Farmers cause less peat degradation with high water levels

Parts of the western and northern Netherlands consist of peat grassland areas, a type of soil formed by decayed plants in marshes. During the 1960s and 70s, many of these areas were drained by reducing the water level in ditches. This resulted in degradation of the peat, causing the soil to settle and subside. Every few years, the water boards review the water levels. However, due to increasing costs for dewatering and draining the water, managing soil subsidence is becoming increasingly expensive.

Additional soil subsidence

Peat degrades because oxygen gets to the decayed plants, making the soil subside. Wet conditions protect peat soils against oxygen penetration. Degradation accelerates not only because of low water levels in ditches, but also due to drier spells caused by climate change. CO2 is released in this process, further exacerbating climate change. Thus, saturating (or rewetting) the soil helps to counter soil subsidence and CO2 emissions. Many dairy farms are established in peat grassland areas, so there is a limit to which this saturation technique can be used. Grassland should not get too marshy to have cows and machines on it.

Farmers dealing with high water levels

Severe saturation calls for a change in the farmer's business operations. Together with various partners, WUR is conducting research into how dairy farms can operate with very high groundwater levels at the high groundwater farm in Zegveld in the province of Utrecht. With high water levels, farms are likely to be able to produce less grass per hectare, which increases costs. It is important to quantify the impact of groundwater levels on business operations so that the economic disadvantage can be calculated. It is up to farm managers to decide how to proceed with this.

Water infiltration

At the high groundwater farm in Zegveld, the water in ditches is kept at twenty centimetres below the surface level. Perforated horizontal pipes spaced four metres apart allow water to flow out of the ditches into the soil to further raise the groundwater level. WUR is studying how best to do this and what the effects are. The aim is to maintain the groundwater level in peat grasslands at twenty centimetres below ground level all year round. It is currently at an average of around sixty centimetres below ground level in summer and can drop to more than a metre during long dry spells. WUR expects that, with a water level of twenty centimetres below ground level, the peat degradation will be 25% less than it is today. The Zegveld farm is also one of the locations of the National Research Programme for GHG Peat Grasslands in which WUR, Deltares, and other research partners are collaborating. The partners of this project measure the impact of groundwater levels on CO2 emissions for plots with and without water infiltration. In this way, the partners are aiming for minimal peat degradation to combat climate change.