Naturally CO2-rich mineral water springs (pouhons) in east Belgium occur in the context of the Rhenohercynian domain of the Variscan fold-and-thrust belt, mostly within the Cambro-Ordovician Stavelot-Venn Massif. The origin of the CO2 is still unclear, although different hypotheses exist. In this review study, we show pouhon waters are of the calcium bicarbonate type (~310 mg/l HCO3- on average), with notable Fe (~15 mg/l) and some Ca (~43 mg/l). Pouhon waters are primarily meteoric waters, as evidenced by H and O isotopic signature. The δ13Cof CO2 varies from -7.8 to +0.8‰ and contains up to ~15% He from magmatic origin, reflecting a combination of carbonate rocks and mantle as CO2 sources at depth. Dinantian and Middle Devonian carbonates at 2–6 km depth could be potential sources, with CO2 generated by dissolution. However, carbonates below the Stavelot-Venn Massif are only predicted by structural models that assume in-sequence thrusting, not by the more generally accepted out-of-sequence thrust models. The mantle CO2 might originate from degassing of the Eifel magmatic plume or an unknown shallower magmatic reservoir. Deep rooted faults are thought to act as preferential pathways. Overall low temperatures of pouhons (~10 °C) and short estimatedresidence times (up to 60 years) suggest magmatic CO2 is transported upwards to meet infiltrating groundwater at shallower depths, with partial to full isotopic exchange with carbonate rocks along its path, resulting in mixed magmatic-carbonate signature. Although the precise role and interaction of the involved subsurface processes remains debatable, this review study provides a baseline for future investigations.
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RBINS Staff Publications 2020
WKTRADE3 developed methods and data flows that allow the assessment of seabed abrasion, economic value, weight of landings and impact on the seabed of mobile bottom-contacting gears in European waters by MSFD broad habitat type and métier. This report provides regional-specific assessments of pressure and impact of bottom-contacting fishing gears on the seabed and of trade-offs between fisheries and seafloor habitat protection. We also present an analysis of spatial and temporal variation in core fishing grounds, and review and evaluate any potential consequences to the ecosystem that could arise, if greater areas of seabed are left undisturbed by bottom fishing. An attempt was made to disaggregate variable costs from the STECF Annual Economic Report out on VMS data. The assessment covers four MSFD (sub)regions, 22 sub-divisions and four countries from Mediterranean and Black Sea. It is spanning from Norway and Finland in the North to Bulgaria in the south. For all areas, the surface abrasion data were avail-able for at least one year. For the Greater North Sea and Baltic Sea, it was possible to perform a complete analysis, while in the other regions data availability was more limited and it was not possible to assess the seabed impact. The impact of mobile bottom-contacting gears (MBCG) on seabed biota was assessed using two different methods and the percentage unfished c-squares was used as an indicator of fishing pressure. The average fishing intensity varies widely between habitat types and regions. Landings per swept area, and landings per unit impact also vary be-tween métiers by an order of magnitude. Effort reductions resulted in different responses between the two impact indicators and the fishing pressure indicator. For PD, the reduction of effort resulted in proportional reductions between benthic impact and fisheries value. For the two other indicators, L1 and percentage area unfished, the relationship between the weight/value and the indicators was not linear, meaning that larger improvements in the indicators could be obtained at small decreases in fisheries landings. There are many other direct and indirect benefits to eco-system and ecosystem services that could result from a reduction in MBCG, but currently the methods and data are not available to quantify these at the required spatial scale. Collectively, ICES expert groups produce many valuable reports each year. Some of these are very long (up to 1000 pp.). As much of the target audience will not have time to read the whole of each document, it is imperative that reports start with a clear, succinct, and factual executive summary that presents the key issues addressed in the main report.
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RBINS Staff Publications 2021
