Can peat reduce evaporation during dry periods?

Peat soils not only provide a habitat for distinctive fauna and flora, but are also the most efficient carbon sink on the planet, as peatland flora captures carbon dioxide released from the peat. However, many peatlands are currently drained because of agriculture, peat extraction, or forestry, thus leading to oxidation and decomposition of the organic matter causing carbon dioxide to be released into the atmosphere. Another potential risk of peat drying comes from the increasing probability of heat waves due to climate change. We therefore conducted sub-profile-scale laboratory experiments that aim to answer the question of how extreme heat influences hydrological behaviour of mountain peat from the Sumava mountains, Czechia.

 

The preliminary results suggest that during dry periods, such as prolonged heat waves, our tested peat in fact decreases the evaporation rate, provided that the depth of the groundwater table is kept constant. However, when we allow peat to dry completely without controlling the groundwater table level, desiccation cracks form, which work as conduits for ever deeper subsurface evaporation. Therefore, the level of groundwater table is critical in answering the question.

 

The described negative feedback showing that extreme potential evaporation can cause a decrease in actual evaporation comes as a surprise, since peatlands are usually understood as a wet land cover that cools the surrounding environment. We have shown that this does not always have to be the case, and we suggest that this mechanism should be studied further. Our small-scale laboratory experiments should also be tested in a natural setting to confirm these results.