Contribution of canopy leaching to sulphate deposition in a Scots pine forest

Radioactive sulphate (35SO4) was applied to the soil below a Scots pine forest on 23 June 1989, and its movement into the canopy and into throughfall and stemflow was measured over 4 months. The specific activity, Bq (mg S)(-1), of the canopy increased monotonically; uptake by current-year (1989) expanding needles was initially twice as fast as by older needles or live twigs. By 10 October the canopy average specific activity was 62 Bq (mg S)(-1). The specific activity of net throughfall (throughfall + stemflow - rain), deduced from measurements from six throughfall collectors, six stemflow collectors and two rain collectors, fell rapidly from 12.6 Bq (mg S)(-1) in late July to <1 Bq (mg S)(-1) in mid-August. The results suggest (assuming rapid equilibration of 35S with sulphate in soil) that root-derived sulphate contributed c. 3% of sulphate in net throughfall and that dry deposition of SO2 and sulphate particles contributed c. 97% of the 0.56 g S m(-2) measured in net throughfall over the period. Simultaneous measurements of SO2 at canopy height and of NH3 above and within the canopy gave mean concentrations of 5.9 and 0.86 microg m(-3), respectively, sufficient to account for the sulphate measured in net throughfall only if codeposition of NH3 and SO2 occurred to canopy surfaces. The large values of specific activity observed in July, however, indicate that throughfall composition may be closely related to recent soil input of sulphate, and that equilibrium cannot be safely assumed. The possibility of a significant contribution of soil-derived sulphate to sulphate deposition in net throughfall cannot be ruled out on the basis of this experiment.     

Cadmium availability to the cyanobacterium Synechocystis aquatilis in solutions containing chloride

Availability of cadmium to Synechocystis aquatilis (estimated by 109Cd sorption and cadmium toxicity-14C method) in solutions containing cadmium and complexing (KCl) or non-complexing (KNO3) salts, in the range of 0-0.5 m was investigated. Both cadmium surface adsorption and transport into the cells were lower in solutions containing cadmium chloride complexes (CdCl+, CdCl2, CdCl3-) than in those containing cadmium in the form of Cd2+. Also, cadmium toxicity in solutions of higher KCl concentrations, in which CdCl+ and CdCl2 forms predominated, was significantly limited.     

An introduction to critical loads

The critical loads approach to emission controls of gaseous pollutants is a concept with a short but eventful history. Despite difficulties with definitions and agreed values, its acceptance within the UN-ECE Convention on Long Range Transboundary Air Pollution has provided the impetus for developing methods to put critical loads to a practical use-the revision of the UNECE emission protocols for sulphur and nitrogen. Methodologies first focus upon quantifying a pollutant threshold at which harmful effects occur on particular sensitive receptors (usually biological species). This threshold is known as the critical load for deposited pollutants, and as the critical level for gaseous pollutants acting on receptors. To calculate a critical load, biological effects are usually 'translated' to critical chemical values, e.g. harmful effects on fish 'translate' to alkalinity or aluminium concentrations in water; thus, critical load calculations may be based upon the chemistry of a system. Such calculations may be performed using simple, steady-state models, whilst the use of more complex, dynamic models provides an insight into the past and future trends. Maps of critical loads can be drawn using calculated values, and maps of pollutant deposition data will then show geographical areas where critical loads are exceeded. Spatial emission-deposition models can identify sources contributing to areas of excess loads and quantify necessary emission reductions. Optimization procedures applied to such models can derive abatement strategies related to economic costs and critical load effects. The critical load calculations may also be used to underpin the setting of target loads; these are pollutant loads, determined by political agreement, which take account of social, economic and political considerations.     

Seasonal trend of fog water chemical composition in the Po Valley

Fog frequency in the Po Valley, Northern Italy, can be as high as 30% of the time in the fall-winter season. High pollutant concentrations have been measured in fog water samples collected in this area over the past few years. The combined effects of high fog occurrence and high pollutant loading of the fog droplets can determine, in this area, appreciable chemical deposition rates. An automated station for fog water collection was developed, and deployed at the field station of S. Pietro Capofiume, in the eastern part of the Po Valley for an extended period: from the beginning of November 1989 to the end of April 1990. Time-resolved sampling of fog droplets was carried out during all fog events occurring in this period, and chemical analyses were performed on the collected samples. Statistical information on fog occurrence and fog water chemical composition is reported in this paper, and a tentative seasonal deposition budget is calculated for H+, NH4+, NO3- and SO4(2-) ions. The problems connected with fog droplet sampling in sub-freezing conditions are also addressed in the paper.     

Responses of microbial populations in the rhizosphere to deposition of simulated acidic rain onto foliage and/or soil

Air pollutants or some chemicals applied to plant foliage can alter the ecology of the rhizosphere. Experiments were conducted to distinguish among possible foliage-mediated versus soil- or root-mediated effects of acid deposition on microorganism in the rhizosphere. Seedlings of a sorghum x sudangrass hybrid in pots of non-sterile soil-sand mix in a greenhouse were exposed to simulated rain solution adjusted with H2SO4 + HNO3 to pH 4.9, 4.2, 3.5 or 2.8. Solutions were applied as simulated rain to foliage and soil, foliage only (soil covered by plastic, and deionized water applied directly to the soil), or soil only (solution applied directly to the soil). Solutions were applied on 16 days during a 6-week period (1.5 cm deposition in 1 h per application). Plant shoot and root dry weights and population densities of selected types of bacteria, filamentous actinomycetes and fungi in the rhizosphere were quantified after exposures were completed. Deposition of simulated acidic rain onto foliage alone had no effect on plant biomass or microbial population densities in the rhizosphere (colony-forming units per gram of rhizosphere soil). However, plant growth was stimulated and all microbial populations in the rhizosphere increased 3- to 8-fold with increased solution acidity (relative to pH 4.9 solution) when solution penetrated the soil. Statistical analyses indicated that the acid dose-population response relationships for soil-only and foliage-and-soil applications were not different. Thus, no foliage-mediated effect of simulated acidic rain on rhizosphere ecology was detected.     

Effects of atmospheric ammonia and ammonium sulphate on Douglas fir (Pseudotsuga menziesii)

Three-year-old Douglas firs (Pseudotsuga menziesii) were fumigated with 180 microg m(-3) NH3 or clean (charcoal-filtered) air. During these fumigations the plants received 15 mm artificial rain weekly, supplemented with 20, 500 or 2500 micromol litre(-1) (NH4)2SO4. Exposure to NH3 and NH4+ for 14 weeks resulted in a change of the nutrient status of the needles. The most remarkable effect was the increase in the N/K ratio, due to both uptake of N and leaching of K. The action of NH3 was stronger than that of NH4+. Both NH3 and (NH4)2SO4 affected the epicuticular wax layer and decreased mycorhiza frequency. Following fumigation and artificial rain treatments, needles were incubated for 8 h in a medium containing 0, 50, 250, 500 and 2500 micromol litre(-1) (NH4)2SO4. Almost no exchange of Ca, Mg and K for NH4+ was found. Therefore this ion exchange probably explains only a minor part of the changes in nutrient status of the whole trees.     

Real-world vehicle emissions: a summary of the tenth coordinating research council on-road vehicle emissions workshop

The Coordinating Research Council (CRC) held its tenth workshop in March 2000, focusing on results from the most recent real-world vehicle emissions research. In this paper, we summarize the presentations from researchers who are engaged in improving our understanding of the contribution of mobile sources to emission inventories. Participants in the workshop discussed efforts to improve mobile source emission models and emission inventories, results from gas- and particle-phase emissions studies from spark-ignition and diesel-powered vehicles, new methods for measuring mobile source emissions, improvements in vehicle emission control systems (ECSs), and evaluation of motor vehicle inspection/maintenance (I/M) programs, as well as topics for future research.     

Effects of thiobencarb herbicide to an alga (Nannochloris oculata) and the cladoceran (Daphnia magna)

Chronic toxicity studies were conducted with an algae (Nannochloris oculata) and the cladoceran (Daphnia magna) to determine their relative sensitivities to the thiocarbamate herbicide thiobencarb (S-4-chlorobenzyl diethylthiocarbamate). Most of the algal populations were initially affected by exposure to the herbicide. Thiobencarb concentrations higher than 0.5 mg/L significantly reduced algal densities after 24-h exposure. The 24-h static EC50 in D. magna was 3.01 mg/L. The sublethal effects of 0.3, 0.37, 0.5, 0.75, and 1.5 mg/L of thiobencarb concentrations on the survival, reproduction, and growth of D. magna were monitored for 21 days. The parameters used to determined the effect of the herbicide on D. magna were mean total young per female; mean brood size; days to first brood; intrinsic rate of natural increase (r); growth; and survival. Reproduction was significantly reduced at thiobencarb concentrations of 0.30 mg/L and higher while survival was affected after exposure to 0.75 and 1.5 mg/L of the pesticide. The r value decreased with increasing concentrations of thiobencarb. Growth, as measured by body length, was depressed significantly after exposure to all herbicide concentrations tested.     

The effects of crude oil and the effectiveness of cleaner application following oiling on US Gulf of Mexico coastal marsh plants

Field studies were conducted in two different marsh habitats in Louisiana coastal wetlands to evaluate the effects of oiling (using South Louisiana Crude oil, SLC) and the effectiveness of a shoreline cleaner (COREXIT 9580) in removing oil from plant canopies. The study sites represented two major marsh habitats; the brackish marsh site was covered by Spartina patens and the freshwater marsh was covered by Sagittaria lancifolia. Field studies were conducted in each habitat using replicated 5.8 m2 plots that were subjected to three treatments; oiled only, oiled + cleaner (cleaner was used 2 days after oiling), and a control. Plant gas exchange responses, survival, growth, and biomass accumulation were measured. Results indicated that oiling led to rapid reductions in leaf gas exchange rates in both species. However, both species in 'oiled + cleaned' plots displayed improved leaf conductance and CO2 fixation rates. Twelve weeks after treatment initiation, photosynthetic carbon fixation in both species had recovered to normal levels. Over the short-term, S. patens showed more sensitivity to oiling with SLC than S. lancifolia as was evident from the data of the number of live shoots and above-ground biomass. Above-ground biomass remained significantly lower than control in S. patens under 'oiled' and 'oiled + cleaned' treatments while it was comparable to controls in S. lancifolia. These studies indicated that the cleaner removed oil from marsh grasses and alleviated the short-term impact of oil on gas exchange function of the study plants. However, use of cleaner had no detectable effects on above-ground biomass production or regeneration at the end of the first growing season in S. patens. Similarly, no beneficial effects of cleaner on carbon fixation and number of live shoots were apparent beyond 12 weeks in S. lancifolia.     

Biosurfactant-enhanced solubilization of NAPL mixtures

Remediation of nonaqueous phase liquids (NAPLs) by conventional pump-and-treat methods (i.e., water flushing) is generally considered to be ineffective due to low water solubilities of NAPLs and to mass-transfer constraints. Chemical flushing techniques, such as surfactant flushing, can greatly improve NAPL remediation primarily by increasing the apparent solubility of NAPL contaminants. NAPLs at hazardous waste sites are often complex mixtures. However, the equilibrium and nonequilibrium mass-transfer characteristics between NAPL mixtures and aqueous surfactant solutions are not well understood. This research investigates the equilibrium solubilization behavior of two- and three-component NAPL mixtures (containing akylbenzenes) in biosurfactant solutions. NAPL solubilization is found to be ideal in water (i.e., obeys Raoult's Law), while solubilization in biosurfactant solutions was observed to be nonideal. Specifically, the relatively hydrophobic compounds in the mixture experienced solubility enhancements that were greater than those predicted by ideal enhanced solubilization theory, while the solubility enhancements for the relatively hydrophilic compounds were less than predicted. The degree of nonideality is shown to be a nonlinear function of the NAPL-phase mole fraction. Empirical relationships based on the NAPL-phase mole fraction and/or micelle-aqueous partition coefficients measured in single-component NAPL systems are developed to estimate values for the multicomponent partition coefficients. Empirical relationships that incorporate both the NAPL-phase mole fraction and single-component partition coefficients yield much improved estimates for the multicomponent partition coefficient.