Browsing by study line "Hydrogeology and environmental geology"

Northern peatlands are important carbon storing ecosystems, contributing to carbon cycle as sinks and sources. The two most important greenhouse gases in the carbon cycle are carbon dioxide (CO2) and methane (CH4). The study area of this work consists of two sloping fens in the Kuusamo area. from which the peat geochemistry and peat properties (peat stratigraphy, ash content, and bulk density) are studied. In addition, the chronology, carbon-nitrogen ratio, carbon content, and carbon accumulation are studied in the Puukkosuo from the three sampling sites. In the characterization of peat geochemistry, Puukkosuo in the dolomitic rock area and Suvisuo in the volcanic rock area were divided into different geochemical zones based on the cluster analysis. The paludification in the Puukkosuo area has started around 10 000 years ago, and the accumulation of peat have been ongoing in the whole peat basin after 1000 years. The geochemical zones in the Puukkosuo can be divided into five different groups, from which the deepest part of the peatland basin can be separated due to the high heavy metal concentrations in the oldest peat. Most of the bulk peat is differentiated into alternating groups, from which the changes in the peat nutrients are recorded. The margins of the Puukkosuo are separated based on the geochemical properties. The top part of the northwestern edge can be characterized as high concentrations of atmospheric origin elements, whereas the effect of the nearby road can be noted in the concentrations of the top part of the southeastern edge. The amount of carbon accumulated has varied throughout the development of Puukkosuo, and the highest rates are recorded in the lower part of the peat profiles in all study sites. Highest carbon-nitrogen -ratios are recorded near the basal peat samples especially in the deepest part of the Puukkosuo. The long-term carbon accumulation differs from the other long-term averages in the boreal zone. The largest differences were recorded in the deepest part of the basin in the long-term carbon accumulation rates during the Early Holocene. The respective value in the Puukkosuo is four times higher (60 g m-2 yr-1) in contrast to others. During the Late Holocene the long-term carbon accumulation rates correspond to the other average values in the boreal peatlands (25 g m-2 yr-1).

The research subject is Waste Rock and Tailings Storage Facilities of a Finnish mine in planning. The storage facilities are considered as they will be in the operative phase of the mine. Waste rock is categorized according to its sulfur and metal content as well as buffering capabilities in to two classes; low-sulfur and high-sulfur waste rock. Waste rock is deposited in the form of piles at two different storage facilities determined by their classification. Tailings are deposited as wet slurry within embankment, where most of the tailings are partially or fully saturated with water. The aim of this study was to research contingencies in the quality assesment of seepage water produced by storage facilities. Seepage water in the mine in planning has previously been assessed with humidity cell tests, which serves as the source material for this thesis. The humidity cell tests are performed in laboratory conditions which do not respond to actual mining area conditions, thus the seepage water quality assesment cannot be done based on these tests alone. Instead they are used as source material to assess the quality of the seepage water. The effects of the conditions of humidity cell testing are the contingencies in seepage water quality assessment. The effects of the conditions studied in this thesis are temperature, rainfall, reactive mass of the waste rock and tailings as well as channeling of rain water in the waste rock storage facility. In the composition of seepage water the concentrations of sulfates and metals was examined. Humidity cell test results were fitted to the conditions in the mining area by lab-to-field scaling. The scaling correction factor or complement is based on the effects of the laboratory and mining area conditions on the quality of the seepage water that are defined in the scaling. The effect of condition factors on water quality assessment was investigated by changing the value of the scaling factor and comparing the resulting water compositions. Futhermore, the water quality estimate obtained as a result of the scaling was fed into an equilibrium modeling program to to study the precipitation reactions in the leachate and the amount of precipitation. Based on the scaling results, the sulfate and metal concentrations in the seepage water increased as the proportion of fines, reactive mass, leachable surface area, or temperature increased. If rainfall increased, the concentrations of metals and sulfates decreased. The above properties were observed for each mine wastes examined (low-sulfur and high-sulfur waste rock, tailings). The intensity of the increase or decrease in concentrations was dependent on the acidity of the seepage water of the mine waste. In the alkaline seepage water of low-sulfur waste rock and tailings, the increase in the value of the condition factor, with the exception of rainfall, led to greater changes in concentrations than in the acidic seepage water of high-sulfur waste rock. The seepage water of the high-sulfur waste rock was acidic and therefore the solubility of the metals was high and the changes in acidity didn’t significantly affect the precipitation of the substances. The final conclusion of the work was that the most significant uncertainties for the assessment of leachate quality are the grain size distribution and channeling of water in the waste rock pile, and the thickness of reactive layer in the tailings storage facility. Based on the sensitivity analysis, the effects of climate change did not significantly affect the water quality, as the simultaneous increase in temperature and precipitation offset each other's effects. It should be noted, however, that a more in-depth examination of the effects of climate change would require a seasonal examination of precipitation and temperature. In addition, variations in prolonged rainy and dry seasons should be considered, as they may have significant momentary effects on the seepage water quality.

Methane is a powerful greenhouse gas that is released to the atmosphere in many ways from natural sources. While wetlands are seen as major sources, open water systems, including small boreal lakes, should also be considered when estimating methane emissions locally and globally. Methane is produced the sediments and has several oxidation processes and emission pathways. In this master’s thesis, the sediments of Lake Pääjärvi, southern Finland, were studied using two different porewater sampling methods to analyze methane concentrations and geochemical properties of the porewater. The sampling methods, the Rhizons filter and the cut syringe method, were both performed to total of five sampling sites. A sediment profile was made from two locations, PAME1 and PAME2, and single sampling at 10 cm depth from the other sites. The sampling sites were located on different parts of the lake at depths of 3–16 m. Additionally, the water column was sampled for methane and water quality, and sediment for grain size, organic matter, and the C:N-ratio. As a result, the sampling methods were successful, and the sediment profiles and the sites could be compared. While there was difference in the methane concentrations, reliability of the methods was not concluded. The Rhizons filter method gave higher methane concentrations in only one sampling site, whereas the cut syringe was dominant in all others. Influential factors on the differences could be the use of different sampling cores, or the different duration of sampling between the sampling sites. The sulfate-methane transition zone was recognized from the depth of 4.5–6.5 cm in PAME1 and circa 3 cm in PAME2. The only sediment feature that coincided with high methane concentrations was larger grain size, although the variation between sampling sites was not large. The methane concentrations in the epilimnion were higher than near the sediment-water interface, which suggested that the methane in Lake Pääjärvi originates mainly from the catchment area and not from the sediments.

The aim of this study was to research surface water-groundwater interactions and groundwater flow directions with stable isotopes of water, dissolved silica, d-excess, electrical conductivity, pH and temperature in the Vesioronkangas groundwater area in the city of Imatra, South-Carelia. Elevations of groundwater pipe heads existing in year 2015 were measured and connected to N2000-elevation system, and their coordinates were checked. Groundwater levels were measured, and pipe coordinates checked in the summer of 2015. Water samples were collected in the late winter of 2016 and temperature, pH and electrical conductivity of the samples were determined on site with YSI multiparameter probe. The samples were analyzed in the University of Helsinki laboratory during the spring and summer of 2016. Stable isotopes δ18O and δD were analyzed with Picarro L1115-i device and dissolved silica with Agilent 4100 device. Electrical conductivity was measured again in the laboratory after heating the samples. In the cluster analysis, the water samples formed three groups that were already detectable on the basis of the stable isotope composition of the water and other physical and chemical variables: surface waters, groundwater-influenced surface waters/mixed waters and groundwaters. Maps and flow and structural modellings of the groundwater area were created with QGIS and TopoDrive programs and it seems that there is no hydraulic connection between Lake Saimaa and Lake Immalanjärvi even if there is a bedrock fracture zone. Groundwater flows to many directions in the area, almost all compass points.

The construction of the Savio railway tunnel caused an unexpectedly large decrease in the groundwater heads in part of the observation points in the vicinity of the railway tunnel after the completion of the tunnel construction work. The study aimed to investigate the ability of the groundwater model to forecast such groundwater drawdown caused by a railway tunnel in the urban areas of East Hakkila, Kaskela and Hakunila. The uncertainty of the groundwater model and its sensitivity to certain parameters were studied and analyzed. The groundwater model was built using the GMS (Groundwater Modeling System) numerical groundwater modeling program. For the groundwater flow model, the bedrock mesh was built in Leapfrog Geo - program based on gravimetric measurements and rotary drilling. The groundwater model was calibrated manually and automatically to correspond to the groundwater heads measured in the area. The circumstances after the construction of the railway tunnel were then simulated. The model-calculated groundwater heads were compared to the observed groundwater heads and the observed tunnel leakage. Sensitivity analysis was performed for the horizontal conductivity parameters and recharge parameters of the model. The groundwater model before the construction of the tunnel mimicked the measured groundwater heads and flow directions in the study area. The simulation of the time after the construction of the tunnel caused groundwater drawdown of 0-16 meters at 0-730 meters from the railway tunnel. In the simulation of the time after tunnel construction, the groundwater heads calculated by the model differed by 0,01-24 meters from measured groundwater heads. According to the results of the sensitivity analysis, the model was most sensitive to changes in the horizontal conductivity of the upper bedrock layer and granite. The recharge parameters and soil layer had a marginal impact on the groundwater model. The uncertainty of the model was affected by the few measurement points in relation to the size of the area and the absence of field measurements of the hydraulic conductivity of the parameters. To reduce the uncertainty, the model should be calibrated based on the measured conductivity values of the bedrock. Despite the uncertainty, computational models give indications of the direction of change and are important tools in questions related to nature and the built environment.

Eutrophication and harmful substances of anthropogenic origin threaten the state of the Baltic Sea and especially its geochemistry and oxygen levels near the seafloor. Water exchange between the Baltic Sea and the Atlantic Ocean can affect oxygen circulation and sedimentation rates, but they are considered very sporadic and it is unclear how the water circulation and flow rates affect element concentrations and sediment deposition in the near seafloor environments. One of the less studied basins is the Western Gulf of Finland and its seafloor environment. During the 2019 voyage, the seafloor located to the south of the city of Hanko was investigated through bathymetric sounding tools and other measurements in which element concentration and sediment deposition rate data was acquired. The sounding revealed a large channel cutting the seafloor which was hypothesized to influence the nearbottom conditions. The obtained data consisted of samples from 13 short, 40 cm sediment cores which were analysed for 137Cs activity, organic content, and grain size distribution. The goal of the thesis was to determine the intensity of water exchange taking place in the seabed channels between the mid-Baltic Sea and the Western Gulf of Finland and investigate the effect of the seafloor channel and flow rates on sediment and element deposition, their relationships, and how they affect the overall conditions in the study area. These relationships were analyzed through spatial and statistical methods by utilizing GIS-tools to interpolate the data obtained from the study locations by using the Inverse Distance Weighting (IDW) method, and by multielement analyses in the R-environment, namely Principal Component Analysis (PCA) and Partial Least Regression (PLS) to analyze grain size and element concentration correlations and combine them with obtained flow rate data. The results showed strong correlation in flow rate intensities between the Western Gulf of Finland and the mid-Baltic Sea, and they are strongly linked with sedimentation and element deposition rates. However, no long-term trend was identified for the seafloor channel velocity frequencies. The Cs-activity shows stronger sedimentation activity on the western side of the seafloor channel. The overall element and sediment deposition in the study area was largely controlled by monthly and seasonal current velocity fluctuations among other processes. The element concentration comparison showed weakened oxygen conditions in the study area with increased eutrophication and carbon burial since the 1950s. The principal Component Analysis showed smaller grain sizes (0.15 - 2 mm) having a stronger influence on the datasets with Mo, N, and C providing largest variation in the data. Interpolation showed oxygen, pH, and H2S to have more fluctuation in the study area, which can indicate changes in the vertical gradients in each sample point. It could also be determined that other measured concentrations, such as temperature, turbidity, and salinity do not respond very sensitively to water inflow fluctuations or sedimentation rate changes. The results indicate that harmful substances and eutrophication are most likely going to increase in the near-bottom environment in the Western Gulf of Finland, contributed by anthropogenic activity. Water exchange is likely to become more and more uneven, thus affecting the flow rate effects to the sediment deposition in the Baltic Sea. Further studies are needed to link these processes to large-scale global changes and the general state of changes happening in the Baltic Sea and its surrounding areas. The seafloor of the Western Gulf of Finland could also be studied further to gain a better understanding of longer timescale changes on the seafloor channel currents, and element and sediment deposition rates.

Korroosio voi heikentää kallioperään sijoitettavien ydinpolttoainejätteen säiliöinä toimivien kuparikapselien kestävyyttä. Kalliopohjavedessä esiintyvät sulfaatinpelkistäjäbakteerit pelkistävät sulfaattia korroosiota aiheuttavaksi sulfidiksi. Tämän vuoksi ydinjätteen loppusijoitukseen liittyen on tärkeää selvittää, kuinka paljon ja missä muodossa rikkiä esiintyy kalliopohjavedessä ja mistä sitä päätyy sinne. Sulfaatinpelkistäjäbakteerien esiintyvyys ja sulfaatinpelkistyksen intensiteetti on myös oleellista selvittää loppusijoitukseen liittyvien uhkien minimoimiseksi. Tutkimuskohteena oli Tupoksella sijaitseva 1033 metriä syvä Tupos 001 -kairareikä, joka sijaitsee Muhos-muodostuman savikiviympäristössä, joka muistuttaa ominaisuuksiltaan kuparikapseleiden bentoniittipuskuria. Kairareiän pohjavedestä oli 80-luvulla tehty mittauksia sulfaatin määrästä ja sen isotooppikoostumuksesta. Nyt kairareiän pohjavedestä oli määrä selvittää sulfaattisen, sulfidisen sekä muiden rikkiyhdisteiden eli niin kutsutun X-faasin pitoisuus ja isotooppikoostumus eri osissa kairareikää. Isotooppikoostumuksen perusteella oli tarkoitus selvittää rikin lähteitä ja sulfaatinpelkistyksen intensiteettiä kairareiässä. Pohjavesinäytteet kerättiin letkuprofiilimenetelmällä 100 metrin pätkissä. Pohjavesinäytteistä analysoitiin muun muassa alkuaineiden ja ionien pitoisuuksia spektrometrilla ja ionikromatografilla. Rikin isotooppikoostumus selvitettiin eri rikkifaasien erottelun jälkeen massaspektrometrisin menetelmin. Tupos 001 -kairareiän pohjavedestä havaittiin runsaasti sulfaattia noin 800 metrin syvyyteen asti. Myös sulfidia mitattiin kairareiästä kaikilta syvyyksiltä, minkä lisäksi sulfidipitoisuuksissa havaittiin selkeä piikki 600-700 metrin syvyydellä. Sulfaattisen, sulfidisen ja X-faasin sisältämän rikin δ34S-isotooppikoostumus oli samankaltainen kairareiän ylä- ja keskiosissa vaihdellen noin 6-10 ‰:n (CDT) välillä. Kairareiän pohjalla sulfidinen rikki muuttui selvästi köyhemmäksi ja sulfaattinen ja X-faasiin sitoutunut rikki puolestaan rikastuneemmaksi 34S-isotoopin suhteen. Tupokselta saadut mikrobiologiset tulokset osoittavat sulfaatinpelkistäjäbakteerien runsaan esiintyvyyden pohjavedessä. Tässä tutkielmassa havaittu korkea sulfaattipitoisuus ja sen lasku kairareiän alaosissa, sulfidipiikki sekä sulfaatin ja sulfidin isotooppikoostumus varsinkin kairareiän pohjalla tukevat mikrobiologisia tuloksia. Etenkin tutkimuksessa havaitun sulfidipiikin perusteella sulfaatinpelkistys voi paikoitellen tuottaa huomattavasti kohonneita sulfidipitoisuuksia, minkä perusteella mikrobiologinen sulfaatinpelkistys voi lisätä ydinjäte-säiliöinä käytettävien kuparikapselien korroosion riskiä. Rikkifaasien pitoisuuksiin ja niiden isotooppikoostumukseen on sulfaatinpelkistyksen ohella todennäköisesti vaikuttanut myös merivesi ja rikkimineraalit niin sedimenttikivessä kuin kiteisessä kallioperässäkin. 80-luvulla suoritettuihin rikkitutkimuksiin verrattuna tässä tutkielmassa kolmen eri rikkifaasin ja kattavamman näytemäärän tutkiminen tuotti aiempaa tarkempia tutkimustuloksia rikin geokemiasta Tupoksen kalliopohjavedessä.