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Global warming is affecting the Arctic more significantly as it is warming faster than other places on Earth. The consequences for Arctic as well as sub-Arctic environment are not well understood. Observations in the past decades and climate change impact analysis predicts clear changes in snow cover and snow melt but consequences to frozen soil and related phenomena such as frost quakes are unclear. Frost quakes are non-tectonic seismic events that occur when freezing of water in saturated soils or rocks results in sudden release of seismic energy. Compared to traditional tectonic earthquakes in seismology, frost quakes are much less studied, as they usually occur at random, or less predictable, rarely instrumented locations. Reports and news of frost quakes, resulting in mechanical damage to the pavements, roads and buildings have been received recently from different locations in Finland, Canada and USA and connections between air temperature and frost quakes have been found. The conceptual model of frost quakes is well known but a methodology to predict the occurrence of frost quakes have been missing. In our study, we present a methodology to investigate the connection between thermal stress and frost quakes. Thermal stress is a function of temperature, which can be measured or calculated. We used a hydrological model to calculate snow depth, snow melt rate and soil temperature at different depths in soil. We show that rapid decrease in temperature can cause a thermal stress that is higher than fracture toughness and strength of the soil‐ice mixture. A swarm of frost quakes occurred on 6 January 2016, in in the city of Oulu in Central Finland (sub-Arctic environment). Some of the frost quakes created ruptures in soil, building foundations, and roads. We show that origin of frost quakes was related to rapid decrease in air temperature from -12 °C to –29 °C that created thermal stress in frozen soil and roads which could not withstand the stress.

In sub-Arctic environment as in Finland, soil moisture and temperature dynamics affect the development of soil frost that controls snowmelt runoff, infiltration and recharge in winter periods. This study was initiated to investigate the performance of integrated hydrology model Amanzi-ATS, in simulating dynamics of soil moisture and temperature at different depths to assess recharge rate in unconfined aquifer in Central Finland. Our objective is to study intra- and inter-annual recharge rates, and the impacts of soil ice on groundwater recharge rate. Hourly soil water content and temperature was measured at ten different depths. The groundwater depth and temperature were measure daily from the borehole located 2 meters from the soil monitoring station and the climate data was obtained around 5 km from the soil station. 1D model with varying soil texture was developed to predict recharge rates. Measured soil water content, soil temperature and groundwater temperature were used to calibrate the 1D numerical model. The implications of this study will be understanding the freezing and thawing of soil on groundwater recharge rate and how recharge rate may change from one year to the next in the sub-Arctic environment.

Continuous data on spatial and temporal patterns of snowmelt rates are essential for hydrological studies, but are commonly not available, especially in the subarctic, mainly due to high monitoring costs. In this study, temperature loggers were used to measure local and microscale variations in snowpack temperature, in order to understand snowmelt processes and rates in subarctic northern Finland. The loggers were deployed on six test plots along a hillslope with varying topography (elevation and aspect) and vegetation (forest, transitional zone and mires, i.e. treeless peatlands) during two consecutive winters (2014 and 2015). At each test plot, the sensors were installed in five locations, at two heights in a snow profile. Algorithms were developed to analyse the snowmelt rates from high-resolution snowpack temperature data. The validity of the results was evaluated using snow depth and soil moisture data from adjacent reference sensors and the results were tested using an empirical degree-day snow model calibrated for each test plot. Snowmelt rates were relatively similar in mires (median 2.3 mm d−1 °C−1) and forests (median 2.6 mm d−1 °C−1) with apparent inter-annual variation. The observed melt rates were highest in the highest elevation plots, in transition zone in 2014 (median 4.6 mm d−1 °C−1) and southwest-facing forest line in 2015 (median 3.2 mm d−1 °C−1). The timing of the modelled meltwater outflow and snowpack ablation showed good agreement with the snowpack temperature-derived estimates and the soil moisture and snow depth measurements. The simple approach used represents a novel and cost-effective method to improve the spatial accuracy of in situ snow cover ablation measurements and melt rates and the precision of snowmelt models in the subarctic. An open-access R-based model is provided with this paper for analysis of high-frequency snow temperature data.

Capture zones of water supply wells are most often delineated based on travel times of water or solute to the well, with the assumption that if the travel time is sufficiently large, the concentration of chemical at the well will not exceed the drinking water standards. In many situations, the likely source concentrations or release masses of contamination from the potential sources are unknown; therefore, the exact concentration at the well cannot be determined. In situations in which the source mass can be estimated with some accuracy, the delineation of the capture zone should be based on the maximum chemical concentration that can be expected at the well, rather than on an arbitrary travel time. We present a new capture zone delineation methodology that is based on this maximum chemical concentration. The method delineates capture zones by solving the adjoint of the advection-dispersion-reaction equation and relating the adjoint state and the known release mass to the expected chemical concentration at the well. We demonstrate the use of this method through a case study in which soil heat exchange systems are potential sources of contamination. The heat exchange fluid mixtures contain known fluid volumes and chemical concentrations; thus, in the event of a release, the release mass of the chemical is known. We also demonstrate the use of a concentration basis in quantifying other measures of well vulnerability including exposure time and time to exceed a predefined threshold concentration at the well.

Shallow seismic reflection surveys were conducted at five different locations in central Finland during the period of 2008–2011 in order to test the applicability of this method and different seismic energy sources in providing accurate images of the underlying seismic structure and geology in unconfined and confined esker aquifers. The depth of the aquifers varied from 15 m to 140 m. Reflections from the water table and the bedrock were generally detected. In the deepest aquifers, several features of the inner structure were visible. In the shallowest aquifer (15 m thick), seismic detection of the stratigraphic units proved difficult. Analysis of the theoretical travel times and the shallow structure suggested that a higher frequency seismic source might have been needed. In the deeper aquifers, reflections near the bedrock were detected, but information regarding their thicknesses could not be obtained. An unsaturated layer with a thickness of 25 m did not completely attenuate the seismic signal, and reflections from the water table and bedrock (~80 m) could still be obtained. For the amount of explosives and the type of vibrator used in this study, explosives generally produced clearer reflections due to the higher signal-to-noise ratio compared with the vibrator source. On the other hand, shot-to-shot fluctuations in signal-to-noise ratio and source irreproducibility were found to be greater for explosives than for the vibrators. Loose lake sediments above the aquifer inhibited seismic energy transmission to the bedrock. In such situations, the use of explosives is recommended in order to obtain clearer reflections from the subsurface soil boundaries.

The impact of climate change and Baltic Sea level rise on groundwater resources in a shallow, unconfined, low-lying coastal aquifer in Hanko, southern Finland, was assessed using the UZF1 model package coupled with the three-dimensional groundwater flow model MODFLOW to simulate flow from the unsaturated zone through the aquifer. The snow and PET models were used to calculate the surface water availability for infiltration from the precipitation data used in UZF1. Infiltration rate, flow in the unsaturated zone and groundwater recharge were then simulated using UZF1. The simulation data from climate and sea level rise scenarios were compared with present data. The results indicated changes in recharge pattern during 2071–2100, with recharge occurring earlier in winter and early spring. The seasonal impacts of climate change on groundwater recharge were more significant, with surface overflow resulting in flooding during winter and early spring and drought during summer. Rising sea level would cause some parts of the aquifer to be under sea level, compromising groundwater quality due to intrusion of sea water. This, together with increased groundwater recharge, would raise groundwater levels and consequently contribute more surface leakage and potential flooding in the low-lying aquifer.

Summary The time-stability concept suggests that the spatial pattern of the soil water content does not change with time when the observations are ranked according to the magnitude of the soil water. The time-stability holds for soils in agricultural fields and forest compartments, yet broader scale effects of boreal climate on time-stability are poorly understood. We studied the spatial persistence of soil water through the boreal climatic gradient (60–68°N) on the Baltic Shield using multi-year (2002–2010) automatic monitoring at sites (up to 18 in number) with diverse soil texture and land use. We found that the soils exhibited significant time-stability, Spearman’s rank correlation coefficients rs = 0.94–0.95, p

Summary Methodology was developed to estimate surface water–groundwater interactions in a changing climate in cold, snow-dominated regions and tested on an unconfined esker aquifer in northern Finland. The Watershed Simulation and Forecasting System (WSFS) model was used to simulate surface water levels. A coupled heat and mass transfer model for soil–plant–atmosphere systems (CoupModel) was used to simulate recharge. The CoupModel is able to simulate water flow through frozen soil. The simulated surface water level and recharge data were linked to the Groundwater Modelling System (GMS) version 6.5, and the three-dimensional groundwater flow model MODFLOW was used to study the impact of climate variability on groundwater levels and groundwater–surface water interactions. In addition, under A1B climate change scenario changes in aquifer storage and groundwater–surface water interactions were studied through the end of the 21st century. Recharge was shown to be sensitive to changes in soil frost and hence modelling approaches should include a soil frost component to account for the impact of frost on hydraulic conductivity. Under A1B climate change scenario study, groundwater recharge is projected to increase in winter months due to increase in snowmelt and decrease in soil frost depth. The spring snowmelt peak in late spring will decrease. This will reduce aquifer storage in early spring, increasing the vulnerability to summer droughts.

A literature review of the impacts of anticipated climate change on unconfined aquifers is presented, along with a conceptual framework for evaluating the complex responses of surface and subsurface hydrology to climate variables in cold regions. The framework offers a way to conceptualize how changes in one component of the system may impact another by delineating the relationships among climate drivers, hydrological responses, and groundwater responses in a straight-forward manner. The model is elaborated in the context of shallow unconfined aquifers in the boreal environment of Finland. In cold conditions, climate change is expected to reduce snow cover and soil frost and increase winter floods. The annual surface water level maximum will occur earlier in spring, and water levels will decrease in summer due to higher evapotranspiration rates. The maximum recharge and groundwater level are expected to occur earlier in the year. Lower groundwater levels are expected in summer due to higher evapotranspiration rates. The flow regimes between shallow unconfined aquifers and surface water may change, affecting water quantity and quality in the surface and groundwater systems.

In this study, the effects of ozonation on municipal treated wastewater were investigated. Batch experiments were conducted using two water samples from the same plant: post precipitation plant effluent and the same effluent after a polishing treatment in a wetland. The effects of ozonation on chemical oxygen demand (COD), biological oxygen demand (BOD(7)), colour and turbidity were investigated. Ozonation with dosages up to 2.7 mg/L substantially decreased the COD of biochemically treated municipal wastewater. One gram of ozone decreased the amount of COD by 1.5 g. With higher dosages, the effectiveness of ozone on COD decreased rapidly. Ozone was a very effective colour and turbidity reducer.

In this research the characteristics of fresh wastewater were studied by filtration of organic material and nutrients. Besides the short-term dissolving of phosphorus was determined. The size fractions of oxygen demand for 7 days (BOD7), total organic carbon (TOC), phosphorous (P) and nitrogen (N) were separated to 0.1 microm. Most of the phosphorous, nitrogen and organic carbon was under 0.1 microm fractions. Most of the biological oxygen demand was over 12 microm fractions although the fraction under 0.1 microm was 37%. The amount of phosphorus over 0.45 microm increased 25% after 3 days' storage.