Predictions that around 80,000ha of the country’s farmed peatlands will have to be rewet were “over-estimated”, a senior Teagasc scientist has claimed.
A significant proportion of the 335,000ha of farmed peatlands are effectively rewet at the moment, since the shallow drainage in place means the water table remains high, Pat Tuohy contended.
The Teagasc scientist also maintained that the carbon emissions estimates for Ireland’s farmed peatlands are significantly overstated and could be halved if revisited.
The emissions estimates of 9m tonnes of CO2 equivalent for farmed peatlands are based on the assumption that the actual drainage status of these lands is unknown and therefore all the ground is considered to be deep drained, Tuohy told an Agricultural Science Association webinar.
The drainage status and the consequent emissions estimates are now being challenged by Irish researchers and this could result in significant reductions, he pointed out.
Detailing Ireland’s emissions under the category of land use, land use change and forestry (LULUCF), Tuohy said Ireland is “an outlier” by being a net emitter in this area. Total annual emissions are put at 7.25m tonnes.
The main culprit from a land use perspective is drained peatlands, which are estimated to release around 9m tonnes of CO2.
This emissions estimate is based on the assumption –made under Intergovernmental Panel on Climate Change (IPCC) guidelines – that the drainage status of these lands is unknown and they therefore must be considered to be deep-drained. The emissions are calculated at 26t/ha/year or close to 9m tonnes in total, Tuohy explained.
Irish research is trying to “throw a bit of a spanner in the works” by challenging the assumption that the drainage status is unknown, the Teagasc scientist said.
“We’ve drawn up alternative scenarios that are reducing that 9m figure effectively by half or more if adjusted accordingly,” he claimed.
The assumption that all these lands are deep drained is “hard to justify” because of the level of investment and the level of maintenance that such drains would require across the 335,000ha, Tuohy said.
“So that number of the 9m figure is likely to come down,” he predicted.
However, even if 3m tonnes or 4m tonnes were cut from the overall peatlands emissions total, the figure still remains high and some level of water table management or rewetting of grazing ground will be required, the Teagasc scientist warned.
But he said that the 80,000ha figure was probably inflated given that much of the farmed peatlands were not in fact deep drained.
Tuohy claimed that farming could continue on this rewet ground, but he accepted that the grazing period would be reduced.
“The mean water table position would be 20cm, 30cm, 40cm closer to the surface, which means your summer is effectively shorter,” he explained.