GTK’s HYGLO WOLL stations - A Living Lab for Groundwater Research

HYGLO WOLL is a network of nine hydrogeological test sites in Finland Fig. 1 operated by Geological Survey of Finland (GTK). These sites are part of Water Europe’s living laboratory network (Water Europe 2025) for innovative, international groundwater research. Through automated data collection and regular groundwater sampling, HYGLO WOLL test sites (established in 2022-2023) provide a platform to study the impacts of global change on groundwater resources in subarctic and arctic regions. Each HYGLO WOLL test site has its own research questions, which the data collection aims to better understand. The key research questions include understanding the groundwater – surface water interaction, evaluating the effectiveness of aquifer recharge, and studying the impact of human activities like mining and forestry on groundwater quality and quantity. Additionally, the monitoring data is used to study the role of groundwater in the carbon cycle. Two of the HYGLO WOLL test sites – Lammi and Oulanka – belong to the European LTER sites. Lammi The HYGLO WOLL Lammi station is located in Lammi, in the Eastern part of Hämeenlinna municipality, near the border of Päijänne-Tavastia. The main study area covers about 30 hectares and contains preserved broad-leaf woodlands, agricultural fields and the Biological Research Station of Lammi (Lammi LTER 2025), owned by the University of Helsinki. The aim of the Lammi test site is to produce new hydrogeological knowledge of till lands containing shallow groundwater aquifers. Till (moraine) is the most abundant sediment in Finland and, as such, presents the most common geological environment for small household wells. The geological setting in the overall area is dominated by II Salpausselkä, an extensive ice-marginal ridge system which, genetically, is a wide terminal moraine formation that formed during the Younger Dryas period (approx. 11,790-11,590 years ago). In the study site the soil is mostly consisted of typically coarse-grained till which has widely been covered by a thinner, more fine-grained sedimentary unit. The overall sediment thickness in the study area is rarely more than 10 meters. The bedrock is granodioritic and considered as aquitard. Aquifer in the area is shallow, with a near-surface water table and saturated depth of only few meters in general. The HYGLO WOLL Lammi station was established 2022. Remotely-readable CTD (conductivity, temperature and depth) -sensors were installed in 4 groundwater monitoring wells. Biannual sampling campaigns include in situ measurements, as well as groundwater and surface water sampling with a wide range of hydrogeochemical analytics and stabile isotopes. Oulanka The sediments of the Oulanka test site at Haaralamminkangas aquifer consist of Late Weichelian glacial sediments, fine-grained basin sediments, valley delta sand deposits, sandy gravels of the braided river system, and fine-grained flood sediments. River Oulankajoki and the aquifer are in interaction. The bedrock is dolomite rock. The HYGLO WOLL Oulanka station was established 2022. Remotely-readable CTD (conductivity, temperature and depth)-sensors were installed in 5 groundwater monitoring wells in total. There has been one sampling campaign a year including in situ measurements, as well as groundwater and surface water sampling with a wide range of hydrogeochemical analytics, stabile isotopes and microbiology. From 2025 there will be biannual sampling campains in Oulanka as well. In addition to HYGLO WOLL data collection the Oulanka research station (Oulanka LTER 2025) has its own weather monitoring, which measures precipitation, temperature, wind speed, air pressure, atmospheric humidity and long-wave radiation. Furthermore, there is monitoring of the snow water equivalent and depth of the snow in the area. Soil temperature and water content are also monitored in the study area. Oulanka 3D model was generated to visualize sedimentary structures and the hydrogeological properties. Puukkosuo 3D model was constructed to visualize the humification levels in peat. Co-operation In collaboration with the local partners, water utilities, universities, research stations, municipalities, regional governmental agencies, governmental institutes and forestry company, GTK will gather and share data to enhance understanding of groundwater systems in changing climate. This collaborative approach enables us to develop innovative solutions for sustainable water resource management and supports data-based decision-making. Together with existing and forthcoming partners and collaborators GTK will actively develop the HYGLO WOLL network.