Nutrient ion exchange was examined between simulated acid rain solutions and northern red oak (Ouercus rubra L.) leaves of trees growing in fertile, limestone-derived soil and less fertile, sandstone/shale-derived soil. Leaves harvested from trees growing on the fertile site had greater concentrations of total N, P, K, Ca, and Mn but less total Mg than leaves of trees on the less fertile site. Cation losses from leaves of both sites were similar when exposed T3 to simulated rain solutions of pH 5.6, 4.3, and 3.0. Simulated rain solutions of pH 3.0 leached the greatest amount of total cations from leaves of both sites. Differences in acidity between leachates and starting rain solutions increased as the acidity of starting solutions contacting leaves of either site increased. Differences in leaf nutrient status between sites typically did not affect leachate acidity. Hydrogen ion exchange, believed to be the main mechanism of cation loss from leaves of both sites, accounted for 30 to 44% of all cations leached from leaves of both sites. Concentrations of inorganic ions were measured in bulk rainfall and bulk throughfall collected beneath northern red oak trees growing on the fertile and less fertile sites. Rainfall passing through crowns at both sites was enriched with S0₄²⁻, P0₄³⁻, Ca²⁺, Mg²⁺, K⁺, Mn²⁺, and Fe²⁺, but lost NH₄⁺ to the crowns. There was little difference in the inorganic chemistry of incident rainfall between sites. Large-particle dryfall ionic concentrations, rainfall volume, and leaf area were all larger at the fertile than at the less fertile site. Higher concentrations of Ca²⁺, Mg²⁺, NH₄⁺, Mn²⁺, and S0₄²⁻in throughfall at the fertile site compared to that of the less fertile site are likely due to the combination of these three factors. Historical northern red oak crown areas were estimated for the fertile and less fertile sites by a two step procedure using annual growth ring chronologies and published regression equations. These equations related total crown area to total crown dry weight. The usefulness of crown area estimates in throughfall studies was demonstrated by applying nutrient ion exchange data, collected beneath northern red oak crowns in 1984, to 1982 and 1930 crown area estimates. Smaller nutrient ion exchange estimates in 1930 were due to smaller crown area estimates. / Ph. D.

No description available.

Depth profiles of S(IV) and S(VI) in snow exposed to 20-140 ppbv SO₂ for 6 to 12 hours have been determined in 48 laboratory experiments. Surface deposition velocity (v(d)) averaged 0.06 cm s⁻¹. Well-metamorphosed snow, longer run times, higher SO₂ concentrations and colder snow were associated with lower values of v(d), and vice versa. Melting followed by draining increased v(d) greatly (0.14 cm s⁻¹. Any effect of ozone on SO₂ v(d) was undetectable. Most sulfur in the snow was as S(VI), even without added ozone, indicating the presence of other oxidants, especially in new snow. Four NO₂ deposition experiments (average v(d) = 0.007 cm s⁻¹), and one combined SO₂-NO₂ deposition experiment were conducted. Ozone, sunlight and SO₂ did not enhance NO₂ deposition; NO₂ and sunlight did not enhance SO₂ deposition. The deposition of SO₂ into a snowpack is modelled as an aqueous system, where the liquid water is considered to be present on snow grain surfaces. Gas transport into the snow, air-water partitioning, and aqueous-phase reactions are explicitly considered. Three oxidants (Fe- or Mn-catalyzed O₂, O₂, and H₂O₂) act to convert S(IV) to S(VI), acidify the film, and inhibit further S(IV) uptake. Model calculations illustrate the primary importance of liquid-water mass fraction (X(m)) and the secondary importance of oxidative reactions on SO₂ v(d) to snow. Model and experimental results are similar for assumed X(m) on the order of one percent. Experiments were also conducted on the incorporation of SO₂ into ice depositing from the vapor at -7 and -15°C. Remarkably, SO₂ is captured in deposited ice at concentrations comparable to Henry's Law equilibrium with water at 0°C. Ozone and HCHO appear to inhibit, not enhance, SO₂ capture. An aqueous-film model accounting for the capture of SO₂ by depositing ice was developed. S(IV) concentrations may be enhanced in the liquid-like layer on growing ice surfaces due to solute exclusion from the bulk ice and greatly-retarded diffusional transport from the ice/film interface, leading to significant incorporation into the ice despite low distribution coefficients. SO₂ snow scavenging ratios may be comparable to sulfate scavenging ratios in the remote troposphere.

No description available.

No description available.

No description available.

No description available.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand Johannesburg for the degree of Master of Science. Johannesburg, 1992. / Acidified rain is thought to have the potential to affect the ability of plants to acquire nutrients. The effects of artificially acidified rain on calcium (Ca) and magnesium (Mg) uptake by Pinus patula were investigated in terms of changes in the Ca and Mg-levels in the soil and changes in root growth and mycorrhizal coloniZation that might result from exposure to acidified precipitation. The uptake of these ions was also investigated in order to determine the possible effects of acid rain on the uptake process [Abbreviated Abstract. Open document to view full version] / AC2017

This thesis reports an investigation into methods of determining the long term deposition field for atmospheric aerosols in areas of complex topography using the soil inventories of atmospherically derived radionuclides. Measurements of the radionuclides ²¹⁰Pb, ¹³⁷Cs, ¹³⁴Cs and ⁷Be in vegetation and soil have been made at five mountain locations in northern Britain. A description of the field sampling procedure, sample processing and y-ray analysis is given. Loss-on-ignition experiments to determine the organic fraction of sampled soils were also conducted on selected samples. The presence of frequent low level cloud shrouding mountain tops in the uplands of northern and western Britain leads to enhanced precipitation and also deposition of the major acidic ions, eg SO₃²⁻ and N0₃, due to the washout of the low level cloud by falling rain ('seeder-feeder scavenging') and also the direct deposition of cloud droplets ('occult deposition'). It is important to quantify the inputs of acidic deposition in these acid sensitive regions and direct measurements present many logistical problems. The radionuclide ²¹⁰Pb is attached to the same sub-micron aerosol size range in the atmosphere as the major acidic ions and following deposition attaches very strongly to organic matter in soils. In this study the soil inventory of atmospherically derived ²¹⁰Pb is used as a tracer of the deposition of acidic ions. As the half-life of ²¹⁰Pb is 22.3 years the soil inventory of ²¹⁰Pb(atmos), at a site undisturbed for - 100 years, represents deposition integrated over several decades. Initial sampling took place at the Merrick, an isolated mountain close to the coast in southwest Scotland, to test and develop the technique. Measurements showed the ²¹⁰Pb(atmos) inventory to increase with altitude at a greater rate than precipitation. Sampling at Great Dun Fell in Cumbria enabled the measured radionuclide inventories to be compared with detailed measurements of the variation of the wet deposition pattern with altitude, and also with a model of sulphate deposition. Close correspondence was found between the ²¹⁰Pb deposition profile and the deposition pattern, with altitude, for the major acidic ions. The three mountains Ben Cruachan, Beinn Dorain and Ben Lawers lie along an 80 km transect running roughly west to east from the western coast into the central Highlands. Sampling at these three mountains has yielded information on the change in the wet deposition field with distance inland. The measurements suggest that deposition of ²¹⁰Pb decreases, with distance from the western coast, at a greater rate than does precipitation. The soil inventory of ²¹⁰Pb(atmos) increases with altitude at a greater rate than rainfall at 4 of the 5 mountains. The results show that, around summits, on average, the concentration of ²¹⁰Pb in low level cloud is a factor of - 2 greater than in the frontal ('seeder') rain falling from higher altitude. This finding is in good agreement with detailed wet deposition measurements. The ²¹⁰Pb measurements are important in themselves as they help define the global and UK ²¹⁰Pb budget. From measurements made at 65 individual sites the mean ²¹⁰Pb(atmos) inventory is 0.44 ± 0.03 Bq cm⁻², with the mean of the average annual rainfall being 2,060 ± 70 mm yr⁻¹. These figures correspond to a mean concentration of ²¹⁰Pb in rainfall of 66 mBql⁻¹. The ¹³⁷Cs inventory has been separated into the fraction originating from nuclear weapons testing, ¹³⁷Cs(bomb), and the fraction due to the Chernobyl accident, ¹³⁷Cs(Chern). The measured ¹³⁷Cs(bomb) inventory ranges from a mean of 3,300 Bq m⁻² at Ben Lawers to 5,200 Bq m⁻² at Beinn Dorain. The ¹³⁷Cs(Chern) inventory is highly variable between locations ranging from a mean of 440 Bq m⁻² at Great Dun Fell to 14,900 Bqm⁻² at Ben Lawers reflecting the patchy nature of deposition, due largely to convective storms, during the passage of the radioactive plume. The radionuclide ¹³⁷Cs is shown to be relatively mobile in the organic soils which characterise the study areas. The cosmogenic radionuclide ⁷Be was measured in samples collected from the Merrick on 26th Oct 1988. The mean inventory was 0.039 Bq cm⁻², being associated with vegetation and the top few cm of the soil profile.