Chemical inputs from a karstic submarine groundwater discharge (SGD) into an oligotrophic Mediterranean coastal area

Variability of the trophic state in a coastal reef system associated with submarine groundwater discharge in the Mexican Caribbean

Submarine groundwater discharges (SGD) have been associated with important sources of nutrients between the land and oceans that can generate eutrophication conditions. This study aims to analyze the behavior of nitrogen and phosphorus using the mixing curve method, to examine the variation of the trophic state using the Karydis Index, and to evaluate the δ15N in benthic organisms to trace the origin of nitrogen in neap tide (November) and spring tide (January) in the Manatí Cenote, and Nohoch-Teek reef lagoon in the Mexican Caribbean. Nitrogen and phosphate enrichment was in the Manatí Cenote during neap and spring tides. This enrichment was particularly noticeable in the reef lagoon during low tides in the areas influenced by SGD. In the Cenote, differences in the nitrate trophic state were observed, indicating an eu-mesotrophic condition during neap tide and a mesotrophic condition during spring tide. However, no significant differences were observed for ammonium (oligo-mesotrophic), nitrites, or phosphate compounds (oligotrophic). The trophic state reef lagoon exhibited a similar pattern but with different spatial variations. In both systems, phosphorus was a limiting nutrient, while δ15N suggested anthropogenic nitrogen uptake by several benthic organisms.

Comparing nearshore and embayment scale assessments of submarine groundwater discharge: Significance of offshore groundwater discharge as a nutrient pathway

Submarine groundwater discharge (SGD) can influence biogeochemical cycles in coastal seas by delivering nutrients from the seafloor. Comparison between the nearshore and embayment scale assessments of SGD against river water discharge would be crucial for understanding biogeochemical impacts on the coastal seas because the discharge pattern (non-point or point pathway) is different. Here, we quantified SGD contribution to rivers in nutrient budgets at two scales within a coastal embayment (Obama Bay, Japan) by mass balance models of radon and radium isotopes. We then compared the SGD contribution between the two scales by the meta-analysis for regional data sets conducted in nearshore and embayment scales. The estimated SGD rates in the nearshore and embayment scales in the bay were 7.8 cm d-1 and 20.0 cm d-1, indicating that offshore SGD was more significant than nearshore. The ratios of nutrient fluxes derived from SGD to rivers (SGD:River) in the nearshore scale were 1.7 for dissolved inorganic nitrogen (DIN), 3.0 for phosphorus (DIP), and 0.5 for silica (DSi), while those in the embayment scale increased to 10.4 for DIN, 18.5 for DIP, and 3.9 for DSi. This result indicates that SGD-derived nutrients become more important at larger spatial scales. Meta-analysis revealed that the difference in the contribution of SGD to rivers was affected by the seafloor size and there was no significant difference in SGD rates between nearshore and embayment scale studies. However, our regional study shows the site-specific pattern that SGD rates in the embayment scale were higher than those in the nearshore scale. Overall, we clarified that SGD can be a crucial nutrient pathway for coastal embayments regardless of the spatial scales and contribute to coastal nutrient biogeochemistry in more offshore areas.

Groundwater contamination pathways of phthalates and bisphenol A: origin, characteristics, transport, and fate - A review

Phthalic acid esters (PAEs) or phthalates and bisphenol A (BPA) are emerging organic contaminants (EOCs) that may harm biota and human health. Humans can be exposed to these contaminants by drinking water consumption from water sources such as groundwater. Before their presence in aquifer systems, phthalates and BPA can be found in many matrices due to anthropogenic activities, which result in long-term transport to groundwater reservoirs by different mechanisms and reaction processes. The worldwide occurrence of phthalates and BPA concentrations in groundwater have ranged from 0.1 × 10^-3 to 3 203.33 µg L^-1 and from 0.09 × 10^-3 to 228.04 µg L^-1, respectively. Therefore, the aim of this review is to describe the groundwater contamination pathways of phthalates and BPA from the main environmental sources to groundwater. Overall, this article provides an overview that integrates phthalate and BPA environmental cycling, from their origin to human reception via groundwater consumption. Additionally, in this review, the readers can use the information provided as a principal basis for existing policy ratification and for governments to develop legislation that may incorporate these endocrine disrupting compounds (EDCs) as priority contaminants. Indeed, this may trigger the enactment of regulatory guidelines and public policies that help to reduce the exposure of these EDCs in humans by drinking water consumption.

Sorption methods in marine radiochemistry

The review presents the general methodology of using sorption methods to solve problems of marine radiochemistry, including sampling, preconcentration and radiochemical preparation and methods for measuring the activity of radionuclides. The possible methodological errors at various stages of sampling and sample concentration are discussed. The most widely used artificial (90Sr, 134Cs, 137Cs, 239Pu, 240Pu), natural (210Pb, 210Po; radium quartet: 223Ra, 224Ra, 226Ra, 228Ra; thorium isotopes, mainly 234Th) and cosmogenic (7Be, 32P, 33P) radiotracers are considered. The sorption of uranium from seawater is not addressed, since its concentration in seawater is usually calculated from the known dependence of uranium concentration on seawater salinity.

The bibliography includes 200 references.

Submarine karstic springs as a source of nutrients and bioactive trace metals for the oligotrophic Northwest Mediterranean Sea

Groundwater springs in karstified carbonate aquifers are known to transport carbon, nutrients and trace elements to the coastal ocean. The biogeochemical significance of submarine karstic springs and their impact on coastal primary production are often difficult to quantify. We investigated several karstic springs, including the first-order Port-Miou spring, in an urbanized watershed that is also severely impacted by sewage effluent (Calanques of Marseille-Cassis, France). Karstic springs were elevated in major nutrients and bioactive trace metals over Mediterranean seawater, with relatively low concentration ranges. Groundwater NO₃^- was likely derived from atmosphere-aquifer interactions, while DOC:DON ratios reveal that NO₂^- and NH₄⁺ was autochthonously produced during mixing between karst groundwater and seawater. Submarine groundwater discharge (SGD) during March 2018 (wet season, baseflow conditions) was 6.7 ± 2.0 m³ s^-1 for the entire investigated coastline, determined from simultaneous ²²⁴Ra and ²²⁶Ra mass balances. The contribution of groundwater PO₄^3-, the major limiting nutrient of the Mediterranean Sea, sustained only 1% of primary production adjacent to sewage outfall, but between 7 and 100% of the local primary production in areas that were not impacted by sewage. Groundwater and seawater Fe:DIN and Fe:DIP ratios suggest that Fe was not a limiting micro-nutrient during the period of study, where bioactive trace metal fluxes were dominated by sewage and atmospheric deposition, although excess Fe from groundwater may locally enhance N fixation. Groundwater solute fluxes may easily vary by a factor of two or more over time because karst aquifers are sensitive to precipitation, as is the case of the regional carbonate karstified aquifer of Port-Miou, highlighting the critical importance of properly characterizing nutrient and trace metal inputs in these coastal environments.

Remobilization of dissolved metals from a coastal mine tailing deposit driven by groundwater discharge and porewater exchange

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 (²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra) 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 Fe²⁺ 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.

Bacterial and Archaeal Assemblages from Two Size Fractions in Submarine Groundwater Near an Industrial Zone

Nutrients and organic pollutants transported by submarine groundwater discharge (SGD) play a significant role in controlling water quality, and can lead to the concerned deleterious effects on marine ecosystems. Subterranean estuaries are complicated habitats of diverse microbial communities that mediate different biogeochemical processes. However, there is less information on how microorganisms mediate biogeochemical cycles in the submarine groundwater system. In this study, we investigated the changes in bacterial and archaeal assemblages from two size fractions (0.2–0.45 μm and >0.45 μm) in the submarine groundwater of Qinzhou Bay, China. Phylogenetic analysis showed that Bathyarchaeota was dominant in archaeal communities in the >0.45 μm size fraction, but was seldom in the 0.2–0.45 μm fraction. The co-occurrence of sequences belonging to Bathyarchaeota and Methanosaeta was found in the >0.45 μm size fraction. Since a gene encoding acetate kinase of Bathyarchaeota is involved in acetate production, and acetate is also a necessary growth factor for Methanosaeta, the acetate produced by Bathyarchaeota can provide food or energy sources for Methanosaeta in this very >0.45 μm size fraction. The most abundant bacterial sequences in the >0.45 μm size fraction was closely related to biomineral iron-oxidizing Gallionella spp., whereas the dominant bacterial sequences in the 0.2–0.45 μm fraction were affiliated with Limnohabitans spp., which can utilize dissolved organic matter as an important source of growth substrates. Notably, approximately 10% of the bacterial sequences in both of the two size fractions belonged to Novosphingobium spp., which plays an important role in the degradation of pollutants, especially aromatic compounds. Furthermore, the predictive functional profiling also revealed that the pathways involved in the degradation of aromatic compounds by both bacteria and archaea were identified. The presence of nutrients or pollutants in our study site provides different substrates for the growth of the specific microbial groups; in turn, these microbes may help to deplete pollutants to the ocean through submarine groundwater. We suggest that these specific microbial groups could be potential candidates for effective in situ bioremediation of groundwater ecosystems.

Mobile underwater in situ gamma-ray spectroscopy to localize groundwater emanation from pockmarks in the Eckernförde bay, Germany

Eckernförde Bay in the Baltic Sea is well-known for the pockmarks areas which are located in the centre and off the southern shore-line of the bay emanating groundwater in a non-continuous but episodic way. Mobile underwater in situ gamma-ray spectroscopy is exploited proving that both ²¹⁴Bi and ⁴⁰K are efficient radiotracers for localization of seepage areas whenever either sediment is in mixture with the emanating fluid or resuspension of surface sediment occurs as a side effect of the fluid emanation.

Are submarine groundwater discharges affecting the structure and physiological status of rocky intertidal communities?

This study evaluated the impacts of submarine groundwater discharges (SGD) on a rocky intertidal community of South Portugal, during April-November 2011. Chlorophyll-a concentration was higher at the SGD site in respect to the Reference site. Epibenthic community structure differed between sites, with an increase in Chthamalus spp. and a decrease in macroalgae coverage at the SGD site. The abundance and body size of Mytilus galloprovincialis were consistently higher at the SGD site. During mid-spring, under potentially higher SGD and less favorable conditions for coastal phytoplankton, the ecophysiological condition of M. galloprovincialis and G. umbilicalis was also higher at the SGD site. These beneficial effects on filter-feeders and herbivores probably resulted from local increases in prey availability, supported by SGD-driven nutrient inputs. Conversely, P. depressa was not favoured by SGD, probably due to a lower dependency on algae as food. The analysis of epibenthic community structure and ecophysiological condition represents a promising approach to disentangle the ecological impacts of SGD on intertidal ecosystems.

Constraining the temporal variations of Ra isotopes and Rn in the groundwater end-member: Implications for derived SGD estimates

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 (²²³Ra, ²²⁴Ra, ²²⁶Ra_,²²⁸Ra) and radon (²²²Rn) 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 ²²²Rn 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 ~19, ~14, ~6, and ~11 for ²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra, 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 ²²²Rn concentrations in groundwater and when applying both tracers in dynamic microtidal coastal systems.

Estimation of coastal residence time of submarine groundwater discharge using radium progenies

A methodology based on γ-spectrometry measurements of untreated coastal water samples is proposed for the direct estimation of coastal residence time of submarine discharged groundwater. The method was applied to a submarine spring at Stoupa Bay covering all seasons. The estimated residence time exhibited an annual mean of 4.6±1.7 d. An additional measurement using the in situ underwater γ-spectrometry technique was performed, in the same site. The in situ method yielded a value of 2.8±0.2 d that was found consistent with the corresponding value derived using the developed lab-based method (3.4±2.0 d) for the same period.

Effects of olive oil wastes on river basins and an oligotrophic coastal marine ecosystem: a case study in Greece

This work aims to contribute to the knowledge of the impacts of olive oil waste discharge to freshwater and oligotrophic marine environments, since the ecological impact of olive oil wastes in riverine and coastal marine ecosystems, which are the final repositories of the pollutants, is a great environmental problem on a global scale, mostly concerning all the Mediterranean countries with olive oil production. Messinia, in southwestern Greece, is one of the greatest olive oil production areas in Europe. During the last decade around 1.4×10(6)tons of olive oil mill wastewater has been disposed in the rivers of Messinia and finally entered the marine ecosystem of Messiniakos gulf. The pollution from olive oil mill wastewater in the main rivers of Messinia and the oligotrophic coastal zone of Messiniakos gulf and its effects on marine organisms were evaluated, before, during and after the olive oil production period. Elevated amounts of phenols (36.2-178 mg L(-1)) and high concentrations of ammonium (7.29-18.9 mmol L(-1)) and inorganic phosphorus (0.5-7.48 mmol L(-1)) were measured in small streams where the liquid disposals from several olive oil industries were gathered before their discharge in the major rivers of Messinia. The large number of olive oil units has downgraded the riverine and marine ecosystems during the productive period and a period more than five months is needed for the recovery of the ecosystem. Statistical analysis showed that the enrichment of freshwater and the coastal zone of Messiniakos gulf in ammonia, nitrite, phenols, total organic carbon, copper, manganese and nickel was directly correlated with the wastes from olive oil. Toxicity tests using 24h LC50 Palaemonidae shrimp confirm that olive mill wastewater possesses very high toxicity in the aquatic environment.