Long term effects of enhanced nitrogen deposition on a lowland dry heath in southern Britain

Experimental additions of ammonium sulphate to a nitrogen-poor dry heathland have been carried out since 1989. There are four nitrogen treatments: a control (receiving artificial rain only), a low treatment which receives an additional 7.7 kg N ha^?1 yr^?1, a high treatment receiving 15.4 kg N ha^?1 yr^?1 and an alternating treatment which receives either the control or the high nitrogen additions, in alternate years. The estimated background deposition at the study site is 13–18 kg N ha^?1 yr^?1, a value similar to the critical load that has been suggested for the conversion of lowland heath to grassland. Over the past 5 years there have been significant stimulations in shoot growth, flowering, canopy density and litter production. Flowering, in particular, strongly reflects nitrogen additions in the alternating treatment. Current models of the response of dry Calluna heathlaud to enhanced nitrogen deposition suggest that higher tissue nitrogen levels will occur and will be accompanied by heightened sensitivity to secondary stresses. This may in turn lead to canopy breakdown and replacement by grassland. The application of nitrogen at deposition rates only slightly in excess of the critical load over five years has produced small, non-significant increases in shoot nitrogen content. However, there is clear evidence of a large positive effect on shoot growth, flowering, litter production and canopy density of Calluna. The observation of these responses at the application rates used in this study supports the current proposals for critical loads of nitrogen for lowland heaths.     

Response of two Adirondack watersheds to acidic deposition

Responses of two lake-watersheds to changes in atmospheric deposition were simulated using the Integrated Lake-Watershed Acidification Study (ILWAS) Model. The simulated annual chemical outlet fluxes were continuous functions of both S and N deposition. No acidification threshold was observed. The slopes of the response curves quantified the contrasting sensitivities of the two systems to changes in deposition.     

A comparative regional analysis of the status of aquatic resources with respect to acid deposition

A national scale assessment of the effects of acid deposition on aquatic resources is currently unavailable for the United States. A more limited assessment has been performed in three potentially sensitive geographical regions the Adirondack Mountains of New York, the Southern Blue Ridge Province of North Carolina, Tennessee and Georgia, and the Upper Midwest of Minnesota, Wisconsin and Michigan. A series of questions organized the assessment, and historical and current data from each region were employed to address the questions. Where possible, independent data sets were used singly and in combination within a given case study area, to respond to the questions and to provide an estimate of confidence. Conclusions among regions were also compared. In general, the impact of acid deposition on aquatic resources is difficult to detect, but positive correlations between atmospheric deposition and effects do exist. Thus, there is evidence to suggest that acid deposition is at least partially responsible for the acidification of aquatic resources. The extent of acidification, however, varies from region to region. The Adirondacks appear to represent the region of greatest impact, but independent studies indicate that the area of acidified lakes is a small percentage of the total resource. Despite the observation of minimal damage, application of damage estimates from the Adirondacks to other regions would be inappropriate. Future Assessments will seek to predict the rate of acidification of watersheds with other regional characteristics under alternative loading scenarios.     

Long term trends in atmospheric deposition and seepage output in northwest German forest ecosystems

Long term trends of element fluxes in atmospheric deposition and of concentrations in seepage output of seven coniferous and deciduous forest stands in northwestern Germany have been evaluated for the period 1981 – 1994. Decreasing deposition rates of SO₄ (50 – 70%) and H⁺ (60 – 80%) occured at all sites concomitant with the decline of SO₂ emission rates in the former Federal Republic of Germany. Deposition of Ca, Mg, and K decreased at the Soiling and Göttinger Wald stands. During this period no consistent trends in the flux rates of NH₄ and NO₃ were apparent. Sulfate concentrations in soil solution decreased at the Soiling and Göttinger Wald stands, whereas an increase occured at Lange Bramke south slope. As a consequence of reduced deposition and mobile anion concentrations a decrease of Ca, Mg, K, Al, and Mn in soil solution has been observed at the Soiling stands. At the other stands trends of cations in soil solution are not consistent. Nitrate concentrations in soil solution decreased at the Göttinger Wald. A rising tendency with great fluctuations of NO₃ concentrations occured at the Soiling spruce stand.     

Arylsulphatase activity in peat in relation to acidic deposition

Arylsulphatase activity was measured in blanket peat from 29 sites in northern England and Wales. Low activities (<0.5 μmolp-nitrophenol h^?1 g^?1 dry wt) were observed in sites close to urban and industrial areas. Sites remote from such areas had activities an order of magnitude higher.Peat transplanted into a polluted site showed a rapid loss in arylsulphatase activity which declined linearly over 12 weeks. Similar peat transplanted into a less-polluted site showed no such decline over the same period.Laboratory experiments in which peat was watered with solutions containing components of acidic deposition at realistic concentrations showed that these, with the exception of NH⁺₄ ions, decreased enzyme activity. HSO^?₃ ions (or dissolved and unreacted SO₂) produced the greatest decrease in enzyme activity.The results are discussed in relation to the precise cause of the low arylsulphatase activity observed in polluted blanket peat, and the possible use of this as a monitor of the ecological effects of acidic deposition.     

Terrestrial ecosystem sensitivity to acidic deposition in developing countries

Acidic deposition is considered a problem in Europe and North America but the potential for ecosystem damage from this pollution is also increasing rapidly in many developing countries. It is therefore important to assess current and future risks of ecosystem effects due to acidic deposition in these areas. It is possible to indicate risk areas by linking an assessment of sensitivity to net acidic input rates derived from deposition estimates for sulphur and nitrogen compounds and base cations. A method to assess and map a relative scale of terrestrial ecosystem sensitivity using international datasets is presented. The assessment relies on the determination of buffering mechanisms that prevent effects related to acidic deposition. Land-cover data, edaphic and climate datasets are combined using a GIS. Large areas are assessed as highly sensitive to acidic deposition in tropical regions of Asia, South and Central America and Africa, and also in the Boreal forests of northern Asia. Sensitive areas cover forest and non-forest ecosystems and some areas of agricultural production. Critical loads are not evaluated in this project but initial estimates will be applied to sensitivity classes at a further stage which will allow estimation of areas at risk by comparison with deposition.     

Crustacean plankton in northeastern Ontario lakes subjected to acidic deposition

During the summer of 1981, crustacean plankton was sampled in 249 northeastern Ontario lakes, including a large proportion of acidic lakes. Species cluster analysis showed that a major species group containing B. longirostris, D. minutus, H. gibberum, and M. edax was common to most lakes. Two species subgroups most associated with more productive waters (D. retrocurva, D. oregonensis, T. p. mexicanus, and Diaphanosoma sp.) and less productive waters (D. longiremis, C. scutifer, D. g. mendotae, C. b. thomasi, E. longispina, and E. lacustris) in the study area were identified. Acidic lakes were characterized by reduced numbers of species related to declines in the importance of cyclopoids, Daphnidae, L. kindtii and E. lacustris and high relative abundance of D. minutus. Stepwise multiple linear regression of physico-chemical lake characteristics against percent composition of individual species failed to explain much of the variation in species proportions. However, variables related to lake thermal structure were most frequently the primary correlates with species proportions in near-neutral lakes while in acidic lakes the best statistical predictors of species percent composition were most often variables directly related to lake acidity.     

Human exposure to mercury may decrease as acidic deposition increases

It has been hypothesized that human mercury (Hg) exposure via fish consumption will increase with increasing acidic deposition. Specifically, acidic deposition leads to reduced lake pH and alkalinity, and increased sulphate ion concentration ([SO₄ ^2?]), which in turn should cause increased Hg levels in fish, ultimately resulting in increased human Hg exposure via fish consumption. Our empirical test of this hypothesis found it to be false. We specifically examined Hg levels in the hair of Ontario Amerindians, who are known consumers of fish from lakes across the province, and observed a weak negative association with increasing sulphate deposition. An examination of Hg levels in lake trout, northern pike and walleye, three freshwater fish species commonly consumed by Ontario Amerindians, found a similar weak negative association with increasing sulphate deposition. Further analysis of these fish data found that fish [Hg] was most significantly (positively) associated with lake water concentrations of dissolved organic carbon (DOC), not pH, alkalinity or [SO₄ ^2?]. Lake DOC levels are lower in regions of greater acidic deposition. We propose an alternate hypothesis whereby human Hg exposure declines with increasing acidic deposition. In particular, we propose that increasing sulphate deposition leads to reduced lake DOC levels, which in turn leads to lower Hg in fish, ultimately reducing human Hg exposure via fish consumption.     

Acid deposition and effects in Nordic Europe. Damage to fish populations in Scandinavia continue to apace

Although the decline in fish populations due to acidicwater in Norway started as early as in the 1920's the most rapid losses appeared during the 1960–70's. Until 1978, the populations of Atlantic salmon had disappeared from the southernmost part of Norway, and in these areas, more than half of the brown trout populations had been lost. Today, in spite of no increase in acid depositions, the fishery problems seems to continue at the same speed. Data based on interviews of the local fish authority shows that lakes still holding a fish population in the late 70's, have experienced a 30% loss of brown trout populations and a 12% loss of perch in the period 1978–1983. This trend have been confirmed by testfishing in lake systems having long data series. Salmon rivers on the western coast of Norway have experienced several episodes of fish kills due to rapid changes in water quality. These fish kills have mainly affected smolts of Atlantic salmon. Spawning migrating salmon on entering their acidified home river have also been affected. In Sweden, several salmon populations along the western coast have been lost due to acidification with no positive trends so far in the 1980's. Areas in central Sweden and in some high mountain areas are still experiencing a continuous and increasing acidification with detrimental effects on invertebrates and fish. In Finland, an increase in acidic deposition during the last decades have occurred, leading to acidification in the most sensitive freshwater systems. Although some acidified freshwater lakes are reported to have lost their fish stocks, few data on fish population effects are available.     

酸沉降对生态环境的影响

阐述了酸沉降产生的原因及其对生态环境和人类健康的影响,指出由于矿质燃料的燃烧、人为排放SO_2和NO_x导致气溶胶和云雨逐渐酸化。当森林暴露在高浓度SO_2和NO_x下时森林会衰退,表现为叶片发黄和落叶甚至死亡,土壤持续酸化导致盐基离子淋失和土壤溶液中铝离子富集是森林衰退的主要机制,土壤养分亏缺也是森林衰退的主要原因。在酸沉降敏感地区水体酸化和铝离子富集造成湖泊和河流严重酸化及鱼类大量损失。酸沉降与气态污染对水生与陆地生态系统造成大面积损害,并影响到人类的健康。     

Long term effects of a brown coal-based amendment on the properties of soil humic acids

In this study a typical grey-brown podzolic soil was amended with different doses of a brown coal-based preparation called Rekulter (R) largely used in Poland. After seven years, soils were analyzed and humic acids (HAs) were extracted both from the control soil and from the amended soils. All HAs were characterized by Fourier transform infrared spectroscopy and fluorescence spectroscopy both in emission, excitation and synchronous-scan mode and as Excitation-Emission-Matrix (EEM) contour maps. A higher carbon content was observed in the amended soils whereas significant differences were highlighted between the unamended and the amended soil HAs. HAs from amended soils showed a higher content of carboxyl groups and a more aromatic character, particularly HA extracted from the soil amended with the highest dose of R.     

A quality assurance program and quality assessment of the acidic precipitation in Ontario study (APIOS) deposition monitoring networks

Kinetics of H+ consumption by mineral dissolution in a surface soil and a subsoil of an acid woodland soil were studied by means of batch type experiments and stationary pH titrations. Mineral dissolution in the subsoil could effectively be described by congruent dissolution of illite (K_0.6Mg_0.25A1_2.3S1₃0₁₀(OH)₂) followed by an incongruent dissolution stage. In the incongruent stage the concentration of Al decreased while concentrations of K and Mg continued to increase. Congruent dissolution rates of illite could be predicted with power type relationships from transition state theory. In the incongruent dissolution stage the activities of H and Al appeared to be controlled by precipitation of A1(OH)₃. Results of this kind of experiments could be helpful to understand the behavior of Al and base cations in acid soils and soils with high atmospheric loadings of acid. Comparison of the results of batch experiments for a surface soil and a subsoil showed that initially proton consumption in the surface soil is faster and more effective due to the presence of a relatively high cation exchange capacity and base saturation value. However with progressive proton consumption and increasing reaction times proton consumption in the subsoil becomes faster than in the surface soil, presumably due to higher rates of mineral dissolution in the subsoil. Lower dissolution rates in the surface soil may result from lower contents of easily weatherable minerals, due to excessive leaching in the past which is reflected in a 17% lower acid neutralizing capacity than in the subsoil.     

Aluminum toxicity in forests exposed to acidic deposition: The ALBIOS results

The ALBIOS project was conducted to examine the influence of acidic deposition on aluminum transport and toxicity in forested ecosystems of eastern North America and northern Europe. Patterns of aluminum chemistry were evaluated in 14 representative watersheds exposed to different levels of sulfur deposition. Controlled studies with solution and soil culture methods were used to test interspecific differences in aluminum sensitivity for one indicator species (honeylocust - Gleditsia triacanthos L. ) and six commercial tree species (red spruce - Picea rubens Sarg., red oak - Quercus rubra L., sugar maple - Acer saccharum Marsh., American beech - Fagus grandifolia Ehrh., European beech - Fagus sylvatica, and loblolly pine - Pinus Taeda L. ). Overall, red spruce was the tree species whose growth was most sensitive to soluble aluminum, with significant biomass reductions occurring at Al concentrations of approximately 200–250 umol/L. Analyses of soil solutions from the field sites indicated that the conditions for aluminum toxicity for some species exist at some of the study areas. At these watersheds, aluminum toxicity could act as a contributing stress factor affecting forest growth.     

Acidic deposition in California: Findings from a program of monitoring and effects research

California's 14-year, $25 million acidic deposition program has studied the causes and effects of acidic air pollutants. In contrast to the eastern United States where sulfur-derived (S-derived) by-products from coal combustion dominate precipitation chemistry, nitrogen-derived (N-derived) acids predominate in wet and dry deposition in California. Adverse effects on the human lung have not been observed after short-term exposures to acidity, but extended exposures to ambient acidity may pose a chronic risk. No irreversible, adverse effects on surface waters in the Sierra Nevada mountain range or to the state's forests have been found due to extant acidic inputs. The longer-term outlook for forests is less certain because the impacts observed elsewhere occurred after decades of S and N deposition, but at lower ambient ozone levels. Ozone is the major air pollutant stressor for forests, but atmospheric N has the potential to cause adverse changes in soil nutrient cycling. Impacts on man-made materials in southern California (e.g., galvanized steel) were found to be minor. While California does not have an ambient air quality standard for acidic air pollutants, emissions of precursors have declined since the 1960's due to changes in industrial practices, improvements in technology, and adoption of control measures for ozone. Lowering emissions from motor vehicles will be emphasized to prevent future increases in N deposition.     

Long‐term effects on soil microbial properties of heavy metals from industrial exhaust deposition

Soil samples were taken at 0—10 cm and 10—20 cm depth from 7 clay‐marsh sites used as grassland close to Nordenham in the north of Lower Saxony, Germany. The sites had been contaminated by deposition of heavy metals from industrial exhausts, the level of contamination varying according to their distances from a lead factory. The soils were analyzed to assess the depth‐specific effects of NH₄NO₃ extractable and total amounts of Zn, Pb, and Cu on basal respiration, adenylates, ergosterol, and biomass C estimated by fumigation extraction (FE) and substrate‐induced respiration (SIR). Most of the chemical and biological properties studied decreased with depth, but depth‐specific differences in the relationships between these properties rarely occurred. The biomass C/soil organic C ratio was at a relatively high level, but most consistently reflected pollution as a decrease with increasing heavy metal load, independently of the method used for biomass C estimation. However, the SIR estimates were on average 44 % lower than those of FE, mainly due to pH effects. The metabolic quotient SIR‐qCO₂ increased with increasing NH₄NO₃ extractable and total heavy metal contents, but also with decreasing pH, whereas the FE‐qCO₂ remained unaffected by heavy metals and pH. The ATP/FE‐biomass C ratio was on average 8.2 μmol g^—1 and negatively affected by soil pH, but also by total Zn, NH₄NO₃ extractable Zn and Cu. The ergosterol/FE‐biomass C ratio was on average 0.29 %, i.e. at a very low level, and increased with increasing heavy metal content. This indicates a change in the community structure towards fungi.     

Ion leaching from a sugar maple forest in response to acidic deposition and nitrification

Year-to-year variation in acidic deposition within a mature sugar maple-dominated forest and in leaching of ions from the associated podzolic soil were examined at the Turkey Lakes Watershed between 1981 and 1986. Below-canopy inputs to the soil of SO₄ ^2? and NO₃ ^? in throughfall averaged 640 and 295 eq. ha^?1 yr^?1; the corresponding ranges were 493–917 and 261–443 eq. ha^?1 yr^?1. The contribution of atmospheric deposition to SO₄ ^2? NO₃ ^? and Ca²⁺ leaching decreased over the six years. During the study period, the mean annual volume-weighted NO₃ ^? concentration decreased in throughfall and forest-floor percolate and increased in the mineral-soil solution collected below the effective rooting zone. A substantial shift in the balance between SO₄ ^2? and NO₃ ^?leaching from the mineral soil was observed; leaching of SO₄ ^2?decreased and NO₃ ^? leaching increased with time. Leaching of Ca²⁺ and Mg²⁺ from the soil was increased as a result of excess NO₃ ^? production in the soil. The calculated output of NO₃ ^? from the soil, which averaged 1505 eq. ha^?1 yr^?1, considerably exceeded the atmospheric deposition of NO₃ ^?, whereas SO₄ ^2? outputs were only moderately greater than inputs.