Acid Rain - Deposition to Recovery

Most ammonia (NH

3

) emission inventories have been calculated on an annual basis and do not take into account the seasonal variability of emissions that occur as a consequence of climate and agricultural practices that change throughout the year. When used as input to atmospheric transport models to simulate concentration fields, these models therefore fail to capture seasonal variations in ammonia concentration and dry and wet deposition. In this study, seasonal NH

3

emissions from agriculture were modelled on a monthly basis for the year 2000, by incorporating temporal aspects of farming practice. These monthly emissions were then spatially distributed using the AENEID model (Atmospheric Emissions for National Environmental Impacts Determination). The monthly model took the temporal variation in the magnitude of the ammonia emissions, as well as the fine scale (1-km) spatial variation of those temporal changes into account to provide improved outputs at 5-km resolution. The resulting NH

3

emission maps showed a strong seasonal emission pattern, with the highest emissions during springtime (March and April) and the lowest emissions during summer (May to July). This emission pattern was mainly influenced by whether cattle were outside grazing or housed and by the application of manures and fertilizers to the land. When the modelled emissions were compared with measured NH

3

concentrations, the comparison suggested that the modelled emission trend corresponds fairly well with the seasonal trend in the measurements. The remaining discrepancies point to the need to develop functional parametrisations of the interactions with climatic seasonal variation.

Inter-annual variability of surface ozone (O

3

) and nitrogen dioxide (NO

2

) over Europe has been studied over the period 1958–2003 using a three-dimensional Chemistry-Transport Model coupled to meteorological data from the ERA40 data set produced at the European Centre of Medium-range Weather Forecasts (ECMWF). Emissions and boundary conditions were kept at present levels throughout the simulation period. It was found that the annual mean NO

2

concentration varies between ±50% and the summer mean O

3

concentration varies between −10 and +20 percent (%) compared to the 46-year average over the model domain. There is also variation in ozone and NO

2

over longer time scales. The last 22 years display high concentrations of ozone in central and south-western Europe and low concentrations in north-eastern Europe. The first 22 years display very high concentrations of NO

2

over the North Sea. There is indication of trends in ozone and nitrogen dioxide but this has to be investigated further. Such information is one factor that should be taken into account when considering future control strategies.

Within the European monitoring network (EMEP, http://www.emep.int) several different sampling procedures for measuring the main air components have been applied. This has contributed to systematic concentration differences and a comparability problem. Since 1997 co-located experiments in 15 countries have been carried out to quantify these differences. In addition, three major measurement campaigns were organized by EMEP between 1985 and 1991. Differences among results depend on the concentration level and methods used. The decrease in SO

2

concentrations over the last twenty years has placed greater demands on the methodology. Absorbing solutions methods for SO

2

, (H

2

O

2

and tetrachloromercurate (TCM)) typically have higher detection limits than the reference method, which uses KOH impregnated filters. The TCM method also has problems with negative interference, especially in summertime. UV fluorescence monitors have in a few cases proven to give good results, but interferences, detection limit and poor maintenance can be problems. For NO

2

, many countries are using the TGS absorption solution method, which has a higher detection limit than the reference method using NaI impregnated glass sinters.

The research concerns the Wielkopolski National Park (West Poland), which suffered a huge human impact in the 1970s and 1980s owing to the nearby location of an industrial plant. Since then, fundamental technological changes that it introduced into its production of phosphate fertilizers have radically reduced the amount of pollution emitted. A three-year study (2002–2004) of fluorides in precipitation in open terrain and under tree crowns showed their concentrations to range from levels below the detection limit (0.003 mg/l) to 0.560 mg/l. Those registered under tree crowns were several times higher and indicated substantial dry deposition of fluorides on the trees. The highest values were recorded in 2003, with 43% of samples ranging from 0.01 to 0.05 mg/l, and with 51% of throughfall ranging from 0.10 to 0.50 mg/l. A strong connection was shown to exist between fluoride and sulphate concentrations in the precipitation. An analysis was made of the available data on F concentrations in the air and the dust levels around the factory, but these figures did not show an unequivocal effect on F concentrations in precipitation. A great similarity was found to occur between the fluoride content in rainwater in the Wielkopolski National Park and in the centre of the nearby Poznań metropolitan area, which indicates that there are also other F sources besides the local factory.

Emissions of sulphur and oxidized nitrogen compounds in Europe have been reduced following a series of control measures during the last two decades. These changes have taken place during a period in which the primary gases and the wet deposition throughout Europe were extensively monitored. Since the end of the 1970s, for example land based sulphur emissions declined by between 90 and 70% depending on the region. Over the same period the total deposition of sulphur and its partitioning into wet and dry deposition have declined, but the spatial pattern in the reduction in deposition differs from that of emission and has changed with time. Such nonlinearities in the emission-deposition relationship are important to understand as they complicate the process of assessing the effects of emission reduction strategies. Observed non-linearities in terrestrial sulphur emission-deposition patterns have been identified in north west Europe due to increases in marine emissions, and are currently slowing the recovery of freshwater ecosystems. Changes in the relative amounts of SO

2

and NH

3

in air over the last two decades have also changed the affinity of terrestrial surfaces for SO

2

and have therefore changed the deposition velocity of SO

2

over substantial areas. The consequence of this effect has been the very rapid reduction in ambient SO

2

concentration in some of the major source areas of Europe, where NH

3

did not change much. Interactions between the different pollutants, generating non-linearities are now being incorporated in long-range transport models to simulate the effects of historical emission trends and to provide projections into the future. This paper identifies non-linearities in emission deposition relationships for sulphur and nitrogen compounds in Europe using data from the EMEP long-rang transport model and measured concentration fields of the major ions in precipitation and of SO

2

and NO

2

in surface air.

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 monitoringnetwork (MERA) in order to bring out spatiotemporal 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 SO

2

and NO

x

emissions decreased (−3.3 and −2.0% year

−1

, respectively) contrary to NH

3

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

. SO

2−

4

and nss — SO

2−

4

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 SO

2

emissions in France (−3.3% year

−1

). A good correlation (

R

2

=0.84) between SO

2

emissions and nss — SO

2−

4

concentrations was obtained. The decreasing trend of NH

+

4

was more significant (−5.4±5.2% year

−1

) than that of NO

−

3

(−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 HNO

3

to acidity precipitation increased by 51% over the studied period.

Data from the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) indicate significant changes have occurred in precipitation chemistry and the chemical climate in the United States (US). A Seasonal Kendall Trend (SKT) analysis shows statistically significant increases in precipitation ammonium concentrations at 64% of 159 continental US NADP/NTN sites evaluated from Winter 1985 to Fall 2004 (Dec. 1984 – Nov. 2004). Sulfate decreases were widespread, with an SKT analysis indicating statistically significant decreases at 89% of sites evaluated. Ratios of chemical equivalent concentrations of ammonium to sulfate in precipitation have risen to the extent that ammonium now exceeds sulfate over more than half of the continental U.S. on a precipitation-weightedmean annual basis. These trends in the concentrations of ammonium, sulfate, and other species have been accompanied by significant decreases in the frequency of acidic precipitation (pH<5.0) in the last decade.

Temporal trends of non-sea salt (nss-) sulfate and nitrate were analyzed from nationwide precipitation chemistry measurements provided by the Ministry of the Environment (MOE) for the 1988–2002 fiscal years (April–March). The concentrations and deposition of nss-sulfate were found to be decreasing, and those of nitrate were stable or slightly increasing at most sites. These deposition trends were discussed from the viewpoint of emissions of SO

2

and NO

X

during the period of interest. Because monitoring techniques have changed in the number of active sites, samplers, and analytical methods during the operation period, the median of all annual depositions measured in Japan in a specific year was selected as the annual representative. The contribution of specific emission sources was also calculated for 1990 on the basis of the nss-sulfate and nitrate deposition in Japan obtained with a model simulation in which the model did not include volcanic emissions from Mt. Oyama, Miyakejima Island, which began to erupt suddenly and violently in 2000. For nss-sulfate, the calculated deposition agrees well with the intensity and trends of the median up to 1999. After 2000, a higher deposition than calculated in the preceding years was evident, which is attributable to the volcanic SO

2

from Mt. Oyama. For nitrate, both the calculated and observed depositions were slightly increasing; however, the calculation was found to exceed the observation.

The SO

4

-S and NO

3

-N concentrations and pH in bulk precipitation, throughfall, stemflow and soil water for the 1994–2004 period were studied in pine forests in Latvia (Rucava and Taurene Integrated Monitoring stations). The SO

4

-S and NO

3

-N concentrations decreased over the study period, simultaneously with a decrease of acidity in precipitation. The changes were more evident in the western part of Latvia, probably due to declining long-range air pollution from West Europe. The trend of decreasing sulphate concentrations and increasing pH in precipitation were not followed by respective changes in soil water. In the upper soil horizon sulphate ion concentrations and acidity increased in soil water. Over the observation period, nitrate concentrations also showed an increasing trend in soil water at Rucava and Taurene, but these changes were not statistically significant.

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

+

, NH

4

+

, K

+

, Ca

2+

, Mg

2+

, Cl

−

, NO

3

−

, SO

4

2−

) and carboxylic acids (acetic, formic and oxalic) using ion chromatography. The volume weighted mean, VWM, of the anions NO

3

−

,SO

4

2−

and Cl

−

was, respectively, 20.3, 12.1 and 10.7 μmol 1

−1

. Rainwater in São Paulo was acidic, with 55% of the samples exhibiting a pH below 5.6. The VWMof the free H

+

was 6.27 μmol 1

−1

), corresponding to a pH of 5.20. Ammonia (NH

3

), determined as NH

4

+

(VWM=32.8 μmol 1

−1

), was the main acidity neutralizing agent. Considering that the H

+

ion is the only counter ion produced from the non-seasalt fraction of the dissociated anions, the contribution of each anion to the free acidity potential has the following profile:

SO

4

2−

(31.1%),

NO

3

−

(26.0%), CH

3

COO

−

(22.0%), Cl

−

(13.7%), HCOO

−

(5.4%) and

C

2

O

4

2−

(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.

Pollution of the atmosphere with cadmium (Cd), mercury (Hg), and lead (Pb) is a consequence of human activities. Natural archives are necessary to reconstruct the long-term history of metal deposition because accurate measurement of atmospheric deposition is a recent accomplishment. Reconstructions require: (1) accurate determination of concentrations of elements and isotopes, (2) accurate chronology of archives, and (3) archives that faithfully record atmosphere deposition. The most useful long-term archives are accumulations of ice and snow, peat, and lake sediment. Quantification of Cd deposition is uncommon because of its low concentration and substantial chemical mobility. Nonetheless, trends in peat and lake sediment are similar to those of Hg and Pb since ca. 1800 A.D. Both Hg and Pb are relatively chemically immobile and thus the peat and lake archives are believed to record historic trends of atmospheric deposition. Isotopic and concentration studies of Pb indicate a history of northern hemisphere atmospheric pollution extending back prior to 0 A.D. Although measurements of Hg concentration are now routine, isotopic measurements are in their infancy. Some Hg pollution sources have unique isotopic ratios, thereby contributing unique signals to the total Hg.

The consequences of nitrogen (N) enrichment for terrestrial and freshwater ecosystems are of increasing concern in many areas due to continued or increasing high emission rates of reactive N. Within terrestrial ecosystems various conceptual frameworks and modelling approaches have been developed which have enhanced our understanding of the sequence of changes associated with increased N availability and help us predict their future impacts. Here, some recent findings are described and their implications for these conceptual frameworks and modelling approaches discussed. They are: (a) an early loss of plant species that are characteristic of low N conditions as N availability increases and a loss of species with high N retention efficiencies (so called N ‘filters’), (b) suppression of microbial immobilisation of deposited NO

3

−

due to increased NH

4

+

availability in the early stages of N saturation, (c) the early onset of NO

3

−

leaching due to these changes (a and b above) in both plant and microbial functioning, (d) reduced sensitivity of vegetation to N additions in areas with high historical N deposition, (e) delayed changes in soil C:N changes due to increased net primary productivity and reduced decomposition of soil organic matter. Some suggestions of early indicators of N saturation are suggested (occurrence of mosses; NH

4

+

: NO

3

−

ratio in surface soils) which indicate either a shift in ecosystem function and/or structure.

Regular additions of NH

4

NO

3

(35–140 kg N ha

−1

yr

−1

) and (NH

4

)

2

SO

4

(140 kg N ha

−1

yr

−1

) to a calcareous grassland in northern England over a period of 12 years have resulted in a decline in the frequency of the indigenous bryophyte species and the establishment of non-indigenous calcifuge species, with implications for the structure and composition of this calcareous bryophyte community. The lowest NH

4

NO

3

additions of 35 kg N ha

−1

yr

−1

produced significant declines in frequency of

Hypnum cupressiforme, Campylium chrysophyllum

, and

Calliergon cuspidatum

. Significant reductions in frequency at higher NH

4

NO

3

application rates were recorded for

Pseudoscleropodium purum, Ctenidum molluscum

, and

Dicranum scoparium

. The highest NH

4

NO

3

and (NH

4

)

2

SO

4

additions provided conditions conducive for the establishment of two typical calcifuges —

Polytrichum spp.

and

Campylopus introflexus

, respectively. Substrate-surface pH measurements showed a dose-related reduction in pH with increasing NH

4

NO

3

deposition rates of 1.6 pH units between the control and highest deposition rate, and a further significant fall in pH, of >1 pH unit, between the NH

4

NO

3

and (NH

4

)

2

SO

4

treatments. These results suggest that indigenous bryophyte composition may be at risk from nitrogen deposition rates of 35 kg N ha

−1

yr

−1

or less. These effects are of particular concern for rare or endangered species of low frequency.

The atmospheric deposition of reactive nitrogen on turf grassland in Tsukuba, central Japan, was investigated from July 2003 to December 2004.The target components were ammonium, nitrate, and nitrite ions for wet deposition and gaseous ammonia, nitric and nitrous acids, and particulate ammonium, nitrate, and nitrite for dry deposition. Organic nitrogen was also evaluated by subtracting the amount of inorganic nitrogen from total nitrogen. A wet-only sampler and filter holders were used to collect precipitation and the atmospheric components, respectively. An inferential method was applied to calculate the dry deposition velocity of gases and particles, which involved the effects of surface wetness and ammonia volatilization through stomata on the dry deposition velocity. The mean fraction of the monthly wet to total deposition was different among chemical species; 37, 77, and 1% for ammoniacal, nitrate-, and nitrite-nitrogen, respectively. The annual deposition of inorganic nitrogen in 2004 was 47 and 48 mmol m

−2

yr

−1

for wet and dry deposition, respectively; 51% of atmospheric deposition was contributed by dry deposition. The annual wet deposition in 2004 was 20, 27, and 0.07 mmol m

−2

yr

−1

, and the annual dry deposition in 2004 was 35, 7.4, and 5.4 mmol m

−2

yr

−1

for ammoniacal, nitrate-, and nitrite-nitrogen, respectively. Ammoniacal nitrogenwas the most important reactive nitrogen because of its remarkable contribution to both wet and dry deposition. The median ratio of the organic nitrogen concentration to total nitrogen was 9.8, 17, and 15% for precipitation, gases, and particles, respectively.

To obtain basic information for evaluating critical levels of O

3

under different nitrogen loads for protecting Japanese beech forests, two-year-old seedlings of

Fagus crenata

Blume were grown in potted andisol supplied with N as NH

4

NO

3

solution at 0, 20 or 50 kg ha

−1

year

−1

and exposed to charcoal-filtered air or O

3

at 1.0, 1.5 and 2.0 times the ambient concentration from 16 April to 22 September 2004. The O

3

induced significant reductions in the wholeplant dry mass, net photosynthetic rate at 380 μmol mol

−1

CO

2

(

A

380

), carboxylation efficiency (

CE

) and concentrations of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and total soluble protein (TSP) in the leaves. The concentrations of Rubisco and TSP were negatively correlated with the concentration of leaf acidic amino acid, suggesting that O

3

enhanced the degradation of protein such as Rubisco. The N supply to the soil did not significantly change the whole-plant dry mass and

A

380

, whereas it significantly increased the

CE

and concentrations of Rubisco and total amino acid. No significant interactive effects of O

3

and N supply to the soil were detected on the growth, photosynthetic parameters and concentrations of protein and amino acid in the leaves. In conclusion, N supply to the soil at ≤50 kg ha

−1

year

−1

does not significantly change the sensitivity to O

3

of growth and net photosynthesis of

Fagus crenata

seedlings.

Liming and/or application of specific nutrients have been proposed as countermeasures to the acidification of forest soils in southern Sweden. In this study the stem growth of

Picea abies

(L.) Karst. growing on acidic mineral soils in SW Sweden was investigated 10 years after additions of lime (Ca; 3000 kg lime ha

−1

), lime plus P (25 kg ha

−1

) and K (80 kg ha

−1

), or N in low doses (2×10 kg ha

−1

yr

−1

) (treatments: CaPK, Ca, N, CaPKN, and 2Ca2P2K, respectively). Compared with the control, stem growth was increased following all treatments involving lime additions, including liming alone. The PK addition did not seem to affect growth. The most plausible cause of the observed growth increases was that the lime additions indirectly increased the supply of plant-available N. The annual low-dose N addition did not significantly affect growth. This suggests that air-borne deposition of N, which supplies very small doses of N throughout the year, has a minor or even negligible influence on

P. abies

growth.

Douglas fir [

Pseudotsuga menziesii

(Mirb.) Franco] shoots from mature trees were collected from two sites of contrasting soil pH: the Glendon campus of York University in Toronto, Canada (pH 6.7 at 40 cm) designated Can.; and Breuil Forest, Morvan, France (pH 4 to 4.5) designated Fr.. Needles were removed from the shoots, frozen in liquid nitrogen, and kept in a cryo-biological storage system prior to X-ray microanalysis on the cold stage (−170°C) of a cryo-SEM. Four elements detected, potassium, phosphorus, sulphur and chlorine, were ubiquitous in the needle tissues from both sites. Manganese was infrequently found in needle tissues from the Fr. site. Calcium was localized most heavily in the outer tangential wall of the hypodermis and also in the epidermal walls. Silicon (Si) concentrations were higher in the Fr. site than in the Can. site. The epidermis, hypodermis and mesophyll of needles from the Fr. site exhibited the highest Si content, with greater amounts in the tip and middle of the needle than in the base. Aluminium was distributed fairly evenly throughout the tissues, and there were few major sites of concentration.

Leaching experiments of rebuilt soil columns with two simulated acid rain solutions (pH 4.6–3.8) were conducted for two natural soils and two artificial contaminated soils from Hunan, southcentral China, to study effects of acid rain on competitive releases of soil Cd, Cu, and Zn. Distilled water was used in comparison. The results showed that the total releases were Zn>Cu>Cd for the natural soils and Cd>Zn»Cu for the contaminated soils, which reflected sensitivity of these metals to acid rain. Leached with different acid rain, about 26–76% of external Cd and 11–68% external Zn were released, but more than 99% of external Cu was adsorbed by the soils, and therefore Cu had a different sorption and desorption pattern from Cd and Zn. Metal releases were obviously correlated with releases of TOC in the leachates, which could be described as an exponential equation. Compared with the natural soils, acid rain not only led to changes in total metal contents, but also in metal fraction distributions in the contaminated soils. More acidified soils had a lower sorption capacity to metals, mostly related to soil properties such as pH, organic matter, soil particles, adsorbed SO

4

2−

, exchangeable Al

3+

and

H+

, and contents of Fe

2

O

3

and Al

2

O

3

.

The ForSAFE model, designed for modelling biogeochemical cycles (water, acidity, base cation, nitrogen and carbon) in terrestrial ecosystems, was modified with a vegetation response module (VEG), incorporating the effects of: nitrogen pollution, acidification, soil moisture, temperature, wind chill exposure, light and shading by trees, grazing by animals, competition between plants, above ground for light and below ground for water and nutrients. The model calculates the response of important ground vegetation plant groups. The integrated model was tested and validated at integrated level II forest monitoring sites across Sweden. Four are shown here, and are used to assess the effect of acidification and nitrogen pollution in relation to factors such as climate change, forest management and changing grazing pressure. The response functions have been derived from single-factor experiments and integrated through the model structure for use on whole systems. The tests with the model suggest that the ground vegetation composition is reasonably well predicted, that much research remains before the model is fully tested and operational, and that the model may serve as a tool for assessing impacts of climate change, acid rain and forest management on plant biodiversity in forested areas.

We used laboratory experiments to investigate surface resistance (

R

c

) to dry deposition of ozone (O

3

) on different types of soil samples collected from the arid deserts and the Loess Plateau of northern China. Furthermore, we measured the factors that affected

R

c

, which depends on the physical and chemical interaction between trace constituents and the deposition surface, and evaluated deposition velocity (

V

d

). There was little influence of geometric surface area, soil weight, or O

3

concentration on

V

d

of O

3

. The effect of relative humidity (RH) (i.e. moisture content of the soil) on O

3

uptake was in agreement with results reported in the literature: a distinct RH dependence of

V

d

and little uptake under water-saturated conditions were observed.

R

c

values for all the soil samples examined were in the range 0.21–3.3 s mm

−1

and were exponentially related to the surface area of the particles and the organic carbon content of each soil sample at RH of both <10 and 60%.

Estimates of ozone concentration and deposition flux to coniferous and deciduous forest in the Czech Republic on a 1 × 1 km grid during growing season (April–September) of the year 2001 are presented. Ozone deposition flux was derived from ozone concentrations in the atmosphere and from its deposition velocities. To quantify the spatial pattern in surface concentrations at 1 km resolution incorporating topography, empirical methods are used. The procedure maps ozone concentrations from the period of the day when measurements are representative for the forest areas of countryside. The effects of boundary layer stability are quantified using the observed relationship between the diurnal variability of surface ozone concentration and altitude. Ozone deposition velocities were calculated according to a multiple resistance model incorporating aerodynamic resistance (

R

a

), laminar layer resistance (

R

b

) and surface resistance (

R

c

). Surface resistance (

R

c

) comprises stomatal resistance (

R

sto

).

R

sto

was calculated with respect to global radiation, surface air temperature and land cover. Modelled total and stomatal ozone fluxes are compared with the maps describing equivalent values of AOT40 (accumulated exposure over threshold of 40 ppb). for forests, the critical level (9,000 ppbh May–July daylight hours) is exceeded over 50% of forested territory.

The effects of harvesting on the long-term mass balances of calcium (Ca), magnesium (Mg) and potassium (K) were evaluated on a regional level in Sweden. A new high-resolution weathering database was used together with estimates of total deposition, losses through harvest and leaching. Estimates were made for pine and spruce separately and for two harvesting intensity scenarios: stem harvesting and whole-tree harvesting. The mass balance calculations showed net losses of Ca and Mg in almost the whole country for both scenarios. The losses were smaller for pine than for spruce. The K balances were mainly positive for pine but negative for spruce. Leaching was a main factor in the mass balances, especially for Ca and Mg. Whole-tree harvesting in spruce forests led to substantially higher net losses of K and Ca than stem harvesting, according to the calculations. In the whole-tree harvesting scenario in spruce forests the estimated yearly net losses of Ca, Mg and K corresponded to at least 5%, 8% and 3% of the pools of exchangeable base cations, respectively, at 25% of the analysed sites. If losses of this magnitude continue the depletion of the pools of Ca, Mg and K may lead to very low base saturation of the soils, possibly accompanied by negative effects on soil fertility, runoff water quality, tree vitality and tree growth within a forest rotation in parts of Sweden.

In order to test the hypothesis of aluminium toxicity induced by acid deposition, an experimental acid irrigation was carried out in a mature Norway spruce stand in Southern Germany (Höglwald). The experiment comprised three plots: no irrigation, irrigation (170 mm a

−1

), and acid irrigation with diluted sulphuric acid (pH of 2.6–2.8). During the seven years of acid irrigation (1984–1990) water containing 0.43 mol

c

m

−2

a

−1

of protons and sulphate was added with a mean pH of 3.2 (throughfall+acid irrigation water) compared to 4.9 (throughfall) on both control plots. Most of the additional proton input was consumed in the organic layer and the upper mineral soil. Acid irrigation resulted in a long lasting elevation of sulphate concentrations in the seepage water. Together with sulphate both aluminium and appreciable amounts of base cations were leached from the main rooting zone. The ratio between base cations (Ca+Mg+K) and aluminium was 0.79 during acid irrigation and 0.92 on the control. Neither tree growth and nutrition nor the pool of exchangeable cations were affected significantly. We conclude that at this site protection mechanisms against aluminium toxicity exist and that additional base cation runoff can still be compensated without further reduction of the supply of exchangeable base cations in the upper mineral soil.

A nitrogen (N) budget was constructed for a period of 6 years (1988–1993) in a Norway spruce stand with current deposition of 19 kg N and 22 kg S ha

−1

year

−1

. The stand was fertilized annually by addition of 100 kg N and 114 kg S ha

−1

(NS). Above and below ground biomass, litterfall, fine- root litter production, soil solution and net mineralization were measured to estimate pools, fluxes and accumulation of nitrogen. The average needle litterfall in control (C) and NS plots in 1993 was 2.2 and 2.5 ton ha

−1

year

−1

, respectively. The fine root litter production prior to treatment (1987) was 4.4 ton ha

−1

year

−1

and after treatment (1993) it was 4.5 and 3.9 ton ha

−1

year

−1

in C and NS plots, respectively. Net N mineralization in the soil profile down to 50 cm was estimated to be 86 and 115 kg ha

−1

year

−1

in C and NS plots, respectively in 1992. During the treatment period the uptake of N in the needle biomass in C and NS plots was 29 and 77 kg ha

−1

year

−1

, respectively. No N was accumulated in needles of C plot where the NS plots accumulated 34 kg ha

−1

year

−1

. Of the annually added inorganic N to NS plots 47% was accumulated in the above and below ground biomass and 37% in the soil. N fluxes via fine-root litter production in the C plots were much higher (54 kg ha

−1

year

−1

) than that via litterfall (29 kg ha

−1

year

−1

).

Four umbric A horizons from acid forest soils were acidified in a batch type experiment and its effect in the Al pools of the solid phase analysed by means of selective dissolution methods. The results showed that Al release accounted for the consumption of 85–99% of the added protons, and causes a decrease of 2–33% of the ‘reactive’ Al pool of the soil solid phase. In these A horizons, inorganic noncrystalline Al and high stability Al-humus complexes are the main sources of the dissolved Al. The contribution of the complexes with intermediate stability only was relevant in the more acid horizon developed from phyllites (P18-A). The increase of equilibration time from 96 to 720 h did not caused significant differences in the decrease of the ‘reactive’ Al pool suggesting the acid neutralising reactions occurred in less than 96 h. In most cases the quantity of released Al is in agreement with the decrease of the different reactive Al pools of the solid phase.

Many national exposure programmes have been performed in tropical and subtropical climates during the last 50 years. However, ambitious programmes involving more than a few countries are scarce. In this paper a recently formed network of test sites is described involving 12 test sites in Asia (India, Vietnam, Thailand, Malaysia and China including Hong Kong) and four test sites in Africa (South Africa, Zambia and Zimbabwe). This effort is part of the 2001–2004 Swedish International Development Agency (SIDA) funded Programme on Regional Air Pollution in Developing Countries (RAPIDC). Corrosion attack after one (2002–2003) year of exposure (carbon steel, zinc, copper, limestone and paint coated steel) are presented together with environmental data (SO

2

, NO

2

2, HNO

3

, O

3

, particles, amount and pH of precipitation, temperature and relative humidity) for all the test sites. The obtained corrosion values are substantially higher than expected for limestone, higher than expected for carbon steel and lower than expected for zinc compared to values calculated using the best available dose—response functions.

A “multi-pollutant exposure programme” reflecting the new pollution situation where SO

2

is no longer the dominating pollutant has been performed by the International Co-operative Programme on Effects on Materials, including Historic and Cultural Monuments (ICP Materials) within the activities of the Convention on Long-range Transboundary Air Pollution. The main results obtained in the period 1997–2003 are summarised. Dose-response functions are presented for carbon steel, zinc, copper, bronze and limestone. Parameters involved in the functions include besides SO

2

and pH, which were included in the previously developed functions from ICP Materials, also the effect of particulate matter and HNO

3

.

Since 1983, the Ministry of the Environment of Japan has conducted nation-wide acid deposition surveys. To investigate the effects of acid deposition on surface water, we used the nonparametric Mann—Kendall test to find temporal trends in pH, alkalinity, and electrical conductivity (EC) in more than 10 years of data collected from five lakes and their catchments (Lake Kuttara: northernmost; Lake Kamakita: near Tokyo; Lake Ijira: central; Lake Banryu: western; and Lake Unagiike: southernmost). The pH of Lake Ijira water has declined slightly since the mid-1990s, corresponding with the downward trends seen in the pH and alkalinity of the river water flowing into the lake. There were significant upward trends in the EC of both the lake and stream water; the same trends were also found for NO

3

−

concentrations. These trends show evidence of acidification due to atmospheric deposition, and this is the first such finding in Japan based on significant long-term trends. Lake Ijira is located about 40 km north of the Chukyo industrial area near Nagoya. The annual depositions of H

+

, nss-SO

4

2−

, and NO

3

−

in Lake Ijira were among the highest of all deposition monitoring sites, suggesting that this is the main cause of the significant acidification observed in Lake Ijira. No significant trends suggesting acidification were observed in any of the other lake catchments in spite of the significant upward trends in EC. Upward trends in pH and alkalinity at Lake Banryu and upward trends in alkalinity at Lake Kamakita were detected, but no change in pH or alkalinity at Lake Kuttara and Lake Unagiike was observed.

In 1989, a watershed acidification experiment was begun on the Fernow Experimental Forest in West Virginia, USA. Ammonium sulfate fertilizer (35.5 kg N ha

−1

yr

−1

and 40.5 kg S ha

−1

yr

−1

) was applied to a forested watershed (WS3) that supported a 20-year-old stand of eastern deciduous hardwoods. Additions of N and S are approximately twice the ambient deposition of nitrogen and sulfur in the adjacent mature forested watershed (WS4), that serves as the reference watershed for this study. Acidification of stream water and soil solution was documented, although the response was delayed, and acidification processes appeared to be driven by nitrate rather than sulfate. As a result of the acidification treatment, nitrate solution concentrations increased below all soil layers, whereas sulfate was retained by all soil layers after only a few years of the fertilization treatments, perhaps due to adsorption induced from decreasing sulfate deposition. Based on soil solution monitoring, depletion of calcium and magnesium was observed, first from the upper soil horizons and later from the lower soil horizons. Increased base cation concentrations in stream water also were documented and linked closely with high solution levels of nitrate. Significant changes in soil chemical properties were not detected after 12 years of treatment, however.

Strongly decreasing atmospheric emissions and acidic deposition during the 1990s have initiated chemical reversal from acidification in several drinking-water reservoirs of the Erzgebirge, SE Germany. We studied responses of phytoplankton, zooplankton and fish stocks in five reservoirs and at enclosure scale after experimental neutralization of 1,200 m

3

of lake water. About 4 months after this treatment, diatoms and cryptomonads replaced the predominating chrysophytes and dinoflagellates. The colonization by acid-sensitive species of green algae, cryptomonads, rotifers and Cladocera (e.g.

Bosmina longirostris

) is explained by the occurrence of dormant stages or by survival of individuals in very low abundances. Analogous to the enclosure experiment, three reservoirs showed significantly (

p

<0.01) falling trends of chlorophyll

a

and phytoplankton biovolume, mainly due to the decline of dinoflagellates. Picoplankton and diatoms increased slightly in two reservoirs. The zooplankton communities were dominated by rotifers and small Cladocera. Representatives of the genus

Daphnia

were lacking. Two reservoirs were re-colonized by zooplanktivorous fish populations of either perch (

Perca fluviatilis

) or sunbleak (

Leucaspius delineatus

). The latter exhibited extremely high fluctuating abundance and biomass and even suffered from a population crash.

We describe the development of the fish community in the acidified and limed river Litleåna in southern Norway, and describe how chemical restoration, compensatory introductions of exotics, and accidental invasion of exotics interact to influence the population of the naturally occurring brown trout (

Salmo trutta

). The river Litleåna is a tributary to the river Kvina in Vest-Agder County, southern Norway. During the years 1996–2004, annual mean pH was 4.9–5.0 and 6.1–6.4 above and below the liming facility, which was installed in 1994. Originally, brown trout was the only fish species in the river, but brook trout (

Salvelinus fontinalis

) have been intentionally introduced, whereas European minnow (

Phoxinus phoxinus

) was introduced by accident. Fish densities were recorded by means of electrofishing annually over the ten year period 1995–2004. Although close to extinction before liming was initiated, brown trout fry densities increased from 1995 to 1999, with subsequent varying densities. There has been a simultaneous major increase in the occurrence and density of European minnow since 1997. Our results show that both brown trout and European minnow increase after liming. Minnow densities are negatively affected by low pH episodes in the river. The growth rates of brown trout fry are negatively correlated to minnow densities, indicating competition between the species. Brook trout densities have decreased since liming started, and during the brown trout recovery.

High mortality rates due to predation from fish may reduce densities of preferred prey animals. Predation may also depress the rate of recovery from environmental stress. In an alpine ecosystem damaged by acidification, we compared three different techniques of monitoring the recovery of two large species of crustaceans, the amphipod

Gammarus lacustris

and the notostrachan

Lepidurus arcticus

. The methods used were: (1): benthic littoral kick samples, (2): artificial substrate in the form of jute bags, (3): examination of brown trout stomachs. The monitoring took place in two limed lakes at the Hardangervidda mountain plateau in Central Norway, L. Svartavatn and L. Svartavasstjørni. Brown trout,

Salmo trutta

, is the only fish species in the lakes. Liming as a water quality improvement measure was started in 1994. All stomach samples were negative with respect to

Gammarus

and

Lepidurus

during the period 1987–1998. In 1999, the first records of both species were done in trout stomachs collected from Lake Svartavatnet. In Lake Svartavasstj–rni,

Lepidurus

and

Gammarus

reappeared in fish stomachs in 2001 and 2002, respectively. During the period of monitoring, no records of these crustaceans were done in benthic samples and on artificial substrate in any of the two lakes. In an unacidified reference site, Lake Skiftesjøen, both benthic samples and the jute bags indicated a dense population of

Gammarus

. Our results strongly indicate that studies of fish stomachs are the best method for monitoring low-density populations of attractive fish food animals.

In response to reduced sulphur emissions, there has been a large decrease in sulphate (SO

2−

4

; –0.97 μeq l

−1

year

−1

) and hydrogen (−1.18 −eq l

−1

year

−1

) ion concentration in bulk precipitation between 1980 and 2000 at Plastic Lake in central Ontario. The benefit of this large reduction in SO

2−

4

deposition on stream water chemistry was assessed using the gauged outflow from a conifer-forested catchment (PC1; 23.3 ha), which is influenced by a small wetland located immediately upstream of the outflow. Sulphate concentrations declined, but not significantly due to large inter-annual variation in SO

2−

4

concentration. Between 1980 and 2000, there were significant increases in dissolved organic carbon, ammonium and potassium concentration likely reflecting increased mineralisation in the wetland. Calcium concentrations in PC1 decreased during the two decade period (−2.24 μeq l

−1

year

−1

), as a consequence there was no improvement in stream pH and the Ca:Al ratio in PC1 continued to decline. A similar response was noted in an upland-draining subcatchment of PC1-08 that has been monitored since 1987. Despite large reductions in SO

2−

4

deposition and almost complete retention of nitrogen in soil, there has been no improvement (in terms of pH) in stream water at PC1 due to a combination of soil acidification and climatic (droughts, increased mineralisation) perturbations.

To evaluate the acid deposition reduction negotiated for 2010 within the UNECE LRTAP Gothenburg Protocol, sulphur and nitrogen deposition timeseries (1880–2100) were compared to critical loads of acidity on five French ecosystems: Massif Central basalt (site 1) and granite (2); Paris Bassin tertiary sands (3); Vosges mountains sandstone (4) and Landes eolian sands (5). The SAFE model was used to estimate the response of soil solution pH and [Al]/[BC] ratio to the deposition scenario. Among the five sites, critical loads were exceeded in the past at sites 3, 4 and 5. Sites 3 and 4 were still expected to exceed in 2010, the Protocol year. Further reduction of atmospheric deposition, mainly nitrogen, would be needed to achieve recovery on these ecosystems. At sites 3, 4 and 5, the delay between the critical load exceedance and the violation of the critical chemical criterion was estimated to be 10 to 30 years in the top soil and 50 to 90 years in the deeper soil. At site 5, a recovery was expected in the top soil in 2010 with a time lag of 10 years. Unexpectedly, soil pH continued to decrease after 1980 in the deeper soil at sites 2 and 5. This time lag indicated that acidification moved down the soil profile as a consequence of slow base cation depletion by ion exchange. This delayed response of the soil solution was the result of the combination of weathering rates and vegetation uptake but also of the relative ratio between base cation deposition and acid compounds.

Over 7,000 lakes around Sudbury, Ontario, Canada were acidified by S deposition associated with emissions from the Sudbury metal smelters and more distant S sources. Air pollution controls have led to widespread changes in damaged Sudbury lakes, including increased pH and decreased concentrations of SO

4

, metals and base cations. While chemical improvements have often been substantial, many lakes are still acidified, although water quality recovery is continuing. Biological recovery has been observed in some lakes among various groups of organisms including fish, zooplankton, phytoplankton and zoobenthos. Generally, however, biological recovery is still at an early stage. Lakes around Sudbury are also showing that the recovery of acid-damaged lakes is closely linked to the effects of other major environmental stressors such as climate change, base cation depletion and UV-B irradiance. Future studies of the recovery of acid-damaged lakes around Sudbury, and in other regions, will need to consider the interactions of these and other stressors.

Gradient analyses were used to correlatively determine the importance of acid-related variables for littoral macroinvertebrate assemblages. To better ascertain the effects of acidity on macroinvertebrate assemblages we removed sites judged to be affected by other stressors such as agriculture, urbanization and liming. PCA of land use and water chemistry confirmed the presence of an acidity gradient; several acidity variables (e.g. pH and buffering capacity) were strongly correlated with the first PC axis, which explained Ca 32% of the variance in the environmental data. Partial constrained ordination of littoral macroinvertebrate assemblages with water chemistry, after removing the effect of other confounding variables (e.g. land use/type), showed that acidity variables accounted for significant amounts of among-lake variability in assemblage structure. Regression of canonical scores (a metric of community composition) and diversity with pH and alkalinity was used to visually determine ecological breakpoints or threshold values. Five classes were established for pH: pH≺5 (extremely acid), 5≺pH⩽5.6 (very acid), 5.6≺pH⩽6.2 (acid), 6.2≺pH⩽6.8 (weakly acid) and pH≻6.8 (neutral-alkaline). Similarly, three classes were determined for alkalinity/acidity: ≺0.02, 0.02–0.1 and ≻0.1 meq/L.

The recovery from acidification has led to the demand for more precise criteria for classification of acidification. The Swedish Environmental Protection Agency has revised Sweden's Ecological Quality Criteria for acidification to improve the correlation between the chemical acidification criteria and biological effects. This paper summarises the most relevant findings from several of the studies commissioned for this revision. The studies included data on water chemistry in 74 reference lakes in southern Sweden with data on fish in 61 of the lakes, as well as data on littoral fauna in 48 lakes. We found that the acidity variable most strongly correlated to the biota was the median pH from the current year. Our results probably do not reflect the mechanisms behind the negative effects of acidity on the biota, but are fully relevant for evaluation of monitoring data. The biogeochemical models used for predicting acidification reference conditions generate a pre-industrial buffering capacity. In order to get an ecologically more relevant criteria for acidification based on pH, we transferred the estimated change in buffering capacity into a corresponding change in pH. A change of 0.4 units was defined as the threshold for acidification. With this criterion a considerably lower number of Swedish lakes were classified as acidified when compared with the present Ecological Quality Criteria.

We studied the effects of liming on fish and crustaceans in a watershed which is in a region known to have one of the highest diversity of aquatic biota in Norway. This watershed, Enningdal, is shared between Norway (1/3) and Sweden (2/3) and includes 61 lakes > 1.0 ha in Norway. Liming started on a large scale in the 1980s. Currently, a total of 26 of lakes (43%) are limed, covering 93% of the total lake area. The mean value±S.D. of pH and the concentration of inorganic labile Al in these lakes is 6.62+−0.35 and 3+−4 μg l

−1

, respectively. Historical data of fish communities have been obtained from surveys, while test-fishing and sampling of crustaceans were conducted in 24 lakes in recent years (2002–2004). The present study shows that crustaceans to a greater extent than fish has responded to improved water quality after more than 20 years of liming. Of a total of 120 fish populations, 42 (35%) have gone extinct. Only five of the lost fish populations (12%) have been re-established, all due to human re-introductions. Physical barriers are considered to be the main factor preventing fish from invading limed lakes.

Reduced emissions of acidifying pollutants have changed the acidification process, and as a result, forest soils and surface waters are slowly recovering in Sweden. However, model calculations show that some areas may never recover completely unless further measures, such as liming, are undertaken. Liming of surface waters (lakes, rivers and wetlands) has been successfully practised in Sweden since the 1970s, but repeated treatments are necessary. A full recovery of acidified lakes and streams without frequent liming is however not possible until soil acidification is reversed in the most strongly affected areas. In this study, the recovery of acidified streams was examined using ‘the total catchment approach’ i.e. treatment of both recharge and discharge areas. The aim was to compare the quantitative effect of different treatments on run off chemistry and the recovery of brown trout. Catchments in southwest Sweden were treated with a combination of 2 tons of wood ash and 4, 6 or 12 tons of crushed limestone per hectare in 1998/1999. Treatment of both recharge and discharge areas resulted in fast and significant changes in stream water quality, e.g. increased concentrations of calcium, higher pH and ANC and a decreased concentration of inorganic aluminium. The initial changes were dependent on the distribution of the applied lime between discharge and recharge areas rather than the average dose on the total catchment. Treatment of recharge areas only, resulted in smaller but still significant effects on calcium, pH and ANC in stream water.

The purpose of this study is to evaluate cost-effective reduction strategies for nitrogen oxides (NO

x

) in the Asian region. The source-receptor relationships of the Lagrangian “puff” model of long-range transportation, ATMOS-N, were used to calculate the wet/dry deposition of the nitrogen (N) in Asia. Critical loads of N deposition in Asia were calculated from the relationships between the critical load of sulfur (S) and balance of N in and out using the data of S critical load of RAINS-ASIA. The cost functions of N reduction of Asian countries were derived by the regression analysis with the data of cost functions of European countries used in RAINS. In order to assess the environmental impact, the gaps between N deposition and critical load of N were calculated. The emission of NO

x

was reduced in some cases of this model, and the changes of gaps between N deposition and critical load were observed as well as the changes of the reduction cost. It is shown that a uniform reduction of NO

x

emissions by countries in Asia is not cost-effective strategy.

Critical loads of cadmium, lead and mercury were computed by 18 countries of the LRTAP Convention. These national data were collated into a single database for the purpose of identifying sensitive areas in Europe. Computing exceedances, i.e. comparing the critical loads to atmospheric deposition, shows that cadmium was not a widespread risk in 2000, that the risk from lead deposition has decreased since 1990 but was still widespread in 2000, and that the risk from mercury remains high without much change from 1990 to 2000 in most of the countries.

European critical loads and novel dynamic modelling data have been compiled under the LRTAP Convention by the Coordination Centre for Effects. In 2000 9.8% of the pan-European and 20.8% of the EU25 ecosystem area were at risk of acidification. For eutrophication (nutrient

N

) the areas at risk were 30.1 and 71.2%, respectively. Dynamic modelling results reveal that 95% of the area at risk of acidification could recover by 2030 provided acid deposition is reduced according to present legislation. Insight into the timing of effects of exceedances of critical loads for nutrient

N

necessitates the further development of dynamic models.

In this study critical load functions and target load functions of nitrogen and sulphur deposition with respect to acidity and minimum base cation to aluminium ratio were calculated with the SAFE model using three different averaging strategies: (1) averaging based on current forest generation, (2) averaging based on next generation and (3) averaging based on the entire simulation period. From the results it is evident that although target load calculation and indeed critical load calculation is straight forward, there is a problem in translating a predicted recovery according to the target load calculation back to a site-specific condition. We conclude that a policy strategy for emission reductions that ensures recovery, according to calculated target load functions, is likely to be beneficial from an ecosystem point of view. However, such a strategy may not be sufficient to achieve actual nonviolation of the chemical criteria throughout the seasonal or rotational variations. To address this issue we propose a method for calculating dynamic critical loads which ensures that the chosen criteria is not violated.

Critical loads have been used to develop international agreements on acidifying air pollution abatement, and within the UK and other countries, to develop national policies for pollution abatement. The Environment Agency (England and Wales) has regulatory obligations to protect sites of high conservation value from the threat of acidification, and hence requires a practical methodology for acidification assessments at the site-specific scale. The Environment Agency has therefore posed the question: Are the national critical load exceedance models sufficiently robust to form the basis for methods to assess harm to individual sites or are they only useful for national policy development? In order to provide one measure of the appropriateness of applying the models at the site-specific scale we incorporated estimates of uncertainty in both national and sitespecific data into the calculation of critical load exceedance for individual sites. The exceedance calculations use data from a wide range of sources and the accuracy of the exceedance will be influenced by the accuracy of the input data sets. Using Monte Carlo methods to incorporate the uncertainty in the input data sets into the calculation a distribution of critical load exceedance values is generated rather than a single point estimate. This paper compares uncertainty analyses for coniferous forested sites in England and Wales using both national scale and site-specific data sets and uncertainty ranges.

There is an increasing demand from conservation agencies for site-specific critical loads (CL); unfortunately, there is often very little specific information on a site to determine the important parameters needed to calculate the CL or on the spatial location of the “designated feature” in a site. Determining the most appropriate CL therefore involves using expert judegement to make decisions with incomplete and uncertain information. Endorsement Theory (Cohen, 1985) and Dempster—Shafer statistics (Dempster, 1967; Shafer, 1976) are, respectively, a decision-theoretic and a statistical technique for reasoning under those conditions (uncertainty and incompletness). A key reason for applying these techniques is that they make expert opinion explicit and available for scrutiny. Both techniques have been applied to the problem of setting an appropriate site specific CL, using heathland sites as a case study. Inital findings are encouraging; the uncertainty in expert judgement is made explict, the end results are intuitively reasonable and the methodology apparently acceptable to decision makers.

Numerous assumptions have been made over the past 17 years when calculating critical loads for soils, both for acidity (based upon base cation steady state mass balances (SMB)) and for N (eutrophication, based upon N mass balances), often without

all

the assumptions being explicitly stated. The tacit assumptions that the author believes to be implicit in the SMB approach are critically reviewed, with particular reference to upland regions where slope processes are highly significant. It is concluded that many of them cannot be justified, especially those that involve ignoring many key processes known to be important to biogeochemical cycling and soil evolution in upland catchments. The evidence presented suggests that critical loads of acidity and of N for soils should be based upon effective pollutant and, for acidity, also effective base cation deposition concentrations, rather than upon pollutant deposition fluxes. This is because of the dominant role of cation exchange equilibria, rather than weathering rate, in regulation of the pH and base status of the more acidification-sensitive soils, and because of the importance of transport down slope of base cations, alkalinity and N species.

Critical loads have been successfully used within Europe in the development of effects-based policies for pollution abatement, including the Second Sulphur Protocol and the Protocol to abate acidification, eutrophication and ground-level ozone (CLRTAP, 1979). This success has encouraged the UK Environment Agency and Conservation Agencies to use the national critical load maps as a screening tool in assessing the threats from acidification and eutrophication to designated (Natura 2000) sites. The UK maps of critical loads are based on national-scale data sets appropriate for national-scale assessments, and were never intended for use at the site-specific level. Site-based assessments are often targeted at Special Areas of Conservation, a sub-set of the UK Natura 2000 sites. The spatial data available includes the boundaries of the sites but not the location of the designated features. Ancillary data is variable from one site to another; habitat types may be described in detail with cross-reference to classes of the National Vegetation Classification (NVC: Rodwell, 1991 et seq), but information available on soils and geology is generalised and has not been related to the habitats or species being protected. Hence it can be difficult to relate the individual sites to the national maps, even where appropriate to do so. This paper examines the underlying uncertainties in the national critical load maps showing how the maps could give misleading results if used for site-specific assessments. It also includes advice on how to determine when the national data may be appropriate as a policy-tool at the site-level.