Aquatic effects of peat extraction and peatland forest drainage : a comparative sediment study of two adjacent lakes in Central Finland

The aquatic effects of forestry practices and peat extraction continue to cause serious concerns. The effect mechanisms of peat extraction on water quality and aquatic ecology of the receiving surface waters are well known, but the impacts are often difficult to differentiate from those of forest management. A pairwise temporal sediment study was conducted on two adjacent lakes in Central Finland to study whether the unique effects of peat extraction can be detected in an area of intensive forest drainage. Both lakes are affected by forestry, but the reference lake has no history of peat extraction in its watershed. The deepest parts of the lakes were cored through the lacustrine sediments, and the recent carbon and dry matter sedimentation rates were compared to their site-specific reference values. Recent changes in benthic macroinvertebrates (chironomids) and diatom algae were studied to assess the ecological effects of these practices in the lakes. No significant differences in recent increases in carbon accumulation were found between the peat extraction-impacted lake and the reference lake. The pairwise comparison allowed identification of a regional pattern of impacts that is closely related to the history of land use, particularly forestry, in the region. The approach also allowed identification of the transient signs of peat extraction in the chemical and chironomid records of the impacted lake. The recent changes in chironomids and diatoms suggest eutrophication and deterioration in benthic conditions likely caused by drainage ditch network maintenance activities in the catchments.