Leaching of nitrogen, phosphorus and other solutes from a controlled drainage cultivated peatland in Ruukki, Finland

Tung Pham; Markku Yli-Halla; Hannu Marttila; Timo Lötjönen; Maarit Liimatainen; Jarkko Kekkonen; Miika Läpikivi; Björn Klöve; Erkki Joki-Tokola

doi:10.1016/j.scitotenv.2023.166769

Leaching of nitrogen, phosphorus and other solutes from a controlled drainage cultivated peatland in Ruukki, Finland

Sci Total Environ. 2023 Dec 15:904:166769. doi: 10.1016/j.scitotenv.2023.166769. Epub 2023 Sep 1.

Authors

Tung Pham¹, Markku Yli-Halla², Hannu Marttila³, Timo Lötjönen⁴, Maarit Liimatainen⁴, Jarkko Kekkonen⁴, Miika Läpikivi³, Björn Klöve³, Erkki Joki-Tokola⁴

Affiliations

¹ Water, Energy and Environmental Engineering Research Unit, P.O. Box 8000, FI-90014, University of Oulu, Finland. Electronic address: thanh.pham@oulu.fi.
² Department of Agricultural Sciences, P.O. Box 56, FI-00014, University of Helsinki, Finland.
³ Water, Energy and Environmental Engineering Research Unit, P.O. Box 8000, FI-90014, University of Oulu, Finland.
⁴ Natural Resources Institute, Paavo Havaksentie 3, FI-90014, University of Oulu, Finland.

PMID: 37660806
DOI: 10.1016/j.scitotenv.2023.166769

Abstract

Cultivated peatlands are important for grass production in Northern Europe, but the potential impact of nutrients leaching to surface waters is a major concern. Due to a lack of data on nitrogen (N), phosphorus (P) and organic carbon leaching, a monitoring programme was established at Ruukki (Siikajoki, Finland), an agricultural, subsurface drained peat site with a peat thickness of 20-80 cm. Concentrations and loading of N, P, and total organic carbon (TOC) were monitored, along with other water quality parameters for the field discharge, in 2018-2021. We observed N leaching from subsurface discharge to be 25 kg N ha^-1 year^-1 (range 11-40 kg N ha^-1 year^-1, 74 % as nitrate NO₃-N). The least N leaching was recorded from plots of thinner peat topsoil and those with grass cover, while the majority of N leaching originated from thicker peat plots (bare or under barley) in spring. Leaching of N strongly decreased during periods of thick grass cover. Significant N leaching also occurred during the mild winter of 2019-2020, characterized by alternating freeze and thaw periods. Annual P loading from subsurface drainage was 0.30 kg P ha^-1 (0.20-0.43 kg P ha^-1), low compared to that of average cultivated soils in Finland. It was estimated that 13 % of the total N leaching and 50 % of the total P leaching occurred in surface runoff. Leaching of TOC was significant at 87 kg ha^-1 year^-1 (31-137 kg ha^-1 year^-1). Leaching of dissolved P and TOC increased with peat thickness. Abundant loading of sulfur and acidity indicates the oxidation of sulfidic material in the subsoil. Leaching concentrations correlated with discharge quantity, suggesting that mobilization processes during the dry periods resulted in leaching during high discharge periods. The results show the importance of avoiding bare peat soil for NO₃-N leaching reduction, even during wintertime in cultivated peatlands.

Keywords: Acid sulfate soils; AnaEE network; Grass cultivation; Peat soils; Subsurface drainage; Water quality.