Salt Marsh Sediments Research Articles

Late-Holocene evolution of the Northern Bay of Cádiz from geomorphological, stratigraphic and archaeological data

The present paper deals with the historical evolution of the northern Bay of Cádiz (SW Spain) between the last eustatic maximum (6.5 ka BP) and the present day, by means of a series of independent proxies. The zone is constituted by the tidal estuary of the Guadalete River, filled with saltmarsh sediments during the late Holocene, due to the sheltering of the zone by a confining outer sandy barrier. The northern border of the Bay records an urban settlement of Phoenician Age (first millennium BC), Doña Blanca. A detailed survey was made in the contact between the Phoenician city and the saltmarshes in order to detect other possible urban structures related to the morphological and sedimentary evolution of this environment during historical times. Two campaigns with GPR Stream-X array were carried out as well as aerial imaging and topographic survey with UAV. In parallel, a total of 8 boreholes were made in different parts of the saltmarshes, including radiocarbon dating of selected samples for estimating sedimentation rates in the saltmarshes. Results obtained by georadar prospection and UAV survey revealed the presence of a second urban settlement on the marginal sedimentary plain, very probably installed upon a sandy fluvial island of the Guadelete River. The urban remains, of Punic Age, are partly covered by clay sediments due to the subsequent evolution of these saltmarshes, where sedimentation rates of up to nearly 2.4 mm/yr have been estimated for environments close to fluvial and/or tidal channels and hence more affected by sediment aggradation during flooding episodes. In recent times, river regulation by dams and the artificial desiccation and cropping of the saltmarshes have interrupted the natural trend of the area towards sedimentary silting up.

Young soils of a temperate barrier island under the impact of formation and resetting by tides and wind

The island Spiekeroog (Germany) at the southern North Sea coast exhibits an island tail (Ostplate) of which large parts formed after 1860 by gradual eastward deposition of marine sediments. This study aimed to (i) provide a first overview of soils on the Ostplate, (ii) verify whether soil formation stages in different landscape elements (dune chain, dune slacks, saltmarsh, pioneer zone) are linked to the island’s gradual development and (iii) to assess the impact of tides and winds on soil formation. Standard physicochemical properties of dune -and dune slack topsoils and 19 pedons (i.a. pH, total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and mean weight diameter (MWD) of water stable aggregates) were analyzed. Soils of the dune slacks, the saltmarsh and the pioneer zone classified as Gleysols which showed no trend towards differences along the Ostplate. The dune chain exhibited Protic Arenosols that were initially acidified in lee positions (min. pH = 5.1). Carbon (C) and nitrogen (N) isotopes (δ13C, δ15N) signatures of saltmarsh sediments were used as a proxy for the tidal influence on soil formation. In addition, sulfur (S) isotope (δ34S) signatures revealed insights on sulfur sources in the saltmarsh. The δ13C signatures of organic matter (OM) decreased and TOC/TN -and TOC/total sulfur (TS) ratios increased with increasing elevation and decreasing flooding frequency. At higher flooding frequency, δ15N resembled the dominant input of OM from the southern North Sea, at a lower interaction level, mixing of a wider range of sources was indicated. S isotopes indicated dissolved sulfate and reduced species as sulfur sources. It was concluded that an ongoing impact of wind-induced sand movement at the dunes, and flooding-induced sediment movement in the saltmarsh and the pioneer zone, repealed any potential disparities in soil formation stages, which might have existed along the Ostplate.

Onset of runaway fragmentation of salt marshes

Summary Salt marshes are valuable but vulnerable coastal ecosystems that adapt to relative sea level rise (RSLR) by accumulating organic matter and inorganic sediment. The natural limit of these processes defines a threshold rate of RSLR beyond which marshes drown, resulting in ponding and conversion to open waters. We develop a simplified formulation for sediment transport across marshes to show that pond formation leads to runaway marsh fragmentation, a process characterized by a self-similar hierarchy of pond sizes with power-law distributions. We find the threshold for marsh fragmentation scales primarily with tidal range and that sediment supply is only relevant where tides are sufficient to transport sediment to the marsh interior. Thus the RSLR threshold is controlled by organic accretion in microtidal marshes regardless of the suspended sediment concentration at the marsh edge. This explains the observed fragmentation of microtidal marshes and suggests a tipping point for widespread marsh loss.

Tidal rewetting in salt marshes triggers pulses of nitrous oxide emissions but slows carbon dioxide emission

Pulsed emission of CO2 following rainfall in terrestrial ecosystems is well characterized, but coastal wetlands show the opposite trend for CO2, and less is known about the responses of other biogenic greenhouse gases like CH4 and N2O. Tidal inundation in coastal wetlands such as salt marshes is an additional form of rewetting with the potential to cause biological pulses that may not resemble rain-induced pulses. Accurately predicting the carbon and nitrogen cycling in salt marshes requires estimates of pulse responses to both rainfall and tidal inundation, in addition to baseline greenhouse gas flux rates. We measured CO2, CH4, and N2O fluxes from salt marsh sediment cores while we simulated rewetting by rainfall and/or tidal inundation, and we measured the total and potentially-active microbial communities at the end of the experiment. Rewetting from tidal inundation and from rainfall led to a short term (begun within 1 h, concluded within ~1 d) pulse of N2O, a sustained drop in CO2 emission, but no change in CH4. The N2O pulse peaked on average at 20× and 10× baseline flux rates after tidal inundation and rainfall respectively. Peak N2O fluxes far exceeded the highest emission observed in field measurements at these sites. By global warming potential, the pulse of N2O only slightly offset the drop in CO2 emission, therefore rewetting had a net cooling effect on marsh radiative forcing. Microbial communities were similar in rewetted and non-rewetted cores two days after rewetting, which reflects rapid recovery and/or resilience of the community to rewetting. We estimated the contribution of pulsed vs. baseline N2O emissions to annual totals by modelling rewetting events over 65-year tide gauge and precipitation records, and found that pulsed emissions constitute the majority of salt marsh N2O emissions, and could constitute the entirety in marshes with a net-sink baseline.

Early Warning Signals for Rate-induced Critical Transitions in Salt Marsh Ecosystems

Intertidal ecosystems are important because of their function as coastal protection and ecological value. Sea level rise may lead to submergence of salt marshes worldwide. Salt marshes can exhibit critical transitions if the rate of sea level rise exceeds salt marsh sedimentation, leading to a positive feedback between reduced sedimentation and vegetation loss, drowning the marshes. However, a general framework to recognize such rate-induced critical transitions and predict salt marsh collapse through early warning signals is lacking. Therefore, we apply the novel concept of rate-induced critical transitions to salt marsh ecosystems. We reveal rate-induced critical transitions and new geomorphic early warning signals for upcoming salt marsh collapse in a spatial model. These include a decrease in marsh height, the ratio of marsh area to creek area, and creek cliff steepness, as well as an increase in creek depth. Furthermore, this research predicts that increasing sediment capture ability by vegetation would be an effective measure to increase the critical rate of sea level rise at which salt marshes collapse. The generic spatial model also applies to other intertidal ecosystems with similar dynamics, such as tidal flats and mangroves. Our findings facilitate better resilience assessment of intertidal ecosystems globally and identifying measures to protect these ecosystems.

Bioturbation has a limited effect on phosphorus burial in salt marsh sediments

Abstract. It has been hypothesized that the evolution of animals during the Ediacaran–Cambrian transition stimulated the burial of phosphorus in marine sediments. This assumption is centrally based on data compilations from marine sediments deposited under oxic and anoxic bottom waters. Since anoxia excludes the presence of infauna and sediment reworking, the observed differences in P burial are assumed to be driven by the presence of bioturbators. This reasoning however ignores the potentially confounding impact of bottom-water oxygenation on phosphorus burial. Here, our goal is to test the idea that bioturbation increases the burial of organic and inorganic phosphorus (Porg and Pinorg, respectively) while accounting for bottom-water oxygenation. We present solid-phase phosphorus speciation data from salt marsh ponds with and without bioturbation (Blakeney salt marsh, Norfolk, UK). In both cases, the pond sediments are exposed to oxygenated bottom waters, and so the only difference is the presence or absence of bioturbating macrofauna. Our data reveal that the rate of Porg and Pinorg burial are indistinguishable between bioturbated and non-bioturbated sediments. A large terrestrial fraction of organic matter and higher sedimentation velocity than generally found in marine sediments (0.3 ± 0.1 cm yr−1) may partially impact these results. However, the absence of a clear effect of bioturbation on total P burial puts into question the presumed importance of bioturbation for phosphorus burial.

Mechanistic strategies of microbial communities regulating lignocellulose deconstruction in a UK salt marsh

BackgroundSalt marshes are major natural repositories of sequestered organic carbon with high burial rates of organic matter, produced by highly productive native flora. Accumulated carbon predominantly exists as lignocellulose which is metabolised by communities of functionally diverse microbes. However, the organisms that orchestrate this process and the enzymatic mechanisms employed that regulate the accumulation, composition and permanence of this carbon stock are not yet known. We applied meta-exo-proteome proteomics and 16S rRNA gene profiling to study lignocellulose decomposition in situ within the surface level sediments of a natural established UK salt marsh.ResultsOur studies revealed a community dominated by Gammaproteobacteria, Bacteroidetes and Deltaproteobacteria that drive lignocellulose degradation in the salt marsh. We identify 42 families of lignocellulolytic bacteria of which the most active secretors of carbohydrate-active enzymes were observed to be Prolixibacteracea, Flavobacteriaceae, Cellvibrionaceae, Saccharospirillaceae, Alteromonadaceae, Vibrionaceae and Cytophagaceae. These families secreted lignocellulose-active glycoside hydrolase (GH) family enzymes GH3, GH5, GH6, GH9, GH10, GH11, GH13 and GH43 that were associated with degrading Spartina biomass. While fungi were present, we did not detect a lignocellulolytic contribution from fungi which are major contributors to terrestrial lignocellulose deconstruction. Oxidative enzymes such as laccases, peroxidases and lytic polysaccharide monooxygenases that are important for lignocellulose degradation in the terrestrial environment were present but not abundant, while a notable abundance of putative esterases (such as carbohydrate esterase family 1) associated with decoupling lignin from polysaccharides in lignocellulose was observed.ConclusionsHere, we identify a diverse cohort of previously undefined bacteria that drive lignocellulose degradation in the surface sediments of the salt marsh environment and describe the enzymatic mechanisms they employ to facilitate this process. Our results increase the understanding of the microbial and molecular mechanisms that underpin carbon sequestration from lignocellulose within salt marsh surface sediments in situ and provide insights into the potential enzymatic mechanisms regulating the enrichment of polyphenolics in salt marsh sediments.2Bi9cdUnFhfykPyYYU2FLjVideo

Pollen Geochronology from the Atlantic Coast of the United States during the Last 500 Years

Building robust age–depth models to understand climatic and geologic histories from coastal sedimentary archives often requires composite chronologies consisting of multi-proxy age markers. Pollen chronohorizons derived from a known change in vegetation are important for age–depth models, especially those with other sparse or imprecise age markers. However, the accuracy of pollen chronohorizons compared to other age markers and the impact of pollen chronohorizons on the precision of age–depth models, particularly in salt marsh environments, is poorly understood. Here, we combine new and published pollen data from eight coastal wetlands (salt marshes and mangroves) along the Atlantic Coast of the United States (U.S.) from Florida to Connecticut to define the age and uncertainty of 17 pollen chronohorizons. We found that 13 out of 17 pollen chronohorizons were consistent when compared to other age markers (radiocarbon, radionuclide 137Cs and pollution markers). Inconsistencies were likely related to the hyperlocality of pollen chronohorizons, mixing of salt marsh sediment, reworking of pollen from nearby tidal flats, misidentification of pollen signals, and inaccuracies in or misinterpretation of other age markers. Additionally, in a total of 24 models, including one or more pollen chronohorizons, increased precision (up to 41 years) or no change was found in 18 models.

Fine-tuning of 210Pb-based methods for dating vegetated saltmarsh sediments

Abstract Saltmarshes, wetlands, inter-tidal mudflats are highly productive natural ecosystems with significant ecological value. 210Pb and 137Cs have been used for establishing chronologies at a centennial scale in these sediments. They are relevant for assessing how saltmarshes are vulnerable to climate change, natural hazards and contamination from human inputs. This paper aims to review and adapt existing methods for the 210Pb-based radiometric dating of these sediments where the subterranean production and decay of OM are sources of achronicity. This limits the use of the basic assumption of considering the sediment as a continuous medium. From the available evidence, 210Pb fluxes onto sediments may be mediated by the activities bound to the mass flows, suggesting that models assuming a constant flux should be handled with care. The activity concentrations of excess 210Pb required by CF-CS, CIC and TERESA radiometric models must be those of the sediment mineral fraction, while CRS and PLUM can work with the composite sediment matrix. A review of these issues and application of the models is illustrated with new data from two recent saltmarsh sediment cores. The effects of non-ideal boundary conditions in radiometric dating and the system time-average of 137Cs fluxes are discussed. Although specific to vegetated saltmarshes, this topic and the present results have generic applications for other vegetated coastal sediments.

Abundance and niche specificity of different types of complete ammonia oxidizers (comammox) in salt marshes covered by different plants

The recently discovered complete ammonia oxidizers (comammox), which are ubiquitous in various natural and artificial ecosystems, have led to a paradigm shift in our understanding of aerobic nitrification. The coastal salt marsh covered by various plant species is an important ecosystem to link nitrogen cycles of terrestrial and marine environments; however, the distribution and structure of comammox in such ecosystems have not been clearly investigated. Here, we applied quantitative PCR and partial nested-PCR to investigate the abundance and community composition of comammox in salt marsh sediment samples covered by three plant types along the southern coastline of China. Our results showed a predominance of comammox clade A in majority of the samples, suggesting their ubiquity and the important role they play in nitrification in salt marsh ecosystems. However, variations by the sites were found when comparing the abundance of subclades of comammox clade A. Redundancy analysis demonstrated a coexistence pattern by comammox clade A.1 with ammonia-oxidizing archaea and comammox clade A.2 with canonical ammonia-oxidizing bacteria, indicating their differences in potential niche preference. However, the abundance of comammox clade B was lower than that of comammox clade A and other ammonia oxidizers in most samples. Moreover, pH and salinity were found to be the most significant factors affecting comammox community structures, suggesting their roles in driving niche partitioning of comammox, whereas plant types did not show a significant effect on the comammox community structure. Our study provided insights into the abundance, community diversity, and niche partitions of comammox, broadening the current understanding of the relationship of comammox with other ammonia oxidizers in salt marsh ecosystems.

Late-Holocene sea-level reconstruction (1200 BC–AD 100) in the Westergo terp region of the northern Netherlands

AbstractIn the early 20th century, archaeological research in the terp (artificial dwelling-mound) region of the northern Netherlands focused, besides settlement history, on natural salt-marsh dynamics and sea-level rise. In particular Van Giffen used salt-marsh deposits under dated terp layers to reconstruct the rate of sedimentation of the developing salt marsh and relative sea-level rise.This line of research in archaeology was rekindled during excavations in the terp of Wijnaldum-Tjitsma between 1991 and 1993. Since then, geology has become an integral part of archaeological research in the terp region. This paper focuses on the northwestern part of the province of Friesland (Westergo), where most archaeological terp research during the past three decades has been carried out, owing to several research programmes by the Province of Friesland. The primary aim of the geoarchaeological research is to better understand the interaction between human inhabitants and the salt-marsh landscape. The sedimentary record exposed in the excavation trenches makes it possible to collect data on the development of the coastal environments of the Wadden Sea prior to habitation, including data on sea-level rise. The sea-level data collected in the geoarchaeological studies in Westergo are the topic of this paper. The measured levels of the tidal-flat/salt-marsh boundary underneath the terps make it possible to reconstruct palaeo-Mean High Water (palaeo-MHW) levels. Such sea-level index points (SLIPs), based on marine shell data points from 12 locations, now make it possible to establish a palaeo-MHW diagram for this part of the Wadden Sea, for the period between 1200 BC and AD 100. In this period the palaeo-MHW in the Westergo region rose fromc.1.8 m to 0.3 m −NAP: a mean sea-level rise ofc.0.12 m per century.We discuss the fact that elevation of the palaeo-MHW SLIP is not only determined by relative sea level (RSL), but also by the magnitude of the tidal amplitude. The tidal range, and therefore the MHW elevations in a tidal basin, can change from place to place and also in time. Also in a single tidal basin the tidal range is variable, due to the distortion of the tidal wave as a result of the morphology of the tidal system. Such local tidal range fluctuations – not related to sea-level rise – influence the palaeo-MHW curve of Westergo and other tidal basins in the Wadden Sea and need to be taken into account when interpreting the curve.In this paper, we will go into the causes of changes in palaeotidal ranges in meso- and macrotidal systems, analyse the tidal range variations in recent and subrecent basins and estuaries and discuss the implications of these changes on the sea-level curve of the Westergo region in NW Friesland.

North Sea salt-marsh archives trace past storminess and climate variability

Intertidal coastal wetlands are regularly exposed to storm surges and associated flooding, resulting in the recurrent accretion of reworked sediments on the salt-marsh surfaces. In this context, well-stratified salt-marsh sediment sequences provide an exceptional archive to evaluate the response of coastal wetlands to past storm-climate variability. Hence, this study focusses on the investigation of two sedimentary salt-marsh sequences from the south-eastern German North Sea coast (Bay of Tümlau and Friedrichskoog) to understand how and to which extent changes in the storm-surge climate are transferred into the sediment archive. This objective is particularly challenging as German mainland salt marshes have been greatly altered by human activities over the last century. To overcome this problem, this study combines different sedimentological and geochemical proxy data, using mean grain sizes together with ln(Br/Cl), Br/Corg, and ln(Zr/Rb) ratios, to allow for the identification of storm-surge layers. Local changes in the sedimentary organic matter supply are reflected by the ln(Br/Cl) ratio. There, abrupt drops in the ln(Br/Cl) data coincide with relatively coarser textured sand layers, indicating impacts by regional storm surges during winter, while intervals of comparable higher ln(Br/Cl) values may represent deposition during spring to fall. The Br/Corg record reflects the marine versus terrestrial organic matter input and reveals a long-term increase starting during the first half of the 20th century towards recent times, resembling the observed amplification in North Sea storminess. A similar trend is reflected by the ln(Zr/Rb) ratio (since 1950 CE), which can be used as a proxy for the grain-size distribution. Periodic fluctuations in the ln(Zr/Rb) ratio at inter-decadal timescales (10–19 years) suggest a close linkage between local sediment accretion and large-scale atmosphere-ocean climate oscillations over the North Atlantic and Europe, and thus related storm-surge frequency and intensity. Periodic variability on decadal scales was also identified in the ln(Br/Cl) record at the less human-modified and more naturally developed salt marsh at the Bay of Tümlau (12–22 years), likewise indicating a relation between North Sea storminess and associated shifts in the seasonal signal of the primary production and sediment texture to oscillations in the atmosphere-ocean system. On the contrary, similar periodicities are lacking for the intense modified salt marsh at Friedrichskoog. Apparently, the salt-marsh depositional system in the Bay of Tümlau reacts more sensitively to super-regional climatic changes, respectively, the natural depositional processes in the salt marsh at Friedrichskoog are superimposed by the more intense local human activities.

Saltmarsh rhizosphere fungal communities vary by sediment type and dominant plant species cover in Nova Scotia, Canada.

We surveyed Spartina saltmarsh sediment rhizosphere fungal communities at three saltmarshes and two timepoints in coastal Nova Scotia. Based on ITS2 Illumina miSeq rDNA data and multivariate analysis, neither sediment zone nor collection period correlated with fungal ASV richness, but collection site did. However, Shannon diversity indicated that sediment zone played a significant role in fungal diversity. For unweighted and weighted UniFrac distance, site was the major factor driving beta-diversity, with sediment zone and collection period having smaller roles. Sediment type and saltmarsh plant species may play important roles in structuring rhizosphere fungal assemblages, here dominated by ascomycetes. To our knowledge, our study is the first to assess fungal sediment communities in saltmarshes in Atlantic Canada using metabarcoding. It provides a biodiversity analysis of sediment fungi in a poorly studied but highly important ecosystem and points to their roles in nutrient cycling, blue carbon, coastal stability and coastal restoration. Our work will inform ongoing saltmarsh restoration in Atlantic Canada.

Assessing the role of the “estuarine filter” for emerging contaminants: pharmaceuticals, perfluoroalkyl compounds and plasticisers in sediment cores from two contrasting systems in the southern U.K.

The environmental occurrence, fate and ecotoxicity of emerging contaminants (ECs) has been the subject of increasing research, policy and public concern over the past two decades. While a wide range of publications have examined the environmental persistence and sediment/soil interactions of ECs following their discharge into aquatic environments, the extent to which ECs are sequestered in estuarine sediments, and the impact of this on their environmental persistence and supply to the ocean, in comparison remains unclear. This Article examines the environmental concentrations of seven, relatively water-soluble and environmentally mobile, ECs (including pharmaceuticals, perfluoroalkyl compounds, and plasticisers) in dated intertidal saltmarsh cores from two contrasting estuarine sites in the southern U.K. (one heavily urbanised/industrial, the other non-urbanised). Mean sediment EC concentrations are similar in both estuarine systems (in the range 0.1 (acetaminophen) to 17 (4-hydroxyacetophenone) ng/g dry weight). Despite their variable reported Log Kow values (from ca. 0.5 to > 7), the ECs are all apparently mobile in the marsh systems studied, and where subsurface concentration maxima are present these most likely relate to local flushing or diffusive processes and cannot be clearly linked to likely input trends or changes in sediment geochemistry (including sedimentary organic carbon content). The “estuarine filter” here, at least with respect to intertidal saltmarsh sediments, shows reduced potential to sequester the seven ECs examined and mediate their supply to coastal and shelf environments.

Creating a New England Salt Marsh Sediment Profile: Methods and Implications for Climate Change Mitigation Strategies

Salt marshes and other blue carbon systems (mangroves, sea grasses) sequester large amounts of carbon primarily through sedimentation and therefore naturally aid in climate change mitigation. However, disturbances caused by anthropogenic activity (agriculture, ditching, invasive species, construction) are leading to New England salt marsh habitat destruction. The loss of this carbon sink could result in the system becoming a carbon source, potentially contributing to climate change rather than abating it. In this study, a sediment profile of a temperate New England salt marsh was created. Vernier sensors were used to collect both discrete sediment samples (soil pH) and in situ sediment samples (soil salinity, soil moisture, soil temperature) weekly for one year (June 2018 – June 2019) at the Neponset River Salt Marsh in Boston, Massachusetts. The objective was to observe seasonal variations in sediment between two locations dominated by different types of marsh vegetation (Spartina alterniflora and Spartina patens). Soil pH was determined to not seasonally differ at either location. Soil pH and temperature showed no difference between soils under different types of marsh vegetation. At both locations, soil salinity, soil moisture, and soil temperature were significantly different between each season. Additionally, soil moisture and salinity were significantly different between locations in the summer and autumn. This work shows how marshes may respond to future climate scenarios, particularly increased temperatures and increased sea-level.

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4 +/15NH4 + Analyses via Sequential Conversion to N2O.

The importance of understanding the fate of nitrate (NO3-), which is the dominant N species transferred from terrestrial to aquatic ecosystems, has been increasing because global nitrogen loads have dramatically increased following industrialization. Dissimilatory nitrate reduction to ammonium (DNRA) and denitrification are both microbial processes that use NO3- for respiration. Compared to denitrification, quantitative determinations of the DNRA activity have been carried out only to a limited extent. This has led to an insufficient understanding of the importance of DNRA in NO3- transformations and the regulating factors of this process. The objective of this paper is to provide a detailed procedure for the measurement of the potential DNRA rate in environmental samples. In brief, the potential DNRA rate can be calculated from the 15N-labeled ammonium (15NH4+) accumulation rate in 15NO3- added incubation. The determination of the 14NH4+ and 15NH4+ concentrations described in this paper is comprised of the following steps. First, the NH4+ in the sample is extracted and trapped on an acidified glass filter as ammonium salt. Second, the trapped ammonium is eluted and oxidized to NO3- via persulfate oxidation. Third, the NO3- is converted to N2O via an N2O reductase deficient denitrifier. Finally, the converted N2O is analyzed using a previously developed quadrupole gas chromatography-mass spectrometry system. We applied this method to salt marsh sediments and calculated their potential DNRA rates, demonstrating that the proposed procedures allow a simple and more rapid determination compared to previously described methods.

Facies Distribution of Borehole DC01 in the West Coastal Plain of Bohai Bay Since MIS3 Using Clayey Water Electric Conductivity and Grain Size Analysis

Zhang, L.P.; Fang, J.; Wang, F.; Shang, Z.W.; Li, J.F.; Chen, Y.S., and Tian, L.Z., 2020. Facies distribution of borehole DC01 in the west coastal plain of Bohai Bay since MIS3 using clayey water electric conductivity and grain size analysis. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 795–803. Coconut Creek (Florida), ISSN 0749-0208.To investigate the sedimentary evolution in the West Coastal Plain of the Bohai Bay since Marine Isotope Stage 3 (MIS3), clayey water electric conductivity, grain size, and foraminifera species were measured. According to the AMS14C ages, borehole DC01 was divided into eight units: Unit I (30–29 m), watercourse sediment formed earlier than 46 ka cal BP; Unit II (29–22.4 m), flood plain sediment formed in 45.8 ka cal BP; Unit III (22.4–14.5 m), sediment affected by the storm surge and formed in 45.8–11.2 ka cal BP; Unit IV (14.5–12.6 m), tidal creek sediment representing the rising sea-level in the postglacial period; Unit V (12.6–9.5 m), watercourse-flood plain sediment; Unit VI (9.5–8.34 m), the salt marsh layer affected by seawater that formed during 8.3–7.5 ka cal BP; Unit VII (8.34–3.6 m), watercourse sediment; Unit VIII (3.6–1 m), flood plain with multiple currents that formed in about 3.7 ka cal BP. Studies show that borehole DC01 was affected by seawater twice. (1) The tidal creek sediment and the salt marsh sediment from the postglacial period to 7.5 ka cal BP, which was affected by seawater, represents the rising sea-level and the maximum period of the Holocene MIS1 transgression in the western plain of the Bohai Bay. (2) The storm surge sediment in 45.8 ka cal BP, which was affected by seawater during the MIS3, when the Paleoshorelines were located 20-45 km from borehole DC01.

Oxygen-reducing microbial cathodes in hypersaline electrolyte

Hypersaline electrolytes offer a way to boost the development of microbial fuel cells by overcoming the issue due to the low conductivity of the usual media. Efficient halotolerant bioanodes have already been designed but O2-reducing cathodes remain a strong bottleneck. Here, O2-reducing biocathodes were designed by using salt marsh sediment as the inoculum and a hypersaline media (45 g/L NaCl) of high conductivity (10.4 S m−1). Current density up to 2.2 A m−2 was reached from potential of +0.2 V/SCE. The efficiency of the biocathodes was correlated to the presence of Gammaproteobacteria strain(s) related to Thiohalobacter thiocyanaticus, which were considerably enriched in the best performing biocathodes. This work opens up new perspectives to overcome the O2 reduction issue in hypersaline MFCs by designing efficient halotolerant microbial cathodes and pointing out the strains that should now be focused to improve them.

Integrated stratigraphy of foreland salt-marsh sediments of the south-eastern North Sea region

Integrated stratigraphy of foreland salt-marsh sediments of the south-eastern North Sea region

Phenanthrene contamination and ploidy level affect the rhizosphere bacterial communities of Spartina spp.

Spartina spp. are widely distributed salt marsh plants that have a recent history of hybridization and polyploidization. These events have resulted in a heightened tolerance to hydrocarbon contaminants, but the effects of this phenomenon on the rhizosphere microbial communities are unknown. Here, we grew two parental Spartina species, their hybrid and the resulting allopolyploid in salt marsh sediments that were contaminated or not with phenanthrene. The DNA from the rhizosphere soil was extracted and the bacterial 16S rRNA gene was amplified and sequenced, whereas the abundances of the genes encoding for the PAH (polycyclic aromatic hydrocarbon) ring-hydroxylating dioxygenase (RHD) of Gram-negative and Gram-positive bacteria were quantified by real-time PCR. Both the contamination and the plant genotype significantly affected the bacterial communities. In particular, the allopolyploid S. anglica harbored a more diverse bacterial community in its rhizosphere. The interspecific hybrid and the allopolyploid also harbored significantly more copies of the PAH-RHD gene of Gram-negative bacteria in their rhizosphere than the parental species, irrespective of the contamination treatments. Overall, our results are showing that the recent polyploidization events in the Spartina affected its rhizosphere bacterial communities, both under normal and contaminated conditions, possibly increasing its phytoremediation potential.