Andrew D. Thomas

The role of soil moisture in controlling water repellency : new evidence from forest soils in Portugal

Water repellency (hydrophobicity) is known to be temporally variable. Most studies indicate that soils are most repellent when dry and least repellent or non-repellent (hydrophilic) when moist. In several studies, attempts have been made to establish a critical soil moisture threshold, demarcating water-repellent and non-repellent conditions. The reported thresholds vary widely and the exact relationship between hydrophobicity and soil moisture remains far from being understood. Using field and laboratory measurements, this study explores the effect of soil moisture on water repellency for Portuguese sandy loam and loamy sand forest soils. The results indicate that for these soils, repellency is absent when soil moisture exceeds 28%, but show that after wetting, repellency is not necessarily re-established when soils become dry again. It is thought that short-term and seasonal changes in soil water repellency are not simply a function of variations in soil moisture as indicated in the literature. It is suggested that, after wetting, re-establishment of repellency may also require a fresh input of water-repellent substances. The mechanisms of wetting and drying in water-repellent soils are discussed and associated hydrological implications are explored.

Nutrient losses in eroded sediment after fire in eucalyptus and pine forests in the wet Mediterranean environment of northern Portugal

Nutrients sorbed onto eroded sediment from small bounded plots installed in newly burned and unburned Eucalyptus globulus and Pinus pinaster forests in the Agueda Basin, north-central Portugal were measured over an 18-month period. The data are used to determine: (i) the effects of fire on nutrient loss, (ii) the importance of fire-induced losses on soil fertility, and (iii) temporal variations in nutrient losses. Fire increased losses of total nitrogen, exchangeable potassium and available phosphorus by 3–4 orders of magnitude. This is attributed to increased erosion and high nutrient concentrations at the soil surface in the burned forests, where burning of organic matter and vegetation increased nutrient availability. Enhanced rates of loss were sustained for at least 3 years, resulting in much greater post-fire nutrient losses than reported in drier regions of the Mediterranean. Losses of available P had the greatest potential for reductions in soil fertility.

Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana

Biological soil crusts (BSCs) are an important source of organic carbon, and affect a range of ecosystem functions in arid and semiarid environments. Yet the impact of grazing disturbance on crust properties and soil CO2 efflux remain poorly studied, particularly in African ecosystems. The effects of burial under wind-blown sand, disaggregation and removal of BSCs on seasonal variations in soil CO2 efflux, soil organic carbon, chlorophyll a and scytonemin were investigated at two sites in the Kalahari of southern Botswana. Field experiments were employed to isolate CO2 efflux originating from BSCs in order to estimate the C exchange within the crust. Organic carbon was not evenly distributed through the soil profile but concentrated in the BSC. Soil CO2 efflux was higher in Kalahari Sand than in calcrete soils, but rates varied significantly with seasonal changes in moisture and temperature. BSCs at both sites were a small net sink of C to the soil. Soil CO2 efflux was significantly higher in sand soils where the BSC was removed, and on calcrete where the BSC was buried under sand. The BSC removal and burial under sand also significantly reduced chlorophyll a, organic carbon and scytonemin. Disaggregation of the soil crust, however, led to increases in chlorophyll a and organic carbon. The data confirm the importance of BSCs for C cycling in drylands and indicate intensive grazing, which destroys BSCs through trampling and burial, will adversely affect C sequestration and storage. Managed grazing, where soil surfaces are only lightly disturbed, would help maintain a positive carbon balance in African drylands.

Post-fire forestry management and nutrient losses in eucalyptus and pine plantations, Northern Portugal

The impact of different logging techniques on nutrient losses in burnt eucalyptus and pine forests in northern Portugal was investigated. A variety of logging techniques is used in the region resulting in varying amounts of slash debris on the slopes. The efficacy of this litter in reducing soil erosion is well established but less is known about the impact on nutrient losses. Small bounded plots were used to examine the impact of varying amounts of slash debris and pine-needle cover on nutrient losses in overland flow and adsorbed to eroded sediment over 19 months during the first two-three years after fire. Nutrient losses in solution and adsorbed to eroded sediment were substantially higher on burnt terrain due to increased erosion and overland flow generation and high nutrient concentrations at the soil surface in the burned forests. Post-fire logging techniques in eucalyptus forests resulting in large amounts of litter debris on the slopes are effective at reducing eroded sediment nutrient losses but less effective at reducing losses in solution. In pine forests, litter is largely ineffective in reducing solute and sediment nutrient losses. However, a covering of pine needles was shown to be highly effective in reducing eroded sediment nutrient losses and to a lesser extent solute losses. Conservational methods of logging are suggested for both eucalyptus and pine forests in the region. In the absence of such measures, the sustainability of short-rotation eucalyptus forestry is questioned in northern Portugal. Copyright

The implications for dust emission modeling of spatial and vertical variations in horizontal dust flux and particle size in the Bodele Depression, Northern Chad

The Bodele Depression has been confirmed as the single largest source of atmospheric mineral dust on Earth. It is a distinctive source because of its large exposure of diatomite and the presence of mega-barchan dunes. Direct measurements of horizontal dust flux and particle size were made to investigate dust emission processes and for comparison with mechanisms of emission assumed in current dust models. More than 50 masts, with traps mounted on each, were located across and downwind of three barchans in 56 km2 study area of the eastern Bodele. The size-distribution of surface material is bi-modal; there are many fine dust modes and a mixed mineralogy with a particle density three times smaller than quartz. Horizontal fluxes (up to 70 m above the playa) of particles, up to 1000 μm in diameter, are produced frequently from the accelerated flow over and around the barchans, even in below-threshold shear conditions on the diatomite playa. Our data on dust sizes do not conform to retrievals of dust size distributions from radiance measurements made in the same area. Dust emission models for the region may need to be revised to account for: saltators in the Bodele, which are a mixture of quartz sand and diatomite flakes; the great spatial and vertical variation in the abundance, mass and density of dust and abraders; and the patterns of surface erodibility. All of these have important local effects on the vertical dust flux and its particle sizes.

Solutes in overland flow following fire in eucalyptus and pine forests, northern Portugal

Small bounded plots were used to investigate dissolved nutrient losses in overland flow in eucalyptus and pine forests in northern Portugal following understorey fires. Losses of NO - 3 -N, PO 3- 4 , Ca 2+ , Mg 2+ and K + were measured over 19 months during the first 2-3 years after fire. Solute losses in overland flow increased after fire in eucalyptus and pine terrain due to the mineralization of litter and vegetation and increased overland flow. The data suggest that (i) elevated losses persist for at least 2 and 3 years at the pine and eucalyptus sites respectively and (ii) soluble losses of PO 3- 4 and K + in a post-fire cycle may exceed those adsorbed to eroded material. Losses of PO 3- 4 , although relatively small, are potentially the most detrimental to soil fertility and forest productivity because of the limited opportunity for P replenishment and correspondingly high P losses adsorbed to eroded sediment.

Barriers to women in the UK construction industry

Purpose – This paper aims to identify the main barriers that lead to the under‐representation of women in the UK construction industry. The study, funded by ConstructionSkills, seeks to explore the issues that women face and investigate the potential positive impact that continuous professional development (CPD) may have upon improving the retention and career progression of women.Design/methodology/approach – The study uses an open‐ended grounded theory (GT) approach, including 231 semi‐structured questionnaires and nine focus groups with women from a range of professional occupations. All the findings were analysed using keyword analysis to identify the top two barriers that women face, alongside a series of cross‐cutting key themes and issues.Findings – The findings reveal that male‐dominated organisational cultures and inflexible working practices are the main barriers to women in the UK construction industry, irrespective of job role or profession. This paper concludes by arguing for a sea‐change in ...

Establishing the sediment stratigraphy of reservoirs in the southern Pennines, UK

Abstract Reservoirs in the southern Pennines have been investigated to determine their potential for reconstructing a history of atmospheric pollution. A selection procedure has been used to identify sites with the best chance of obtaining a usable sedimentary record prior to sample collection. Five reservoirs were selected for core collection and sediment analysis using magnetic susceptibility (χlf), particle size, spheroidal carbonaceous particle (SCP) analysis and radiometric dating. Analysis reveals that largely undisturbed sedimentary records exist in the deepest zones of these reservoirs, thus reservoir sediments represent a valuable resource for investigating pollution histories in the southern Pennines.

Soil fungal abundance and plant functional traits drive fertile island formation in global drylands

Dryland vegetation is characterized by discrete plant patches that accumulate and capture soil resources under their canopies. These “fertile islands” are major drivers of dryland ecosystem structure and functioning, yet we lack an integrated understanding of the factors controlling their magnitude and variability at the global scale. We conducted a standardized field survey across 236 drylands from five continents. At each site, we measured the composition, diversity and cover of perennial plants. Fertile island effects were estimated at each site by comparing composite soil samples obtained under the canopy of the dominant plants and in open areas devoid of perennial vegetation. For each sample, we measured 15 soil variables (functions) associated with carbon, nitrogen and phosphorus cycling and used the relative interaction index to quantify the magnitude of the fertile island effect for each function. In 80 sites, we also measured fungal and bacterial abundance (quantitative PCR) and diversity (Illumina MiSeq). The most fertile islands, i.e. those where a higher number of functions were simultaneously enhanced, were found at lower elevation sites with greater soil pH values and sand content under semiarid climates, particularly at locations where the presence of tall woody species with a low-specific leaf area increased fungal abundance beneath plant canopies, the main direct biotic controller of the fertile island effect in the drylands studied. Positive effects of fungal abundance were particularly associated with greater nutrient contents and microbial activity (soil extracellular enzymes) under plant canopies. Synthesis. Our results show that the formation of fertile islands in global drylands largely depends on: (1) local climatic, topographic and edaphic characteristics, (2) the structure and traits of local plant communities and (3) soil microbial communities. Our study also has broad implications for the management and restoration of dryland ecosystems worldwide, where woody plants are commonly used as nurse plants to enhance the establishment and survival of beneficiary species. Finally, our results suggest that forecasted increases in aridity may enhance the formation of fertile islands in drylands worldwide.

An assessment of the effects of forest reserve management on the livelihoods of forest fringe communities in the Atwima Mponua District of Ghana

ABSTRACT The effect of forest reserve management on the livelihoods of forest communities is an important, yet poorly researched issue. This study examines the effect of management on the livelihoods of communities living near the Tano-Offin forest reserve in the Atwima Mponua District of Ghana. Information was gathered from one hundred and fifty forest fringe community members in Atwima Mponua District using semi-structured questionnaires. In addition, interviews were undertaken with staff from the Forest Services Division at Nkawie, the Atwima Mponua District Assembly, and a Non-Governmental Organization. We found that the communities in the study area have limited livelihood pathways due to restrictions on their access to forest resources. Furthermore, over 70% of respondents had incomes below the international poverty line of US