Preserving peat

Summary: research at the Polderlab

The central intervention is rewetting the agricultural peat soil. The Polderlab consists of 32 ha of agricultural plots in which groundwater levels are raised while different forms of land use are tested. In the grassland system, for example, the water level can be raised by up to 35 cm. Other plots are managed much wetter and used for wet crops.

There are three focus points connected to stopping peat degradation by rewetting the peat soil:

• Can a higher water table slow peat subsidence? Higher groundwater levels keep more of the peat waterlogged, thereby limiting the conditions under which peat oxidation occurs. One particularly interesting recent Polderlab study investigates furrow infiltration as a way of getting water into the peat soil. The Polderlab research page reports that this can effectively raise groundwater levels and thereby help slow land subsidence.
• What happens to greenhouse-gas emissions? This is particularly interesting because rewetting peat soils does not necessarily mean that fewer greenhouse gases are emitted from the soil. The Polderlab has installed automated greenhouse-gas measuring systems – the rather wonderful-looking “Moon landers” – in different land-use systems. They continuously measure emissions in grassland, rice, cranberry plots, higher areas and even ditches. Researchers can therefore compare emissions among land uses and investigate what happens when water levels are changed.

!!Trade-off alert!! CO₂–CH₄ trade-off

Keeping peat wet should reduce aerobic decomposition and thus CO₂ emissions from peat oxidation, but wetter/anoxic conditions can favour methane production. So scientists need to measure the overall greenhouse-gas balance, rather than simply assume that wetter is always better. You may try to find out more about such trade-offs yourself. For now it’s important to be aware that these trade-offs exist and that scientists always need to investigate into potential trade-offs and that simple solutions hardly suffice.

• What happens to water quality and nutrients? The researchers also monitor water quality. This matters because changing the hydrological conditions changes biogeochemical processes in the peat. An earlier Polderlab-associated study explicitly points to the possibility that rewetting can alter nitrogen and phosphorus availability and potentially release previously less-mobile phosphorus. The experimental design also pays considerable attention to water quality: rainwater is retained and moved between plots, and aquatic/riparian plants are being investigated partly for their potential role in water purification.

Have you clicked on the ‘Scientists’ button?

It’s important to learn that variables are not studied in isolation. For example, PhD researcher Fleur van Duin describes large field experiments in which the effects of different interventions and crops on biodiversity and greenhouse-gas emissions are monitored. The Polderlab is deliberately a living laboratory: interventions are tested at realistic field scale while agriculture continues.

Take away message from visiting the Polderlab: not only to ask whether a measure works, but also what its wider consequences are: researchers raise water levels and study the consequences for soil subsidence, greenhouse-gas emissions and water quality. But changing one part of the peatland system affects many others. A measure that reduces peat oxidation may also change methane emissions, nutrient availability, biodiversity and the possibilities for agriculture.