Suchergebnisse

18 pages, 1 table, 11 figures.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) ; Due to the widespread pollution of coastal groundwaters with fertilizers, submarine groundwater discharge (SGD) is often thought to be a large dissolved inorganic nitrogen (DIN) source to the ocean. Whether this N is autochthonous or allochthonous to the subterranean estuary (STE), the availability of large quantities of DIN can nevertheless interact with the cycling of other elements, such as carbon (C). In previous studies, we documented the discharge of large quantities of freshwater and NO3– from the mouth of an STE into the Ria Formosa lagoon (SW Iberian Peninsula). For the period covered in this study (2009–2011), the same STE site was dominated by recirculating seawater due to a prolonged fall in piezometric head in the coupled coastal aquifers. Total SGD rates remained similarly high, peaking at 144 cm day–1 at the lower intertidal during fall. We observed a progressive increase of NO3– availability within the STE associated with the recovery of piezometric head inland. Interestingly, during this period, the highest SGD-derived dissolved organic C and DIN fluxes (112 ± 53 and 10 ± 3 mmol m–2 day–1, respectively) originated in the lower intertidal. NO3– enrichment in the STE influences the benthic reactivity of fluorescent dissolved organic matter (FDOM): when seawater recirculation drives STE dynamics, only small changes in the benthic distribution of recalcitrant humic-like FDOM are observed (from −2.57 ± 1.14 to 1.24 ± 0.19 10–3 R.U. "bulk" sediment h–1) in the absence of DIN. However, when DIN is available, these recalcitrant fractions of FDOM are actively generated (from 1.32 ± 0.15 to 11.56 ± 3.39 10–3 R.U. "bulk" sediment h–1), accompanied by the production of labile protein-like FDOM. The results agree with previous studies conducted with flow-through reactor experiments at the same site and suggest that DIN enrichment in the STE enhances the metabolic turnover of sedimentary organic matter up to the point of discharge to surface waters. DIN pollution of coastal aquifers may therefore promote a contraction of the residence time of particulate organic C within the STE, driving carbon from continental storage into the sea ; Data collection and sample analysis were funded by the Portuguese Foundation for Science and Technology (FCT), the EU (FEDER), and the Portuguese Government through grant contract SFRH/BD/39170/2007 and project NITROLINKS [NITROgen loading into the Ria Formosa through Coastal Groundwater Discharge (CGD) – Pathways, turnover, and LINKS between land and sea in the Coastal Zone, PTDC/MAR/70247/2006]. Data analysis and manuscript preparation were funded by project SUBACID [SUBmarine Groundwater Discharge (SGD) impact on coastal ACIDification processes in contrasting European Atlantic Shores: toward securing ecosystem services and food production], funded by the Irish Research Council and the European Union's Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement no. 713279 through the CAROLINE program (CLNE/2017/210) ; Peer reviewed

19 pages, 2 tables, 8 figures.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) ; Subterranean estuaries (STEs), where continental groundwaters and saltwaters meet, are zones of intense biogeochemical reactivity. As such, STEs significantly modify groundwater-borne nutrient fluxes to the coastal zone. Thus, evaluating their reactive role is crucial to anticipate impacts of submarine groundwater discharge (SGD) over coastal ecosystems. Here, we studied the nitrogen biogeochemistry of two STEs with contrasting wave-exposure and redox conditions in Panxón and Ladeira beaches (Ría de Vigo, NW Iberian Peninsula). Seasonal surveys were performed at the permanently saturated zone of both beaches during low tide in February, May, July, and October 2019. Sediment was sampled and porewater samples collected using push-pull piezometers. Salinity, 222Rn and 226Ra activities were used to trace water circulation inside each beach. Porewater nitrate, ammonium, nitrite and dissolved oxygen were used to evaluate the role of these STEs as reactive sinks or sources of inorganic nitrogen. Our results showed a marked seasonal variability of water circulation inside both beaches, with strong salinity gradients in February and May and weakened circulation in July and October. The presence of a gravel layer in Panxón beach completely altered the typical structure of STEs by increasing porewater transport and mixing through the beach interior. As a result, Panxón beach profiles were highly enriched in nitrate and oxygen. Conversely, suboxic, and anoxic conditions were prevalent in Ladeira beach during the study period, with ammonium being the prevailing inorganic nitrogen form. High nitrate concentrations occurred associated to the tidal circulation cell during February and May, being the only effective mechanism of sediment oxygenation in Ladeira beach. Although nitrate reduction and production were observed in both STEs, comparison with averaged conservative mixing porewater profiles showed that Ladeira beach acted as a net nitrogen sink whereas Panxón beach acted as a net nitrogen source. The presence of a gravel layer oxygenates the interior of Panxón beach, thus limiting nitrate reduction and promoting the amplification of groundwater-borne nitrogen fluxes to the coast ; This research was supported by the SUBACID project (SUBmarine groundwater discharge (SGD) impact on coastal ACIDification processes in contrasting Atlantic Shores: towards securing ecosystem services and food production) that has received funding from the Irish Research Council and the European Union's Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement No. 713279 through the CAROLINE program (CLNE/2017/210) ; Peer reviewed

18 pages, 10 figures, 2 tables.-- This is an open access article under the terms of the Creative Commons Attribution License, ; Submarine groundwater discharge is recognized as a major source of chemicals to the global ocean, exerting large control over coastal water composition. Radon and 226Ra are used to evaluate, for the first time, the occurrence and magnitude of submarine groundwater discharge in the Ría de Vigo, a large, highly productive embayment affected by seasonal, wind-driven upwelling. The system is naturally enriched in 222Rn due to the regional granitic basement geology: high 222Rn activities (up to 106 Bq m−3) are detected in wells and boreholes in the drainage basin of the embayment. High 222Rn activities (>400 Bq m−3) are also measured in certain areas of the embayment. Comparatively lower 226Ra activities (<4 103 Bq m−3) were measured in the freshwater sources to the bay. Mass balances obtained with a box model are used to perform a volumetric estimate of fresh and saline submarine groundwater discharge in the Ría de Vigo under contrasting circulation patterns. Fresh groundwater is shown to be a relevant hydrological component of the Ria de Vigo water balance, equivalent to 9% ± 4% and 23% ± 9% of the volume discharged by tributary rivers during winter and summer, respectively. On the other hand, recirculation of seawater through permeable sediments is capable of filtering the entire upper volume of the Ria de Vigo through its seafloor in <100 days and might thus be a previously overlooked major source of regenerated solutes to the system ; This study was financed by the SUBACID project (SUBmarine groundwater discharge [SGD] impact on coastal ACIDification processes in contrasting European Atlantic Shores: toward securing ecosystem services and food production), funded by the Irish Research Council and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 713279 through the CAROLINE program (CLNE/2017/210) ; Peer reviewed

2 pages.-- International Estuarine Biogeochemistry Symposium, Vigo (Spain), 4-5th June 2019 ; Submarine Groundwater Discharge (SGD), i.e. any flow across the sedimentwater interface (Burnett et al. 2003), is recognized as a major source of continental water to the global ocean, thus exerting a major control over coastal water composition (Kwon et al. 2014). Radioisotopes are used to evaluate, for the first time, the seasonal occurrence and magnitude of SGD in Ría de Vigo, a large embayment affected by seasonal, wind-driven upwelling. The activities of 222Rn and 226Ra are determined in surface and deep waters of Ría de Vigo during five seasonal basin-scale surveys. Additionally, the activities of 222Rn and 226Ra are also seasonally determined in the aquifer systems surrounding the ría, beach porewaters, sediment incubations, atmosphere and the adjacent coastal sea. The system reveals as naturally enriched in 222Rn due to the widespread presence of granitic basement rocks in the region. High 222Rn activities (up to 105 Bq m-3) are detected in boreholes surrounding the ría, with a general strong seasonal variation in the 222Rn content. Concomitantly, high 222Rn activity (>400 Bq m-3) is measured in certain areas of the ría showing also strong seasonality. Box model, mass balance techniques are used to account for the different circulation patterns found in the embayment and thus, to perform a volumetric estimation of total and freshwater SGD in Ría de Vigo. The contribution of fresh groundwater revealed a relevant component of solute transport to the ría, equivalent to ~10% of the volume discharged through surface freshwaters to the system. On the other hand, the large magnitude of seawater recirculating through permeable sediments, determined by the circulation pattern inside the embayment and enhanced during storm events, shows the potential for being a large source of regenerated solutes to the ría ; SUBACID (SUBmarine groundwater discharge (SGD) impact on coastal ACIDification processes in contrasting European Atlantic Shores: towards securing ecosystem services and food production) has received funding from the Irish Research Council and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 713279 through the CAROLINE program (CLNE/2017/210) ; Peer reviewed