Acidity and Nutrient Content of Throughfall and Soil Leachate in Three Pinus Sylvestris Stands

The quantity and quality of throughfall and soil leachate were measured in 1983-1985 in three Scots pine stands of different age situated in Ilomantsi, eastern Finland. Soil leachate was collected using percolation lysimeters. Free precipitation pH varied from 4.0 to 5.2. Throughfall was more acidic than free precipitation. The closed canopy layer intercepted about 70% of the free precipitation. The canopy acted as a sink for nitrate and ammonium, and as a source for Mn, K, Mg and Ca. The quality of the throughfall and soil leachate varied seasonally. The hydrogen ion input into the soil was greatest at snow melt. The major part of the nitrogen load was deposited during winter. Part of the winter-time nitrate load was leached through the surface soil. However, during the growing season all the nitrogen was efficiently taken up or immobilized. Basic cations K, Ca and Mg, as well as Mn, Fe and Al, were leached from the upper soil layers. Manganese was leached especially at snow melt. The output of magnesium in the leachate was greater than its input as deposition. The output of K and Ca from the humus and upper mineral soil layers (0-15 cm) was also greater than their input as deposition, but a major part of these nutrients were readsorbed deeper in the profile.