Thickness of oxidable peat

The peat thickness map was drawn up by Alterra Wageningen UR (2016) on behalf of the province of Zuid-Holland. The aim was to gain insight into the areas where oxidation of peat will occur due to dewatering. Since the dewatering of the peatlands there has been a decrease in ground level and as long as that situation continues, the ground level continues to fall until the peat, in so far as it comes into contact with oxygen, is up. Presented are the locations and thicknesses of oxidable peat with steps of 0.5 meters until as deep as there is peat. How much peat can oxidise in the long run depends on a number of factors such as draining, precipitation/temperature (climate change) and land use. Without further action, climate change will increase ground level decline due to higher temperatures and deeper groundwater levels in the summer. Of course, how long there is peat and which ground level/depth is reached in the long run also depends on the current peat thickness. That thickness can be derived from the Bottom Card, along with deep profile descriptions. Because there are few releatively deep profile descriptions, a grid file is composed of the geological profiles. The peat thickness is defined here as the thickness that can oxidise in agricultural dewatering. A mineral substrate or intermediate layer of > 40 cm has been considered as the bottom of the oxidable peat layer. So peat can still occur under the mineral layer, but that remains anaerobic and will not oxidise. An updated map has been used to determine the peat thickness from the Soil Map, which incorporates recent revisions. As a result, the card is based on a wide range of recording dates: from 1961 to 2014. For the determination of peat thickness, the profiles for the soil units set up by the Vries (1999) were used as far as possible. These profiles are based on the original profile descriptions. For profiles that are missing, the ‘average’ layer thicknesses have been observed according to the legend of the Soil Card. Soil surfaces where a mineral surface has been found within 120 cm, for example Vk, has been assumed to be so thick that any peat under that layer will never oxidise. There (and for all mineral soils) the geological profiles have not been taken into account. Because the recording dates of the Soil Map differ for more than half a century, there may have been decimeters difference in ground descent. In order to estimate the current peat thickness, this decrease has been calculated and subtracted from the peat thickness card. The method described in Jansen (2009) was used for the calculation.