Confronting the vicinity of the surface water and sea shore in a shallow glaciogenic aquifer in southern Finland

The groundwater in a shallow, unconfined, low-lying coastal aquifer in Santala, southern Finland, was chemically characterised by integrating multivariate statistical approaches, principal component analysis (PCA) and hierarchical cluster analysis (HCA), based on the stable isotopes delta H-2 and delta O-18, hydrogeochemistry and field monitoring data. PCA and HCA yielded similar results and classified groundwater samples into six distinct groups that revealed the factors controlling temporal and spatial variations in the groundwater geochemistry, such as the geology, anthropogenic sources from human activities, climate and surface water. High temporal variation in groundwater chemistry directly corresponded to precipitation. With an increase in precipitation, KMnO4 consumption, EC, alkalinity and Ca concentrations also increased in most wells, while Fe, Al, Mn and SO4 were occasionally increased during spring after the snowmelt under specific geological conditions. The continued increase in NO3 and metal concentrations in groundwater indicates the potential contamination risk to the aquifer. Stable isotopes of delta O-18 and delta H-2 indicate groundwater recharge directly from meteoric water, with an insignificant contribution from lake water, and no seawater intrusion into the aquifer. Groundwater geochemistry suggests that local seawater intrusion is temporarily able to take place in the sulfate reduction zone along the freshwater and seawater mixed zone in the low-lying coastal area, but the contribution of seawater was found to be very low. The influence of lake water could be observed from higher levels of KMnO4 consumption in wells near the lake. The integration of PCA and HCA with conventional classification of groundwater types, as well as with the hydrogeochemical data, provided useful tools to identify the vulnerable groundwater areas representing the impacts of both natural and human activities on water quality and the understanding of complex groundwater flow system for the aquifer vulnerability assessment and groundwater management in the future.Peer reviewe

Vulnerability of groundwater resources to interaction with river water in a boreal catchment

A low-altitude aerial infrared (AIR) survey was conducted to identify hydraulic connections between aquifers and rivers and to map spatial surface temperature patterns along boreal rivers. In addition, the stable isotopic compositions (delta O-18, delta D), dissolved silica (DSi) concentrations and electrical conductivity of water in combination with AIR data were used as tracers to verify the observed groundwater discharge into the river system in a boreal catchment. Based on low temperature anomalies in the AIR survey, around 370 groundwater discharge sites were located along the main river channel and its tributaries (203 km altogether). On the basis of the AIR survey, the longitudinal temperature patterns of the studied rivers differed noticeably. The stable isotopes and DSi composition revealed major differences between the studied rivers. The groundwater discharge locations identified in the proximity of 12 municipal water intake plants during the low-flow seasons should be considered as potential risk areas for water intake plants during flood periods (groundwater quality deterioration due to bank infiltration), and should be taken under consideration in river basin management under changing climatic situations.Peer reviewe

Groundwater recharge/discharge patterns and groundwater-surface water interactions in a sedimentary aquifer along the River Kitinen in Sodankyla, northern Finland

Areas of groundwater-surface water interaction in riverbanks and open mires are important habitats for groundwater-dependent species. In order to preserve these ecosystems, the planning and development of mining operations on such locations require a fundamental understanding of the groundwater discharge-recharge and flow patterns. In this study. 3D flow modelling and a TIR survey were used to define the groundwater discharge. Simultaneously, the flow modelling and groundwater table fluctuation were used for defining groundwater recharge at a mining development site in northern Finland. The results indicated flow towards the River Kitinen and the discharge of groundwater in the banks of the river. The discharge also occurred within the mire area, which may provide suitable habitats for groundwater-dependent plant species. The modelling results and stable isotope variations indicated complex flow patterns and a potential groundwater connection from the Viiankiaapa mire through possible bedrock fractures to the river. Recharge mainly occurred in the sorted sediment accumulations of the riverbanks and partly also in the mire area.Peer reviewe

GIS-based 3D sedimentary model for visualizing complex glacial deposition in Kersilö, Finnish Lapland

Complicated Quaternary sediment strata have been preserved within the ice-divide zone of northern Finland because of weak glacial erosion. Geographic Information System (GIS) databases, 3D modelling and ground penetrating radar surveys were used to construct the 3D structure of unconsolidated sediments and bedrock topography for Kersilo, Sodankyla, to provide information for freshwater management and environmental studies in the mineral exploration area. The model was created using a combination of explicit and implicit modelling covering an area of 10.5 km(2). The surficial deposits in the study area are a few metres thicker than their average thickness in northern Finland. They include three till units and four sandy or gravelly units. Fluvial action has repeatedly deposited sorted sediments in the channel valley of the Kitinen river. Basins in the bedrock have preserved thick sediment packages (> 15 m), indicating that the bedrock topography controls the sedimentary features. Aquifers in the area are small and disconnected, and perched aquifers exist due to the low hydraulic conductivity of interlayered tills.Peer reviewe