Marine Bay Research Articles

Phytoplankton Diversity Across a Coastal Urbanization and Eutrophication Gradient: The Sepetiba Bay—Ilha Grande Bay Continuum in Rio de Janeiro

ABSTRACTDensely populated coastal zones are significantly impacted by anthropogenic pressures, particularly urbanized semi‐enclosed bays with long residence times of waters and nutrients. Eutrophication is a primary issue resulting from human settlement in coastal zone, as it drastically modifies the structure of biological communities, particularly the phytoplankton. The aim of this study is to assess whether eutrophication functions as an environmental filter on the phytoplankton community along an 80 km gradient of eutrophication in two contrasting bays, Sepetiba and Ilha Grande. By categorizing phytoplankton species based on characteristic traits and comparing them with in situ environmental data, we assess the distribution of phytoplankton functional groups. Sampling was conducted in November 2021 and April 2022 from the semienclosed, mesohaline, and shallow Sepetiba Bay to the more open and marine oligotrophic Ilha Grande Bay. During the two sampling campaigns, functional groups including strict autotrophs (diatoms and filamentous cyanobacteria) and both constitutive and non‐constitutive mixotrophs (dinoflagellates) were represented by different abundance of species along this gradient. Classical diversity indices and Beta‐Turnover analyses indicate significant community differences between the bays, with species replacement driving differentiation rather than species loss between the sampled points. However, with increased eutrophication in Sepetiba Bay, a decrease in the dispersion of functional traits was observed, suggesting that eutrophication acts as an environmental filter promoting trait convergence and the selection of specialist organisms.

Insights into PFAS contaminants before and after sewage discharges into a marine protected harbour

Per and polyfluoroalkyl substances (PFAS) and their degradation products are a concern to human and ecosystem health. Wastewater treatment plants are not efficient at removing PFAS compounds and are thought to be a major source of these compounds to marine environments. The sewerage infrastructure in the UK, has over 20,000 combined stormwater overflows (CSOs). These CSOs are relief values whereby untreated wastewater can discharge under permit from the Environment Agency with exceptional rain/snowfall conditions. CSOs discharged 3.6 million monitored hours of untreated wastewater into English rivers and coasts in 2023. Concerns have been raised about the proximity of these CSO discharges to highly protected marine habitats. This study is the first to determine that PFAS concentrations are elevated in a highly protected marine bay (Langstone Harbour, England) following recent sewage releases compared to an extended period without discharge. Analysis was carried out into a suite of 54 PFAS compounds of which only one (PFHpA) was detectable above LOD prior to discharges but 8 afterwards. These included banned PFOS (Linear and Branched 8.6 ng/L ∓ 0.90) and PFOA (2.9 ng/L ∓ 0.29) which were above annual average EQS for inland and ‘other’ surface waters. Most of the PFAS compounds detected doubled in concentration above LODs. These two-fold increases we discuss are likely conservative estimates based on the use of LODs and tidal conditions. Additional Oysters (Crassostrea gigas) and Seaweed (Fucus vesiculosus) were taken revealing high concentrations of the shorter chain PFBA (6.99μg/kg ∓ 2.42 ww) in seaweed samples. These seaweeds were calculated to have conservative bioaccumulation factors (BAF) > 6000 for PFBA indicating these algae might be an important reservoir of some PFAS contamination. We discuss these results in the context of the largescale discharges of untreated wastewater nationally and globally, and call upon a need for a better understanding of the transfer of PFAS contaminants into marine food chains.

Temporal variations of food web in a marine bay ecosystem based on LIM-MCMC model

Temporal variations of food web in a marine bay ecosystem based on LIM-MCMC model

Shallow-water whale-fall communities: Evidence from the middle–late Eocene basilosaurid whale bones, Wadi El-Hitan, Fayum, Egypt

The present study examines the basilosaurid whale bone specimens collected from the Sandouk El-Borneta section, Wadi El-Hitan (Valley of Whales), Fayum, Egypt. These specimens are embedded in highly fossiliferous calcareous sandstones of the middle Eocene Gehannam and the upper Eocene Birket Qarun formations. These whale bones display some post-mortem alterations, representing good signs of at least three distinct stages in what is called the whale fall. The co-occurrence of shark, ray, and crocodile fossil specimens with the examined whale bones may indicate the first mobile-scavenger stage. Borings of the siboglinid polychaete genus Osedax represent the most common worm type that deeply bioeroded the whale bones, contributing to their rapid degradation, and representing the enrichment-opportunist stage. These fossil traces of the bone-eating worm Osedax represent the first record in the Eocene Epoch regionally and inter-regionally, filling the gap between the Late Cretaceous and the Oligocene occurrences. Subsequently, the studied whale bones served as hard substrates for some calcareous tube-dwelling encrusting polychaetes, balanoid barnacles, sheet‐like cheilostome bryozoans, and scleractinian corals. Furthermore, a bioerosion structure produced by polychaete annelids was also observed. The presence of these sclerobionts assemblage confirms the well-developed final reef stage with prolonged exposure and colonisation of these whale bones prior to final burial. Based on the recorded post-mortem alterations, together with other sedimentological and palaeontological data, the studied whale bones were deposited in a shallow open marine bay to sheltered gulf environments, which were characterised by low depositional energy, low to moderate rate of sedimentation, and high surface water productivity.

Rich diversity and active spatial-temporal dynamics of Thalassiosira species revealed by time-series metabarcoding analysis.

Thalassiosira is a species-rich genus in Bacillariophyta that not only contributes positively as primary producer, but also poses negative impacts on ecosystems by causing harmful algal blooms. Although taxonomical studies have identified a large number of Thalassiosira species, however, the composition of Thalassiosira species and their geographical distribution in marine ecosystems were not well understood due primarily to the lack of resolution of morphology-based approaches used previously in ecological expeditions. In this study, we systematically analyzed the composition and spatial-temporal dynamic distributions of Thalassiosira in the model marine ecosystem Jiaozhou Bay by applying metabarcoding analysis. Through analyzing samples collected monthly from 12 sampling sites, 14 Thalassiosira species were identified, including five species that were not previously reported in Jiaozhou Bay, demonstrating the resolution and effectiveness of metabarcoding analysis in ecological research. Many Thalassiosira species showed prominent temporal preferences in Jiaozhou Bay, with some displaying spring-winter preference represented by Thalassiosira tenera, while others displaying summer-autumn preference represented by Thalassiosira lundiana and Thalassiosira minuscula, indicating that the temperature is an important driving factor in the temporal dynamics. The application of metabarcoding analysis, equipped with appropriate molecular markers with high resolution and high specificity and databases of reference molecular marker sequences for potential all Thalassiosira species, will revolutionize ecological research of Thalassiosira species in Jiaozhou Bay and other marine ecosystems.

МОРСКОЕ ОСАДКОНАКОПЛЕНИЕ НА ПОБЕРЕЖЬЕ ЮГО-ЗАПАДНОЙ ОКРАИНЫ ПРИМОРЬЯ В СРЕДНЕМ ГОЛОЦЕНЕ

A comprehensive study of marine sediments deposited at the southwestern margin of Primorye (Khasan settlement area) allowed us to consider in detail the palaeogeography of the coast in the second half of the Atlantic period of the Holocene, about 6 500–6 000 yr BP / 7 400–6 800 cal BP. Sedimentation in marine environments began with the development of postglacial oceanic transgression around 6 500 yr BP / 7 400 cal BP. A shallow marine bay formed on the coastal accumulation plain, into which the Tumannaya (Tumangan) River, the largest in the Sea of Japan basin, flowed. Avalanche sedimentation proceeded in the bay at an average rate of 16–24 mm/year within the confines of the estuary. The final phase of sedimentation after 6 200 yr BP / 7 100 cal BP occurred at a time when the transgression of the sea slowed down and sea level reached its maximum height of +1 m in the coastal area. Multi-species broad-leaved oak-dominated forests mixed with thermophilic hornbeam species clearly indicate optimum climatic conditions in the territory adjacent to the coast. The marine sedimentation stopped around 6 000 yr BP / 6 800 cal BP to resume in the middle of the Sub-Atlantic period of the Holocene.

Palaeoenvironmental changes in eastern Crimea over the last 7600 years inferred from a multi-proxy study of a sediment archive from Lake Chokrak

The study presents a multi-proxy archive from hypersaline coastal Lake Chokrak in eastern Crimea, a steppe region which is particularly susceptible to moisture fluctuations. XRF, organic carbon and nitrogen, and palynological analyses are used to reconstruct the evolution of the lake and landscape development around it and to provide information about the driving forces behind those changes, such as climate and human impact. The findings show that the basin was an open marine bay between 7640 and 5500 cal. yr BP. After 5500 cal. yr BP, the low rates of sea-level rise led to gradual infilling of the basin. The prevalence of mesic herb-grass steppe around the site, as well as the expansion of broad-leaved trees in the Crimean mountains, indicate relatively warm and humid climate conditions during the Mid-Holocene. Elemental proxies and marine NPPs point to a transition to lagoonal conditions from 4270 cal. yr BP. The progressive shallowing of the basin was accompanied by the spread of more xeric Artemisia-grass steppe, which suggests a shift to arid conditions. The occurrence of cereal pollen from 3660 cal. yr BP may indicate the first signs of cultivation in the study area. The active build-up of a sand barrier from 3000 cal. yr BP led to a gradual separation of the basin from the sea. By 900 cal. yr BP, the fully-formed sand barrier resulted in a transformation of the lagoon into a hypersaline lake. The closing of the lagoon was accompanied by an expansion of halophytic communities around the site. Human-induced vegetation changes became more pronounced with the development of agrarian and pastoral activities around the site from ca. 750 cal. yr BP.

Holocene geomorphological evolution of a sediment-starved coastal embayment in response to sea level change: Insights from the Qing'ao Embayment, southern China

Aiming to gain a better understanding of the response of sediment-starved coastal systems to the climate-driven sea level change, this study examines the Holocene evolution history of Qing'ao Embayment, southern China, as a case study. Results suggest three distinct stages of the evolution history: Stage 1 (8400–6000 cal yr BP) records an initial sedimentation phase associated with the early Holocene marine transgression into the embayment. Stage 2 (6000–3000 cal yr BP) records early sediment deposition under relatively strong hydrodynamic inshore/open-bay environment during early marine regression. Stage 3 (3000 cal yr BP to present) records two substages: Stage 3a relates to the semi-enclosed bay, intertidal and lagoonal salt marsh facies between 3000 and 1300 cal yr BP, and Stage 3b records the final infilling of the embayment into a lagoonal plain. This evolution model suggests that the rates of sea level change and sediment accretion are the two major controlling factors for the Holocene geomorphological evolution of sediment-starving coastal systems.Comparison of the evolution of Qing'ao embayment with sediment-supply rich large-river estuary/deltas reveals unique features in the response to Holocene sea level change of this sediment-starved embayment: During the early Holocene marine transgression, sediment starts to accumulate in the small embayment around 8400 cal yr BP, hundreds of years later than in large river estuaries. During 8400–6000 cal yr BP, sediment accretion rate remains dramatically lower than sea level rise rate, which results in the quick growth of sediment accommodation space during this stage. Around 6000 cal yr BP, though sea level has remained relatively stable and large-river deltas have been growing for about 1000 years, the sediment-starved embayment was still under shallow marine and/or open bay conditions. At 3000 cal yr BP, shoreline started to prograde in sediment-starved embayment, which is about 3000 years later than large river deltas. Finally, agricultural activity started around 1300 cal yr BP in the embayment, thousands of years later than large river deltas. Limited or minimal fluvial sediment supply to the small embayment has constrained the land expansion during the sea level stabilization since mid-Holocene, and the limited living space might result in the much later agricultural activity in such coastal system.Due to the different balances between sea level change and sediment flux, sediment-starved coasts are expected to be under higher risks than large river deltas. However, earlier and more extensive human activities in large river basins have resulted in the reduction of sediment discharge that heighten the risks of large river deltas against future sea level rise. Thus, more attention should be paid to the coastal sediment supply budgets in the context of the background of rising sea level.

Gastrochaenolites as Palaeoenvironmental Information Traps: The Case of the Tholos of La Pastora (Valencina de la Concepción, SW Spain)

ABSTRACT In the Mio-Pliocene calcareous sandstone slabs used as capstones at La Pastora tholos in the Copper Age megasite of Valencina de la Concepción-Castilleja de Guzmán (SW Spain), marine bioerosion structures produced in the 3rd millennium BCE were recognised. In this work, we focus on the perforations made by the lithophage bivalve Petricola lithophaga, called Gastrochaenolites, specifically on its functionality as a ‘trap’ of sediment of the environment where they were produced and of which there are no observable outcrops. The microfaunal content consisting of planktonic and benthic foraminifera as well as ostracods was studied. It was possible to infer the palaeoenvironmental conditions of the place where the slabs were quarried, c. 4700–4600 years ago, which correspond to a wide marine bay. The presence of benthic foraminifera like Astrononium stelligerum, Elphidum crispum, Ammonia beccarii and ostracods like Loxoconcha elliptica and Cytherois fischeri implies that the sector of the bay had a water temperature of no more than 20°C, a bathymetry between 0 and 25 m of depth. Also, episodes of fluvial influence caused a variation in water salinity between 30 and 35‰, attested by the presence of euryhaline species of ostracods from low energy environments and clay substrates, thus confirming estuarine conditions.

Benthic foraminifera in the Nakdong River Delta (southeast Korea) and their response to middle Holocene climatic change in the coastal environment of the East Asian margin

• Benthic foraminifera in the NRD contain the Marine, Bay, and Opportunistic taxa. • Precipitation and resultant river discharge increased in Korean Peninsula at ∼ 4 ka. • Two small maxima of low oxygen-resistant taxon represent the fluctuated TWC. • Replacement of two species implies the enhanced East Asian winter monsoon at 4.6 ka. Fossil benthic foraminifera from five cores in the Nakdong River Delta (southeast Korea) were investigated to reveal paleoenvironmental changes across the middle/late Holocene transition, particularly focusing on ∼4 ka climatic event. Based on multi-dimensional scaling, benthic foraminifera are divided into (1) Marine taxa, (2) Bay taxa, and (3) Opportunistic taxa. Planktonic/total (benthic and planktonic) foraminiferal ratio decreased abruptly during 4.6–3.3 ka, and Nonionella stella was found commonly across ∼4 ka in core ND-01 (intermediate site among the five cores). These results imply that the ∼4 ka climatic event led to the stratification of less saline epilimnetic water underlain by more saline oxygen-poor hypolimnetic water in the Nakdong River Delta. This indicates temporal increase in precipitation in the Nakdong River drainage, which can be attributed to the intensified rainfall with the second Changma peak, associated with typhoons toward the Korean Peninsula. The small twin maxima of N. stella across ∼4 ka in core ND-01 were similar to those of the total sulfur contents in both Yeja Bay (southern Korea) and Lake Togo-ike (southwestern Japan). Such similarity in the stratigraphic patterns among the remote locations can be explained by the small-scale sea-level variations with the fluctuation of the Tsushima Warm Current, in addition to changes in precipitation. The common species of Haynesina sp. A was replaced by Elphidium somaense after ∼4.6 ka, which is likely due to the shift of passive dispersal as a result of the enhanced East Asian winter monsoon and/or the change in the westerly jet path.

Nordlaguna – A unique lake basin at the foot of the Beerenberg volcano, Jan Mayen, containing partially enigmatic sediments

Sediments from the only permanent lake on the island of Jan Mayen (71°N, 08°30′W), Lake Nordlaguna (NL), were investigated. The lake, with an area of ∼1 km2, is situated at the foot of the world's northernmost active subaerial volcano and is separated from the sea by a 150–240 m wide beach barrier, which reaches 4–5 m above sea level. Most of the lake is deeper than 25 m, with the deepest part being 36 m. Altogether five coring sites, evenly spread out, were chosen and the sediment cores were retrieved from the lake ice with Uwitec and Nesje corers. After detailed descriptions of the very organic-poor and silt dominated sediments (of supposedly tephra-dominated origin), three sites were chosen for further analyses: macrofossils for 14C dating, tephra chemistry, C, S, grain-size, and XRF analyses. Based on 14C dates and the occurrence of the so-called Eggøya tephra (AD 1732), age models show variable bottom ages for the three sites: ∼3000, 600 and 400 cal yr BP. Due to the position of the core sites, with different sediment source areas, the elemental signals vary considerably between sites. An interesting feature of the lake is an isolated stock of Arctic char, which shows that the now land-locked lake has once been in contact with the sea. The almost total lack of organic material excluded any advanced paleo-ecologic investigations of the lake, and the study therefore focused on its marine-limnic history by different examinations of the XRF data with focus on the oldest and longest record. This development is based on elemental ratios (Br/Zn), PCA analyses of a center log ratio (clr) transformation of the original XRF data and magnetic susceptibility. It shows that the lake was isolated just before the time of the Eggøya tephra fall-out (∼220 cal yr BP), when the stock of Arctic char was most likely isolated from the sea. This was preceded by a ∼2200 yr long period of marine bay with a more or less open connection with the sea, and thus varying fresh-water impact. Between ∼2400 and 2600 cal yr BP the basin was more or less isolated, preceded by almost full marine conditions for at least the 300–400 preceding years we have data from, a period when relative sea level might have been higher.

From the sea strait to the meromictic lake: Evolution and ecosystem of a water body at the Fiard Coast (Lake Kislo-Sladkoe at the Karelian Coast of the Kandalaksha Bay, the White Sea, Russia)

Fiard coasts are common on the periphery of the areas previously covered by ice sheets. The conditions in such areas are favorable for separation of bays and straits from the sea. As a result of the glacial isostatic adjustment of the area the fiards would be transformed into coastal lakes. To discover the regularities of evolution of such water bodies, we studied topography, sea and lake sediments, hydrology and diatom associations of meromictic Lake Kislo-Sladkoe at the Karelian Coast of the Kandalaksha Bay, the White Sea, Russia (66°32′54″N, 33°08′05″E). Detailed geomorphological, geodetic, bathymetric, and aerial imagery field works have been completed on the coastal area. We built a Digital Elevation Model (DEM) of the coast and seabed. Radioisotope dating (210Pb, 14С), grain size distribution, loss on ignition, Corg/Norg ratio and diatom analysis have been completed for the entire 1.5-m sequence of the Lake's sediments. Currently, the Lake Kislo-Sladkoe communicates with the sea through a rising sill. We have established that the water body is meromictic due to its upper water layer being of variable salinity, middle layer comprising of aerated salty water, and the near-bottom water layer being anaerobic. However, several-year-long periods of water stratification alternate there with occasional late-autumn or early-winter flushes. The water body evolution falls into four stages: (1) a strait with an active hydrodynamic environment (prior to 1500–1560s), (2) a strait with a variable hydrodynamic environment (1500–1560s to 1850–1890s), (3) a semi-isolated lagoon with a quiet hydrodynamic environment (1850–1890s to early 1950s), and (4) a meromictic lake at an early stage of separation from the sea (early 1950s to present). We show how coastal processes on fiard coasts change the mode and duration of isolation of coastal water bodies from the sea. Based on the assessment of the rate of the post-glacial rebound and hydrological conditions of the coastal area we propose an approach to estimating the duration of transitional phase between a marine bay or strait and freshwater lake, including its meromictic stage. We predict that the meromictic stage of the lake will be completed no earlier than c. 100–200 years after the sill rises above the tidal zone.

Progressive opening of a shallow-marine bay (Oliete Subbasin, Spain) and the record of possible eustatic fall events near the Barremian-Aptian boundary

In this paper, we analyse the upper Barremian-lowermost Aptian Alacón Formation (Oliete subbasin, Maestrazgo Basin) of Spain to understand the progressive opening of a shallow-marine bay found on the northeastern margin of Iberia. The succession consists of four transgressive-regressive sequences (S1S4) bounded by widespread unconformities caused by rapid base-level fall. The transgressive interval of each sequence is characterized by relatively high detrital input and fresh-water inflow that caused the demise of shallow-marine benthic communities. The regressive interval of each sequence triggered progressive regeneration of the benthic carbonate producers. Sequences 1 and 2 consist of lacustrine to restricted shallow-marine facies, followed by accumulations of the gryphaeid oyster Ceratostreon , with progressive colonization of the bay by marine benthic communities subjected to frequent salinity oscillations. Sequences 3 and 4 represent the stabilization of open-marine conditions in the bay with widespread development of high-energy bioclastic tidal dunes. The long-term transgression around the Barremian-Aptian boundary, which gave rise to the progressive flooding of the Oliete bay, was episodically interrupted by shorter-term episodes of abrupt base-level fall, with the eventual subaerial exposure of the entire bay at the end of the deposition of the Alacón Formation. Our data suggest that the observed sequence architecture was mostly controlled by climatic and eustatic sea-level oscillations, with local synsedimentary tectonics having a minor impact. Two major sea-level fall events responsible for the discontinuities found on top of sequences 3 and 4 are possibly correlated to the cooling episodes close to the Barremian-Aptian boundary and during the earliest Aptian (predating the OAE 1a) described in many other worldwide basins. • The progressive opening of a shallow marine bay in Iberia (W Tethys) is documented. • Four sequences register progressive paleogeographical and paleoecological changes. • Sequence boundaries are tentatively linked to major cooling events KBa5 and KAp1.

Liquefaction and re-liquefaction of sediments induced by uneven loading and glacigenic earthquakes: Implications of results from the Latvian Baltic Sea coast

Seven internally-deformed layers were recognised in the shallow marine bay sediments deposited during mid Marine Isotope Stage 2 along the Latvian Baltic Sea coast bluff at Baltmuiža. Detailed sedimentological analyses of these deformed layers indicate that liquefaction was responsible for the development of soft-sediment deformation structures (SSDS) including injection structures, load casts, flame structures and pseudonodules. Traces of both initial liquefaction and re-liquefaction were recognised within at least four of the seven layers with SSDS (two different generations of pseudonodules and injection structures, clastic injection pipes, disrupted load casts). This is a unique finding, as it is difficult to re-liquefy sediment affected by previous liquefaction due to the increased packing of grains and decreased hydration after initial liquefaction. Furthermore, all layers with SSDS are characterised by eroded tops, which indicate that deformation took place when these layers were at the contemporary surface of sedimentation. We suggest that the initial liquefaction of fluidised coastal sediments was caused by various triggers (uneven loading, glacigenic earthquake), while the re-liquefaction could be related to a single trigger of mid-Late Weichselian glacigenic earthquakes at the front of the advancing last Fennoscandian Ice Sheet. Our results show that despite compaction after liquefaction, sediment re-liquefaction caused by an allogenic trigger is still possible under favourable conditions, i.e., sediment anisotropy, cyclic loading, and preserved high water saturation. Our findings are also the first to demonstrate the sedimentological imprints of re-liquefaction.

Environmental Implications and Chalcolithic Ornamental Use of Marine Barnacle Shells Present in the Tholos of ‘La Pastora’ (Valencina de la Concepción, Sevilla, Spain)

ABSTRACT The study of a set of marine arthropod shells from an archaeological excavation carried out in 1991–1992 in the tholos of La Pastora (Cooper Age Mega-site of Valencina-Castilleja, S Spain), has highlighted the environmental implications and ornamental use as beads not cited so far for this purpose. It is the barnacle species Chthamalus montagui Southward, 1976, of which are preserved 71 complete specimens. In this study a taxonomic analysis of these organisms is carried out, determining their classification and their physical and ecological characteristics, which make them especially suitable for this use. The interpretation is made regarding the environment in which these organisms were collected during the 3rd millennium BCE. Thus, it points towards a protected coastal area, but with a predominant marine influence, such as the wide marine bay that formed the mouth of the Guadalquivir River in those times. Finally, a radiocarbon analysis of one of these beads and two specimens of another species of barnacle collected in the rocks of the monument, provide a time range of 2760–2200 yr BCE. This range is consistent with the period of activity in the monument estimated by other authors.

A geo-chemo-mechanical study of a highly polluted marine system (Taranto, Italy) for the enhancement of the conceptual site model

The paper presents the results of the analysis of the geo-chemo-mechanical data gathered through an innovative multidisciplinary investigation campaign in the Mar Piccolo basin, a heavily polluted marine bay aside the town of Taranto (Southern Italy). The basin is part of an area declared at high environmental risk by the Italian government. The cutting-edge approach to the environmental characterization of the site was promoted by the Special Commissioner for urgent measures of reclamation, environmental improvements and redevelopment of Taranto and involved experts from several research fields, who cooperated to gather a new insight into the origin, distribution, mobility and fate of the contaminants within the basin. The investigation campaign was designed to implement advanced research methodologies and testing strategies. Differently from traditional investigation campaigns, aimed solely at the assessment of the contamination state within sediments lying in the top layers, the new campaign provided an interpretation of the geo-chemo-mechanical properties and state of the sediments forming the deposit at the seafloor. The integrated, multidisciplinary and holistic approach, that considered geotechnical engineering, electrical and electronical engineering, geological, sedimentological, mineralogical, hydraulic engineering, hydrological, chemical, geochemical, biological fields, supported a comprehensive understanding of the influence of the contamination on the hydro-mechanical properties of the sediments, which need to be accounted for in the selection and design of the risk mitigation measures. The findings of the research represent the input ingredients of the conceptual model of the site, premise to model the evolutionary contamination scenarios within the basin, of guidance for the environmental risk management. The study testifies the importance of the cooperative approach among researchers of different fields to fulfil the interpretation of complex polluted eco-systems.

Evaluating the impacts of El Niño events on a marine bay ecosystem based on selected ecological network indicators

El Niño events have great impacts on marine ecosystems worldwide, ranging from low trophic plankton production to fishery resources. Understanding how ecosystems respond to El Niño is the key to the success of ecosystem-based fisheries management (EBFM). However, few studies have focussed on the ecosystems respond to this natural perturbation in China seas, and the selection of effective ecological network analyses (ENA) indicators to evaluate the ecosystem response under El Niño conditions needs to be assessed. In this study, we constructed Ecopath models for Haizhou Bay in ENSO-neutral (2013) and El Niño (2015) years. Comprehensive analyses were conducted to evaluate ENA indicators in terms of sensitivity to the ecosystem variations, robustness to the model parameters uncertainties, and statistical check. Results showed that there were obvious variations in the species composition and biomass in the Haizhou Bay ecosystem under the El Niño event. Four optimal ENA indicators were selected, including total system throughput, total primary production, total system non-cycled throughflow, and ascendency. The indicators further showed a shrunken ecosystem size, increased energetic efficiency, and less organised ecosystem under the El Niño event. These findings enhance our understanding of ecosystem dynamics and underscore the need for precautionary management under El Niño conditions. Moreover, this work can be helpful in guiding the further selection of ENA indicators for evaluating and managing marine ecosystems during El Niño events elsewhere and thusly contribute to the implementation of EBFM.

Population dynamics of Donax trunculus on the sandy beach of Taghazout (southern Morocco)

The study of the structure and the dynamics of populations exposed to environmental pollutants can be a useful investigative tool for finding the connections between different levels of biological organizationPopulation dynamics on wedge clam, Donax trunculus is still unknown in Morocco. FiSAT software (FAO-ICLARM Stock Assessment Tools) was used for calculating population parameters of this species. The specimens of D. trunculus (Linnaeus, 1758) were collected monthly in the Agadir Marine Bay (South of Morocco) for two years (January 2016–December 2017) from three stations (S1, S2 and S3), which are directly exposed to eventual pollutants owing to the developing tourism resort Taghazout Bay.The study of the population dynamics of D. trunculus shows that the annual mean of density, biomass and condition index, presents significant seasonal variations depending on the physico-chemical parameters and the animal’s life cycle. The monitoring of age-class frequency distributions of D. trunculus individuals revealed a slighter difference at the three study stations. Asymptotic length (L∞) was 37.96 mm and growth coefficient (K) was estimated at 1.93 year −1. Total mortality (Z) for D. trunculus was 3.30 year −1. Natural mortality (M) and fishing mortality (F) were 1.73 year−1 and 1.57 year −1 respectively. Exploitation level (E) was computed as 0.48, indicating an optimum level of exploitation of D. trunculus in the coastal waters of Taghazout. It is well demonstrated that bimodal recruitment takes place twice a year; one in late summer–early autumn and the other in spring. The results of this study provide information on the health status of this ecosystem receiving Taghazout Bay project.

Wastewater input reductions reverse historic hypereutrophication of Boston Harbor, USA.

This paper documents the changes that followed large nutrient (N and P) and organic matter input reductions to a major metropolitan marine bay, Boston Harbor (USA). Before input reduction, its N and P inputs fell in the upper range of the < 1-> 300 gNm-2 year-1 and < 0.1-> 40gPm-2 year-1 for coastal systems. Elevated nutrient and organic matter inputs are recognized causes of coastal eutrophication. Treatment upgrades and then diversion of its wastewater discharges offshore, lowered its N, P, and organic C inputs by 80-90%. The input decreases lowered its trophic status from hypereutrophic to eutrophic-mesotrophic. With the reversal of hypereutrophication, pelagic production and phytoplankton biomass decreased, and the nitrogen limitation relative to phosphorus limitation increased. Benthic metabolism and dissolved inorganic N fluxes decreased, and benthic-pelagic coupling was altered. Bottom-water dissolved oxygen, already at healthy levels, increased, and seagrass expanded. Coastal management requires that the changes, following the nutrient and organic matter input reductions implemented to address eutrophication, be understood. Boston Harbor's recovery, because its water column was vertically well mixed and marine, was more pronounced than in many other systems.

Spatial-temporal changes and the influences of Hg sources in Jiaozhou Bay

Using investigation on Hg in May and August 1990 in Jiaozhou Bay, this paper analyzed the spatial-temporal changes of Hg sources, and the influences on spatial-temporal changes of Hg contents. Results showed that the major Hg sources in May were atmosphere deposition in the center of the bay and the wharf in the north of the bay, whose source strengths were 0.208 μg L−1 and 0.194 μg L−1, respectively. Meanwhile, the major Hg sources in August were also atmosphere deposition in the center of the bay and the wharf in the north of the bay, yet whose source strengths were relative low as 0.055 μg L−1 and 0.053 μg L−1, respectively. In May, Hg contents in surface waters were higher than in bottom waters. After three months from May to August, a large amount of Hg was accumulated in sea bottom by means of continuous sediment process, resulting in Hg contents in surface waters in the center of the bay were lower than in bottom waters in August, while in the north of the bay mouth Hg contents were homogeneous between surface and bottom waters. At temporal scale, the source input amounts were decreasing from May to August, and Hg contents were decreasing from May to August. However, by means of sediment and accumulation effects, Hg contents in bottom waters were tending to be higher than or closed to what in surface waters. In general, the spatial-temporal changes of Hg contents in marine bay were strongly influenced by the spatial-temporal changes of the Hg sources.