Pore Water Analyses Research Articles

Microbial communities and functions are structured by vertical geochemical zones in a northern peatland

Northern peatlands are important carbon pools; however, differences in the structure and function of microbiomes inhabiting contrasting geochemical zones within these peatlands have rarely been emphasized. Using 16S rRNA gene sequencing, metagenomic profiling, and detailed geochemical analyses, we investigated the taxonomic composition and genetic potential across various geochemical zones of a typical northern peatland profile in the Changbai Mountains region (Northeastern China). Specifically, we focused on elucidating the turnover of organic carbon, sulfur (S), nitrogen (N), and methane (CH4). Three geochemical zones were identified and characterized according to porewater and solid-phase analyses: the redox interface (<10 cm), shallow peat (10–100 cm), and deep peat (>100 cm). The redox interface and upper shallow peat demonstrated a high availability of labile carbon, which decreased toward deeper peat. In deep peat, anaerobic respiration and methanogenesis were likely constrained by thermodynamics, rather than solely driven by available carbon, as the acetate concentrations reached 90 μmol·L−1. Both the microbial community composition and metabolic potentials were significantly different (p < 0.05) among the redox interface, shallow peat, and deep peat. The redox interface demonstrated a close interaction between N, S, and CH4 cycling, mainly driven by Thermodesulfovibrionia, Bradyrhizobium, and Syntrophorhabdia metagenome-assembled genomes (MAGs). The archaeal Bathyarchaeia were indicated to play a significant role in the organic carbon, N, and S cycling in shallow peat. Although constrained by anaerobic respiration and methanogenesis, deep peat exhibited a higher metabolic potential for organic carbon degradation, primarily mediated by Acidobacteriota. In terms of CH4 turnover, subsurface peat (10–20 cm) was a CH4 production hotspot, with a net turnover rate of ∼2.9 nmol·cm−3·d−1, while the acetoclastic, hydrogenotrophic, and methylotrophic methanogenic pathways all potentially contributed to CH4 production. The results of this study improve our understanding of biogeochemical cycles and CH4 turnover along peatland profiles.

Unravelling the signatures of submarine groundwater discharge and seawater intrusion along the coastal plains of Odisha, India: a multi-proxy approach.

Submarine Groundwater Discharge (SGD) and Seawater Intrusion (SWI) are two contrary hydrological processes that occur across the land-sea continuum and understanding their nature is essential for management and development of coastal groundwater resource. Present study has attempted to demarcate probable zones of SGD and SWI along highly populated Odisha coastal plains which is water stressed due to indiscriminate-exploitation of groundwater leading to salinization and fresh groundwater loss from the alluvial aquifers. A multi-proxy investigation approach including decadal groundwater leveldynamics, LANDSAT derived sea surface temperature (SST) anomalies and in-situ physicochemical analysis (pH, EC, TDS, salinity and temperature) of porewater, groundwater and seawater were used to locate the SGD and SWI sites. A total of 340 samples for four seasons (85 samples i.e., 30 porewater, 30 seawater and 25 groundwater in each season) were collected and their in-situ parameters were measured at every 1-2km gap along ~ 145km coastline of central Odisha (excluding the estuarine region). Considering high groundwater EC values (> 3000 μS/cm), three probable SWI and low porewater salinities (< 32 ppt in pre- and < 25 ppt in post-monsoons), four probable SGD zones were identified. The identified zones were validated with observed high positive hydraulic gradient (> 10m) at SGD and negative hydraulic gradient (< 0m) at SWI sites along with anomalous SST (colder in pre- and warmer in post-monsoon) near probable SGD locations. This study is first of its kind along the Odisha coast and may act as initial basis for subsequent investigations on fresh-saline interaction along the coastal plains where environmental integrity supports the livelihood of coastal communities and the ecosystem.

Hydration of a 2-component CSA-OPC-mix – timing of component blending &amp; setting on demand

With the ongoing development of new technologies like 3D printing, the requirements for the performance of cementitious materials become more complex. Setting on demand, while the workability of the material is retained until placement, is an important aspect of this usage. A ternary CSA-OPC-C$ system was developed to achieve setting on demand in a 2-component setup, where two retarded cementitious components were mixed after specific times of storage. The kinetics of the individual systems and the blend were examined by heat flow calorimetry, quantitative X-ray diffraction and pore water analysis. The rheological development was monitored by a penetration test method. The results show that the performance of the blend is independent of the storage time of the individual components and can be tailored by changes in the retarder dosage in the individual components. The initial reaction in the blend is characterized by the simultaneous dissolution of ye'elimite and C3S, resulting in the formation of ettringite as the sole detectable hydrate phase. The fate of silicon remains unclear as with the methodology at hand no silicon incorporating hydrate phase can be identified.

Cadmium concentrations in pore waters can largely increase during soil incubation: Artefacts with consequences for Cd limits in fertilisers

A sound evaluation of the cadmium (Cd) mass balance in agricultural soils needs accurate data of Cd leaching. Reported Cd concentrations from in situ studies are often one order of magnitude lower than predicted by empirical models, which were calibrated to pore water data from stored soils. It is hypothesized that this discrepancy is related to the preferential flow of water (non-equilibrium) and/or artefacts caused by drying and rewetting soils prior to pore water analysis. These hypotheses were tested on multiple soils (n = 27) with contrasting properties. Pore waters were collected by soil centrifugation from field fresh soil samples and also after incubating the same soils (28 days, 20 °C), following two drying-rewetting cycles, the idea being that chemical equilibrium in the soil is reached after incubation. Incubation increased pore water Cd by a factor 4, on average, and up to a factor 16. That increase was statistically related to the decrease of pore water pH and the increase of nitrate, both mainly related to incubation-induced nitrification. After correcting for both factors, the Cd rise was also highest at higher pore water Ca. This suggests that higher Ca in soil enlarges Cd concentration gradients among pore classes in field fresh soils because high Ca promotes soil aggregation and separation of mobile from immobile water. Several empirical models were used to predict pore water Cd. Predictions exceeded observations up to a factor 30 for the fresh pore waters but matched well with those of incubated soils; again, deviations from the 1:1 line in field fresh soils were largest in high Ca (>0.8 mM) soils, suggesting that local equilibrium conditions in field fresh soils are not found at higher Ca. Our results demonstrate that empirical models need recalibration with field fresh pore water data to make accurate soil Cd mass balances in risk assessments.

РАСПРЕДЕЛЕНИЕ БИОГЕННЫХ ЭЛЕМЕНТОВ НА ГРАНИЦЕ ВОДА–ДНО В ПОРОВЫХ И НАДДОННЫХ ВОДАХ КАРСКОГО МОРЯ И МОРЯ ЛАПТЕВЫХ

The paper presents data from the 63rd cruise of the R/V “Akademik Mstislav Keldysh” in August–October 2015. The main areas of work included the western part of the Kara Sea, the bays of Novaya Zemlya (Sedova, Oga and Tsivolki), a transect through the Voronin Trench, a transect from the Lena River delta to the continental slope of the Laptev Sea. During the cruise, a chemical analysis of pore and bottom waters was carried out for the content of nitrite, nitrate nitrogen, silicon, phosphates, total alkalinity and pH. The patterns of distribution of silicon and phosphorus concentrations at the water-bottom interface are considered. In the Kara Sea analysis of the data showed that the maximum concentrations of nutrients are located in the upper 10 cm sediment layer, below that concentrations gradually decrease. In all studied bays of Novaya Zemlya, the concentrations of nutrients in the silt waters were lower than on the adjacent shelf. In the Laptev Sea, the content of nitrates in silt waters is higher, and phosphates are lower than in the Kara Sea. Differences in the content of nutrients in the bottom and silt water are associated both with external factors (river runoff) and physical and geological features of the upper sediment layer of the studied areas.

Application of a portable ion chromatograph for real-time field analysis of nitrite and nitrate in soils and soil pore waters

Real-time monitoring of nitrite and nitrate is crucial for maintaining soil health and promoting plant growth. In this study, a portable ion-chromatograph (IC, Aquamonitrix) analyser, coupled with a field-applicable ultrasonic-assisted extraction method, was utilised for in-field determination of nitrate and nitrite in soils. This is the first application of this type of analyser to soil nutrients. On-site analysis of soil from a local sports field showed 94.8 ± 4.3 μg g−1 nitrate, with LODs of 32.0 μg g−1 for nitrate and 5.4 μg g−1 for nitrite. The results were in close agreement with those obtained using a conventional lab-based IC. Relative standard deviations (%RSDs) for soil analysis using Aquamonitrix were consistently below 10%. The obtained average recoveries of samples spiked with nitrite were 100% and 104% for the portable IC and conventional IC, respectively. Furthermore, to assess the suitability of portable IC for samples with high organic matter content, various natural organic fertilisers were extracted and analysed. The results showed 16.2 ± 0.7 μg g−1 nitrite and 28.5 ± 5.6 μg g−1 nitrate in sheep manure samples with LODs of 2.0 μg g−1 for nitrite and 12.0 μg g−1 for nitrate. The portable IC system was further demonstrated via real-time on-site analysis of soil pore-water acquired using a portable battery-based ceramic pore-water sampler. A continuous increase in nitrate concentration over time was observed (from 80 to 148 μg mL−1) in the soil pore-water in a vegetable garden four days after heavy rain. Unlike conventionally sampled natural waters, 7-day storage of the studied pore water samples revealed no changes in nitrate concentrations. An average of 558 ± 51 μg mL−1 nitrate was detected in the soil pore-water samples analysed on a spinach farm, immediately after irrigation.

Seaward alteration of arsenic mobilization mechanisms based on fine-scale measurements in Pearl River estuarine sediments

Identification of key As mobilization processes in estuarine sediments is challenging due to the transitional hydrodynamic condition and the technical restriction of obtaining fine-scale results. Herein, high-resolution (μm to mm) and in situ profiling of As with associated elements (Fe, Mn, and S) by the diffusive gradients in thin-film (DGT) technique were applied and coupled with pore water and solid phase analysis as well as microbial high-throughput sequencing, to ascertain the driving mechanisms of As mobilization in the sediments of Pearl River Estuary (PRE). Significant diffusion fluxes of As from sediment to water were observed, particularly in the upper estuary. With the seaward increase of salinity, the driving mechanism of As mobilization gradually shifted from microbial-induced dissimilatory Fe reduction to saltwater-induced ion exchange. Correspondingly, the dominant Fe-reducing bacteria (FeRB) in sediments changed from the genera Clostridium_sensu_stricto_1 and Bacillus to Ferrimonas and Deferribacter. The presence of dissolved sulfide in deeper sediments contributes to As removal through the formation of As-S precipitates as supported by theoretical calculations. Fine-scale findings revealed seaward changes of As mobilization mechanism in the sediments of a human-impacted estuary and may benefit the understanding of As biogeochemical behavior in estuaries worldwide.

Dynamics of cadmium and arsenic at the capillary fringe of paddy soils: A microcosm study based on high-resolution porewater analysis

Arsenic (As) and cadmium (Cd) are prevalent in paddy soils, posing potential threats to food safety and public health. The concentrations of soluble ​As and Cd are sensitive to moisture-driven changes in soil pH and Eh, which is rarely described at the critical dry-wet interface. Here, tempo-spatial changes of soluble As and Cd were captured by In-situ Porewater Iterative samplers at the capillary fringe that extended from saturated to unsaturated moisture gradient at the millimeter scale (60 ​mm profile in depth) through two episodic dry-wet cycles (55 days in total). The As and Cd concentrations showed less significant fluctuation in second cycle compared to the initial dry-wet cycle. The study also revealed at the capillary fringe profile (20–40 ​mm), the As concentrations increased from 4.6 μg L−1 in unsaturated soils to 13.5 μg L−1 in saturated soils, while Cd decreased from 3.3 to 0.2 μg L−1. This observed correlation was aligned with the vertical changes in soil Eh (+287 to +381 ​mV) and pH (3.42 to 6.07). This study found a distinct zone characterized by low As and low Cd concentrations, typically situated approximately 10–30 ​mm beneath the capillary fringe. Upon further analysis, it was determined that soil with an Eh of 249 ​mV and a pH of 4.3 potentially serves as an optimal environment for decreasing As and Cd levels in porewater. These findings suggest that it is feasible to reduce As and Cd concentration in the soil by implementing appropriate depth-controlled water management techniques.

Multi-media interaction improves the efficiency and stability of the bioretention system for stormwater runoff treatment

Bioretention systems are one of the most widely used stormwater control measures for urban runoff treatment. However, stable and effective dissolved nutrient treatment by bioretention systems is often challenged by complicated stormwater conditions. In this study, pyrite-only (PO), pyrite-biochar (PB), pyrite-woodchip (PW), and pyrite-woodchip-biochar mixed (M) bioretention systems were established to study the feasibility of improving both stability and efficiency in bioretention system via multi-media interaction. PB, PW, and M all showed enhanced dissolved nitrogen and/or phosphorus removal compared to PO, with M demonstrating the highest efficiency and stability under different antecedent drying durations (ADD), pollutant levels, and prolonged precipitation depth. The total dissolved nitrogen and dissolved phosphorus removal in M ranged between 64%–86% and 80%–95%, respectively, with limited organic matter and iron leaching. Pore water, microbial community, and material analysis collectively indicate that pyrite, woodchip, and biochar synergistically facilitated multiple nutrient treatment processes and protected each other against by-product leaching. Pyrite-woodchip interaction greatly increased nitrate removal by facilitating mixotrophic denitrification, while biochar further enhanced ammonium adsorption and expanded the denitrification area. The Fe3+ generated by pyrite aerobic oxidation was adsorbed on the biochar surface and potentially formed a Fe-biochar composite layer, which not only reduced Fe3+-induced pyrite excessive oxidation but also potentially increased organic matter adsorption. Fe (oxyhydr)oxides intermediate product formed by pyrite oxidation, in return, controlled the phosphorus and organic matter leaching from biochar and woodchip. Overall, this study demonstrates that multi-media interaction may enable bioretention systems to achieve stable and effective urban runoff treatment.

Geochemical, mineralogical, and geophysical methods to establish the geoenvironmental characteristics of the King River delta, Queenstown, Western Tasmania

Throughout most of the 20th century, the Mount Lyell Mining and Railway company discharged tailings from the Mount Lyell mine into the Queen River. Tailings migrated downstream of the King River and deposited on riverbanks, the riverbeds and in the King River delta in Macquarie Harbour. This research combines mineralogical, geochemical, and geophysical techniques to characterise the King River delta and to constrain the volume of mine tailings on the King River delta. For this purpose, 25 trenches were excavated across the delta with 145 sediments samples and 20 water samples collected.Tailings in the delta are abundant in quartz (average 50 wt %), muscovite (average 16 wt %), chlorite (mean 11 wt %), pyrite (average 4 wt %), Fe-oxyhydroxides such as goethite (average 0.8 wt %), hematite (average 0.4 wt % and ferrihydrite (average 0.2 wt %), jarosite (average 0.8 wt %) and chalcopyrite (average 0.1 wt %). Sediments are dominated by Fe (average 77,468 ppm) and include high concentrations of Cu (average 1425 ppm) and trace elements such as Co (average 350 ppm). Chalcopyrite is the primary Cu mineral whereas pyrite is the main mineral host for Co. Geoenvironmental tests show tailings in the delta have acid-forming potential, as validated by pore water analyses with pH between 3.1 and 6.3. These conditions enable metal dissolution, with high contents of dissolved heavy metals, especially Fe, Cu, Co and Zn, detected in the pore waters.Apparent resistivity and shear wave profiles suggest the base of tailings is located at depths of 3–5 m. Low resistivity (i.e., <2 Ωm) indicate a saltwater intrusion into likely natural sediments below the tailings, whereas resistivity values between approximately 5 to 12 Ωm, below 15 m depth, suggests a transition to bedrock. The volume of tailings is estimated at ∼14.0 Mt and concentrations of Cu and Co imply that reprocessing of this material could be a feasible option with significant economic and environmental benefits.

A rock creep model based on Atangana-Baleanu fractional derivative with coupled damage effects of pore water pressure, stress and time

Pore water pressure is an important factor affecting long-term rock failure and instability. On the basis of the assumptions that the rock microunit strength follows Weibull distribution and the rock failure compliances Drucker-Prager criterion, a pore water pressure-stress coupled damage (PSCD) variable is constructed in this paper. Considering the effect of pore water pressure, stress and time (PST), a pore water pressure-stress-time coupled damage (PSTCD) variable is put forward by introducing the damage variable considering time effect. Based on the characteristics and advantages of fractional differential theory in viscoelastic analysis of rock materials, one-dimensional and three-dimensional pore water pressure-stress-time coupled damage fractional (PSTCDF) creep models are proposed by Atangana-Baleanu (AB) fractional derivative. By fitting and analyzing the laboratory experimental data of rock creep under the combined action of PST, the relevant parameters for PSTCDF creep model can be deduced. The analysis of the goodness of fit and the generalization accuracy prove the rationality, validity and generalization of the proposed model. The sensitivity of the PSTCDF model is analyzed by different the stress level, pore water pressure, fractional derivative order and damage variable coefficient. The results show that the creep model changes flexibly when the model parameters change, and the specific creep state of rock can be reflected by reasonable selection of the model parameters.

Lack of detectable chemosynthesis at a sponge dominated subarctic methane seep

We used high-resolution imagery within a Geographic Information System (GIS), free gas and porewater analyses and animal bulk stable isotope measurements to characterize the biotic and abiotic aspects of the newly discovered Vestbrona Carbonate Field (VCF) seep site on the Norwegian shelf (63°28′N, 6° 31′E, ∿270 m water depth). Free gas was mainly composed of microbial methane. Sediment porewater sulfide concentrations were in the millimolar range and thus high enough to sustain seep chemosymbiotrophic animals. Nonetheless, the VCF lacked chemosymbiotrophic animals despite an abundance of methane-derived carbonate crusts which are formed by the same anaerobic processes that sustain chemosymbiotrophic animals at seeps. Furthermore, none of the sampled taxa, across various trophic guilds exhibited a detectable contribution of chemosynthetically fixed carbon to their diets based on bulk stable isotope values, suggesting a predominantly photosynthetic source of carbon to the VCF seep food web. We link the absence of chemosymbiotrophic animals to highly localized methane flow pathways, which may act as a “shunt-bypass” of the anaerobic oxidation of methane (AOM) and by extension sulfide generation, thus leading to sediment sulfide concentrations that are highly heterogeneous over very short lateral distances, inhibiting the successful colonization of chemosymbiotrophic animals at the VCF seep. Instead, the seep hosted diverse biological communities, consisting of heterotrophic benthic fauna, including long lived taxa, such as soft corals (e.g., Paragorgia arborea) and stony corals (i.e., Desmophyllum pertusum, formerly known as Lophelia pertusa). Compared to the surrounding non-seep seafloor, we measured heightened megafaunal density at the seep, which we attribute to increased habitat heterogeneity and the presence of a variety of hard substrates (i.e., methane-derived authigenic carbonates, dropstones and coral rubble), particularly since the most abundant taxa all belonged to the phylum Porifera. Compared to the surrounding non-seep seafloor, marine litter was denser within the VCF seep, which we link to the more variable local topography due to authigenic carbonates, which can rip off parts of bottom trawling nets thereby making the seep act as catchment area for marine litter.

Carbonate Sedimentation in High-Mineralized Lake Bolshoi Bagan (South of West Siberia): Dependence on Holocene Climate Changes

Abstract ––We present the results of comprehensive studies of Holocene bottom sediments from the shallow hypersaline (mineralization up to 282 g/L) Lake Bolshoi Bagan, located in the East Baraba lowland (south of Western Siberia). The research methods include X-ray diffractometry (XRD), IR spectroscopy, laser granulometry, scanning electron microscopy, elemental analysis of sediments and pore water, radiocarbon (14C AMS) dating. It has been found that during the Holocene an intensive authigenic mineral formation took place in the lake basin; gypsum, halite and carbonates of calcite-dolomite series dominate among the newly formed mineral phases. Mg-calcites with different Mg contents, excess-Ca dolomites, aragonite and occasionally Mg-siderite have been found in the assemblage of carbonate minerals by mathematical modeling of complex XRD patterns. Mineralogical and crystallochemical studies, supplemented by the results of geochemical analyses, allowed us to identify four stages of the evolution of Lake Bolshoi Bagan in the Holocene, due to regional climate variations. The boundaries of the stages in general correspond to the boundaries of the climatostratigraphic phases by the Blytt–Sernander system: Stage I (the end of the Boreal) – the lake formation, humid climate; Stage II (Atlantic) – climate aridization, shallowing of the lake; Stage III (Subboreal) – unstable climate, frequent change of conditions; Stage IV (Subatlantic) – moderately cool and dry climate.

Fertilization Enhances Grain Inorganic Arsenic Assimilation in Rice

To investigate how soil fertilization/amendments alters arsenic speciation grain off-take in paddy rice, rice was grown to maturity in growth chambers fertilized with standard mineral fertilizer, wood ash (rich in silica), pig slurry (rich in organic matter), and non-amended control. The soil was sourced from a Chinese paddy field. The primary fertilized elements (nitrogen, phosphorus, potassium) were kept constant across treatments. Porewater chemistry and soil microbiology were monitored throughout the experiments. Total grain arsenic, sum of inorganic arsenic and dimethylarsinic acid (DMA), was significantly different between treatments (P = 0.024), with inorganic arsenic varying from 0.025 to 0.08 mg/kg and DMA from 0.08 to 0.16 mg/kg for control compared to fertilized, respectively. Fertilizer source made no difference to arsenic speciation concentration in grain. Porewater analysis found that as anaerobism set in, inorganic arsenic, phosphorus and manganese greatly lowered in concentration. Methylated arsenic species concentrations increased over time, concurrent with an increase in pH, decrease in Eh, and increase in total organic carbon and iron, with no strong treatment effects, except for pig slurry that enhanced pH and decreased Eh. Methanogenic archaea, sulfate-reducing bacteria and Acidobacteria increased with time and some Actinobacteria and Firmicutes increased due to slurry, but then decreased with time (P < 0.01). Methanogenic archaea and sulphate-reducing bacteria correlated positively with porewater DMA and negatively with porewater inorganic arsenic (P < 0.05). Genera within the Actinobacteria and Burkholderiaceae correlated negatively with DMA, while genera with iron-reducing capacity (Clostridiales) correlated positively with porewater inorganic arsenic and DMA (P < 0.05).

Volcanogenic aluminosilicate alteration drives formation of authigenic phases at the northern Hikurangi margin: Implications for subseafloor geochemical cycles

Alteration of volcanogenic aluminosilicates (VAs) in marine sediments is recognized as critical in regulating geochemical cycles and sustaining the oceanic deep biosphere, but rates of VA alteration and its associated authigenic mineral formation are not commonly reported. Here we present results on analyses of sediments and pore water recovered from the upper 150 mbsf of four sites drilled on the northern Hikurangi margin during IODP Expeditions 372 and 375. Petrographic analyses show that volcanogenic materials (glass shards, feldspar, volcanic lithoclasts) constitute important components (15–45 wt%) of the hemipelagic mud, and reveal ongoing glass alteration with accompanying authigenic phase formation. A reaction-transport model constrained by pore water Sr, 87Sr/86Sr, Ca, Mg, and Si was applied to simulate VA diagenetic reactions. Our model results yield VA alteration rates of 0.047–0.64 mmol Sr m−2 yr−1, with substantially higher values at Sites U1517 and U1520 that experienced rapid sediment emplacement. In addition, our simulations show that >99% of the dissolved Si generated by VA alteration is fixed in silica cement and authigenic clay, and that ∼50% of Ca incorporated in the authigenic carbonate is supplied by VA alteration. First-order estimates suggest that, in addition to authigenic carbonate precipitation, authigenic clay formation may represent an important sink for dissolved Mg. This study quantitatively examines the linkage between VA alteration and formation of authigenic phases, highlights its role in subsurface geochemical cycles, and indicates that slope instability may play an important role in promoting VA diagenesis.

Integrative toolbox to assess the quality of freshwater sediments contaminated with potentially toxic metals

The Guadiana Basin is a transnational basin, presenting historical contamination with potentially toxic metals (PTM), which origin can be both natural and anthropogenic. This study explores the use of a set of observational, chemical and ecotoxicological assays with Heterocypris incongruens, Vibrio fischeri, Pseudokirchneriella subcapitata, Thamnocephalus platyurus, identifying the most sensitive to be included in a toolbox to analyze the quality of freshwater sediments related to this type of contamination. The study included the analysis of a reservoir and streams sediments of Guadiana basin, in two consecutive years with different climate conditions 2017 (dry year) and 2018 (normal year). The results showed high chemical variability along the basin, with greater contamination with PTM in the reservoir sediments. The calculated Enrichment Factors (EF) indicated high anthropogenic contamination by Cd, followed by Pb (EF > 1.5). The geoaccumulation index (Igeo) revealed that the sediments were severely polluted with Cd, and slightly polluted with Pb and Cu, inducing a higher sublethal toxicity to Heterocypris incongruens. Among the parameters evaluated, and after the use of multivariate statistical techniques, the toolbox for assessing sediments quality, in similar climate and geological conditions, should include the analysis of: meteorology, land use/cover in the area, granulometry, organic matter content, PTM concentrations, contamination indices (e.g., Igeo and EF), and sublethal bioassays with H. incongruens (total sediment analysis) and Vibrio fisheri luminescence inhibition (pore water analysis).

Benthic Dissolved Silicon and Iron Cycling at Glaciated Patagonian Fjord Heads.

Glacier meltwater supplies silicon (Si) and iron (Fe) sourced from weathered bedrock to downstream ecosystems. However, the extent to which these nutrients reach the ocean is regulated by the nature of the benthic cycling of dissolved Si and Fe within fjord systems, given the rapid deposition of reactive particulate fractions at fjord heads. Here, we examine the benthic cycling of the two nutrients at four Patagonian fjord heads through geochemical analyses of sediment pore waters, including Si and Fe isotopes (δ30Si and δ56Fe), and reaction-transport modeling for Si. A high diffusive flux of dissolved Fe from the fjord sediments (up to 0.02mmolm-2day-1) compared to open ocean sediments (typically <0.001mmolm-2day-1) is supported by both reductive and non-reductive dissolution of glacially-sourced reactive Fe phases, as reflected by the range of pore water δ56Fe (-2.7 to +0.8‰). In contrast, the diffusive flux of dissolved Si from the fjord sediments (0.02-0.05mmolm-2day-1) is relatively low (typical ocean values are >0.1mmolm-2day-1). High pore water δ30Si (up to +3.3‰) observed near the Fe(II)-Fe(III) redox boundary is likely associated with the removal of dissolved Si by Fe(III) mineral phases, which, together with high sedimentation rates, contribute to the low diffusive flux of Si at the sampled sites. Our results suggest that early diagenesis promotes the release of dissolved Fe, yet suppresses the release of dissolved Si at glaciated fjord heads, which has significant implications for understanding the downstream transport of these nutrients along fjord systems.

Tropical storm-induced disturbance of deep-water porewater profiles, Gulf of Aqaba

Storms have long been recognized as a force that agitates sediments, even in the deep-water. In shallow water depths (<40 m) sediments are affected dominantly by wave actions, while in deeper-water (>100 m) the impact is primarily due to suspended sediment flow. While such transport events have been studied sedimentologically extensively, their impact on porewater chemistry is yet poorly understood. The March 2020 tropical storm which impacted the Gulf of Aqaba (GoA) offered a unique opportunity to investigate this particular topic. Detailed sedimentological, mineralogical and porewater analyses were carried out on two sets of short cores collected along a transect from 270 m to 700 m water depths before and after the storm on the western margins of the GoA, which represents a steep slope with a potential for high energy transport events. The cores exhibited a decrease in grain size in the mid-slope water depth and an increase at the base of the slope after the storm, with the top of the core being enriched with terrestrial material. Both Fe2+ and NOx profiles exhibited a marked shift in the aftermath of the storm. NOx concentrations increased in the top 5 cm of all the cores and the ferruginous zone migrated upwards in both the top and bottom of the slope. We postulate that the storm event remixed the top of the sediment column and infused it with fine material. This filled burrows and decreased the diffusive coefficient across the sediment-water interface, limiting the exchange of ions. As a result, the porewater trapped in the sediment has developed along the terminal electron acceptor chain.

Formation of calcium chloride brines in volcaniclastic-rich sediments

The Amami-Sankaku Basin, located in the Philippine Sea, records approximately 50 million years of sediment accumulation and diagenesis of volcanic ash derived from the Kyushu-Palau and Kyushu-Ryukyu arcs. Analyses of porewater and sediment samples from the 1461-m core recovered at IODP Expedition 351, Site U1438, included major and trace elements, strontium radiogenic isotope ratio (87Sr/86Sr), and taxonomic identification of archaeal classes and bacterial orders. Sediment X-ray diffraction and thin section analyses show that smectite, zeolites and chlorite are the main authigenic minerals. A multicomponent solute diffusion and reaction numerical model was developed to simulate the long-term diagenesis that took place in this sedimentary sequence and to account for the transition to a calcium chloride brine at about 670 mbsf. Numerical results indicate that 45% of the initial amount of volcanic ash has been dissolved at 750 mbsf. At this depth, 13% of the initial water (H2O) in the pore space is estimated to have been transferred to the solid phase by the formation of zeolites, which accounts for an increase in porewater chloride concentration. In contrast, dissolution of anorthite and volcanic ash combined with sodium uptake by zeolites accounts for the predominance of calcium in the brine. In the upper 160 m of the sedimentary column, the electrochemical migration of solutes causes chloride to move in the opposite direction of the concentration gradient, i.e., uphill diffusion, sustaining downward diffusion of seawater chloride into the sediments.

Geochemical cycling in aquifers contributes to the transport, storage and transfer of anthropogenically-derived phosphorus to surface waters

Phosphorus (P) is a key element which can contribute to the eutrophication of waters draining intensively farmed or populated catchments, driving adverse impacts on ecosystem and human health. An often overlooked source of P in permeable catchments is weathering of P-bearing minerals in bedrock. P release from primary minerals, present when the rock formed, controls background P concentrations in groundwater, but secondary P-bearing minerals may form in aquifers in the presence of anthropogenic P fluxes from agriculture and septic tanks. Using cores from the Upper Greensand (UGS) aquifer, United Kingdom, we show the relative contributions of P from primary and secondary minerals. Bulk rock chemical analysis indicates solid P concentrations of 0–0.8 wt%, while porewater analyses from the same samples indicate phosphate-P concentrations of &amp;lt;5 μg/L - 1 mg/L and dissolved organic P concentrations of &amp;lt;5 μg/L - 0.7 mg/L. These data, coupled with core stratigraphy, reveal the presence of multiple primary and secondary P-bearing minerals in the UGS, and suggest that secondary P-bearing minerals are largely of anthropogenic origin. The weathering of primary P nodules produces a very low background P flux to surface waters, while the anthropogenic P-bearing minerals undergo rapid dissolution, re-precipitation and re-dissolution cycles, controlled by porewater pH and P concentrations, in turn controlling dissolved P flux to groundwater. We show that secondary P-bearing minerals are a dynamic component of the P transfer system linking anthropogenic activities on the land surface to P in groundwater and surface waters and contributing to the eutrophication of surface waters.