Coastal Marine Sediments Research Articles

Impact of organic carbon reworking upon GDGT temperature proxies during the Paleocene-Eocene Thermal Maximum

Glycerol dialkyl glycerol tetraethers (GDGTs) have been widely applied to coastal marine sediments to reconstruct past temperature variability. However, coastal environments are characterised by variability in the source, age and/or thermal maturity of different organic carbon (OC) pools and may bias various GDGT-based proxies. Here we analyse TEX86 and MBT5MEvalues within a shallow marine sediment core (South Dover Bridge, Maryland) from the Paleocene-Eocene Thermal Maximum (PETM; 56 million years ago (Ma)) to explore how changes in OC reworking influence GDGT-derived sea surface and terrestrial temperature estimates, respectively. We demonstrate that TEX86 values are unaffected by an increase in soil- and fossil organic carbon during the PETM. In contrast, we find large and unexpected variations in MBT5ME-derived temperature estimates (∼6 to 25 °C) during the onset and core of the PETM at some sites. This coincides with input of reworked terrestrial OC from the Cenomanian-aged Raritan Formation. However, there is also an increase in the degree of cyclisation of tetramethylated branched GDGTs, suggesting that branched GDGTs are also derived from marine in-situ production. These factors preclude terrestrial temperature reconstructions at this site. We explored whether OC reworking is problematic in other PETM-aged coastal environments. Using GDGT metrics and the Branched and Isoprenoid GDGT Machine learning Classification algorithm (BIGMaC), we demonstrate that TEX86 values are mostly unaffected by changes in OC sources. However, MBT5ME values are affected by marine and/or freshwater overprints, especially in environments with low terrestrial OC input. Taken together, this study highlights the importance of constraining the provenance of different GDGTs in marine and lacustrine environments.

Temporal and Spatial Trends in Benthic Infauna and Potential Drivers, in a Highly Tidal Estuary in Atlantic Canada

Infaunal invertebrate communities of coastal marine sediments are often impacted by human activities, particularly in harbours and estuaries. However, while many studies have attempted to identify the key factors affecting benthic infauna, few have done so for highly energetic tidal estuaries. Samples were collected over a decade (2011–2020) from a series of reference sites in Saint John Harbour (45.25° N, 66.05° W), a highly tidal estuary in the Bay of Fundy, Canada. These data were used to examine spatial and temporal trends in infaunal invertebrate communities and sediment properties and to determine the extent to which the biological patterns were driven by measured physical and chemical variables. There were substantial differences among sites in infaunal invertebrate abundance (median ranging from 688 to 13,700 individuals per square meter), infaunal species richness (median ranging from 8 to 22), and Shannon diversity (median ranging from 1.26 to 2.34); multivariate analysis also revealed variation in species composition among sites. Sediment contaminant concentrations also varied among sites, but differences tended to be smaller (e.g. median chromium concentrations ranging from 21.6 to 27.6 mg/kg). Sample contaminant concentrations were all below probable effect levels, and almost all below threshold effect levels (Canadian interim sediment quality guidelines), but relationships with biological data were still detectable. However, physical variables (depth, sediment characteristics) were better predictors of biological variables and community composition. These results confirm the importance of physical factors in shaping infaunal communities in soft-sediment habitats in tidally influenced coastal waters.

Response of microbial communities to nutrient removal in coastal sediment by using ecological concrete.

Ecological concrete (eco-concrete) is a kind of environment-friendly material with porous characteristics. In this study, the eco-concrete was used to remove the total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in marine coastal sediment. The bacterial communities in sediment and on eco-concrete surface were also investigated by using high-throughput sequencing and quantitative PCR of 16S rRNA gene. We found that the mean removal efficiencies of TN, TP, and TOC in treatment group were 8.3%, 8.4%, and 12.3% after 28days. The bacterial community composition in the treatment group was significantly different from that in the control group on day 28. In addition, the bacterial community composition on eco-concrete surface was slightly different from that in sediment, and the copy numbers of 16S rRNA gene were higher on eco-concrete surface than in sediment. The types of eco-concrete aggregates (gravel, pebble, and zeolite) also had effects on the bacterial community composition and 16S rRNA gene copy numbers. Furthermore, we found the abundant genus Sulfurovum increased significantly on eco-concrete surface in the treatment group after 28days. Bacteria belonging to this genus were found having denitrification ability and were commonly detected in bioreactors for nitrate removal. Overall, our study expands the application scopes of eco-concrete and suggests that the bacterial communities in eco-concrete can potentially enhance the removal efficiency of nutrients in coastal sediment.

Spatial and temporal distribution of hydrogen sulfide and sulfur species in coastal marine sediments collected from Osaka Bay, Japan

The identification of sulfur species in coastal marine sediments provides insight into the sulfur cycle in coastal seas. This study revealed the spatial and temporal distribution of hydrogen sulfide in the sediment pore water and sulfur species in the marine sediments in Osaka Bay, Japan using a combination of detection tubes with the formation of a color band of lead sulfide and X-ray absorption fine structure spectroscopy to identify sulfur species. The sulfur species present in the sediment in this study were somewhat affected by the sediment pore water, and the solid sulfur species identified in the surface sediments were sulfate, thiosulfate, elemental sulfur, and pyrite. These results revealed that the process of change in the sulfur species in the sediments could be categorized into three subprocesses. (1) Hydrogen sulfide was generated in the sediment pore water and scavenged by oxidation into sulfur and pyrite formation. Pyrite was successively oxidized into thiosulfate and sulfate when the dissolved oxygen in the bottom water was sufficient. (2) When the dissolved oxygen was depleted at the innermost part of the Bay in October and November, pyrite might have been oxidized into sulfate by iron and manganese in the sediment. (3) For the western and southern parts of the Bay, because vertical mixing supplies oxygen to the seabed, the formation and oxidative scavenging of hydrogen sulfide in the sediment pore water was balanced. Thus, the hydrogen sulfide in the sediment pore water remained undetected.

Marine Fungi Select and Transport Aerobic and Anaerobic Bacterial Populations from Polycyclic Aromatic Hydrocarbon-Contaminated Sediments.

The organization of microbial communities in marine sediment relies on complex biotic and abiotic interactions. Among them, the interaction between fungi and bacteria plays a crucial role building specific microbial assemblages, resulting in metabolic networks adapted to environmental conditions. The fungal-bacterial interaction (FBI) includes bacterial translocation via fungal mycelia, allowing bacterial dispersion, and ecological niche colonization. In order to demonstrate that the translocation of bacteria through fungal mycelia involves bacterial selection, the mycelia of two fungi isolated from marine coastal sediment, Alternaria destruens F10.81 and Fusarium pseudonygamai F5.76, showing different strategies for uptake of polycyclic aromatic hydrocarbon (PAH), homogenous internalization and vacuole forming respectively, were used to translocate bacteria through hydrophobic hydrocarbon contaminated sediments. A. destruens F10.81 selected four specific bacteria, while bacterial selection by F. pseudonygamai F5.76 was not evident. Among the bacteria selected by A. destruens F10.81, Spirochaeta litoralis, known as strictly anaerobic bacterium, was identified, indicating that A. destruens F10.81 selects and transports both aerobic and anaerobic bacteria. Such a result is consistent with the observed formation of anoxic micro-niches in areas surrounding and affected by fungal hyphae. Our findings provide new insights on the selection and dispersion of bacterial communities by fungi, which are crucial for the organization of microbial communities and their functioning in coastal PAH-contaminated sediments. IMPORTANCE The study provides advances for understanding fungal-bacterial relationships, particularly on the selection and dispersion of bacterial communities by fungi, which are crucial for the organization of microbial communities and their functioning in coastal PAH-contaminated sediments. The transportation of bacteria via fungal hyphae (fungal highway) results in bacterial selection; in particular, fungal hyphae offer adequate conditions for the transport of both aerobic and anaerobic bacteria through hydrophobic patches for the colonization of novel niches.

POLYCHRONIC-POLYGENIC PARAGENETIC-SPATIAL TITANIUM ORE SYSTEM OF THE SEDIMENTARY COVER OF THE SOUTH-WESTERN PART OF THE KORSUN-NOVOMYRHOROD PLUTON

Information is provided on the titanium-zirconium ore content of the weathered crust and continental and coastal Mesozoic- Cenozoic deposits within the Byrzulivska, Valuivska, Likarivska, Andriivska, Novomyrgorodska, Vytiazivska areas, which are located in the southwestern part of the Korsun-Novomyrhorod pluton within the Novomyrgorod massif. On the basis of the coordinates, description and results of testing wells for the specified areas, a target database was created on the basis of which cartographic constructions were made. The results of studies of the spatial distribution of the thickness of the weathering crust, sands and redeposited kaolins of the Lower Cretaceous within the Byrzulivska, Valuivska, Likarivska, Andriivska areas are presented; sands and redeposited kaolins of the lower-middle Eocene within the boundaries of the Novomyrhorodska area; Quaternary sands within the Vytiazivska area. It was found that the lateral distribution of the thickness of the weathering crust is due to the relief of the surface of the crystalline rocks of the foundation and the partial erosion of the eluvium during the geological development of the territory. Instead, the uneven distribution of the thickness of Mesozoic-Cenozoic sediments is caused by the amount of terrigenous material entering the sedimentation basin, facies conditions of formation, and erosion and redeposition of sediments to higher stratigraphic levels. The lateral distribution of the average content of ilmenite, rutile, and zircon and the correlations between these minerals in the weathering crust, redeposited kaolins, and sands of the specified areas were studied. It was found that the ore bearing of the weathered crust and the Mesozoic-Cenozoic continental and coastal marine sediments is paragenetically and spatially related to each other and is determined by the ore bearing of the crystalline rocks of the foundation. The average content of ilmenite, rutile and zircon in the weathering crust is determined by their average content in the parent rocks of the crystalline basement, in the continental and coastal formations of the Mesozoic and Cenozoic — by the content of minerals in the weathering crust and intermediate reservoirs (for deposits that do not lie on the weathering crust), facial conditions of formation. As a rule, aureoles of increased mineral content do not coincide spatially, and correlations between their average content are mostly very weak or absent. The obtained results confirm and complement the results of previous studies on ore bearing capacity and prospects for increasing the mineral-raw material base of critical raw materials within the Novomyrhorod massif. Research results can serve as an information base for forecasting, prospecting and mining operations within the investigated areas.

GEOLOGICAL STRUCTURE AND ORE-BEARING OF THE YURSKA AREA OF THE MEZHYRICHNЕ TITANIUM ORE DEPOSIT

Information on the geological structure of the Yurska area of the Mezhyrichnе titanium ore deposit is provided. It was found out that the geological structure of the site involves crystalline rocks of the foundation, their weathered crust and continental and marine deposits of different ages of the Mesozoic and Cenozoic: Lower Cretaceous continental (Irshan suite), Upper Cretaceous coastal marine (Moshno-Rudnyan suite), Paleogene (marine and continental), Neogene and Quaternary continental sediments. A useful mineral of the Jurassic area is ilmenite, which forms ore bodies in the crust of weathering of crystalline rocks of the foundation, sediments formed due to erosion and redeposition of eluvium (Irshan suite), as well as in rocks formed due to erosion of secondary ilmenite reservoirs (Moshno-Rudnyan suite and, to a lesser extent, heterogeneous genetic formations of the Quaternary system). The maximum content of ilmenite in the weathering crust is 430.2 kg/m3; in fluvial kaolins of the Irshan suite — 1447.4 kg/m3; in differently-grained sands of this suite — 506.2 kg/m3; in the sandy-siliceous horizon of the Moshno-Rudnyan suite — 256.7 kg/m3; in Quaternary loams and sandy loams — 146.4 kg/m3. The industrial placers of ilmenite are localized in the formations of the Irshan suite. Sandy-siliceous rocks of the Moshno-Rudnyan suite with an ilmenite content of more than 15 kg/m3 are included in the composition of the upper part of the industrial placer layer. On the basis of the coordinates, description and testing of the 1613 wells, a target database was created, on the basis of which a set of maps was built: maps of the lateral distribution of the average ilmenite content in the gruss of zone dezintegration of weathering rocks, in the kaolins of eluvial, in the fluvial kaolins and sands of the Irshan suite, and in the sandy-siliceous rocks of the Moshno-Rudnyan suite; maps of bottom and top surface relief and thickness of kaolins and sands of the Irshan suite and sandy-siliceous rocks of the Moshno-Rudnyan suite. The structural (nature of the relief of the bottom and top surfaces of ore-bearing deposits and their thickness) and material (lithological composition, distribution of ilmenite along the lateral and in the vertical cross-section of ore-bearing deposits) of placers parameters were studied. It was found that the relief of the bottom and of the top of the ore-bearing formations is uneven with local elevations and depressions. It was found that the content of ilmenite in the weathering crust increases, as a rule, up the section from the zone of disintegration and leaching to the zone of final hydrolysis and oxidation of weathering products. The vertical distribution of ilmenite in the Irshan and Moshno-Rudnyan rocks is uneven with a general tendency to decrease upwards along the section. Sometimes there are several enrichment horizons of insignificant thickness, or a significant content of ilmenite is present in the top of the rocks. Sometimes there are several enrichment horizons in the rocks, as a rule, in the lower and upper parts of the geological section. The directionality and strength of correlations between the relief of the sole and the surface, thickness and average content of ilmenite in ore-bearing rocks of different-ages and different-genetics of the Cretaceous system were investigated. It was found that the correlations have different directions and are mostly very weak, weak, sometimes moderate, medium and rarely strong. It was established that the distribution and content of ilmenite in the weathering crust is determined by its distribution and content in the crystalline rocks of the foundation. The distribution and content of ilmenite in the continental fluvial formations of the Irshan suite is determined mainly by the facies conditions of sedimentation and is rarely determined by its significant content in the underlying rocks. The distribution of ilmenite in the formations of the Moshno-Rudnyan suite is determined by the facies conditions of formation, and its content is determined by its content in the underlying rocks.

Early Jurassic Flood Basalt Volcanism on the Franz Josef Land Archipelago: Geological and Palynostratigraphical Data

Biostratigraphic evidence of the presence of Early Jurassic flood basalts on the Franz Josef Land archipelago is presented. The flood basalts form layered section with two units, which is not discovered for Early Cretaceous basalts. The lower unit is composed by large-columnar basalts (colonnade), and the upper unit by small-columnar (entablature) chaotic-fan basalts. On the Hooker Island, the basalt flow is exposed on the Sedov Plateau, on the Lunacharsky Rock Cape and, possibly, on Al’banov Cape. On the southern slope of the Sedov Plateau, the basalt flow overlaps sands and sandstones, which contain palynoassemblage of the lower Toarcian. In the Lunacharsky Rock Cape outcrop, the underlying basalt sands are of the Pliensbachian to Early Toarcian chronostratigraphic interval. Apart from the Hooker Island, we observed basalts with the “colonnade/entablature” on three other islands: Scott Keltie, May and Leigh-Smith. The most complete section was found in the western part of the Leigh-Smith Island, where basalts are underlain and overlapped by sand units. The underlying sands in contact with basalts have a quenching zone. There is no quenching zone at the contact with the overlapping sands. A palynocomplex from the lower sand unit is early Toarcian in age. The palynocomplex found in the upper sand unit indicates its accumulation in the interval from the lower part of the late Toarcian to the early Aalenian. A palynological study of the underlying and overlying deposits of the basalt flow has shown that the flow is underlain by continental and coastal-marine sediments of the Pliensbachian to the upper part of the early Toarcian age interval. Basalt flow is overlain by the earliest late Toarcian–early Aalenian marine sediments. According to the modern chronostratigraphic scale, the age of the basalt flow can be estimated as approximately 180 million years, which is quite consistent with the earlier obtained 40Ar/39Ar data of 189.1 ± 11.4 million years. These data indicate that the basalt flow was formed during a narrow stratigraphic interval of the uppermost lower–earliest upper Toarcian.

New insights into microbial community coalescence in the land-sea continuum

The land-sea continuum constitutes a mixing zone where soil microbial communities encounter, via runoff, those inhabiting marine coastal sediment resulting in community coalescence. Here, we propose an experimental approach, mimicking the land-sea continuum, to study the microbial community coalescence events in different situations, by 16S and 18S rRNA genes metabarcoding. The microbial community structure of sediment diverged with the soil inputs. For prokaryotes, phylogenetic enrichment and amplicon sequence variants (ASVs) replacements characterized the community changes in sediment receiving soil inputs. For fungi, despite phylogenetic enrichment was not observed, the fungal ASVs richness was maintained by soil inputs. Comparison of microbial communities revealed ASVs specific to sediment receiving soil inputs, and also ASVs shared with soil and/or runoff. Among these specific ASVs, four bacterial and one fungal ASVs were identified as indicators of coalescence. Our study provides evidences that coalescence involves the mixing of microorganisms and of the environment.

Mobility of metal-organic pollutants in the emerging coastal-marine sediment of the Baltic Sea: The case-example of organotin compounds in sediments of the Gulf of Finland

Results of organotin and heavy metals pollution study of bottom sediment within three key areas in the Eastern Gulf of Finland (Baltic Sea) in the vicinity of Gogland and Moschny Islands and Vyborg Bay sampled during two seasons of 2017 and 2018 are presented.The studied bottom sediments contain organotin compounds in amounts (∑OTs from 5.7 to 123 ng/g) exceeding the permissible international standards, which can have a toxic effect and lead to pathological changes of aquatic organisms. The tributyltin was the prevail component of organotin compounds in bottom sediments in 2017, which high content (average 6.3 and 30 ng/g for Moschny and Gogland islands respectively) and low degradation coefficient (BDI: 0.1–0.8) indicate a permanent source of pollution. But the 2018 samples show an increase in BDI up to 1.7–3.3 that reveals the degradation of tributyltin over the annual period. But further monitoring of environmental pollution in the study areas is obviously necessary in view of the potential impact of these components on the irreversible change in the environmental situation for the entire Baltic region.

Climatic change around the 4.2 ka event in coastal areas of the East China Sea and its potential influence on prehistoric Japanese people

Climate change during the Holocene is thought to have had a significant impact on human migration and development. In Japan, the earliest prehistoric culture based on hunting and gathering began about 16,000 years ago (the Jomon era). At least 3000 years ago, people with paddy rice cultivation skills started to migrate from mainland China, causing an explosion of population growth, lifestyle changes, and changes to the level of civilisation (Yayoi era). To clarify the climatic changes that potentially led to the movement of the Yayoi people to Japan, we analysed the palaeotemperature changes recorded in coastal marine sediment cores obtained from the Zhejiang coast in China, where the first paddy rice cultivation occurred, and northern Kyushu Island, where it was introduced to Japan. The reconstructed temperature fluctuations over the past 7000 years from both sites were similar on the scale of hundreds to thousands of years. The cold periods that occurred approximately 300 and 4200 years ago, which are related to the Little Ice Age and 4.2 ka events, respectively, may have been caused by modulations of the East Asian summer monsoon. Our study suggests that enhanced coastal upwelling may have amplified the cold climate of the 4.2 ka event on the Zhejiang coast. Our results support the recently proposed hypothesis that climate change prompted the collapse of the Yangtze civilisation and the migration of paddy rice farmers to other parts of Asia, including Japan. In contrast, the Jomon people, who still survived mainly based on hunting and gathering at that time, might have avoided a major population collapse.

Characterising contaminants distribution in marine-coastal sediments through multivariate and nonparametric statistical analyses: a complementary strategy supporting environmental monitoring and control

This work investigates a statistical approach analysing data from monitoring activities on marine-coastal areas for environmental quality determination and surveillance. Analyses were performed on a database of the Environmental Protection and Prevention Agency of the Puglia Region. As, Cr, Ni, and Pb concentration values in marine sediments and biota from 2013 to 2015 and 2017 were processed to investigate different contaminant characteristics. Hierarchical cluster analysis identified three contaminant distribution classes with (1) highest Cr, Ni, and Pb concentrations, (2) highest As concentration, and (3) lowest contaminants concentration. The Kruskal-Wallis and Friedman tests showed that contaminant distributions were statistically different when considering the monitoring years and classes. However, statistical similarities resulted during the 2013–2017 and 2014–2015 periods. Spearman’s coefficients displayed positive correlations among the pollutants in each matrix and mainly negative correlations for matrices comparison. This methodology aims to provide a practical support for monitoring to identify potential environmental deterioration over time and correlations with specific contamination sources.

Ecological risk assessment of heavy metal pollutants and total petroleum hydrocarbons in sediments of the Bohai Sea, China.

Heavy metals and organic pollutants like total petroleum hydrocarbons (TPHs) in coastal marine sediments are receiving extensive attention, as they may pose a serious threat to the aquatic environment and ecosystem health. To date, however, data on the long-term variations in the levels of sedimentary heavy metals and TPHs as well as their ecological risks are relatively limited. Here, we conducted 12 cruises spanning 3years in the Bohai Sea and obtained ~1400 sediment samples to explore the long-term variations of heavy metals (i.e., Hg, As, Cu, Zn, Pb, Cd) and TPHs, and to assess their potential ecological risks. The results suggested that the ranges for the levels of Hg, As, Cu, Zn, Pb, Cd, and TPHs in sediments between 2019 and 2021 were <0.01-0.07, 0.23-10.72, 8.07-20.67, 25.52-46.55, 10.94-28.19, 0.14-0.56, and 9.14-18.41mgkg-1, respectively. Based on the single factor evaluation (Fi) for sediment quality, we found that most of the evaluation factors in the study area met the requirements of sediment quality standard (i.e., Fi<1), except for the factor of metal Cd in some cases. The implication is that the sediment in the Bohai Sea was fairly clean in terms of heavy metals and TPHs. However, the concentration of metal Cd exceeded the sediment quality standard during May 2019 and 2020 (i.e., Fi>1), indicating that Cd could be identified as a major pollutant in surface sediments. Also, based on the ecological risk assessment (Ei) of heavy metal pollutants, we found that the metal Cd had reached a level with potential ecological risk in some cases (80≤Ei<160). As such, we further suggested that the Cd contamination might have a potential risk on the Bohai Sea' ecosystem.

Factors structuring microbial communities in highly impacted coastal marine sediments (Mar Menor lagoon, SE Spain).

Coastal marine lagoons are environments highly vulnerable to anthropogenic pressures such as agriculture nutrient loading or runoff from metalliferous mining. Sediment microorganisms, which are key components in the biogeochemical cycles, can help attenuate these impacts by accumulating nutrients and pollutants. The Mar Menor, located in the southeast of Spain, is an example of a coastal lagoon strongly altered by anthropic pressures, but the microbial community inhabiting its sediments remains unknown. Here, we describe the sediment prokaryotic communities along a wide range of environmental conditions in the lagoon, revealing that microbial communities were highly heterogeneous among stations, although a core microbiome was detected. The microbiota was dominated by Delta- and Gammaproteobacteria and members of the Bacteroidia class. Additionally, several uncultured groups such as Asgardarchaeota were detected in relatively high proportions. Sediment texture, the presence of Caulerpa or Cymodocea, depth, and geographic location were among the most important factors structuring microbial assemblages. Furthermore, microbial communities in the stations with the highest concentrations of potentially toxic elements (Fe, Pb, As, Zn, and Cd) were less stable than those in the non-contaminated stations. This finding suggests that bacteria colonizing heavily contaminated stations are specialists sensitive to change.

The influence of sedimentation regime on natural radionuclide activity concentration in marine sediments of the East Siberian Arctic Shelf

Transport and accumulation of radionuclides in the Arctic depends on many biogeochemical processes, which are changing at accelerated rates due to climate change and human economic activity. We present the results of a study on the features distribution of some natural radionuclides in the marine sediments on the East Siberian Arctic Shelf collected during several expeditions from 2008 to 2019. Average activity concentration of 232Th, 40K and 226Ra under the influence of different sedimentation regime increases from 40.7, 418 and 30.8 Bq/kg to 41.6, 423 and 34.9 Bq/kg respectively from coastal shelf marine sediments (<50% clay) to outer shelf marine sediments (>50% clay). Sediment particle size has a greater impact on radionuclides in the coastal shelf. An increase in the activity concentrations of 232Th and 226Ra with the increasing clay particles were found. On the outer shelf with a change in the sedimentation regime, the influence of the size composition decreased, at the same time, there is a correlation between the organic carbon concentration and the radionuclide activity concentration. Absolute maximums of natural radionuclide activity concentration (232Th = 70.9, 226Ra = 70.4, 40K = 591 Bq/kg) were detected in the Chaun Bay. The highest activity concentration of 226Ra was found in paleo-river valleys marine sediments. A low 232Th/226Ra activity concentration ratio indicates the enrichment of paleo-river valleys marine sediments with 226Ra. In the deep-sea sediments of the shelf slope on the contrary paleo-river valleys, this ratio is greatly increased.

Microbial succession during the degradation of bioplastic in coastal marine sediment favors sulfate reducing microorganisms

Marine environments are sinks for many contaminants, including petroleum-based plastic waste. Bioplastics, or biodegradable plastics derived from renewable resources, are considered promising alternatives as numerous studies have demonstrated their degradation in marine environments. However, their rates of degradation vary and microbial consortia responsible for its degradation are not well characterized. Previous research by our group has shown that polyhydroxyalkanoate (PHA) stimulates sulfate reducing microorganisms (SRM), enriches sulfate reduction gene pools, and accumulates antibiotic and metal resistance genes. Here, we quantify the degradation rate of PHA pellets in marine sediment and present the long-term temporal changes in PHA-associated SRM communities over 424 days. For comparative purposes, polyethylene terephthalate (PET) and ceramic served as biofilm controls and the free-living microorganisms in the overlying water column served as a non-biofilm control. PHA experienced a 51% mass loss after 424 days and a generalized additive mixed model predicted that 100% mass loss would require 909 days. Throughout the course of the 424-day exposure, PHA was colonized by a distinct microbial community while PET and ceramic were colonized by similarly structured communities. SRM comprised a larger proportion of the overall community (25 – 40%) in PHA-associated biofilms as compared to PET and ceramic controls across all timepoints. Further, the diversity of SRM was greater within PHA biofilms than PET and ceramic biofilms. This study shows that PHA degrades relatively slowly and promotes a long-term shift in microbial community structure toward sulfate reduction, demonstrating the ability of this manufactured polymer to alter its environment via the disruption of biogeochemical cycling, indicating that PHA rises to the level of pollutant in benthic marine systems.

Spatial variability of water quality and sedimentary organic matter during winter season in coastal aquaculture zone of Korea

We investigated the composition, source, and reactivity of sedimentary organic matter (OM) present in aquaculture systems along the Korean coast. A multi-isotopic approach was applied to 216 surface sediments from five sections: western (W)-1, W-2, southern (S)-1, S-2, and eastern (E)-1 sections. The 15N-enriched total nitrogen signatures in the surface sediments of the W-1 section may indicate that a substantial fraction of sedimentary OM has anthropogenic origins exported through the Han River. Simultaneously, the deposition of allochthonous OM is predominant in the S sections (Jinhae and Masan Bays). The 34S-depleted patterns at the S-2 section may indicate that sulfate reduction occurring at the sedimentary boundary contributes to active OM decomposition, depending on the increased sedimentation of the aquaculture-derived OM. Our results highlight that isotopic-based source tracking near aquaculture systems provide important information for identifying anthropogenic contamination in coastal marine sediments and for improving environmental management.

Antibiotic Resistance Genes Associated with Marine Surface Sediments: A Baseline from the Shores of Kuwait

Marine sediments are a sink for antibiotic resistance genes (ARGs) and antibiotic-resistant microbes (ARMs). Wastewater discharge into the aquatic environment is the dominant pathway for pharmaceuticals reaching aquatic organisms. Hence, the characterization of ARGs is a priority research area. This baseline study reports the presence of ARGs in 12 coastal sediment samples covering the urban coastline of Kuwait through whole-genome metagenomic sequencing. The presence of 402 antibiotic resistance genes (ARGs) were recorded in these samples; the most prevalent were patA, adeF, ErmE, ErmF, TaeA, tetX, mphD, bcrC, srmB, mtrD, baeS, Erm30, vanTE, VIM-7, AcrF, ANT4-1a, tet33, adeB, efmA, and rpsL, which showed resistance against 34 drug classes. Maximum resistance was detected against the beta-lactams (cephalosporins and penam), and 46% of genes originated from the phylum Proteobacteria. Low abundances of ESKAPEE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumanii, Pseudomonas aeruginosa, Enterobacter sps., and Escherichia coli) were also recorded. Approximately 42% of ARGs exhibited multiple drug resistance. All the ARGs exhibited spatial variations. The major mode of action was antibiotic efflux, followed by antibiotic inactivation, antibiotic target alteration, antibiotic target protection, and antibiotic target replacement. Our findings supported the occurrence of ARGs in coastal marine sediments and the possibility of their dissemination to surrounding ecosystems.

Effects of Field Simulated Marine Heatwaves on Sedimentary Organic Matter Quantity, Biochemical Composition, and Degradation Rates.

Simple SummaryMarine heatwaves (MHWs) are intensifying due to global warming. Based on their effects on biochemical reactions, they are also likely to affect coastal biogeochemistry. We investigated organic matter quantity, composition and degradation rates in nearshore sediments affected by simulated MHWs, with 1.5 and 5.0 °C anomalies, before and after 3 and 11 weeks from the release of an artificial warm water plume. MHWs enhanced organic loads (by >100%), with larger effects in the short-term under the highest temperature anomaly. Phytopigment contents increased (by 50–90%) in the short term but decreased to initial values in the longer one. The autotrophic and lipid contents decreased with time (by 15–50% 53–79%, respectively), suggesting a drop in the nutritional quality of organic matter, along with a slowdown of its turnover. We contend that MHWs’ intensification will affect not only species and communities but will also alter sediment biogeochemistry and, possibly, the energy transfer towards higher trophic levels.Since rising temperature (T) will enhance biochemical reactions and coastal marine sediments are hotspots of carbon cycling, marine heatwaves’ (MHWs’) intensification caused by climate change will affect coastal biogeochemistry. We investigated the effects of MHWs on sediment organic matter (OM) in a nearshore locality (NW Sardinia, Mediterranean Sea) receiving an artificial warm water plume generating T anomalies of 1.5–5.0 °C. Sediments were collected before and after 3 and 11 weeks from the initial plume release. Both MHWs influenced sedimentary OM quantity, composition, and degradation rates, with major effects associated with the highest T anomaly after 3 weeks. Both MHWs enhanced sedimentary OM contents, with larger effects associated with the highest T anomaly. Phytopigment contents increased in the short term but dropped to initial levels after 11 weeks, suggesting the occurrence of thermal adaptation or stress of microphytobenthos. In the longer term we observed a decrease in the nutritional quality of OM and a slowdown of its turnover mediated by extracellular enzymes, suggestive of a decreased ecosystem functioning. We anticipate that intensification of MHWs will affect benthic communities not only through direct effects on species tolerance but also by altering benthic biogeochemistry and the efficiency of energy transfer towards higher trophic levels.

Microplastics cause neurotoxicity and decline of enzymatic activities in important bioturbator Hediste diversicolor

Microplastics (MPs) tend to accumulate in marine sediments thus benthic fauna is particularly vulnerable to microplastic pollution. Hediste diversicolor is a widespread species in coastal marine sediments. It plays key ecological functions mostly related to bioturbation process which means sediment reworking due to the worm burrowing activity and building a network of galleries. Herein, we show that commercial plastic microspheres of two sizes (63–75 and 300–355 μm) have the potential to cause neurotoxicity in H. diversicolor. The whole-body acetylcholinesterase (AChE) activity – a common indicator of neurotoxic effect - was on average 60% lower in polychaetes exposed for 28 days to MPs served at environmentally relevant concentrations (0.08% sediment d. wt.), than in unexposed ones. Significantly reduced activities of antioxidant enzymes (SOD, CAT, GST) indicated suppression of the cellular antioxidative system in worms exposed to MPs. No changes were, however, observed in tGSH, lipid or protein oxidation measures (CBO, MDA), and in the energetic value of these polychaetes. The response was generally similar with no regard to MPs size. Only very few microspheres were found in polychaetes exposed to MPs spiked sediment.The potential role of MPs-associated pollutants as a factor responsible for observed biochemical effects, is discussed.