EFFECTS OF LIMING ON WATER CHEMISTRY IN SHALLOW ACIDIFIED POOLS IN THE NETHERLANDS - ENCLOSURE EXPERIMENTS

Enclosure experiments have been carried out in two shallow acidified moorland pools in order to study the effects of liming on the water chemistry. The addition of buffering substances (sodium bicarbonate and calcium chloride or powdered marlstone) to enclosures in the Ven bij Schaijk, an oligotrophic acidified moorland pool with a mineral sediment, did not demonstrate internal eutrophication. After addition of NaHCO3 and CaCl2 the pH and alkalinity increased and all macronutrient concentrations, such as that of phosphate, remained low. After treatment with powdered marlstone, there was only a slight increase of pH and alkalinity, due to the slow weathering of marlstone. The alkalinity in this moorland pool remained more stable on a mineral sandy substrate than on an organic substrate, probably as a result of a higher acid release from the organic sediment. In enclosures in the Padvindersven, an eutrophied, acidified moorland pool with an organic gyttja-type of sediment, internal eutrophication took place after adding buffering substances. The phosphate concentration and turbidity of the water increased significantly after treatments with NaHCO3 and CaCl2 as well as with powdered marlstone. The acid release was even higher than from the organic sediment from the Ven bij Schaijk. It was concluded from these experiments that in case of the Ven bij Schaijk, liming with marlstone would be a sufficient way to restore the original water chemistry. In the Padvindersven, however, recovery of the non acidified poorly buffered conditions is only possible by liming in combination with the removal of the organic top layer of the sediment.