A Comparison of Temporal Patterns in Trace Metal Concentration in Tree Rings of Four Common European Tree Species Adjacent to a Cu-Cd Refinery

Metal processing at a Cu-Cd refinery at Prescot in N.W. England has led to severe contamination of the surrounding soils and vegetation, although Cu and Cd in bulk deposition declined dramatically between 1975 and 1990. Despite high spatial and temporal variability in metal deposition, mean Cd concentrations in annual tree rings of sycamore (Acer pseudoplatanus L.), lime (Tilia europaea L.) and beech (Fagus sylvatica L.) at Prescot were correlated with annual bulk Cd deposition. In contrast, mean Cd concentrations in ash (Fraxinus excelsior L.) were unrelated to Cd deposition and there was no significant relationship between mean Cu concentrations in tree rings and Cu deposition in any species. Mean Pb concentrations in sycamore, lime and beech at Prescot and the reference site also decreased over time. At Prescot however, Cd concentrations in tree rings formed in the mid 1990s were up to 10-fold higher than the reference site despite Cd deposition values during this period that were typical of levels expected for urban areas in the UK. The high Cd concentrations in wood during this period indicate that the majority of Cd in tree rings at Prescot is derived from soil, limiting the usefulness of dendrochemistry for monitoring temporal changes in metal deposition. It appears that trees are not simply passive recorders of metal deposition and other possibilities, in addition to decreasing atmospheric deposition, may explain the patterns of Cd and Pb found in sycamore, lime and beech. More research on the physiology of metal cycling in trees is required before dendrochemical techniques can be applied with confidence in environmental monitoring programs.     

Natural changes in the planktonic rotifera of a small acid lake near Sudbury,Ontario following water quality improvements

Swan Lake is a small, acidic, metal-contaminated lake located near Sudbury, Ontario. During the past 8 yr, the lake has experienced a substantial increase in pH, together with significant reductions in the concentrations of heavy metals and base cations. These changes were observed only after acid and metal emissions from Sudbury area smelters were reduced. The composition of the planktonic Rotifera in the lake has changed concurrent with improvements in water chemistry. Dominance of the rotifer community by the acidophile Keratella taurocephala has been sharply reduced in recent years, while significant increases in the densities of Polyarthra spp., Chromogaster ovalis, Conochiloides natans and Trichocerca similis have been observed.     

Neutralization of acidic raindrops on leaves of agricultural crop and boreal forest species

The abilities of foliage of selected agricultural crop and native boreal forest species to neutralize acidic raindrops were compared. The species differed widely in their responses. Neutralization was influenced to a large extent by leaf wettability and was poorly related with species' susceptibility to foliar injury from acid rain sprayings. Little neutralization of pH 3.0 droplets occurred on very waxy leaves, e.g. cabbage (Brassica oleracea L.), due to the small contact area between the leaf surface and raindrops. In contrast, on sunflower (Helianthus annuus L.) and radish (Raphanus sativus L.) leaves, which are pubescent and easily wettable, neutralization was considerable. For all agricultural crop species examined, the pH of droplets drying on cotyledons was consistently higher than on the leaves. The pH values of raindrops were also higher when the foliage was injured by the acid rain, probably due to leakage of cellular contents. Among boreal forest species examined, bunchberry (Cornus canadensis L.) was particularly good at neutralizing natural acid rain, increasing the pH from 3.9 to 6.6 after 9 hr of foliar contact, while the response of other boreal species ranged from a final pH of 4.8 to 5.7 under the same conditions. Simulated raindrops on wild sarsaparilla (Aralia nudicaulis L.) were never neutralized but increased in acidity as they evaporated. Chemical analyses of droplets collected from foliage showed calcium (Ca) and potassium (K) to he the major cations entering the neutralized droplets. Neutralization of acidic raindrops appears to occur through two processes: solubilization of alkaline dusts and exudates on the leaf surface, and ion exchange removal of H⁺ by the foliage.     

Impact of heavy metals on the degradative capabilities of soil bacterial communities

The degradative capabilities of six heavy-metal-affected and six unaffected bacterial communities from Canadian and German soils were determined by enumerating colony-forming units on 20 specific media. Each of these contained an aromatic substrate as the sole source of C and energy. Comparisons of plate counts revealed that heavy metal stress caused a decrease in the eveness of the distribution of the 20 degradative capabilities This suggests that in heavy-metal-affected bacterial communities, relatively rare degradative capabilities, irrespective of their nature, are even rarer than in unaffected communities, while the reverse is true for more common capabilities. The results are discussed with respect to the ease with which aromatic substrates can serve as C and energy sources.     

Effects of nickel addition on nitrogen mineralization,nitrification, and nitrogen leaching in some boreal forest soils

The effects of Ni additions on nitrification, N mineralization, and N leaching were examined in soils from boreal jack pine (Pinus banksiana Lamb.) forests. The results of a series of incubation experiments suggested that under certain conditions, Ni at 100 μg g^?1 soil can stimulate nitrification, and at 500 μg g^?1 can stimulate N mineralization. Nitrification rates were very low overall, but were higher in soils from the vicinity of the Sudbury, Ontario Ni-Cu smelters than in uncontaminated soils. The nitrifier populations, estimated by the most probable number method, were extremely low in uncontaminated soils, but also increased following some Ni additions. Increased leaching of NO_f3 ^p was observed in soil columns treated with Ni. Since N tends to be in low supply in boreal forests, and therefore tightly cycled, the observed disruptions caused by Ni inputs could have an effect on forest productivity.     

Root distribution under seepage-irrigated potatoes in Northeast Florida

Much of commercial potato production in Florida is irrigated using sub-surface seepage irrigation. A perched water table is maintained during the season within 50 cm below the top of the potato ridge. Fertilizer placement is critical in this system to maximize plant uptake and to minimize leaching potential. Optimal placement of fertilizers is dependent on root distribution. The objectives of this study were to develop and test a new methodology to spatially describe potato root distribution as affected by nitrogen rate and irrigation system. Soil slices containing representative samples of the potato root system at full flowering were taken from plots fertilized with ammonium nitrate at 168, 224, and 280 kg N ha^?1. The proposed sampling methodology performed satisfactorily. Root length density (cm root cm^?3 soil) and specific root length (cm root mg^?1 root dry weight) were not affected by nitrogen rate, but were affected by spatial position in the soil profile. The highest root length density value (0.72 average) was observed within 12 to 15 cm of the seedpiece. Low root length density values averaging 0.036 were observed between 24 and 36 cm from the top of the ridge. Specific root length values indicated a relatively homogeneous root system in terms of the quantity of invested biomass by unit of root length except in the two central units below 24 cm from the top of the ridge where thickened roots caused significant lower values averaging 6.47 as compared with the average of 15.87 from the surrounding Units in the slice. Root thickening in deep apical roots suggested aerenchyma formation promoted by a combination of saturated soil conditions in the root zone caused by inappropriate irrigation management and soil compaction. Fertilizer placement under the seedpiece should be a good alternative to increase potato nitrogen uptake under seepage irrigation.     

The prevalence, organ distribution and fertility of cystic echinoccosis in feral pigs in tropical North Queensland, Australia

An investigation was carried out to study the prevalence of Echinococcus granulosus hydatidosis in feral pigs (Sus domesticus) in the Charters Towers region of tropical North Queensland. Data were collected from a total of 238 carcasses, which were hunted and shot in the Burdekin River catchment area. Organs of the abdominal, thoracic, and pelvic cavities were examined for the presence of hydatid cysts. In the laboratory, cysts and hydatid cyst fluids were examined under a stereoscopic binocular microscope and a compound microscope. An overall prevalence of E. granulosus hydatid cysts in feral pigs was found to be 31.1%. There was no significant difference in either sex or age between infected and non-infected feral pigs. The predilection sites of cysts were livers (23%) and lungs (62%), with more cysts in lungs (252) than livers (48). The ratio of livers to lungs infected with fertile cysts was 1:4 compared to 1:8 sterile cysts. The overall fertility of cysts was 70.1%. The percentage of fertile cysts in liver and lung was 79.2% and 68.7%, respectively. The diameter of fertile cysts ranged from 15 to over 60 mm. There was no significant difference in size between fertile and non-fertile cysts in lungs. The high prevalence rate and fertility of cysts in feral pigs confirm that feral pigs can take part in the sylvatic cycle of the parasite in the region. The public health significance of this observation is potentially very important.     

Lead contamination around secondary smelters: estimation of dispersal and accumulation by humans

A high rate of lead fallout around two secondary lead smelters originated mainly from episodal large-particulate emissions from low-level fugitive sources rather than from stack fumes. The lead content of dustfall, and consequently of soil, vegetation, and outdoor dust, decreased exponentially with distance from the two smelters. Between 13 and 30 percent of the children living in the contaminated areas had absorbed excessive amounts of lead (more than 40 micrograms per 100 milliliters of blood and more than 100 micrograms per gram of hair) as compared with less than 1 percent in a control group. A relationship between blood and hair was established which indicated that the absorption was fairly constant for most children examined. It seemned that the ingestion of contaminated dirt and dusts rather than "paint pica" was the major route of lead intake. Metabolic changes were found in most of 21 children selected from those with excessive lead absorption; 10 to 15 percent of this group showed subtle neurological dysfunctions and minor psychomotor abnormalities.     

Quantum cascade laser

A semiconductor injection laser that differs in a fundamental way from diode lasers has been demonstrated. It is built out of quantum semiconductor structures that were grown by molecular beam epitaxy and designed by band structure engineering. Electrons streaming down a potential staircase sequentially emit photons at the steps. The steps consist of coupled quantum wells in which population inversion between discrete conduction band excited states is achieved by control of tunneling. A strong narrowing of the emission spectrum, above threshold, provides direct evidence of laser action at a wavelength of 4.2 micrometers with peak powers in excess of 8 milliwatts in pulsed operation. In quantum cascade lasers, the wavelength, entirely determined by quantum confinement, can be tailored from the mid-infrared to the submillimeter wave region in the same heterostructure material.     

Interactions between elevated atmospheric CO2 and defoliation on North American rangeland plant species at low and high N availability

Although common disturbances of grazing lands like plant defoliation are expected to affect their sensitivity to increasing atmospheric CO₂ concentration, almost no research has been conducted to evaluate how important such effects might be on the direct responses of rangelands to CO₂. This growth chamber experiment subjected intact plant–soil cylinders from a Wyoming, USA, prairie to a 3‐way factorial of CO₂ (370 vs. 720 μL L^?1), defoliation (non‐clipped vs. clipped) and soil nitrogen (control vs. 10 g m^?2 added N) under simulated natural climatic conditions. Above‐ and below‐ground biomass and N dynamics of the functional groups C₃ grasses, C₄ grasses and forbs were investigated. CO₂ and defoliation had independent influences on biomass and N parameters of these rangeland plants. Growth under CO₂‐enriched conditions enhanced above‐ground biomass 50% in C₃ grasses alone, while shoot N concentration declined 16% in both C₃ and C₄ grasses. Plant‐soil ¹⁵N uptake was unaffected by CO₂ treatment. In contrast, defoliation had no effect on biomass, but increased tissue N concentration 29% across all functional groups. Without additional N, forage quality, which is in direct relation to N concentration, will decline under increasing atmospheric CO₂. Increased dominance of C₃ grasses plus reduced forage quality may necessitate changes in grazing management practices in mixed‐species rangelands.