Comparison of the AVI, modified SINTACS and GALDIT vulnerability methods under future climate-change scenarios for a shallow low-lying coastal aquifer in southern Finland

Peer reviewe

Groundwater vulnerability of a shallow low-lying coastal aquifer in southern Finland under climate change

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

Challenges to climate change adaptation in coastal small towns:Examples from Ghana, Uruguay, Finland, Denmark, and Alaska

The ability of a coastal settlement to adapt to climate change is largely dependent upon access to a range of resources, which many coastal towns and small cities lack. Coastal small towns of less than 10,000 are therefore at a significant disadvantage compared to larger settlements when it comes to adaptation. One way to begin to overcome this disadvantage is to compare coastal small towns in order to identify efficiencies and support knowledge sharing. In this article we present and analyse five case studies of coastal small towns: Fuvemeh, Ghana; Kiyú, Uruguay; Hanko, Finland; Lemvig, Denmark; and Nome, Alaska, USA. A number of key outcomes and lessons were identified which highlights the need for a formal network of international coastal small towns to encourage and develop knowledge sharing practices going forward. A further lesson is the importance of using a range of indicators in order to establish the regional/national importance of a town. Basing this solely on population size can result in an erroneous interpretation of the significance (and therefore adaptive capacity) of a coastal small town. Finally, despite many barriers to adaptation in coastal small towns, being small offers some potential advantages, such as the possibility of being able to form a community consensus more easily, using 3D visualisations for adaptation planning, and having managed realignment as a realistic management option. It is imperative that climate change resilience in coastal small towns is increased by focussing on overcoming barriers and developing appropriate adaptation approaches by governments, non-governmental organisations, business, and researchers

Challenges to climate change adaptation in coastal small towns: examples from Ghana, Uruguay, Finland, Denmark, and Alaska

The ability of a coastal settlement to adapt to climate change is largely dependent upon access to a range of resources, which many coastal towns and small cities lack. Coastal small towns of less than 10,000 are therefore at a significant disadvantage compared to larger settlements when it comes to adaptation. One way to begin to overcome this disadvantage is to compare coastal small towns in order to identify efficiencies and support knowledge sharing. In this article we present and analyse five case studies of coastal small towns: Fuvemeh, Ghana; Kiyú, Uruguay; Hanko, Finland; Lemvig, Denmark; and Nome, Alaska, USA. A number of key outcomes and lessons were identified which highlights the need for a formal network of international coastal small towns to encourage and develop knowledge sharing practices going forward. A further lesson is the importance of using a range of indicators in order to establish the regional/national importance of a town. Basing this solely on population size can result in an erroneous interpretation of the significance (and therefore adaptive capacity) of a coastal small town. Finally, despite many barriers to adaptation in coastal small towns, being small offers some potential advantages, such as the possibility of being able to form a community consensus more easily, using 3D visualisations for adaptation planning, and having managed realignment as a realistic management option. It is imperative that climate change resilience in coastal small towns is increased by focussing on overcoming barriers and developing appropriate adaptation approaches by governments, non-governmental organisations, business, and researchers

Impacts of Future Climate Change and Baltic Sea Level Rise on Groundwater Recharge, Groundwater Levels, and Surface Leakage in the Hanko Aquifer in Southern Finland

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

Arseenin luontaiset pitoisuudet Pirkanmaalla

vokMAAMP

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

&amp;lt;p&amp;gt;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.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;This study investigated the behavior of &amp;lt;sup&amp;gt;87&amp;lt;/sup&amp;gt;Sr/&amp;lt;sup&amp;gt;86&amp;lt;/sup&amp;gt;Sr, &amp;amp;#948;&amp;lt;sup&amp;gt;7&amp;lt;/sup&amp;gt;Li and &amp;amp;#948;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S in the STE and three seafloor pockmarks with different degrees of groundwater influence, as constrained based on &amp;amp;#948;&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;H and &amp;amp;#948;&amp;lt;sup&amp;gt;18&amp;lt;/sup&amp;gt;O, at the Hanko SGD site in Finland, in the northern Baltic Sea. These data were supplemented by groundwater and seawater measurements. &amp;lt;sup&amp;gt;87&amp;lt;/sup&amp;gt;Sr/&amp;lt;sup&amp;gt;86&amp;lt;/sup&amp;gt;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. &amp;amp;#948;&amp;lt;sup&amp;gt;7&amp;lt;/sup&amp;gt;Li values were shifted down to &amp;amp;#8722;1.75&amp;amp;#8240; below that expected for conservative mixing in the STE and in groundwater-influenced pockmark porewaters, whereas &amp;amp;#948;&amp;lt;sup&amp;gt;7&amp;lt;/sup&amp;gt;Li was elevated up to 1.53&amp;amp;#8240; in the porewater of organic-rich mud in a pockmark where groundwater influence had ceased. &amp;amp;#948;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S deviated between &amp;amp;#8722;16.78&amp;amp;#8240; and 10.51&amp;amp;#8240; from the conservative mixing in the STE and porewaters of groundwater-influenced pockmarks, while &amp;amp;#948;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S was elevated up to 16.85&amp;amp;#8240; in the porewater of the pockmark with no groundwater influence.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In the Hanko STE, the isotopic fractionation of Sr and Li was explained by chemical weathering of silicate minerals and clay minerals, respectively, whereas &amp;amp;#948;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S was fractionated by complex interactions of microbial sulfate reduction and sulfide reoxidation. In the pockmark porewater with no groundwater influence, &amp;amp;#948;&amp;lt;sup&amp;gt;7&amp;lt;/sup&amp;gt;Li and &amp;amp;#948;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S isotopes were enriched in the heavier isotopes as a consequence of early-diagenetic mineral formation in the organic-rich muds. The measured &amp;lt;sup&amp;gt;87&amp;lt;/sup&amp;gt;Sr/&amp;lt;sup&amp;gt;86&amp;lt;/sup&amp;gt;Sr and &amp;amp;#948;&amp;lt;sup&amp;gt;7&amp;lt;/sup&amp;gt;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 &amp;amp;#948;&amp;lt;sup&amp;gt;34&amp;lt;/sup&amp;gt;S of groundwater-derived S flux to the coastal ocean at a spatial scale of a few hundreds of meters.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Original publication: Ikonen, J., Hendriksson, N., Luoma, S., Lahaye, Y. and&amp;amp;#160;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,&amp;amp;#160;https://doi.org/10.1016/j.apgeochem.2022.105471, 2022.&amp;lt;/p&amp;gt;</jats:p