A new peatland probability map for Flanders, northern Belgium highlighting the importance of peat buried in the subsoil for C storage.

In present-day global to regional peatland maps, Belgium is mostly a white spot showing that almost no peat is present. Nevertheless, many detailed soil and sediment stratigraphical studies have pointed out that much peat is present, both at the surface, but also in buried positions in the immediate subsoil. Here we present a new peatland map for the northern part of Belgium, Flanders, using a combination of an extensive database on soil/sediment profile descriptions with random forest digital soil mapping techniques to present for the first time a high-resolution (50m) peat probablity map.  In a first step, information about peat was extracted from a series of existing datasets for Flanders that contain information about peat. These observations include soil profile and sediment coring descriptions and this for three different depth-zones: peat at the surface, peat within the soil profile (up to 1.5 m depth) and peat in the deeper subsoil (1.5 - 10 m depth). This information was then harmonized and merged into a peat database of 61422 point observations. Through digital soil mapping techniques, including random forest tools, peatland maps for each depth zone were created based on environmental data. In order to include uncertainty in the maps, seven peat probability classes were mapped instead of a binary map, and these peat probability classes were finally retained after validation with the original peat observations. These classes represent the likelihood of peat occurrence for three depth zones and reflect the spatial variation and the chance of peat occurrence in each 50 by 50 m spatial unit. Comparison of the peat point database with the national soil maps or ecological habitat maps shows that these are a poor predictor of peat presence in Flanders and performs much worse compared to the new peat probality map. The peatland maps shows that river valleys in flat, sandy landscapes are the most imporant landform units where peat is surfacing at present, but that river valleys in hilly loes areas charecterised by intense sedimentation as well as the coastal plains have much more peat in the subsoil. Similarly, the amount of C stored in buried peatlands is much larger than in active peatlands, with values up to 2000 t C/ha for some river valleys.  Given that these buried peatlands are threatened by drainage, the new peatland map offers policy makers an important tool to identify target areas for restoration projects such as reversing drainage and rewetting of floodplains.