Chemistry of Lake Hovvatn, Norway, Following Liming and Reacidification

Hovvatn, a 1-km 2 , chronically acidified lake in southernmost Norway, was treated with 200 metric tons of powdered limestone in March 1981. An additional 40 metric tons was added to a 0.046-km 2 pond (Pollen) draining into Hovvatn. At ice-out, pH rose from 4.4 to 6.3 (Hovvatn) and 7.5 (Pollen), Ca and alkalinity increased, and total Al decreased by about 120 μg/L. The amount of limestone dissolved, calculated from the lake Ca budgets, was 50% after 3.5 yr in Hovvatn and 25% in Pollen. A greater fraction dissolved at Hovvatn because the limestone lay in the active surf zone. In Pollen, limestone that was not dissolved at ice-out formed a layer on the sediment surface from which only minimal dissolution occurred. Hovvatn and Pollen reacidified to pH 4.9 and 5.5, respectively, 3 yr after liming. A simple flushing model describes the reacidification of Pollen. In Hovvatn, however, dissolution of additional limestone during the 3.5 yr since liming has considerably slowed reacidification.