Artificial Sediment Research Articles

Applicability of Acoustic Concentration Measurements in Suspensions of Artificial and Natural Sediments Using an Acoustic Doppler Velocimeter

For the investigation of turbulence and particles, interaction measurement systems are required, which are able to measure velocity and concentration fluctuations simultaneously. Acoustic Doppler Velocimeters (ADV) are widely used for velocity and turbulence measurements in natural and artificial flows. Based on the acoustic sonar theory, a model is presented that correlates the ADV’s Signal-to-Noise Ratio (SNR) and the suspended solids concentration of several natural (Ems Estuary, Lake Eixendorf, Lake Altmühl) and artificial sediments (Chinafill, quartz powder, bentonite, metakaolin) for the range 0.001 g/L–50 g/L. Within the presented method, the sound absorption in water and on particles is considered in a continuous approach for sampling frequencies up to 100 Hz. The widely-used log-linear relation between the SNR and the concentration, which is only valid for low concentrations, was extended for the high concentration regime. Measurement results show a similar behavior of the SNR with respect to varying suspended solid concentrations for different sediments. However, the analysis of the fit parameters shows systematic differences depending on the type of sediment. It is concluded that the proposed model is applicable as well for laboratory use as for measurements in rivers and estuaries. Finally, we discuss the reliability of the results and the methodology with regard to measurements in rivers, lakes, and estuaries.

Substrate Flow by Different Biochemical Activities in the Urban Sewage Network

In order to investigate the consumption mechanism of organic contaminants in different biological metabolism pathways within an urban sewage network, a pilot-scale system using two kinds of sediments (urban sewage sediment and artificial sediment) was constructed. The pilot system was operated to study the migration and transformation characteristics of COD, methane, nitrate, and sulfate between sediment and sewage. Results showed that the variation of COD in sewage was 170.58 mg·L-1, with change of COD by deposition and bioreaction of 101.53 mg·L-1 and 69.05 mg·L-1, respectively. Due to biological metabolism, the generation of methane in sewers was of 7.39 mg·L-1; the decrease of nitrate and sulfate in sewage was 0.33 mg·L-1 and 21.35 mg·L-1, respectively. Based on our calculations, the consuming concentration of COD was 32.51 mg·L-1for methane generation, 8.04 mg·L-1 for denitrification, and 6.41 mg·L-1for sulfate degradation by sulfate reducing bacteria. The decrease in COD by deposition was responsible for 65.38% of total variation of COD in sewage. The decrease in COD by bioreaction was responsible for 34.62% of total variation in COD. Meanwhile, total variation values of COD for methane generation, denitrification, and sulfate degradation were responsible for 68.01% of COD variation by bioreaction. Deposition was therefore the main pathway for removal of organic contaminants from the sewer system; biochemical activities of methane generation, denitrification, and sulfate degradation also played important roles.

Insight into deep-sea life – Cibicidoides pachyderma substrate and pH-dependent behaviour following disturbance

Most palaeo-deep-water reconstructions are based on geochemical information stored in the calcareous shells of Cibicidoides species but hardly anything is known about their life cycle, population dynamics or ecology. The number of specimens of a single Cibicidoides species can locally be very limited and species may be lacking completely during certain intervals in the geological past. As a consequence, geochemical analyses are often carried out on lumped Cibicidoides spp. assuming that they share the same epizoic to epifaunal habitat and precipitated their shell in comparable offsets to surrounding bottom water mass properties. However, there is a growing body of evidence that particularly Cibicidoides pachyderma and its morphotypes C. mundulus and C. kullenbergi, may not be reliable bottom water recorders.We have recently developed aquaria that allowed, for the first time, observations of Cibicidoides pachyderma var. C. mundulus under in situ pressure and temperature. Experiments were carried out with and without artificial sediments to simulate soft sediments and rocks, respectively. Seawater was set to pH 8 and pH 7.4 to simulate more or less particulate carbon export or more or less ventilation of bottom water. Our experiments demonstrate that C. mundulus may opt for an epifaunal or an infaunal habitat depending on elapsed time following physical disturbance, pH, current activity, the availability of sediments and growth. The specimen's initial response following transfer from atmospheric pressure into the high-pressure aquaria was to immerse into the sediment or to cover more or less parts of the test with aggregated sediments or algae. However, within 24 h a strong rheotaxis became apparent and most specimens moved to sites of increased current activity under normal pH conditions (pH 8). Only few specimens remained in algae cysts or in the sediment in the pH-8 experiment. On the contrary, all specimens under pH 7.4 agglutinated a firm sediment cyst around their test and remained infaunal throughout the experimental period of three months.Independent of pH, growth was only observed in specimens that lived within an agglutinated cyst or infaunal. A solid thick cyst covered the specimens of the pH 7.4 experiment throughout the experiment and possibly restricted water exchange between the in-cyst water and the surrounding artificial bottom water mass. We suggest that a more fragile and possibly more porous sedimentary envelope may, at least temporally, have covered the infaunal specimens under pH 8 but no evidence for this was found upon termination of the experiment.

Hydrate Formation Characteristics during Carbon Dioxide Flow Through Depleted Methane Hydrate Deposits

AbstractDepleted methane hydrate (MH) reservoirs are potential sites for CO2 storage. Hydrate formation during the CO2 flow process in a dissociated MH sample was simulated to clarify the formation characteristics of CO2 hydrates and their effect on CO2 storage. Experiments included MH formation and dissociation, CO2 injection, water‐injection and CO2 hydrate dissociation, and liquid‐water distribution as monitored by magnetic resonance imaging (MRI). It was observed that the initial water saturation determined the hydrate saturation in the artificial sediment, and the depressurization range was the main factor influencing MH dissociation for the excess gas sample. Pressure is the key factor influencing hydrate formation during CO2 flow. An increase of the CO2 flow rate led to a decrease of both hydrate saturation and conversion of the injected CO2. The cumulative amount of injected water is not the key factor controlling CO2 hydrate formation, but it does determine the residual water saturation.

Seagrass rhizosphere microenvironment alters plant-associated microbial community composition.

The seagrass rhizosphere harbors dynamic microenvironments, where plant-driven gradients of O2 and dissolved organic carbon form microhabitats that select for distinct microbial communities. To examine how seagrass-mediated alterations of rhizosphere geochemistry affect microbial communities at the microscale level, we applied 16S rRNA amplicon sequencing of artificial sediments surrounding the meristematic tissues of the seagrass Zostera muelleri together with microsensor measurements of the chemical conditions at the basal leaf meristem (BLM).Radial O2 loss (ROL) from the BLM led to ∼300µm thick oxic microzones, wherein pronounced decreases in H2 S and pH occurred. Significantly higher relative abundances of sulphate-reducing bacteria were observed around the meristematic tissues compared to the bulk sediment, especially around the root apical meristems (RAM; ∼57% of sequences). Within oxic microniches, elevated abundances of sulphide-oxidizing bacteria were observed compared to the bulk sediment and around the RAM. However, sulphide oxidisers within the oxic microzone did not enhance sediment detoxification, as rates of H2 S re-oxidation here were similar to those observed in a pre-sterilized root/rhizome environment. Our results provide novel insights into how chemical and microbiological processes in the seagrass rhizosphere modulate plant-microbe interactions potentially affecting seagrass health.

Toxicity of sediment-bound lufenuron to benthic arthropods in laboratory bioassays

This paper deals with species sensitivity distributions (SSDs) for the lipophilic insecticide lufenuron and benthic arthropods based on sediment-spiked laboratory toxicity tests. This compound that inhibits chitin synthesis and moulting of arthropods persists in sediment. Using field-collected sediment, toxicity tests were conducted with three macro-crustaceans and six insects. The Hazardous Concentration to 5% of the tested species, the HC5 (and 95% confidence limit), derived from an SSD constructed with 10d-LC50′s was 2.2 (1.2–5.7) μg/g organic carbon (OC) in dry sediment. In addition, HC5 values derived from SSDs constructed with 28d-LC10 and 28-d LC50 values were 0.13 (0.02–1.50) μg/g OC and 2.0 (1.3–5.5) μg/g OC, respectively. In 28d toxicity tests with Chironomus riparius and Hyalella azteca, a higher sensitivity was observed when using lufenuron-spiked field-collected sediment than in lufenuron-spiked artificial sediment. Overall, the non-biting midge C. riparius appeared to be a representative and sensitive standard test species to assess effects of lufenuron exposure in sediment. The Tier-1 (based on standard test species), Tier-2 (based on standard and additional test species) and Tier-3 (model ecosystem approach) regulatory acceptable concentrations (RACs) for sediment-spiked lufenuron did not differ substantially. The Tier-2 RAC was the lowest. Since to our knowledge this study is the first in the open literature that evaluates the tiered approach in the sediment effect assessment procedure for pesticides, we advocate that similar evaluations should be conducted for pesticides that differ in toxic mode-of-action.

From picture to porosity of river bed material using Structure-from-Motion with Multi-View-Stereo

Common methods for in-situ determination of porosity of river bed material are time- and effort-consuming. Although mathematical predictors can be used for estimation, they do not adequately represent porosities. The objective of this study was to assess a new approach for the determination of porosity of frozen sediment samples. The method is based on volume determination by applying Structure-from-Motion with Multi View Stereo (SfM-MVS) to estimate a 3D volumetric model based on overlapping imagery. The method was applied on artificial sediment mixtures as well as field samples. In addition, the commonly used water replacement method was applied to determine porosities in comparison with the SfM-MVS method. We examined a range of porosities from 0.16 to 0.46 that are representative of the wide range of porosities found in rivers. SfM-MVS performed well in determining volumes of the sediment samples. A very good correlation (r = 0.998, p < 0.0001) was observed between the SfM-MVS and the water replacement method. Results further show that the water replacement method underestimated total sample volumes. A comparison with several mathematical predictors showed that for non-uniform samples the calculated porosity based on the standard deviation performed better than porosities based on the median grain size. None of the predictors were effective at estimating the porosity of the field samples.

Geomorphic effects of gravel augmentation on the Old Rhine River downstream from the Kembs dam (France, Germany)

During the last 30 years, river restoration activities aiming to improve the functionality of degraded fluvial ecosystems increased markedly. For large rivers, it remains difficult to evaluate restoration efficiency and sustainability due to the lack of standardized monitoring metrics. From 2010 to 2016, three gravel augmentations were performed on the Old Rhine, a by-passed reach downstream from the Kembs dam (France- Germany). A geomorphic monitoring combining topo-bathymetric surveys, bedload tracking and hydraulic modelling allows to evaluate the successfulness of these actions. Results show that, to be mobilized, artificial sediment deposit should be located in concavity rather than convexity areas, due to higher shear stresses for moderate floods (Q2). Sediment starvation appeared rapidly on the restored reaches once the sediment wave moved downstream, as a consequence of limited upstream sediment supply. Bathymetric homogenization was observed along and downstream from the restored reaches without creation of new fluvial forms. This research highlights that future actions should include channel enlargement downstream of gravel augmentations, which would promote sediment deposition and habitat diversification. Sediments excavated during artificial widening could be stored and injected progressively into the upstream part of the Old Rhine to benefit the downstream sections.

A data-driven fuzzy approach to simulate the critical shear stress of mixed cohesive/non-cohesive sediments

Purpose The critical shear stress of cohesive and mixed cohesive/non-cohesive sediments is affected by multiple interacting physical, chemical and biological parameters. There are various mathematical approaches in the scientific literature for computing critical shear stress. However, processes that influence sediment stability are still not fully understood, and available formulas differ considerably. These discrepancies in the literature arise from random system behaviour (natural variability of the sediments), different definitions of the critical shear stress, different measurement techniques and different model frameworks (scope of the parameters, undisturbed versus artificial sediment samples). While analytical approaches fail to address the involved uncertainties, fuzzy logic-based models integrate uncertainty and imprecision.

A comparative experimental approach to ecotoxicology in shallow-water and deep-sea holothurians suggests similar behavioural responses

Exploration of deep-sea mineral resources is burgeoning, raising concerns regarding ecotoxicological impacts on deep-sea fauna. Assessing toxicity in deep-sea species is technologically challenging, which promotes interest in establishing shallow-water ecotoxicological proxy species. However, the effects of temperature and hydrostatic pressure on toxicity, and how adaptation to deep-sea environmental conditions might moderate these effects, are unknown. To address these uncertainties we assessed behavioural and physiological (antioxidant enzyme activity) responses to exposure to copper-spiked artificial sediments in a laboratory experiment using a shallow-water holothurian (Holothuria forskali), and in an in situ experiment using a deep-sea holothurian (Amperima sp.). Both species demonstrated sustained avoidance behaviour, evading contact with contaminated artificial sediment. However, A. sp. demonstrated sustained avoidance of 5mgl−1 copper-contaminated artificial sediment whereas H. forskali demonstrated only temporary avoidance of 5mgl−1 copper-contaminated artificial sediment, suggesting that H. forskali may be more tolerant of metal exposure over 96h. Nonetheless, the acute behavioural response appears consistent between the shallow-water species and the deep-sea species, suggesting that H. forskali may be a suitable ecotoxicological proxy for A. sp. in acute (≤24h) exposures, which may be representative of deep-sea mining impacts. No antioxidant response was observed in either species, which was interpreted to be the consequence of avoiding copper exposure. Although these data suggest that shallow-water taxa may be suitable ecotoxicological proxies for deep-sea taxa, differences in methodological and analytical approaches, and in sex and reproductive stage of experimental subjects, require caution in assessing the suitability of H. forskali as an ecotoxicological proxy for A. sp. Nonetheless, avoidance behaviour may have bioenergetic consequences that affect growth and/or reproductive output, potentially impacting fecundity and/or offspring fitness, and thus influencing source-sink dynamics and persistence of wider deep-sea populations.

Mapping short-lived radium isotopes in estuarine residential canals (Gold Coast, Australia)

Distributions of short-lived radium isotopes (224Ra and 223Ra) were investigated on the Gold Coast waterways, one of the largest residential estuarine canal systems on Earth, in an attempt to estimate radium-derived residence times and obtain insights into sources of radium isotopes. Surface and bottom canal waters were sampled in 61 locations over ~300 km of waterways. Radium isotope activities were 12-fold higher in groundwater than estuarine waters. Surprisingly, radium activities were usually higher in surface waters than bottom waters implying a radium source associated with tidal pumping in artificial beach sediments. Estimated radium ages were usually younger within artificial canal surface waters than in the natural estuarine waterways. This study shows that the tidally driven groundwater radium source can be enhanced by the extended canal shoreline.

Detrital magnetization of laboratory-redeposited sediments

Abstract We conducted several redeposition experiments in laboratory using natural and artificial sediments in order to investigate the role of grain size and lithology on sedimentary remanence acquisition. The role of grain size was investigated by using sorted sediment from natural turbidites. Taking advantage of the magnetic grain size distribution within turbidites, we compared redeposition experiments performed with coarse magnetic grains taken from the bottom layers of a turbidite with fine grains from the upper layers of the same turbidite. In order to document the magnetization acquired for increasing sediment concentrations that is analogous to increasing depth in the sediment column, the samples were frozen at temperatures between −5 and −10 °C. Magnetization acquisition behaved similarly in both situations, so that little smearing of the palaeomagnetic signal should be linked to grain size variability within this context. Other series of experiments were aimed at investigating the influence of lithology. We used clay or carbonated sediments that were combined with magnetic separates from basaltic rocks or with single-domain biogenic magnetite. The experiments revealed that the magnetization responded differently with clay and carbonates. Clay rapidly inhibited alignment of magnetic grains at low concentrations and, therefore, significant magnetization lock-in occurred despite large water contents, perhaps even within the bioturbated layer. Extension of the process over a deeper interval contributes to smear the geomagnetic signal and therefore to alter the palaeomagnetic record. In carbonates, the magnetization was acquired within a narrow window of 45–50 per cent sediment concentration, therefore, little smearing of the geomagnetic signal can be expected. Finally, experiments on carbonate sediments and biogenic magnetite with increasing field intensities indicate that magnetization acquisition is linear with respect to field intensity. Altogether, the results suggest that sediments with dominant carbonate content should be favoured for records of geomagnetic field changes provided that the minor clay fraction does not vary excessively. They confirm the advantage of using cultures of magnetotactic bacteria for redeposition experiments.

Partitioning of nanoparticle-originated dissolved silver in natural and artificial sediments.

Sediments are believed to be a major sink for silver nanoparticles (AgNPs) in the aquatic environment, but there is a lack of knowledge about the environmental effects and behavior of AgNPs in sediments. The release of highly toxic Ag+ through dissolution of AgNPs is one mechanism leading to toxic effects in sediments. We applied an ultrasound-assisted sequential extraction method to evaluate the dissolution of AgNPs and to study the partitioning of dissolved Ag in sediments. Silver was spiked into artificial and 2 natural sediments (Lake Höytiäinen sediment and Lake Kuorinka sediment) as silver nitrate (AgNO3 ), uncoated AgNPs, or polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs). In addition, the total body burdens of Ag in the sediment-dwelling oligochaete Lumbriculus variegatus were assessed over a 28-d exposure period. The dissolution rate was found to be similar between the uncoated AgNP and PVP-AgNP groups. In all sediments, dissolved Ag was mainly bound to the residual fraction of the sediment, followed by iron and manganese oxides or natural organic matter. In Lake Kuorinka sediment, dissolved Ag that originated from PVP-AgNPs was relatively more bioaccessible, also resulting in higher total body burden in L. variegatus than that from uncoated AgNPs or AgNO3 . In artificial sediment and Lake Höytiäinen sediment, AgNO3 was significantly more bioaccessible than AgNPs. Our results highlight the importance of sediment properties and AgNP surface chemistry when evaluating the environmental exposure of AgNPs. Environ Toxicol Chem 2017;36:2593-2601. © 2017 SETAC.

Bridging between litterbags and whole-ecosystem experiments: a new approach for studying lake sediments

&lt;p&gt;Nearshore sediments have a major influence over the functioning of aquatic ecosystems, but predicting their response to future environmental change has proven difficult. Previous manipulative experiments have faced challenges controlling environmental conditions, replicating sediment mixing dynamics, and extrapolating across spatial scales. Here we describe a new approach to manipulate lake sediments that overcomes previous concerns about reproducibility and environment controls, whilst also bridging the gap between smaller microcosm or litterbag experiments and whole-ecosystem manipulations. Our approach involves submerging moderate-sized (~15 L) artificial substrates that have been standardised to mimic natural sediments within the littoral zones of lakes. We show that this approach can accurately mirror the absolute dissolved organic carbon concentrations and pH of pore water, and to a lesser degree inorganic carbon concentrations, from natural lake sediments with similar organic matter profiles. On a relative basis, all measured variables had similar temporal dynamics between artificial and adjacent natural sediments. Late-summer zooplankton biomass also did not differ between natural and artificial sediments. By offering a more realistic way to manipulate freshwater sediments than previously possible, our approach can improve predictions of lake ecosystems in a changing world.&lt;br /&gt;&lt;br /&gt;&lt;img src="/public/site/images/ttaccini/88x31.png" alt="" /&gt; &lt;br /&gt;This work is licensed under a &lt;a href="https://creativecommons.org/licenses/by/4.0/" target="_blank"&gt;Creative Commons Attribution 4.0 International&lt;/a&gt;.&lt;/p&gt;

Changing coastlines in NE England: a legacy of colliery spoil tipping and the effects of its cessation

Historical tipping of vast quantities of colliery spoil at various foreshore locations in NE England has changed the morphology and sedimentology of large areas of the shoreline and nearshore sea bed, and has impacted adversely upon the ecology and amenity use of the area. Tipping started early in the 20th Century, well before statutory controls to regulate impacts of activities on the marine environment came into force in the UK in 1974, and ended with the closure of the last colliery in 2005. The spoil tipping acted as a form of artificial sediment recharge to the foreshore, akin to conventional beach recharge schemes that use sand or shingle to replenish foreshores for coastal defence and amenity purposes, but creating a legacy of contaminated beaches and prograding (advancing) shores. Since closure of the collieries, however, the foreshores have received no artificial supply of material, and the shoreline in all former tipping areas has since been in retreat due to natural erosion. This has caused problems where assets are present at the rear of the spoil beaches, requiring coastal defence structures for their protection. As well as collating and analysing historical maps, records, literature and data relating to colliery spoil tipping, the coastal changes that have occurred since its cessation have been assessed by reference to more recent maps, literature, aerial photographs and new and up-to-date beach profile transect survey data from contemporary coastal monitoring programmes. It is envisaged that where sea cliffs are protected by colliery spoil beaches, and hence currently are dormant, they could become re-activated by erosion and start to retreat at short term rates of several metres per year and longer-term rates of up to 0.3 m/year in the foreseeable future.

Feeding the hungry river: Fluvial morphodynamics and the entrainment of artificially inserted sediment at the dammed river Isar, Eastern Alps, Germany

Dams interrupt the sediment continuum in rivers by retaining the bedload; combined with flow diversion, bedload retention in tributaries and river engineering measures, this causes a bedload deficit leading to changes in river planform and morphodynamics, with potentially detrimental downstream effects. As part of the SedAlp joint project (Sediment management in Alpine basins: integrating sediment continuum, risk mitigation and hydropower), this study investigates changes within a section of the dammed river Isar between the Sylvenstein reservoir and the city of Bad Tölz.We use a multi-method approach on a range of spatial and temporal scales. First, we analysed historical maps and aerial photos to analyse river planform and landcover changes within the river corridor of the whole study area on a temporal scale of over 100years. Results show that major changes occurred before the construction of the Sylvenstein reservoir, suggesting that present morphodynamics represent the reaction to different disturbances on different time scales. Second, changes in mean bed elevation of cross profiles regularly surveyed by the water authorities are analysed in light of artificial sediment insertion and floods; they are also used to estimate the sediment budget of river reaches between consecutive cross profiles. Results suggest stability and a slight tendency towards incision, especially near the Sylvenstein reservoir; further downstream, the sediment balance was positive. Third, we acquired multitemporal aerial photos using an unmanned aerial vehicle and generated high-resolution digital elevation models to show how sediment artificially inserted in the river corridor is entrained. Depending on the position of the artificial deposits in relation to the channel, the deposits are entrained during floods of different return periods.

Biomarkers in Tubifex tubifex for the metalaxyl and metalaxyl-M toxicity assessment in artificial sediment.

Efficacy and potential environmental risks should be considered when applying enantiopure pesticides. In this study, Tubifex tubifex and its oxidative stress biomarkers were assessed for the toxicity of metalaxyl and metalaxyl-M in sediment. The toxicity assessment was conducted with artificial sediment and reconstituted water. Five test concentrations (from 0 to 100mg/kg) were set for the short-term (4days) exposure. The long-term (28days) exposure was conducted with the environmental concentration (from 0.5 to 5mg/kg). For the short-term exposure, the increase of superoxide dismutase (SOD) activity was observed, and a clear concentration-response relationship was found in the metalaxyl treatments. The decrease of catalase (CAT) and glutathione peroxidase (GPx) activity could be caused by oxidative stress. The decrease of glutathione (GSH) content and the increase of glutathione-S-transferase (GST) might be due to antioxidation defense and detoxification mechanisms. The increase of malondialdehyde (MDA) might be due to the saturation of antioxidant systems and the accumulation and toxicity of contaminations. In the long-term exposure, the changes of biomarkers in T. tubifex reflected the oxidative stress and detoxification metabolisms. GSH and the related enzymes were important in detoxification processes and involved in the oxidative stress in toxicity mechanism. The long-term direct contact bioassay is sensitive and appropriate to reflect the lower concentration of contaminants.

Population dynamics of the endangered shrub Myricaria germanica in a regulated Alpine river is influenced by active channel width and distance to check dams

Despite its high conservation and indicator value, there is a lack of information on the long-term dynamics of Myricaria germanica (L.) Desv. (German tamarisk), and of factors affecting its population density and viability. Here we studied the dynamics of adult and juvenile M. germanica at 19 sites during a seven year period (2009–2015) along a 30km long stretch of an Italian Eastern Alpine river, by assessing a set of anthropogenic and geomorphological factors. Adult (239–571 individuals) and juvenile (62–292 individuals) population numbers showed no significant difference between years, and a remarkably uneven distribution among sites. Yet, several remnant populations have declined or disappeared in recent years and a few populations have increased. We found a positive effect of the width of the active channel on adult and juveniles plants. This means that anthropogenic river narrowing is a leading cause of the decline of the species along river banks. For juveniles, abundance also decreased with distance from downstream check dams. We conclude that in the regulated river studied, the conservation of M. germanica appears to be possible not only as a result of natural flow dynamics, but also at an artificial sediment storage area upstream of a check dam with a semi-natural river dynamic that maintains favourable riverine habitats. Our results are useful in a decision-making framework for the conservation of M. germanica, for river restoration and for flood protection in alpine valleys.

Effects of sediment-spiked lufenuron on benthic macroinvertebrates in outdoor microcosms and single-species toxicity tests

Sediment ecotoxicity studies were conducted with lufenuron to (i) complement the results of a water-spiked mesocosm experiment with this lipophilic benzoylurea insecticide, (ii) to explore the predictive value of laboratory single-species tests for population and community-level responses of benthic macroinvertebrates, and (iii) to calibrate the tier-1 effect assessment procedure for sediment organisms. For this purpose the concentration-response relationships for macroinvertebrates between sediment-spiked microcosms and those of 28-d sediment-spiked single-species toxicity tests with Chironomus riparius, Hyalella azteca and Lumbriculus variegatus were compared. Lufenuron persisted in the sediment of the microcosms. On average, 87.7% of the initial lufenuron concentration could still be detected in the sediment after 12 weeks. Overall, benthic insects and crustaceans showed treatment-related declines and oligochaetes treatment-related increases. The lowest population-level NOEC in the microcosms was 0.79μg lufenuron/g organic carbon in dry sediment (μg a.s./g OC) for Tanytarsini, Chironomini and Dero sp. Multivariate analysis of the responses of benthic macroinvertebrates revealed a community-level NOEC of 0.79μg a.s./g OC. The treatment-related responses observed in the microcosms are in accordance with the results of the 28-d laboratory toxicity tests. These tests showed that the insect C. riparius and the crustacean H. azteca were approximately two orders of magnitude more sensitive than the oligochaete L. variegatus. In our laboratory tests, using field-collected sediment, the lowest 28-d EC10 (0.49μg a.s./g OC) was observed for C. riparius (endpoint survival), while for the standard OECD test with this species, using artificial sediment, a NOEC of 2.35μg a.s./g OC (endpoint emergence) is reported. In this particular case, the sediment tier-1 effect assessment using the chronic EC10 (field-collected sediment) or chronic NOEC (artificial sediment) of C. riparius and an assessment factor of 10, seems to be protective for the treatment-related responses observed in the sediment-spiked microcosms.

Nanoparticle-based measurements of pH and O2 dynamics in the rhizosphere of Zostera marina L.: effects of temperature elevation and light-dark transitions.

Seagrasses can modulate the geochemical conditions in their immediate rhizosphere through the release of chemical compounds from their below-ground tissue. This is a vital chemical defence mechanism, whereby the plants detoxify the surrounding sediment. Using novel nanoparticle-based optical O2 and pH sensors incorporated in reduced and transparent artificial sediment, we investigated the spatio-temporal dynamics of pH and O2 within the entire rhizosphere of Zostera marina L. during experimental manipulations of light and temperature. We combined such measurements with O2 microsensor measurements of the photosynthetic productivity and respiration of seagrass leaves. We found pronounced pH and O2 microheterogeneity within the immediate rhizosphere of Z. marina, with higher below-ground tissue oxidation capability and rhizoplane pH levels during both light exposure of the leaf canopy and elevated temperature, where the temperature-mediated stimuli of biogeochemical processes seemed to predominate. Low rhizosphere pH microenvironments appeared to correlate with plant-derived oxic microzones stimulating local sulphide oxidation and thus driving local proton generation, although the rhizoplane pH levels generally where much higher than the bulk sediment pH. Our data show that Z. marina can actively alter its rhizosphere pH microenvironment alleviating the local H2 S toxicity and enhancing nutrient availability in the adjacent sediment via geochemical speciation shift.