Sprinkling infiltration as an artificial groundwater recharge method – Long-term effects on boreal forest soil, tree growth and understory vegetation

Abstract The artificial recharge of groundwater by infiltrating surface water through forest soil has been introduced as a groundwater producing practice in Finland. As a result, the forest soil, as well as the whole ecosystem, is subjected to extremely high inputs of carbon and nutrient rich lake water. The effects of sprinkling infiltration on forest soil, tree growth and understory vegetation and their respective recovery were studied on a forested esker in central Finland. The Scots pine-dominated experimental plots were sprinkled with lake water in 1998–2001 and sampled after a 12–15-year recovery period. Soil pH and base cation concentration, as well as the rate of net N mineralization were significantly higher at the plots that had been infiltrated. The concentrations of base cations calcium and magnesium were thousands of times higher in the infiltrated soil than in the untreated soil. In addition, sprinkling infiltration had favored early-successional herbs, grasses and forbs and negatively affected late successional, slow-growing mosses and lichens. Sprinkling infiltration had significantly increased tree radial growth. Sprinkling infiltration is an environment altering soil treatment method which, based on the findings of this study, can have long-term effects on tree growth, soil processes and understory vegetation.