The effect of lake-water infiltration on the acidity and base cation status of forest soil

In this article, the effects of the artificial recharging of groundwater by infiltrating surface water through forest soil, i.e. sprinkling infiltration, on the acidity and base cation status of the soil are described. The study was carried out in the Ahvenisto esker area, Hameenlinna, southern Finland, during 1996-1998. The sample plots were located in a 110- to 160-yr-old Scots pine (Pinus sylvestris L.) stand. The site was classified as the Oxalis-Maianthemum type. The soil consisted of a mixture of till and glaciofluvial sediments. The pH of the organic layer increased from 4.7 to >6.5 soon after the start of irrigation on the infiltration plot. The pH of the 0-10 cm mineral soil layer also increased from 4.9 to 6.4 as a result of infiltration. Sprinkling infiltration increased the exchangeable Ca and Mg concentrations in the organic and uppermost mineral soil layers. The output of Ca and Mg in percolation water from the 0-100 cm thick layer was lower than the input to the soil surface via irrigation in 1996. The retention of Ca and Mg on cation exchange sites took place within a relatively short period of time, since retention was observed only in 1996 but no longer in 1997 or 1998 indicating saturation of the cation exchange sites by base cations. Lake water infiltration leads to the neutralisation of forest soil acidity, and increases the capacity of the soil to withstand acidic inputs by increasing the concentrations of exchangeable base cations on cation exchange sites in the soil.