Bulk Sediment Research Articles

Decreased spatial variation and deterministic processes of bacterial community assembly in the rhizosphere of Phragmites australis across the Middle-Lower Yangtze plain.

Comparison of the spatial distribution and assembly processes between bulk and rhizosphere bacterial communities at multiple spatial scales is vital for understanding the generation and maintenance of microbial diversity under the influence of plants. However, biogeographical patterns and the underlying mechanisms of microbial communities in bulk and rhizosphere sediments of aquatic ecosystems remain unclear. Here, we collected 140 bulk and rhizosphere sediment samples of Phragmites australis from 14lakeshore zones across a 510-km transect in the Middle-Lower Yangtze plain. We performed high-throughput sequencing to investigate the bacterial diversity, composition, spatial distribution and assembly processes of these samples. Bacterial communities in the rhizosphere sediment exhibited higher alpha diversity but lower beta diversity than those in the bulk sediment. Both bulk and rhizosphere sediment bacterial communities had significant distance-decay relationships, but spatial turnover of the rhizosphere sediment bacterial community was strikingly lower than that of bulk sediment. Despite variable selection dominating the assembly processes of bacterial communities in bulk sediment, the rhizosphere of P. australis enhanced the role of dispersal limitation in governing bacterial communities. The relative importance of different ecological processes in determining bacterial assembly presented distinct patterns of increasing or decreasing linearly with an increase of scale. This investigation highlights the convergent selection of the aquatic plant rhizosphere for surrounding bacterial communities and emphasizes the importance of different ecological processes on bacterial community assembly in sediment environments over different scales. Furthermore, we provide a preliminary framework for exploring the scale dependence of microbial community assembly in aquatic ecosystems.

Calibration of Short-Wave InfraRed (SWIR) hyperspectral imaging using Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTS) to obtain continuous logging of mineral abundances along sediment cores

Sediment cores are a major source of sub-surface data for a variety of environmental research endeavors, as well as mining and civil engineering applications. In paleo-environmental studies, fluctuations in mineral abundances along sediment cores are used to study climate change, sea-level variations, sediment dynamics, and landscape evolution. Increasing reliance on such proxies spurs the need for reliable and time-saving analytical tools and procedures. Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTS) is a rapid, non-destructive and accurate tool for quantification of mineral abundances. We use DRIFTS to calibrate Short-Wave InfraRed (SWIR) hyperspectral images (HSIs) of a sediment core, in order to convert point-specific DRIFTS measurement of mineral abundances into a continuous record of mineral abundances along the core. Initially, single-phase and mineral assemblages of quartz, calcite, and clay mineral are created and measured by DRIFTS to establish calibration curves to convert DRIFTS data into mineral abundances, as %wt of bulk sediment samples. Mineral abundances are then measured by DRIFTS in a set of 60 samples from a core drilled into the Albegna River delta, Tuscany, Italy in the Fall of 2020. SWIR-HSIs of the core are then obtained and averaged over the areas corresponding to the samples taken for point-specific DRIFTS measurements. Least squares regressions are established between SWIR-HSI and DRIFTS data over these areas. This calibration is then used to convert SWIR-HSIs of the entire core into a continuous prediction of quartz, calcite, and clay mineral abundances along the core. The continuous record highlights sharp changes in mineral composition, smeared out in the discontinuous DRIFTS record. The advantages and limitations of the method, as well as its applicability to other sedimentary environments are discussed.

Elemental and Sr–Nd isotopic compositions of surface clay-size sediments in the front end of major ice shelves around Antarctica and indications for provenance

Geochemical observations of continental outcrops and marine sediments provide insights into the nature of bedrock and erosion in Antarctica. The accelerated melt of ice shelves has increased the flux of terrigenous materials to the marginal seas and has changed the sedimentological environment. We characterized the provenance of the surficial fine-grained detrital sediments in the front ends of major ice shelves in the Amundsen Sea, Ross Sea, and Prydz Bay sections through comparisons to proximal rocks using the elemental compositions, as well as the Sr and Nd isotopic compositions, of the clay-size (<2 μm) fraction, rock samples, and bulk sediments and some residual fractions. The results show that the 87Sr/86Sr ratios of clay-size sediments range from 0.70962 to 0.71662, 0.70936 to 0.71960, and 0.72569 to 0.73492, and that the εNd values range from −2.1 to +0.8, −10.9 to −1.43, and −22.3 to −17. 3 in the Amundsen Sea, Ross Sea, and Prydz Bay, respectively, while those of rocks range from 0.70350 to 0.77080 and from 5.1 to −22.4 in all three areas. Elemental compositions of both bulk sediments and the clay-size fraction in the Western Ross Sea have similar patterns to those in Prydz Bay, showing that most major elements (e.g., Mg, Ca, and Fe) are lower than in the upper continental crust (UCC). Chondrite-normalized rare earth elements (REEs) are highest in the bulk sediments of the Amundsen Sea and lowest in the clay-size fraction of all three sections. We concluded that clay-size sediments in the Western Amundsen Sea shelf are largely from the Eastern Amundsen Sea coastal area, while some sediments reflect contributions from the Hobbs Coast due to gravitational currents. The Western Ross Sea can receive sediments from both East Antarctica and West Antarctica, while the clay-size fractions of western sites in Transect R (a latitudinal transect near Inexpressible Island, East Antarctica) in this study are mainly from southeastern Victoria Land, transported northward by bottom currents. The contribution from coarse ice-rafted debris (IRD) is minor, possibly because of blocking by the Drygalski Ice Tongue. The clay-size sediments of Eastern Prydz Bay are largely contributed by Princess Elisabeth Land and western Wilhelm II Land, while those in Western Prydz Bay are possibly derived from the Lambert-Amery Ice Shelf system and the western coast. These very fine-grained sediments are generally affected by oceanic currents (e.g., Antarctic Coastal Currents and Antarctic Bottom Currents). Most residual fraction show very similar εNd values to the bulk of clay-size sediments. It indicates that authigenic phases are generally sourced from similar regions to the silicate component of clay-size sediments.

Lithium Storage and Release From Lacustrine Sediments: Implications for Lithium Enrichment and Sustainability in Continental Brines

AbstractDespite current and projected future reliance on lithium (Li) as a resource, deficiencies remain in genesis models of closed‐basin Li brines. Subsurface geochemical interactions between water and bulk solid phases from lacustrine sediments, are shown here to be the most important process for brine genesis and sustainability of the Clayton Valley, NV brine deposit. A new subsurface basin model was developed and used to select Li‐bearing solids to test the release mechanisms for Li. Ash (20–350 ppm Li) and bulk sediments (1,000–1,700 ppm Li) samples across depths in the basin represent the majority of the subsurface Li‐bearing materials. Temperature dependent (25°C–95°C) batch reaction experiments using low‐salinity groundwater from the basin indicate a positive relationship between the amount of Li released and temperature. Four‐step sequential extractions on a subset of bulk sediments indicate most Li is released from water and weak acid‐soluble portions with approximately 30% of the total Li contained in the sediments released overall. We conceptualize that Li is released from these samples via three mechanisms: (a) release of adsorbed Li; (b) cation exchange of Li and Mg and; (c) possible minor release from the silicate structure at elevated temperatures. Based on these results and the abundance of Li‐bearing sediments in the subsurface we estimate the mean Li mass in the basin materials to be between 24.4 and 58.0 Mt which provides a continuous supply from water‐rock interactions. This is now the largest known accumulation of Li in a basin‐fill continental setting on a global scale.

Geomorphologic evolution of the northern Tibetan Plateau in the Quaternary: Tectonic and climatic controls

Situated in the northwestern Qinghai-Tibet Plateau, the Qaidam Basin is the largest Cenozoic terrestrial intermountain (enclosed) basin in the world. It is an ideal place for understanding the coupling control of tectonics and climate on sedimentary evolution. Numerous studies on the Quaternary sedimentary evolution of the Qaidam Basin have been done, most of which are local, conceptual, and qualitative in nature. We have investigated the entire Qaidam Basin and its surrounding mountains quantitatively as a single entity to probe the Quaternary evolution of the basin-range system in the northern Qinghai-Tibet Plateau. We used a basin and landscape dynamics ( Badlands) modeling algorithm that is capable of modeling landscape evolution by simulating erosion, sediment transport, and deposition in a source-to-sink context by considering climate changes and tectonic uplift/subsidence. We have simulated the evolution of the Qaidam Basin and its surrounding mountains since 2.5 Ma quantitatively. Tectonic uplift and climate changes appear to have a direct impact on the denudation and deposition rates, but the impact varies through time. The deposition in the Qaidam Basin was mainly affected by tectonic movement during the period of 2.5–0.6 Ma, reaching a maximum deposition thickness of 2130 m at the end of 0.6 Ma, which was prevailed by climate after 0.6 Ma during the last four glacial-interglacial periods, reaching a maximum deposition thickness of 3200 m. The Qilian Mountains and the Kunlun Mountains contributed the bulk sediments to the Qaidam Basin of approximately 35% and 40%, respectively. The Altun Mountains made a significant contribution to the sediments in the Qaidam Basin during the early period of the Quaternary from 2.5 to 2.4 Ma due to a high denudation rate. The findings provide new insights for analyzing geomorphic and landscape evolution as well as source-to-sink systems in the Northern Qinghai-Tibet Plateau or elsewhere.

Deep-Water Circulation over the Last Two Glacial Cycles Reconstructed from Authigenic Neodymium Isotopes in the Equatorial Indian Ocean (Core HI1808-GPC04)

We reconstructed the past deep-water character of the equatorial Indian Ocean using the isotope ratio of neodymium (εNd) in the Fe–Mn coating of mixed-species foraminifera. When compared with previous εNd records at the same site (ODP 758) and at another site to the west (SK 129), the three datasets were consistent and showed glacial-interglacial variations, even though the other two records were extracted from different media (cleaned foraminifera and bulk sediment leach). This confirms that while the foraminiferal coating is the preferred medium for reconstructing past bottom water εNd records, for carbonate-dominated lithologies, weak acid extraction of bulk sediment is also a viable option offering high-resolution capabilities. When the lithology includes volcanic particles or high organics, the extraction protocol may need to be adjusted to guard against detrital contamination or a slight correction may need to be applied. During glacials, the deep waters bathing the equatorial Indian Ocean had a larger AABW component and during interglacials a larger NADW component. Our HI1808-GPC04 record supplements the ODP 758 record in the interval with prominent AABW signal (MIS 6/5 transition and MIS 7) and reveals regional effects in some non-radiogenic intervals. The smaller differences between the HI1808-GPC04/ODP 758 and SK 129 records seem to reflect regional Nd input from river systems and non-radiogenic Nd from the boundaries.

Mg-Ba-Sr-Nd isotopic evidence for a mélange origin of early Paleozoic arc magmatism

In recent years, the mélange model has been increasingly considered as an important way to transfer slab components to arc sources in modern subduction zones. This model differs from the classic slab fluid/melt metasomatism model in that it invokes physical mixing of bulk sediment, altered oceanic crust (AOC), serpentinite, and mantle wedge at the slab-mantle interface. However, due to the lack of subducted sediment compositions, the mélange model has not been applied to any significant extent in paleo-subduction zones. The lack of evidence for bulk AOC and serpentinite components in mélange sources also hinders our understanding of any mélange origin for arc-type magmas. Here, we report Mg-Ba-Sr-Nd isotope compositions of the early Paleozoic Fushui mafic rocks in the Qinling orogen of central China, to trace their origin and constrain slab component transfer. The Fushui mafic rocks show typical arc-type geochemical features and enriched Sr-Nd isotope compositions, indicating the likely contribution of subducted sediments. They have low Rb/Ba ratios (<0.1), and most samples show δ138/134Ba values of −0.38 to +0.10‰, similar to those of sediments (−0.2 to +0.1‰) but lower than those of MORBs (+0.03 to +0.14‰), indicating that these low δ138/134Ba values are most likely derived from sediment components. One Fushui sample has a high δ138/134Ba of +0.31‰, similar to that of AOC (up to +0.4‰). This high δ138/134Ba is not correlated with fluid input; instead, it results from the contribution of bulk AOC. The Fushui rocks exhibit variable δ26Mg values (−0.23 to −0.11‰), slightly higher than those of MORBs. This most likely reflects 26Mg-enriched subducted serpentinite components in their source. Our results not only identify the variable slab components (sediment, AOC, and serpentinite) in the arc source, but also suggest that these slab components may be transferred to their arc source by the mélange process. This study therefore provides solid evidence for the generation of arc magmas by mélange processes in paleo-subduction zones, which confirms an important role for the mélange model in slab material transport.

Particle-size dependent magnetic property variations in the Yangtze delta sediments of late Holocene: Effects of pedogenesis and diagenesis

Late Holocene is a key period for the formation of modern deltas, and environmental magnetism is commonly used to infer paleoenvironmental information. Magnetic properties of bulk sediments are influenced by both hydrodynamic sorting and post-depositional pedogenesis and diagenesis, and the relationship between them is unclear. Detailed magnetic study on particle size fractions is a tool for understanding this issue and has been used in surface sediments, while the applications in delta core sediments are rare. Here we investigated the bulk and particle size dependent magnetic properties of the Yangtze River Delta core sediments over the past 3 ka, to determine the main mechanism for bulk magnetic property changes under the effects of pedogenesis and diagenesis. Our results showed that, in all particle size fractions, pedogenesis occurred in the top ∼2 m (within 0.3 ka) and the dissolution of fine magnetic minerals driven by early diagenesis appeared below this depth and completed at ∼20 m in depth (∼1.5 ka). These effects, including the dissolution of fine-grained ferrimagnetic minerals and the precipitation of authigenic greigite, were most obvious in the <16 μm fraction and decreased with coarsening particle sizes. The grain sizes of magnetic minerals were the finest in the <16 μm sediments and the coarsest in the 32–63 μm sediments, with intermediate similar features observed in the 16–32 and 63–125 μm sediments. Bulk magnetic properties were dominated by the <16 μm sediments. Our findings distinguished the differences between the effects of pedogenesis and early diagenesis among size fractions, which may provide a better approach to recognize redox states and provenance in delta sediments since the late Holocene.

Effect of barite-bound Sr on detrital Sr isotope systematics in marine sediments

In marine sediments, the Sr content and isotope composition (87Sr/86Sr) of the terrigenous detrital component are widely used to track changes in provenance and related transport and weathering processes. Accurately separating detrital-Sr from other sedimentary Sr-phases is a prerequisite for such studies. Conventionally, it is assumed that Sr in the carbonate-free residue corresponds to detrital Sr alone. However, the decarbonated residue may contain barite with significant Sr content and a non-detrital 87Sr/86Sr composition; this may substantially affect the measured Sr signal. To examine this chronically overlooked phenomenon, the Mediterranean Sea is an ideal area because 1) detailed provenance studies have been done using Sr and 87Sr/86Sr of the residual fraction, and 2) enhanced levels of barite repeatedly occurred in association with distinct, organic-rich sapropel sediments.Here, we use the most-recent sapropel S1 interval to evaluate the effect of barite-bound Sr in the residual fraction after decarbonation. A total of 130 samples were taken from 10 cores in the eastern Mediterranean Sea (EMS) and 1 core in the western Mediterranean Sea. This selection represents a geographic and bathymetric coverage of the EMS and permits the basin-wide comparison between organic-rich and -lean sediments. After decarbonation using 1 M HCl solution, the residual sediments were subject to NH4Cl extraction (2 M, pH 7), known to selectively dissolve barite. Our results demonstrate the presence of Sr-bearing barite after traditional carbonate removal and its effect on the derived “detrital” Sr signature. This barite-Sr effect is considerable for samples with barite-Ba >400 μg/g in bulk sediment. The impact of barite is prominent if accompanied by a detrital provenance background of high 87Sr/86Sr (>0.713) or low Sr/Al (<1.0 mg/g). In such cases, removal of remaining barite is required to obtain an unbiased detrital Sr signal. We recommend an improved procedure for detrital Sr separation in marine sediments, with an additional NH4Cl leaching step to eliminate any remaining barite after decarbonation. This approach is particularly important for areas/times of high biological productivity, where sediments are often characterized by abundant barite content.

Going with the flow: Experimental simulation of sediment transport from a foraminifera perspective

AbstractTransport of continental shelf sediments to the deep ocean can be studied from displaced symbiont‐bearing larger benthic foraminifera found in turbidity current deposits. The larger benthic foraminifera habitat depth, physical characteristics and preservation serve as indicators for understanding sediment transport dynamics near the seabed and in the water column. Here, an experiment was designed to explore sediment transport in a closed flume system using simulated high current velocities. Shelf sediments from the Gulf of Eilat/Aqaba, dominated by Amphistegina papillosa and Operculina ammonoides, were subjected to 60 cm s−1 and 80 cm s−1 current velocities while collected in a 10 cm vertical sediment trap. Larger benthic foraminifera abundance, shell physical properties and preservation were analyzed and compared with the original bulk sediments. The experiment results showed that at 80 cm s−1 velocity, larger benthic foraminifera shells of all sizes and preservations are efficiently resuspended and transported in large quantities throughout the water column, as opposed to their transport as bedload by the lower velocity current. Larger benthic foraminifera shape also has a role in the transport distances and accumulation depths. Operculina ammonoides shells were found to be more portable, compared to Amphistegina papillosa, due to their flatter discoid shape. The results suggest that a threshold velocity of ca 80 cm s−1 was needed to generate the thick coarse deposits found in the Gulf of Eilat/Aqaba slope sedimentary record, which were previously suggested to be triggered by large magnitude seismic events. Lower velocities probably winnowed minor amounts of larger benthic foraminifera shells (with little or no coarser sediments) that were deposited as a thin sand layer may point to lower magnitude seismic triggers. In conclusion, larger benthic foraminifera shells are transported and deposited in accordance with their hydrodynamic properties, resulting in assemblage differentiation along the transport pathway. This study shows that the fossil biogenic composition in slope sediments includes valuable information on current velocities, transport dynamics and possible triggers in the geological record.

An experimental approach to assess the post-depositional mobility of 134Cs

The partitioning coefficient, Kd, which is defined by the reversible sorption processes between a solid and an aqueous phase at equilibrium, is one of the most important parameters to assess environmental transport and risk. In this study, a series of simple laboratory experiments were conducted to investigate sorption properties of 134Cs on a model sediment under two treatments (shaken vs non-shaken) and with three (small: <75 μm, large: > 75 μm and bulk i.e., composite) particle size fractions. Vertical transport of 134Cs across the water-sediment interface and into sediment was also evaluated. As expected, grain size had the strongest influence on 134Cs Kd values, with the small particle size fraction yielding significantly higher Kd values than the large and bulk fractions. The mean Kd values obtained from the various experiments ranged from 89 ± 13–130 ± 5 L kg−1 (small), 44 ± 10–91 ± 13 L kg−1 (large), 73 ± 3–112 ± 11 L kg−1 (bulk, shaken) and 73 ± 5–110 ± 4 L kg−1 (bulk, non-shaken). Most of the 134Cs partitioning processes occurred rapidly (<2 h) into the experiment. Physical mixing (shaken) did not appear to significantly affect the 134Cs Kd values. In complement, a separate experiment on the vertical penetration of 134Cs into a bulk sediment column showed that 134Cs was able to penetrate up to 5 cm into the sediment column after 88 days (∼0.6 mm d−1) and this flux rate is comparable to natural settings. Adsorption and contact time were found to be key for the 134Cs penetration process. Results from these experiments add to the literature on post-event radionuclide transport studies in marine settings and provide an experimental perspective that can be built upon to complement field observations.

Mechanistic insights into trace metal mobilization at the micro-scale in the rhizosphere of Vallisneria spiralis

Mobilization of trace metals in the rhizosphere of macrophytes is controlled by root-driven chemical changes, especially the steep gradients of O2 and pH from the rhizosphere to bulk sediments. Here, the O2 and pH dynamics, and the distribution of trace metal, in the rhizosphere of Vallisneria spiralis were obtained using planar optodes and diffusive gradients in thin films, respectively. Radial O2 loss (ROL) and acidification occurred on all visible roots of V. spiralis and exhibited highly spatiotemporal dynamics depending on the root growth and various environmental conditions. Trace metals showed different mobilization mechanisms in the rhizosphere. ROL and produced Fe(III) (oxyhydr)oxides decreased the mobility of Fe, As, Co, V and W in the rhizosphere. However, Mn, Ni and Cu exhibited greater mobility in the rhizosphere than bulk sediments as a result of the oxidation of metal sulfide and proton-induced dissolution of minerals. In particular, Co and Ni presented increased activity at the interface between rhizosphere and bulk sediment, which was attributed to the redox dissolution processes of Fe and Mn as a result of ROL and rhizosphere acidification. These results provide new insights into the roles of macrophyte root-induced O2 and pH changes in controlling trace metal mobility in sediments.

Bioaccumulation and chronic toxicity of arsenic and zinc in the aquatic oligochaetes Branchiura sowerbyi and Tubifex tubifex (Annelida, Clitellata).

Oligochaetes feed on bulk sediment and penetrate the sediment through the construction of burrows, making them especially vulnerable to sediment metal contamination. However, the few oligochaete species that have been tested to date are almost exclusively temperate test species. Although the warmwater adapted species Branchiura sowerbyi has been indicated as a promising candidate for tropical sediment toxicity testing, few (especially chronic) studies have been conducted so far to confirm this. Therefore, the aim of the present study was to evaluate the bioaccumulation and chronic 28d lethal and sublethal toxicity of arsenic (As) and zinc (Zn) to both the warmwater-adapted B. sowerbyi and the coldwater-adapted oligochaete Tubifex tubifex for comparison. Arsenic was more toxic to both oligochaete species than Zn. Inter- and intra-species variability in toxicity values of the two test species and other benthic invertebrates was within an order of magnitude. However, B. sowerbyi was the most sensitive species to As even for sediment concentration (EC50: 36.6 ± 2.1 µg/g and 147.1 ± 21.7 µg/g, for B. sowerbyi and T. tubifex, respectively) and for tissue concentration (ER50: 9.2 ± 0.9 µg/g and 887.0 ± 35.0 µg/g, for B. sowerbyi and T. tubifex, respectively). Finally, the Tissue Residue-effects Approach (TRA) using Effective Tissue Residues appears to be a promising way forward in advancing in this since it considers internal body concentrations.

Shallow water transmission loss inversion for seafloor characterization

A Bayesian inference algorithm has been developed for seafloor geoacoustic parameter determination through analysis of transmission loss measurements taken in shallow water environments. It uses a parallel tempering scheme for improved parameter space sampling and bias reduction, and evaluates ray acoustic forward models in Bellhop. The algorithm is verified by application to synthetic data generated using finite element and ray acoustic propagation models for frequencies from 0.5 to 5 kHz. Verification is assessed through the ability to recover inversion parameter values prescribed within the synthetic data, and inspection of ambiguous inversion situations. Initial inversion parameters include bulk sediment density, sound speed, and attenuation, as well as ripple height and wavelength for some seafloors. The inversion yields posterior probability distributions for each inversion parameter, which inform parameter resolvability and covariance. Algorithm accuracy, efficiency, and applicability to data from different ocean environments will be discussed. [This work has been supported by the Office of Naval Research, Task Force Ocean.]

Mollusk death assemblages in 210Pb-dated marine sediment cores reveal recent biotic changes in the Gulf of Guanahacabibes, NW Cuba

We investigated stratigraphic changes in mollusk death assemblages and geochemistry in sediment cores from four seagrass beds and one unvegetated site in the Gulf of Guanahacabibes (GG), NW Cuba. There was a transition from mangrove to seagrass beds, associated with sea level rise ∼6000 years ago. Sediment accumulation rates during the last century showed a general rise, but increased sharply after ∼1980, likely because of human activities. The GG displayed overall high mollusk γ-diversity, and our estimate of 189 species is biased toward the low end. High β-diversity was driven by inter-site differences in grain size, vegetation cover, and nutrient input. Spatial heterogeneity within the basin influenced downcore abundance and diversity metrics, highlighting the influence of local drivers. Herbivorous gastropods dominated in seagrass beds and suspension feeder bivalves were dominant on sandy bottom. In the top parts of cores, species richness declined at two sites that were subject to high, human-mediated bulk sedimentation rates and eutrophication. Conservation measures are needed to preserve this hotspot of marine diversity.

Alkaline mine drainage drives stream sediment microbial community structure and function

With advances in eDNA metabarcoding, environmental microbiomes are increasingly used as cost-effective tools for monitoring ecosystem health. Stream ecosystems in Central Appalachia, heavily impacted by alkaline drainage from mountaintop coal mining, present ideal opportunities for biomonitoring using stream microbiomes, but the structural and functional responses of microbial communities in different environmental compartments are not well understood. We investigated sediment microbiomes in mining impacted streams to determine how community composition and function respond to mining and to look for potential microbial bioindicators. Using 16s rRNA gene amplicon sequencing, we found that mining leads to shifts in microbial community structure, with the phylum Planctomycetes enriched by 1-6% at mined sites. We observed ~51% increase in species richness in bulk sediments. In contrast, of the 31 predicted metabolic pathways that changed significantly with mining, 23 responded negatively. Mining explained 15-18% of the variance in community structure and S, Se, %C and %N were the main drivers of community and functional pathway composition. We identified 12 microbial indicators prevalent in the ecosystem and sensitive to mining. Overall, alkaline mountaintop mining drainage causes a restructuration of the sediment microbiome, and our study identified promising microbial indicators for the long-term monitoring of these impacted streams.

The contribution of sediment desiccation and rewetting process to eutrophication in the presence and absence of emergent macrophytes.

The purpose of current study was to investigate the effects of sediment desiccation on nutrient dynamics and eutrophication in wetlands during the presence or absence of wiry and sturdy rooted emergent macrophytes, based on the hypothesis that sediment desiccation negatively correlated with plants nutrient uptake abilities and positively with nutrients fluxes at sediment-water interface. Growth of four emergent macrophytes, including two wiry rooted plants, i.e., Alocasia cucullata and Aglaonema commutatum, and two sturdy rooted plants, i.e., Cannabis indica and Acorus calamus, were grown and investigated in dried-rewetted sediments (DS) and constantly wet sediments (WS), respectively, for 6 months. The findings revealed that sediment drying and rewetting process significantly decreased the diffusion of overlying nutrient into sediment and the particle size density, porosity, and nutrients' repository ability in DS treatments, while the sediment bulk density and mineralization of organic macronutrients increased. Compared to WS treatments, the DS treatments impaired plant growth, root biomass, shoot biomass, and stimulated higher fluxes of ammonium nitrogen ([Formula: see text]-N, 0.042-0.081 mg m - 2 d - 1) and phosphate (P[Formula: see text] 0.009-0.030 mg m-2 d-1) at sediment-water interface upon rewetting. The higher internal release of macronutrients and dissolved organic carbon (DOC) from DS led to the higher chlorophyll-a (Chl-a) concentrations (34.47-21.28 to 41.76-33.36 μg L-1) in their water column than in the water column of WS. The wiry rooted plants with higher root biomass displayed lower internal release of [Formula: see text]-N, PO43-P and DOC and water column Chl-a concentrations than the sturdy rooted plants in two sediment types. Root biomass of plants correlated positively with TN (63-87%) and TP (56-78%) removal percentages from WS and DS. These results demonstrated that sediment desiccation process reduced plant growth and enhanced internal loading of nutrients and consequently accelerated eutrophication in these wetlands.

Surface hydrographic changes at the western flank of the Sicily Channel associated with the last sapropel

In the eastern Mediterranean Sea, the early Holocene was characterized by major climatic and oceanographic changes that led to the formation of the last sapropel (S1) between 10.8 and 6.1 kyr cal. BP. These hydrographic changes might have altered the water exchange between the eastern and western Mediterranean sub-basins through the Strait of Sicily, but the existing evidences are inconclusive. In the present study we show new evidence from sediment core NDT-6-2016 located at the western flank of the Sicily channel, a key location to monitor the surface/intermediate water exchange between the two Mediterranean sub-basins. We perform paleo-hydrographic reconstructions based on planktic foraminifera ecology for the last 15 kyr cal. BP, including the S1 deposition interval. In addition, δ 18 O measurements in both Globigerina bulloides and Globigerinoides ruber and also major elements analyses in bulk sediment are presented. Our results show that significant changes in surface water properties occurred in W-Sicily characterized by a strong contrast in the seasonal hydrographic conditions during the S1 interval. This study proposes that the oceanographic changes in the eastern Mediterranean associated with the surface freshening promoted by the African monsoon likely triggered a restricted water exchange through the Strait of Sicily. This situation led to limited influence of the surface Atlantic waters into the studied area that favored the development of intense summer stratification and vertical winter mixing. This situation changed at about 7 kyr cal. BP when a decrease in the summer stratification probably reflected the influence of the eastward path of the surface Atlantic Waters. This situation would suggest a reinforcement of the water exchange through the Strait of Sicily that marked the end of the extreme conditions that prevailed in the eastern Mediterranean during the S1 formation. • Surface hydrographic reorganization related to the sapropel S1 is observed for the first time in the central Mediterranean. • The acquired data provide new evidences of a restricted sea surface water exchange during the S1 across the Strait of Sicily. • Paleo-hydrographic reconstructions are based on planktic foraminifera ecology, major element analyses and δ 18 O measurements.

Provenance analysis of sediments in the south-east Aegean during the Upper Quaternary: a composite approach based on bulk and clay mineralogy and geochemistry

AbstractSediments from the ST5 deep-sea bottom core collected from the south-east Aegean Sea between Symi and Tilos islands, Greece, were examined by quantitative mineralogical analysis and geochemical analysis to infer provenance and palaeoenvironmental control over sediment deposition. The mineralogical composition comprises carbonates (mainly calcite and Mg-calcite), quartz, feldspars, serpentine, amphibole and clay minerals. Chlorite is the most abundant clay mineral, whereas smectite and illite are less abundant than in the sediments in the south-west Aegean and the Cretan Sea. Semi-quantitative analysis of clay minerals from oriented clay fractions overestimates significantly the smectite content and underestimates the abundances of illite, chlorite and kaolinite. The studied sediments are enriched in MgO, Ni and Cr, which decrease in abundance with decreasing depth, following the distribution of serpentine. By contrast, the abundances of SiO2, Al2O3, Fe2O3, Na2O and K2O increase upcore. The regional S1 sapropel horizon is enriched in V and Co and has considerably greater Ba/Al ratios than the remaining sequence. The mineralogical and geochemical relationships indicate a strong ultrabasic influence, probably from the Marmaris ophiolite in the Lycian nappes. The clay mineral distribution suggests that the smectite was mainly of volcanogenic origin, the illite was supplied by the nearby landmasses of west Anatolia and the islands of Rhodes, Tilos and Symi and the contribution from the south-east Mediterranean was limited or totally lacking. The combined use of the mineralogical and geochemical analysis of bulk sediments rather than the clay fractions is not only extremely useful in tracing sediment provenance in relatively closed basins, but it also enables a more realistic assessment of the importance of water circulation patterns on sedimentation processes in such environments.

Mapping the Terrain for Pathogen Persistence and Proliferation in Non-potable Reuse Distribution Systems: Interactive Effects of Biofiltration, Disinfection, and Water Age

Diverse pathogens can potentially persist and proliferate in reclaimed water distribution systems (RWDSs). The goal of this study was to evaluate interactive effects of reclaimed water treatments and water age on persistence and proliferation of multiple fecal (e.g., Klebsiella, Enterobacter) and non-fecal (e.g., Legionella, mycobacteria) gene markers in RWDSs. Six laboratory-scale RWDSs were operated in parallel receiving the influent with or without biologically active carbon (BAC) filtration + chlorination, chloramination, or no disinfectant residual. After 3 years of operation, the RWDSs were subject to sacrificial sampling and shotgun metagenomic sequencing. We developed an in-house metagenome-derived pathogen quantification pipeline, validated by quantitative polymerase chain reaction and mock community analysis, to estimate changes in abundance of ∼30 genera containing waterborne pathogens. Microbial community composition in the RWDS bulk water, biofilm, and sediments was clearly shaped by BAC filtration, disinfectant conditions, and water age. Key commonalities were noted in the ecological niches occupied by fecal pathogen markers in the RWDSs, while non-fecal pathogen markers were more varied in their distribution. BAC-filtration + chlorine was found to most effectively control the widest range of target genera. However, filtration alone or chlorine secondary disinfection alone resulted in proliferation of some of these genera containing waterborne pathogens.