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75 pages, Radionuclides, both from natural and anthropogenic origin, are powerful ocean tracers that provide key information on fluxes, pathways and time scales of marine processes. Their added value compared to hydrographic parameters (e.g., temperature and salinity) relies either on their known rates of radioactive decay and production or on their time-variable releases from sources. Both aspects introduce a temporal dimension that allows quantifying rates or time scales of marine processes. Their wide range of half-lives and historical inputs, together with their physicochemical characteristics allow tracing a broad spectrum of marine processes. This chapter aims at providing an overview of the application of radionuclides as tracers of ocean processes. The chapter is structured in four sections: The first part reviews the main principles of radioactivity and the origin of radionuclides. The second section introduces the key aspects that allow using radionuclides as ocean tracers, followed by (third section) three real and contemporary instructive examples that cover different marine processes and require radionuclides with specific properties: i) thorium-234/uranium-238 (234Th/238U) pair to quantify the biological pump, ii) radium (Ra) isotopes to estimate the magnitude of submarine groundwater discharge, and iii) iodine-129 (129I) to investigate the large-scale ocean circulation. Finally, this chapter provides a summary of the different methods and techniques used to measure radionuclides in seawater

Submarine groundwater discharge (SGD) links terrestrial and marine systems, but has often been overlooked in coastal nutrient budgets because it is difficult to quantify. In this Review, we examine SGD nutrient fluxes in over 200 locations globally, explain their impact on biogeochemistry and discuss broader management implications. SGD nutrient fluxes exceed river inputs in ~60% of study sites, with median total SGD fluxes of 6.0 mmol m−2 per day for dissolved inorganic nitrogen, 0.1 mmol m−2 per day for dissolved inorganic phosphorus and 6.5 mmol m−2 per day for dissolved silicate. SGD nitrogen input (mostly in the form of ammonium and dissolved organic nitrogen) often mitigates nitrogen limitation in coastal waters, since SGD tends to have high nitrogen concentrations relative to phosphorus (76% of studies showed N:P values above the Redfield ratio). It is notable that most investigations do not distinguish saline and fresh SGD, although they have different properties. Saline SGD is a ubiquitous, diffuse pathway releasing mostly recycled nutrients to global coastal waters, whereas fresh SGD is occasionally a local, point source of new nutrients. SGD-derived nutrient fluxes must be considered in water quality management plans, as these inputs can promote eutrophication if not properly managed. Submarine groundwater discharge transports nutrients from terrestrial to marine systems, but is often ignored in coastal biogeochemistry. In this Review, the fluxes, impacts and management implications of this discharge are examined and compared with riverine fluxes globally.

20 pages, 8 figures, 2 tables, supporting Information https://doi.org/10.1111/mec.16695.-- Data availabitiy statement: DNA sequences and associated metadata: European Nucleotide Archive (ENA) under accession numbers PRJEB52186. The environmental metadata and the nonrarefied ASV and taxonomic tables are provided as Tables S2–S4, Subterranean estuaries are biogeochemically active coastal sites resulting from the underground mixing of fresh aquifer groundwater and seawater. In these systems, microbial activity can largely transform the chemical elements that may reach the sea through submarine groundwater discharge (SGD), but little is known about the microorganisms thriving in these land-sea transition zones. We present the first spatially-resolved characterization of the bacterial assemblages along a coastal aquifer in the NW Mediterranean, considering the entire subsurface salinity gradient. Combining bulk heterotrophic activity measurements, flow cytometry, microscopy and 16S rRNA gene sequencing we find large variations in prokaryotic abundances, cell size, activity and diversity at both the horizontal and vertical scales that reflect the pronounced physicochemical gradients. The parts of the transect most influenced by freshwater were characterized by smaller cells and lower prokaryotic abundances and heterotrophic production, but some activity hotspots were found at deep low-oxygen saline groundwater sites enriched in nitrite and ammonium. Diverse, heterogeneous and highly endemic communities dominated by Proteobacteria, Patescibacteria, Desulfobacterota and Bacteroidota were observed throughout the aquifer, pointing to clearly differentiated prokaryotic niches across these transition zones and little microbial connectivity between groundwater and Mediterranean seawater habitats. Finally, experimental manipulations unveiled large increases in community heterotrophic activity driven by fast growth of some rare and site-specific groundwater Proteobacteria. Our results indicate that prokaryotic communities within subterranean estuaries are highly heterogeneous in terms of biomass, activity and diversity, suggesting that their role in transforming nutrients will also vary spatially within these terrestrial–marine transition zones, This work was funded by the Spanish Ministry of Science, Innovation and Universities (MICINN) through the GRAMMI project (RTI2018-099740-J-I00), the Ramon y Cajal contract (RYC2019-026758-I) and partly by the project MEDISTRAES III (PID2019-110311RB-C22 and PID2019-110212RB-C21). Additional financial support was provided by grants SPIP2020-02595 (Ministry for the Ecological Transition and the Demographic Challenge [MITECO]) with funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). JGO acknowledges the financial support of the Spanish Ministry of Science, Innovation and Universities, through the “Maria de Maeztu” programme for Units of Excellence (CEX2019-000940-M). VR acknowledges financial support from the Beatriu de Pinós postdoctoral programme of the Catalan Government (2019-BP-00241). AAK acknowledges financial support from ICTA “Unit of Excellence” (MinECo, MDM2015-0552-17-1) and PhD fellowship, BES-2017-080740. The coauthor AF is a Serra Húnter Fellow. MDF acknowledges the economic support from the FI-2017 fellowships of the Generalitat de Catalunya autonomous government (2017FI_B_00365). The authors would like to thank the support of the Generalitat de Catalunya to MERS (2017 SGR-1588), GHS (2017 SGR 1485) and 2017SGR/156, for additional fundin

Anchialine caves are common in Mediterranean karstic shorelines and elsewhere, delivering point-source fresh groundwater and nutrients to the coastal ocean. Here, we first quantified submarine groundwater discharge (SGD) in a typical karstic system (Zaton Bay, Croatia) receiving groundwater from anchialine caves using a radon (222Rn) mass balance model. We then combine our new observations with the literature to provide a Mediterranean-scale estimate of karstic fresh SGD nutrient fluxes. We found that SGD and related nutrient fluxes in the upper brackish layer were much higher than those in the underlying layer in Zaton Bay. In the upper brackish layer, both SGD (m d−1) and associated nutrient fluxes (mmol m−2 d−1) in the wet season (SGD: 0.29–0.40; DIN: 52; DIP: 0.27) were significantly higher than those in the dry season (SGD: 0.15; DIN: 22; DIP: 0.08). Red tides were observed in the wet season but not in the dry season. Nutrient budgets imply that SGD accounted for >98% of the total dissolved inorganic nitrogen (DIN) and phosphorous (DIP) sources into Zaton Bay. These large SGD nutrient fluxes with high N/P ratios (190–320) likely trigger and sustain red tide outbreaks. Combining our results with 30 previous studies in the region revealed that point-source DIN and DIP fluxes via karstic fresh SGD may account for 8–31% and 1–4%, respectively, of riverine inputs in the Mediterranean Sea. Overall, we demonstrate the importance of karstic SGD as a source of new nutrients with high N/P ratios to the Mediterranean Sea and emphasize how SGD lagging precipitation can drive red tide outbreaks.

Mining impacts on coastal environments have been extensively studied around the world. However, the role of Submarine Groundwater Discharge (SGD) and Porewater Exchange (PEX) as pathways for pollutants from mining waste deposits into seawater has been largely overlooked. Portmán Bay is located in the Cartagena-La Unión Pb-Zn sulphur mining district in Murcia, SE of Spain. The disposal of about 60 million tons of metal-rich mine tailings from 1957 to 1990 led to the infill of most of the bay. Although the effects of metals on indicator organisms have been shown previously, there is a major lack of knowledge on the release of dissolved metals from the emerged tailing deposit into the sea, more than 25 years after the closure of the mining activities. Samples for Ra isotopes (Ra, Ra, Ra and Ra) and dissolved metals (Ag, Cd, Co, Pb, Zn) were analyzed in porewaters and seawater in order to separately estimate SGD and PEX driven dissolved metal fluxes. Our results show a continuous release of dissolved metals into the sea driven by both PEX and SGD. Most of dissolved metals are remobilized and released into the water column by PEX, which is a ubiquitous mechanism acting along the shoreline. Although SGD only represents 13% of the water flow, it drives large fluxes of dissolved Fe into the sea, mainly restricted to the west side of the bay. Large inputs of dissolved Fe from the anoxic tailings deposit trigger a massive precipitation of iron hydroxides that enables the removal of most dissolved metals from the water column. This study highlights the role of PEX and SGD as significant mechanisms for the land to ocean transfer of dissolved metals from coastal mine tailings deposits., We want to express our gratefulness to “Liga de Vecinos” of Portmán Bay for their help. This project has been funded by the Spanish projects NUREIEV (CTM2013-44598-R) and NUREIEVA (CTM2016-75953-C2-1-R). The authors also acknowledge support from Generalitat de Catalunya autonomous government through its funding schema to excellence research groups (grants 2017 SGR 1588, 2014 SGR 1356 and 2017 SGR 315). This work is a contribution to ICTA ‘Unit of Excellence’ (MinECo, MDM2015-0552). V Rodellas acknowledges financial support from the Beatriu de Pinós postdoctoral programme of the Catalan Government (2017-BP-00334).

Coastal environments have experienced a rapid transformation due to the expansion of tourism. This growth may enhance problems as over-saturation of spaces or environmental pollution. One of the main problems is associated with the collapse of environmental infrastructures, which may become saturated during high seasons. Indeed, wastewater treatment plants (WWTP) can be located in coastal areas delivering high concentrations of nutrient effluents into the marine environment. Alternatively, WWTP effluents are introduced into coastal aquifers via injection wells, given that the geological matrix is used to filter naturally the transported effluent solutes. However, the injection of significant amounts of WWTP effluents can modify the hydrogeological dynamics and enrich substantially the solute concentrations in groundwaters. Zones with a hydraulic connection between the coastal aquifer and the sea, these contaminated groundwaters may be transferred to coastal environments via Submarine Groundwater Discharge (SGD). Thus, SGD may act as a pathway delivering part of the WWTP-derived nutrients and pollutants into the marine environment, which may lead to eutrophication or harmful algal blooms. More importantly, such process may become threatening for society when the discharge occurs into bathing waters, affecting the ecosystem and perception of stakeholders.In this study, we evaluate the role of SGD as a conveyor of nutrients from a karstic coastal aquifer affected by the injection of WWTP effluents to the Deià cove in Mallorca (Balearic Islands). Results show that the tourism seasonality changes the coastal aquifer natural dynamics during the dry season, delivering via SGD, nutrients concentrations above the maximum limits established by the Spanish and European water framework directives. Due to those enriched nutrient fluxes, the coastal water ecosystem has registered the highest values of ∂15N in Posidonia oceanica in the Balearic Islands and suffers periodic algal blooms, creating a conflict among stakeholders.

Altres ajuts: acords transformatius de la UAB Unidad de excelencia María de Maeztu CEX2019-000940-M Submarine Groundwater Discharge (SGD) is recognized as a fundamental hydrological process that supports many coastal biogeochemical cycles and social-ecological systems. However, very little has been investigated about how SGD affects society and, specifically, human well-being. This study systematically examines the published scientific literature on the social implications of SGD by using an Ecosystem Service (ES) perspective. Coastal services provided by ecosystems dependent on SGD are analyzed and clustered in the four main categories of Ecosystem Services (i.e., Provisioning, Supporting, Regulating and Cultural), which are in turn divided into subcategories defined as outcomes. This allows identifying and discussing both benefits and threats to coastal societies resulting from SGD outcomes. From the 1532 articles initially reviewed, the most frequently mentioned category was the supporting services (835) due to the mainstream trend in scientific literature to focus on the role of SGD as a process influencing coastal biogeochemical cycles. Conversely, cultural ES were mentioned in only 49 cases, which should not necessarily be interpreted as a lack of research or interest in this topic, but that this type of references are often not found in the scientific literature but in the grey literature. A detailed publication review was additionally conducted, identifying 114 case studies from 96 different locations worldwide that reported cases in which SGD had social implications on the well-being. Our review also shows how the different types of Ecosystem Services can have multiple synergies and trade-offs between them, resulting in unequal impacts among stakeholder groups. Overall, this study identifies research gaps related to Ecosystem Services provided by SGD as well as opportunities for further studies, while developing an analytical framework that relies on the Ecosystem Services approach to guide future research on the social implications of SGD.

International audience; The Radium Delayed Coincidence Counter (RaDeCC) is one of the most extensively used equipment for measuring 223Ra and 224Ra activities in water and sediment samples. Samples are placed in a closed He-circulation system that carries the Rn produced by the decay of Ra to a scintillation cell. Each alpha decay recorded in the cell is routed to an electronic delayed coincidence system which enables the discrimination of 223Ra and 224Ra. In this study, the measurement and quantification methods using the RaDeCC system are assessed through analyses of registered data in different RaDeCC systems worldwide and a set of simulations. Results of this work indicate that the equations used to correct for 223Ra and 224Ra cross-talk interferences are only valid for a given range of activities and ratios between isotopes. Above certain limits that are specified in this study, these corrections may significantly overestimate the quantification of 223Ra and 224Ra activities (up to ~40% and 30%, respectively), as well as the quantification of their parents 227Ac and 228Th. High activities of 226Ra may also produce an overestimation of 224Ra activities due to the buildup of 222Rn, especially when long measurements with low activities of 224Ra are performed. An improved method to quantify 226Ra activities from the buildup of 222Rn with the RaDeCC system is also developed in this study. Wethus provide a new set of guidelines for the appropriate quantification of 223Ra, 224Ra, 227Ac, 228Th, and 226Ra with the RaDeCC system.

International audience; Porewater fluxes, including fresh groundwater discharge and circulation of surface waters through sediments, are increasingly documented to play an important role in hydrological and biogeochemical cycles of coastal water bodies. In most studies, the magnitude of porewater fluxes is inferred from geochemical tracers, but a detailed understanding of the underlying physical forces driving these fluxes remains limited. In this study, we evaluate the mechanisms driving porewater fluxes in the shallow coastal La Palme lagoon (France). We combined measurements of variations of salinity and temperature in the subsurface with 1-dimensional fluid, salt and heat transport models to evaluate the dynamics of porewater fluxes across the sediment-water interface in response to temporally variable forcings. Two main processes were identified as major drivers of porewater fluxes: i) temporal variations of lagoon water depths (forcing porewater fluxes up to 25 cm d−1) and ii) locally-generated wind waves (porewater fluxes of ~50 cm d−1). These processes operate over different spatial and temporal scales; Wind-driven waves force the shallow circulation of surface lagoon waters through sediments (mostly < 0.2 m), but are restricted to strong wind events (typically lasting for 1–3 days). In contrast, porewater fluxes driven by variations of lagoon water depths flush a much greater depth of sediment (>1 m). The spatial and temporal scales of driving forces will largely determine the significance of porewater fluxes, as well as their chemical composition. Thus, an appropriate evaluation of the magnitude of porewater-driven solute fluxes and their consequences for coastal ecosystems requires a solid and site-specific understanding of the underlying physical forces.

The characterization of saline water intrusion (SWI) and its hydrodynamics is a key issue to understand sub-marine groundwater discharge (SGD) and manage groundwater resources in coastal areas. To test and comparedifferent methods of characterization and monitoring, a new experimental site has been constructed in a coastalalluvial aquifer north of Barcelona city (Catalonia, Spain). The site is located between 30 and 90 m from theseashore and comprises 16 shallow piezometers organized in nests of three with depths ranging between 15 and25 m and 4 solitary piezometers. The objective of this paper is to combine different recently developed mon-itoring techniques to evaluate temporal variations in the aquifer hydrodynamics of the site at different spatialscales before and after the dry season of 2015. At the site scale,fibre optic distributed temperature sensing (FO-DTS), for thefirst time applied to study SWI, and cross-hole electrical resistivity tomography (CHERT) has beenapplied. At the meter/borehole scale, electrical conductivity of the formation has been applied not only in arepeated manner (¿time lapse¿), but also for thefirst time at relatively high frequency (1 sample every 10 min).CHERT has provided a better characterization of the seawater intrusion than electrical conductivity data ob-tained from piezometers. The combination of techniques has allowed improving the understanding of the systemby: 1) characterizing the extent and shape of SWI; 2) differentiating two different dynamics in the aquifer; and 3)identifying preferentialflow paths over different time and spatial intervals. Future challenges and the appli-cation of these techniques in other areas are also discussed., This work was funded by the projects CGL2013-48869-C2-1-R/2-R and CGL2016-77122-C2-1-R/2-R of the Spanish Government. We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the Consell Comarcal del Maresme in the construction of the research site. The authors want to thank the support of the Generalitat de Catalunya to MERS (2018 SGR-1588). This work is contributing to the ICTA ‘Unit of Excellence’ (MinECo, MDM2015-0552). Part of the funding was provided by the French network of hydrogeological observatories H+ (hplus/ore/fr/en) and the ANR project EQUIPEX CRITEX (grant ANR-11-EQPX-0011). V Rodellas acknowledges financial support from the Beatriu de Pinós postdoctoral program of the Generalitat de Catalunya (2017-BP-00334). M. Diego‐Feliu acknowledges the economic support from the FI‐2017 fellowships of the Generalitat de Catalunya autonomous government (2017FI_B_00365). This project also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 722028.

Submarine groundwater discharge (SGD) is now recognized as an important process of the hydrological cycle worldwide and plays a major role as a conveyor of dissolved compounds to the ocean. Naturally occurring radium isotopes (223Ra, 224Ra, 226Ra and 228Ra) are widely employed geochemical tracers in marine environments. Whilst Ra isotopes were initially predominantly applied to study open ocean processes and fluxes across the continental margins, their most common application in the marine environment has undoubtedly become the identification and quantification of SGD. This review focuses on the application of Ra isotopes as tracers of SGD and associated inputs of water and solutes to the coastal ocean. In addition, we review i) the processes controlling Ra enrichment and depletion in coastal groundwater and seawater; ii) the systematics applied to estimate SGD using Ra isotopes and iii) we summarize additional applications of Ra isotopes in groundwater and marine studies. We also provide some considerations that will help refine SGD estimates and identify the critical knowledge gaps and research needs related to the current use of Ra isotopes as SGD tracers.

This study presents the results of the accumulation of (210)Po and (210)Pb in fish tissues and organs in a brackish-water marshland that is characterized by high concentrations of (222)Rn and (226)Ra supplied by submarine groundwater discharge (SGD). Tissues and organs from Cyprinus carpio, Chelon labrosus and Carassius auratus in the wetland were significantly enriched by both (210)Pb and (210)Po (up to 55 and 66 times, respectively) compared to blanks. The major input route of (210)Pb and (210)Po into the fish body seems to be through ingestion, due to the high levels of (210)Pb and (210)Po found in the gut content as well as in organs involved in digestion and metabolism (i.e. gut, kidney and hepatopancreas). Results showed that (210)Po was more accumulated in all fish tissues and organs except for the spine, which showed a higher affinity for (210)Pb, due to its capacity to replace Ca from apatite in bones. Over all the variables analyzed, fish tissues/organs and, secondarily, fish species were the most important factors explaining the concentration of radionuclides, whereas fish length and the sampling location played a minor role. The relationship of the two radionuclides varied markedly among tissues and their concentration levels were only correlated in gills, gut and, marginally, in spines. In general, the highest values of (210)Pb and (210)Po concentrations in tissues were found on C. labrosus tissues rather C. auratus and C. carpio. This study demonstrates that inputs of natural radionuclides supplied by SGD to coastal semi-enclosed areas (such as marshlands, lagoons or ponds) may significantly increase the contents of (210)Pb and (210)Po in fish tissues/organs. Thus, this study represents one of the first evidences of direct ecological effects derived from SGD.

The subterranean flow of water through sand barriers between coastal lagoons and the sea, driven by a positive hydraulic gradient, is a net new pathway for solute transfer to the sea. On the sea side of sand barriers, seawater circulation in the swash-zone generates a flux of recycled and new solutes. The significance and temporal variability of these vectors to the French Mediterranean Sea is unknown, despite lagoons constituting ~ 50% of the coastline. A one-dimensional Ra-224(ex)/Ra-223 reactive-transport model was used to quantify water flow between a coastal lagoon (La Palme) and the sea over a 6-month period. Horizontal flow between the lagoon and sea decreased from ~ 85 cm d(-1) during May 2017 (0.3 m(3) d(-1) m(-1) of shoreline) to ~ 20 cm d(-1) in July and was negligible in the summer months thereafter due to a decreasing hydraulic gradient. Seawater circulation in the swash-zone varied from 10 to 52 cm d(-1) (0.4-2.1 m(3) d(-1) m(-1)), driven by short-term changes in the prevailing wind and wave regimes. Both flow paths supply minor dissolved silica fluxes on the order of ~ 3-10 mmol Si d(-1) m(-1). Lagoon-sea water exchange supplies a net dissolved inorganic carbon (DIC) flux (320-1100 mmol C d(-1) m(-1)) two orders of magnitude greater than seawater circulation and may impact coastal ocean acidification. The subterranean flow of water through sand barriers represents a significant source of new DIC, and potentially other solutes, to the Mediterranean Sea during high lagoon water-level periods and should be considered in seasonal element budgets.

International audience; Understanding the transference of water resources within hydrogeological systems, particularly in coastal aquifers, in which groundwater discharge may occur through multiple pathways (through springs, into rivers and streams, towards the sea, etc.), is crucial for sustainable groundwater use. This research aims to demonstrate the usefulness of the application of conventional recharge assessment methods coupled to isotopic techniques for accurately quantifying the hydrogeological balance and submarine groundwater discharge (SGD) from coastal carbonate aquifers. Sierra Almijara (Southern Spain), a carbonate aquifer formed of Triassic marbles, is considered as representative of Mediterranean coastal karst formations. The use of a multi-method approach has permitted the computation of a wide range of groundwater infiltration rates (17-60%) by means of direct application of hydrometeorological methods (Thornthwaite and Kessler) and spatially distributed information (modified APLIS method). A spatially weighted recharge rate of 42% results from the most coherent information on physiographic and hydrogeological characteristics of the studied system. Natural aquifer discharge and groundwater abstraction have been volumetrically quantified, based on flow and water-level data, while the relevance of SGD was estimated from the spatial analysis of salinity, Rn-222 and the short-lived radium isotope Ra-224 in coastal seawater. The total mean aquifer discharge (44.9-45.9 hm(3) year(-1)) is in agreement with the average recharged groundwater (44.7 hm(3) year(-1)), given that the system is volumetrically equilibrated during the study period. Besides the groundwater resources assessment, the methodological aspects of this research may be interesting for groundwater management and protection strategies in coastal areas, particularly karst environments.

International audience; The circulation of seawater through permeable coastal sediments is increasingly recognized as an important source of nutrients, including dissolved silica (DSi), to the coastal ocean. Here, we utilized a Ra isotope (223 Ra, 224 Ra ex , 228 Ra) mass balance to quantify DSi fluxes driven by water circulation to a small shallow coastal lagoon (La Palme; French Mediter-ranean) during June 2016, as compared to karstic groundwater spring inputs. The DSi flux driven by lagoon water circulation (derived from 224 Ra ex) was approximately one order of magnitude greater (1900 ± 1700 mol d À1) than the DSi load of the karstic groundwater spring (250 ± 50 mol d À1) and greater than molecular diffusion (970 ± 750 mol d À1). Lagoon water circulation was a negligible source of 228 Ra, indicating that circulation-driven DSi inputs occur over a timescale of days. Offshore transects were studied to quantify fluxes of marine-derived submarine groundwater discharge (SGD) from the permeable sandy coastline adjacent to the lagoon, into the Mediterranean Sea. Surface water transects revealed near-shore enrichments of Ra and DSi, attributed to wave-setup and water exchange through the permeable beach between the lagoon and the sea. Upscaling over the 9.5 km stretch of sandy beaches results in a marine SGD-driven DSi flux of 2.3 ± 1.3 Â 10 4 mol d À1 , similar in magnitude to the Têt river during November 2016 (3.3 ± 2.4 Â 10 4 mol d À1), the largest river in the region. A positive relationship between DSi and 224 Ra ex in lagoon water and seawater, but not 228 Ra, suggests that 224 Ra ex and DSi enrichments are derived from a similar source, the sediment (i.e. lithogenic particle dissolution), operating on short timescales. A marine SGD-driven DSi flux to the Gulf of Lions (3.8 ± 2.2 Â 10 5 mol d À1) is likely continuous over time. The relatively constant DSi inputs from water circulation for the shallow lagoons and beaches along the French Mediterranean Sea

International audience; Tracer approaches to estimate both porewater exchange (the cycling of water between surface water and sediments, with zero net water flux) and groundwater inflow (the net flow of terrestrially derived groundwater into surface water) are commonly based on solute mass balances. However, this requires appropriate characterization of tracer end-member concentrations in exchanging or discharging water. Where either porewater exchange or groundwater inflow to surface water occur in isolation, then the water flux is easily estimated from the net tracer flux if the end-member is appropriately chosen. However, in most natural systems porewater exchange and groundwater inflow will occur concurrently. Our analysis shows that if groundwater inflow (Q g) and porewater exchange (Q p) mix completely before discharging to surface water, then the combined water flux (Q g 1 Q p) can be approximated by dividing the combined tracer flux by the difference between the porewater and surface water concentrations, (c p – c). If Q g and Q p do not mix prior to discharge, then (Q g 1 Q p) can only be constrained by minimum and maximum values. The minimum value is obtained by dividing the net tracer flux by the groundwater concentration, and the maximum is obtained by dividing by (c p – c). Dividing by the groundwater concentration gives a maximum value for Q g. If porewater exchange and groundwater outflow occur concurrently, then dividing the net tracer flux by (c p – c) will provide a minimum value for Q p. Use of multiple tracers, and spatial and temporal replication should provide a more complete picture of exchange processes and the extent of subsurface mixing.

International audience; Groundwater discharge in coastal karst aquifers worldwide represents a substantial part of the water budget and is a main pathway for nutrient transport to the sea. Groundwater discharge to the sea manifests under different forths, making its assessment very challenging particularly in highly heterogeneous coastal systems karst systems. In this study, we present a methodology approach to identify and quantify four forms of groundwater discharge in a mixed lithology system in southern Spain (Maro-Cerro Gordo) that includes an ecologically protected coastal area comprised of karstic marble. We found that groundwater discharge to the sea occurs via: (1) groundwater-fed creeks, (2) coastal springs, (3) diffuse groundwater seepage through seabed sediments, and (4) submarine springs. We used a multi-method approach combining tracer techniques (salinity, Ra-224, and Rn-222) and direct measurements (seepage meters and flowmeters) to evaluate the discharge. Groundwater discharge via submarine springs was the most difficult to assess due to their depth (up to 15 m) and extensive development of the springs conduits. We determined that the total groundwater discharge over the 16 km of shoreline of the study area was at least 11 +/- 3 x 10(3) m(3) d(-1) for the four types of discharge assessed. Groundwater-derived nitrate (NO3-) fluxes to coastal waters over similar to 3 km (or 20%) in a highly populated and farmed section of Maro-Cerro Gordo was 641 +/- 166 mol d(-1), or similar to 75% of the total NO3- loading in the study area. We demonstrate in this study that a multi-method approach must be applied to assess all forms of SGD and derived nutrient fluxes to the sea in highly heterogeneous karst aquifer systems.

Altres ajuts: the government of Spain and the Fulbright Commission for a post-doctoral fellowship to J.G-O. (ref 2007-0516) The approach to quantify submarine groundwater discharge using Ra isotopes generally involves developing a Ra mass balance in an estuary, bay or lagoon. In this work we present a 224Ra mass balance used to evaluate the importance of the submarine groundwater discharge (SGD) in Long Island Sound (NY, US), the third most important estuary in US, located between Long Island and Connecticut that is usually affected by summertime hypoxia in the western basin. Three surveys were conducted between April 2009 and August 2010 where 25 water stations were sampled for Ra isotopes, oxygen and Mn. Stations were oriented along 4 transects: one axial extending from the western to the eastern Sound and three longitudinal transects in the western, central and eastern Sound. The inventory of 224Ra in the water column in summer was circa 2 times greater than in winter, suggesting an increased 224Ra flux to the Sound in summer. A mass balance for 224Ra was constructed considering tidal exchange, inputs from rivers, desorption from resuspended particles, diffusive fluxes (including bioirrigation) from bottom sediments and radioactive decay in the water column. Fluxes of 224Ra from bottom sediments were measured by incubating cores under oxic conditions in a continuous flow mode such that the overlying water was circulated through a Mn-oxide fiber to maintain a constant activity of 224Ra. Fluxes from muddy sediments (comprising ~67% of the Sound bottom) ranged from 127 to 312dpmm-2d-1 and were ~60dpmm-2d-1 in sandy sediments (33% of the Sound). Incubations under hypoxic conditions showed variable fluxes depending on reduction and mobilization of Mn. The 224Ra mass balance shows a net input of Ra to the Sound of 106±50×1012dpmy-1 in spring and 244±112×1012dpmy-1 in the summer that is attributed to SGD. Elevated 224Ra values were observed near shore and in the pore fluids of the coarse beach sands along the Long Island and Connecticut coasts, suggesting that SGD driven by tidal recirculation through the beach face is a major source of 224Ra to the Sound. Seasonal variation in this source seems unlikely, and the calculated 224Ra SGD fluxes for spring and summer overlap within the uncertainties. Nevertheless we conclude that variations in the 224Ra water column inventories could be produced by seasonal changes in bioirrigation and/or redox cycling of Mn as well as sediment resuspension and desorption of 224Ra from resuspended particles, and that our mass balance underestimates these terms, particularly in the summer. 224Ra fluxes from sediments in estuaries, especially those with significant areas of muddy sediments and seasonal hypoxia, are important and should be well constrained in future uses of this isotope as a tracer for SGD.

Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peniscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra-enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra-rich groundwater have induced high activities of Ra isotopes and 222Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (224Ra, 222Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater-fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.

International audience; Submarine groundwater discharge (SGD) has been identified as an important source of Sr to the ocean and the SGD-driven Sr flux to the global ocean has been recently re-evaluated (Beck et al., 2013). However, the uncertainty of this value is still high because of the uncertainties related to the determination of SGD flow rates and the paucity of (Sr/Sr)-Sr-87-Sr-86 data in SGD end-members. As carbonates have high Sr concentrations and are subjected to intense heightened weathering, they might significantly influence the SGD input of Sr to the ocean. Here we present data on Sr concentrations and Sr-87/Sr-86 ratios in three carbonate dominated sites of the western area of the Mediterranean Sea, a semi-enclosed basin characterized by abundant coastal carbonates. The Sr-87/(86) Sr ratios in groundwater were lower compared to modern seawater (similar to 0.70916), as expected for areas dominated by carbonate lithologies. Concentrations of Sr and Sr-87/Sr-86 ratios in groundwater showed conservative mixing in the studied subterranean estuaries. By using SGD flow rates reported in the literature for the study areas, a flow-weighted fresh SGD end-member characterized by a Sr concentration of 27-30 mu M and a Sr-87/Sr-86 ratio of 0.707834-0.708020 was calculated for the eastern coast of the Iberian Peninsula. Integrating these Sr data with literature data (i.e. values of Sr concentration and Sr-87/Sr-86 ratio from other lithologies as well as SGD flow rates), we also calculated the fresh SGD-driven Sr flux to the entire Mediterranean Sea, obtaining a value of (0.34-0.83) . 10(9) mol y(-1), with a Sr-87/Sr-86 of 0.7081-0.7086. Thus, for the entire Mediterranean basin, SGD is globally a source of Sr less radiogenic compared to seawater. The SGD Sr flux to the Mediterranean Sea represents 5-6% of the SGD Sr flux to the global ocean and the Mediterranean SGD end-member has higher Sr concentration (5-12 mu M) than the global SGD end-member (2.9 mu M). This confirms the significant role of carbonate lithologies on SGD-driven Sr fluxes to seawater. The fresh SGD-driven Sr flux to the Mediterranean Sea is about 20-50% of the riverine Sr input and significantly higher than the input through atmospheric dust deposition. Therefore SGD should be considered as an important continental source of Sr to the basin. (C) 2016 Elsevier Ltd. All rights reserved.

International audience; Submarine groundwater discharge (SGD) has been recognized as an important supplier of chemical compounds to the ocean that may influence coastal geochemical cycles. Radium isotopes (Ra-223, Ra-224, Ra-226, Ra-228) and radon (Rn-222) have been widely applied as tracers of SGD. Their application requires the appropriate characterization of both the concentrations of tracers in the discharging groundwater and their distribution in the coastal water column. This study evaluates the temporal evolution of Ra isotopes and Rn-222 concentrations in a dynamic subterranean estuary of a microtidal Mediterranean coastal aquifer that experiences large displacements of the fresh-saltwater interface as a necessary initial step in evaluating the influence of SGD in coastal waters. We show that changes in groundwater salinities due to the seaward displacement of the fresh-saltwater interface produced large variations in Ra activities in groundwater (by a factor of similar to 19, similar to 14, similar to 6, and similar to 11 for Ra-223, Ra-224, Ra-226 and Ra-228, respectively), most importantly during rainfall events. In contrast, the 222Rn activities in groundwater oscillated only by a factor of 3 during these rainy periods. The large temporal variability in Ra activities hampers the characterization of the SGD end-member when using Ra isotopes as tracers, and thus presents a challenge for obtaining accurate SGD estimates. This study emphasizes the need to understand the hydrodynamics of coastal aquifers to appropriately constrain the Ra isotopes and Rn-222 concentrations in groundwater and when applying both tracers in dynamic microtidal coastal systems. (C) 2017 Elsevier B.V. All rights reserved.

International audience; Submarine groundwater discharge (SGD) to the Gulf of Bothnia, Baltic Sea, has been believed to be insignificant from hydrological models, yet geochemical investigations of SGD in this basin are limited. In this study, Ra-223, Ra-224, Ra-226, and Ra-228 a have been complemented by stable delta O-18 and delta H-2 isotopes to characterize and quantify SGD rates from the coast of Forsmark, Sweden to Oregrundsgrepen Strait (Gulf of Bothnia). In shallow bays, SGD has been traced using relations between Ra, delta H-2 and delta O-18 isotopes and salinity. Zonal SGD from deformation zones, expressed as hydraulically conductive fractures, overlain by the Borstilasen esker, a strip of conductive gravel sediment, have been traced through offshore Ra-224(xs) and Ra-226 trends. On the basis of a Ra-224(xs) mass balance, the SGD flow rate ranges from (5.5 +/- 3.0).10(3) m(3) d(-1) to (950 +/- 520).10(3) m(3) d(-1). These rates are up to two orders of magnitude higher than those determined from local hydrological models, which consider only the fresh component of SGD. From the divergence between the hydrological and Ra-224(xs) models, it is inferred that the site is influenced by a component of recirculated seawater.

Bioactive trace metals play a significant role as micronutrients in the ocean and therefore it is important to evaluate their sources. Submarine groundwater discharge (SGD) has been recognized as an input of trace metals to the coastal sea. Here, we investigated the significance of SGD as a source of dissolved trace metals (dTM) to the coastal sea in a regional area such as the North Western (NW) Mediterranean Sea. We analysed dTM concentrations in SGD end-members and incorporate data on SGD dTM concentrations and water flows reported in previous studies carried out in this area, to estimate the following ranges of SGD-driven dTM fluxes (in 10 mol y): Cd: 0.0007–0.03, Co: 0.004–0.11, Cu: 0.09–1.9, Fe: 1.8–29, Ni: 0.09–1.9, Pb: 0.002–0.06, Zn: 0.38–12. These fluxes were compared to dTM fluxes from riverine discharge and atmospheric deposition, demonstrating that SGD is a major source of dTM to the NW Mediterranean Sea. Whilst riverine inputs are limited to the surrounding of river mouths and atmospheric fluxes are distributed throughout the whole basin mainly during sporadic depositional events, SGD represents a permanent, albeit seasonally variable, source of metals to most of the coastal areas. SGD-driven dTM inputs may be even more significant, in relative terms, in other coastal regions of the Mediterranean Sea where rivers are scarce, as it is the case of the African coast and many islands. This study highlights the relevance of SGD as a source of dTM to the Mediterranean Sea and the need of its consideration in the calculation of metal budgets in the basin and in the investigation of biogeochemical cycles in coastal areas., This project has been partially funded by the European Union Seventh Framework Programme through the MetTrans Initial Training Network, Marie Curie Actions, which also provide financial support through a PhD fellowship to G.T. (EU FP7-People-2011-ITN-290336). Support provided by the Generalitat de Catalunya to MERS (2014 SGR – 1356) is also acknowledged. V.R. acknowledges financial support from the European Union's FP7 (Marie Curie Actions PCOFUND-GA-2013-609102), through the PRESTIGE programme coordinated by Campus France. The Spanish Government (MINECO) is acknowledged for support to E.G-S through a post-doctoral grant (FPDI-2013-15660) and support of ECOALFACS project (CTM2009-09581) to the ICM-CSIC. This research is also a contribution to the ANR @RAction chair (ANR-14-ACHN-0007-01) and Labex OT-Med (ANR-11-LABEX-0061) funded by the “Investissements d'Avenir” program through the A*MIDEX project (ANR-11-IDEX-0001-02) of the French National Research Agency (ANR).

11 pages, 8 figures, 3 tables, Submarine groundwater discharge (SGD) was investigated at El Gorguel Bay (Cartagena-La Unión Pb–Zn mining district, Murcia, Spain), a Mediterranean region where mine tailings have been accumulated for decades at the shoreline. At this site, groundwater may become enriched in metals prior to discharge to the coastal sea and may lead to significant releases that can contaminate the coastal environment. The distribution of dissolved metals and Ra isotopes were studied in seawater and groundwater samples collected during the summer season in 2013. Cross-shore gradients of 224Ra in the bay allowed the calculation of a SGD flow of (39 ± 14) 103 m3 day−1. SGD-driven metal fluxes were 47–180 mol day−1 km− 1 for Zn, 0.20–0.60 mol day− 1 km− 1 for Pb, 4–32 mol day− 1 km− 1 for Fe, 0.8–2.3 mol day− 1 km− 1 for Cu and 0.9–2.8 mol day− 1 km− 1 for Ni. Compared to other coastal zones not affected by mining activities, SGD-driven metal fluxes were especially significant for dissolved Zn and Pb. The magnitude of these SGD-driven metal fluxes indicates that SGD is a relevant pathway in delivering metals to the coastal environment at El Gorguel Bay. This fact highlights the importance of investigating the role of SGD as a possible source of contamination to the sea in mining districts located in the proximity of the coast., This project has been partially funded by the European Union Seventh Framework Programme, Marie Curie Actions, through the MetTrans Initial Training Network, which also provide financial support through a PhD fellowship to G.T. (EU FP7-People-2011-ITN-290336). The research has been funded partially also by the Spanish Government project NUREIEV (CTM2013-44598-R). Support from the CSIC, under the program JAE-Doc (Junta para la Ampliación de Estudios) co-funded by the Fondo Social Europeo (FSE) is acknowledged for the post-doctoral fellowship (JAEDOC038) to J.S.-E. V.R. was supported through a Ph.D. fellowship (AP2008-03044) from the Spanish Government. A Beatriu de Pinós Postdoctoral fellowship from the Generalitat de Catalunya (2011BP-B00225) and a post-doctoral grant (FPDI-2013-15660) from the Spanish Government to E.G.-S. are also acknowledged. P.M. was supported in part by a Gledden Visiting Fellowship awarded by the Institute of Advanced Studies at The University of Western Australia. The support of the Generalitat de Catalunya to MERS (2014 SGR — 1356) is also acknowledged.

The Mediterranean Sea (MS) is a semienclosed basin that is considered one of the most oligotrophic seas in the world. In such an environment, inputs of allochthonous nutrients and micronutrients play an important role in sustaining primary productivity. Atmospheric deposition and riverine runoff have been traditionally considered the main external sources of nutrients to the MS, whereas the role of submarine groundwater discharge (SGD) has been largely ignored. However, given the large Mediterranean shore length relative to its surface area, SGD may be a major conveyor of dissolved compounds to the MS. Here, we used a (228)Ra mass balance to demonstrate that the total SGD contributes up to (0.3-4.8)⋅10(12) m(3) ⋅ y(-1) to the MS, which appears to be equal or larger by a factor of 16 to the riverine discharge. SGD is also a major source of dissolved inorganic nutrients to the MS, with median annual fluxes of 190⋅10(9), 0.7⋅10(9), and 110⋅10(9) mol for nitrogen, phosphorous, and silica, respectively, which are comparable to riverine and atmospheric inputs. This corroborates the profound implications that SGD may have for the biogeochemical cycles of the MS. Inputs of other dissolved compounds (e.g., iron, carbon) via SGD could also be significant and should be investigated.

© 2015 Elsevier B.V. The influence of sediments on the determination of SGD by using Ra isotopes was investigated in the Port of Maó (Balearic Islands, NW Mediterranean). This natural harbor was selected because SGD occurs all along its southern boundary and it is covered by fine-grained sediments that are frequently resuspended due to vessel maneuvering. Comprehensive seasonal Ra mass balances were constructed for the waters of the Port of Maó using both short-lived (224Ra) and long-lived (228Ra) Ra isotopes. SGD flows to the Port of Maó obtained by using 228Ra revealed a seasonal pattern, likely dominated by the recharge cycle, with maximum SGD rates during the wet seasons ((180±100)·103m3·day-1 in fall) and minimum flows during summer ((56±35)·103m3·day-1). The results also showed that the Ra flux from bottom sediments, through diffusion and due to releases associated to resuspension events, represented a significant source of Ra to the harbor waters. This sedimentary source accounted for a major fraction of the 224Ra supplied to the system (30-90%, depending on the season), whereas the sediment influence on the 228Ra mass balance was significantly lower (10-40%) due to its slower production rate. These findings suggested that attributing Ra inputs to the water column solely to SGD in systems covered by fine-grained sediments and/or affected by processes that favor Ra exchange across the sediment-water interface might not be accurate, requiring a detailed evaluation of the sediment sources. The inputs from sediments are often difficult to quantify, but using long-lived Ra isotopes to estimate the SGD flow may minimize the effect of a poor characterization of the sediment source., This project has been partially funded by the Spanish Government Project EHRE (ref. CTM2009-08270). V.R. acknowledges financial support through a PhD fellowship (AP2008-03044) from MICINN (Spain). Authors want to thank the support of the Generalitat de Catalunya to MERS (2014 SGR-1356). Support for the research of P.M. was received through the prize ICREA Academia, funded by the Generalitat de Catalunya and by a Gledden Visiting Fellowship awarded by the Institute of Advanced Studies at the University ofWestern Australia

© 2014 American Chemical Society. Submarine groundwater discharge (SGD) and derived nutrient (NO2 -, NO3 -, NH4 +, PO4 3-, and SiO2) and trace element (Cd, Co, Cu, Fe, Mo, Ni, Pb, V and Zn) loadings to the coastal sea were systematically assessed along the coast of Majorca Island, Spain, in a general survey around the island and in three representative coves during 2010. We estimated that brackish water discharges through the shoreline are important contributors to the DIN, SiO2, Fe, and Zn budgets of the nearshore waters. Furthermore, our results showed that SGD-derived elements are conditioned by the hydrogeological formations of the aquifer and discharge type. Thus, while rapid discharges through karstic conduits are enriched in SiO2 and Zn, the large detrital aquifers of the island typically present enhanced concentrations of Fe. The estimated total annual inputs of chemicals constituents discharged by SGD to the coastal waters were as follows: DIN: 610 × 103 kg yr-1, SiO2: 1400 × 103 kg yr-1, Fe: 3.2 × 103 kg yr-1, and Zn: 2.0 × 103 kg yr-1. Our results provide evidence that SGD is a major contributor to the dissolved pool of inorganic nutrients and trace metals in the nearshore waters of Majorca., This research has been funded by the Spanish Government projects EDASE (ref CGL2008-00047/BTE) and GRADIENTS (CTM2012-39476-C02-01). D.S.-Q. was supported by the JAE-predoc program of the Spanish National Research Council (CSIC). V.R. was supported through a Ph.D. fellowship (AP2008-03044) from MICINN (Spain). P.M. was partially supported by the ICREA Academia prize, funded by the Generalitat de Catalunya. Authors want to thank the support of the Generalitat de Catalunya to MERS (2014 SGR − 1356).

Submarine Groundwater Discharge (SGD) from a detrital coastal aquifer into the adjacent marine environment was investigated in a Mediterranean bay (Palma Beach, Balearic Islands). In this region, agriculture and tourism are potential sources of groundwater contamination. A survey in the Palma Beach revealed N, Fe and chlorophyll a enhancement associated to areas of preferential groundwater discharge from the nearby coastal aquifer. Groundwater sampling from wells and coastal piezometers indicated high concentrations of dissolved inorganic nitrogen and Fe (up to 2800μmolL-1 and 8100nmolL-1, respectively). Other nutrients, such as DIP, and trace elements were not particularly elevated, which is attributed to the adsorptive characteristics of the carbonated composition of this detrital aquifer and/or the lack of major sources. Cross-shore gradients of 223,224,226Ra isotopes indicated a diffusive shore-based source of these radionuclides and allowed estimates of a SGD flow of 56,000±13,000m3d-1. Our results show that SGD is a major pathway for delivering DIN (1900mmolm-1d-1), dissolved Fe (4.1mmolm-1d-1) and, to a lesser extent, DIP (16mmolm-1d-1) into the nearshore waters. This allochthonous input may sustain a substantial phytoplankton biomass resulting in an onshore-offshore gradient (4.7-7.1mgm-3 in nearshore seawater as compared with, This project has been funded partially by the Spanish Government projects EDASE (ref. CGL2008-00047/BTE) and GRADIENTS (CTM2012-39476-C02-01). V.R. acknowledges financial support through a PhD fellowship (AP2008-03044) from MICINN (Spain). Support from a post-doctoral fellowship to E.G.-S. (EX2009-0651; Plan Nacional de I-D+i 2008–2011, Spain) is acknowledged. Support for the research of P.M. was received through the prize ICREA Academia, funded by the Generalitat de Catalunya.

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Moreno, Victoria Garcia-Solsona, Ester Masque, Pere Masque, Pere/B-7379-2008 Masque, Pere/0000-0002-1789-320X Spanish Government project EDASMAR [CGL2006-09274/HID]; Consejo de Seguridad Nuclear project [2686-SRA]; MICINN (Spain) [AP2008-03044]; ICREA Academia; Generalitat de Catalunya The authors would like to thank the assistance in field and laboratory work from our colleagues at the Laboratori de Radioactivitat Ambiental (Universitat de Barcelona). This project has been funded partially by the Spanish Government project EDASMAR (Ref. CGL2006-09274/HID) and the Consejo de Seguridad Nuclear project (Ref. 2686-SRA). V.R. acknowledges financial support through a PhD fellowship (AP2008-03044) from MICINN (Spain). Support for the research of PM was received through the prize ICREA Academia, funded by the Generalitat de Catalunya. We also want to thank the collaboration of Anna Cherta, Maribel Forner (Hotel Marina), Camping Eden, FACSA, School "Jaume Sainz" and the Peniscola Municipality. We want also to thank Gerard Carmona and Lluis Benejam for their support during fish sampling. 1 ELSEVIER SCIENCE BV AMSTERDAM MAR CHEM SI; Submarine groundwater discharge (SGD) has attracted the interest from the scientific community over the past decade for its impact on biogeochemical cycles of coastal ecosystems and/or management of water resources. SGD is associated with a flow of natural radionuclides (Ra isotopes and Rn-222), which are often used as SGD tracers that can significantly increase the natural background radiation. Although in many circumstances the discharge is produced directly to the sea and therefore the increase of natural radioactivity levels can generally be considered negligible due to a dilution processes, the discharge into coastal wetlands (marshes, coastal lagoons or ponds), with somewhat restricted exchange with the open sea, may require a detailed study of the distribution of natural radionuclides and their effects on the coastal ecosystem. The Peniscola marsh is a Mediterranean coastal wetland where such studies may be of special interest because it is fed exclusively by groundwater, mainly discharging from a deep aquifer with high natural radioactivity content. In the Peniscola marsh, brackish groundwater discharging through the wetland sediments is enriched in radionuclides to maximum values of 2.8 and 616 kBq m(-3) of Ra-226 and Rn-222, respectively. These high dissolved concentrations result in high levels of Rn-222 in air (up to 36 Bq m(-3)) and Pb-210 and Po-210 dissolved in water (20 and 5.7 Bq m(-3), respectively). These elevated levels of natural radionuclides in the Peniscola marsh are also responsible of the significant increase in Po-210 and Pb-210 contents in both fish and plants. (C) 2013 Elsevier B.V. All rights reserved.