School of Civil Engineering & Geosciences

The water retention behaviour of soils is an essential aspect of understanding the unsaturated
behaviour of soil materials. This paper looks at a relatively new method of measurement for soil water reten-
tion curves, using high capacity tensiometers. New equipment for carrying out continuous measurements of
water content, suction  and volume change is  described. The results are compared with traditional pressure
plate measurements, as well as filter paper and chilled mirror hygrometer tests. It has been suggested that ten-
siometer measurements and pressure plate data give different results. This is confirmed by the larger data set
provided here. It is found that the differences between the techniques can be explained by different volumetric
responses.

The development of cracking as a result of desiccation is increasingly under investigation. This work is set within the context of climate change effects on surface processes influencing infrastructure slope stability. The inherent changes to the mechanical and hydrological behaviour of clayey soils subjected to desiccation are significant. The preferential transmission of water due to cracking is widely cited as a source of strength reduction that leads to infrastructure slope failure. In order to gain a better understanding of the cracking mechanism in typical compacted fill conditions, finite difference continuum modelling has been undertaken using FLAC 2D. The two-phase flow add-on has enabled the unsaturated behaviour of the desiccating soil to be included within the mesh. Physical behaviour observed in laboratory experiments has informed the development of the numerical model by allowing better constraint of boundary conditions. Model development has featured the inclusion of ...

The near surface properties of engineered fill have a significant impact on its engineering behaviour. A common way in which soil will change is through cracking due to the effects of desiccation, vegetation and climate. This has an impact on soil mass permeability, strength and stiffness and hence slope failure susceptibility. Knowledge of the tensile strength and degree of saturation relationship is essential to understand the development of desiccation cracking. This paper presents a study to establish the cyclic rela-tionship between tensile strength and soil water content in a re-moulded glacial till. Testing was conducted using a direct tensile strength test modification to standard direct shear apparatus. As with the soil-water re-tention, the relationship between soil water content and tensile strength shows hysteretic characteristics. Fur-thermore, this relationship was found to develop upon repeated drying and re-wetting cycles. This has impli-cations for the degradation o...

The development of cracking as a result of desiccation and the apparent increase in permeability of cracked fill is increasingly under investigation. Rainfall infiltration into soil surfaces that experience cracking increases due to the additional, preferential transmission of water. This in turn results in cycles of rapidly elevated pore water pressure and is widely cited as a significant mechanism for strength reduction that leads to embankment failure. A two-phase flow numerical model that allows the partially saturated behaviour of the desiccated medium to be captured is presented based on the finite difference code FLAC 2D. The material properties of the developed model, including soil stiffness and strength, are incorporated as a function of drying. The model has allowed investigation into the factors influencing the incidence and scale of cracking. RÉSUMÉ : L'infiltration des précipitations dans les sols sensibles à la dessiccation augmente comme résultat de la transmissi...

The cost of materials is one of the biggest barriers for wastewater driven microbial fuel cells (MFCs). Many studies use expensive materials with idealistic wastes. Realistically the choice of an ion selective membrane or nonspecific separators must be made in the context of the cost and performance of materials available. Fourteen membranes and separators were characterized for durability, oxygen diffusion and ionic resistance to enable informed membrane selection for reactor tests. Subsequently MFCs were operated in a cost efficient reactor design using Nafion, ethylene tetrafluoroethylene (ETFE) or polyvinylidene fluoride (PVDF) membranes, a nonspecific separator (Rhinohide), and a no-membrane design with a carbon-paper internal gas diffusion cathode. Peak power densities during polarisation, from MFCs using no-membrane, Nafion and ETFE, reached 67, 61 and 59 mWm-2, and coulombic efficiencies of 68±11%, 71±12% and 92±6%, respectively. Under 1000Ω, Nafion and ETFE achieved an aver...

ABSTRACT Thousands of Neolithic and Bronze Age open-air rock art panels exist across the countryside in northern England. However, desecration, pollution, and other factors are threatening the survival of these iconic stone monuments. Evidence suggest that rates of panel deterioration may be increasing, although it is not clear whether this is due to local factors or wider environmental influences accelerated by environmental change. To examine this question, 18 rock art panels with varied art motifs were studied at two major panel locations at Lordenshaw and Weetwood Moor in Northumberland. A condition assessment tool was used to first quantify the level of deterioration of each panel (called “staging”). Stage estimates then were compared statistically with 27 geochemical and physical descriptors of local environments, such as soil moisture, salinity, pH, lichen coverage, soil anions and cation levels, and panel orientation, slope, and standing height. In parallel, climate modelling was performed using UKCP09 to assess how projected climatic conditions (to 2099) might affect the environmental descriptors most correlated with elevated stone deterioration. Only two descriptors significantly correlated (P < 0.05) with increased stage: the standing height of the panel and the exchangeable cation content of the local soils, although moisture conditions also were potentially influential at some panels. Climate modelling predicts warming temperatures, more seasonally variable precipitation, and increased wind speeds, which hint stone deterioration could accelerate in the future due to increased physiochemical weathering. We recommend key panels be targeted for immediate management intervention, focusing on reducing wind exposures, improving site drainage, and potentially immobilizing soil salts.

Effective domestic wastewater treatment is among our primary defenses against the dissemination of infectious waterborne disease. However, reducing the amount of energy used in treatment processes has become essential for the future. One low-energy treatment option is anaerobic-aerobic sequence (AAS) bioreactors, which use an anaerobic pretreatment step (e.g., anaerobic hybrid reactors) to reduce carbon levels, followed by some form of aerobic treatment. Although AAS is common in warm climates, it is not known how its compares to other treatment options relative to disease transmission, including its influence on antibiotic resistance (AR) in treated effluents. Here, we used metagenomic approaches to contrast the fate of antibiotic-resistant genes (ARG) in anaerobic, aerobic, and AAS bioreactors treating domestic wastewater. Five reactor configurations were monitored for 6 months, and treatment performance, energy use, and ARG abundance and diversity were compared in influents and e...

Insect pollinators provide a crucial ecosystem service, but are under threat. Urban areas could be important for pollinators, though their value relative to other habitats is poorly known. We compared pollinator communities using quantified flower-visitation networks in 36 sites (each 1 km2) in three landscapes: urban, farmland and nature reserves. Overall, flower-visitor abundance and species richness did not differ significantly between the three landscape types. Bee abundance did not differ between landscapes, but bee species richness was higher in urban areas than farmland. Hoverfly abundance was higher in farmland and nature reserves than urban sites, but species richness did not differ significantly. While urban pollinator assemblages were more homogeneous across space than those in farmland or nature reserves, there was no significant difference in the numbers of rarer species between the three landscapes. Network-level specialization was higher in farmland than urban sites. Relative to other habitats, urban visitors foraged from a greater number of plant species (higher generality) but also visited a lower proportion of available plant species (higher specialization), both possibly driven by higher urban plant richness. Urban areas are growing, and improving their value for pollinators should be part of any national strategy to conserve and restore pollinators.

ABSTRACT Background/Question/Methods Cities are novel ecosystems characterized by fragmented and disturbed environments, high densities of fabricated structures and impervious surfaces, and elevated levels of certain resources. Globally, these commonalities, in combination with human mediated biotic interchange, may result in the homogenization of species composition among cities. In addition, cities are often located in species rich regions where native species are threatened by habitat loss and species introductions. Given the World’s urban population is growing 1% per-annum on average, a better understanding of the global patterns and drivers of urban biodiversity is necessary for sustainable planning and conservation. We compiled city-wide bird species lists for 54 cities and city-wide floras of spontaneously established vascular plants for 110 cities. The lists encompass 36 countries on six continents and represents the largest compilation of urban biodiversity data to date. We examined patterns of species diversity within and among cities and their environmental and anthropogenic correlates. Results/Conclusions Bird and plant species richness (median: birds = 112.5, plants = 762) and the number of non-native species (median: birds = 3.5, plants = 213) differed broadly among cities with cities containing, on average, more native species. The number of species in each city was predicted primarily by the physical features of the city related to population size and land-cover, with the species-area relationship playing a dominant role. The proportion of non-native plants in each city was predicted by multiple factors suggesting their prevalence was not determined exclusively by human activities. Globally, the compositions of plant and bird species were highly dissimilar among cities. Within regions, the composition of non-native plants and birds were more similar among cities, particularly within regions outside of Europe. Non-native plants identified as European archaeophytes (introduced into Europe prior to ad 1500) and species of plants and birds identified as global invaders were shared more broadly among cities, particularly within regions outside of Europe. Younger cities further from the equator with close climatic and cultural associations to Europe tended to have more similar compositions of plant species. For birds, compositional patterns did not differ along similar gradients, likely due to the presence of a limited number of identical non-native bird species. Despite worldwide biodiversity loss, cities currently retain their regional biological identities, with Europe playing a historical role as a source of urban adapted species. Urban biodiversity can play an important role supporting conservation, restoration, and education initiatives in a rapidly urbanizing world.