A shallow unconfined low-lying coastal aquifer in southern Finland surrounded by the Baltic Sea is vulnerable to changes in groundwater recharge, sea-level rise and human activities. Assessment of the intrinsic vulnerability of groundwater under climate scenarios was performed for the aquifer area by utilising the results of a published study on the impacts of climate change on groundwater recharge and sea-level rise on groundwater–seawater interaction. Three intrinsic vulnerability mapping methods, the aquifer vulnerability index (AVI), a modified SINTACS and GALDIT, were applied and compared. According to the results, the degree of groundwater vulnerability is greatly impacted by seasonal variations in groundwater recharge during the year, and also varies depending on the climate-change variability in the long term. The groundwater is potentially highly vulnerable to contamination from sources on the ground surface during high groundwater recharge rates after snowmelt, while a high vulnerability to seawater intrusion could exist when there is a low groundwater recharge rate in dry season. The AVI results suggest that a change in the sea level will have an insignificant impact on groundwater vulnerability compared with the results from the modified SINTACS and GALDIT. The modified SINTACS method could be used as a guideline for the 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 conditions. Un aquifère côtier libre, peu profond, du Sud de la Finlande, entouré par la mer baltique, est vulnérable aux changements de recharge de la nappe, d’élévation du niveau de la mer, et des activités humaines. L’évaluation de la vulnérabilité intrinsèque des eaux souterraines sous des scénarios climatiques a été effectuée pour la zone aquifère en utilisant les résultats d’une étude publiée sur les impacts du changement climatique sur la recharge de la nappe et l’élévation du niveau de la mer sur l’interaction eau souterraine - eau de mer. Trois méthodes de cartographie de la vulnérabilité intrinsèque, l’indice de vulnérabilité de l’aquifère (AVI), la méthode SINTACS modifiée et la méthode GALDIT, ont été appliquées et comparées. D’après les résultats, le degré de vulnérabilité des eaux souterraines est fortement impacté par les variations saisonnières de la recharge de la nappe durant l’année, et il varie également en fonction de la variabilité du changement climatique sur le long terme. Les eaux souterraines sont potentiellement très vulnérables aux contaminations issues de la surface lors des périodes de forte recharge de la nappe suite à la fonte des neiges, tandis qu’une forte vulnérabilité à l’intrusion de l’eau de mer pourrait avoir lieu lorsque le taux de recharge de la nappe est faible en saison sèche. Les résultats de l’AVI suggèrent que la variation du niveau de la mer aura un impact négligeable sur la vulnérabilité de la nappe, en comparaison des résultats des méthodes SINTACS modifiée et GALDIT. La méthode SINTACS modifiée pourrait être utilisée comme référence pour l’évaluation de la vulnérabilité des eaux souterraines des dépôts glaciaires et inter-glaciaires dans les aquifères à l’intérieur des terres. Combinée à la méthode GALDIT, elle pourrait constituer un outil utile pour évaluer la vulnérabilité des eaux souterraines aux contaminations issues de la surface et à l’intrusion d’eau de mer, pour des aquifères côtiers libres et peu profonds dans des conditions de changement climatique. Un acuífero costero somero no confinado en tierras bajas en el sur de Finlandia, rodeado por el mar Báltico es vulnerable a los cambios en la recarga del agua subterránea, al ascenso del nivel del mar y a las actividades humanas. La evaluación de la vulnerabilidad intrínseca del agua subterránea para los escenarios climáticos en el área del acuífero se llevó a cabo mediante la utilización de los resultados de un estudio publicado sobre los impactos del cambio climático en la recarga del agua subterránea y el ascenso del nivel del mar en la interacción del agua subterránea - agua de mar. Se aplicaron y compararon tres métodos de mapeo de la vulnerabilidad intrínseca, el índice de vulnerabilidad del acuífero (AVI), un SINTACS modificado y GALDIT. Según los resultados, el grado de vulnerabilidad del agua subterránea es impactado considerablemente por las variaciones estacionales durante el año de la recarga del agua subterránea, y también varía en función de la variabilidad a largo plazo del cambio climático. El agua subterránea es potencialmente altamente vulnerable a la contaminación a partir de fuentes de la superficie del suelo durante las altas tasas de recarga del agua subterránea después del derretimiento de la nieve, mientras que una alta vulnerabilidad a la intrusión de agua de mar podría existir cuando hay una baja tasa de recarga del agua subterránea en la estación seca. Los resultados de AVI sugieren que un cambio en el nivel del mar tendrá un impacto insignificante sobre la vulnerabilidad del agua subterránea en comparación con los resultados del SINTACS modificado y del GALDIT. El método SINTACS modificado podría ser utilizado como una guía para la evaluación de la vulnerabilidad del agua subterránea en los acuíferos de depósitos glaciares y deglaciales del continente, y en combinación con el GALDIT, podría proporcionar una herramienta útil para evaluar la vulnerabilidad del agua subterránea tanto de la contaminación de fuentes en la superficie del suelo como de la intrusión de agua de mar en los acuíferos costeros no...

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.

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.

Submarine groundwater discharge (SGD) has been implicated as a significant source of nutrients and potentially harmful substances to the coastal sea. Although the number of reported SGD sites has increased recently, their stratigraphical architecture and aquifer geometry are rarely investigated in detail. This study analyses a multifaceted dataset of offshore seismic sub-bottom profiles, multibeam and side-scan sonar images of the seafloor, radon measurements of seawater and groundwater, and onshore ground-penetrating radar and refraction seismic profiles in order to establish the detailed stratigraphical architecture of a high-latitude SGD site, which is connected to the Late-Pleistocene First Salpausselkä ice-marginal formation on the Hanko Peninsula in Finland. The studied location is characterized by a sandy beach, a sandy shore platform that extends 100–250 m seaward sloping gently to ca. 4 m water depth, and a steep slope to ca. 17 m water depth within ca. 50 m distance. The onshore radar and offshore seismic profiles are correlated based on unconformities, following the allostratigraphical approach. The aquifer is hosted in the distal sand-dominated part of a subaqueous ice-contact fan. It is interpreted that coarse sand interbeds and lenses in the distal fan deposits, and, potentially, sandy couplet layers in the overlying glaciolacustrine rhythmite, provide conduits for localized groundwater flow. The SGD takes place predominantly through pockmarks on the seafloor, which are documented on the shore platform slope by multibeam and side-scan sonar images. Elevated radon-222 activity concentrations measured 1 m above seafloor confirm SGD from two pockmarks in fine sand sediments, whereas there was no discharge from a third pockmark that was covered with a thin organic-rich mud layer. The thorough understanding of the local stratigraphy and the geometry and composition of the aquifer that have been acquired in this study are crucial for successful hydrogeological modelling and flux studies at the SGD site.

Three-dimensional geological and groundwater flow models of a submarine groundwater discharge (SGD) site at Hanko (Finland), in the northern Baltic Sea, have been developed to provide a geological framework and a tool for the estimation of SGD rates into the coastal sea. The dataset used consists of gravimetric, ground-penetrating radar and shallow seismic surveys, drill logs, groundwater level monitoring data, field observations, and a LiDAR digital elevation model. The geological model is constrained by the local geometry of late Pleistocene and Holocene deposits, including till, glacial coarse-grained and fine-grained sediments, post-glacial mud, and coarse-grained littoral and aeolian deposits. The coarse-grained aquifer sediments form a shallow shore platform that extends approximately 100–250 m offshore, where the unit slopes steeply seawards and becomes covered by glacial and post-glacial muds. Groundwater flow preferentially takes place in channel-fill outwash coarse-grained sediments and sand and gravel interbeds that provide conduits of higher hydraulic conductivity, and have led to the formation of pockmarks on the seafloor in areas of thin or absent mud cover. The groundwater flow model estimated the average SGD rate per square meter of the seafloor at 0.22 cm day⁻¹ in autumn 2017. The average SGD rate increased to 0.28 cm day⁻¹ as a response to an approximately 30% increase in recharge in spring 2020. Sensitivity analysis shows that recharge has a larger influence on SGD rate compared with aquifer hydraulic conductivity and the seafloor conductance. An increase in recharge in this region will cause more SGD into the Baltic Sea.