The role of earthworms and water infiltration in clay mixing in peat meadows

Peat meadows in the Netherlands emit around 3% of the country’s total CO₂ emissions. Measures to reduce the CO₂ emissions in agricultural peat areas are mostly based on water management, the clay-in-peat project researches a soil based measure: the addition of 1-2 cm of clay on top of a peat meadow. In lab experiments, where the peat and clay are completely mixed, some combinations of clay and peat show a reduction of CO₂. It is still unclear what the working mechanisms of clay in peat are. These could vary from clay-peat-complex formation to the binding of enzymes or changes in the pore structure.

In field applications we see large differences between fields as to how the clay is spreading through the peat profile. This variation could influence the effectiveness of the measure depending on the working mechanism.

Clay can be transported and transformed by various processes such as biological activity or infiltration into the soil with water. It is not yet known how the clay could infiltrate into a peat meadow, and which processes are most important.

We want to understand how clay spreads through the profile in a peat meadow. The way the clay is spread determines how it is present and in what way it could influence the emission of greenhouse gasses. A better understanding of the way the clay moves could help explain CO₂ measurement and the effects of various clay types.

We have set up an experiment using columns (30 cm height, 9 cm diameter) both hand-filled with peat and intact cores of a peat meadow. To all columns a layer of 1 cm clay was applied. To half of these columns three earthworms were added. And half of the columns received a ‘rain’ treatment. After 2 and 4 months the columns were harvested to find out how the clay had spread.

The worm treatment had most effect on the spreading of the clay. The water treatment did displace the clay, however, the total amount of displaced clay was lower than in the worm treatment. It was clearly visible that clay transported by worms settles in clumps and the water caused settling layers. There was no clear difference between the worm and the worm+water treatment.

In this experiment the role of soil fauna is most important in spreading the clay. Understanding the mechanisms that spread clay through the peat profile can help assess the suitability of a certain field or clay type for emission reduction using the clay-in-peat method. Furthermore an understanding of the clay mixing could help explain the results of CO₂-measurements in clay in peat sites.