Assessment of enrichment,geo-accumulation and ecological risk of heavy metals in surface sediments of the Msimbazi mangrove ecosystem,coast of Dar es Salaam,Tanzania

Results of the assessment of enrichment, accumulation and the ecological risk associated with three heavy metals (Cd, Cu and Pb) and one metalloid (As) in surface sediments of Msimbazi estuary are presented. Surface sediment samples (0–5 cm) were collected from Msimbazi River estuary in September 2016 using handheld PVC short corers. Long-sediment cores from the site were also collected using PVC pipes and their vertical profiles of metals concentrations assessed with the aim of establishing site-specific baseline metals concentrations. The established site-specific baseline values were used for the determination of normalised enrichment factors (EF) and geoaccumulation (Igeo) of metals instead of using average crustal values. Iron-based enrichment factors show that the sediments of Msimbazi have experienced enrichment of metals that originate from anthropogenic sources of pollution (EF > 1). Geo-accumulation results indicate that Msimbazi sediments can be designated as uncontaminated to moderately-contaminated with As, Cd and Pb (class 1–2). Geoaccumulation indices for Cu indicate that sediment can be designated as uncontaminated to moderately contaminated (class 1) and moderately to strongly contaminated (class 3). Results show further that the Ecological Risk associated with the accumulation of these metals in Msimbazi sediments was low based on Hakanson approach.     

Ozone uptake (flux) as it relates to ozone-induced foliar symptoms of Prunus serotina and Populus maximowiziixtrichocarpa

Field studies were conducted during 2003 and 2004 from early June to the end of August, at 20 sites of lower or higher elevation within north-central Pennsylvania, using seedlings of black cherry (Prunus serotina, Ehrh.) and ramets of hybrid poplar (Populus maximowiziixtrichocarpa). A linear model was developed to estimate the influence of local environmental conditions on stomatal conductance. The most significant factors explaining stomatal variance were tree species, air temperature, leaf vapor pressure deficit, elevation, and time of day. Overall, environmental factors explained less than 35% of the variation in stomatal conductance. Ozone did not affect gas exchange rates in either poplar or cherry. Ozone-induced foliar injury was positively correlated with cumulative ozone exposures, expressed as SUM40. Overall, the amount of foliar injury was better correlated to a flux-based approach rather than to an exposure-based approach. More severe foliar injuries were observed on plants growing at higher elevations.     

The ‘new’ economics of iron and steel

The author commences his analysis of the iron and steel industry by examining the historical background of the industry, and discusses its importance for the world economy. He examines the implications for the world industry of the successful development of the steel industry in Japan, and traces the evolution of a commodity cartel in the iron ore market, analysing the price levels of the commodity in the ‘free’ and ‘controlled’ markets. Following a discussion of the role of energy and coking coal supplies in the industry, the author examines the evolution of this industry in the less developed countries, with particular reference to the role of technology in the industry's development. He concludes that there have been important structural changes in the world industry, embraced by the concept of ‘partial demise’.     

Response of native plants of northeastern United States and southern Spain to ozone exposures; determining exposure/response relationships

Tropospheric ozone has been identified as the most important regional scale air pollutant across much of eastern United States of America and many areas of Mediterranean climes in southern Europe. Recent field surveys in the northeastern USA and in southeastern Spain have revealed many additional plant species that exhibit symptoms typical of ozone-induced injuries. Objectives of this study were to confirm ozone as the cause of the observed foliar symptoms, determine ozone induced exposure/response relationships, and identify possible bio-indicator species. Thirteen native species of northeastern USA and 27 native species of southeastern Spain were selected for study. Plant species were exposed to ozone within 16 CSTR chambers in a greenhouse during the summer seasons of 2000 and 2001; ozone exposures of 30, 60, 90, and 120 ppb were delivered for 7 h/day, 5 days/week. Results have confirmed that with few exceptions, symptoms observed in the field were induced by exposures to ambient ozone. Species differed significantly in terms of the exposures required for the initiation of visible symptoms and subsequent injury progression.     

Physiological and foliar symptom response in the crowns of Prunus serotina, Fraxinus americana and Acer rubrum canopy trees to ambient ozone under forest conditions

The crowns of five canopy dominant black cherry (Prunus serotina Ehrh.), five white ash (Fraxinus americana L.), and six red maple (Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0-5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake (U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential (psi(L)) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor (g(wv)) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity (P(n)), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions (P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between g(wv) and P(n) demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.