REWET (REstoration of WETlands to minimise emissions and maximise carbon uptake – a strategy for long term climate mitigation) – Water level and quality in a minerotrophic open mire Ylpässuo in Kiuruvesi, Finland

Wetlands store 33% of the world's terrestrial carbon although they occupy only 7% of the earth's surface. Especially peatlands contain great amounts of carbon locked in the submerged soil or as waterlogged undecomposed organic material. When these ecosystems are drained to be converted into agricultural or forestry exploitations or for peat extraction, they release greenhouse gas (GHG) emissions, which accelerate climate change. Also, leaching of dissolved organic carbon (DOC) and nitrogen (N) into aquatic ecosystems may increase (Nieminen 2004). The REWET/EU-Horizon project (2022-2026) aims to improve knowledge on the status of EU wetlands to understand their capacity as carbon sinks or GHG sources for climate mitigation, and improve assessment of the added value of wetland, peatland and floodplain restoration approaches under different scenarios and monitor their benefits and trade-offs in terms of GHG emissions, climate change adaptation and disaster risk reduction. The project has seven Open Labs across Europe. In the Finnish Open Lab (OL3), coordinated by University of Eastern Finland (UEF), the carbon sink strength and biodiversity of Ylpässuo (Kiuruvesi, Finland) is being investigated. The area is conserved by The Natural Heritage Foundation after donation by UEF but has been affected by edge drains and forest ditching in the surrounding area. In this poster presentation, water level and quality measurements in OL3 are presented. The data has been collected for water quality (nutrients, other ions, conductivity, pH, temperature, turbidity, DOC, elements, alkalinity) and water level by University of Oulu once a month from June to October in 2023 and from May to October in 2024. Water quality samples were collected from three sample points through perforated pipes installed into the wet ground. Samples for analysing nutrients, other ions, DOC and elements were filtered through 0.2 µm polyethersulfone filters. Water level data was collected from two samples points with water level HOBO logger (HOBO U20L-04 water level). Also, pH and temperature were detected with HOBO logger (Onset Hobo MX2501) from the sample point right next to the weather station. Air pressure and temperature were measured on this point as well. The water at OL3 was detected to be moderately acidic (pH 4–5; based on grab samples) and low in alkalinity (< 0.08 mmol/L) and conductivity (< 40 µS/cm). DOC and total N were remarkably higher (30–50 mg/L and 400–1400 µg/L, respectively) during the sampling period 2023, which was rainier than the sampling period 2024 (15–20 mg/L DOC, 400–700 µg/L TN). During both sampling periods, DOC also decreased from spring to autumn. In the concentration of phosphorus (P), there was not that clear difference between the two sampling periods. However, during both periods, P concentration was the highest on the first sampling date in the spring. The results are in correlation with the fact that in boreal and temperate freshwater ecosystems, the increased concentrations and leaching of DOC and N from peatlands have been connected to increased rainy periods and changes in soil frost periodicity and moisture conditions related to the climate change (Raymond and Saiers 2010, Mattsson et al. 2015, Lepistö et al. 2014), whereas leaching of P is usually less affected (Kløve 2001). Water temperature stayed quite stable during the measurement period being between 12–24 Celsius degrees. The pH of water varied between 4.5 – 5.5 based on the online pH readings. Water levels were compared to the air pressure and during the rainy season water levels were higher as well as in the beginning of the summer period (Rocchio et al. 2021). During the warm summertime the water levels dropped. Differences in the water levels were 45.9 cmH 2 0 in maximum.