Nitrogen and phosphorus concentrations in discharge from drained peatland forests are increasing Mika Nieminen a, ⁎, Tapani Sallantaus b , Liisa Ukonmaanaho a , Tiina M. Nieminen a , Sakari Sarkkola a a Natural Resources Institute Finland, Latokartanonkaari 9, FI-00790 Helsinki, Finland b Finnish Environment Institute, Mechelininkatu 34a, FI-00260 Helsinki, Finland HIGHLIGHTS • N and P concentrations in discharge from pristine and forestry-drained peatlands were studied. • N and P concentrations in drained peatlands were studied in relation to the timing of initial drainage. • N and P concentrations were increasing from drained peatlands with years since their drainage. • Drainage of peat soils for forestry con- tributes to water quality more than esti- mated previously. GRAPHICAL ABSTRACT abstract article info Article history: Received 5 June 2017 Received in revised form 23 July 2017 Accepted 23 July 2017 Available online xxxx Editor: Jay Gan The current understanding, based on previous studies, is that increased discharge nutrient concentrations from boreal peatlands drained for forestry return to similar levels as those of pristine peatlands within about 20 years after their drainage. As an implicit consequence of this finding, it has been assumed that there are no long-term increasing trends in nutrient exports from these peatlands after the establishment of forestry. We analysed discharge total nitrogen (TN) and phosphorus (TP) concentration data from 54 catchments with un- drained pristine peatlands and 34 catchments with drained peatlands using data with considerably longer drain- age history than in previous studies. Our results agree with previous studies in that discharge TN and TP concentrations in areas drained 20–30 years ago did not differ much from those in pristine sites. However, we also observed that the TN and TP concentrations were increasing with years since drainage of these catchments. Discharge TN and TP concentrations were over two times higher in areas drained 60 years ago when compared with more recently drained areas. Our results challenge the current perceptions by showing that forestry-drained peatlands may contribute to water eutrophication considerably more than previously estimated. © 2017 Elsevier B.V. All rights reserved. Keywords: Drainage Hydrochemistry Peat mineralization Peat subsidence Water quality 1. Introduction About 15 million ha of peatlands and paludified mineral soils have been drained for forestry purposes in the temperate and boreal regions (Paavilainen and Päivänen, 1995). Due to the recent efforts to shift to more bio-based economy, the demand for forest biomass is increasing. In the Nordic and Baltic countries and the British Isles, a significant pro- portion of this demand is covered by biomass harvest from peatlands drained for forestry. Drainage of peat soils for forestry has fundamental impacts on their hydrochemical and hydrological processes (Prévost et al., 1999; Holden Science of the Total Environment 609 (2017) 974–981 ⁎ Corresponding author. E-mail address: mika.nieminen@luke.fi (M. Nieminen). http://dx.doi.org/10.1016/j.scitotenv.2017.07.210 0048-9697/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv