depositions

In collaboration with the University of Heidelberg, Metla has been able to apply the German researchers’ age-dating methods for peat. The studies at Metla focused on ombrotrophic peatlands exposed to large depositions of heavy metals. Since several environmental changes have occurred during the last 100 years, it was important to measure the recent accumulation rate history of carbon and heavy metals.

Peat cores were measured to determine recent accumulation rates using both bomb pulse 14 C and 210Pb age-dating methods. The bomb pulse method is suitable for measuring small samples and it can be used in precision dating of the recent past based on radiological isotopes released in nuclear explosions on the Earth.

-By using age-dated peat cores it is possible to calculate net accumulations of peat and carbon during a specified time period. In addition, the exact age-dating and heavy metal concentrations provide information about the local heavy metal exposure history, explains Senior Researcher Tiina Nieminen from Metla.

The annual accumulation of carbon varied during the last 125 years on the studied peat bogs subjected to heavy metal loads. The recent carbon depositions were explored on three peat bogs contaminated with heavy metals and a background site in Hietajärvi, in the Patvinsuo National Park. The most easterly of the contaminated sites is approximately 8 km from Outokumpu, where mining activities were shut down in the 1980s, the second one is in south-western Finland approximately 6 km from the Harjavalta copper and nickel smelters, and the third one in Alkkia, Karvia, in south-western Finland.

With the exception of Alkkia, the carbon deposit was proven to be related to annual precipitation, among other factors. The results also suggest that the pollution history of the area may have affected the carbon accumulation, even though the current vegetation on the peat bogs showed no damage on visual inspection.

In 1962 an ore-prospecting simulation was set up at the Alkkia peat bog; the aim was to determine the post-depositional migration of copper and nickel to peat vegetation. To test this, 200 kg ha -1 copper and nickel sulphates were spread on test grids.

The age-dating of Alkkia peat samples showed that peat formation was completely stopped after the spreading of the metal sulphates. Today, more than 40 years after the metal applications the vegetation on the test grids is still damaged, and Sphagnum, the most important peat forming plant, is still almost totally missing.

The research project “Carbon accumulation in ombrotrophic peatlands near heavy metal emission sources” was part of the “Pools and fluxes of carbon in Finnish forests and their socio-economic implications (HMS)” programme.

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