Interaction webs in arctic ecosystems: Determinants of arctic change?

How species interact modulate their dynamics, their response to environmental change, and ultimately the functioning and stability of entire communities. Work conducted at Zackenberg, Northeast Greenland, has changed our view on how networks of arctic biotic interactions are structured, how they vary in time, and how they are changing with current environmental change: firstly, the high arctic interaction webs are much more complex than previously envisaged, and with a structure mainly dictated by its arthropod component. Secondly, the dynamics of species within these webs reflect changes in environmental conditions. Thirdly, biotic interactions within a trophic level may affect other trophic levels, in some cases ultimately affecting land–atmosphere feedbacks. Finally, differential responses to environmental change may decouple interacting species. These insights form Zackenberg emphasize that the combination of long-term, ecosystem-based monitoring, and targeted research projects offers the most fruitful basis for understanding and predicting the future of arctic ecosystems.     

High-level arsenite removal from groundwater by zero-valent iron

The objectives of this study were to conduct batch and column studies to (i) assess the effectiveness of zero-valent iron for arsenic remediation in groundwater, (ii) determine removal mechanisms of arsenic, and (iii) evaluate implications of these processes with regard to the stability of arsenic and long-term remedial performance of the permeable reactive barrier (PRB) technology. A high concentration arsenic solution (50 mg l(-1)) was prepared by using sodium arsenite (arsenic (III)) to simulate groundwater at a heavily contaminated Superfund site in the USA. Batch studies indicate that the removal of arsenic is a two-step reaction with fast initial disappearance of arsenite followed by a slow subsequent removal process. Flow-through columns were conducted at a flow rate of 17 ml h(-1) under reducing conditions for 6.6 mo. Kinetic analysis suggested that arsenic removal behaves as a zero-order reaction at high arsenic concentrations. Arsenic removal rate constants decreased with time and arsenic breakthrough was observed in the column study. Arsenic removal capacity of zero-valent iron was determined to be approximately 7.5 mg As/g Fe. Carbonate green rust was identified from the analysis of surface precipitates; arsenite uptake by green rust may be a major mechanism responsible for arsenic remediation by zero-valent iron. Analysis of HCl-extractable arsenic from iron samples indicated that approximately 28% of arsenic was in the form of arsenate suggesting that a surface oxidation process was involved in the arsenic removal with zero-valent iron.     

Long-term increases in surface water dissolved organic carbon: observations, possible causes and environmental impacts

Dissolved organic carbon (DOC) concentrations in 22 UK upland waters have increased by an average of 91% during the last 15 years. Increases have also occurred elsewhere in the UK, northern Europe and North America. A range of potential drivers of these trends are considered, including temperature, rainfall, acid deposition, land-use, nitrogen and CO2 enrichment. From examination of recent environmental changes, spatial patterns in observed trends, and analysis of time series, it is suggested that DOC may be increasing in response to a combination of declining acid deposition and rising temperatures; however it is difficult to isolate mechanisms based on monitoring data alone. Long-term DOC increases may have wide-ranging impacts on freshwater biota, drinking water quality, coastal marine ecosystems and upland carbon balances. Full understanding of the significance of these increases requires further knowledge of the extent of natural long-term variability, and of the natural "reference" state of these systems.     

Degradation of 2,4,6-trinitrotoluene by selected helophytes

Four emergent plants (helophytes, synonyms emersion macrophytes, marsh plants, etc.) Phragmites australis, Juncus glaucus, Carex gracillis and Typha latifolia were successfully used for degradation of TNT (2,4,6-trinitrotoluene) under in vitro conditions. The plants took up and transformed more than 90% of TNT from the medium within ten days of cultivation. The most efficient species was Ph. australis which took up 98% of TNT within ten days. The first stable degradation products 4-amino-2,6-dinitrotoluene (4-ADNT) and 2-amino-4,6-dinitrotoluene (2-ADNT) were identified and analysed during the cultivation period. [14C] TNT was used for the detection of TNT degradation products and their compartmentalization in plant tissues after two weeks of cultivation. Forty one percent of 14C was detected as insoluble or bound in cell structures: 34% in roots and 8% in the aerial parts. These results open the perspective of using the above-mentioned plants for the remediation of TNT contaminated waters.     

Inter- and intra-species variation in acute zinc tolerance of field-collected cladoceran populations

Acute zinc toxicity was assessed for 10 freshwater cladoceran species collected in six different ecosystems across Europe and for two standard laboratory-reared species (Daphnia magna and Ceriodaphnia dubia). The collected organisms belonged to five different genera: Daphnia (subgenus Daphnia and Ctenodaphnia), Ceriodaphnia, Simocephalus, Acroperus and Chydorus. The 48-h EC50 of the field-collected organisms tested in standard laboratory water ranged from 375+/-141 to 4314+/-1513 microg Znl(-1). The laboratory clone of D. magna was less sensitive than the majority of the field-collected species, while our laboratory Ceriodaphnia dubia was the second most sensitive. Considerable inter-species variation was found within the genus of Ceriodaphnia (factor 6) and within the genus Daphnia (factor 8). Among the different (sub)genera tested, Chydorus and Ctenodaphnia were significantly more tolerant than the others (up to a factor 3 difference). A significant positive relationship (r2=0.67, p<0.05) between the mean cladoceran 48-h EC50 and the ambient zinc concentration of the different aquatic systems was demonstrated, suggesting a role of acclimation and/or adaptation. No significant correlation between the acute zinc tolerance and the length of the organisms was found.     

Monitoring of the booster biocide dichlofluanid in water and marine sediment of Greek marinas

Dichlofluanid (N-dichlorofluoromethylthio-N'-dimethyl-N-phenylsulphamide) is used as booster biocide in antifouling paints. The occurrence of dichlofluanid and its metabolite DMSA (N'-dimethyl-N-phenyl-sulphamide) was monitored in seawater and marine sediment from three Greek marinas. Seawater and sediment samples were collected at three representative positions and one suspected hotspot in each marina and shipped to the laboratory for chemical analysis. As part of the project, an analytical method had been developed and validated. Furthermore, some additional experiments were carried out to investigate the potential contribution of paint particle bound dichlofluanid on the total concentration in the sediment. As expected, given its known high hydrolytic degradation rate, no detectable concentrations of dichlofluanid were measured in any of the seawater samples. DMSA was detected in seawater samples at very low concentrations varying from <3 ng l(-1) (LOD) to 36 ng l(-1). During method validation, it had already been demonstrated that dichlofluanid is unstable in sediment and can therefore only be determined as its metabolite DMSA. In a separate experiment, in which marine sediment was spiked with artificial paint particles containing dichlofluanid and then analysed according to the validated method, it was demonstrated that if there is any dichlofluanid originating from paint particles, this would be determined as DMSA. No DMSA was detected in any of the sediment samples. It could therefore be concluded that there were no significant concentrations of dichlofluanid in the sediment samples.     

Bioaccumulation of perfluoroalkyl acids in dairy cows in a naturally contaminated environment

Beef and dairy products may be important vectors of human exposure to perfluoroalkyl acids (PFAAs), but the understanding of how PFAAs are accumulated and transferred through agricultural food chains is very limited. Here, the bioaccumulation of PFAAs in dairy cows receiving naturally contaminated feed and drinking water was investigated by conducting a mass balance of PFAAs for a herd of dairy cows in a barn on a typical Swedish dairy farm. It was assumed that the cows were able to reach steady state with their dietary intake of PFAAs. Perfluorooctane sulfonic acid (PFOS) and perfluoroalkyl carboxylic acids (PFCAs) with 8 to 12 carbons were detected in cow tissue samples (liver, muscle, and blood) at concentrations up to 130 ng kg^?1. Mass balance calculations demonstrated an agreement between total intake and excretion within a factor of 1.5 and consumption of silage was identified as the dominant intake pathway for all PFAAs. Biomagnification factors (BMFs) were highly tissue and homologue specific. While BMFs of PFOS and PFCAs with 9 and 10 fluorinated carbons in liver ranged from 10 to 20, perfluorooctanoic acid (PFOA) was not biomagnified (BMF?<?1) in any of the investigated tissues. Biotransfer factors (BTFs; defined as the concentration in tissue divided by the total daily intake) were calculated for muscle and milk. Log BTFs ranged from ?1.95 to ?1.15 day kg^?1 with the highest BTF observed for PFOS in muscle. Overall, the results of this study suggest that long-chain PFAAs have a relatively high potential for transfer to milk and beef from the diet of dairy cows. However, a low input of PFAAs to terrestrial systems via atmospheric deposition and low bioavailability of PFAAs in soil limits the amount of PFAAs that enter terrestrial agricultural food chains in background contaminated environments and makes this pathway less important than aquatic exposure pathways. The BTFs estimated here provide a useful tool for predicting human exposure to PFAAs via milk and beef under different contamination scenarios.     

Contaminated sediments and bioassay responses of three macroinvertebrates, the midge larva Chironomus riparius, the water louse Asellus aquaticus and the mayfly nymph Ephoron virgo

Bioassays are widely used to estimate ecological risks of contaminated sediments. We compared the results of three whole sediment bioassays, using the midge larva Chironomus riparius, the water louse Asellus aquaticus, and the mayfly nymph Ephoron virgo. We used sediments from sixteen locations in the Dutch Rhine-Meuse Delta that differed in level of contamination. Previously developed protocols for each bioassay were followed, which differed in sediment pretreatment, replication, and food availability. The Chironomus bioassay was conducted in situ, whereas the other two were conducted in the laboratory. The measured endpoints, survival and growth, were related to contaminant levels in the sediment and to food quantity in water and sediment.

Only the response of A. aquaticus in the bioassay was correlated with sediment contamination. Food availability in overlying water was much more important for C. riparius and E. virgo, thereby masking potential sediment contaminant effects. We conclude that growth of A. aquaticus was depressed by sediment contamination, whereas growth of E. virgo and C. riparius was stimulated by seston food quantity. We discuss that the trophic state of the ecosystem largely affects the ecological risks of contaminated sediments.     

The effects of perennial ryegrass and alfalfa on microbial abundance and diversity in petroleum contaminated soil

Enhanced rhizosphere degradation uses plants to stimulate the rhizosphere microbial community to degrade organic contaminants. We measured changes in microbial communities caused by the addition of two species of plants in a soil contaminated with 31,000 ppm of total petroleum hydrocarbons. Perennial ryegrass and/or alfalfa increased the number of rhizosphere bacteria in the hydrocarbon-contaminated soil. These plants also increased the number of bacteria capable of petroleum degradation as estimated by the most probable number (MPN) method. Eco-Biolog plates did not detect changes in metabolic diversity between bulk and rhizosphere samples but denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified partial 16S rDNA sequences indicated a shift in the bacterial community in the rhizosphere samples. Dice coefficient matrices derived from DGGE profiles showed similarities between the rhizospheres of alfalfa and perennial ryegrass/alfalfa mixture in the contaminated soil at week seven. Perennial ryegrass and perennial ryegrass/alfalfa mixture caused the greatest change in the rhizosphere bacterial community as determined by DGGE analysis. We concluded that plants altered the microbial population; these changes were plant-specific and could contribute to degradation of petroleum hydrocarbons in contaminated soil.     

Oxidative treatment of simulated dyehouse effluent by uv and near-UV light assisted Fenton's reagent

UV/Fenton, near-UV-visible/Fenton, dark Fenton, and H₂O₂/UV reactions have been used to treat simulated dyehouse effluents representing wastewater from the textile dyeing and rinsing process. Experiments were carried out in a lab - scale photochemical reactor using concentrations of 0.5–25 mM H₂O₂, 0.04-0.5 mM Fe²⁺-ion and different dilutions of textile wastewater. To assess the extent of mineralization, decolourization kinetics and the effect of different fight sources on treatment efficiency, DOC, optical density at 254 nm and 600 nm wavelength and residual H₂O₂ concentrations were measured during the course of the advanced oxidation reactions. Comparative evaluation of the obtained results revealed that the decolourization rate increased with applied H₂O₂ and Fe²⁺-ion dose as well as the strength of the synthetic textile wastewater. The best results were obtained by the near - UV/visible/Fenton process with a decolourization rate constant of 1.57 min⁻¹, a UV_254nm reduction of 97% and a DOC removal of 41% at relatively low doses of the H₂O₂ oxidant and Fe²⁺-ion catalyst within 60 min treatment time.