Dissolved Organic Carbon Export from Harvested Peatland Forests with Differing Site Characteristics

Calibration period and control area method were used to study the impact of forest tree harvesting on the dissolved organic carbon (DOC) export from drained peatland forests using data from 17 harvested and five control catchments. The results indicated highly increased DOC exports; during the first 3 years following harvesting, the average extra export ranged from over 200 kg ha(-1) in nutrient-poor ombrotrophic to over 400 kg ha(-1) in fertile minerotrophic peatland forest sites. The results indicated that a high iron (Fe) content in peat, as well as a high nitrogen (N) content and a low carbon (C) N ratio, are the site characteristics that contribute to large harvest-induced DOC exports. The effect of Fe is probably caused by the reduction of Fe in previously aerobic peat layers that have undergone harvest-induced water level rise and thus enhanced the DOC export, and the effects of the peat N and CN ratio indicate that the impacts of harvesting on DOC are the greatest from the sites with a high overall microbial activity. The calibration period/control area analysis revealed a high uncertainty in our data, the 95 % confidence intervals for average DOC exports overlapping between the groups with differing site characteristics. Given the uncertainties involved in our data, we conclude that significant changes in water colour and other water characteristics associated with large DOC inputs may be expected, where harvested forests on peatlands cover large proportions of catchments of small lakes and rivers.