Organic Sediments Research Articles

Sedimentation strategies provide effective but limited mitigation of relative sea-level rise in the Mekong delta

The Mekong delta is experiencing rapid environmental change due to anthropogenic activities causing accelerated subsidence, sea-level rise and sediment starvation. Consequentially, the delta is rapidly losing elevation relative to sea level. Designating specific areas for sedimentation is a suggested strategy to encourage elevation-building with nature in deltas. We combined projections of extraction-induced subsidence, natural compaction and global sea-level rise with new projections of fluvial sediment delivery to evaluate the potential effectiveness of sedimentation strategies in the Mekong delta to 2050. Our results reveal that with current rates of subsidence and sediment starvation, fluvial sediments alone can only preserve elevation locally, even under optimistic assumptions, and organic sedimentation could potentially assume a larger role. While sedimentation strategies alone have limited effectiveness in the present context, combined with enhanced organic matter retention and interventions reducing anthropogenic-accelerated subsidence, they can considerably delay future relative sea-level rise, buying the delta crucial time to adapt.

Organic carbon accumulation at the northern Gondwana paleomargin (Tunisia) during the Toarcian Oceanic Anoxic Event: Sedimentological and geochemical evidence

During the early Toarcian (Early Jurassic; ~183 Ma) global environmental changes promoted the expansion of oxygen-deficient conditions across vast shelf areas around the globe. Ocean margin deoxygenation favored the preservation of organic matter in shelf sediments and is considered to reflect a Toarcian Oceanic Anoxic Event (T-OAE). Higher-level global drivers controlled temperature fluctuations, sea level evolution, oceanic circulation patterns, marine primary productivity, and stable carbon isotope excursions. Lower-level factors, controlled by individual basin bathymetry and paleogeography, operated on local to regional scale and here regulated organic matter accumulation. Accordingly, the T-OAE has been described as global event with a strong regional character. During the Toarcian, preferentially organic matter-lean sediments have been deposited at the northern Gondwana paleomargin. Enhanced connectivity to the Tethys Ocean and low marine primary productivity are considered to have been major factors preventing the formation of oxygen-deficient conditions and organic matter preservation. We here report on early Toarcian sediments from the Châabet El Attaris Section (Tunisia), located at the northern Gondwana paleomargin that episodically became enriched in organic matter. Bio- and chemostratigraphy both confirm that organic matter-rich sediments preferentially formed during the T-OAE but also predate the T-OAE. Sedimentological and micropaleontological characterization in concert with bulk, molecular and stable isotope geochemical investigations reveal that accumulation of marine organic matter occurred under anoxic, but not under euxinic, conditions. Limitation in the supply of reactive iron regulated organic matter sulfurization indicating that during most of the depositional history the levels of free H 2 S in bottom waters were rather low but limited to the sediment pore water. We conclude that the chemocline was either situated within the sediment or close to the sediment water interface. Spatiotemporally-restricted occurrence of organic matter enriched sediments and anoxic pore waters was promoted by restriction in water column ventilation in a local graben structure. • Organic matter-enriched strata in Tunisia predates but maximizes in the T-OAE. • Organic matter preservation occurred under anoxic but non-euxinic conditions. • Formation of oxygen deficient conditions was promoted by local paleobathymetry and basin restriction.

Oscylacje klimatyczne w zakresie 20 000–11 000 cal BP zapisane w utworach formacji Piaski i Szerokie w odkrywkach Kopalni Węgla Brunatnego Bełchatów: spojrzenie poprzez analizę dat radiowęglowych

Radiocarbon dates of organic sediments, taken from the soil horizon, gyttja, peats, plant remains and mineral-organic sediments – silts and silty-sandy sediments with admixture of organic material – were collected and analysed. Age determinations were made for samples collected over a number of years from the upper part of sediments of the Piaski and Szerokie Formations in the Bełchatów Lignite Open Cast Mine (28 dates) and their surroundings (2 dates) (Fig. 1; Tab. 1). The organic sediments analysed are mainly associated with the valleys of the Krasówka, Struga Żłobnicka, Świętojanka and Widawka Rivers. They were formed within alluvia (probably fillings of oxbow lakes). Some of the organic deposits were formed in the vicinity of dunes or aeolian covers (mid-dune depressions). During the Late Glacial in this area, aggradation dominated the river valleys. Fluvial processes were accompanied by aeolian processes. A large proportion of aeolian grains is characteristic of the upper part of the profile of the sands formations. Despite the filling of the valleys with fluvio-aeolian sediments, fluvial erosion also occurred in places. The Folwark 1 and 2 sites in the Struga Żłobnicka River valley yielded 12 age determinations (from 14 810±170 to 11 130±120 BP, i.e. 18 270–12 900 cal BP). In the Widawka valley, the sites Bełchatów 3/88 BM, JG, I/83/JG, II/83/JG, Buczyna 8, Rogowiec 1 and Wola Grzymalina yielded 12 dates falling in the pe-riod 14 350±580 to 10 160±140 BP, i.e. 18 240––11 400 cal BP. In the Kleszczów 3/90 site, only one date of 11 460±120 BP (13 460–13 190 cal BP) related to peat in the Świętojanka River valley. The last two determinations, archived as site unknown and Kuców C–IIa, are dated 15 850±180 (19 360–18 930 cal BP) and 13 780±130 BP (16 950–16 520 cal BP). In the area of the present Szczerców field, the Parchliny-Chabielice site yielded three dates in the Krasówka River valley – 10 290±90 (12 450–11 830 cal BP), 11 840±110 BP (13 800–13 520 cal BP) and 15 440±160 (18 910–18 360 cal BP) (Tab. 1). Based on the collected dates, so-called PDF (Probability Density Functions) curves were drawn up in the range 20 000–11 000 cal BP (Fig. 3). The analysis used the shape analysis method of the summed probability density distributions of the calibrated radiocarbon dates (Fig. 3). The position of peaks of the obtained distributions on the time axis is in good agreement with the oxygen curve from the Greenland core NGRIP. There is a clear clustering of dates around the beginning of GI–1, but also around GI–1d, GI–1c2 and GI–1b. This was contributed to by the preferential sampling for dating from locations where changes in sediment lithology were evident (bottom and top of peat layer, soil on mineral deposits, bottom of oxbow fill, etc.). Therefore, the peaks of the obtained distributions should not be linked only to warm periods, but rather to transitions from cold to warm conditions or from warm to cold conditions. Although the dataset analysed is smallscale, the evident clustering of dates makes it possible to identify environmental responses to climate change over several time scales: - 19 500–18 900 cal BP (peak within GS–2b); - 17 800–17 300 cal BP (peak at transition GS––2b/GS–2a); - 16 800–16 600 cal BP (peak located at GS– –2a); - 15 200–14 300 cal BP (peak at GS–2a/GI–1e transition); - 14 100–13 800 cal BP (peak around GI–1d); - 13 600–13 550 cal BP (peak around GI–1c2); - 13 250–13 050 cal BP (peak around GI-1b); - 12 500–11 700 cal BP (peak around the second half of GS–1) The resolution of the analyses carried out does not make it possible to determine whether there were delays in the environmental response of the study area in relation to the changes recorded in the Greenlandic core, but any delays must be less than the average uncertainty of the radiocarbon dates analysed, i.e. ~100 years. The analyses carried out used dates made using conventional techniques, which have relatively large uncertainties. It is probable that including new sites and precise 14C age determinations by the AMS technique would contribute to a higher resolution of this type of analysis.

Trójdzielność młodszego dryasu obserwowana w rozwoju roślinności w otoczeniu torfowiska Żabieniec w środkowej Polsce

The Żabieniec mire is located in central Poland on the Łódź Highlands. Paleogeographical and paleoecological research have been being conducted there from a few decades. Organic sediments accumulated during the Eemian Interglacial, Vistulian Glaciation and Holocene reveal a continuous and detailed record of vegetation succession and environmental changes during these periods. Initially, a lake existed there and gyttja constitutes the sediment of the lower part of investigated core. Nowadays, there is still a small area of open water surrounded by mire. The high thickness of organic sediments, which is exceptional for old-glacial areas, enabled palaeoecological analyses and a detailed description of environmental history during the Late Glacial and Holocene. This article presents the pollen analysis record of vegetation development during the Younger Dryas, the last cold period of the Late Glacial. The chronology is based on radiocarbon dating made at the Gliwice Radiocarbon Laboratory of the Silesian University of Technology (Petera-Zganiacz et al. 2022). The course and proportions of dominating taxa and important “cold” species allowed for the division of the diagram into three phases. The first one lasted ca 900 years (50 cm of sediments) and shows a cooling, the development of cold-demanding plant communities, deforestation and an increase in trophy. The cooling of the climate was revealed in higher curves of Juniperus, Poaceae and Artemisia. The presence of pollen grains of light-demanding Hippophaë proved deforestation and dominance of open plant communities. Apart from aforementioned Artemisia, there grew steppe plants like Ephedra distachya and E. fragilis, Helianthemum and some herbs of identified: Chenopodiaceae, Anthemis type, Cichorioidae. Dwarf shrubs developed in wet habitats, namely Betula nana type and Salix polaris type. Dryas octopetala appeared on soil patches rich in calcium carbonate. The second phase lasted not longer than 230 years (50 cm of sediments) and shows preservation of cold-demanding vegetation and high trophy of the lake. This is the phase of stable ex-istence of cold-demanding species. A cold steppe dominated by Poaceae and Artemisia was enriched by many herbal plants represented in pollen types: Gypsophila repens type, Rumex acetosella, Bupleurum, Senecio type, Anthemis type, Cichorioidae. Thalictrum, Valeriana officinalis, Solanum dulcamara, Rumex acetosa developed next to dwarf shrubs of Betula nana and Salix. Exclusively in this phase, there appeared pollen type of Saxifraga hieraciifolia, a plant of calcareous habitats in subarctic regions and high moun-tains. At the same time, Juniperus and steppe elements (Helianthemum, Ephedra) decreased. High curves of Pediastrum and disappearance of spores of Isoëtes revealed high trophy of the lake during this phase. The third phase lasted ca 120 years (30 cm) and shows a decrease in cold- and light-demanding tundra and steppe taxa. There were only single pollen grains of Betula nana, Salix polaris type, Dryas octopetala. Meanwhile, Ephedra, Helianthemum and Gypsophila repens type disappeared. Trophy was clearly decreasing. Significant changes in trophy are suggested mainly based on the presence of Isoëtes, a plant of a very nutrient-poor water. The main changes in trophy are revealed mainly by high curve of oligotrophic Isoëtes found at the end of Allerød and then at the end of the Younger Dryas, while a phase of high tro-phy is marked by growing curves of some varieties of Pediastrum boryanum. Pollen analyses of some sites in Poland suggest that vegetation succession driven by macro-climatic features is significantly modified by local factors such as geomorphology, topography and physico-chemical properties of the ground/ habitat. Periods of cooling and warming at the be-ginning and end of the Younger Dryas have previously been defined in detail for the laminated sediments of Lake Gościąż. Microfacies, isotops and other paleoclimatic analyses done for that site indicated that the decrease in temperature at the beginning of the Younger Dryas and its in-crease at the end lasted, respectively, 180 and 70 years. They are shorter periods than phases of vegetation changes, because the reac-tion of plants and ecosystems development takes more time. Most Younger Dryas pollen diagrams in Poland can be divided into two parts. The first, older one reveals the development of tundra and cold steppe vegetation as a result of the climate cooling. The second shows the disappearance of cold-demanding species and tundra vegetation and the development of plants of warmer climate such as Typha latyfolia and Filipendula. Such a division can be found on diagrams from the Witów, Gościąż, Kaniewo, Łukie sites. Some pollen records, however, show stable curves during the entire Younger Dryas (Perespilno, Imiołki).

Pull the trigger: interplay between benthic and pelagic cues driving the early recruitment of a natural bivalve assemblage

AbstractLarval settlement and recruitment are crucial phases in the benthic‐pelagic life cycle of marine benthic invertebrates that controls population dynamic and habitat connectivity. Our study investigated potential triggers driving the settlement of bivalve larvae in a highly dynamic intertidal coarse sand habitat. The early recruitment rate of five dominant bivalve families and abiotic conditions, particulate (<20 µm) organic matter and sediment organic matter, were monitored from May to October 2014. Pelagic particulate organic matter (<20 µm) was dominated by picoplankton throughout the sampling period, with a substantial diatom bloom in spring. Sediment was characterized by fresh organic matter in spring, as suggested by the dominant contribution of polyunsaturated fatty acids, and by a higher proportion of bacterial fatty acid markers during late summer. Different dynamics were also observed in early bivalve recruitment rates, with four different patterns observed over the sampling period. Multiple regression analysis on selected bivalve families showed species‐specific responses to trophic settlement triggers. Indeed, the larva recruitment rate of Mytilidae paralleled pelagic concentration of picoeucaryotes, with the peak early recruitment rate occurring in spring. Surprisingly, the early recruitment rate of Mactridae larvae showed a significant relation to bacterial concentration in the surficial sediment at the end of summer. While the Mytilidae results in such a eutrophic system confirmed those of a previous study in oligotrophic lagoons, therefore supporting the trophic settlement trigger hypothesis, more work is needed to understand the potential role of bacteria in the early recruitment of Mactridae. These results highlight for the first‐time inter‐specific differences in trophic cues that potentially trigger primary settlement in natural bivalve assemblages.

Assessment of ecosystem health status using benthic diversity as tools in coastal sediments off the South West Coast, India

The southwest coast of India is densely populated and experiences a wide range of natural and anthropogenic pressures. The diversity of macro and meiobenthos was documented in order to assess the ecosystem health of an anthropogenically impacted coastal ecosystem for the first time along the southwest coast of Tamil Nadu. Offshore sediment and water samples (n=63) were collected from 14 sampling stations using the grid sampling method. Water and sediment samples were analysed for environmental variables such as pH, temperature, electrical conductivity (EC), total dissolved solids (TDS), salinity, sulphate, dissolved oxygen (DO), carbohydrate (CHO), protein, lipid, labile organic matter (LOM), total organic carbon (Corg), total organic matter (TOM) and sediment texture. Benthic macro and meiobenthos were isolated and identified using standard identification keys. A total of 5 phyla of macrobenthos with 29 species and 5 phyla of meiobenthos with 60 species were identified in the study area. Relative abundance analysis showed that the largest numbers of species belonged to Polychaeta for macrobenthos and foraminifera for meiobenthos. Redundancy analysis indicated that sediment carbohydrate content was the highest determining factor for explaining variation in the diversity of benthos. AMBI & M-AMBI results revealed that among the 14 stations, 2 were categorized as “poor” and 9 as “bad”. Multiple anthropogenic activities in the coastal environment leading to increased organic matter input have resulted in a decline in the ecosystem health of this region, which warrants site-specific management to control organic pollution.

Combined models of growth, waste production, dispersal and deposition from cage-cultured Atlantic salmon to predict benthic enrichment

Models of particulate waste production and deposition can be used in performance-based management approaches as cost-effective tools to assess environmental effects of open-pen finfish aquaculture. XLDEPMOD is an MS Excel® spreadsheet-based depositional model for predicting particulate organic carbon (POC) waste production and sedimentation from net-pen cultured finfish. Calculations are based on temperature-dependent fish growth and mass-balance calculations of feed input, growth, respiration and 3 size classes of feces. Depth-average and near-bottom directional currents are used to determine waste dispersion by fitted Gaussian distribution functions. Near-bottom velocity and substrate-based resuspension thresholds and loss of deposited waste due to decomposition and consumption by wild fish and invertebrates are used to calculate net POC sedimentation. The model was applied to 2 Atlantic salmon farms in southwestern Bay of Fundy, Canada. Sensitivity analysis showed that reduction in waste flux due to resuspension depends on the magnitude of current and wave-driven bottom shear and mass fractions of feces with different settling velocities. Depending on depth, current speed, substrate type and fecal mass fractions, resuspension can remove up to 80% of deposited waste from under net-pens. Steep gradients with high rates (>5 g POC m-2 d-1) of sedimentation predicted under and close to cages and lower rates (<1 g POC m-2 d-1) >50 m away are consistent with published DEPOMOD results and sediment trap observations at the farm sites. The model can be used by regulators to determine if acceptable environmental standards for benthic impacts due to waste deposition from salmon aquaculture are being maintained.

Gözenekli Agregalı Betonların Isıl ve Mekanik Özellikleri

The results of an experimental study on the thermal and mechanical properties of concretes using porous aggregates instead of conventional aggregates are presented in this study. Oriented at this purpose, eleven concrete samples containing organic sediment stones, volcanic stones and artificial porous aggregates were prepared as porous aggregates. The concrete samples were subjected to certain tests at the end of 28 days of drying period and their thermal and mechanical properties were determined accordingly. With this study, the following values were obtained: i) The lowest heat transfer coefficient for concrete with expanded polystyrene aggregates from the group of artificial porous aggregates: 0.175 W/mK, ii) The highest compressive strength value is basalt-type stone (Karaca dag) from the group of volcanic stones: 117 MPa.

Coexistence of Lobelia dortmanna and Cladium mariscus, an ecological and paleobotanical study

Lobelia dortmanna L. (Lobeliaceae family) is an indicator species that is predominantly found in oligotrophic and acidic lakes. They are mainly distributed in northwestern Europe. Their occurrence in Poland is highly threatened by the increasing grade of human activity and environmental eutrophication; however, new sites of Lobelia were discovered in the last few decades, for example, in Lake Krzywce Wielkie situated in Bory Tucholskie National Park (BTNP), Poland. The existence of Lobelia in this lake was unexpected because Cladium mariscus was also found in the lake. Cladium has different ecological demands and is regarded as a species typical of calcareous habitats where calcium is found in abundance in the substrate. To explain the coexistence of both species in Krzywce Wielkie, pollen analysis of organic sediments was performed for four short cores collected from the littoral zone of the lake and for one long deep-water core. Additionally, macrofossil analysis was done for all the short cores. Pollen analysis revealed the existence of Cladium from the early Holocene period up to the present time. Pollen and seeds of Lobelia were found to be present since the beginning of the 20th century. Development of L. dortmanna and Myriophyllum alterniflorum populations and a decrease in the number of aquatic macrophytes in the eutrophic water indicate oligotrophication of water. This process started following the construction of drainage canal and the consequent water level decrease. This situation can be attributed to the abandonment of the agricultural areas adjoining the lake, which causes a decrease in the inflow of nutrients into the lake. Development of pine forest and establishment of BTNP enabled the protection and conservation of the surrounding catchment areas, thus restricting the potential eutrophication of the habitats.

Oxic urban rivers as a potential source of atmospheric methane

Urban rivers play a vital role in global methane (CH4) emissions. Previous studies have mainly focused on CH4 concentrations in urban rivers with a large amount of organic sediment. However, to date, the CH4 concentration in gravel-bed urban rivers with very little organic sediment has not been well documented. Here, we collected water samples from an oxic urban river (Xin'an River, China; annual mean dissolved oxygen concentration was 9.91 ± 1.99 mg L−1) with a stony riverbed containing very little organic sediment. Dissolved CH4 concentrations were measured using a membrane inlet mass spectrometer to investigate whether such rivers potentially act as an important source of atmospheric CH4 and the corresponding potential drivers. The results showed that CH4 was supersaturated at all sampling sites in the five sampling months. The mean CH4 saturation ratio (ratio of river dissolved CH4 concentration to the corresponding CH4 concentration that is in equilibrium with the atmosphere) across all sampling sites in the five sampling months was 204 ± 257, suggesting that the Xin'an River had a large CH4 emission potential. The CH4 concentration was significantly higher in the downstream river than in the upstream river (p < 0.05), which suggested that human activities along the river greatly impacted the CH4 level. Statistical analyses and incubation experiments indicated that algae can produce CH4 under oxic conditions, which may contribute to the significantly higher CH4 concentration in August 2020 (p < 0.001) when a severe algal bloom occurred. Furthermore, other factors, such as heavy rainfall events, dissolved organic carbon concentration, and water temperature, may also be vital factors affecting CH4 concentration. Our study enhances the understanding of dissolved CH4 dynamics in oxic urban rivers with very little organic sediment and further proposes feasible measures to control the CH4 concentration in urban rivers.

Influence of Key Environmental Drivers on the Performance of Sediment Diversions

A Delft3D morphodynamic model for Barataria Bay, Louisiana, USA is used to quantify a plausible range of land change in response to a proposed sediment diversion under a range of environmental drivers. To examine the influence of environmental drivers, such as Mississippi River water hydrographs, mineral and organic sediment loading, sea level rise rates, subsidence, and a projected implementation (or operation) date, 240 multi-decadal (2020–2100) numerical experiments were used. The diversion was assumed to begin operation in 2025, 2030, or 2035. The experiments revealed persistent benefits of the sediment diversion through 2100. Start data of 2025 result in a median net positive land change of 32 km2 by 2100; whereas the 90th, and 10th percentiles are 69 and 10 km2. A delay in the operation date of the diversion to 2030 or 2035 would reduce the net positive land change by approximately 15–20% and 20–30%, respectively.

Biogeochemical responses of a highly polluted tropical coastal lagoon after the passage of a strong hurricane (Hurricane Irma)

Abstract Laguna Larga (Cayo Coco, Cuba) is a eutrophic coastal lagoon due to tourism development. As part of long-term monitoring of Laguna Larga, we were able to follow the lagoon's water quality from 2015 to 2018 and could assess the impacts of Hurricane Irma (September 8–9, 2017) by intensifying our sampling frequency. Physicochemical parameters (salinity, pH, dissolved oxygen, dissolved inorganic nitrogen, dissolved reactive silicate and total nitrogen) exhibited significant variations associated with Hurricane Irma. Salinity decreased due to the extraordinary rainfall of the hurricane (339.8 mm/24 h, a new record for Cayo Coco). The water level in the lagoon rose 0.85 m. Strong hurricane winds and intense runoff drove organic matter and sediment resuspension. Anoxia and an increase of nutrients occurred throughout the lagoon. The main biogeochemical impact was that it boosted these eutrophic conditions of the lagoon, to levels that lasted for several months. A significant correlation among nutrients, salinity and dissolved oxygen was found. After 6 months, water quality in the lagoon had recovered to conditions similar to those before the hurricane. The case of Laguna Larga shows that those coastal systems under anthropic pressure can take longer to recover after extreme climatic events, and highlights the need for long-term monitoring of tropical coastal ecosystems.

Assessing the genotoxic potential of freshwater sediments after extensive rain events – Lessons learned from a case study in an effluent-dominated river in Germany

Wastewater treatment plant effluents and releases from rainwater overflow basins can contribute to the input of genotoxic micropollutants in aquatic ecosystems. Predominantly lipophilic genotoxic compounds tend to sorb to particulate matter, making sediment a source and a sink of pollution. Therefore, the present study aims to investigate the genotoxic potential of freshwater sediments (i) during the dry period and (ii) after extensive rain events by collecting sediment samples in one small anthropogenically impacted river in Germany up- and downstream of the local wastewater treatment plant. The Micronucleus and Ames fluctuation assays with Salmonella typhimurium strains TA98, TA100, YG1041, and YG1042 were used to assess the genotoxic potential of organic sediment extracts. For evaluation of possible genotoxicity drivers, target analysis for 168 chemical compounds was performed.No clastogenic effects were observed, while the genotoxic potential was observed at all sampling sites primarily driven by polycyclic aromatic hydrocarbons, nitroarenes, aromatic amines, and polycyclic heteroarenes. Freshwater sediments' genotoxic potential increased after extensive rain events due to sediment perturbation and the rainwater overflow basin release. In the present study, the rainwater overflow basin was a significant source for particle-bound pollutants from untreated wastewater, suggesting its role as a possible source of genotoxic potential. The present study showed high sensitivity and applicability of the bacterial Salmonella typhimurium strains YG1041 and YG1042 to organic sediment extracts to assess the different classes of genotoxic compounds. A combination of effect-based methods and a chemical analysis was shown as a suitable tool for a genotoxic assessment of freshwater sediments.

Postdiagenetic Bacterial Transformation of Nickel and Vanadyl Sedimentary Porphyrins of Organic-Rich Shale Rock (Fore-Sudetic Monocline, Poland).

Nickel and vanadyl porphyrins belong to the so-called fossil geo- or sedimentary porphyrins. They occur in different types of organic matter-rich sediments but mostly occur in crude oils and their source rocks, oil shales, coals, and oil sands. In this study, we aimed to understand the process of bacterial transformation of geoporphyrins occurring in the subsurface shale rock (Fore-Sudetic Monocline, SW Poland). We studied these transformations in rock samples directly obtained from the field; in rock samples treated with bacterial strain isolated from shale rock (strain LM27) in the laboratory; and using synthetic nickel and vanadyl porphyrins treated with LM27. Our results demonstrate the following: (i) cleavage and/or degradation of aliphatic and aromatic substituents of porphyrins; (ii) degradation of porphyrin (tetrapyrrole) ring; (iii) formation of organic compounds containing 1, 2, or 3 pyrrole rings; (iv) formation of nickel- or vanadium-containing organic compounds; and (v) mobilization of nickel and vanadium. Our results also showed that the described bacterial processes change the composition and content of geoporphyrins, composition of extractable organic matter, as well as nickel and vanadium content in shale rock.

Millennial-Scale Carbon Storage in Natural Pine Forests of the North Carolina Lower Coastal Plain: Effects of Artificial Drainage in a Time of Rapid Sea Level Rise

Coastal forested wetlands provide important ecosystem services along the southeastern region of the United States, but are threatened by anthropogenic and natural disturbances. Here, we examined the species composition, mortality, aboveground biomass, and carbon content of vegetation and soils in natural pine forests of the lower coastal plain in eastern North Carolina, USA. We compared a forest clearly in decline (termed “ghost forest”) adjacent to a roadside canal that had been installed as drainage for a road next to an adjacent forest subject to “natural” hydrology, unaltered by human modification (termed “healthy forest”). We also assessed how soil organic carbon (SOC) accumulation changed over time using 14C radiocarbon dating of wood sampled at different depths within the peat profile. Our results showed that the ghost forest had a higher tree density at 687 trees ha−1, and was dominated by swamp bays (Persea palustric), compared to the healthy forest, which had 265 trees ha−1 dominated by pond pine (Pinus serotina Michx). Overstory tree mortality of the ghost forest was nearly ten times greater than the healthy forest (p &lt; 0.05), which actually contributed to higher total aboveground biomass (55.9 ± 12.6 Mg C ha−1 vs. 27.9 ± 8.7 Mg ha−1 in healthy forest), as the dead standing tree biomass (snags) added to that of an encroaching woody shrub layer during ecosystem transition. Therefore, the total aboveground C content of the ghost forest, 33.98 ± 14.8 Mg C ha−1, was higher than the healthy forest, 24.7 ± 5.2 Mg C ha−1 (p &lt; 0.05). The total SOC stock down to a 2.3 m depth in the ghost forest was 824.1 ± 46.2 Mg C ha−1, while that of the healthy forest was 749.0 ± 170.5 Mg C ha−1 (p &gt; 0.05). Carbon dating of organic sediments indicated that, as the sample age approaches modern times (surface layer year 2015), the organic soil accumulation rate (1.11 to 1.13 mm year−1) is unable to keep pace with the estimated rate of recent sea level rise (2.1 to 2.4 mm year−1), suggesting a causative relationship with the ecosystem transition occurring at the site. Increasing hydrologic stress over recent decades appears to have been a major driver of ecosystem transition, that is, ghost forest formation and woody shrub encroachment, as indicated by the far higher overstory tree mortality adjacent to the drainage ditch, which allows the inland propagation of hydrologic/salinity forcing due to SLR and extreme storms. Our study documents C accumulation in a coastal wetland over the past two millennia, which is now threatened due to the recent increase in the rate of SLR exceeding the natural peat accumulation rate, causing an ecosystem transition with unknown consequences for the stored C; however, much of it will eventually be returned to the atmosphere. More studies are needed to determine the causes and consequences of coastal ecosystem transition to inform the modeling of future coastal wetland responses to environmental change and the estimation of regional terrestrial C stocks and flux.

Earthquake effects and insights on fault activity at the Beatrice Cenci cave (Abruzzo, Central Apennines)

he focus of this study is the analysis of a cave in Central Italy, the Beatrice Cenci cave, in order to point out and constrain evidence of possible past earthquakes and of fault activity in the area. We performed a survey of seismic related damages within the cave. This included the analysis of broken/collapsed speleothems, the recognition of structural collapse, of tilting/growth alteration in the speleothems, and the mapping of fractures, joints and/or faults. To timely set the occurrence of the recognized damage, organic sediments were dated with 14C radiocarbon method. The results merged toward the recognition of two distinct seismic shaking events affecting the cave environment, one older than 30 kyr and another around 7 kyr. The deformation observed within the cave led us to the hypothesis that the events of damage were possibly linked to the activity of the regional tectonic lineament that crosses the cave, i.e., the Liri normal fault. The morphology and the evolution of the cave appear controlled by the fault zone. These speleoseismological results provided a new contribution on the knowledge of the past activity of the Liri fault and on the earthquake history of this sector of Central Apennines.

Spatial and seasonal change in algal community structure and its interaction with nutrient dynamics in a gravel-bed urban river

Harmful algal blooms frequently occur in urban rivers due to intense human activities. However, little is known about the change in algal community structure and its interactions with nutrient dynamics in gravel-bed urban rivers. In present study, water samples were collected from a gravel-bed River Xin’an, China for five months over four seasons and a rainy month to measure algal community structure, dissolved nitrogen gas (N2) and Argon (Ar) concentrations, and other water quality parameters. The results showed that the harmful Cyanophyta accounted for 31.6 ± 24.1% of the total community in the hot season while Bacillariophyta contributed more than 60% to the community in the other three seasons. The N2 was supersaturated in the moderate and cold seasons but it was unsaturated in the hot season, along with high concentrations of nitrogen-fixing cyanobacteria (Anabaena), indicating that the nitrogen fixation capacity was strong and even stronger than denitrification and anammox in the hot season. However, nitrogen fixation was not the main source of nitrogen in the water column. The concentrations of nutrients and Chla in the downstream river were significantly higher than those in the upstream river (p < 0.001 for nutrients and p = 0.029 for Chla), suggesting that human activities along the river greatly affected nutrient concentrations, as well as algal growth. Our study provides new insights into the algal community succession in a gravel-bed urban river and puts forward effective measures such as controlling exogenous nutrient input and dredging organic sediment for mitigating the harmful algal blooms in urban rivers.

Oyster Biodeposition Alleviates Sediment Nutrient Overload: A Case Study at Shenzhen Bay, China.

Oysters are ecological engineers, and previous studies have examined their role as competent facilitators of ecological restoration. However, the decisive role of oysters in the aquatic environment is still debatable because oyster biodeposition (OBD) may also increase the nutrients enriched in sediments. In order to better interpret this problem, we sampled sediment cores from representative oyster culture areas and uncultured areas in Shenzhen Bay. The results have shown that the TOC (total organic carbon) and TN (total nitrogen) decreased significantly (p < 0.05) at the surface sediment layer (0–20-cm deep) and the sediment layer (20–40-cm deep) of the oyster site compared with the reference site. The decreased TOC and TN were also observed at 60- to 100-cm sediment depth in the oyster site. This indicated that the OBD significantly impacted the concentration of TOC and TN in the sediment. To confirm the alleviative role of OBD, we conducted stable isotope (δ13C and δ15N) analyses, which further demonstrated the presence of heavier and less lighter forms of organic carbon and nitrogen sediment. The surface sediment layer (0–20 cm) at the oyster site showed 8% more δ13C‰ compared with the control site (p < 0.05), reflecting the reduction in the TOC. In order to reveal the potential microbial mechanisms involved in OBD, we performed a functional analysis using the Geochip5 advanced microarray technology. Regarding carbon metabolism, we observed that genes (encoding pullulanase, glucoamylase, exoglucanase, cellobiase, and xylanase) involved in the degradation of relatively labile C-based molecules (e.g., starch, cellulose, and hemicellulose) were highly represented in an experimental area (p < 0.05). In addition, microbes in the experimental area exhibited a greater capacity for degrading recalcitrant C (e.g., lignin), which involves glyoxal oxidase (glx), manganese peroxidase (mnp), and phenol oxidase. Among the genes controlling nitrogen metabolism, the genes involved in denitrification, assimilation, ammonification, and nitrification were differentially expressed compared with the control area. These results indicated that microbial metabolic roles might have enhanced the C/N-flux speed and reduced the overall nutrient status. We concluded that OBD alleviates sediment nutrient overload under oyster farming from a microbial ecological perspective in a rapidly urbanized coastal area.

Mantle-Derived Helium Distribution and Tectonic Implications in the Sichuan-Yunnan Block, China.

The geochemical characteristics of mantle degassing observed on the surface of the earth can indicate the origin and migration path of mantle fluids. Compared with the plate boundary tectonic environment, the intraplate tectonic environment does not have a large number of active volcanoes and active faults, and the observation of mantle volatiles in hot spring gas is relatively limited. We selected the Sichuan–Yunnan block to discuss mantle degassing based on the carbon and noble gas isotopes of the spring gases and previous studies on the fault slip rate and geophysical research. A total of five hot spring gas samples (including two free gases and three dissolved gases) were collected from the Sichuan–Yunnan block. Chemical and isotopic compositions were analyzed in N2-dominant hot spring gases. The 3He/4He ratio (0.068–0.541 Ra) indicates the occurrence of mantle-derived helium throughout the Sichuan–Yunnan block, which has been diluted by a crustal radiogenic 4He component. The occurrence of mantle-derived helium in the study areas ranges from 0.74 to 5.67%. The lower proportion of mantle-derived helium in YNWQ and HGWQ than that in other spring gases near the Jinghe-Qinghe fault may be caused by the smaller scale of fault around YNWQ and HGWQ than the Jinghe-Qinghe fault. The correlation between 4He, 20Ne, and N2 concentrations implies a common trapping mechanism for 4He, 20Ne, and N2 in hot spring gases. The 40Ar/36Ar ratios and N2/Ar ratios indicate that N2 and Ar are mostly meteoric, and YNWQ and HGWQ have more crustal-derived Ar contribution (40.56 and 51.49%, respectively). The δ13C(CO2)o values calculated by Rayleigh fractionation and CO2 concentration suggest that CO2 has inorganic and organic origins. The plot of Rc/Ra versus δ13C(CO2) indicates that the spring gas CO2 origin in the Sichuan–Yunnan block is mainly derived from mixing of limestone and organic sediments with minor mantle CO2. The δ13C(CH4) versus CH4/3He values indicate that the origin of methane is thermogenic and microbial oxidation. The low mantle-derived helium distribution pattern is most likely controlled by the weak fault activity rate, the small fault scale, and not obvious magmatic activity in the Sichuan–Yunnan block.

Inland saline aquaculture increased carbon accumulation rate and stability in pond sediments under semi-arid climate

Similar to fresh- and brackish water aquaculture ponds, commercial shrimp farming in degraded saline areas holds the potential to bury carbon (C) in the sediments. However, studies on the mechanisms of sediment C dynamics and C-flux in response to inland saline aquaculture management practices are still scarce. Therefore, the objectives of the present study are to quantify the C burial rate in inland saline aquaculture ponds and assess the impact of inland saline aquaculture on sensitive C fractions in the bottom sediment of the ponds. The sediment samples (n = 12 from each pond) were collected from six shrimp farming ponds (1000 m2 area of each pond) of different ages. The sediment depth, sediment accumulation rate and the levels of total carbon (TC), total organic carbon (TOC) and sediment oxidizable organic carbon (SOC) and its different fractions were determined using standard procedures. The data were analysed by one-way analysis of variance (ANOVA), followed by the Duncan's multiple range test for comparing the means, and the Pearson correlation test was used to assess the relationship between the different pond sediment parameters and SOC content. The results revealed that the annual C accumulation rates varied from 902 to 1346 kg C ha−1 year−1 in 7-year-old earthen ponds (EPs) and bottom cemented ponds (BCPs), respectively. The sediment C fractions, including TC, TOC, SOC and its fractions (very labile, VLc; labile, Lc; less labile, LLc), and non-labile carbon (NLc)) were progressively increased over the pond age. The inland saline aquaculture practices over the years increased both active (AC) and passive carbon (PC) pools in the pond sediments, helped in the restoration and improvement of sediment quality and enhanced C sequestration potential of the sediments. Furthermore, a significant increase in the level of particulate organic carbon (POC) in BCPs justified that the non-ploughing practices at BCPs facilitated the formation of macro- and micro-aggregates, thereby increasing the C retention and stability of the pond sediments. This study suggested that the shrimp farming ponds in semi-arid saline soils represented considerable C burial hotspots, enhanced the stable passive C pools and improved the sediment quality.