Modelling the effects of climate change, acidic deposition and forest harvesting on the biogeochemistry of a boreal forested catchment in Finland

The relative importance of climate change, acidic deposition and forest harvesting/clearcutting on soil and streamwater chemistry of Rudbäcken, a small forested catchment in southern Finland, was evaluated by using a linked model system. The emphasis was on the assessment of long-term effects of different impact scenario combinations. The models were calibrated to measured values of soil and streamwater chemistry as well as forest biomass and growth increment. Deposition scenarios were based on atmospheric transport models. The effects of the three main driving forces (climate, deposition and forest harvesting) showed complex interactions, which were not always easy to interpret. Climate change (high change scenario), considerable emission reductions, and the clearcut scenario, were almost equally significant for parameters related to acidification effects. Considerable emission reductions resulted in either a slight improvement (streamwater pH) or steady-state (soil base saturation) compared with the current situation. The most negative response was predicted for the high climate change scenario, where high nitrogen immobilisation dependence on temperature was assumed. With the exception of the clearcut scenario, a clear increase in NO3 leaching in the long run was predicted for the site until the year 2050. Although the scenarios are hypothetical, they demonstrate the combined effects of elevated deposition inputs and climate change for the N leaching and accumulation processes.