Salt Marsh Sediments Research Articles

Mass concentrations, compositions and burial fluxes of nano- and micro-plastics in a multi-species saltmarsh

Plastic pollution poses a serious threat to marine ecosystems; yet quantifying the mass concentrations of nano- and microplastics (NMPs) in saltmarsh sediments at the ocean-land interface remains a critical research gap. Here, the study employed reliable and efficient analytical techniques, namely pressurized liquid extraction and the double-shot model of thermal desorption/pyrolysis-gas chromatography-mass spectrometry, to quantify six different types of NMPs in the sediment of a multi-species saltmarsh, providing the first comprehensive assessment of NMP mass concentration and burial in this saltmarsh environment. The results demonstrate that polyethylene, polyvinyl chloride, and polypropylene dominated the NMP composition in sediments, constituting 72.6%, 17.3%, and 4.5% of the total NMPs, respectively. The measured NMPs represent an anthropogenic intrusion, constituting 0.10%–0.23% of the carbon storage in the saltmarsh. By examining the vertical concentration profiles, this study unveiled the influence of saltmarsh vegetation on NMP deposition in sediments, establishing a connection with local sedimentation patterns and the historical zonation of plant species such as Scirpus mariqueter, Phragmites australis and Spartina alterniflora. These findings underscore the crucial role of saltmarsh vegetation in facilitating NMP settling and retention, highlighting the necessity of considering vegetation dynamics in examining the emerging NMP pollution in coastal wetlands.

Passive revegetation limited by seed availability in a salt marsh sediment addition site

Many approaches to restoring salt marsh habitats assume flora will naturally colonize the restoration site following the reinstatement of tidal hydrology that is appropriate for halophytes. However, this passive strategy can fail to meet restoration targets because of unfavorable site conditions and/or limited propagule dispersal. This study analyzes propagule availability in a restored southern California salt marsh that experienced slow passive revegetation following sediment addition to combat subsidence‐driven habitat loss. We performed a seedling emergence experiment to assess the quantity and species composition of viable halophyte seeds in the restoration site compared to nearby established salt marsh habitat. Additionally, we irrigated seed bank samples with freshwater or saltwater to test the effects of restoration site salinity conditions on seedling emergence and survival. Due to the proximity of the restoration site to seed sources, we expected to find ample seeds within its seed bank. However, only two seedlings emerged from restoration site seed bank samples (collected over 1.18 m2 of soil surface area), compared to an average of 44.33 seedlings from control site samples. Control site samples receiving saltwater irrigation had similar quantities of seedlings emerge, but seedlings in salt water had a reduced survival rate compared to seedlings in the freshwater treatment. Overall, these results suggest that passive restoration should be paired with techniques that retain seeds, such as increasing the topographic complexity of the restoration site. However, in scenarios where salinity or elevation may limit seedling recruitment, active planting should be considered to speed restoration trajectories.

Flooding promotes the coalescence of microbial community in estuarine habitats

Microbial community coalescence describes the mixing of microbial communities and their integration with the surrounding environment, which is common in natural ecosystems and has potential impacts on ecological processes. However, few studies have focused on microbial community coalescence between different habitats in estuarine regions. In this study, we comprehensively investigated the environmental characteristics and bacterial community changes of different habitats (water body (Water), subtidal sediments (SS) and intertidal salt marsh sediments (SM)) in Luanhe estuary during flood and normal flow periods. The results showed that flood event significantly reduced the salinity of the estuarine habitats, changed the nutrient structure and intensified the eutrophication of estuarine water. By calculating the proportion of overlapping groups and applying the ‘FEAST’ algorithm, we revealed that flood event facilitated the migration of bacterial communities along alternative pathways across habitats, markedly enhanced the cross-habitat mobility of bacterial communities, which underscores the pivotal role of flood event in driving bacterial community coalescence. Flood-induced community coalescence not only increased the α-diversity of bacterial communities within habitats, but also increased the proportion of overlapped species between habitats, ultimately leading to homogenization between habitats. Canonical correlation analysis combined co-occurrence network analysis revealed that flood event attenuated the role of environmental filtration in microbial assembly, while increased the impact of dispersal processes and intensified interspecific competition among microorganisms, led to the change of keystone species and reduced the complexity and stability of bacterial communities. In conclusion, this study demonstrates the complex effects of flood events on estuarine microbial communities from the perspective of multi-habitat interactions in the estuary, and emphasizes the key role of river hydrodynamic conditions in facilitating the coalescence of estuarine microbial communities. We look forward to further attention and research on estuarine microbial coalescence, which will provide new insights into assessing the stability and resilience of estuarine ecosystems under flood challenges and the sustainable management of estuarine wetlands.

Sedimentary dolomite in Western Australia and the dolomite problem: Genesis of channel and playa uranium deposits

ABSTRACTQuaternary to Recent sedimentary dolomite in groundwater calcrete and saltmarsh sediments of Lake Way and Lake Maitland, Western Australia, provide new information about the formation of low‐temperature dolomite. Dolomite can form through numerous pathways depending on the depositional and diagenetic environment. Many pathways involve microbial processes and/or the presence of a nucleation substrate which help overcome kinetic barriers preventing precipitation in the laboratory. Petrographic, mineralogical, hydrogeochemical and stable isotopic data in this study reveal the importance of Mg‐clays as nucleation sites for dolomite precipitation in a range of aquifer environments. There is also a close association between authigenic Mg‐clays, dolomite and the potassium–uranyl–vanadate ore mineral carnotite in channel and playa uranium deposits. It is interpreted that evaporation‐driven precipitation of dolomite establishes a positive feedback loop promoting the dissociation of aqueous uranyl–carbonate complexes and concomitant increase in carnotite saturation. Critical to this model is the presence of authigenic Mg‐clays because they facilitate dolomite precipitation and promote carnotite nucleation by concentrating potassium ions on clay surfaces via adsorption. This Mg‐clay–dolomite–carnotite relationship is widespread throughout Western Australian channel and playa uranium deposits and has been observed in similar deposits in Namibia and Botswana. In addition to this economic implication, Mg‐clay mediated nucleation of dolomite potentially has global relevance as a precipitation mechanism for low temperature dolomite in sedimentary deposits where detrital and/or authigenic Mg‐clays are present. Maturation of sedimentary dolomite from disordered high‐calcian dolomite to ordered low‐calcian dolomite occurs very early in the meteoric realm making it resistant to alteration during burial diagenesis. Diagenetic resistance may be further increased by early meteoric silicification related to the degradation of associated Mg‐clays. These findings indicate that Mg‐clay associated sedimentary dolomite has potential to retain a primary isotopic signature indicative of its origin, making it a useful recorder of palaeoenvironmental conditions.

Application of remote sensing methods for monitoring extent, condition and blue carbon storage in salt marshes

Salt marshes are fragile coastal ecosystems that provide a wide range of ecosystem services, including carbon sequestration and storage. Despite the importance of salt marshes for blue carbon sequestration, few studies have been done on blue carbon monitoring using satellite remote sensing techniques. This study arose to fill this knowledge gap, and aimed to determine the amount of blue carbon sequestered in salt marshes by analyzing the particular case of the Pancas salt marsh (Tagus Estuary, Portugal). To achieve this, the extent and condition of the Pancas salt marsh were assessed using remote sensing methods, by establishing a methodology that effectively identified and validated its extent based on Sentinel-2 imagery from 2016 to 2022. This method involves generating a reference salt marsh extent map followed by mapping salt marsh extent through four Vegetation Indices (VI) from Sentinel-2 data to compare and thus validate the salt marsh extent based on the information provided by the satellite. Considering the extent of the salt marsh and the changes it has undergone over the 7 years studied, together with reference values for sequestered carbon in the salt marsh sediments, approximate values for sequestered blue carbon were determined. The results highlighted the validation of Normalised Difference Vegetation Index (NDVI) as the best-performing VI for this study and as a proxy for the condition of the salt marsh in terms of the spatial and temporal distribution of its aboveground biomass. It was also verified that the salt marsh expanded its frontal region by 0.22 km2 between 2016 and 2022, while certain areas of high marsh have suffered dieback. Concerning sequestered carbon, an increase of 508.2 tonnes since 2016 was quantified, corresponding to 66500 tonnes of blue carbon stored for 2022. Our study revealed the intrinsic relationship between the extent of a salt marsh and its carbon sequestration capacity highlighting the importance of future application of more remote sensing techniques, to emphasize the significant role of these ecosystems in carbon sequestration and climate change mitigation.

Tolerance of the Australian halophyte, beaded samphire, Sarcocornia quinqueflora, to Pb and Zn under glasshouse conditions: Evaluating metal uptake and partitioning, photosynthetic performance, biomass, and growth

Saltmarsh sediments are susceptible to accumulation of excessive concentrations of anthropogenically elevated metals such as lead (Pb) and zinc (Zn). The resident salt tolerant plants of saltmarsh ecosystems form the basal underpinning of these ecosystems. As such, metal-associated adverse impacts on their physiology can have detrimental flow-on effects at individual, population, and community levels. The present study assessed the accumulation and partitioning of ecologically relevant concentrations of Pb, Zn, and their combination in a dominant Australian saltmarsh species, Sarcocornia quinqueflora. Plants were hydroponically maintained under glasshouse conditions for 16 weeks exposure to either Pb (20 µg l–1), Zn (100 µg l–1), or their mixture. We evaluated the chronic toxicological effects of single and mixed metal treatments with reference to metal uptake and partitioning, photosynthetic performance, photosynthetic pigment concentration, biomass and growth. Lead was more toxic than Zn, and Zn appeared to have an antagonistic effect on the toxicological effects of Pb in S.quinqueflora in terms of metal uptake, photosynthetic performance, photosynthetic pigment concentrations, and growth. Indeed, the tolerance index was 55 % in plants treated with Pb compared to 77 % in Zn treated plants and 73 % in Pb+Zn treated plants. Finally, Sarcocornia quinqueflora primarily accumulated both Pb and Zn in roots at concentrations exceeding unity whilst translocation of these metals to above ground tissues was restricted regardless of treatment. This suggests that S. quinqueflora may be suitable for phytostabilisation of Zn, and of Pb particularly in the presence of Zn.

Influence of the Keystone Grazer, Sesarma reticulatum, on the Hydrology and Organic Matter Cycling in Salt Marshes of the Southeastern USA

AbstractIn salt marshes of the Southeastern USA, purple marsh crabs (Sesarma reticulatum), hereafter Sesarma, aggregate in grazing and burrowing fronts at the heads of tidal creeks, accelerating creek incision into marsh platforms. We explored the effects of this keystone grazer and sediment engineer on salt marsh sediment accumulation, hydrology, and carbon (C) and nitrogen (N) turnover using radionuclides (210Pb and 7Be), total hydrolyzable amino acids (THAA), and C and N stable isotopes (δ13C and δ15N) in sediment from paired Sesarma-grazed and un-grazed creeks. Sesarma-grazed-creek sediments exhibited greater bioturbation and tidal inundation compared to sediments in un-grazed creeks, as indicated by larger 210Pb and 7Be inventories. Total organic carbon (TOC) to total nitrogen (TN) weight ratios (C:N) were higher and δ15N values were lower in grazed-creek sediments than in un-grazed-creek sediments, suggesting Sesarma remove and assimilate N in their tissues, and excrete N with lower δ15N values into sediments. In support of this inference, the percent total carbon (TC) and percent TOC declined by nearly half, percent TN decreased by ~ 80%, and the C:N ratio exhibited a ~ threefold increase between Sesarma fore-gut and hind-gut contents. An estimated 91% of Sesarma’s diet was derived from Spartina alterniflora, the region’s dominant salt marsh plant. We found that, as Sesarma grazing fronts progress across marsh landscapes, they enhance the decay of Spartina-derived organic matter and prolong marsh tidal inundation. These findings highlight the need to better account for the effects of keystone grazers and sediment engineers, like Sesarma, in estimates of the stability and size of blue C stores in coastal wetlands.

Role of Extremophiles in Biodegradation of Emerging Pollutants

AbstractEmerging pollutants, also referred to as emerging contaminants, are substances that have recently been recognized or are gaining attention due to their potential adverse impacts on the environment, human health, or ecosystems. These pollutants present a significant threat to both environmental and human well-being and are challenging to eliminate using conventional remediation methods. Extremophiles, organisms adapted to extreme environmental conditions like high or low temperatures, high pressure, and elevated salt concentrations, play a crucial role in this context. They produce a diverse array of enzymes capable of breaking down complex organic compounds, some of which remain stable and functional even in harsh environmental conditions, making extremophiles well-suited for use in bioremediation applications. Numerous studies have demonstrated the capability of extremophiles to degrade various pollutants, including toxic solvents, heavy metals, and industrial chemicals. Halophilic archaea, a type of extremophile, have particularly shown promise in degrading emerging contaminants in salt marsh sediments. Despite their potential, there are challenges associated with using extremophiles in bioremediation, such as the limited availability of extremophilic microorganisms capable of degrading specific pollutants and a reduction in enzyme stability when operating outside their optimum range. Nevertheless, ongoing research in this field is anticipated to result in the development of new and innovative bioremediation strategies for effectively removing emerging pollutants from the environment.

Seasonal drivers and patterns of sediment temperatures in a New England salt marsh

AbstractSalt marshes are globally important ecosystems and thus their resilience to climate change holds societal importance. To date, studies addressing salt marsh responses to climate change have focused on sea‐level rise and biogeochemical feedbacks with increasing inundation. Less is known about how salt marsh sediment temperatures, which impact physical, biological, and chemical ecosystem processes, will respond to climate change. In this study, we present multi‐depth sediment temperature and porewater level data from low‐, mid‐, and high‐marsh sites at a New England salt marsh for a 1‐year period and investigate how salt marsh sediment temperatures respond to atmospheric and oceanic forcing. We use spectral analyses to identify the frequencies at which sediment temperatures vary and link the temperature variations to specific forcing mechanisms. We find that all sites across the marsh responded to air temperature with roughly equal amplitude whereas the responses to radiative heating and ocean tides varied spatially. The high‐marsh site is more sensitive to radiative heating than the mid‐ and low‐marsh sites. The low‐marsh is affected by tidal processes and inundation whereas the high‐ and mid‐marsh sites are not. In addition, we find that the bulk thermal diffusivity of the saturated sediments decreases with distance from the tidal channel. These factors contribute to considerable temporal and spatial variability in sediment temperatures with elevation, distance from the tidal channel, and time of year (season) being most important.

Marsh sediments chronically exposed to nitrogen enrichment contain degraded organic matter that is less vulnerable to decomposition via nitrate reduction

Blue carbon habitats, including salt marshes, can sequester carbon at rates that are an order of magnitude greater than terrestrial forests. This ecosystem service may be under threat from nitrate (NO3−) enrichment, which can shift the microbial community and stimulate decomposition of organic matter. Despite efforts to mitigate nitrogen loading, salt marshes continue to experience chronic NO3− enrichment, however, the long-term consequence of this enrichment on carbon storage remains unclear. To investigate the effect of chronic NO3− exposure on salt marsh organic matter decomposition, we collected sediments from three sites across a range of prior NO3− exposure: a relatively pristine marsh, a marsh enriched to ~70 μmol L−1 NO3− in the flooding seawater for 13 years, and a marsh enriched between 100 and 1000 μmol L−1 for 40 years from wastewater treatment effluent. We collected sediments from 20 to 25 cm depth and determined that sediments from the most chronically enriched site had less bioavailable organic matter and a distinct assemblage of active microbial taxa compared to the other two sites. We also performed a controlled anaerobic decomposition experiment to test whether the legacy of NO3− exposure influenced the functional response to additional NO3−. We found significant changes to microbial community composition resulting from experimental NO3− addition. Experimental NO3− addition also increased microbial respiration in sediments collected from all sites. However, sediments from the most chronically enriched site exhibited the smallest increase, the lowest rates of total NO3− reduction by dissimilatory nitrate reduction to ammonium (DNRA), and the highest DNF:DNRA ratios. Our results suggest that chronic exposure to elevated NO3− may lead to residual pools of organic matter that are less biologically available for decomposition. Thus, it is important to consider the legacy of nutrient exposure when examining the carbon cycle of salt marsh sediments.

Plumage microorganism communities of tidal marsh sparrows

Microorganism communities can shape host phenotype evolution but are often comprised of thousands of taxa with varied impact on hosts. Identification of taxa influencing host evolution relies on first describing microorganism communities and acquisition routes. Keratinolytic (keratin-degrading) microorganisms are hypothesized to be abundant in saltmarsh sediments and to contribute to plumage evolution in saltmarsh-adapted sparrows. Metabarcoding was used to describe plumage bacterial (16S rRNA) and fungal (ITS) communities in three sparrow species endemic to North America's Atlantic coast saltmarshes. Results describe limited within-species variability and moderate host species-level patterns in microorganism diversity and community composition. A small percentage of overall microorganism diversity was comprised of potentially keratinolytic microorganisms, warranting further functional studies. Distinctions between plumage and saltmarsh sediment bacteria, but not fungal, communities were detected, suggesting multiple bacterial acquisition routes and/or vertebrate host specialization. This research lays groundwork for future testing of causal links between microorganisms and avian host evolution.

A baseline for microplastic occurrence in three New England estuaries

Although microplastics (MP) have been documented in estuarine habitats, limited published data exist for New Hampshire and northern Massachusetts hampering meaningful, regional comparison with other geographies. Here we synthesize previously unpublished data from several independent baseline studies spanning three estuarine systems including Great Bay Estuary (GBE), Hampton-Seabrook Estuary (HSE), and Great Marsh Estuary (GME) to compare geographic data for MP to other published regional studies. Data include water column in GBE (n = 179 from 7 sites), surface waters and salt marsh sediment cores from HSE (n = 72 water samples from 12 sites and n = 77 sediment cores from 8 sites), and surface waters from GME (n = 42 water samples at 10 sites). Samples were analyzed for MP characteristics initially via either automated confocal microscopy or light microscopy, allowing initial estimation of the number and size distribution of putative MP. Particles from representative samples were analyzed using laser direct infrared spectrometry (LDIR) to determine elemental analysis. MP were found in > 98% of samples collected including surface waters, water column, and marine sediments. Counts ranged from 1 to 144,000 MP particles m-3 and mean MP differed significantly among regions, sites within regions, and across years. In the GBE water column, MP tended to peak during June-August in 4 of the 5 years studied. Most MP were roughly circular and ~50 μm in diameter. LDIR confirmed that many types of plastics are in these estuarine waters and also revealed that despite the digestion processes, biogenic materials often remained, predominantly chitin, rubber, wood, and coal. These data allow us to address the realistic levels of risk that estuarine MP pose in NH and northern MA estuaries and can be used to populate existing hydrodynamic models that will predict the tributary sources, movements, and fate of MP within these aquatic habitats.

Microbial drivers of DMSO reduction and DMS-dependent methanogenesis in saltmarsh sediments

Saltmarshes are highly productive environments, exhibiting high abundances of organosulfur compounds. Dimethylsulfoniopropionate (DMSP) is produced in large quantities by algae, plants, and bacteria and is a potential precursor for dimethylsulfoxide (DMSO) and dimethylsulfide (DMS). DMSO serves as electron acceptor for anaerobic respiration leading to DMS formation, which is either emitted or can be degraded by methylotrophic prokaryotes. Major products of these reactions are trace gases with positive (CO2, CH4) or negative (DMS) radiative forcing with contrasting effects on the global climate. Here, we investigated organic sulfur cycling in saltmarsh sediments and followed DMSO reduction in anoxic batch experiments. Compared to previous measurements from marine waters, DMSO concentrations in the saltmarsh sediments were up to ~300 fold higher. In batch experiments, DMSO was reduced to DMS and subsequently consumed with concomitant CH4 production. Changes in prokaryotic communities and DMSO reductase gene counts indicated a dominance of organisms containing the Dms-type DMSO reductases (e.g., Desulfobulbales, Enterobacterales). In contrast, when sulfate reduction was inhibited by molybdate, Tor-type DMSO reductases (e.g., Rhodobacterales) increased. Vibrionales increased in relative abundance in both treatments, and metagenome assembled genomes (MAGs) affiliated to Vibrio had all genes encoding the subunits of DMSO reductases. Molar conversion ratios of <1.3 CH4 per added DMSO were accompanied by a predominance of the methylotrophic methanogens Methanosarcinales. Enrichment of mtsDH genes, encoding for DMS methyl transferases in metagenomes of batch incubations indicate their role in DMS-dependent methanogenesis. MAGs affiliated to Methanolobus carried the complete set of genes encoding for the enzymes in methylotrophic methanogenesis.

Tidal effects on carbon dioxide emission dynamics in intertidal wetland sediments

Understanding the control mechanisms of carbon dioxide (CO2) emissions in intertidal wetland sediments is beneficial for the concern of global carbon biogeochemistry and climate change. Nevertheless, multiple controls on CO2 emissions from intertidal wetland sediments to the atmosphere still need to be clarified. This study investigated the effect of tidal action on CO2 emissions from salt marsh sediments covered by Spartina alterniflora in the Jiaozhou Bay wetland using the static chamber method combined with an infrared CO2 detector. The results showed that the CO2 emission fluxes from the sediment during ebb tides were higher than those during flood tides. The whole wetland sediment acted as a weak source of atmospheric CO2 (average flux: 24.44 ± 16.80 mg C m−2 h−1) compared to terrestrial soils and was affected by the cycle of seawater inundation and exposure. The tidal influence on vertical dissolved inorganic carbon (DIC) transport in the sediment was also quantitated using a two-end member mixing model. The surface sediment layer (5–15 cm) with maximum DIC concentration during ebb tides became the one with minimum DIC concentration during flood tides, indicating the DIC transport from the surface sediment to seawater. Furthermore, aerobic respiration by microorganisms was the primary process of CO2 production in the sediment according to 16 S rDNA sequencing analysis. This study revealed the strong impact of tidal action on CO2 emissions from the wetland sediment and provided insights into the source-sink pattern of CO2 and DIC at the land-ocean interface.

Natural and anthropogenic carbon input affect microbial activity in salt marsh sediment.

Salt marshes are dynamic, highly productive ecosystems positioned at the interface between terrestrial and marine systems. They are exposed to large quantities of both natural and anthropogenic carbon input, and their diverse sediment-hosted microbial communities play key roles in carbon cycling and remineralization. To better understand the effects of natural and anthropogenic carbon on sediment microbial ecology, several sediment cores were collected from Little Sippewissett Salt Marsh (LSSM) on Cape Cod, MA, USA and incubated with either Spartina alterniflora cordgrass or diesel fuel. Resulting shifts in microbial diversity and activity were assessed via bioorthogonal non-canonical amino acid tagging (BONCAT) combined with fluorescence-activated cell sorting (FACS) and 16S rRNA gene amplicon sequencing. Both Spartina and diesel amendments resulted in initial decreases of microbial diversity as well as clear, community-wide shifts in metabolic activity. Multi-stage degradative frameworks shaped by fermentation were inferred based on anabolically active lineages. In particular, the metabolically versatile Marinifilaceae were prominent under both treatments, as were the sulfate-reducing Desulfovibrionaceae, which may be attributable to their ability to utilize diverse forms of carbon under nutrient limited conditions. By identifying lineages most directly involved in the early stages of carbon processing, we offer potential targets for indicator species to assess ecosystem health and highlight key players for selective promotion of bioremediation or carbon sequestration pathways.

Salt marsh expansion into estuarine mangrove mudflats reduces nitrogen removal capacity

Salt marsh (Spartina alterniflora) has been rapidly encroaching into mangrove wetlands worldwide. However, the potential effects of salt marsh expansion on coastal nitrogen cycling and ecosystem function remain unclear. In this study, sediment cores were seasonally collected from mangroves, salt marshes and mudflats from 2020 to 2021 to assess their nitrogen cycling. Nitrogen transformation rates of mineralization, immobilization, nitrification, denitrification, anaerobic ammonium oxidization (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) were determined using 15N isotope tracer techniques. Rate measurements were paired with analysis of physicochemical properties, carbon isotopes, and nitrogen functional genes. The results showed that compared to mangrove sediments, salt marsh sediments mostly exhibited lower mineralization and denitrification rates but higher nitrification rates. Mudflat sediments had the lowest mineralization and denitrification rates among the studied habitats, while the nitrification rates were close to those of salt marshes. The differences in carbon quantity and source, nitrogen gene abundances, and carbon and nitrogen substrate availabilities controlled the variations in nitrogen transformation rates. The balance of these rates was used to indicate the net nitrogen retention or removal capacity of the three habitats. On an annual scale, salt marshes exhibited ammonium (NH4+-N) removal while mangroves had net NH4+-N retention. Nitrate (NO3--N) was removed both in salt marsh and mangrove sediments with larger removal capacity in mangroves. Salt marsh sediments had lower NH4+-N removal but higher NO3--N removal levels than mudflat sediments. In summary, salt marsh invasion decreased the overall nitrogen removal levels in the mangrove-mudflat wetland. The future scenarios of increasing salt marsh coverage suggest a decreased removal of nitrogen loads, which has important implications for mitigating coastal eutrophication.

Marsh archive reveals human population history and future implications for estuarine health in Long Island Sound

Coastal marshes are efficient ecosystems providing a multitude of benefits for invertebrates, birds, fish and humans alike. Yet despite these benefits, wetlands are threatened by anthropogenic inputs such as human wastewater which contain high levels of nitrogen (N). Increased nitrogen loads cause eutrophication and hypoxia in estuaries leading to further degradation of these valuable ecosystems that are already stressed by sea level rise and climate change. Policies to protect wetlands via wastewater treatments are reactive rather than proactive and a growing body of research shows that characteristics associated with population health and economic activity can be identified in wastewater. Analysis of a 2-m salt marsh sediment core reveals δN15 signatures indicative of human population rise and connects human impact to ecosystem health. Using key X-ray fluorescence (XRF), pollen, sediment and nitrogen signatures along the core, a robust chronology was produced dating back to 1700. This result was coupled with population data to observe the relationship between δN15 levels and population over three centuries. There is a statistically significant positive correlation between δN15 and population. Other external factors such as federal government policies (regulating clean water) show a clear reduction in this association but the use of synthetic nitrogen fertilizer masks the strength of this relationship. Further research to refine the relationship between population and δN15 could be beneficial in predicting nitrogen loads as human population grows, which in turn would create a proactive system to protect our coastal ecosystems.

Holocene environmental evolution and relative sea-level change in the Oka estuary (Urdaibai Biosphere Reserve, northern Spain)

The Holocene environmental evolution in coastal areas, including deltas and estuaries, is vital to understanding coastal dynamics and how they may change in the future. Here, we studied the Holocene environmental evolution of the Oka estuary (Urdaibai Biosphere Reserve, northern Spain) from sedimentary cores that were 11–49 m long. We applied a multi-proxy approach of benthic foraminifera and grain size, and a temporal framework of radiocarbon dates to reconstruct paleoenvironments. The benthic foraminifera assemblages varied from near-marine (allochthonous and autochthonous hyaline species such as Lobatula lobatula, Rosalina irregularis, Ammonia tepida and Haynesina germanica) to brackish intertidal (autochthonous hyaline species such as A. tepida and H. germanica) to salt-marsh (autochthonous agglutinated species Trochammina inflata and Entzia macrescens) environments. Grain size analysis supported the foraminiferal assemblages and the sedimentary sequences were sand-dominated in near-marine intertidal environments and mud-dominated in the brackish intertidal and salt-marsh environments. The chronology was constrained by thirty four radiocarbon dates from plant macrofossils, marine shells and wood fragments. Our paleoenvironmental reconstructions were used to produce an updated local Holocene relative sea-level (RSL) record based on new data, revised reconstructions, and age recalibration of previous research. Marine limiting dates showed that RSL changed from above −20.4 ± 0.2 m at ∼9100 cal. yrs. BP to above −4.2 ± 0.2 m at ∼6700 cal. yrs. BP. In the late Holocene, sea-level index points (SLIPs) reconstructed the RSL position from −2.7 ± 1.2 m at ∼4900 cal. yrs. BP to −1.4 ± 1.2 m at ∼1500 cal. yrs. BP. Estimates of rates of RSL change from the Errors-in-Variables Integrated Gaussian Process (EIV-IGP) model show RSL gradually rose at 0.3 ± 2.1 mm yr−1 in the late Holocene. There was a progressive shallowing of the estuary as rates of RSL rise reduced during the Holocene. Between ∼9000 and 7000-6000 cal. yrs. BP pre-Holocene fluvial gravels (Lowstand Systems Tract) were replaced by both sandy marine and brackish intertidal sediments (Transgressive Systems Tract). After ∼7000-6000 cal. yrs. BP salt-marsh sediments deposited (Highstand Systems Tract). The sequence was overlain by anthropogenic deposits derived from agricultural, dredging and dumping activities since the 18th century (Anthropogenic Systems Tract). The Holocene environmental evolution and relative sea-level change of Oka is broadly consistent with previous studies in northern Spain, although it places the onset of the Highstand Systems Tract ∼2000 years earlier.

Contemporary Salt-Marsh Foraminifera from Southern California and Implications for Reconstructing Late Holocene Sea-Level Changes

Abstract We report on the distribution of contemporary foraminifera in salt marshes in Mission Bay and Carpinteria Slough, Southern California. Combining these data with existing datasets from Seal Beach and Tijuana, we explore the potential for a regional training set to underpin quantitative reconstructions of paleoenvironmental change from foraminifera preserved in salt-marsh sediments. We demonstrate that species’ distributions are highly dependent on elevation, suggesting fossil foraminiferal assemblages here, as in many other regions, are useful depositional elevation indicators. Transfer functions provide predictions from Mission Bay cores with decimeter-scale uncertainties. Nevertheless, interpretation of marsh-surface elevation change is complicated by a complex geomorphic setting and anthropogenic impacts. An abrupt change in elevation in the mid-1700s may be related to lateral spreading of water-saturated sediments during an earthquake on the Rose Canyon fault, suggesting the potential for foraminifera to support new palaeoseismic and sea-level records for the region.

Effects of Large Macropores on Saline Water Evaporation From Marsh Soil

AbstractMacropores such as crab burrows are a common feature of salt marsh sediment and are recognized as an important factor influencing pore‐water flow in salt marshes. In this study, we examined the effect of macropores on saline water evaporation and pore‐water salinity based on laboratory experiments and numerical simulations. Soil columns with and without an artificial macropore were packed with clay‐loam and were set with different hydraulic heads fixed at the bottom. The results showed that increase in pore‐water salinity significantly reduced evaporation rates. The preferential flow induced by macropores recharged the soil surrounding macropores and maintained higher evaporation rates in comparison with homogeneous soil without macropores. As macropores induced lateral flow, the pore‐water salinity in shallow soil around the macropores was reduced but that in the area away from the macropores was increased. These impacts were more remarkable on the soil layers with higher hydraulic heads. A sensitivity analysis showed that with a higher initial pore‐water salinity, the macropore's impact on soil evaporation rates was more remarkable for both clay‐loam and silt‐loam. These results revealed the effect of macropores on soil evaporation processes and soil conditions, and also shed light on associated biogeochemical processes in salt marshes.