Mapping the spatial and temporal changes of peatland in farming systems is crucial to the study of soil quality and productivity and the modeling of the global carbon cycle (in relation to climate change). This study compiles a contemporary map (2010) of peatland coverage (according to Kyoto protocol) across the cultivated wetlands of Denmark and compares this actual map to a historical 1975 peat coverage map using simple indicator kriging. For the contemporary peatland mapping, extensive soil sampling databases consisting of 42,568points with 32,817 historical samples and 9,751 contemporary samples were used. These databases contain partly categorical information on parent material (organic [peat, gytje] and mineral [sand, silt and clay]) and partly continuous data (soil organic carbon, in %) reclassified into organic and mineral soils (using 12% soil organic carbon as a cutoff value). In the simple indicator kriging procedure, the values 0 and 1 were assigned to the stationary means of the indicator codes to represent two hypotheses, that is, mineral and organic (peat) soils, respectively. The collected and analyzed contemporary unbiased organic samples (measured on different rectangular grid scales of 250, 275, and 500m) in addition to some transformed historical organic samples (according to certain decision rules) were used to estimate the recent areal coverage of peat (2010) that was equivalent to 70,176 ha, and this estimate corresponds to an indicator kriging probability of 0.35. Results revealed there has been a total areal coverage loss of 35%(37,786 ha) of the Danish organic cultivated wetlands during a period of 35 years (map 1975 had 107,962-ha coverage of peat). The peat depletion is related to peat mining and agricultural drainage/tillage activities, rather than natural geological processes.
Journal of Soil Science, 2014, Vol 179, Issue 5, p. 250-257