Estimates Of Atmospheric Deposition Research Articles

Concentrations, Accumulations, and Inventories of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Sediments of the Great Lakes

The chronology of PCDD/F accumulation was determined in sediment cores from Lakes Superior, Michigan, and Ontario and two small “control” lakes. Accumulation rates began increasing about 1940, increased to maxima at 1970 ± 10 yr, and then declined to the present rates that are 30−70% of the maxima. The observed accumulations ranged from <0.03 ng cm-2 yr-1 in the control lakes and Lake Superior to 0.39 ng cm-2 yr-1 in Lake Ontario. By comparing the PCDD/F sedimentary accumulation in the control lakes to those in the Great Lakes, we estimate that Lake Superior receives ∼0%, southern Lake Michigan receives ∼20%, northern Lake Michigan receives ∼60%, and Lake Ontario receives >90% of their current PCDD/F inputs from subregional atmospheric (air parcels having higher concentrations of PCDD/F than remote air due to local sources) and/or non-atmospheric sources. We also compared the sedimentary accumulations to estimates of atmospheric deposition. The PCDD/F accumulation rates in the control lakes were similar to atmospheric deposition of PCDD/Fs from remote air in the Great Lakes basin. Atmospheric deposition from suburban air can support the accumulation of PCDD/F in southern Lake Michigan but some non-atmospheric sources to northern Lake Michigan are implicated. Lake Ontario may be receiving >70% of its current inputs of PCDD/F from non-atmospheric sources.

The impact of canopy exchange on differences observed between atmospheric deposition and throughfall fluxes

To study the impact of canopy exchange on differences observed between atmospheric deposition and throughfall fluxes, several field experiments were performed at the Speulder forest in The Netherlands. Relevant information was obtained by (i) measuring open-field precipitation and throughfall fluxes with different time resolutions, using two canopy exchange models, (ii) by comparing results from surface wash experiments using real and artificial twigs, respectively, and (iii) by comparing throughfall flux estimates with atmospheric deposition estimates from micrometeorological measurements and inferential modelling. Canopy uptake of gases through stomata was estimated using measured air concentrations and a stomatal conductance model. Specific information on canopy leaching of soil-derived sulphate was provided by a 35S tracer experiment. Sulphur was found to behave conservatively within the canopy, with SO 2 uptake more or less balancing leaching of soil-derived SO 2− 4. Significant stomatal uptake of NO 2, HNO 2 and NH 3 was calculated as well as uptake of H + and NH 4 + from water layers covering the tree surface. Experiments did not indicate significant uptake of N0 3 − in solution. Canopy uptake of H + and NH4+ was countered by leaching of K +, Ca 2+ and Mg 2+. Part of the leaching of K +, Ca 2+ and Mg 2+ (15%) took place along with weak organic acids. No significant canopy exchange was found for Na + and Cl −. Differences observed between atmospheric deposition and throughfall fluxes could almost completely be explained by canopy exchange, the difference between NO y deposition and N0 3 throughfall flux being the only exception.

Particle deposition to forests—Summary of results and application

Particle deposition to forest was studied at Speulder forest using experimental and modelling results. In this paper a short overview of the main results is given and they are applied in generalisation of deposition in The Netherlands. The results of the Aerosol project show that the deposition of particles to forests has been underestimated until now. Particle deposition makes a reasonable contribution to the total deposition of acidifying components and base cations to forests. Parametrisations of the deposition processes were derived from the experiments and model developed for particle deposition to Speulder forest. The parametrisations were used together with concentrations, meteorological observations and land-use data to determine the deposition on a 5 x 5 km basis in The Netherlands. Results of the canopy exchange experiments at Speulder forest and of the comparison of atmospheric deposition estimates and throughfall estimates at Speuld and other locations in The Netherlands show that throughfall fluxes and atmospheric deposition estimates are reasonably in agreement for all components, except nitrate. There is still large uncertainty in canopy exchange processes of oxidised nitrogen and in deposition estimates of the different gases contributing to the total oxidised nitrogen flux. The contribution of aerosol deposition to the total deposition in The Netherlands is 7% for SO 4 2−, 11% for NH 4 + and 9% for NO 3 −; for deciduous forests these numbers are 14,15 and 17%, and for coniferous forests 10, 17 and 20%, respectively. Dry deposition is estimated to amount to about 21% of total deposition for Na +, 20% for K +, 27% for Mg 2+ and 25% for Ca 2+.

The application of throughfall measurements for atmospheric deposition monitoring

An overview of the technical requirements of throughfall, stemflow and precipitation measurements used for monitoring atmospheric deposition to forests is presented. A mechanistic basis is presented to link throughfall fluxes to atmospheric deposition. For homogeneous forest stands with a closed canopy, the overall uncertainty in annual mean soil loads can be as low as 10–15% if state-of-the-art measurement and analytical techniques are used in combination with a sufficiently large number of replicate samplers. The uncertainty in atmospheric deposition estimates, however, is estimated much larger, i.e. up to 30% for sulphur and 40% for nitrogen and base cations. This is mainly attributed to (i) uncertainties associated with the estimation of canopy exchange, and (ii) dry deposition to the forest floor and understorey vegetation which is usually not addressed in throughfall studies. Additional research on canopy exchange in relation to tree species, ecological setting and pollution climate is recommended, especially for nitrogen compounds and base cations, and may serve as a basis for improvement of current canopy budget models.

Biogeochemistry of a forested watershed in the central Adirondack Mountains: Temporal changes and mass balances

Information on atmospheric inputs, water chemistry and hydrology were combined to evaluate elemental mass balances and assess temporal changes in elemental transport from 1983 through 1992 for the Arbutus Lake watershed. This watershed is located within a northern hardwood ecosystem at the Huntington Forest within the central Adirondack Mountains of New York (USA). Changes in water chemistry, including increasing NO3 − concentrations (1.1 μmol c , L−1 yr-1), have been detected during this study period. Starting in 1991 hydrological flow has been measured from Arbutus Lake and these measurements were compared with predicted flow using the BROOK2 hydrological simulation model. The model adequately (r2=0.79) simulated flow from this catchment and was used to estimate drainage for earlier periods when direct hydrological measurements were not available. Modeled drainage water losses coupled with estimates of wet and dry atmospheric deposition were used to calculate solute budgets. Export of SO4 2− (831 mol c ha−1 yr−1) from the greater Arbutus Lake watershed exceeded estimates of atmospheric deposition in an adjacent hardwood stand suggesting an additional source of S. These large drainage losses of SO4 2− also contributed to the drainage fluxes of basic cations (Ca2+, Mg2+, K+ and Na+). Most of the atmospheric inputs of inorganic N were retained (average of 74% of wet precipitation and 85% total deposition) in the watershed. There were differences among years (56 to 228 mol ha−1 yr−1) in drainage water losses of N with greatest losses occurring during a warm, wet period (1989–1991).

Atmospheric PCB deposition in Finland during 1970s and 1980s on the basis of concentrations in ombrotrophic peat mosses ( Sphagnum)

Sphagnum moss samples were congener-specifically analysed for polychlorinated biphenyls. Mean total PCB concentration in the study material (surface moss) was 140 ng/g in southern and 51 ng/g in northern Finland. Tri- and tetrachlorobiphenyls are responsible for more than half of the total concentration in moss with PCB congeners 18, 28, 33, 52 and 101 dominating. Estimates of atmospheric deposition for two ombrotrophic peat bogs in southern Finland ranged from 13 to 63 μg/m 2/yr and showed consistent decrease from 1970s to 1980s.

Estimates of atmospheric deposition and canopy exchange for three common tree species in the Netherlands

During one year, dry and wet deposition onto thirty forest stands is studied by sampling throughfall and bulk precipitation. Nine measurement sites are situated in Douglas fir (Pseudotsuga menziesii Mirb. Franco) stands, ten in Scotch pine (Pinus sylvestris L.) and eleven in Oak (Quercus robur L.) stands. Because the stands are situated in each other's proximity (i.e. within a radius of approximately 1.4 km) it is assumed that they experience an approximately equal air pollution load. For the acidifying compounds SO42−, NO3− and NH4+ spatial variability in wet deposition was small within the area studied. Dry deposition, as estimated by net throughfall, displayed a much higher spatial variability. Significant differences existed between tree species and growing seasons. Douglas fir mostly displayed the highest, Oak the lowest and Scotch pine intermediate values for net throughfall fluxes of acidifying compounds. The annual net throughfall fluxes for nitrogen compounds were significantly higher for the coniferous tree species than the broadleaved tree species. For SO42−, however, Oak showed a relatively high throughfall flux during the summer. By comparing the temporal pattern of net throughfall fluxes between the three tree species it was concluded that considerable canopy leaching occurred for SO42−, Mg+, PO43−, HCO3− and K+ in Oak stands during the sprouting of leaves in spring. From surface wash experiments in the laboratory it is concluded that canopy leaching of these ions may also be enhanced when Oak leaves are infected by Oak mildew, a fungal disease caused by the fungus Microshaera aliphilitoides.

The atmospheric input flux of trace metals to the North Sea; A review and recommendations for research

Quantitative estimation of atmospheric deposition to the North Sea is complicated by an inadequate understanding of wet and dry deposition processes over marine areas. This review examines the mechanisms involved and highlights the gaps in knowledge. Estimates of metal inputs based upon field measurements are reviewed in the light of the methods used and assumptions made in each study. The more recent advent of the application of atmospheric transport/deposition models to the estimation of deposition fluxes has provided useful insights into spatial patterns, but is subject to many of the limitations inherent in the measurement-based estimates. In general, estimates of atmospheric input fluxes have diminished in recent years, which may reflect both improved methodology in estimation, and/or decreased anthropogenic emissions in Western Europe. Finally, recommendations for future work are made.

Detailed Analysis of Sulphate and Nitrate Atmospheric Deposition Estimates at the Turkey Lakes Watershed

Daily concentrations of sulphates and nitrates in air and precipitation were measured atthe Turkey Lakes Watershed from September 1980 until December 1984. The measurement data were used to estimate wet, dry, and total deposition of sulphates and nitrates to the watershed. Over the 4 yr, the annual values of total (wet plus dry) deposition ranged from 34 to 38 (± 15%) mmol∙m−2∙yr−1 for SO42− and from 38 to 47 (± 30%) mmol∙m−2∙yr−1 for NO3−. On a molar basis, the deposition of total NO3− exceeded the deposition of total SO42− by 19%. However, when converted to equivalents, total SO42− exceeded total NO3− by 68%. Dry deposition represented approximately 15 and 25% of the total deposition of SO42− and NO3−, respectively, to the watershed. Wet and dry deposition of sulphate and nitrate was found to be highly episodic, with the top 20% of daily events delivering 60–70% of the total sulphur and nitrogen deposition to the watershed. Statistically significant seasonal cycles were found in the concentration and deposition values of most of the sulphur and nitrogen species measured at the watershed.

Atmospheric, riverine and oceanic sources of seven trace constituents to the arctic ocean

The Arctic atmosphere contains surprisingly high concentrations of aerosol during the winter half-year, to the point that deposition to the Arctic Ocean becomes of interest. For lack of better information, we assume that wet deposition dominates dry deposition in the Arctic to the same degree as in midlatitudes. If so, most of the Arctic deposition should take place in winter, when anthropogenic contributions to the Arctic aerosol are the greatest. Thus, anthropogenic influences should be seen in Arctic deposition, but to a lesser extent than in the Arctic aerosol. Estimates of atmospheric deposition and riverine transport of seven trace species (A1, V, Mn, Cd, Pb, SO 4 2−, NO 3 −) to the Arctic Ocean suggest that riverine sources deposit more material than atmospheric sources, that riverine fluxes are often comparable to oceanic fluxes, and that atmospheric fluxes are usually much less than riverine or oceanic fluxes. Under certain circumstances, riverine Al, Mn, Cd and NO 3 − may significantly affect the oceanic concentrations. Atmospheric and riverine sources of SO 4 2− and V are both unimportant. Pb was the only element considered here whose atmospheric flux equals or exceeds the riverine and oceanic fluxes into and out of the Arctic basin; the atmosphere should thus have a major effect on Pb concentration in the Arctic Ocean.