Are peatlands cool humid islands in a landscape?

This study proposed that due to their high standing water tables that peatlands would be cold humid islands within their landscape relative to farmland on mineral soils. Long term satellite observation of across England’s largest raised bog (t km² former raised bog - Thorne Moors, northern England) showed that as the bog was restored the air temperature over the bog decreased by 1.7 ^oC relative to the surrounding farmland. So this study set out to test this hypothesis with real field observations.

We measured air temperature and humidity at 17 locations along a 7.8 km transect across the Thorne Moors site. Air temperature and humidity were measured hourly for 1 year and supported with spot albedo measurements. The study represented a factorial experiment with respect to sites of measurement; the type of land use (peat vs arable land); and time of sampling over both the seasonal and diurnal cycles. We could show:

• That although mean annual temperature was not significantly different between arable and peatlands the arable land showed a decreased amplitude to its seasonal cycle – this is the reverse of the expected pattern.
• The peatland was colder at night and warmer during the day than the surrounding land.
• The albedo of the peatland was significantly lower than that of arable land showing that vegetated peatland still absorbed more solar radiation.
• The specific humidity was lower on the peatland than on the surrounding arable land.

The study therefore could show that whilst shrubby vegetation exists over a peatland then energy budgets are more likely to be dominated by the greater surface roughness and lower albedo of the vegetated peatland relative to arable land. Thus, shrub-dominated peatlands will not be a cold humid island in their landscape.