Macrobenthic biodiversity and oxygen uptake in estuarine systems: the example of the Seine estuary

Purpose

Bioturbation is a major process influencing the functioning of benthic ecosystems. Although controlled experiments with species in monoculture or in artificial combinations have increased the knowledge about the role of biological diversity on geochemical processes, specific interactions have been neglected, making the extrapolation of experimental results to natural systems difficult. In this context, the main objective of this study was to measure the effects of a whole natural macrobenthic community on benthic oxygen uptake.

Materials and methods

The relationships between macrofauna and oxygen uptakes were investigated in the estuarine system of the Seine, France, during the winter and fall according to the variability of river discharge. Four undisturbed sediment cores with associated macrofauna and overlying water were sampled at nine subtidal stations in order to perform whole core incubations and measure total oxygen uptake (TOU). Moreover, values of diffusive oxygen uptake (DOU) were obtained using microelectrode profiling and fauna-mediated oxygen uptake (FOU) was calculated as the difference between TOU and DOU. FOUs were thus linked to macrofaunal parameters; both traditional (species richness, abundance and biomass) and functional (trophic guilds and bioturbation modes).

Results and discussion

The average FOU (±SD) ranged from 170?±?36 to 1,324?±?701???mol?m^?2?h^?1, and values represented 33 to 89?% of TOU. Each of the traditional macrofauna parameters had a significant and positive correlation with FOU. In addition, abundance, biomass and species number of some functional groups (e.g. suspension feeders and biodiffusors) were also correlated to FOU, supporting the diversity?Cstability hypothesis of McArthur (Ecology 36:533?C536, 1955). Nevertheless, the relationship between FOU and other functional groups such as conveyors illustrated the idiosyncratic nature of this hypothesis, underlining the difficulty of clearly identifying the role of a macrofaunal community on oxygen exchanges at the sediment?Cwater interface.

Conclusions

Our results confirm the importance of functional biodiversity on mineralization processes as well as the need to take into account the whole community. They also suggest that future studies should focus on the functional consequences of species loss and the potential resilience of the communities as a way to maintain ecosystem processes.     

Shift in abundance and structure of soil ammonia-oxidizing bacteria and archaea communities associated with four typical forest vegetations in subtropical region

Purpose

Nitrogen (N) is one of the most important elements that can limit plant growth in forest ecosystems. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are considered as the key drivers of global N biogeochemical cycling. Soil ammonia-oxidizing microbial communities associated with subtropical vegetation remain poorly characterized. The aim of this study was to determine how AOA and AOB abundance and community structure shift in response to four typical forest vegetations in subtropical region.

Materials and methods

Broad-leaved forest (BF), Chinese fir forest (CF), Pinus massoniana forest (PF), and moso bamboo forest (MB) were widely distributed in the subtropical area of southern China and represented typical vegetation types. Four types of forest stands of more than 30 years grew adjacent to each other on the same soil type, slope, and elevation, were chosen for this experiment. The abundance and community structure of AOA and AOB were characterized by using real-time PCR and denaturing gradient gel electrophoresis (DGGE). The impact of soil properties on communities of AOA and AOB was tested by canonical correspondence analysis (CCA).

Results and discussion

The results indicated that AOB dominated in numbers over AOA in both BF and MB soils, while the AOA/AOB ratio shifted with different forest stands. The highest archaeal and bacterial amoA gene copy numbers were detected in CF and BF soils, respectively. The AOA abundance showed a negative correlation with soil pH and organic C but a positive correlation with NO₃ ^??N concentration. The structures of AOA communities changed with vegetation types, but vegetation types alone would not suffice for shaping AOB community structure among four forest soils. CCA results revealed that NO₃ ^??N concentration and soil pH were the most important environmental gradients on the distribution of AOA community except vegetation type, while NO₃ ^??N concentration, soil pH, and organic C significantly affected the distribution of the AOB communities.

Conclusions

These results revealed the differences in the abundance and structure of AOA and AOB community associated with different tree species, and AOA was more sensitive to vegetation and soil chemical properties than AOB. N bioavailability could be directly linked to AOA and AOB community, and these results are useful for management activities, including forest tree species selection in areas managed to minimize N export to aquatic systems.     

The impact of acidification on aquatic biota in North America: A comparison of field and laboratory results

Acidification of lakes and streams can lead to adverse effects on aquatic biota, and the recognition of widespread atmospheric deposition of strong acids in eastern North America has led to considerable concern over its existing and potential impact on th flora and fauna of sensitive (i.e. low alkalinity) systems. While most of the concern has been directed toward the impact on the fisheries resource, it is well documented that all levels of biota are affected (Almer et al., 1974; Likens et al., 1983; Dillon et al., 1984), and full appreciation of the impact of acidification requires examination of all living components of the aquatic ecosystem. Although extensive work has already been conducted in tho Scandinavian countries, there are numerous differences in species between those countries and North America, and a sound appraisal of the threat to North American biota requires comparable work for this continent. Large scale surveys and monitoring programs are under development or are in the early phases of execution by various institutions, but much has already been learned from laboratory and field acidification experiments, and from comparisons of acidic and non-acidic lakes and streams. The purpose of this paper is to compare the results of these studies for several dominant species from several major groups of organisms. We hope to focus attention on the nature and quality of information about the sensitivity of organisms with known or apparent significant ecological roles, identify gaps or weaknesses, and provide insight into the merits and limitations of the various methods of study.     

Ecotoxicological risk assessment of a quarry filling with seaport sediments using laboratory freshwater aquatic microcosms

Purpose

In France, contaminated seaport sediments cannot be discharged into the sea according to recent regulation. Hence, they must be managed on land. Among the solutions identified, that of filling terrestrial quarries located in the littoral zone is one of the most promising. However, this requires developing a methodology for ecological risk assessment; which was the aim of the SEDIGEST research program. In the present study, we report the results of toxicological impacts of three sediments on aquatic ecosystems close to a quarry. These results were used to formulate a risk assessment methodology.

Materials and methods

The ecotoxicological approach was based on laboratory microcosm assays applied to leachates obtained from the sediments. The microcosms contained synthetic water and sediment and five pelagic (micro-algae, duckweeds and daphnids) and benthic (chironomids and amphipods) freshwater species. The biota were exposed for 3 weeks to a range of leachate concentrations; metals were monitored in the water column and the effects (i.e. mortality, growth inhibition and midge emergence) were measured.

Results and discussion

The results showed an absence of acute toxicity at concentrations of <10% (v/v) but sublethal effects for concentrations between 1 and 10%. Given the complex nature of the leachates, it was difficult to determine the factors of toxicity. Metals, especially Cu, might have been responsible for some of the effects on the amphipods.

Conclusions

Future quarries filled with seaport sediments might emit pollutants to aquatic ecosystems in their vicinity, and risk assessors should ensure that predicted environmental concentrations of leachates are below the maximum leachate concentration acceptable for the whole ecosystem; for example, by multiplying the concentration safe for the microcosm organisms by a factor of 10.     

Form,function and physics: the ecology of biogenic stabilisation

Purpose

The objective of this work is to better understand the role that biological mediation plays in the behaviour of fine sediments. This research is supported by developments in ecological theory recognising organisms as “ecosystem engineers” and associated discussion of “niche construction”, suggesting an evolutionary role for habitat modification by biological action. In addition, there is acknowledgement from engineering disciplines that something is missing from fine sediment transport predictions.

Materials and methods

Advances in technology continue to improve our ability to examine the small-scale 2D processes with large-scale effects in natural environments. Advanced molecular tools can be combined with state-of-the-art field and laboratory techniques to allow the discrimination of microbial biodiversity and the examination of their metabolic contribution to ecosystem function. This in turn can be related to highly resolved measurements and visualisation of flow dynamics.

Results and discussion

Recent laboratory and field work have led to a paradigm shift whereby hydraulic research has to embrace biology and biogeochemistry to unravel the highly complex issues around on fine sediment dynamics. Examples are provided illustrating traditional and more recent approaches including using multiple stressors in fully factorial designs in both the laboratory and the field to highlight the complexity of the interaction between biology and sediment dynamics in time and space. The next phase is likely to rely on advances in molecular analysis, metagenomics and metabolomics, to assess the functional role of microbial assemblages in sediment behaviour, including the nature and rate of polymer production by bacteria, the mechanism of their influence on sediment behaviour.

Conclusions

To fully understand how aquatic habitats will adjust to environmental change and to support the provision of various ecosystem services, we require a holistic approach. We must consider all aspects that control the distribution of sediment and the erosion-transport-deposition-consolidation cycle including biological and chemical processes, not just the physical. In particular, the role of microbial assemblages is now recognised as a significant factor deserving greater attention across disciplines.

     

A combined hydraulic and toxicological approach to assess re-suspended sediments during simulated flood events—part II: an interdisciplinary experimental methodology

Purpose

Flood events are expected to increase both in intensity and frequency due to climate change in the near future. From an environmental toxicology perspective, there is concern that such flood events could lead to the remobilization of contaminated sediment layers in rivers. The aim of this pilot study was to establish a novel and interdisciplinary framework combining methods of hydrodynamic engineering and ecotoxicological assessment to enable investigation of the potential risks associated with such remobilization events.

Materials and methods

Formulated sediment was prepared according to OECD guideline 218 and spiked with a mixture of four polycyclic aromatic hydrocarbons (phenanthrene, chrysene, pyrene, benzo[a]pyrene) at concentrations of 3.3?C8.3?mg?kg^?1 dry weight. Rainbow trout (Oncorhynchus mykiss) were exposed as test animals to re-suspended sediments in three out of five experiments. The experiments were carried out in an annular flume designed to investigate transport behaviour of fine-grained sediments. Several physicochemical (e.g. pH) and sedimentological (e.g. turbidity) parameters were measured to characterise environmental conditions and erosion behaviour of sediments. Furthermore, exposure concentrations were measured by means of an in vitro assay (7-ethoxyresorufin-o-deethylase (EROD), RTL-W1 cell assay) and chemical analysis.

Results and discussion

Preparation and spiking of large amounts of formulated sediments were feasible but not practical. Successful spiking could be confirmed by the bioanalytical methods with the spiked sediments showing significantly elevated EROD induction compared to control sediments. Conditions within the annular flume remained stable throughout all experiments and were adequate to support rainbow trout. Flood events were successfully simulated, resulting in re-suspension of formulated sediment. Different erosion behaviours of sediments during the simulated flood events were observed and could be associated with changes in microbial composition of sediments due to differences in storage conditions. Therefore, maintaining constant storage conditions of formulated sediments is crucial to enable consistency and comparability among erosion experiments.

Conclusions

This study clearly demonstrated the feasibility of a combined hydro-toxicological approach in support of the investigation of the potential ecotoxicological relevance of sediment re-suspension events. However, based on the results presented here, it is recommended to include additional physicochemical parameters, such as redox potential and conductivity, and to extend the experimental setup to natural sediments and different aquatic organisms. Future studies will use natural sediments containing representative microbial communities and extracellular polymeric substances to enable extrapolation from the annular flume to conditions in natural flowing waters.     

A combined hydraulic and toxicological approach to assess re-suspended sediments during simulated flood events. Part I–multiple biomarkers in rainbow trout

Purpose

One of the central issues related to global changes in weather is the increasing occurrence of flood events that can result in the re-suspension of contaminated sediments in rivers. Here, we report on a proof-of-concept study combining hydraulic engineering and ecotoxicology in a new interdisciplinary approach to assess the toxicity of re-suspended polluted sediments after a simulated flood event.

Materials and methods

Rainbow trout (Oncorhynchus mykiss) were exposed for 5 days under simulated flood conditions in an annular flume with artificial sediments that were spiked with a mixture of polycyclic aromatic hydrocarbons (PAH) at environmentally relevant concentrations. Specifically, the objective of this study was to bridge the gap between the physical re-suspension of pollutants and resulting toxicological impacts on aquatic organisms. A suite of different molecular, biochemical and histological markers was used to test the hypothesis that re-suspension of sediments can lead to re-mobilization of PAHs and subsequently to effects on aquatic organisms.

Results and discussion

The micronucleus frequency was significantly 4.3-fold elevated after exposure. There was no significant indication of Aryl hydrocarbon receptor signaling (no EROD induction or increased CYP1A protein content, only slight induction of CYP1A gene expression). Biliary metabolite concentration was the most sensitive marker of PAH exposure. Results for other biomarkers (glutathione-S-transferase, catalase and lipid peroxidation) were inconclusive.

Conclusions

In combination with chemical analyses of suspended matter, the presented approach will be used to improve understanding of the re-mobilization of pollutants from sediments in support of environmental risk assessment.     

Occurrence and distribution of earthworms in agricultural landscapes across Europe with regard to testing for responses to plant protection products

Purpose

Within the regulatory framework for authorisation of plant protection products (PPPs) (EU Directive 91/414/1991/EEC replaced by Regulation (EC) 1107/2009), higher tier risk assessments and earthworm field tests are conducted in different countries across Europe. This paper describes dominant earthworm species for regulatory and biogeographical regions in agricultural landscapes across Europe and examines regional differences in earthworm communities and densities and their respective response to a toxic reference.

Materials and methods

For the assessment of earthworm abundance and species distribution, data of untreated control plots from 30 earthworm field studies were analysed; each conducted according to the ISO 11268–3 (1999) guideline by European Crop Protection Association member companies in the context of registration of PPPs. For the evaluation of the response to PPPs under different regional and climatic conditions, the effect on earthworm abundance was assessed by comparing plots treated with toxic references with untreated control plots. Additionally, a comparative literature review was included providing an overview of earthworm species composition and densities in agricultural crops from 14 European countries.

Results and discussion

The assessment of earthworm field studies from six different European countries revealed that common earthworm species of anecic and endogeic ecological groups are present at most field sites. Dominant species groups of endogeic and anecic earthworms can be defined that are abundant in all assessed countries. These are the endogeic species Aporrectodea caliginosa, Aporrectodea rosea and Allolobophora chlorotica, and the anecic species Lumbricus terrestris (Northern and Central Europe) and Lumbricus friendi (Southern Europe). Taking into account the high variability in total earthworm abundances, it can be concluded that the variability within regions was larger than the variability between regions.

Conclusions

Analysis of the earthworm community and data of toxic references lead to the conclusion that testing in different zones is not considered necessary.     

Carbon and nitrogen turnover in response to warming and nitrogen addition during early stages of forest litter decomposition—an incubation experiment

Purpose

Little is known about the interactive effects of temperature, nitrogen (N) supply, litter quality, and decomposition time on the turnover of carbon (C) and N of forest litter. The objective of this study was to investigate the interactive effects of warming, N addition and tree species on the turnover of C and N during the early decomposition stage of litters in a temperate forest.

Materials and methods

A 12-week laboratory incubation experiment was carried out. The leaf litters including two types of broadleaf litters (Quercus mongolica and Tilia amurensis), a needle litter (Pinus koraiensis), and a mixed litter of them were collected from a broad-leaved Korean pine mixed forest ecosystem in northeastern China in September 2009. Nine treatments were conducted using three temperatures (15, 25, and 35 °C) combined with three doses of N addition (equal to 0, 75, and 150 kg?·?ha^?1?a^?1, respectively, as NH₄NO₃).

Results and discussion

After 12 weeks of incubation, the mass loss ranged between 12 and 35 %. The broadleaf litters had greater mass loss and cumulative CO₂–C emission than the needle litter. Temperature and N availability interacted to affect litter mass loss and decomposition rate. The dissolved organic carbon (DOC) and nitrogen (DON) concentrations in litter leachate varied widely with litter types. DOC increased significantly with increased temperature but decreased significantly with increased N availability. DON increased significantly with increased N availability but showed a higher level at the moderate decomposition temperature. The amounts of CO₂ and N₂O emission were significantly higher at 25 °C than those at 15 and 35 °C, and were significantly increased by the N addition.

Conclusions

The present study indicated relatively intricate temperature and N addition effects on C and N cycling during early stages of litter decomposition, implying that future increases in temperature and N deposition will directly affect C and N cycling in broad-leaved Korean pine mixed forest ecosystem, and may indirectly influence the ecosystem composition, productivity, and functioning in NE China. It is, therefore, important to understand the interactive effects of biotic and abiotic factors on litter decomposition in field conditions in order to assess and predict future ecosystem responses to environmental changes in NE China.     

Taxonomic and functional characterization of microbial communities in Technosols constructed for remediation of a contaminated industrial wasteland

Purpose

The construction of Technosols is an emergent technology based on the assemblage of technogenic materials for ecological reclamation of polluted land and waste recycling. Although this technology is in expansion, knowledge about the microbial communities in Technosols is limited, despite their central role in ecosystem functioning. In this 2-year study, the diversity and the abundance of total and functional microbial communities were characterized in two types of Technosols constructed to reclaim contaminated sites.

Materials and methods

The structure of the microbial community was analyzed by automated ribosomal intergenic spacer analysis fingerprinting in both types of Technosols, and the taxonomic diversity was further assessed by 16S rRNA clone library sequencing. Real-time PCR was used to quantify the abundance of the total bacterial and crenarchaeal community and of the functional guilds involved in N-cycling.

Results and discussion

16S rRNA sequencing showed that Proteobacteria was the main phylum in the Technosols (50?C80?%). The other significant phyla identified were Bacteroidetes, Firmicutes, Choloroflexi, and Actinobacteria. Real-time PCR quantification of the abundance of ammonia oxidizers, nitrate reducing, and denitrifying microbial communities involved in nitrogen cycling revealed that bacterial ammonia oxidizers were more abundant than crenarchaeal ammonia oxidizers. A high spatial variability of the microbial community, which decreased with time, was also observed.

Conclusions

At the phyla and class levels, the composition of the microbial community in constructed Technosols was similar to ??natural?? soils. Both the total bacteria and microbial guilds involved in N-cycling were abundant, but in contrast to most natural soils, bacteria and not crenarchaea were the numerically dominant ammonia oxidizers in both types of Technosols. The decrease with time of the variability in microbial community structure support early pedogenic evolution of recently constructed Technosols.     

Adaptation, tolerance, and evolution of plant species in a pyrite mine in response to contamination level and properties of mine tailings: sustainable rehabilitation

Purpose

The impacts of mining contaminations and physico-chemical properties and geochemistry of mine tailings on the density, richness, biodiversity, evolution and succession of plant species and vegetation recovery in the mining area is very poorly reported in the literature. Therefore, the present study conducted an investigation on vegetation development and succession of plant communities at the abandoned São Domingos pyrite mining area.

Materials and methods

We conducted the field survey to estimate the vegetation development and succession of plant communities, collect vegetation (plant species, lichen and moss) and tailing (and soil) samples, and finally analyzed the physico-chemical and geochemical properties and metal levels in mine tailings, soil and vegetation samples.

Results and discussion

The results showed that the communities of low height and biomass like grass, legume, shrub, moss and lichen were dominating on the mine tailings and waste dumps at the inner sites and center of the mine, and the vegetation coverage was explicitly very poor. The reddish brown colluvia had poor soil quality, but high acidity and metal concentrations. However, at the outer edge of the mine the loamy soil and relatively lower acidity and metal contamination favored the higher vegetation cover and a gradual increase in the number of species and plant succession, where the taller, higher biomass and broad leaf trees were abundantly grown forming a dense forest and canopy. The succession of several plant communities dominating in the mining area, vegetation coverage and species richness were strongly related to the different levels of contamination, soil properties and adverse factors of mine tailings.

Conclusions

Although the high concentrations of toxic trace elements and low pH soil are important factors for limiting the plant growth, however, proper soil development with enriched nutrients and properties on mining wastes, by either natural or external soil aided process, can help to promote the high vegetation growth, mine rehabilitation and ecological restoration of the mining degraded lands.     

Combined effects of technical grade fenitrothion, humic acids and particulate matter on cholinesterase activity in freshwater invertebrates

Purpose

The relative sensitivity of two freshwater invertebrate organisms to the organophosphorus insecticide fenitrothion was assessed by measuring cholinesterase (ChE) activity, a well-known biomarker of both exposure and effect to organophosphorus pesticides. The influence of different concentrations of humic acids (HAs) and particulate matter on fenitrothion bioavailability was assessed in the more sensitive species.

Materials and methods

The selected invertebrates were the dwelling feeding oligochaete Lumbriculus variegatus and the pulmonate gastropod Biomphalaria glabrata. Acute 48-h bioassays were performed exposing organisms to different fenitrothion concentrations. The concentrations that induced 50 % inhibition of enzyme activity (EC₅₀) were calculated. Fenitrothion bioavailability was investigated using different concentrations of commercial HA or particulate matter. Sand and a diverse selection of chromatographic resins that have been proposed as analogues of natural sediments were selected. For these experiments, animals were exposed to a fenitrothion value similar to the EC₅₀.

Results and discussion

The 48-h EC₅₀ values were 12?±?2 and 23?±?3 μg?l^?1 for L. variegatus and B. glabrata, respectively. Depending on HA concentration and the characteristics of particles, ChE activity was similar or higher than the value recorded for animals exposed only to the pesticide in aqueous solution.

Conclusion

The results indicated that L. variegatus was the more sensitive species of the two. In this species, fenitrothion bioavailability did not increase due to the presence of either different HA concentrations or particulate matter. The experimental approach may constitute a useful tool to predict the influence of dissolved organic matter and sediment particles on fenitrothion bioavailability and toxicity to non-target aquatic invertebrates.     

Abundance and composition of ammonia oxidizers in response to degradation of root cap cells of rice in soil microcosms

Purpose

Nitrification is a key process in the global nitrogen cycle, of which the first and rate-limiting step is catalyzed by ammonia monooxygenase. Root cap cells are one of substrates for microorganisms that thrive in the rhizosphere. The degradation of root cap cells brings about nitrification following ammonification of organic nitrogen derived from the root cap cells. This study was designed to gain insights into the response of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to mineralized N from root cap cells and the composition of active bacterial and archaeal ammonia oxidizers in rice soil.

Materials and methods

Rice callus cells were used as a model for root cap cells, and unlabelled (¹²C) and ¹³C-labelled callus cells were allowed to decompose in aerobic soil microcosms. Real-time quantitative polymerase chain reaction (PCR), DNA-based stable isotope probing (SIP), and denaturing gradient gel electrophoresis (DGGE) were applied to determine the copy number of bacterial and archaeal amoA genes and the composition of active AOB and AOA.

Results and discussion

The growth of AOB was significantly stimulated by the addition of callus cells compared with the growth of AOA with a much lesser extent. AOB communities assimilated ¹³C derived from the callus cells, whereas no AOA communities grew on ¹³C-callus. Sequencing of the DGGE bands in the SIP experiments revealed that the AOB communities belonging to Nitrosospira spp. dominated microbial ammonia oxidation with rice callus amendment in soil.

Conclusions

The present study suggests that root cap cells of rice significantly stimulated the growth of AOB, and the active members dominating microbial ammonia oxidation belonged to Nitrosospira spp. in rice rhizosphere.     

Acute toxicity of zinc and arsenic to the warmwater aquatic oligochaete <Emphasis Type="Italic">Branchiura sowerbyi</Emphasis> as compared to its coldwater counterpart <Emphasis Type="Italic">Tubifex tubifex</Emphasis> (Annelida,Clitellata)

Purpose

This study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.

Materials and methods

Water-only (96 h) and sediment (14 days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC₁₀ and LC₅₀) and effect (EC₁₀ and EC₅₀) concentrations were also determined to assess metal sensitivity for both species.

Results and discussion

Both test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.

Conclusions

Study findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.

     

Toxicity survey of Canadian Arctic marine sediments

Purpose

This paper reports a toxicity survey of Canadian Arctic marine sediments. During the Amundsen scientific cruise, eight sites distributed across the Canadian Arctic and sub-Arctic regions were selected to highlight sensitive areas affected by either atmospheric deposition, ocean current, river drainage, or anthropogenic activities. As part of the Canadian-led ArcticNet research program, this study aims to monitor and to better understand potential changes likely to impact the Arctic.

Materials and methods

Surface sediments were investigated with bioanalytical tests to assess sediment toxicity. Testing of sediment elutriates was undertaken with the ARTOXKIT M, Microtox liquid phase (MLPA), and ROTOXKIT M toxicity assays, while whole sediment testing was carried out with the Microtox solid phase assay (MSPA) toxicity test procedure. Sediment mercury (Hg) content was also determined in each sample since Hg transport and toxicity is specifically an important issue in the Arctic and is generally a key indicator of the pollution status in many aquatic ecosystems.

Results and discussion

Based on bioassay results and sediment granulometric criteria, these Arctic sediments must be considered nontoxic. However, based on MSPA half maximal inhibitory concentrations (IC50s) and/or MLPA threshold effect concentration (TEC) values, some degree of toxicity may be measureable particularly in the sediments located in southern and northeast Hudson Bay. The Hudson Bay watershed drains 30% of Canadian rivers and extends to northern USA. Despite the large Hg concern in the Arctic, the input of local or long-range Hg sources does not appear to be a contributing factor to sediment toxicity.

Conclusions

These initial results are valuable in that they set baseline quality levels for these sediments as of 2005. As such, future comparisons can be made to assess temporal and spatial trends. Human activity and climate change is expected to impact these regions in the future, resulting in further reduction of sea ice extent, access to new Arctic seaways, and drilling associated with the exploitation of natural resources.     

Sediment and society: an approach for assessing management of contaminated sediments and stakeholder involvement in Norway

Introduction

Management options for large-scale contaminated sediment remediation projects can be challenging with regard to competing stakeholder interests. This has become apparent during the Oslofjord sediment remediation project (2005–2009) which caused considerable public discussion.

Background

To learn from this project, the ‘Sediment and society’ project was initiated to develop a collaborative approach that will incorporate local and scientific knowledge in order to achieve mutual gains, win-win outcomes for the stakeholders, in the management of contaminated marine sediments.

Method development

The project focuses on two Norwegian harbours: Oslo Harbour and Bergen Harbour. The Oslo Harbour case has been analysed ex-post, using elements of risk governance: participation, communication, information/knowledge and risk perception. The Bergen Harbour case is focused on the establishment of a citizens' jury as well as a stakeholder panel in Bergen Harbour.

Preliminary results and observations

Thus far, the results suggest three important commonalities or challenges for stakeholder involvement: (1) how to include people who have important management information and local knowledge, but not much influence in the decision-making process; (2) how to secure resources to ensure participation and (3) how to engage and motivate stakeholders to participate early in the sediment remediation planning process.     

The development of rare earth element-labelled potassium-depleted clays for use as cohesive sediment tracers in aquatic environments

Purpose

Understanding the transport behaviour of fine cohesive sediment is fundamental to the sustainable management of aquatic environments. Sediment tracing techniques are widely used for measuring the transport pathways of sand-sized material in the field. However, the development of tracers, including geochemically labelled clays, for fine, cohesive sediment is more problematic. Such tracers should have chemical signatures that can be easily detected following significant dilution in the field and should remain constant for the duration of the tracer study.

Materials and methods

We have examined the potential of rare earth element (REE)-labelled phlogopite and hydrobiotite as cohesive sediment tracers. Clays were first treated with sodium tetraphenylborate to extract interlayer potassium and enhance their cation exchange capacity. Ho, La and Sm were then sorbed to the clays in batch experiments. Desorption of the chemical signature in both fresh and saline conditions was examined after 1 and 10 days.

Results and discussion

Potassium extraction enhanced REE sorption, resulting in REE concentrations in excess of 40,000 mg kg^?1 in the labelled clays, and these signatures should be easily detected following dilution in the aquatic environment. In both fresh and saline conditions, over 90% of the tracer signature was retained over a 1-day period. However, over longer time scales, there was considerable loss of the REE signature.

Conclusions

Over short time scales, there is considerable potential to use these materials as cohesive sediment tracers. Over longer time scales, although much of the label is lost, the tracers could still provide qualitative information identifying net sediment transport pathways.     

Diversity, abundance and vertical distribution of methane-oxidizing bacteria (methanotrophs) in the sediments of the Xianghai wetland, Songnen Plain, northeast China

Purpose

Methanotrophs in wetlands are of great importance because up to 90 % of the methane (CH₄) produced in such wetlands could be oxidized by methanotrophs before reaching the atmosphere. The Xianghai wetland of Songnen Plain represents an important ecosystem in northeast China. However, methanotrophic characteristics in this ecosystem have not been studied in detail. The aim of this study is to give an overview of methanotrophic diversity and vertical distribution in the sediments of this important wetland.

Materials and methods

Sediment cores were collected from three freshwater marshes, each dominated by a particular vegetation type: Carex alata, Phragmites australis and Typha orientalis. The diversity of methanotrophs was studied by phylogenetic analysis of both the 16S rRNA gene and the particulate methane monooxygenase (pmoA) gene. Methanotroph abundance was determined by quantitative PCR (qPCR) targeting the pmoA gene; group-specific pmoA gene quantification was also used to estimate the abundance of each methanotrophic group.

Results and discussion

16S rRNA and pmoA gene homological analysis revealed the presence of type Ia, Ib and II methanotrophs. Novel pmoA sequences distantly affiliated to cultured Methylococcus sp. were detected, implying the existence of novel methanotrophs in the wetland. Most obtained representatives of Methylobacter genus (both 16S rRNA and pmoA genes) were closely clustered in relation to sequences acquired from the Zoige wetland, Tibet and Siberia permafrost soils, therefore suggesting methanotrophs belonging to Methylobacter genus shared characteristics with methanotrophs in cold areas. The dominance of type I methanotrophs (especially the Methylobacter genus) was detected by both clone library analysis and group-specific qPCR assay. The relatively high methanotroph diversity and pmoA copy numbers measured in the T. orientalis marsh sediments indicated that vegetation type played an important role during CH₄ oxidation in the wetland.

Conclusions

We present the first data set on methanotroph diversity and vertical distribution in the sediments of the Xianghai wetland. DNA sequences information of Methylococcus-like methanotrophs in the wetland will facilitate the isolating of novel methanotrophs from the wetland. In a worldwide context, our study has enriched the database of genotypic diversity of methanotrophs, which will help in the understanding of the geographical distribution of methanotrophic communities.     

Ecological effects of acidification on primary producers in aquatic systems

For each of the aquatic communities of the phytoplankton, the periphyton and the macrophytes, recent studies of community structure related to acidification are reviewed. While biomass and productivity do not generally decrease, there are rather consistent decreases in species richness and profound changes in species composition as pH decreases. It is unclear whether these changes result from the effect of H⁺, lowered concentrations of nutrients, change in chemical form of nutrients, toxic metals, or alterations in grazing pressure, but evidence for each of these is considered. We have most information on the plankton, less on periphyton and little on macrophytes. The massive invasion of Sphagnum and the resulting oligotrophication hypothesized to have occurred in Swedish lakes does not seem to be occurring in other regions under acid stress. Implications for the aquatic ecosystem as a result of these structural changes include loss of resilience in the plant communities, habitat effects related to excessive growth of periphyton and macrophytes, modification of nutrient cycling by the benthic mats, and alteration of the food base for grazers. More studies are required on functional changes in primary producer communities related to acidification; these will lead to more testable hypotheses concerning mechanisms.