Ecosystem Response to Climatic Change: The Importance of the Cold Season

Winter climate and snow cover are the important drivers of plant community development in polar regions. However, the impacts of changing winter climate and associated changes in snow regime have received much less attention than changes during summer. Here, we synthesize the results from studies on the impacts of extreme winter weather events on polar heathland and lichen communities. Dwarf shrubs, mosses and soil arthropods were negatively impacted by extreme warming events while lichens showed variable responses to changes in extreme winter weather events. Snow mould formation underneath the snow may contribute to spatial heterogeneity in plant growth, arthropod communities and carbon cycling. Winter snow cover and depth will drive the reported impacts of winter climate change and add to spatial patterns in vegetation heterogeneity. The challenges ahead lie in obtaining better predictions on the snow patterns across the landscape and how these will be altered due to winter climate change.     

Fate of pathogens in a simulated bioreduction system for livestock carcasses

The EU Animal By-Products Regulations generated the need for novel methods of storage and disposal of dead livestock. Bioreduction prior to rendering or incineration has been proposed as a practical and potentially cost-effective method; however, its biosecurity characteristics need to be elucidated. To address this, Salmonella enterica (serovars Senftenberg and Poona), Enterococcus faecalis, Campylobacter jejuni, Campylobacter coli and a lux-marked strain of Escherichia coli O157 were inoculated into laboratory-scale bioreduction vessels containing sheep carcass constituents. Numbers of all pathogens and the metabolic activity of E. coli O157 decreased significantly within the liquor waste over time, and only E. faecalis remained detectable after 3months. Only very low numbers of Salmonella spp. and E. faecalis were detected in bioaerosols, and only at initial stages of the trial. These results further indicate that bioreduction represents a suitable method of storing and reducing the volume of livestock carcasses prior to ultimate disposal.     

Colonisation of various types of sediment by estuarine nematodes via lateral infaunal migration: a laboratory study

A small-scale laboratory study was conducted to assess the capability of nematode species collected at an intertidal mudflat to migrate laterally into defaunated sediment by using an experimental design that excluded hydrodynamic influences. The colonisation of native mud, non-native sand and two types of non-native mud-sand mixture was monitored over a period of 2 months. Results revealed that the composition of source and colonist communities differed significantly between treatments and over time. Within the first 2 weeks of the experiment, dominance patterns in the control sediments were most similar to the sand treatment, indicating that the majority of species were able to migrate easily into non-native sandy sediment. Over the course of the experiment, colonist communities in the muddy sediments became more similar to the control microcosms, whereas the structure of the sand assemblage became increasingly dissimilar to that of the source community. The temporal patterns observed might be related to factors associated with sediment granulometry, such as the availability of appropriate food sources. The outcome of this study demonstrated that the colonisation of defaunated sediment via lateral interstitial migration is a directed, species-specific process that can lead to the establishment of colonist communities that are significantly different from source communities.Communicated by J.P. Thorpe, Port Erin     

Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha^?1 year^?1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing ¹⁵N labelled ammonium nitrate (+35 kg N ha^?1 year^?1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of ¹⁵N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.     

Minimizing Impacts of Maintenance Dredged Material Disposal in the Coastal Environment: A Habitat Approach

At present, coastal disposal of maintenance dredged material constitutes one of the most important problems in coastal zone management and in some coastal areas represents the major anthropogenic disturbance to the benthos. In this review we first propose, based on the classic literature, that macrofaunal communities typical of environmentally stressed habitats are more resilient than those of more environmentally stable habitats, and we outline the macrofaunal successional changes following a disturbance. Second, from a review and analysis of the published and unpublished literature on macrofaunal recovery following maintenance dredged material deposition in the coastal environment, we compare the successional sequences and recovery rates in euhaline and polyhaline systems. The review reveals that invertebrate recovery following dredged material disposal in relatively unstressed marine environments generally takes between 1 and 4 years, while in more naturally stressed areas, recovery is generally achieved within 9 months, although deeper polyhaline habitats can take up to 2 years to recover. Differences in recovery times are attributed to the number of successional stages required to regain the original community composition and that species typical of naturally unstressed assemblages do not possess life-history traits to allow rapid recolonization of disturbances. In the last section of this review, the management implications of these findings are discussed in terms of minimizing dredged material disposal impacts on fisheries resources. Since the natural disturbance regime appears to be very important in determining the response of a benthic community following dredged material disposal, it is recommended that when predicting the potential environmental impact of an operation, the nature of the physical environment in combination with the status (and role) of associated marine benthic communities should be considered.     

Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha^–1 year^–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing ¹⁵N labelled ammonium nitrate (+35 kg N ha^–1 year^–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of ¹⁵N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.     

Metal immobilization by sludge-derived biochar: roles of mineral oxides and carbonized organic compartment

Pyrolyzing sludge into biochar is a potentially promising recycling/disposal solution for municipal wastewater sludge, and the sludge-derived biochar (SDBC) presents an excellent sorbent for metal immobilization. As SDBC is composed of both mineral oxides and carbonized organic compartment, this study therefore compared the sorption behaviour of Pb and Zn on SDBC to those of individual and mixture of activated carbon (AC) and amorphous aluminium oxide (Al₂O₃). Batch experiments were conducted at 25 and 45 °C, and the metal-loaded sorbents were artificially aged in the atmosphere for 1–60 days followed by additional sorption experiments. The Pb sorption was generally higher than Zn sorption, and the co-presence of Pb reduced Zn sorption on each studied sorbent. Higher sorption capacities were observed at 45 °C than 25 °C for SDBC and AC, while the opposite was shown for Al₂O₃, indicating the significance of temperature-dependent diffusion processes in SDBC and AC. Nevertheless, metal sorption was more selective on Al₂O₃ that showed a greater affinity towards Pb over Zn under competition, correlating with the reducible fraction of sequential extraction. Furthermore, significant amounts of Pb and Zn were additionally sorbed on SDBC following 30-day ageing. The X-ray diffraction revealed the formation of metal-phosphate precipitates, while the X-ray photoelectron spectroscopy showed a larger quantity of metal–oxygen bonding after 30-day ageing of metal-loaded SDBC. The results may imply favourable long-term transformation and additional sorption capacity of SDBC. In conclusion, SDBC resembles the sorption characteristics of both organic and mineral sorbents in different aspects, presenting an appropriate material for metal immobilization during soil amendment.     

Identifying Change-Points in Biological Sequences via Sequential Importance Sampling

The genomes of complex organisms, including the human genome, are highly structured. This structure takes the form of segmental patterns of variation in various properties and may be caused by the division of genomes into regions of distinct function, by the contingent evolutionary processes that gave rise to genomes, or by a combination of both. Whatever the cause, identifying the change-points between segments is potentially important, as a means of discovering the functional components of a genome, understanding the evolutionary processes involved, and fully describing genomic architecture. One property of genomes that is known to display a segmental pattern of variation is GC content. The GC content of a portion of DNA is the proportion of GC pairs that it contains. Sharp changes in GC content can be observed in human and other genomes. Such change-points may be the boundaries of functional elements or may play a structural role. We model genome sequences as a multiple change-point process, that is, a process in which sequential data are separated into segments by an unknown number of change-points, with each segment supposed to have been generated by a different process. We consider a Sequential Importance Sampling approach to change-point modeling using Monte Carlo simulation to find estimates of change-points as well as parameters of the process on each segment. Numerical experiments illustrate the effectiveness of the approach. We obtain estimates for the locations of change-points in artificially generated sequences and compare the accuracy of these estimates to those obtained via Markov chain Monte Carlo and a well-known method, IsoFinder. We also provide examples with real data sets to illustrate the usefulness of this method.