Geo-Chip analysis reveals reduced functional diversity of the bacterial community at a dumping site for dredged Elbe sediment

Application of equilibrium passive sampling to assess the influence of anthropogenic activities and bioturbation on the distribution of hydrophobic organic chemicals in North Sea sediment cores

The pollution state in the German Bight was investigated by determination of pollutant concentrations of sediment samples using equilibrium passive sampling. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAH) were determined in the pore water of North Sea sediment. The freely dissolved pore water concentration (C_free) was measured applying Solid Phase Microextraction (SPME) by using PDMS-coated glass fibers. The obtained results show that the North Sea contamination level with the investigated pollutants is relatively low. However, the stations close to the sediment-dumping site were higher contaminated. A macrofauna analysis showed that bioturbation activities were mostly present in the upper sediment layers, but a direct bioturbation influence on the sediment concentration distribution could not be shown. Overall, the contamination load was below baseline toxicity, but considering that several other priority pollutants will also make a contribution to the baseline toxicity, it can be counted as relatively high.

Dredging transforms the seafloor and enhances functional diversity in urban seascapes

Landscape modification alters the condition of ecosystems and the complexity of terrain, with consequences for animal assemblages and ecosystem functioning. In coastal seascapes, dredging is routine practice for extracting sediments and maintaining navigation channels worldwide. Dredging modifies processes and assemblages by favouring species with wide trophic niches, diverse habitat requirements and tolerances to dredge-related eutrophication and sedimentation. Dredging also transforms the three-dimensional features of the seafloor, but the functional consequences of these terrain changes remain unclear. We investigated the effects of terrain modification on the functional diversity of fish assemblages in natural and dredged estuaries to examine whether dredging programs could be optimised to minimise impacts on ecological functioning. Fish assemblages were surveyed with baited remote underwater video stations and variation in functional niche space was described using species traits to calculate metrics that index functional diversity. Terrain variation was quantified with nine complementary surface metrics including depth, aspect, curvature, slope and roughness extracted from sonar-derived bathymetry maps. Functional diversity was, surprisingly, higher in dredged estuaries, which supported more generalist species with wider functional niches, and from lower trophic levels, than natural estuaries. These positive effects of dredging on functional diversity were, however, spatially restricted and were linked to both the area and orientation of terrain modification. Functional diversity was highest in urban estuaries where dredged channels were small (i.e. <1% of the estuary), and where channel slopes were orientated towards the poles (i.e. 171-189°), promoting both terrain variation and light penetration in urban estuaries. Our findings highlight previously unrecognised functional consequences of terrain modification that can easily be incorporated into dredging programs. We demonstrate that restricting the spatial extent of dredging operations and the orientation of dredged channel slopes, wherever this is practical, could help to limit impacts on ecosystem functioning and productivity in urban seascapes.

Functional diversity and redundancy across fish gut, sediment and water bacterial communities

This article explores the functional diversity and redundancy in a bacterial metacommunity constituted of three habitats (sediment, water column and fish gut) in a coastal lagoon under anthropogenic pressure. Comprehensive functional gene arrays covering a wide range of ecological processes and stress resistance genes to estimate the functional potential of bacterial communities were used. Then, diversity partitioning was used to characterize functional diversity and redundancy within (α), between (β) and across (γ) habitats. It was showed that all local communities exhibit a highly diversified potential for the realization of key ecological processes and resistance to various environmental conditions, supporting the growing evidence that macro-organisms microbiomes harbour a high functional potential and are integral components of functional gene dynamics in aquatic bacterial metacommunities. Several levels of functional redundancy at different scales of the bacterial metacommunity were observed (within local communities, within habitats and at the metacommunity level). The results suggested a high potential for the realization of spatial ecological insurance within this ecosystem, that is, the functional compensation among microorganisms for the realization and maintenance of key ecological processes, within and across habitats. Finally, the role of macro-organisms as dispersal vectors of microbes and their potential influence on marine metacommunity dynamics were discussed.

Elucidation of the methanogenic potential from coalbed microbial communities amended with volatile fatty acids

The potential for modern coalfield methanogenesis was assessed using formation water from the Illinois Basin, Powder River Basin and Cook Inlet gas field as inocula for nutrient-replete incubations amended with C1-C5 fatty acids as presumed intermediates formed during anaerobic coal biodegradation. Instead of the expected rapid mineralization of these substrates, methanogenesis was inordinately slow (∼1 μmol day-1), following long lag periods (>100 days), and methane yields typically did not reach stoichiometrically expected levels. However, a gene microarray confirmed the potential for a wide variety of microbiological functions, including methanogenesis, at all sites. The Cook Inlet incubations produced methane at a relatively rapid rate when amended with butyrate (r = 0.98; p = 0.001) or valerate (r = 0.84; p = 0.04), a result that significantly correlated with the number of positive mcr gene sequence probes from the functional gene microarray and was consistent with the in situ detection of C4-C5 alkanoic acids. This finding highlighted the role of syntrophy for the biodegradation of the softer lignite and subbituminous coal in this formation, but methanogenesis from the harder subbituminous and bituminous coals in the other fields was less apparent. We conclude that coal methanogenesis is probably not limited by the inherent lack of metabolic potential, the presence of alternate electron acceptors or the lack of available nutrients, but more likely restricted by the inherent recalcitrance of the coal itself.