<p>The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemist... more <p>The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemistry and water quality has been demonstrated in many recent studies. However, the isotopic behavior of terrestrially-derived solutes in the groundwater-seawater mixing zone of coastal aquifers (the subterranean estuary, STE) has been less studied, although solutes such as Li, S and Sr are commonly used as tracers of weathering and biogeochemical processes taking place in aquifers and in coastal sea sediments.</p><p>This study investigated the behavior of <sup>87</sup>Sr/<sup>86</sup>Sr, δ<sup>7</sup>Li and δ<sup>34</sup>S in the STE and three seafloor pockmarks with different degrees of groundwater influence, as constrained based on δ<sup>2</sup>H and δ<sup>18</sup>O, at the Hanko SGD site in Finland, in the northern Baltic Sea. These data were supplemented by groundwater and seawater measurements. <sup>87</sup>Sr/<sup>86</sup>Sr showed non-conservative behavior with values elevated up to 0.0167 units above that expected for the conservative mixing in the STE and in the most groundwater-dominated pockmark (up to 100% groundwater), but the deviation was masked by much stronger seawater contributions in the other pockmarks. δ<sup>7</sup>Li values were shifted down to −1.75‰ below that expected for conservative mixing in the STE and in groundwater-influenced pockmark porewaters, whereas δ<sup>7</sup>Li was elevated up to 1.53‰ in the porewater of organic-rich mud in a pockmark where groundwater influence had ceased. δ<sup>34</sup>S deviated between −16.78‰ and 10.51‰ from the conservative mixing in the STE and porewaters of groundwater-influenced pockmarks, while δ<sup>34</sup>S was elevated up to 16.85‰ in the porewater of the pockmark with no groundwater influence.</p><p>In the Hanko STE, the isotopic fractionation of Sr and Li was explained by chemical weathering of silicate minerals and clay minerals, respectively, whereas δ<sup>34</sup>S was fractionated by complex interactions of microbial sulfate reduction and sulfide reoxidation. In the pockmark porewater with no groundwater influence, δ<sup>7</sup>Li and δ<sup>34</sup>S isotopes were enriched in the heavier isotopes as a consequence of early-diagenetic mineral formation in the organic-rich muds. The measured <sup>87</sup>Sr/<sup>86</sup>Sr and δ<sup>7</sup>Li were higher than the previously estimated isotopic compositions of their groundwater-derived fluxes to the oceans, and partly higher than the global riverine values. The heterogeneity in the seafloor biogeochemical environment, caused by the focusing of SGD in pockmarks, resulted in strongly variable δ<sup>34</sup>S of groundwater-derived S flux to the coastal ocean at a spatial scale of a few hundreds of meters.</p><p>Original publication: Ikonen, J., Hendriksson, N., Luoma, S., Lahaye, Y. and Virtasalo, J. J.: Behavior of Li, S and Sr isotopes in the subterranean estuary and seafloor pockmarks of the Hanko submarine groundwater discharge site in Finland, northern Baltic Sea, Applied Geochemistry, 147, 105471, https://doi.org/10.1016/j.apgeochem.2022.105471, 2022.</p>
Hanke: Risk Assessment and Risk Management Procedure for Arsenic in the Tampere Region.Nimekkeen ... more Hanke: Risk Assessment and Risk Management Procedure for Arsenic in the Tampere Region.Nimekkeen selvennys: Arseeni ja eräitä muita alkuaineita Suomen maatalousekosysteemeissä, etenkin Pirkanmaalla.vokMAA. Yksikön huom.: MAA, MPLMP
Sediment samples were collected using a box corer, and cut in 1-cm sub-sample slices. The Cs-137 ... more Sediment samples were collected using a box corer, and cut in 1-cm sub-sample slices. The Cs-137 activity content of sub-samples was measured for 60 min using a BrightSpec bMCA-USB pulse height analyser coupled to a well-type NaI(Tl) detector. The same sub-samples were then analysed for water content and weight loss on ignition (LOI) by weighing sub-samples fresh, weighing after drying at 105 °C for 16 h, and weighing again after ignition at 550 °C for 2 h.
Water column profiles were measured at the locations of pockmarks B, D and E, using a Sea & Sun C... more Water column profiles were measured at the locations of pockmarks B, D and E, using a Sea & Sun CTD90M multiprobe. The sensors for pressure, temperature, conductivity and optical dissolved oxygen in the multiprobe were manufactured by Sea & Sun Technology GmbH. The turbidity sensor was manufactured by Seapoint Sensors Inc., and the ISM-2001C inductive 2D current meter with compass by HS Engineers GmbH.
Sea surface radon-222 measurements were carried out onboard the research boat Gridi. The survey w... more Sea surface radon-222 measurements were carried out onboard the research boat Gridi. The survey was run at 1.4 knots, with the boat position recorded by DGPS. Two pumps that continuously supplied water for the measurements were fixed at ca. 50 cm water depth with a Sea & Sun Technology CTD90M multiprobe that was recording pressure (depth), temperature and conductivity (salinity). The radon measurements were carried out using two identical systems in parallel, each equipped with a 3M MiniModule gas contractor that separates the dissolved gas from the continuously pumped water. The gas was dried with a Drierite gas-drying unit, and analysed with a Durridge RAD7 radon detector. The radon-in-water activity concentrations were calculated using the salinity and temperature dependent fractionation of radon-222 between air and water.
This report presents the final results of an Applied Research Project conducted within the framew... more This report presents the final results of an Applied Research Project conducted within the framework of the ESPON 2013 Programme, partly financed by the European Regional
Potential risks for shallow groundwater aquifers in coastal areas of the Baltic Sea, a case study... more Potential risks for shallow groundwater aquifers in coastal areas of the Baltic Sea, a case study in the Hanko area in South Finland
<p>The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemist... more <p>The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemistry and water quality has been demonstrated in many recent studies. However, the isotopic behavior of terrestrially-derived solutes in the groundwater-seawater mixing zone of coastal aquifers (the subterranean estuary, STE) has been less studied, although solutes such as Li, S and Sr are commonly used as tracers of weathering and biogeochemical processes taking place in aquifers and in coastal sea sediments.</p><p>This study investigated the behavior of <sup>87</sup>Sr/<sup>86</sup>Sr, δ<sup>7</sup>Li and δ<sup>34</sup>S in the STE and three seafloor pockmarks with different degrees of groundwater influence, as constrained based on δ<sup>2</sup>H and δ<sup>18</sup>O, at the Hanko SGD site in Finland, in the northern Baltic Sea. These data were supplemented by groundwater and seawater measurements. <sup>87</sup>Sr/<sup>86</sup>Sr showed non-conservative behavior with values elevated up to 0.0167 units above that expected for the conservative mixing in the STE and in the most groundwater-dominated pockmark (up to 100% groundwater), but the deviation was masked by much stronger seawater contributions in the other pockmarks. δ<sup>7</sup>Li values were shifted down to −1.75‰ below that expected for conservative mixing in the STE and in groundwater-influenced pockmark porewaters, whereas δ<sup>7</sup>Li was elevated up to 1.53‰ in the porewater of organic-rich mud in a pockmark where groundwater influence had ceased. δ<sup>34</sup>S deviated between −16.78‰ and 10.51‰ from the conservative mixing in the STE and porewaters of groundwater-influenced pockmarks, while δ<sup>34</sup>S was elevated up to 16.85‰ in the porewater of the pockmark with no groundwater influence.</p><p>In the Hanko STE, the isotopic fractionation of Sr and Li was explained by chemical weathering of silicate minerals and clay minerals, respectively, whereas δ<sup>34</sup>S was fractionated by complex interactions of microbial sulfate reduction and sulfide reoxidation. In the pockmark porewater with no groundwater influence, δ<sup>7</sup>Li and δ<sup>34</sup>S isotopes were enriched in the heavier isotopes as a consequence of early-diagenetic mineral formation in the organic-rich muds. The measured <sup>87</sup>Sr/<sup>86</sup>Sr and δ<sup>7</sup>Li were higher than the previously estimated isotopic compositions of their groundwater-derived fluxes to the oceans, and partly higher than the global riverine values. The heterogeneity in the seafloor biogeochemical environment, caused by the focusing of SGD in pockmarks, resulted in strongly variable δ<sup>34</sup>S of groundwater-derived S flux to the coastal ocean at a spatial scale of a few hundreds of meters.</p><p>Original publication: Ikonen, J., Hendriksson, N., Luoma, S., Lahaye, Y. and Virtasalo, J. J.: Behavior of Li, S and Sr isotopes in the subterranean estuary and seafloor pockmarks of the Hanko submarine groundwater discharge site in Finland, northern Baltic Sea, Applied Geochemistry, 147, 105471, https://doi.org/10.1016/j.apgeochem.2022.105471, 2022.</p>
Hanke: Risk Assessment and Risk Management Procedure for Arsenic in the Tampere Region.Nimekkeen ... more Hanke: Risk Assessment and Risk Management Procedure for Arsenic in the Tampere Region.Nimekkeen selvennys: Arseeni ja eräitä muita alkuaineita Suomen maatalousekosysteemeissä, etenkin Pirkanmaalla.vokMAA. Yksikön huom.: MAA, MPLMP
Sediment samples were collected using a box corer, and cut in 1-cm sub-sample slices. The Cs-137 ... more Sediment samples were collected using a box corer, and cut in 1-cm sub-sample slices. The Cs-137 activity content of sub-samples was measured for 60 min using a BrightSpec bMCA-USB pulse height analyser coupled to a well-type NaI(Tl) detector. The same sub-samples were then analysed for water content and weight loss on ignition (LOI) by weighing sub-samples fresh, weighing after drying at 105 °C for 16 h, and weighing again after ignition at 550 °C for 2 h.
Water column profiles were measured at the locations of pockmarks B, D and E, using a Sea & Sun C... more Water column profiles were measured at the locations of pockmarks B, D and E, using a Sea & Sun CTD90M multiprobe. The sensors for pressure, temperature, conductivity and optical dissolved oxygen in the multiprobe were manufactured by Sea & Sun Technology GmbH. The turbidity sensor was manufactured by Seapoint Sensors Inc., and the ISM-2001C inductive 2D current meter with compass by HS Engineers GmbH.
Sea surface radon-222 measurements were carried out onboard the research boat Gridi. The survey w... more Sea surface radon-222 measurements were carried out onboard the research boat Gridi. The survey was run at 1.4 knots, with the boat position recorded by DGPS. Two pumps that continuously supplied water for the measurements were fixed at ca. 50 cm water depth with a Sea & Sun Technology CTD90M multiprobe that was recording pressure (depth), temperature and conductivity (salinity). The radon measurements were carried out using two identical systems in parallel, each equipped with a 3M MiniModule gas contractor that separates the dissolved gas from the continuously pumped water. The gas was dried with a Drierite gas-drying unit, and analysed with a Durridge RAD7 radon detector. The radon-in-water activity concentrations were calculated using the salinity and temperature dependent fractionation of radon-222 between air and water.
This report presents the final results of an Applied Research Project conducted within the framew... more This report presents the final results of an Applied Research Project conducted within the framework of the ESPON 2013 Programme, partly financed by the European Regional
Potential risks for shallow groundwater aquifers in coastal areas of the Baltic Sea, a case study... more Potential risks for shallow groundwater aquifers in coastal areas of the Baltic Sea, a case study in the Hanko area in South Finland
This thesis clarifies the potential impacts of climate change and sea-level rise under future cli... more This thesis clarifies the potential impacts of climate change and sea-level rise under future climate scenarios on groundwater recharge and surface leakage, and consequently on the groundwater vulnerability of a shallow, unconfined, low-lying coastal sedimentary aquifer in southern Finland. The study utilised multiple approaches, including field investigations, well monitoring, three-dimensional (3D) geological modelling, 3D groundwater flow modelling, multivariate statistical approaches (principal component analysis (PCA) and hierarchical cluster analysis (HCA)), the stable isotopes δ2H and δ18O, conventional hydrogeochemistry and groundwater intrinsic vulnerability assessment methods. The UZF1 model was coupled with the 3D groundwater MODFLOW model to simulate flow from the unsaturated zone through the aquifer. The well-calibrated groundwater flow model was used to simulate and predict the potential impacts of climate change on groundwater recharge under future climate and sea-level rise scenarios. The results indicate changes in the groundwater recharge patterns during the years 2071–2100, with recharge occurring earlier in winter and early spring. Because the aquifer is located in a cold snow-dominated region, the seasonal impacts of climate change on groundwater recharge were more significant, with land surface overflow resulting in flooding during the winter and early spring and drought during the summer. Rising sea levels would cause some parts of the aquifer to be submerged under the sea, compromising groundwater quality due to the intrusion of seawater. This, together with increased groundwater recharge, would raise the groundwater level and consequently contribute to more surface leakage. The groundwater geochemistry of the coastal aquifer in Hanko is very similar to that of inland shallow aquifers generally in Finland, where the groundwater is mainly of the Ca–HCO3 type, with low dissolved element concentrations, low pH and alkalinity, and low Ca and Mg concentrations due to rapid percolation or the short residence time. The stable isotopes δ2H and δ18O clearly suggest that the Hanko aquifer recharges directly from meteoric water (snowmelt and rainfall), with minor or insignificant contributions from the Baltic Sea and surface water. However, the geochemistry of the groundwater suggests sulphate reduction in the mixed zone between freshwater and seawater, indicating that local seawater intrusion may temporarily take place, although the contribution of seawater was found to be very low. Further inland, the influence of surface water could be observed from higher levels of KMnO4 consumption in wells near the lake above the aquifer. The findings also demonstrated that the use of stable isotopes δ2H and δ18O alone to identify seawater–aquifer interaction is not sufficient to determine the rate of water exchange. The high temporal variation in groundwater chemistry directly corresponded to groundwater recharge. With an increase in groundwater recharge, KMnO4 consumption, EC, alkalinity and Ca concentrations also increased in most wells, while Fe, Al, Mn and SO4 were occasionally increased during the spring after snowmelt under specific geological conditions. Based on the future climate scenarios, precipitation in the Hanko area is expected to increase and the Baltic Sea level to rise. This could cause increased recharge of the aquifer from surface water, but also some seawater intrusion due to the sea-level rise and storm surges, as well as increased groundwater abstraction. An increase in the concentrations of some dissolved elements and changes in groundwater geochemistry along the coastline can be expected in the future. Thus, in coastal aquifers with low hydraulic gradients, the hydrogeochemistry should be used to confirm the intrusion of seawater. The PCA and HCA multivariate statistical approaches are useful tools to extract the main components that are able to identify the vulnerable areas of the aquifer impacted by natural or human activities, either on regional or site-specific scales. The integration of PCA and HCA with conventional classification of groundwater types, as well as with the hydrogeochemical data, provided an understanding of the complex groundwater flow systems, supporting aquifer vulnerability assessment and groundwater management in the future. The degree of groundwater vulnerability in the Hanko aquifer has been greatly impacted by seasonal variations in groundwater recharge during the year, and will also vary depending on climate change variability in the long term. The potential for high groundwater vulnerability to contamination from sources on the ground surface occurs during the period with a high groundwater recharge rate after snowmelt, while high vulnerability to seawater intrusion could occur when there is a low groundwater recharge rate in the dry season. This thesis study highlighted the importance of the integration of groundwater vulnerability assessment methods for shallow, unconfined, low-lying coastal aquifers from a comparison of three intrinsic vulnerability mapping methods: the AVI, a modified version of SINTACS and the GALDIT method. The modified SINTACS could be used as a guideline for groundwater vulnerability assessment of glacial and deglacial deposits in inland aquifers, and in combination with GALDIT, it could provide a useful tool for assessing groundwater vulnerability to both contamination from sources on the ground surface and to seawater intrusion for shallow, unconfined, low-lying coastal aquifers under future climate change.
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Papers by Samrit Luoma
The groundwater geochemistry of the coastal aquifer in Hanko is very similar to that of inland shallow aquifers generally in Finland, where the groundwater is mainly of the Ca–HCO3 type, with low dissolved element concentrations, low pH and alkalinity, and low Ca and Mg concentrations due to rapid percolation or the short residence time. The stable isotopes δ2H and δ18O clearly suggest that the Hanko aquifer recharges directly from meteoric water (snowmelt and rainfall), with minor or insignificant contributions from the Baltic Sea and surface water. However, the geochemistry of the groundwater suggests sulphate reduction in the mixed zone between freshwater and seawater, indicating that local seawater intrusion may temporarily take place, although the contribution of seawater was found to be very low. Further inland, the influence of surface water could be observed from higher levels of KMnO4 consumption in wells near the lake above the aquifer. The findings also demonstrated that the use of stable isotopes δ2H and δ18O alone to identify seawater–aquifer interaction is not sufficient to determine the rate of water exchange. The high temporal variation in groundwater chemistry directly corresponded to groundwater recharge. With an increase in groundwater recharge, KMnO4 consumption, EC, alkalinity and Ca concentrations also increased in most wells, while Fe, Al, Mn and SO4 were occasionally increased during the spring after snowmelt under specific geological conditions. Based on the future climate scenarios, precipitation in the Hanko area is expected to increase and the Baltic Sea level to rise. This could cause increased recharge of the aquifer from surface water, but also some seawater intrusion due to the sea-level rise and storm surges, as well as increased groundwater abstraction. An increase in the concentrations of some dissolved elements and changes in groundwater geochemistry along the coastline can be expected in the future. Thus, in coastal aquifers with low hydraulic gradients, the hydrogeochemistry should be used to confirm the intrusion of seawater. The PCA and HCA multivariate statistical approaches are useful tools to extract the main components that are able to identify the vulnerable areas of the aquifer impacted by natural or human activities, either on regional or site-specific scales. The integration of PCA and HCA with conventional classification of groundwater types, as well as with the hydrogeochemical data, provided an understanding of the complex groundwater flow systems, supporting aquifer vulnerability assessment and groundwater management in the future.
The degree of groundwater vulnerability in the Hanko aquifer has been greatly impacted by seasonal variations in groundwater recharge during the year, and will also vary depending on climate change variability in the long term. The potential for high groundwater vulnerability to contamination from sources on the ground surface occurs during the period with a high groundwater recharge rate after snowmelt, while high vulnerability to seawater intrusion could occur when there is a low groundwater recharge rate in the dry season. This thesis study highlighted the importance of the integration of groundwater vulnerability assessment methods for shallow, unconfined, low-lying coastal aquifers from a comparison of three intrinsic vulnerability mapping methods: the AVI, a modified version of SINTACS and the GALDIT method. The modified SINTACS could be used as a guideline for groundwater vulnerability assessment of glacial and deglacial deposits in inland aquifers, and in combination with GALDIT, it could provide a useful tool for assessing groundwater vulnerability to both contamination from sources on the ground surface and to seawater intrusion for shallow, unconfined, low-lying coastal aquifers under future climate change.