On the lime transition and decalcification in the coastal dunes of the province of North Holland and the island of Schiermonnikoog

The transition zone between dunes rich and poor in calcium carbonate along a north-south and outer-inner dunes transect in the coastal dunes of the province of North Holland has been described. The calcium carbonate content of the dunes from Wijk aan Zee (52°37'N,4°37'E) ranges from 1-10% in deeper layers (30-40 cm) with lower values in surface layers (0-10 cm). A more or less steep decrease in the calcium carbonate content has been observed in the area between with the milepost numbers 36 Egmond aan Zee and 32 Bergen aan Zee, from above 1% to far below 0.1% CaC03. The transition zone covers the Verbrande Pan area (mile posts 33 and 34) where Buhouwer (1926) located the border between the Waddendistrict (less than 1% CaC03 of the dry soil) and the Dunedistrict (more than 1% CaC03). It seems that the Waddendistrict has now extended southward to milepost 36 during the past 60 years. Factors that influence the rate of decalcification in coastal dunes are discussed. A comparison is made between the carbonate leaching in the North Holland dunes and three differently aged dune systems on the island of Schiermonnikoog, The rate of decalcification in the Schiermonnikoog dunes did not significantly differ from that in the North Holland dunes, with a higher primary CaCOj content of the dune soil. Decalcification rates in surface layers of adjacent soils were found to differ due to the presence of a different vegetation.