Sedimentation Stability Research Articles

Production of highly electro-conductive cellulosic paper via surface coating of carbon nanotube/graphene oxide nanocomposites using nanocrystalline cellulose as a binder

Electro-conductive cellulosic paper has attracted great attention as a promising alternative material in the emerging field of flexible and portable electronic devices. However, the environmentally friendly fabrication of electro-conductive cellulosic paper still remains challenging. Herein, green multi-walled carbon nanotube (MWCNT)/graphene oxide (GO) nanocomposites towards the sustainable development strategy were developed and subsequently used to impart electro-conductivity to cellulosic paper via surface coating process. GO exfoliated from graphite powder was used as a dispersant to improve the dispersion of MWCNTs in water media, and nanocrystalline cellulose (NCC) derived from cotton fibers was employed as a binder for the MWCNT/GO nanocomposites. Effect of NCC amount on the rheological behavior, particle size distribution, sedimentation stability and zeta potential of MWCNT/GO nanocomposites as well as the electro-conductivity and mechanical properties of coated paper was investigated. Results demonstrated that NCC enhanced the dispersion of MWCNT/GO nanocomposites in addition to serving as a binder. Surface coating application of MWCNT/GO nanocomposites was found to impart high electro-conductivity of up to 892 S m−1 to the cellulosic paper while improving its mechanical properties.

Laboratory study of methane hydrate formation kinetics and structural stability in sediments

The natural gas hydrate deposits in the offshore of India are embedded in different sediments, namely clay rich silts and sands, coarse grain sand and volcanic fly ash. The variations in gas hydrate concentrations at different geological locations shows dependency on sediment mineralogy. It is also known that the particle size of the sediments plays an important role in hydrate formation and gas hydrate concentrations in sediments. We carried out systematic studies on the methane hydrate formation kinetics and methane hydrate volumetric yields, in stirred reactor experiments, using suspensions of synthetic silica and natural sediment from Krishna–Godavari (KG) Basin. The hydrate formation behavior in silica and KG basin sediment is also compared with the formation of methane hydrates in a “pure system” without sediment or added silica grains. Our results show that the hydrate formation kinetics is faster in 50 μm silica system followed by that in natural marine sediment. Observed methane hydrate yield in the laboratory is higher (∼39%) in both the pure (no sediment) and 1 μm silica suspensions. The gas intake is much quicker (∼375 min) in the suspension of 50 μm silica system, while the hydrate yield is noticeably less (∼29.38%). The methane hydrates are characterized by Raman spectroscopy and they show characteristic structure I (sI) methane hydrate signatures, with a hydration number in the range 5.93–6.12.

Modification and Comparative Study of Commercial Nanodiamonds

Detonation nanodiamond powders produced by different manufacturers were surface modified to reduce the amount of surface impurities and impart to the particles a high colloidal stability in aqueous suspensions. Modified DNDs (MDNDs) were separated into fractions and evaluated by the zeta potential, particles size distribution and elemental composition. MDNDs retain colloidal stability after the hydrosols are dried and the resulting powders are resuspended. Sedimentation stability and fraction composition are proposed as parameters for standardization of commercial nanodiamonds.

Modelling the effects of Zostera noltei meadows on sediment dynamics: application to the Arcachon lagoon

A three-dimensional model has been modified to describe the complex interactions between hydrodynamics, sediment dynamics and biological parameters in the presence of Zostera noltei. The model treats seagrass leafs as flexible blades that bend under hydrodynamic forcing and alter the local momentum and turbulence fluxes and, therefore, the benthic shear conditions; these changes cause related changes to the mass balance at the boundary of the bed, in turn affecting the suspended matter in the column and ultimately primary productivity and the growth of the dwarf-grass. Modelling parameters related to the impact of Z. noltei to the local flow and to erosion and deposition rates were calibrated using flume experimental measurements; results from the calibration of the model are presented and discussed. The coupled model is applied in the Arcachon Bay, an area with high environmental significance and large abundance of dwarf-grass meadows. In the present paper, results from preliminary applications of the model are presented and discussed; the effectiveness of the coupled model is assessed comparing modelling results with available field measurements of suspended sediment concentrations and seagrass growth parameters. The model generally reproduces sediment dynamics and dwarf-grass seasonal growth in the domain efficiently. Investigations regarding the effects of the vegetation to the near-bed hydrodynamics and to the sediment suspension in the domain show that dwarf-grass meadows play an important part to velocity attenuation and to sediment stabilisation, with flow and suspended sediment concentrations damping, compared to an unvegetated state, to reach 35–50 and 65 %, respectively, at peak seagrass growth.

The bivalve loop: Intra-specific facilitation in burrowing cockles through habitat modification

Human exploitation of bivalve populations has changed intertidal landscapes worldwide. Many bivalves are ecosystem engineers that modify the physical environment, affecting the conditions for their survival. Here we argue that lack of recovery of overexploited intertidal bivalve beds may be partly caused by the loss of important biological feedbacks from depleted populations. In a large-scale experiment we investigated engineering effects of cockles (Cerastoderma edule L.) and lugworms (Arenicola marina L.) on juvenile cockles by adding high densities of either species to 5×5m plots in areas with different hydrodynamic and sediment conditions in the intertidal flats of the Wadden Sea. We hypothesized that cockles would facilitate the new generations by increasing sediment stability, while lugworms would have negative effects on juvenile cockles through sediment disturbance. We found that in sandy areas with high wave and current energy cockles enhanced sediment accumulation and promoted local densities of young cockles, while lugworms did not have any effect on juvenile cockles. In muddy sites sheltered from the tidal currents by mussel reefs (Mytilus edulis L.), juvenile cockle densities were generally high, demonstrating the general importance of biological engineering for recruitment processes in the intertidal. We suggest that the acknowledgement of positive feedbacks between bivalves and sediment stability is essential to achieve long-term restoration goals in coastal ecosystems.

Non-additive increases in sediment stability are generated by macroinvertebrate species interactions in laboratory streams.

Previous studies have shown that biological structures such as plant roots can have large impacts on landscape morphodynamics, and that physical models that do not incorporate biology can generate qualitatively incorrect predictions of sediment transport. However, work to date has focused almost entirely on the impacts of single, usually dominant, species. Here we ask whether multiple, coexisting species of hydropsychid caddisfly larvae have different impacts on sediment mobility compared to single-species systems due to competitive interactions and niche differences. We manipulated the presence of two common species of net-spinning caddisfly (Ceratopsyche oslari, Arctopsyche californica) in laboratory mesocosms and measured how their silk filtration nets influence the critical shear stress required to initiate sediment grain motion when they were in monoculture versus polyculture. We found that critical shear stress increases non-additively in polycultures where species were allowed to interact. Critical shear stress was 26% higher in multi-species assemblages compared to the average single-species monoculture, and 21% greater than levels of stability achieved by the species having the largest impact on sediment motion in monoculture. Supplementary behavioral experiments suggest the non-additive increase in critical shear stress may have occurred as competition among species led to shifts in the spatial distribution of the two populations and complementary habitat use. To explore the implications of these results for field conditions, we used results from the laboratory study to parameterize a common model of sediment transport. We then used this model to estimate potential bed movement in a natural stream for which we had measurements of channel geometry, grain size, and daily discharge. Although this extrapolation is speculative, it illustrates that multi-species impacts could be sufficiently large to reduce bedload sediment flux over annual time scales in streams where multiple species of caddisfly are present.

Reach specificity in sediment E. coli population turnover and interaction with waterborne populations

Sediment-borne Escherichia coli can elevate waterborne concentrations through sediment resuspension or hyporheic exchange. This study sought to correlate hydrological, sediment transport, and water quality variables with: (i) the temporal stability of sediment E. coli populations [concentrations, strain richness and similarity (Raup–Crick index)]; and (ii) the contribution of sediment E. coli to the water column as defined through a library-dependent microbial source tracking approach that matched waterborne E. coli isolates to sediment E. coli populations. Three monitoring locations differing in their hydrological characteristics and adjacent upland fecal sources (dairy operation, low-density residential, and tile-drained cultivated field) were investigated. Sediment E. coli population turnover was influenced by sediment transport at upstream, high-energy reaches, but not at the downstream low-energy reach. Sediment contributions to the water column averaged 13% and 18%, and fecal sources averaged 17% and 21% at the upstream sites adjacent to dairy operations and low-density residential areas, respectively. Waterborne E. coli at the downstream site had low matches to E. coli from reach sediments (1%), higher matches to the upstream sediments (27% and 12%), and an average of 14% matches to the tile drained field. The percentage of waterborne E. coli matching sediment-borne E. coli at each stream reach varied in correlations to hydrological and sediment transport variables, suggesting reach-specific differences in the role of sediment resuspension and hyporheic exchange on E. coli transport.

Pretreatment Effect on the Stability of Coal Hexane Coal-Water Suspension

Stability of coal-water suspension (WCS) is one of the main criteria for obtaining fuel efficient. In the present work we investigated the sedimentation stability of coal-water suspension of 35% (in the presence and absence of hexane) stabilized by sodium dodecyl sulfate. Found that pretreatment of coal hexane (before being crushed) and further stabilization of coal-water suspension of 35% sodium dodecyl sulfate at concentrations of 0.8-.1.0% helps to ensure a stable dispersion system.

Comparative study on different coupling agents used as surfactants: effect on dispersion properties of TiN nanoparticles

Γ-methacryloxypropyl trimethoxy silane (KH-570) and macromolecular coupling agents (MCA) (St/AN/KH-570 random copolymer) were used as surfactants for the surface modification of titanium nitride (TiN) nanoparticles (nanoTiN). The structure and dispersion properties of the modified nanoTiN were investigated by Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy (XPS), a sedimentation stability experiment (SSE), a contact angle measuring instrument (CAMI) and a high-resolution transmission electron micrograph (HRTEM). According to the spectra of FTIR and XPS, it can be inferred that the KH-570 and MCA covalently bonded on the surface of nanoTiN and an organic coating layer was formed. The SSE and the CAMI showed that the stable dispersion and the hydrophobic property were improved significantly. The results of the HRTEM showed that the surfactants improved the dispersibility of particles in the organic solution and the SBR matrix. It is found that the MCA can more effectively improve the dispersion stability of nanoTiN because of a more strong steric stabilisation of the macromolecular structure, which facilitated to hinder the aggregation of nanoparticles.

Maintenance versus Maturation: Constructed Storm-Water Wetland’s Fifth-Year Water Quality and Hydrologic Assessment

Constructed storm-water wetlands (CSWs) have become popular storm water control measures (SCMs) in low-lying coastal environments, offering a hybrid between larger detention practices (wet ponds) and newer green infrastructure technologies. However, it is relatively rare that CSWs are monitored once the practice has aged 4 years, causing some concern among stakeholders about the long-term performance of CSWs. The specific objective of this research was to investigate the effects that wetland maturation and lack of maintenance have on the ability of a 5-year-old CSW to mitigate hydrology and improve water quality. A CSW was monitored from 2012–2013 that had not been maintained since construction in the spring of 2007. Since then, it has established as a diverse and healthy ecosystem. The monitoring results were compared with the results of a study conducted at the same site for a 1-year period immediately following construction (2007–2008). In 2007–2008, runoff volumes were reduced 54% and peak discharges 80%; whereas in 2012–2013, no change was observed in volume, and peak discharges were reduced by 64%. The stark difference in hydrologic mitigation was attributed to less availability of design volume in 2012–2013 because of (1) organic detritus accumulation during the intervening 5 years measured to be 7 cm; (2) modest siltation; and (3) an upward water-table adjustment owing to differing average antecedent dry periods. The 2012–2013 hydrologic performance of this CSW was similar to other CSWs (that were 2 years of age) studied in North Carolina, indicating that ecological systems should be monitored for performance after the point of establishment (2–3 years) for regulatory purposes. Overall nitrogen event mean concentration (EMCs) were reduced as the wetland matured, but not for total phosphorus (TP), as the effluent concentrations increased from 2007–2008 to 2012–2013. CSW maturation seemed to outweigh the lack of maintenance for both nitrogen treatment and stabilization of internal sediment. Maintenance (removal/replacement of forebay sediments and detritus material) need was apparent, however, for TP treatment and hydrologic mitigation. This appeared to be the only form of maintenance that would have been needed in the last 6 years for an SCM treating a 47-ha watershed. In comparison to the other practices, namely bioretention and permeable pavement, similar CSWs may have much lower operation and maintenance costs. This may make CSWs a viable option in areas where little resources exist for SCM maintenance.

Properties of aniline-modified strontium titanyl oxalate-based electrorheological suspension

Aniline-modified strontium titanyl oxalate (STO) particles were fabricated with a precipitation method. The structures of the particles were analyzed by x-ray diffraction analyses, Fourier transform infrared spectrometry and thermogravimetric analysis. Scanning electron microscopy was used to analyze the morphology of the particles. The results indicate chemical bonds are formed between STO and aniline. By tuning the molar ratio of aniline to Ti, the morphology of the aniline-modified STO particles can be sphere, polyhedron and a mixture composed of clusters of nano particles and micro rod-like particles. Electrorheological (ER) properties, temperature effect, thixotropy and sedimentation stability of the ER fluids based on the pure STO and the aniline-modified STO were tested. The results indicate all the properties strongly depend on the content of the aniline during the fabrication process of the particles. The ER fluid with a molar ratio of aniline/Ti of 2 presents the highest shear stress, yield stress, leak current density and the most stable ER behavior at changing temperatures. The reason is the particles have polyhedron morphology and absorbed polar aniline molecules. Because of the stable space grid structure formed by the particles with a molar ratio of aniline/Ti of 3, the ER fluid exhibits better thixotropy and sedimentation stability than the others.

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

Abstract A well-developed Triassic carbonate platform is exposed in the eastern part of the Tulcea Unit, in the Cimmerian North Dobrogean Orogen, southeastern Romania. Facies analysis of the 200 m thick succession of lower Middle Anisian limestones exposed in a large limestone quarry south of the village of Mahmudia suggests a transition from upper slope towards toe-of-slope carbonate facies, reflecting sea-level fluctuations and tectonic tilting. The slope is dominated by in situ microbialites in the upper portion, consisting of reefal boundstone facies, and by molluscan coquina and cement boundstones. A key role is played by the cosmopolitan micro-encruster Tubiphytes, which became common in the aftermath of the mass extinction at the Permian/Triassic boundary, and by autochthonous micrite and synsedimentary marine cement. The absence of metazoan reef builders, such as sponges and corals, reflects the fact that microbes were the first organisms to recover after the Permian/Triassic crisis under unusual marine conditions and that their main role in reef formation was sediment stabilization along the upper slopes. The lower slope is mostly detrital, being dominated by platform-derived bioclastic rudstones and crinoidal floatstones, which are interbedded with basinal carbonate hemipelagics. The toe-of-slope is composed of pelagic wackestones framed by thin tongues of intraclast breccia. All these observations are in agreement with the slopeshedding model described for the Pennsylvanian microbial margin in Asturias (northern Spain) and the Anisian- Ladinian flat-topped, steep-rimmed Latemar platform (Dolomites, Italy). As most of the Anisian reefs were described from western and eastern Tethys (Southern Alps, Hungary, China), the occurrence of the early Middle Anisian Tubiphytes-reef from North Dobrogea (Romania) contributes to resolving the puzzle of the geographic distribution of reef recovery in the Middle Triassic.

Linking solid particle packing of Eco-SCC to material performance

The concept of Eco-SCC aims to achieve self-compacting concrete (SCC) design for intermediate compressive strength mixtures that are commonly used in the ready-mix concrete industry. Contrary to many other approaches, in which the reactive cement clinker is replaced by a less reactive component, Eco-SCC involves the reduction of the total powder content. In the approach presented in this paper, the lubricant volume is increased by using a non-reactive filler. An improved particle packing with an enhanced lattice effect can minimize the lubricant demand and enhance the stability of the concrete. The effect of particle-size distribution on stability and performance of optimized Eco-SCC is evaluated. Fresh and hardened properties, including rheological properties, blocking behavior, sedimentation stability, compressive strength development, and drying shrinkage are determined. Test results are correlated to particle packing characteristics of the aggregate and cementitious materials combinations using the gyratory intensive compaction test (ICT) approach. A clear relationship is observed between the particle-packing characteristics and the performance of Eco-SCC.

Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 503:41-58 (2014) - DOI: https://doi.org/10.3354/meps10747 Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries Thomas Valdemarsen1,*, Cintia O. Quintana1,2, Erik Kristensen1, Mogens R. Flindt1 1Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark 2Institute of Oceanography, University of São Paulo, São Paulo 05508-070, Brazil *Corresponding author: valdemarsen@biology.sdu.dk ABSTRACT: Sediments in eutrophic estuarine ecosystems may become heavily enriched with organic carbon (OC). This OC is primarily of low reactivity and, therefore, has moderate effects on sediment biogeochemical cycling. Nonetheless, OC levels of >1% reduce sediment stability and cause frequent resuspensions and high water turbidity, which affect the recovery of ecosystem functioning. Significant reduction of sediment OC content to <1% is, therefore, needed before ecosystems can fully recover. It was investigated whether organic-rich sediments with 2.5 to 4.4% OC (180–310 mol m–2) from the eutrophic Odense Fjord (Denmark) can recover by microbial degradation. Defaunated sediment cores from various habitats were subjected to long-term (~2 yr) degradation experiments. Total OC content was measured initially and OC degradation was measured regularly from CO2 effluxes and closed anoxic sediment incubations. OC degradation was high initially, but faded exponentially at all stations before stabilizing at 6 to 15 mmol OC m-2 d-1 after 100 to 150 d. Hence, over the 2 yr experiment OC degradation corresponded to only 3 to 5% reduction of initial OC. Temporal degradation patterns analyzed by exponential decay models suggested that sedimentary OC consisted of 2 pools with different reactivity plus a non-reactive pool. OC with the highest turnover (k = 0.5 × 10-2 to 5.5 × 10-2 d-1) was quantitatively the least important (0.3-4.3% of total OC), while OC with lower reactivity (k = 0.1 × 10-3 to 2.0 × 10-3 d-1) constituted a higher proportion (4-58% of total OC in organic-rich sediments). Furthermore, 43 to 95% of sediment OC was non-degradable. Our results suggest that partial recovery (5-57% reduction of initial OC) may occur within 23 to 50 yr. However, complete recovery of organic-rich sediments to <1% OC seems unlikely due to large pools of non-reactive OC. Eutrophication, therefore, leads to irreversible OC accumulation in sediments, which prolongs the recovery time for estuarine ecosystems after reductions in nutrient loading. KEY WORDS: Organic matter · Degradation · Mineralization · Oligotrophication · Recovery time · Exponential decay · G-model Full text in pdf format PreviousNextCite this article as: Valdemarsen T, Quintana CO, Kristensen E, Flindt MR (2014) Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries. Mar Ecol Prog Ser 503:41-58. https://doi.org/10.3354/meps10747 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 503. Online publication date: April 29, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Study on preparation and thermal conductivity of high stability magnetorheological fluids

A surface modifier, which has lipophilic groups and chelating groups, was synthesized, and used to modify the surface characteristics of carbonyl iron particles and prepare composite magnetic particles (CMPs). Then a set of oil-based magnetorheological (MR) fluids based on the CMPs were prepared. Finally, the relationship between thermal conductivity and concentration of MR fluids were studied, and an analysis model on thermal conductivity and concentration of MR fluids was built. The result shows that there is a linear correlation between thermal conductivity and concentration of MR fluids, namely keff = 0.0245 Φ − 0.08 and keff/kf = 0.167 Φ − 0.53 (10 ≤ Φ ≤ 50). Applying this model, the concentration variation of the MR fluids can be acquired on the basis of the thermal conductivity variation, and the model can be used to evaluate the sedimentation stability of the MR fluids.

The efficiency of using fluorine-containing surfactants for property modification of polyurethanes filled with chalk

The efficiency of using fluorine-containing surfactants for increasing the sedimentation stability of filled compositions, uniformity of the disperse-phase distribution in oligomer, and hydrophobization of the cured polyurethane surface is shown.

Ecological structure and function differs between habitats dominated by seagrasses and green seaweeds

Marine vegetated habitats, e.g. seagrass meadows, deliver essential functions and services to coastal ecosystems and human welfare. Impacts induced by humans, however, have facilitated the replacement of seagrasses by alternative vegetation, e.g. green rhizophytic seaweeds. The implications of habitat shifts for ecosystem attributes and processes and the services they deliver remain poorly known. In this study, we compared ecosystem structure and function between Cymodocea nodosa seagrass meadows and bottoms dominated by Caulerpa prolifera, a green, native, rhizophytic seaweed, through 5 ecological proxies: (i) primary production (via community metabolism), (ii) composition and abundance of epifauna (a proxy for provision of habitat for epifauna), composition and abundance of (iii) small-sized (juvenile) and (iv) large-sized (adult) fishes (proxies for provision of habitat for fishes), and (v) sediment retention (a proxy for sediment stabilization). Four of these proxies were greater in C. nodosa seagrass meadows than in C. prolifera beds: gross primary productivity (∼1.4 times), the total abundance, species density and biomass of small-sized fishes (∼2.1, 1.3 and 1.3 times, respectively), the total abundance and species density of large-sized fishes (∼3.6 and 1.5 times, respectively), and sediment stabilization (∼1.4 times). In contrast, the total abundance and species density of epifauna was larger (∼3.1 and 1.7 times, respectively) in C. prolifera than in C. nodosa seagrass beds. These results suggest that ecosystem structure and function may differ if seagrasses are replaced by green rhizophytic seaweeds. Importantly, ecosystem functions may not be appropriate surrogates for one another. As a result, assessments of ecosystem services associated with ecosystem functions cannot be based on exclusively one service that is expected to benefit other services.

Transitions in sandflat biota since the 1930s: effects of sea-level rise, eutrophication and biological globalization in the tidal bay Königshafen, northern Wadden Sea

Conspicuous macrozoobenthos and vegetation of intertidal sandflats in Königshafen (Island of Sylt, SE North Sea) were mapped in 1932, 1988 and 2008. Higher water levels since the 1930s with a concomitant increase in tidal dynamics are assumed to have weakened sediment stability. This dissolved the distinctly banded macrobenthic zonation of the 1930s. Near high water level, cyanobacterial mats with associated beetles, belts of the mudshrimp Corophium volutator and the seagrass Zostera noltii have vanished, while the range of the lugworm Arenicola marina has extended towards the shore. Near low water level, sandy elevations have become permanently submerged because a tidal creek has widened its bed. In 1988, extensive green algal mats and the almost complete absence of seagrass are attributed to peak eutrophication. This partially reversed until 2008. The mussel Mytilus edulis had strongly extended its beds along the creek in 1988. These were taken over by introduced Pacific oysters Crassostrea gigas in 2008. Also in 2008, the cordgrass Spartina anglica, another introduced species, grew into large tussocks where cyanobacterial mats and a Corophium-belt had been mapped in the 1930s. Former benthic patterns may have little chance of resurrection by conventional nature protection because these small-scale shifts represent responses to regional and global change.

Seagrasses are negatively affected by organic matter loading and Arenicola marina activity in a laboratory experiment

When two ecosystem engineers share the same natural environment, the outcome of their interaction will be unclear if they have contrasting habitat-modifying effects (e.g., sediment stabilization vs. sediment destabilization). The outcome of the interaction may depend on local environmental conditions such as season or sediment type, which may affect the extent and type of habitat modification by the ecosystem engineers involved. We mechanistically studied the interaction between the sediment-stabilizing seagrass Zostera noltii and the bioturbating and sediment-destabilizing lugworm Arenicola marina, which sometimes co-occur for prolonged periods. We investigated (1) if the negative sediment destabilization effect of A. marina on Z. noltii might be counteracted by positive biogeochemical effects of bioirrigation (burrow flushing) by A. marina in sulfide-rich sediments, and (2) if previously observed nutrient release by A. marina bioirrigation could affect seagrasses. We tested the individual and combined effects of A. marina presence and high porewater sulfide concentrations (induced by organic matter addition) on seagrass biomass in a full factorial lab experiment. Contrary to our expectations, we did not find an effect of A. marina on porewater sulfide concentrations. A. marina activities affected the seagrass physically as well as by pumping nutrients, mainly ammonium and phosphate, from the porewater to the surface water, which promoted epiphyte growth on seagrass leaves in our experimental set-up. We conclude that A. marina bioirrigation did not alleviate sulfide stress to seagrasses. Instead, we found synergistic negative effects of the presence of A. marina and high sediment sulfide levels on seagrass biomass.

Transport of poly(acrylic acid) coated 2-line ferrihydrite nanoparticles in saturated aquifer sediments for environmental remediation

Groundwater remediation using iron oxide and zero-valent iron nanoparticles (NPs) can be effective, but is limited in many applications due to the NP strong retention in groundwater-saturated porous media after injection, the passivation of the porous surface, and the high cost of nanomaterials versus macro scale iron. In this study, we investigated transport of bare and polymer-coated 2-line ferrihydrite NPs (30–300 nm) in saturated aquifer sediments. The influence of poly(acrylic acid) (PAA) polymer coatings was studied on the colloidal stability and transport in sediments packed column tests simulating groundwater flow in saturated sediments. In addition, the influence of calcium cations was investigated by transport measurements using sediments with calcium concentrations in the aqueous phase ranging from 0.5 (typical for most sediments) to 2 mM. Measurements were also made of zeta potential, hydrodynamic diameter, polymer adsorption and desorption properties, and bio-availability of PAA-coated NPs. We found that NP transport through the saturated aquifer sediments was improved by PAA coating and that the transport properties could be tuned by adjusting the polymer concentration. We further discovered that PAA coatings enhanced NP transport, compared to bare NPs, in all calcium-containing experiments tested, however, the presence of calcium always exhibited a negative effect on NP transport. In tests of bioavailability, the iron reduction rate of the coated and bare NPs by Geobacter sulfurreducens was the same, which shows that the PAA coating does not significantly reduce NP Fe(III) bioavailability. Our results demonstrate that much improved transport of iron oxide NP can be achieved in saturated aquifer sediments by introducing negatively charged polyelectrolytes and optimizing polymer concentrations, and furthermore, these coated NPs retain their bioavailability that is needed for applications in bio-environmental remediation.