Periodic Reporting for period 1 - KARST (KArstic submarine fReshwater Springs)
Periodo di rendicontazione: 2022-09-01 al 2024-08-31
Groundwater acts as a critical link between onshore and offshore environments, connecting freshwater systems to the saline oceans. Coastal aquifers are increasingly under pressure due to expanding coastal populations and growing variability in precipitation and recharge. As freshwater resources in these areas become more scarce, the threat of saltwater intrusion intensifies, and offshore freshened groundwater becomes a critical resource. Meteoric groundwater flow underneath the ocean, with coastal and submarine freshwater springs, as well as the inflow of saltwater into onshore aquifers, are common phenomena observed in coastal regions across the world. Nonetheless, the groundwater flow from land underneath and into the sea and the recharge of offshore groundwater resources remains veiled from our eyes and especially urban areas pose unique challenges for remote sensing techniques to characterise flow pathways for proper management. Groundwater extraction on land and reduction of SGD below a critical limit can induce the inflow of saltwater into the aquifer. In karstic coastal aquifers, submarine groundwater springs are important indicators of the extremely heterogeneous groundwater distribution in the subsurface, where turbulent and fast-flowing groundwater through conduits and caves often results in variable spring discharge and water quality. Despite the importance of submarine groundwater discharge in global hydrology, localizing submarine springs and predicting saltwater inflow into coastal aquifers remains difficult. The aim of this action was to
1)develop new methodological approaches to detect, characterise and quantify submarine springs
2)characterise the architecture of amphibious karst groundwater systems and determine the offshore recharge capabilities
3)to assess the impact of SGD seafloor morphology, habitats, and seagrass distribution
1)develop new methodological approaches to detect, characterise and quantify submarine springs
2)characterise the architecture of amphibious karst groundwater systems and determine the offshore recharge capabilities
3)to assess the impact of SGD seafloor morphology, habitats, and seagrass distribution
As part of the KARST project we investigated the groundwater flow from land to sea, the spatial distribution of SGD sites and its effects on the benthic habitats at four different study sites. We integrated a wide range of datasets and concepts from different disciplines (e.g. geomorphology, remote sensing, geophysics, biology and geostatistics) to assess the spatial variability of SGD and the movement of groundwater into the ocean. Our interdisciplinary methodology makes use of the most appropriate measurement techniques for individual water-depths and has the potential to be applied in many locations worldwide where it will not only be crucial for karstic environments but also for other geological areas where SGD occurs from point sources (e.g. volcanic islands). As freshwater becomes increasingly depleted in coastal areas and offshore freshened groundwater a more valued resource, our newly acquired data and methodologic approach provides additional monitoring options and a greater understanding of SGD to assist proper management of this potential future resource.
The four study sites investigated during the project were Veracruz (Mexico), Antalya (Türkiye), Eckernförde (Germany), and Wellington (New Zealand).
Offshore Mexico, the RV Justo Sierra undertook a voyage between the 1st and 12th of February 2023 to explore SGD in the shelf offshore Veracruz and to determine the effects of the SGD on the local environments and habitats. The data shows a previously unknown large offshore extension of a shallow coral reef system. It appeats that this reef system is closely associated to submarine springs which were monitored with deployed mini CTDs. The morphological analysis additionally shows pockmark features that suggest fluid flow from the seabed.
Offshore and onshore Antalya (Türkiye) we acquired an extensive geophysical dataset. Here we employed an innovative integration of offshore and onshore electrical resistivity and hydroacoustic techniques. This dataset allows us to investigate the dynamic interactions between fresh and salty groundwater across the land-ocean boundary. Together with our Turkish colleagues we were able to identify and characterise submarine springs in the bay, find areas where offshore groundwater is recharged from land and also identify regions where saltwater is intruding into the coastal aquifer on land.
In Eckernförde Bay we used satellite remote sensing techniques in combination with onshore electromagnetic induction data to assess the influence of SGD on local seagrass meadows. Using the electromagnetic induction data from the coast, we were able to identify regions of high and low SGD levels along the shoreline. Additionally, multibeam bathymetric data was used to identify pockmarks indicative of SGD offshore. The onshore EMI data and the offshore identification of pockmarks were remarkably good. We are therefore convinced, that we can determine areas of enhanced groundwater outflow into the Baltic Sea. The distribution of seagrass was previously assessed via satellite images and diver transects. We included detections of seagrass from existing multibeam bathymetric data. We could not find any correlation between the distribution of seagrass and the volume of SGD along the coastline.
Offshore Wellington (New Zealand), a well-defined onshore aquifer system extends beneath the harbour, where substantial amounts of freshwater seep out from the ocean floor. Here recently the first attempts worldwide have been made to use the offshore groundwater as a future source of drinking water. HWe observed several hundred seafloor depressions (pockmarks) that we attribute to continuous seepage of gas and groundwater from the seafloor. Enhanced hydroacoustic reflections in the water column within and above the pockmarks indicate suspended sediment particles, which are likely kept in suspension by discharging groundwater and density boundaries.
The four study sites investigated during the project were Veracruz (Mexico), Antalya (Türkiye), Eckernförde (Germany), and Wellington (New Zealand).
Offshore Mexico, the RV Justo Sierra undertook a voyage between the 1st and 12th of February 2023 to explore SGD in the shelf offshore Veracruz and to determine the effects of the SGD on the local environments and habitats. The data shows a previously unknown large offshore extension of a shallow coral reef system. It appeats that this reef system is closely associated to submarine springs which were monitored with deployed mini CTDs. The morphological analysis additionally shows pockmark features that suggest fluid flow from the seabed.
Offshore and onshore Antalya (Türkiye) we acquired an extensive geophysical dataset. Here we employed an innovative integration of offshore and onshore electrical resistivity and hydroacoustic techniques. This dataset allows us to investigate the dynamic interactions between fresh and salty groundwater across the land-ocean boundary. Together with our Turkish colleagues we were able to identify and characterise submarine springs in the bay, find areas where offshore groundwater is recharged from land and also identify regions where saltwater is intruding into the coastal aquifer on land.
In Eckernförde Bay we used satellite remote sensing techniques in combination with onshore electromagnetic induction data to assess the influence of SGD on local seagrass meadows. Using the electromagnetic induction data from the coast, we were able to identify regions of high and low SGD levels along the shoreline. Additionally, multibeam bathymetric data was used to identify pockmarks indicative of SGD offshore. The onshore EMI data and the offshore identification of pockmarks were remarkably good. We are therefore convinced, that we can determine areas of enhanced groundwater outflow into the Baltic Sea. The distribution of seagrass was previously assessed via satellite images and diver transects. We included detections of seagrass from existing multibeam bathymetric data. We could not find any correlation between the distribution of seagrass and the volume of SGD along the coastline.
Offshore Wellington (New Zealand), a well-defined onshore aquifer system extends beneath the harbour, where substantial amounts of freshwater seep out from the ocean floor. Here recently the first attempts worldwide have been made to use the offshore groundwater as a future source of drinking water. HWe observed several hundred seafloor depressions (pockmarks) that we attribute to continuous seepage of gas and groundwater from the seafloor. Enhanced hydroacoustic reflections in the water column within and above the pockmarks indicate suspended sediment particles, which are likely kept in suspension by discharging groundwater and density boundaries.
In conclusion, we find that SGD has severe effects not only on the seafloor morphology but also on the water columns turbidity and reflectivity. Discharging freshwater from submarine springs during this project permits the settling of particles, keeping them buoyant and increasing turbidity. SGD also removes fine grained sediments from the seafloor creating new and different habitats on the seafloor where rocks become exposed and provide morphological shelter for juvenile fish. We were able to visualize and localize the groundwater flow from land to sea and to determine risks of saltwater intrusions along urban coastlines where groundwater remote sensing techniques are normally challenging to apply. By combining offshore hydroacoustic and electric measurements with onshore geological and hydro-geophysical investigations the recharge and architectural characteristics of an amphibious karstic groundwater system were determined, visualized and located. Our findings contribute valuable insights for water management strategies with implications for safeguarding freshwater resources and mitigating the risk of saltwater intrusions.