Acidification level variability in hemiboreal production forest drained peatland catchments and after different intensity regeneration fellings using critical loads modelling approach.

Forestry activities, i.e., drainage system maintenance or regeneration fellings may alter the water quality in catchments as well as in runoff and induce risks of acidification. In Latvia, most of the anthropogenic pollution to ecosystems is air-borne and comes from transboundary sources, while in drained forested catchments, nutrients may be leached more due to management-induced disturbances. In this study, critical load approaches were used to evaluate acidification risks in five relatively small drained forested peatland catchments, including effects of drainage network maintenance and in three locally typical forest site types of various trophic states after different intensity regeneration fellings (stem-only harvesting, whole-tree harvesting). Studied drainage catchments presented high acidity, S and N critical loads reaching far above factual loads by precipitation, because of organic soils in combination with high basic cation concentrations. Drainage network maintenance significantly increased acidity and S critical loads, while N critical loads increased but not significantly in all catchments. At the felling sites also, no exceedances of critical loads were detected. Higher critical loads were observed with higher trophic levels. At the eutrophic site, higher critical loads were observed after stem-only harvesting while, at the oligotrophic site, higher critical loads were observed after whole-tree harvesting. The critical load modelling approaches demonstrated the potential to assess the impacts of various forestry management practices. With broadened base of knowledge, these methods can be utilised to support decision making and define acceptable levels of disturbance for sensitive sites and in regionally specific conditions.