Search

Land-based sources of groundwater pollution can be a critical threat to coral reefs, and a better understanding of "ridge-to-reef" water movement is required to advance management and coral survival in the Anthropocene. In this study a more complete understanding of the geological, atmospheric, and oceanic drivers behind coastal groundwater exchange on the Kalaupapa peninsula, on Moloka'i, Hawai'i, is obtained by analyzing high resolution geochemical and geophysical time-series data. In concert with multiyear water level analyses, a tidally and precipitation-driven groundwater connection between Kauhakō Crater lake and submarine groundwater discharge (SGD) fluxes are demonstrated. Results include an average discharge rate of 190 cm d

Ocean acidification (OA) is a serious consequence of climate change with complex organism-to-ecosystem effects that have been observed through field observations but are mainly derived from experimental studies. Although OA trends and the resulting biological impacts are likely exacerbated in the semi-enclosed and highly populated Mediterranean Sea, some fundamental knowledge gaps still exist. These gaps are at tributed to both the uneven capacity for OA research that exists between Mediterranean countries, as well as to the subtle and long-term biological, physical and chemical interactions that define OA impacts. In this paper, we systematically analyzed the different aspects of OA research in the Mediterranean region based on two sources: the United Nation’s International Atomic Energy Agency’s (IAEA) Ocean Acidification International Coordination Center (OA-ICC) database, and an extensive survey. Our analysis shows that 1) there is an uneven geographic capacity in OA research, and illustrates that both the Algero-Provencal and Ionian sub-basins are currently the least studied Mediterranean areas, 2) the carbonate system is still poorly quantified in coastal zones, and long-term time-series are still sparse across the Mediterranean Sea, which is a challenge for studying its variability and assessing coastal OA trends, 3) the most studied groups of organisms are autotrophs (algae, phanerogams, phytoplankton), mollusks, and corals, while microbes, small mollusks (mainly pteropods), and sponges are among the least studied, 4) there is an overall paucity in socio-economic, paleontological, and modeling studies in the Mediterranean Sea, and 5) in spite of general resource availability and the agreement for improved and coordinated OA governance, there is a lack of consistent OA policies in the Mediterranean Sea. In addition to highlighting the current status, trends and gaps of OA research, this work also provides recommendations, based on both our literature assessment and a survey that targeted the Mediterranean OA scientific community. In light of the ongoing 2021-2030 United Nations Decade of Ocean Science for Sustainable Development, this work might provide a guideline to close gaps of knowledge in the Mediterranean OA research. Systematic Review Registration: https://www.oceandecade.org/., The IAEA is grateful for the support provided to its Marine Environment Laboratories by the Government of the Principality of Monaco. This is a contribution of the IAEA’s Ocean Acidification International Coordination Centre (OA-ICC), a project generously funded through the Peaceful Uses Initiative of the IAEA. The authors would like to thank the OA-ICC for supporting the OA Med-Hub in expanding its activities and visibility. MG and PZ acknowledge funding from MINECO (BIOCAL Project - PID2020-113526RB-I00.

Net calcification rates for coral reef and other calcifiers have been shown to decline as ocean acidification (OA) occurs. However, the role of calcium carbonate dissolution in lowering net calcification rates is unclear. The objective of this study was to distinguish OA effects on calcification and dissolution rates in dominant calcifying macroalgae of the Florida Reef Tract, including two rhodophytes (Neogoniolithon strictum, Jania adhaerens) and two chlorophytes (Halimeda scabra, Udotea luna). Two experiments were conducted: (1) to assess the difference in gross (45Ca uptake) versus net (total alkalinity anomaly) calcification rates in the light/dark and (2) to determine dark dissolution (45CaCO3), using pH levels predicted for the year 2100 and ambient pH. At low pH in the light, all species maintained gross calcification rates and most sustained net calcification rates relative to controls. Net calcification rates in the dark were ~84% lower than in the light. In contrast to the light, all species had lower net calcification rates in the dark at low pH with chlorophytes exhibiting net dissolution. These data are supported by the relationship (R2 = 0.82) between increasing total alkalinity and loss of 45Ca from pre-labelled 45CaCO3 thalli at low pH in the dark. Dark dissolution of 45CaCO3-labelled thalli was ~18% higher in chlorophytes than rhodophytes at ambient pH, and ~ twofold higher at low pH. Only Udotea, which exhibited dissolution in the light, also had lower daily calcification rates integrated over 24 h. Thus, if tropical macroalgae can maintain high calcification rates in the light, lower net calcification rates in the dark from dissolution may not compromise daily calcification rates. However, if organismal dissolution in the dark is additive to sedimentary carbonate losses, reef dissolution may be amplified under OA and contribute to erosion of the Florida Reef Tract and other reefs that exhibit net dissolution.

Surface-based 2D electrical resistivity tomography (ERT) surveys were used to characterize permafrost distribution at wetland sites on the alluvial plain north of the Tanana River, 20 km southwest of Fairbanks, Alaska, in June and September 2014. The sites were part of an ecologically-sensitive research area characterizing biogeochemical response of this region to warming and permafrost thaw, and the site contained landscape features characteristic of interior Alaska, including thermokarst bog, forested permafrost plateau, and a rich fen. The results show how vegetation reflects shallow (0–10 m depth) permafrost distribution. Additionally, we saw shallow (0–3 m depth) low resistivity areas in forested permafrost plateau potentially indicating the presence of increased unfrozen water content as a precursor to ground instability and thaw. Time-lapse study from June to September suggested a depth of seasonal influence extending several meters below the active layer, potentially as a result of changes in unfrozen water content. A comparison of several electrode geometries (dipole-dipole, extended dipole-dipole, Wenner-Schlumberger) showed that for depths of interest to our study (0–10 m) results were similar, but data acquisition time with dipole-dipole was the shortest, making it our preferred geometry. The results show the utility of ERT surveys to characterize permafrost distribution at these sites, and how vegetation reflects shallow permafrost distribution. These results are valuable information for ecologically sensitive areas where ground-truthing can cause excessive disturbance. ERT data can be used to characterize the exact subsurface geometry of permafrost such that over time an understanding of changing permafrost conditions can be made in great detail. Characterizing the depth of thaw and thermal influence from the surface in these areas also provides important information as an indication of the depth to which carbon storage and microbially-mediated carbon processing may be affected.

International audience; Environmental plastic pollution is a major ecological and societal concern today. Over the past decade, a broad range of laboratory and experimental studies have complemented field observations in the hope of achieving a better understanding of the fate and impact of micro- and/or nanoplastics (MP/NP) on diverse organisms (e.g., birds, fish, and mammals). However, plastic pollution remains challenging to monitor in the environment and to control under laboratory conditions, and plastic particles are often naturally or experimentally co-contaminated with diverse chemical pollutants. Therefore, our understanding of the effects of virgin MP/NP in freshwater and marine fish is still limited. Here, we performed a systematic review of the most up-to-date literature on the effects of virgin MP/NP on fish under laboratory conditions. A total of 782 biological endpoints investigated in 46 studies were extracted. Among these endpoints, 32% were significantly affected by exposure to virgin MP/NP. More effects were observed for smaller plastic particles (i.e., size ≤20 μm), affecting fish behavioral and neurological functions, intestinal permeability, metabolism, and intestinal microbiome diversity. In addition, we propose suggestions for new research directions to lead toward innovative, robust, and scientifically sound experiments in this field. This review of experimental studies reveals that the toxicity of virgin MP/NP on fish should be more systematically evaluated using rigorous laboratory-based methods and aims toward a better understanding of the underlying mechanisms of this toxicity to fish.

Environmental microplastic particles (MPs) represent a potential threat to many aquatic animals, and experimental exposure studies, when done well, offer a quantitative approach to assess this stress systematically and reliably. While the scientific literature on MP studies in aquatic environments is rapidly growing, there is still much to learn, and this chapter presents a brief overview of some of the successful methods and pitfalls in experimental MP exposure studies. A short overview of some experimental design types and recommendations are also presented. A proper experimental exposure study will yield useful information on MP-organism impacts and must include the following: a comprehensive MP characterization (e.g., density, buoyancy, type, nature, size, shape, concentration, color, degree of weathering/biofilm formation, an assessment of co-contaminant/surfactant toxicity and behavior, an understanding exposure modes, dose and duration, and the type and life stage of the target species). Finally, more conventional experimental considerations, such as time, costs, and access to clean water, specialized instrumentation, and use of appropriate controls, replicate, and robust statistical analyses are also vital. This short review is intended as a necessary first step towards standardization of experimental MP exposure protocols so one can more reliably assess the transport and fate of MP in the aquatic environment as well as their potential impacts on aquatic organisms.

In recent years, the North Atlantic and the Caribbean Sea have experienced unusual and unprecedented pelagic Sargassum blooms, which may adversely affect coastal ecosystems and productive ocean. Sargassum has the potential to scavenge trace elements and radionuclides from seawater, and when bioaccumulated and thus concentrated, can pose a potential threat to higher trophic organisms, including humans that consume impacted seafood. In this study, trace elements and naturally-occurring U/Th-series radionuclides were measured in Sargassum that were collected in the coastal waters of the Caribbean Sea (Antigua/Barbuda, Belize, and Barbados) to better define baseline concentrations and activities, and to assess the scavenging potential for these trace elements and radionuclides. The mean concentration of trace elements observed in Sargassum collected across these three Caribbean Sea are ranked accordingly to the following descending order: Sr AsFe Mn Zn Ni V C Cd Se Co Cr Pb Ag Hg. 210-Po and

Microplastic (MP) particles are pollutants of global concern and are ubiquitously distributed in the ocean by physical and biological processes. It has been shown that zooplankton can ingest MP yet the interaction between ciliates and MP is still poorly understood. The discrimination and preferential uptake of MP rather than algal prey by ciliates was assessed in this study. The ciliate Sterkiella sp. was fed a diet that consisted of only Isochrysis galbana or a mixture of the same algae and similarly sized polyethylene beads in a 1:3 ratio. Significant, preferential MP grazing was observed in the Plastic-Algae treatment, which is the first reported evidence of proto-zooplankton preferentially ingesting MP over algal food. The mixed treatment contained fecal pellets with embedded MP. Preferential uptake of MP suggests that Sterkiella sp. is capable of ingesting and then "repackaging" MP that would otherwise be too small for larger taxa. This process would thus offer a mechanism for the reintroduction of MP into different compartments of the marine food web. As a consequence, it is necessary to account for small-sized MP (5 μm) particles, that may have additional and yet unknown, impacts on marine food webs.

The region around the Gulf is moving toward a nuclear energy option with the first nuclear power plant now operational in Bushehr, Iran. Others are soon to be commissioned in Abu Dhabi and in Saudi Arabia. For this reason, radiological safety is becoming a prime concern in the region. This review compiles published data on radionuclide concentrations in seawater, sediment, and biota that have been analyzed in the Gulf countries, along with spatial distribution patterns to enable a synoptic view of the available datasets. The seawater concentrations of 3H, 210Po, 210Pb, 137Cs, and 90Sr varied between 130 and 146, 0.48–0.68, 0.75–0.89, 1.25–1.38, 0.57–0.78 mBq L−1, respectively. The 226Ra concentration in seawater varied between 0.26 and 3.82 Bq L−1. Extremely high 40K concentrations between 132 and 149 Bq L−1 have been reported from the Iranian coast compared to 8.9–9.3 Bq L−1 from the western side of the Gulf. Concentrations of 40K, total 210Pb, 137Cs, 90Sr, 226Ra, 228Ra, 238U, 235U, 234U, 239+240Pu, and 238Pu were determined in sediment and ranged between 353 and 445, 23.6–44.3, 1.0–3.1, 4.8–5.29, 17.3–20.5, 15–16.4, 28.7–31.4, 1.26–1.30, 29.7–30.0, 0.045–0.21 and 0.028–0.03 Bq kg−1 dry weight, respectively. Significantly higher 137Cs values have been reported from the Iranian coast compared to the western coast of the Gulf. Whole fish concentrations of 40K, 226Ra, 224Ra, 228Ra, 137Cs, 210Po and 90Sr ranged between 230 and 447, 0.7–7.3

International audience; Radioisotopes have been used in earth and environmental sciences for over 150 years and provide unique tools to study environmental processes in great detail from a cellular level through to an oceanic basin scale. These nuclear techniques have been employed to understand coastal and marine ecosystems via laboratory and field studies to understand how aquatic organisms respond to environmental stressors including temperature, pH, nutrients, metals, organic anthropogenic compounds and biological toxins. Global marine issues, such as ocean warming, deoxygenation, plastic pollution, ocean acidification, increased duration and intensity of toxic harmful algal blooms (HABs), and coastal contamination are all impacting marine environments, thereby imposing various environmental and economic risks. Being able to reliably assess the health of coastal and marine ecosystems, and how they may respond to future disturbances, can provide vital information for society in the sustainable management of their marine environments. This paper summarises the historical use of radiotracers in these systems, describes how existing techniques of radioecological tracing can be developed for specific current environmental issues and provides information on emerging issues that would benefit from current and new radiotracer methods. Current challenges with using radioecological tracers and opportunities are highlighted as well as opportunities to maximise the uptake of these methods to greatly increase the ability of environmental managers to conduct evidence-based management of coastal and marine ecosystems

International audience; In order to better understand the influence of changing salinity conditions on the trophic transfer of 137 Cs in marine fish that live in dynamic coastal environments, its depuration kinetics was investigated in controlled aquaria. The juvenile turbot Scophthalmus maximus was acclimated to three distinct salinity conditions (10, 25 and 38) and then single-fed with compounded pellets that were radiolabelled with 137 Cs. At the end of a 21-d depuration period, assimilation efficiencies (i.e. AEs = proportion of 137 Cs ingested that is actually assimilated by turbots) were determined from observational data acquired over the three weeks. Our results showed that AEs of 137 Cs in the turbots acclimated to the highest salinity condition were significantly lower than for the other conditions (p < 0.05). Osmoregulation likely explains the decreasing AE observed at the highest salinity condition. Indeed, observations indicate that fish depurate ingested 137 Cs at a higher rate when they increase ion excretion, needed to counterbalance the elevated salinity. Such data confirm that ambient salinity plays an important role in trophic transfer of 137 Cs in some fish species. Implications for such findings extend to seafood safety and climate change impact studies, where the salinity of coastal waters may shift in future years in response to changing weather patterns.

The partitioning coefficient, Kd, which is defined by the reversible sorption processes between a solid and an aqueous phase at equilibrium, is one of the most important parameters to assess environmental transport and risk. In this study, a series of simple laboratory experiments were conducted to investigate sorption properties of 134Cs on a model sediment under two treatments (shaken vs non-shaken) and with three (small: 75 μm and bulk i.e., composite) particle size fractions. Vertical transport of 134Cs across the water-sediment interface and into sediment was also evaluated. As expected, grain size had the strongest influence on 134Cs Kd values, with the small particle size fraction yielding significantly higher Kd values than the large and bulk fractions. The mean Kd values obtained from the various experiments ranged from 89 ± 13–130 ± 5 L kg−1 (small), 44 ± 10–91 ± 13 L kg−1 (large), 73 ± 3–112 ± 11 L kg−1 (bulk, shaken) and 73 ± 5–110 ± 4 L kg−1 (bulk, non-shaken). Most of the 134Cs partitioning processes occurred rapidly (

The widespread decline in oceanic dissolved oxygen (DO), known as deoxygenation, is a threat to many marine ecosystems, and fish are considered one of the more vulnerable marine organisms. While food intake and growth rates in some fish can be reduced under hypoxic conditions (DO ~ 60 μmol kg−1), the dietary transfer of essential metals remains unclear. In this context, we investigated the influence of DO on the dietary acquisition of two essential metals (Zn and Mn) in the commercially important gilthead seabream (Sparus aurata) using radiotracer techniques. Fish were exposed to variable DO conditions (normoxia 100% DO, mild-hypoxia 60% DO, and hypoxia 30% DO), and fed a single radiolabeled food ration containing known activities of 54Mn and 65Zn. Depuration and assimilation mechanisms under these conditions were followed for 19 d. Based on whole body activity after the radio-feeding, food consumption tended to decrease with decreasing oxygen, which likely caused the significantly reduced growth (- 25%) observed at 30% DO after 19 d. While there was an apparent reduction in food consumption with decreasing DO, there was also significantly higher essential metal assimilation with hypoxic conditions. The proportion of 65Zn remaining was significantly higher (~60%) at both low DO levels after 24 h and 19 d while 54Mn was only significantly higher (27%) at the lowest DO after 19 d, revealing element specific effects. These results suggest that under hypoxic conditions, stressed teleost fish may allocate energy away from growth and towards other strategic processes that involve assimilation of essential metals.

Funding: Luke Bridgestock was supported by a Leverhulme Trust Early Career Fellowship (ECF-2019-049) for part of this research. The collection of Johor River estuary samples was supported by funding from the Singapore National Research Foundation (NRF), Prime Minister's Office, under the Marine Science Research and Development Programme (Project MSRDP-03) and the Royal Society's Commonwealth Science Grant (CSC\R1\170048). The IAEA is grateful for the support provided to its Environment Laboratories by the Government of the Principality of Monaco. Barium (Ba) isotope variations offer the potential to trace environmental processes, including long-term changes in river discharge and marine export production. Riverine inputs are an important source of dissolved Ba to the ocean, which we estimate to be ~10 to 20 Gmol yr−1. A large fraction (~20 to 75%) of this net riverine dissolved Ba flux to the ocean is derived from estuarine processes, in particular the release of exchangeable Ba from riverine suspended particles due to exchange with major cations in seawater. Despite the importance of this process for controlling the input of dissolved Ba to the ocean, its impact on the δ138/134Ba of net riverine dissolved Ba fluxes remains unknown. To address this observational gap, Ba concentration and isotope data from across the estuarine mixing zones of the Amazon (Brazil), Fly (Papua New Guinea) and Johor (Malaysia) Rivers are presented. Desorption from suspended riverine particles releases Ba with δ138/134Ba 0.2 to 0.3‰ lower than corresponding river dissolved loads, modifying the isotope composition of net riverine dissolved Ba fluxes that reach the ocean. This offset likely represents an isotope fractionation accompanying the adsorption of Ba by particulate phases within river catchments, which can explain the systematic enrichment of heavier Ba isotopes in river dissolved loads relative to weathering lithologies. River dissolved loads are also systematically offset to higher δ138/134Ba than the main oceanic Ba sink: burial of BaSO4 in marine sediment. This represents an apparent imbalance in the modern marine Ba isotope budget. Our results suggest that accounting for modification of the δ138/134Ba of net riverine Ba fluxes to the ocean by estuarine processes is likely to play a key role towards balancing the modern marine Ba isotope budget. Postprint

The Golden Horn estuary, which is located along the Sea of Marmara adjacent to the center of Istanbul, has been heavily polluted for centuries due to concentrated shipping activities, and a legacy of industrial and municipal discharges. The municipalities and associated governments have implemented environmental rehabilitation projects for over 25 years. However, the Golden Horn estuary is still exposed to various pollutants such as vehicle emissions including from fossil-fuel combustion. In this study, two sediment traps were deployed in the Golden Horn estuary to obtain information on settling particle (SP) composition and fluxes, trace element and radionuclide concentrations, and fluxes thereof. Conventional sediment traps (Trap-1 and Trap-2) were installed side-by-side, at a depth of 15-m and moored for 18 months during which time the sediment traps were periodically sampled. Over this time period, settling particle fluxes (SPFs) were calculated. The concentrations and fluxes of radionuclides (137Cs, 226Ra, 228Ra, 210Po, and 210Pb) and trace elements (Ag, Al, As, Cd, Cu, Fe, K, Mn, Mo, Ni, Pb, Sb Sn, Tl, V, and Zn) were determined in SPs for each sampling period. Normalized enrichment factors (EF) and a Geoaccumulation Index ( I g e o ) showed that Ag, Cd, and Pb were statistically enriched in SPs. Together, the results of this study show that the Golden Horn estuary is still enriched in some environmental pollutants which could be a source term for the water column and associated marine animals.

Ocean acidification (OA), the gradual decline in ocean pH and [ CO32−] caused by rising levels of atmospheric CO2, poses a significant threat to coral reef ecosystems, depressing rates of calcium carbonate (CaCO3) production, and enhancing rates of bioerosion and dissolution. As ocean pH and [ CO32−] decline globally, there is increasing emphasis on managing local stressors that can exacerbate the vulnerability of coral reefs to the effects of OA. We show that sustained, nutrient rich, lower pH submarine groundwater discharging onto nearshore coral reefs off west Maui lowers the pH of seawater and exposes corals to nitrate concentrations 50 times higher than ambient. Rates of coral calcification are substantially decreased, and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the Pacific under equivalent low pH conditions but living in oligotrophic waters. Heavier coral nitrogen isotope (δ15N) values pinpoint not only site-specific eutrophication, but also a sewage nitrogen source enriched in 15N. Our results show that eutrophication of reef seawater by land-based sources of pollution can magnify the effects of OA through nutrient driven-bioerosion. These conditions could contribute to the collapse of coastal coral reef ecosystems sooner than current projections predict based only on ocean acidification.

Water, energy, and food are among the most important and fundamental resources for human beings and society. Despite the large potential for efficiency and reduction of losses, the demand for these resources is likely to increase due to population growth, changes in lifestyles, climate change, and other aspect of global change. The strong interconnectedness of these three vital resources has been termed the “Nexus” in the scientific literature in recent years. While many papers claim its fundamental importance, few provide specific ideas on how to deal with this Nexus in practice. This paper introduces twenty case-studies that are highlighted in this special issue that explore the practice of the Nexus and its scientific basis with particular focus on the Water-Energy-Food Nexus in the Asia-Pacific Region.

Study region Hydrogeologic controls on seasonal land/sea exchange are investigated in Malibu, California, USA. Study focus An assessment of regional groundwater/surface water exchange and associated biogeochemical transport in an intermittently open, coastal lagoon in California is developed using naturally occurring U/Th-series tracers. New hydrological insights for the region Nearshore lagoons that are seasonally disconnected from the coastal ocean occupy about 10% of coastal areas worldwide. Lagoon systems often are poorly flushed and thus sensitive to nutrient over-enrichment that can lead to eutrophication, oxygen depletion, and/or pervasive algal blooms. This sensitivity is exacerbated in lagoons that are intermittently closed to surface water exchange with the sea and occur in populous coastal areas. Such estuarine systems are disconnected from the sea during most of the year by wave-built barriers, but during the rainy season these berms can breach, enabling direct water exchange. Using naturally-occurring 222 Rn as groundwater tracer, we estimate that groundwater discharge to Malibu Lagoon during open berm conditions was one order of magnitude higher (21 ± 17 cm/day) than during closed berm conditions (1.8 ± 1.4 cm/day). The SGD (submarine groundwater discharge) into nearshore coastal waters at the SurferRider and Colony Malibu was 4.2 cm/day on average. The exported total dissolved nitrogen (TDN) through the berm during closed berm was 1.6 × 10 −3 mol/day, whereas during open berm (exported by the Creek) was 3.5 × 10 3 mol/day. Although these evaluations are specific to the collection campaigns the 2009 and 2010 hydro years, these two distinct hydrologic scenarios play an important role in the seasonality and geochemical impact of land/sea exchange, and highlight the sensitivity of such systems to future impacts such as sea level rise and increasing coastal populations.

Freshwater resources on low-lying atoll islands are highly vulnerable to climate change and sea-level rise. In addition to rainwater catchment, groundwater in the freshwater lens is a critically important water resource on many atoll islands, especially during drought. Although many atolls have high annual rainfall rates, dense natural vegetation and high evapotranspiration rates can limit recharge to the freshwater lens. Here we evaluate the effects of land-use/land-cover change and managed aquifer recharge on the hydrogeochemistry and supply of groundwater on Roi-Namur Island, Republic of the Marshall Islands. Roi-Namur is an artificially conjoined island that has similar hydrogeology on the Roi and Namur lobes, but has contrasting land-use/land-cover and managed aquifer recharge only on Roi. Vegetation removal and managed aquifer recharge operations have resulted in an estimated 8.6 × 105 m3 of potable groundwater in the freshwater lens on Roi, compared to only 1.6 × 104 m3 on Namur. We use groundwater samples from a suite of 33 vertically nested monitoring wells, statistical testing, and geochemical modeling using PHREEQC to show that the differences in land-use/land-cover and managed aquifer recharge on Roi and Namur have a statistically significant effect on several groundwater-quality parameters and the controlling geochemical processes. Results also indicate a six-fold reduction in the dissolution of carbonate rock in the freshwater lens and overlying vadose zone of Roi compared to Namur. Mixing of seawater and the freshwater lens is a more dominant hydrogeochemical process on Roi because of the greater recharge and flushing of the aquifer with freshwater as compared to Namur. In contrast, equilibrium processes and dissolution-precipitation non-equilibrium reactions are more dominant on Namur because of the longer residence times relative to the rate of geochemical reactions. Findings from Roi-Namur Island support selective land-use/land-cover change and managed aquifer recharge as a promising management approach for communities on other low-lying atoll islands to increase the resilience of their groundwater supplies and help them adapt to future climate change related stresses.

Groundwater and seawater samples were collected from nearshore wells and offshore along the Kona Coast of the Big Island of Hawaii to investigate rare earth element (REE) behavior in local subterranean estuaries. Previous investigations showed that submarine groundwater discharge (SGD) is the predominant flux of terrestrial waters to the coastal ocean along the arid Kona Coast of Hawaii. Groundwater and seawater samples were filtered through 0.45 μm and 0.02 μm pore-size filters to evaluate the importance of colloidal and soluble (i.e., truly dissolved ionic species and/or low molecular weight [LMW] colloids) fractions of the REEs in the local subterranean estuaries. Mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility (WWTF) proximal to the Kaloko-Hanokohau National Historic Park, and more “pristine” groundwater from a well constructed in a lava tube at Kiholo Bay, were conducted with local seawater to study the effect of solution composition (i.e., pH, salinity) on the concentrations and fractionation behavior of the REEs as groundwater mixes with seawater in Kona Coast subterranean estuaries. The mixed waters were also filtered through 0.45 or 0.02 μm filters to ascertain the behavior of colloidal and soluble fractions of the REEs across the salinity gradient in each mixing experiment. Concentrations of the REEs were statistically identical (two-tailed Student t-test, 95% confidence) between the sequentially filtered sample aliquots, indicating that the REEs occur as dissolved ionic species and/or LMW colloids in Kona Coast groundwaters. The mixing experiments revealed that the REEs are released to solution from suspended particles or colloids when Kona Coast groundwater waters mix with local seawater. The order of release that accompanies increasing pH and salinity follows light REE (LREE) > middle REE (MREE) > heavy REE (HREE). Release of REEs in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each REE that occurs in solution as dicarbonato complexes [i.e., Ln(CO3)2−] as pH increases across the salinity gradient. Input-normalized REE patterns of Kona Coast groundwater and coastal seawater are nearly identical and relatively flat compared to North Pacific seawater, indicating that SGD is the chief source of these trace elements to the ocean along the Kona Coast. Additionally, REE concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open-ocean seawater values from the North Pacific, further demonstrating the importance of SGD fluxes of REEs to these coastal waters. Taken together, these observations indicate that large-scale removal of REEs, which characterizes the behavior of REEs in the low salinity reaches of many surface estuaries, is not a feature of the subterranean estuary along the Kona Coast. A large positive gadolinium (Gd) anomaly characterizes groundwater from the vicinity of the WWTF. The positive Gd anomaly can be traced to the coastal ocean, providing further evidence of the impact of SGD on the coastal waters. Estimates of the SGD fluxes of the REEs to the coastal ocean along the Kona Coast (i.e., 1.3–2.6 mmol Nd day−1) are similar to recent estimates of SGD fluxes of REEs along Florida’s east coast and to Rhode Island Sound, all of which points to the importance of SGD as significant flux of REEs to the coastal ocean.

Pervasive and sustained coral diseases contribute to the systemic degradation of reef ecosystems, however, to date an understanding of the physicochemical controls on a coral disease event is still largely lacking. Water circulation and residence times and submarine groundwater discharge all determine the degree to which reef organisms are exposed to the variable chemistry of overlying waters; understanding these physical controls is thus necessary to interpret spatial patterns in coral health. The recent discovery of coral Black Band Disease at Mākua Reef on Kauaʻi, Hawaiʻi prompted an investigation into the physicochemical drivers and geomorphic controls of reef water circulation, and the temporally variable nutrient fluxes derived from submarine groundwater discharge. Results reveal localized stagnant water parcels at Mākua Reef where groundwater-derived high nutrient loading and low salinities act in concert as stressors to coralline health – and where Black Band Disease was uniquely identified. The observed high nutrient levels during low tide conditions are likely associated with nearby upstream cesspools and drain fields. Information obtained using such a multidisciplinary approach has direct value for successful management of coastal aquifers and the health and sustainability of adjacent nearshore coral reef ecosystems.

Arctic permafrost stores vast amounts of methane (CH4) in subsurface reservoirs. Thawing permafrost creates areas for this potent greenhouse gas to be released to the atmosphere. Identifying ‘hot spots’ of methane flux on a local scale has been limited by the spatial scales of traditional ground-based or satellite-based methane-sampling methods. Here we present a reliable and an easily replicable design using only off-the-shelf, cost-effective methane sensor components and an Unmanned Aerial System (UAS). Our results demonstrate the high efficiency of the design and the advantages of this methodology for environmental methane studies that are subjected to the high spatial variability of methane levels. On Barter Island, NE Alaska, we noted spikes in CH4 concentrations coincident with topographic features or anomalies. Such spikes may be attributed to enhanced land/air transfer and may reveal zones of high methane production and/or minimal oxidation in areas of thermoerosional gullies along thawing coastal zones. Thermoerosional gullies represent hotspots that release significantly higher levels of methane than the surrounding areas, thus suggesting that point sampling is inadequate in characterizing methane releases and that increasing rates of permafrost thaw may result in increasing point sources of high CH4 emissions.

Microplastics (MP) are a pollutant that can be found in all marine ecosystems. Currently one of the most used forms to classify them is through their size. However, the current size categories in use cover an extremely wide range of sizes and are not based on a biological or physical basis. Thus, here we propose to harmonize the MP size categories with the ones already in used on plankton research for more than 120 years. This will allow the implementation of more refined MP size classes that are connected to a biological reality and will also enable the comparison of a myriad of literature on plankton research with the new work on MP., Graphical abstract Image, graphical abstract

The depositional histories of trace metals (Pb, Cu, and Zn) in sediment cores from three Ghanaian estuaries were reconstructed using radioisotope-derived ( 210 Pb and 137 Cs) geochronologies. A core collected from each of the Amisa, Sakumo II and Volta estuaries was analyzed for trace metals and radionuclides. Lead-210 and 137 Cs dating via gamma spectroscopy, and trace metal analysis via inductively coupled plasma mass spectrometry (ICP-MS) were used in deriving sedimentation rates, geochronologies and accumulation trends of trace metals. The sedimentation rates in all three estuaries (in the range of 0.54–0.83 cm yr −1 ) were greater than the predicted sea level rise (∼0.33 cm yr −1 ) for the Accra Coast of Ghana. The 210 Pb depositional rates of 6.83 dpm cm −2 y −1 , 2.74 dpm cm −2 y −1 and 1.75 dpm cm −2 y −1 estimated for the Amisa, Sakumo II and Volta estuaries, respectively, are higher than those recorded in other latitudes. Trace metal analysis revealed differences in the concentrations of Cu, Pb and Zn between deeper and surficial layers of each core to be in the range of 10–20%, which is well within the natural variations attributed to geochemical factors. Relative to the Amisa and Volta estuaries, the temporal profiles of Al-normalized metal concentrations and estimated fluxes suggest anthropogenic processes augmented the natural fluxes of trace metals, particularly Zn into the Sakumo II estuary during the last 7 years.

Widespread bottom trawling on the NW Iberian shelf causes chronic sediment and habitat disturbance. The few studies that have investigated vessel-modified sedimentary-structure and texture of the seabed have typically classified their results as being either impacted by trawling or not. This study indicates that bottom trawling can result in a sequence of vastly different effects to the lithology of seabed sediment, which have in turn different ecological consequences. Here, we combined very high-resolution spatial bottom-trawling data with sedimentological (grain size, porosity) and geochemical datasets (excess 210Pb, 3D petroleum fingerprinting) to study sediment disturbance, including sorting and mixing. Our results were used to develop five conceptual disturbance scenarios: minimal seabed effects, sediment overturning, complete sediment mixing, sediment grading and layering, and loss of sediment. Considering that bottom trawling is a widespread and growing global fishing technique, such impacts need to be considered in the management of habitat conservation as well as in the reconstruction of late Holocene climate history from shallow-water deposits, not just on the NW Iberian shelf, but also globally.

Low-relief environments like the Florida Coastal Everglades (FCE) have complicated hydrologic systems where surface water and groundwater processes are intimately linked yet hard to separate. Fluid exchange within these low-hydraulic-gradient systems can occur across broad spatial and temporal scales, with variable contributions to material transport and transformation. Identifying and assessing the scales at which these processes operate is essential for accurate evaluations of how these systems contribute to global biogeochemical cycles. The distribution of 222Rn and 223,224,226Ra have complex spatial patterns along the Shark River Slough estuary (SRSE), Everglades, FL. High-resolution time-series measurements of 222Rn activity, salinity, and water level were used to quantify processes affecting radon fluxes out of the mangrove forest over a tidal cycle. Based on field data, tidal pumping through an extensive network of crab burrows in the lower FCE provides the best explanation for the high radon and fluid fluxes. Burrows are irrigated during rising tides when radon and other dissolved constituents are released from the mangrove soil. Flushing efficiency of the burrows—defined as the tidal volume divided by the volume of burrows—estimated for the creek drainage area vary seasonally from 25 (wet season) to 100 % (dry season) in this study. The tidal pumping of the mangrove forest soil acts as a significant vector for exchange between the forest and the estuary. Processes that enhance exchange of O2 and other materials across the sediment-water interface could have a profound impact on the environmental response to larger scale processes such as sea level rise and climate change. Compounding the material budgets of the SRSE are additional inputs from groundwater from the Biscayne Aquifer, which were identified using radium isotopes. Quantification of the deep groundwater component is not obtainable, but isotopic data suggest a more prevalent signal in the dry season. These findings highlight the important role that both tidal- and seasonal-scale forcings play on groundwater movement in low-gradient hydrologic systems.

Select coastal regions of the North Slope of Alaska are experiencing high erosion rates that can be attributed in part to recent warming trends and associated increased storm intensity and frequency. The upper sediment column of the coastal North Slope of Alaska can be described as continuous permafrost underlying a thin (typically less than 1–2 m) active layer that responds variably to seasonal thaw cycles. Assessing the temporal and spatial variability of the active layer and underlying permafrost is essential to better constrain how heightened erosion may impact material fluxes to the atmosphere and the coastal ocean, and how enhanced thaw cycles may impact the stability of the coastal bluffs. In this study, multi-channel electrical resistivity tomography (ERT) was used to image shallow subsurface features of a coastal bluff west of Kaktovik, on Barter Island, northeast Alaska. A comparison of a suite of paired resistivity surveys conducted in early and late summer 2014 provided detailed information on how the active layer and permafrost are impacted during the short Arctic summer. Such results are useful in the development of coastal resilience models that tie together fluvial, terrestrial, climatic, geologic, and oceanographic forcings on shoreline stability.

We investigated physiological responses including calcification, photosynthesis and alterations to polar metabolites, in the scleractinian coral Stylophora pistillata exposed to different concentrations of polyethylene microplastics. Results showed that at high plastic concentrations (50 particles/mL nominal concentration) the photosynthetic efficiency of photosystem II in the coral symbiont was affected after 4 weeks of exposure. Both moderate and high (5 and 50 particles/mL nominal) concentrations of microplastics caused subtle but significant alterations to metabolite profiles of coral, as determined by Nuclear Magnetic Resonance (NMR) spectroscopy. Specifically, exposed corals were found to have increased levels of phosphorylated sugars and pyrimidine nucleobases that make up nucleotides, scyllo-inositol and a region containing overlapping proline and glutamate signals, compared to control animals. Together with the photo-physiological stress response observed and previously published literature, these findings support the hypothesis that microplastics disrupt host-symbiont signaling and that corals respond to this interference by increasing signaling and chemical support to the symbiotic zooxanthellae algae. These findings are also consistent with increased mucus production in corals exposed to microplastics described in previous studies. Considering the importance of coral reefs to marine ecosystems and their sensitivity to anthropogenic stressors, more research is needed to elucidate coral response mechanisms to microplastics under realistic exposure conditions.

Changes in seawater pH can alter the chemical speciation of waterborne chemical elements, affecting their bioavailability and, consequently, their bioaccumulation in marine organisms. Here, controlled environmental conditions and a 210Pb radiotracer were used to assess the effect of five distinct pH conditions (pHT ranging from 7.16 to 7.94) on the short-term (9 days) accumulation of Pb in the blue mussel, Mytilus edulis. After 9 days of exposure, higher levels of Pb were observed in the soft tissues of mussels maintained in the lower pH conditions, while Pb levels accumulated by mussel shells showed no difference across pH conditions. These results suggest that pH decreases such as those predicted by ocean acidification scenarios could enhance Pb contamination in marine organisms, with potential subsequent contamination and effect risks for human consumers.

The dissolved oxygen concentration of the world’s oceans has systematically declined by 2% over the past 50 years, and there has been a notable commensurate expansion of the global oxygen minimum zones (OMZs). Such wide-scale ocean deoxygenation affects the distribution of biological communities, impacts the physiology of organisms that may affect their capacity to absorb and process contaminants. Therefore, the bioaccumulation efficiencies of three contrasting radionuclides, 110mAg, 134Cs and 65Zn were investigated using controlled aquaria in the blue mussel Mytilus edulis under three contrasting dissolved oxygen regimes: normoxic; 7.14 mg L−1, reduced oxygen; 3.57 mg L−1 and hypoxic 1.78 mg L−1 conditions. Results indicated that hypoxic conditions diminished 110mAg uptake in the mussel, whereas depuration rates were not affected. Similarly, hypoxia appeared to cause a decrease in the 65Zn bioaccumulation rate, as evidenced by both weakened uptake and rapid elimination rates. Effects of hypoxia on the metabolome of mussels were also explored by untargeted Nuclear Magnetic Resonance (NMR) spectroscopic methods. The metabolic response was characterised by significantly greater abundance of several amino acids, amino sulfonic acids, dicarboxylic acids, carbohydrates and other metabolites in the lowest oxygen treatment, as compared to the higher oxygen treatments. Clearance rates significantly dropped in hypoxic conditions compared to normoxia. Results suggest that hypoxic conditions, and even partly moderate hypoxia, alter ventilation, an-aerobic, oxidative and osmoregulation metabolism of this mussel, which may further influence the trace element bioaccumulation capacity.

Paralytic shellfish poisoning (PSP) events occur regularly along the Mediterranean and Atlantic coast of Morocco, and have been responsible for several severe cases of human intoxication. Along the southern Atlantic coast of Morocco, aquaculture and intensive artisanal fishing practices have recently been particularly heavily impacted, and toxic species have been observed in increasing intensity and frequency. In the 1990's a regulatory monitoring program was established for the coastal waters off Morocco by the National Institute of Fisheries Research (INRH), to reduce the risk of intoxication with biotoxins. The regulatory monitoring is conducted weekly and includes toxic phytoplankton enumeration and identification, as well as saxitoxin (STX) analysis in seafood using the mouse bioassay (MBA). Animal testing remains the most widely used screening method for PSP toxin detection, yet its use is being reconsidered for animal-related ethical issues, as well as for practical considerations. To be able to better evaluate alternatives to animal testing, the performance of a nuclear-based radioligand-receptor binding assay (RBA) for paralytic shellfish toxins was assessed and compared with the MBA using four commercially important shellfish matrices, including cockles Cerastoderma edule, razor shells Solen marginatus, oysters Crassostrea gigas, and mussels Perna perna. Over 50 samples were collected and analysed as part of the regulatory monitoring framework including a suite of monthly samples from 2017 and all samples identified as toxic by MBA since 2011. Testing of reference material and evaluation of assay-critical parameters (e.g. slope of calibration curve, internal quality control QC and IC50) confirmed the robustness of the RBA methodology. With this RBA method, STX-like activity detected in shellfish samples ranged from 33 to 8500 μg STX equivalents per kg. RBA data were significantly correlated (P 0.0001, Pearson r = 0.96) with the MBA-derived dataset. Importantly, the RBA method allowed for the detection and quantification of PSP toxins at levels not detectable by using the mouse bioassay. The limits of quantification of the RBA was calculated and found to be 10-fold lower than that of the MBA, respectively 35.24 ± 5.99 and 325 μg STX equivalents per kg of tissue. In addition, the RBA was easier to use and produced reliable results more rapidly than the MBA and without use of live animals. Considering the increasing risks associated with harmful algal blooms, globally and in Morocco, together with the increased development of aquaculture production and seafood consumption and the difficulties of live animal testing, these findings indicate that the RBA method is a reliable and effective alternative to the MBA method.

Plastic pollution is ubiquitous in aquatic environments and its potential impacts to wildlife and humans present a growing global concern. Despite recent efforts in understanding environmental impacts associated with plastic pollution, considerable uncertainties still exist regarding the true risks of nano- and micro-sized plastics (

Submarine groundwater discharge (SGD) is an important conduit that links terrestrial and marine environments. SGD conveys both water and water-borne constituents into coastal waters, where these inflows may impact near-shore ecosystem health and sustainability. Multichannel electrical resistivity techniques have proven to be a powerful tool to examine scales and dynamics of SGD and SGD forcings. However, there are uncertainties both in data aquisition and data processing that must be addressed to maximize the effectiveness of this tool in estuarine or marine environments. These issues most often relate to discerning subtle nuances in the flow of electricity through variably saturated media that can also be highly conductive (i.e., seawater). Three contrasting field sites were examined for this study to assess the effectiveness of electrical resistivity techniques in varying coastal settings by comparing resistivity data to direct salinity and resistivity observations, quantifying changes in lithology and beach geomorphology, and fine-tuning inversion protocols. The three study sites all have substantial (up to 85 cm day−1) submarine groundwater discharge rates, but the hydrologic, oceanographic, and geologic characteristics of the sites are all very different. At a site in Pelekane Bay on the Big Island of Hawaii, seasonal flooding introduces very high concentrations of fine to coarse sediment into the bay. Near-shore circulation is limited in Pelekane Bay, so this newly introduced sediment can become deposited in the bay where it accumulates over time. At a site in Hood Canal, a fjord within Puget Sound, Washington, SGD rates can be high because of the large tidal range, abundant recharge, and steep hydrologic gradients. At Younger Lagoon in northern California, the flow of groundwater towards the coast is much more parsimonious, but here marine processes, including recirculated seawater, are important in controlling the flow of material towards the coast. Rigorous ground-truthing at each field site showed that multi-channel electrcial resistivity techniques can reproduce the scales and dynamics of a seepage field when such data are correctly collected, and when the model inversions are tuned to field site characteristics. Such information can provide a unique perspective on the scales and dynamics of exchange processes within a coastal aquifer—information essential to scientists and resource managers alike.

In order to better understand the influence of changing salinity conditions on the trophic transfer of

Lead isotopic and trace element records of two contrasting sediment cores were examined to reconstruct historic, industrial contaminant inputs to Lake Tanganyika, Africa. Observed fluxes of Co, Cu, Mn, Ni, Pb, and Zn in age-dated sediments collected from the lake varied both spatially and temporally over the past two to four centuries. The fluxes of trace elements were lower (up to 10-fold) at a mid-lake site (MC1) than at a nearshore site (LT-98-58), which is directly downstream from the Kahama and Nyasanga River watersheds and adjacent to the relatively pristine Gombe Stream National Park. Trace element fluxes at that nearshore site did not measurably change over the last two centuries (1815–1998), while the distal, mid-lake site exhibited substantial changes in the fluxes of trace elements – likely caused by changes in land use – over that period. For example, the flux of Pb increased by 300% from 1871 to 1991. That apparent accelerated weathering and detrital mobilization of lithogenic trace elements was further evidenced by (i) positive correlations (r = 0.77–0.99, p < 0.05) between the fluxes of Co, Cu, Mn, Ni, Pb, and Zn and those of iron (Fe) at both sites, (ii) positive correlations (r = 0.82–0.98, p < 0.01, n = 9) between the fluxes of elements (Al, Co, Cu, Fe, Mn, Ni, Pb, and Zn) and the mass accumulation rates at the offshore site, (iii) the low enrichment factors (EF < 5) of those trace elements, and (iv) the temporal consistencies of the isotopic composition of Pb in the sediment. These measurements indicate that accelerated weathering, rather than industrialization, accounts for most of the increases in trace element fluxes to Lake Tanganyika in spite of the development of mining and smelting operations within the lake’s watershed over the past century. The data also indicate that the mid-lake site is a much more sensitive and useful recorder of environmental changes than the nearshore site. Furthermore, the lead isotopic compositions of sediment at the sites differed spatially, indicating that the Pb (and other trace elements by association) originated from different natural sources at the two locations.

The unadjusted 72-h gross alpha activities in water from two wells completed in marine and alluvial deposits in a coastal southern California aquifer 40 km north of San Diego were 15 and 25 picoCuries per liter (pCi/L). Although activities were below the Maximum Contaminant Level (MCL) of 15 pCi/L, when adjusted for uranium activity; there is concern that new wells in the area may exceed MCLs, or that future regulations may limit water use from the wells. Coupled well-bore flow and depth-dependent water-quality data collected from the wells in 2011 (with analyses for isotopes within the uranium, actinium, and thorium decay-chains) show gross alpha activity in marine deposits is associated with decay of naturally-occurring 238 U and its daughter 234 U. Radon activities in marine deposits were as high as 2230 pCi/L. In contrast, gross alpha activities in overlying alluvium within the Piedra de Lumbre watershed, eroded from the nearby San Onofre Hills, were associated with decay of 232 Th, including its daughter 224 Ra. Radon activities in alluvium from Piedra de Lumbre of 450 pCi/L were lower than in marine deposits. Chromium VI concentrations in marine deposits were less than the California MCL of 10 μg/L (effective July 1, 2014) but δ 53 Cr compositions were near zero and within reported ranges for anthropogenic chromium. Alluvial deposits from the nearby Las Flores watershed, which drains a larger area having diverse geology, has low alpha activities and chromium as a result of geologic and geochemical conditions and may be more promising for future water-supply development.