Interannual variability in acidic deposition on the Mt. Mitchell area forest

Recently the forest decline at high elevation mountains in the eastern U.S. has been suggested to be associated with the deposition of acidic substances on the forest canopy through dry, wet and cloud deposition pathways. To determine the relative importance of these deposition mechanisms, a field study was initiated in May 1986, at Mt. Mitchell, NC. Since Mt. Mitchell is frequently immersed in clouds (immersion time being in the range of 28–41%), our investigations were primarily focused on the collection of cloud water and the monitoring of meteorology and ambient air quality. The precipitation data and related chemistry were obtained from a nearby NADP (National Atmospheric Deposition Program) site (Clingman's Peak). To estimate the dry and cloud deposition, the deposition velocities for gases and the rates of cloud deposition for cloud droplets are calculated with the ATDD (Atmospheric Turbulence and Diffusion Division, National Oceanic and Atmospheric Administration) model and a cloud deposition model (CDM), respectively. The wet deposition is obtained from NADP annual reports. Computations show the deposition velocities for SO₂, NO₂ and O₃ to be in the range of tenths of cm s⁻¹. The mean rate of cloud deposition is about 0.13–0.21 mm h⁻¹. The rainfall ranged from 40 to 60 cm during the growing seasons (from mid-May to the end of September) of 1986–1988. Using these deposition parameters and the 3 year database, the deposition fluxes of sulfur (S) compounds are found primarily contributed through cloud capture mechanism (60%) followed by incident precipitation (25%) and dry deposition (15%). As to the deposition fluxes of nitrogen (N) compounds, cloud, wet and dry deposition contributedf about 50%, 25% and 25%, respectively. A comparison of deposition estimates at Mt. Mitchell with those at other sites shows that the sulfate deposition at sites exceeding 1200 m MSL in elevation in Bavaria, F.R.G., and the eastern U.S. is a almost identical within error limits. Reasons for large uncertainties in deposition estimates are also discussed as the mechanisms for redistribution of the deposited material on the forest canopy.     

Atmospheric sulphur deposition to forest stands: Throughfall estimates compared to estimates from inference

Wet and dry deposition of sulphur was estimated for 30 forest stands in the Netherlands using a throughfall method and an inferential method. Dry deposition estimates of the throughfall method were significantly higher compared to estimates from inference. The major sources of uncertainty of the throughfall dry deposition estimates were associated with non-representative throughfall sampling, wet deposition estimates, canopy exchange processes, deposition of neutral salts, dry deposition directly onto the throughfall collectors, and with the omission of stemflow fluxes and dry deposition directly to the undergrowth vegetation and forest floor. These uncertainties were found to act both ways to approximately the same extent and were not able to explain the observed gap between the two dry deposition estimates. For the inferential method, major sources of uncertainty in the dry deposition estimates arose in calculation of the dry deposition velocity of SO₂ and the omission of occult deposition of SO₄²⁻. In this study, uncertainties associated with the spatial averaging of air concentrations of SO₂ and SO₄ aerosol and the calculation of the deposition velocity of SO₄ aerosol were found to be relatively small. Modifying the R_c parametrization of SO₂, based on recent dry deposition measurements made over heather in the Netherlands, resulted in fairly good agreement between both dry deposition estimates. Occult deposition of SO₄²⁻ was found to contribute significantly to the total sulphur deposition to the forest stands. Both the modified R_c parametrization and the incorporation of occult deposition led to systematically higher sulphur deposition estimates by the inferential method compared to originally inferred deposition. This implies that in the Netherlands, sulphur deposition to forest ecosystems might have been underestimated heretofore.     

Apparent deposition velocity and compensation point of ammonia inferred from gradient measurements above and through alfalfa

Understanding the cycling of ammonia between croplands and the atmosphere is of importance to agriculturalists and atmospheric scientists. Flux densities of gaseous ammonia (NH₃), particulate ammonium (NH₄⁺), and total ammoniacal nitrogen (AN) were measured using an aerodynamic method above an alfalfa (Medicago sativa, L.) canopy between April and July 1981 at a rural location in central New York State. In air not influenced by local sources, NH₃ and NH₄⁺ averaged 1.5 and 3.0 ppb, respectively, at 1 m above the crop. Ambient NH₄⁺ varied consistently with synoptic air masses, being lowest (2.3 ppb) for NW and highest (6.4 ppb) for SW flows. Concentrations and gradients of both species were higher during periods of hay harvest. Gradients of NH₃ were much steeper than those of NH₄⁺ within the alfalfa canopy, but NH₄⁺ contributed appreciably (36% on average) to above-canopy AN gradients. Alfalfa's NH₃ compensation point was estimated by combining concentration and gradient data with transport resistances. Gaseous gradients indicated a compensation point of 2 ppb, lower than previously published estimates. Conversion of NH₃ to NH₄⁺ within the canopy air could have reduced NH₃ gradients and caused a low estimate of the compensation point. Acidic aerosols, by keeping NH₃ levels low, may compete with plants for NH₃. Future studies of ammonia exchange should distinguish between NH₃ and NH₄⁺ if flux densities are to be related to ambient conditions. Total AN level is a poor predictor of soil-plant-atmosphere ammonia exchange since high AN was frequently associated with low NH₃, and NH₃ is more surface reactive than NH₄⁺.     

Effect of acidic deposition on productivity of forest ecosystem and estimation of its economic losses in southern suburbs of Chongqing

In accordance with principle sand methods of ecology,this paper studied the effects of acidic deposition on productivity and volume increment of masson pine and Cinnamomum campora forest which are widely distributed in southern suburbs of Chongqing. Based on the field data and measurements, a multivariable stepwise regression model was established to analyze the effects of multiple environmental factors on the productivity of the forest ecosystems. This model was used to assess the volume and economic losses of these two forest ecosystems caused by acidic deposition. The results showed that, among the environmental factors, pH value of precipitation, soil depth, soil organic contents and slope are the dominant ones influencing the growth of masson pine forest. It is also shown that the acidic deposition has no clear relation to the growth of C.Campora forest, so development of such broad-leaved forest is suitable in the area.     

Effect of acidic deposition on productivity of forest ecosystem and estimation of its economic losses in southern suburbs of Chongqing, China

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A new method for estimation of dry deposition of particles based on throughfall measurements in a forest edge

Throughfall measurements are very often used to calculate the atmospheric input to ecosystems. Such attempts are normally complicated by canopy interaction processes which are difficult to assess. This study presents an approach to calculate dry deposition and canopy leaching of Ca²⁺, Mg²⁺ and K⁺ to forests. The calculations are based on throughfall measurements in a forest edge of a spruce stand and by use of Na⁺ as a model substance for dry deposition of particles. This ‘forest edge approach’ is compared with an approach based on equal Na⁺ to base cation ratios in wet and dry deposition (‘wet/dry ratio approach’), which has been widely used in the literature. Our calculations show that the wet/dry ratio approach may overestimate the dry deposition of Ca²⁺, Mg²⁺ and K⁺ by up to 100% and leaching will correspondingly be underestimated. The assumptions underlying the different approaches and the use of throughfall measurements to estimate dry deposition are discussed and it is suggested that throughfall measurements in forest edges may be a valuable improvement to studies of atmospheric deposition in forests.     

Factor analysis of trends in Texas acidic deposition

Precipitation chemistry data collected between 1980 and 1987 for 11 NADP/NTN sites in Texas have been analyzed using factor analysis and a trend analysis of monthly averages. Factor analysis identified four major factors which differed significantly from site to site: (1) a Gulf factor of Na⁺, Cl^-, and Mg²⁺; (a) a soil factor of Ca²⁺, K⁺, Na⁺, and Mg²⁺; (3) an acid factor of H⁺, NO₋³, and SO₄⁴⁻; and (4) an aged aerosol factor of NO₃⁻, SO₄²⁻, and NH₄⁺. At Longview, the acid and Gulf factors accounted for 18 and 46%, respectively, of the variation of the data. A trend analysis was performed on the logarithm of the monthly averages at the Longview and Victoria sites, the two sites with the largest and most complete data. Results suggest that hydrogen ions have been increasing at both sites, while calcium ions have been decreasing.     

Detecting forest landscape boundary between Mountain Birch and evergreen coniferous forest in the northern slope of Changbai Mountain

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Detecting forest landcape boundary between Mountain Birch and evergreen eoniferous forest in the northern slope of Changbai Mountain

Boundaries between different forest types in Changbai Mountain Eatern China are results from complex interactions between forest ecosystems,topogrphy,and geomorphology.Detecting and quantifying the transitional zones are highly important since high environmental beterogeneity and biodiversity are ofter found within these zpmes.In this study,we used GIS and multivariate statistics techniques(PCA and MSWA) to analyze data from Landsat TM satellite imageries and quantitatively determined the positions and widths of the landscape boundary betweeen mountain birch and evergreen coniferous forests in the northern slope of Changbai Mountain.The results showed that the widths of the landscape boundary ranges from 30-50 m while using the MWW A or/and PC method.Such detected widths are consistent with field transect data that suggest a 50m tranistional zone width.The results further suggest that TM data can be used in combination with GIS and statistical techniques in determining forest landscape boundaries.MSWA is more reliable than PCA,while PCA can also be used to determine the landscape boundary when transects are properly located.     

Cloud chemistry at Mt Rigi,Switzerland: Dependence on drop size and relationship to precipitation chemistry

The chemical composition of winter and spring cloud water sampled at 1620 masl elevation on Mt Rigi in central Switzerland was dominated by NO₃⁻, SO₄²⁻, NH₄⁺ and H⁺. A wide range of concentration levels was observed, with maxima of 3700, 1800 and 4600 micronormal for NO₃⁻, SO₄²⁻ and NH₄⁺, respectively. Concentrations at a lower elevation (1030 masl) site on the mountain were higher due to lower cloud liquid water contents and higher pollutant levels at that site. The lowest pH observed was 2.95; large concentrations of NH₃ in the region prevented pH values from falling even lower. A comparison of simultaneously sampled cloud water and precipitation revealed much higher concentrations for most species in the cloud water, except in one case of extreme precipitation riming when the concentrations in the two phases converged. An exception to the pattern was H⁺; at times the precipitation was more acidic than the cloud water. The chemical composition of the cloud drops varied with drop size. Drops smaller than 10 μm diameter were enriched in NO₃⁻, SO₄²⁻ and NH₄⁺ relative to larger drops. Since the larger drops are the ones most effeciently captured by snow crystals, knowledge of their composition is essential to understanding the chemical implications of accretional growth of precipitation.     

Characterization of pollen deposition in a forest environment

Measurements of the dry deposition of pollen were made during the months of May and June 1987 in northern Wisconsin, using a smooth surrogate surface. Samples were taken on a raft located on Little Rock Lake and at a nearby field monitoring station. Rain samples were also collected at the field station. The wet SO₄²⁻ flux was 102.7 mg m⁻², compared with a dry SO₄²⁻ flux of 118 mg m⁻² at the field monitoring site and 45 mg m⁻² at the lake site.The SO₄²⁻ content of pollen ranged from 0.2 to 0.8% of the weight of the pollen, and NO₃⁻ concentrations were an order of magnitude lower. Between 9 and 22% of the pollen weight was available as total organic carbon (TOC) upon addition to water.The addition of pollen to distilled water produced an acid reaction, due to organic acids and not inorganic acidity.     

Implications of climate change on mitigation potential estimates for forest sector in India

Climate change is projected to impact forest ecosystems, including biodiversity and Net Primary Productivity (NPP). National level carbon forest sector mitigation potential estimates are available for India; however impacts of projected climate change are not included in the mitigation potential estimates. Change in NPP (in gC/m²/yr) is taken to represent the impacts of climate change. Long term impacts of climate change (2085) on the NPP of Indian forests are available; however no such regional estimates are available for short and medium terms. The present study based on GCM climatology scenarios projects the short, medium and long term impacts of climate change on forest ecosystems especially on NPP using BIOME4 vegetation model. We estimate that under A2 scenario by the year 2030 the NPP changes by (−5) to 40% across different agro-ecological zones (AEZ). By 2050 it increases by 15% to 59% and by 2070 it increases by 34 to 84%. However, under B2 scenario it increases only by 3 to 25%, 3.5 to 34% and (−2.5) to 38% respectively, in the same time periods. The cumulative mitigation potential is estimated to increase by up to 21% (by nearly 1 GtC) under A2 scenario between the years 2008 and 2108, whereas, under B2 the mitigation potential increases only by 14% (646 MtC). However, cumulative mitigation potential estimates obtained from IBIS—a dynamic global vegetation model suggest much smaller gains, where mitigation potential increases by only 6% and 5% during the period 2008 to 2108.     

温带亚高山针叶林土壤碳循环微生物群落的时空动态

选取参与碳固定的二磷酸羧化/加氧酶基因（cbbM）、有机碳降解的淀粉酶基因（amylase）和纤维素酶基因（cellulase）作为分子标记,用实时定量PCR方法对温带亚高山华北落叶松（Larix gmelinii var.principis-rupprechtii）林、白杄（Picea meyeri）林、青杄（P.wilsonii）林和油松（Pinus tabulaeformis）林土壤碳循环功能微生物类群丰度的时空动态开展研究.结果显示,总碳（TC）、总氮（TN）、总硫（TS）、有机质（OM）和有机碳（TOC）、pH值、铵态氮（NH₄⁺-N）、硝态氮（NO₃^--N）、过氧化氢酶、蔗糖酶和脲酶活性在4种森林土壤中都有不同程度的差异,且有显著的季节变化特征.高海拔华北落叶松林土壤TC、TN、TS、C/N、OM和TOC含量最高,而pH值最低.土壤TC、TN、亚硝态氮（NO₂^--N）含量、蔗糖酶和脲酶活性,与碳循环微生物类群的丰度呈极显著相关.土壤NO₃^--N含量与有机碳分解和固碳微生物类群的相对丰度显著相关;土壤C/N、NO₂^--N、pH值、OM、TOC、过氧化氢酶及脲酶活性,与降解易分解碳（labile C）和难分解碳（recalcitrant C）的微生物类群的相对丰度呈极显著相关.植被类型和季节变化共同影响土壤碳循环微生物类群的丰度,而季节变化是主导因素.植被和土壤环境因子通过调控微生物群落碳代谢功能类群的结构,影响森林土壤碳源-汇的平衡.     

Laboratory measurements of sulfur dioxide deposition velocity on marble and dolomite stone surfaces

The deposition velocity of SO₂ on marble and dolomite stone surfaces in a humid atmosphere was measured as a function of time in the laboratory using continuous monitoring techniques. The deposition velocity of SO₂ on marble varied between 0.02 and 0.23 cm s⁻¹, and was generally observed to decrease with time. The deposition velocity of SO₂ on dolomite varied between 0.02 and 0.10 cm s⁻¹, and gradually increased over the first 2000 ppm-h of exposure. For both types of stones, the deposition velocity increased significantly when condensed moisture was observed on the stone surface. Chemical analysis of the stone samples indicated that the SO₂ deposited reacted with the stone materials to form gypsum (CaSO₄·2H₂O) on the marble surfaces and gypsum and epsomite (MgSO₄·7H₂O) on the dolomite surfaces.     

Measurement and modelling of cloudwater deposition to a snow-covered forest canopy

Measurements are presented of the flux of cloud droplets, as a function of particle size to a forest canopy (Sitka spruce) before and after a light snowfall. The results are compared to the predivtions of the model of Slinn. Good agreement is found provided that appropriate values for the effective target diameter are chosen, both before and after the snowfall. It is shown that the snowfall results in a considerable reduction in the flux of cloud water to the forest canopy (by a factor of about 2). The snow reduces the surface roughness of the canopy but the most important effect is that it increases the effective target diameter for the droplets impacting on the tree. This effect may considerably reduce the deposition of phytotoxic chemical species to forests at high altitude where snow cover and low cloud are common in winter.     

Comparability and precision of MAP3S and NADP/NTN precipitation chemistry data at an acidic site in eastern North America

Precipitation chemistry data derived from more than six years of concurrent sampling under the MAP3S and NADP/NTN protocols at the Penn State site in rural Pennsylvania are compared. Preprocessing of the data (sample and gage depths, concentrations of H₃O⁺, SO₄²⁻, NO₃⁻, NH₄⁺) included aggregating the event and daily MAP3S data into weekly averages that coincide with the weekly data of the NADP/NTN program. A simple statistical model was applied to the differences of the paired data to look for systematic biases between the networks. The most notable bias occurred for ammonium concentration (NADP/NTN low), a finding consistent with other studies. A minor, but statistically significant, bias was also found for sulfate coccentration (NADP/NTN high). Both the ammonium and sulfate biases may be related to the relatively long time that the NADP/NTN samples remain in the field, thus strengthening arguments in favor of daily sampling protocols. The hydronium and nitrate concentrations exhibited remarkably high levels of comparability between the daily and weekly protocols. Overall, the data from the MAP3S and NADP/NTN networks are comparable, with the possible exception of ammonium, for some applications. The field results from about two years of duplicate sampling under the MAP3S protocol demonstrate that measurement precisions of only a few percent are possible when the protocol is consistently followed and the equipment is well maintained.     

Analysis of atmospheric ozone measurements over a pine forest

Vertical and horizontal profiles of ozone concentration have been measured within the atmospheric boundary layer over the pine forest located in the southwest of France (Landes Forest). Evidence for an ozone depletion in lower layers is obtained from the analysis of vertical profiles recorded at the end of the night. In terms of deposition at the upper canopy level, this corresponds to a disappearance rate ranging between 0.2 and 0.5 cm s⁻¹. The horizontal profiles obtained at midday reveal that ozone vanishes at a rate of the order of 5 × 10⁻⁵ ppb m⁻¹ when air mass moving in the advection direction passes over the forested area. These results are consistent with those obtained by numeric simulation in the case of low emission rates of nitrogen oxides. On the basis of these measurements, the expression of the ozone budget within the atmospheric boundary layer is discussed and compared with the data obtained from the simulation study.     

An analysis of precipitation chemistry measurements in Shimane,Japan

In order to understand the concentration and deposition levels of the major ions in Shimane, on the Japan Sea coast where precipitation chemistry data are scarce, the precipitation was collected at three sites (Matsue, Gotsu and Masuda) from April 1985 to March 1988.The mean precipitation chemistry was very close to each other except for the seasalt concentration. Masuda showed a halved seasalt contribution compared with the other sites. The volume-weighted annual pH mean at each site ranged from 4.6 to 4.9. Nitrate to SO₄⁻² equivalent ratios were in the range of 0.2 and 0.4 throughout the year. Ammonia and calcium species are interpreted to have neutralized approximately 70% of the original sulfuric and nitric acids.The annual depositions of the major ions in g m⁻²y⁻¹ were as follows: H⁺; 0.023–0.037, NH₄⁺; 0.57–0.68, Ca²⁺; 0.51–0.92, SO₄²⁻; 3.29–5.04, NO₃⁻; 1.20–1.70. These levels are of the same intensity as corresponding values of JEA network results.     

Laboratory measurements of ozone deposition to sea water and other saline solutions

Measurements of ozone deposition velocity to fresh seawater samples collected over the course of a year have been made using a static chamber technique. The magnitude of the ozone deposition velocity (ca 0.01 cm s⁻¹) was in broad agreement with the relatively few values reported in the literature. A strong correlation between ozone deposition and dissolved surfactant concentrations was found which is reflected in their similar seasonal trends. Stirring the water resulted in a significant increase in the rate of ozone uptake at the surface which suggests that wave motion may increase deposition velocity by constantly and rapidly replenishing the reactive surface organic layer.     

Sodar estimates of surface heat flux and mixed layer depth compared with direct measurements

Similarity relationships for the convective boundary layer are used to derive surface heat flux and mixed layer depth from sodar measurements of the temperature structure parameter and the vertical velocity variance. Two different methods are presented and compared with direct measurements from the Öresund experiment which took place during the period 15 May–14 June 1984. The analyzed data were taken with two three-axis monostatic Doppler sodars manufactured by Sensitron, Sweden. Comparison with simultaneous direct measurements shows generally good agreement during convective conditions but also reveals some limitations of the methods.