Concern regarding the impacts of continued nitrogen and sulfur deposition on ecosystem health has prompted the development of critical acid load assessments for forest soils. A critical acid load is a quantitative estimate of exposure to one or more pollutants at or above which harmful acidification-related effects on sensitive elements of the environment occur. A pollutant load in excess of a critical acid load is termed exceedance. This study combined a simple mass balance equation with national-scale databases to estimate critical acid load and exceedance for forest soils at a 1-km2 spatial resolution across the conterminous US. This study estimated that about 15% of US forest soils are in exceedance of their critical acid load by more than 250 eq ha-1 yr-1, including much of New England and West Virginia. Very few areas of exceedance were predicted in the western US. This simple mass balance equation estimated that 17% of US forest soils exceed their critical acid load by more than 250 eq ha-1 yr-1, and these areas are predominantly located in the northeastern US.

Simple mass balance equations (SMBE) of critical acid loads (CAL) in forest soil were developed to assess potential risks of air pollutants to ecosystems. However, to apply SMBE reliably at large scales, SMBE must be tested for adequacy and uncertainty. Our goal was to provide a detailed analysis of uncertainty in SMBE so that sound strategies for scaling up CAL estimates to the national scale could be developed. Specifically, we wanted to quantify CAL uncertainty under natural variability in 17 model parameters, and determine their relative contributions in predicting CAL. Results indicated that uncertainty in CAL came primarily from components of base cation weathering (BCw; 49%) and acid neutralizing capacity (46%), whereas the most critical parameters were BCw base rate (62%), soil depth (20%), and soil temperature (11%). Thus, improvements in estimates of these factors are crucial to reducing uncertainty and successfully scaling up SMBE for national assessments of CAL.

Visible symptoms in tree foliage can be used for stress diagnosis once validated with microscopical analyses. This paper reviews and illustrates macroscopical and microscopical markers of stress with a biotic (bacteria, fungi, insects) or abiotic (frost, drought, mineral deficiency, heavy metal pollution in the soil, acidic deposition and ozone) origin helpful for the validation of symptoms in broadleaved and conifer trees. Differentiation of changes in the leaf or needle physiology, through ageing, senescence, accelerated cell senescence, programmed cell death and oxidative stress, provides additional clues raising diagnosis efficiency, especially in combination with information about the target of the stress agent at the tree, leaf/needle, tissue, cell and ultrastructural level. Given the increasing stress in a changing environment, this review discusses how integrated diagnostic approaches lead to better causal analysis to be applied for specific monitoring of stress factors affecting forest ecosystems. Macroscopic leaf symptoms and their microscopic analysis as stress bioindications.

We intensively surveyed the concentrations of chemical species in aerosols and gases using a four-stage filter-pack method at a site in Japan facing the Sea of Japan in winter with 6-h sample intervals. A few chloride species emitted anthropogenically were detected, and the HCl (g) concentration was quite low. The number of chloride species artifacts was also low. The HNO₃ (g) concentration was significantly higher when the monitored air mass passed over the Korean Peninsula compared to when it did not pass over the Korean Peninsula. In addition, the HNO₃ (g) concentration was significantly higher when the air mass arrived at the monitoring site by passing the route at lower latitude than the latitude of the monitoring site. On the other hand, the SO₂ (g) concentration showed no change between various trajectories of the air mass. The [Formula: see text] (p)/non-seasalt- (nss-) [Formula: see text] (p) ratio was intermediate between the compositions of (NH₄)₂SO₄ and NH₄HSO₄ when the air mass passed over the Korean Peninsula, whereas it was intermediate between NH₄HSO₄ and H₂SO₄ when the air mass did not pass over the Korean Peninsula. We detected the transboundary transport of sulfur dioxide with high time-resolution monitoring at two separate monitoring points: the current monitoring site and Oki Island.

A geologic classification scheme was combined with elevation to test hypotheses regarding watershed sensitivity to acidic deposition using available regional spatial data and to delimit a high-interest area for streamwater acidification sensitivity within the Southern Appalachian Mountains region. It covered only 28% of the region, and yet included almost all known streams that have low acid neutralizing capacity (ANC ≤20 μeq l⁻¹) or that are acidic (ANC ≤0). The five-class geologic classification scheme was developed based on recent lithologic maps and streamwater chemistry data for 909 sites. The vast majority of the sampled streams that had ANC ≤20 μeq l⁻¹ and that were totally underlainby a single geologic sensitivity class occurred in the siliceous class, which is represented by such lithologies as sandstone and quartzite. Streamwater acid-base chemistry throughout the region was also found to be associated with a number of watershed features that were mapped for the entire region, in addition to lithology and elevation, including ecoregion, physiographic province, soils type, forest type and watershed area. Logistic regression was used to model the presence/absence of acid-sensitive streams throughout the region.

Analysis of the sensitivity of soils to acidification caused by the deposition of atmospheric pollutants has been one of the major scientific issues in Europe during the past few decades. In the present study, critical loads of acid deposition were calculated using the most accurate datasets available at present for European soils, by the “Simple Mass Balance” method. The results show that the soils most sensitive to acid deposition are Histosols, Cryosols and Podzols in cold areas in northern countries, followed by Lithic and Haplic Leptosols (Dystric) developed on acid parent materials. The highest critical loads corresponded to soils developed over calcareous rocks and soils in areas subject to high precipitation, even those dominated by poorly weatherable primary mineral. In the latter case critical alkalinity leaching is the main variable that determines the value of critical loads, because of the buffering action of the dissolution of aluminium compounds. The results were compared with those obtained by the Stockholm Environmental Institute in the same area, but with a different method of analysis. It was found that the results are highly dependent on the method used to perform the analysis.

Buffer capacity analysis of open atmospheric gas-liquid systems containing main acidic and basic atmospheric pollutants was carried out. Usually the buffer capacity is considered as a function of pH as an independent variable. In this work the buffer capacity is analysed including the dependence of pH on the composition of a system. Such an approach allows finding an important, from the viewpoint of atmospheric water acidification, relationship between the gas phase composition and the buffer capacity. It was found that buffer capacity of the open gas-liquid systems may be very high and it may cause the liquid phase pH to remain at low levels. The buffer capacity of the analysed systems is most strongly affected by the simultaneous presence of ammonia and strong acids in the gas phase. The higher concentrations of strong acid gases the lower NH₃ concentration is sufficient to achieve high buffer capacity. In the presence of strong acid gases, calcium ions affect both the buffer capacity and the liquid phase pH only at low NH₃ concentrations. High buffer capacity of open gas-liquid systems may be one of the reasons why the reduction in emissions of acidic gas pollutants has little effect on decrease in atmospheric water acidity.

A total of nine sediment cores were collected from the five deep basins of Kejimkujik Lake, located in southwestern Nova Scotia, Canada, in order to track changes related to surface-water acidification and to test reproducibility of results between sediment cores from different basins in a large lake. Present-day and pre-industrial (c. 1850) samples were analyzed from all cores and detailed diatom profiles were undertaken on three cores to determine the timing of acidification. All three detailed diatom profiles show declines in inferred pH starting in the early 1930-1940s. Since the 1940s, diatom-inferred lakewater pH has declined from a background pH of ~5.8 (± 0.4) to a current diatom-inferred pH of ~4.9 (± 0.1). This corresponds to the current (2001-2002) range of measured lakewater pH = 4.7-5.2 with a mean pH = 4.9. Species diversity of diatoms also declines markedly in all cores with the Hill's N2 index decreasing from ~5 to near 1. The pre-impact diatom assemblages were dominated by Aulacoseira spp. and have since changed to dominance by Asterionella ralfsii var. americana (>45 μm). All nine sediment cores showed similar changes in diatom assemblages, diatom-inferred pH, and timing of the onset of acidification. Thus, paleolimnological inferences from deepwater sediment cores were highly reproducible in this large, morphometrically complex lake system.

During the period from July 2002 to June 2004, the chemical characteristics of the rainwater samples collected in downtown São Paulo were investigated. The analysis of 224 wet-only precipitation samples included pH and electrical conductivity, as well as major ions (Na⁺, [graphic removed] , K⁺, Ca²⁺, Mg²⁺, Cl-, [graphic removed] , [graphic removed] ) and carboxylic acids (acetic, formic and oxalic) using ion chromatography. The volume weighted mean, VWM, of the anions [graphic removed] , [graphic removed] and Cl- was, respectively, 20.3, 12.1 and 10.7 μmol l-¹. Rainwater in São Paulo was acidic, with 55% of the samples exhibiting a pH below 5.6. The VWM of the free H⁺ was 6.27 μmol l-¹), corresponding to a pH of 5.20. Ammonia (NH₃), determined as [graphic removed] (VWM = 32.8 μmol l-¹), was the main acidity neutralizing agent. Considering that the H⁺ ion is the only counter ion produced from the non-sea-salt fraction of the dissociated anions, the contribution of each anion to the free acidity potential has the following profile: [graphic removed] (31.1%), [graphic removed] (26.0%), CH₃COO- (22.0%), Cl- (13.7%), HCOO- (5.4%) and [graphic removed] (1.8%). The precipitation chemistry showed seasonal differences, with higher concentrations of ammonium and calcium during autumn and winter (dry period). The marine contribution was not significant, while the direct vehicular emission showed to be relevant in the ionic composition of precipitation.

The long-term monitoring of precipitation and its chemical composition are important for identifying trends in rain quality and for assessing the effectiveness of pollution control strategies. A statistical test has been used to the atmospheric concentrations measured in the French rural monitoring network (MERA) in order to bring out spatio-temporal trends in precipitation quality in France over the period 1990-2003. The non-parametric Mann-Kendall test which has been developed for detecting and estimating monotonic trends in the time series was used and applied in our study at annual values of wet-only precipitation concentrations. The emission data suggest that SO₂ and NO x emissions decreased (-3.3 and -2.0% year-¹, respectively) contrary to NH₃ emissions that increased slightly (+0.2% year-¹) over the period 1990-2002 in France. On the national scale, the pH values have a significant decreasing trend of -0.025 ± 0.02 unit pH year-¹. [graphic removed] and [graphic removed] concentrations in precipitation have a significant decreasing trend, -3.0 ± 1.6 and -3.3 ± 0.6% year-¹, respectively, corresponding with the downward trends in SO₂ emissions in France (-3.3% year-¹). A good correlation (R ² = 0.84) between SO₂ emissions and [graphic removed] concentrations was obtained. The decreasing trend of [graphic removed] was more significant (-5.4 ± 5.2% year-¹) than that of [graphic removed] (-1.3 ± 2.4% year-¹). Globally, the concentration of the major ions showed a clear downward trend including marine and alkaline ions. In addition, the relative contribution of HNO₃ to acidity precipitation increased by 51% over the studied period.