Which measures are being studied?
In order to develop measures that will be effective in reducing
CO2 emissions from peatland, it is first necessary to determine
exactly what different measures contribute to that reduction.
For this reason, various measures are being assessed.
In underwater drainage, perforated parallel pipes (drainage tubes) are laid in the ground horizontally. These flow into the ditch, below the ditchwater level. The pipes are intended to provide infiltration in dry periods. The main advantage is that in dry (and warmer) periods, the groundwater level does not fall as low as it otherwise might. In wet periods, the pipes have a draining effect. Wetting the soil reduces peat decomposition and oxidation, reducing CO2 emissions and slowing down subsidence.
Underwater drainage measurements are taken in Zegveld, Rouveen, Vlist and Aldeboarn.
For more information on underwater drainage, see the animation, STOWA’s Underwater drainage Deltafact and the Water infiltration systems fact sheet from the National Soil Subsidence Knowledge Programme (NKB)
Pressure drainage involves perforated pipes (drainage pipes) being laid horizontally in the ground just as with underwater drainage. The difference is that they drain into a water reservoir. The water in the reservoir can be pumped to a higher level than the ditchwater. This additional pressure enables more effective wetting and the groundwater level can be actively controlled. Combating dehydration in this way means that soil subsidence can be slowed down.
Pressure drainage measurements are taken in Zegveld and Assendelft.
With pressure drainage, control via the ditch level can be used as an alternative to a sump. In dry periods, the ditchwater level is then raised somewhat. However, the degree of control is more limited than with pressure drainage. In Driebruggen, the NOBV measures controlled infiltration via the ditchwater level.
In Zegveld, the difference between the high and low ditchwater levels without an infiltration system is measured too.
For more information see the animation on the ditchwater level and the animation on the combination of underwater drainage and raising the ditchwater level.
> Factsheet Lange Weide
REGULATED HIGH GROUNDWATER LEVELS
The NOBV takes measurements of extra-high groundwater levels at the Hoogwaterboerderij near KTC Zegveld. Pressure drainage is used to actively maintain a groundwater level of about 20cm below ground level. The ditchwater is also kept at this level. The assumption is that at this groundwater level, CO2 emissions are greatly reduced without methane emissions getting too high.
UNREGULATED HIGH GROUNDWATER LEVELS
Measurements will also be made at two locations where there have been wet conditions for some time due to a high ditchwater level (whether or not in combination with densely-laid ditches), but where the groundwater level is not controlled with a water infiltration system. This means that the groundwater level can still drop during dry periods. A location will be selected that will still enable the highest possible production within the constraints of the high water levels, as well as a location with extensive use combined with a nature objective.
Also see the animation on groundwater level.
Bulrush grows in water. It means that little or no oxygen penetrates the soil, and CO2 emissions and soil subsidence are strongly inhibited or stopped entirely. However, there may be methane and nitrous oxide emissions. Within the NOBV, bulrush cultivation measurements will be conducted in Zegveld and Ankeveen.
More information on wet crops is available in the Wet crops fact sheet issued by the National Soil Subsidence Knowledge Programme (NKB).
From 2022 onwards, the NOBV will take exploratory measurements of peat moss, cranberry and miscanthus. Peat moss, with water up to ground level, is expected to limit CO2 emissions as much as possible with a much longer emission of methane than other wet crops. Starting this year, exploratory research will also be conducted into the still-experimental cultivation of miscanthus and cranberry. Cranberry is a food crop that is able to grow with limited drainage, under acidic conditions, and virtually without fertiliser. Miscanthus, also known as elephant grass, is a fibre crop like bulrush, which grows with limited drainage and without much fertiliser. It is hoped that cultivating these crops will release little methane or CO2. If the exploratory measurements turn out to be positive, the aim is to conduct more intensive studies of these measures.
> Also see the NKB Wet crops fact sheet.
> Also see the NKB-factsheet Natte teelten.
CLAY IN PEAT
The presence of clay in peat soil can reduce the decomposition of organic matter. This is due to the formation of a clay-humus complex, which is less sensitive to peat decomposition.
Adding clay to a peat soil – also known as peat enrichment with clay – is a new measure to slow down soil subsidence and limit the emission of CO2. It doesn’t involve applying a covering of clay to the peat, but instead introducing relatively small quantities of clay to the soil, for example by flushing them in. Flushing small amounts of clay into the soil one or more times might inhibit greenhouse gas emissions and soil subsidence without the need for changes in land use. Lab tests conducted with samples of peat with the addition of different types of clay show a reduction in emissions of up to approximately 50%. Samples from the field into which clay particles have been flushed also demonstrated a gradually increasing effect. From 2022 onwards, the NOBV will be conducting intensive measurements in Zegveld to determine what reduction can be achieved in practice.
A so-called clay palette will be created, in addition to a large measurement site for practical application. With this clay palette, different types of clay will be tested for their effectiveness in counteracting greenhouse gas emissions.
Finally, measurements will be taken at a number of reference sites. These will serve as a basis for comparison with emissions from grassland (both autonomous and with measures), in the same way as these are measured at the other sites. At these reference sites, emissions will be measured from existing nature areas, from recently-created nature areas, and from swampy soil. This will increase the understanding of soil processes during decomposition, and show the level of emissions from areas of peatland compared to other regions. A reference site is therefore not the same as a reference plot. Most of the abovementioned sites with measures have two measurement plots: a plot where the measure is enforced and where measurements are taken, and a plot right next to it, where the measure is not enforced. This means that measurements are taken under the same conditions, and the effects of the measures can be examined thoroughly.