Calculating Critical Loads of Sulfur Deposition for 100 Surface Waters in China Using the Magic Model

Although decades of acid deposition have apparently not resulted in surface water acidification in China, some surface waters may have the potential trend of being acidified, especially those in southern China. In this paper, a dynamic acidification model–MAGIC was applied to 100 surface waters in southern and northeastern China to evaluate the impact of acid deposition to surface waters and to determine their critical loads of S deposition, both regions having distinguishing soil, geological and acid deposition characteristics. Results indicate that most surface waters included in this paper are not sensitive to acid deposition, with critical loads of S for these waters comparatively high. On the other hand, surface waters in southern China, especially those in Fujian, Jiangxi and Guangdong provinces, are more susceptible to acidification than those in northeastern China, which coincides with their different patterns of soil, geological and acid deposition conditions. Among all the waters, a few small ponds, such as those on top of the Jinyun mountain and Emei mountain, are the most sensitive to acid deposition with critical loads of 1.84 and 3.70 keq·ha^?1·yr^?1, respectively. For the considerable ANC remaining in most 100 surface waters, it is not likely that acidification will occur in the near future for these waters.     

Macroinvertebrate status in relation to critical loads for freshwaters: A case study from N.E. Scotland

The Critical Load concept provides a method for the assessment of an ecosystem's sensitivity to acidification. This paper examines how variations in critical loads for freshwaters are reflected by the diversity and abundance of macroinvertebrates. The results indicate that acidified sites, those with the lowest critical loads, have significantly fewer species than less sensitive sites. The data are discussed in terms of ordination analysis relating catchment attributes to critical loads and macroinvertebrate status. It is concluded that although critical loads provides a good predictor for biotic status it is not as sensitive as parameters such as pH or alkalinity.     

Implications of natural acidification for mitigation strategies in northern Sweden

Northern Sweden has been regarded as unaffected by acid deposition, but many surface waters in the region fall within the definition of acid surface water (pH < 6.0, alkalinity < 50 mmol_c m^?3) permanently or during episodes. Approximatly 100 MSEK in spent annually on liming in northern Sweden. This paper summarizes our conclusions from a workshop on natural versus anthopogenic acidification held in February 1995. It was shown that organic substances have a key role in determining the acidity of surface waters in the region, although anthropogenic effects are documented in some coastal systems and in the southern mountain range. Sulfide oxidation occurs by the coast. It appears clear that many surface waters that were naturally acidic have been limed to unnatural pH levels. New criteria to screen liming candidates should be developed, and one such model based on water chemistry data is proposed.     

Predicting freshwater critical loads from national data on geology,soils and land use

Using information on geology, soils and land use, a map has been generated for Great Britain which indicates five classes of sensitivity of surface waters to acidification. This map has been used for designing sampling strategies for mapping critical loads of acidity for freshwaters. This paper evaluates the freshwater sensitivity map using a data set of water chemistry collected as part of the UK critical loads programme. Discriminant analysis was used to predict five critical load classes from information on geology and soil sensitivity for freshwater sites. This showed geology and soil information can correctly predict approximately 50% of all critical loads classes. In addition, 77% of sites fall within one critical loads class of that predicted. Predictions may be improved by including other variables eg altitude and geographical location. Differences between lake, stream and reservoir sites are also examined. Ranges of critical loads values were determined for each of the five classes of surface water sensitivity. While a trend in critical load values was evident between classes, there was significant overlap. A simplified sensitivity map with only three classes related more closely to critical loads values. The paper demonstrates the usefulness of the surface water sensitivity map for assessing acidification at a national scale, but highlights the difficulties of predicting critical loads for individual sensitive catchments using national data.     

Variation in Freshwater Critical Loads Across Two Upland Catchments in the UK: Implications for Catchment Scale Management

In the UK the "critical loads" approach has been used to derive maps based on the 10km × 10km national grid. However, this grid based approach is inappropriate for catchment scale management and these maps cannot be used for "stock at risk" assessments of the number of water bodies or lengths of streams in a given area that may be vulnerable to acidification. Critical loads are determined across two large river catchments in England (The Duddon) and Wales (The Glaslyn). High resolution, digital datasets are used to characterise the attributes of each subcatchment in terms of land cover, soil, geology, topography and topology. Empirical models used to examine the relationship between these attributes and critical loads indicate that the former can be used to account for significant variation in the latter. However, these relationships can vary from catchment to catchment. Thus, although this approach provides the potential for identifying sensitive surface waters on a catchment wide basis, it is likely that models will need to be parameterised on a catchment specific basis.     

Surface water acidification in the UK; current status,recent trends and future predictions

Data collected at 22 lake and stream sites under the UK Acid Waters Monitoring Network, established in 1988, are assessed. Non-marine sulphate concentrations in surface waters largely reflect the sulphur deposition gradient across the country. Time series analysis indicates an increase in non-marine sulphate concentrations at sites in SW Scotland, the Lake District and in Wales. No similar trends have been detected in deposition data for the same period. Predictions of water chemistry response at each site to the new UNECE sulphur protocol have been made using a long-term, dynamic acidification model (MAGIC). The results indicate that the agreed emissions reductions will lead to recovery at many sites over a 15–20 year timescale but will have little effect at the most impacted sites, within the next 15 years.     

Critical loads of acidity to surface waters

The critical load of acidity to surface water is based on the condition that the inputs of acids to a catchment do not exceed the weathering rate less a given amount of ANC (Acid Neutralizing Capacity). The Steady State Water Chemistry (SSWC) Method is used to calculate critical loads of acidity, using present water chemistry. To calculate the weathering, the so-called F-factor is used to estimate the part of the base cation flux that is due to soil acidification. The F-factor has been estimated empirically from historical data comparisons from Norway, Sweden, U.S.A. and Canada and is considered to be a function of the base cation concentration by the formula: F=sin(BC^*/S), where BC^* is the present base cation concentration and S the base cation concentration at which F=1. At higher values for BC^* F is set to 1. For Norway, Sweden and Finland S has been set to 400 μeq/l (ca. 8 mg Ca/l), giving F-values in the range 0.05–0.2. The importance of the F-factor in the calculations of the critical loads of acidity for Nordic surface waters was tested by calculating the magnitude of the area where the critical load of acidity is exceeded in Norway for different values of S. Similar calculations were carried out for the Finnish and Swedish lake data. Varying S from 100 μeq/l to 1200 μeq/l, the exceeded area in Norway decreases from 31,9 to 28,3%. For F=0 (S=∞, i.e. assuming no soil acidification), the exceeded area is reduced to 27,2%. For Finland and Sweden the the percent of lakes exceeded are reduced from 16,6 to 12,9% and 30 to 23,6%, respectively. For F = 0 the percent of lakes exceeded are reduced to 11,4 and 16,4, repectively. These results indicate that the F-factor is not of great importance for calculating critical load and critical load exceedances in Norway, Finland and Sweden.     

Mapping the Potential Sensitivity of Surface Waters to Acidification Using Measured Freshwater Critical Loads as an Indicator of Acid Sensitive Areas

Environmental organisations in the UK have shown increasing interest in freshwater critical loads and acid sensitivity maps as a means of assessing pollution at the local and regional level. These maps can be used to identify sensitive areas when considering catchment management plans. The use of national data sets to map the sensitivity of freshwaters to acidification, highlighted the problems of relating national datasets to smaller, localised areas. The study described here investigated the use of detailed large-scale maps to predict the sensitivity of surface waters to acidification for two river catchments. Three large-scale acid sensitivity maps were produced and validated using measured freshwater critical loads. In addition, a score system relating to the buffering capacity for each soil and geology type was devised. The score value was found to have a better correlation with water chemistry and freshwater critical loads than the acid sensitivity maps. The study concluded that it was not necessary to use the largest scale data available in order to improve predictions of sensitive areas.     

The Relationship between Topsoil and Stream Sediment Heavy Metal Concentrations and Acidification

Critical loads of acidity have been used by the UNECE Convention on Long Range Transboundary Air Pollution for the development of protocols to control the emissions of acidifying pollutants. Since soil acidity has an effect on the mobilisation of heavy metals in the environment, it is important to understand the relationships between acidity and heavy metal pollution. This paper examines the relationships between soil acidification and heavy metal (cadmium, copper, lead and zinc) concentrations in topsoils and in stream sediments. It makes use of published heavy metal data and two indices of acidification: soil pH and soil acidity critical loads. For cadmium and zinc, a general increase in the ratio of stream sediment to toposil metal concentrations is seen with a decrease in soil pH and soil acidity critical loads. This demonstrates that where soils are more acidic and acid sensitive the metal concentration in the stream sediments is greater relative to that in the topsoil, suggesting mobilisation of these metals under acid conditions. Results for copper are similar but the relationship weaker. However, for lead the ratios tend to decrease with a decrease in pH and critical loads suggesting that where soils are more acid, lead remains in the soil rather than being mobilised into streams and precipitating onto stream sediments. This reflects the association between soil lead concentrations and soil organic matter content, which tends to be greater in acidic, peaty soils.     

Effects of Site Selection Strategy on Freshwater Critical Load Exceedances in Wales

Critical loads are used in international negotiations to reduce acid deposition resulting from emissions of sulphur and nitrogen compounds within Europe. For freshwater ecosystems, the First-order Acidity Balance (FAB) model is used to generate national maps of critical loads and exceedances for both sulphur (S) and nitrogen (N). In Wales, two survey datasets have been used to calculate critical loads and exceedances; one based on water bodies selected to be "most-sensitive" to acidification within a 10 km grid and the other based on a random selection of standing waters. Both datasets indicate that critical loads were exceeded in 1990 in a significant proportion of Welsh lakes and streams; 36% of sites in the grid-based survey and 31% of sites in the random survey. However, implementation of the Gothenburg Protocol would protect all but 6% of sites in the grid-based survey and all sites in the random survey. Assessment of the relative success of the Gothenburg Protocol in protecting Welsh freshwater ecosystems therefore depends on the site selection strategy employed.     

Critical loads of acidity and nitrogen,based on multiple criteria for different swedish ecosystems

The critical loads of acidity and nitrogen has been mapped for Swedish forest soils, using data from the Swedish Forest Inventory. The Swedish critical load map used in negotiations has been based on a number of ecological receptors. For terrestrial ecosystems criteria based on no adverse effect on growth, soil stability and groundwater quality was used. For surface waters, stream and lake biology was used as indicators for setting limits to acidification. A reduction of 75% of the acidity deposition in relation to 1988 is required in order to protect 95% of the forest resource in Sweden from effects of soil acidification. A reduction of 50% of the nitrogen deposition is required to avoid exceedance in more than 5% of the area. The mapping work was carried out by using the PROFILE model.     

Critical loads — A valuable catchment management tool?

Planning advice for forest planting in acid sensitive areas suggests that, where calculated critical loads for acidity are exceeded at a catchment level, new conifer planting may not be appropriate. In south west Scotland, acid waters are currently found in areas where critical loads are not exceeded. The rivers Cree and Bladnoch show a decline in pH of about one unit since 1970, when major afforestation of the headwaters began. No equivalent decline in pH was observed in the adjacent Water of Luce, although it receives similar inputs and has similar geology and soils. Little of the Luce catchment is afforested. Recent surveys of water quality, invertebrate fauna and salmonid fish reveal a picture of widespread acid conditions, impoverished benthos and absence of young salmon. 25 streams (total catchment >150km²) recorded pH <4.5 in high flow conditions. Critical loads for acidity were >1.5keqha^?1yr^?1 for 12 and >2keqha^?1yr^?1 for 6 of the 25 streams. Published deposition data suggested that one stream with pH <4.5 and 7 streams with pH < 5 were in areas where critical load was not exceeded. In 22 catchments, forestry was a major land use. To be effective as planning and management tools, systems must be robust and easy to operate. Critical load exceedance calculations remain research tools at the catchment level where deposition data is generally inadequate. The uncertainties inherent in critical load exceedances render them sources of argument and not beacons of enlightenment.     

Critical loads for soils and waters in a selected Scottish catchment

In the UK, critical loads have been mapped for both soils and freshwaters and the maps indicate that discrepancies may occur between these two receptors over sensitive areas of the UK. Freshwater critical load maps were prepared by calculating the Henriksen critical load for the most sensitive water body in each 10 km grid square. Critical loads for soils were calculated according to the mineralogy and associated soil properties of the dominant soil at a 1 km resolution. To examine the differences between the soil and freshwater data sets it is necessary to calculate critical loads at a smaller scale using the catchment as the focus for study. This was done by selecting a catchment on granitic parent material in the North of Scotland. Data on water chemistry, collected on a weekly basis, was used to calculate temporal variations in critical loads for freshwaters using the Henriksen method. Soil sampling across the catchment was conducted on a grid based system to provide estimates of spatial variability in sensitivity. Profile characteristics and soil chemical data obtained from detailed soil sampling programmes were used in the PROFILE model to determine the spatial variation in critical loads for soils. In general, the results show that the critical loads for soils tend to be lower than those for freshwater. The spatial variation in the soil critical load tends to be small whilst the temporal variation in critical load for freshwaters is large. In order to account for these differences it is important to identify the key processes within the catchment which play a major role in controlling streamwater chemistry. This procedure improves the relationship between critical loads for soils and waters.     

Climate change and the cetacean community of north-west Scotland

1. Climate change is thought to affect the composition and structure of local ecological communities. We investigate whether ocean warming around north-west Scotland since 1981 has been associated with changes in the local cetacean community.2. Analysis of strandings from 1948 to 2003 found that no new species per decade were recorded in north-west Scotland between 1965 and 1981. This rose to 2.0 new species per decade from 1988 onwards. The new species recorded since 1988 are generally restricted to warmer waters, while those recorded prior to 1981 regularly occur in colder waters.3. In the period 1992 to 2003, the relative frequency of stranding of white-beaked dolphin, a colder water species, has declined while strandings of common dolphin, a warmer water species, have increased. Similarly, sightings surveys conducted in May-September 2002 and 2003 show that the relative occurrence and abundance of white-beaked dolphins have declined and common dolphins increased in comparison to previous studies.4. These observations are consistent with changes in the local cetacean community being driven by increases in local water temperature. If such temperature changes continue, some formerly abundant cold-water species, such as white-beaked dolphins, may be lost from this cetacean community. In a wider context, such changes may lead to populations of cetaceans moving out of areas specifically designated for their protection as they respond to changes in local oceanic conditions.     

Critical loads of acid deposition on Scottish soils

The impact of acid deposition, attributable to sulphur and nitrogen pollutants, on the soils of Scotland has been analysed using a critical loads approach. The critical load of a soil (as an indicator of ecological damage) is calculated from the soil parent material controlling weathering and soil development. Using existing soil survey information national maps for critical loads of acidity and the sulphur fraction are presented for soils under natural and semi-natural ecosystems. The results show that highly sensitive soils, that is those derived from quartzite and granite are limited in occurrence. However, there are large areas of sensitive soils predominantly to the north and west of the Midland Valley and in the Southern Uplands, in receipt of acid deposition in excess of their critical load. Enhanced soil acidification should be widespread in these areas and consequently the ecosystems which they support will be adversely affected. The least sensitive soils, overlying limestone or marl, are restricted in occurrence and are confined to the major deposits of marine alluvium. The results of the analysis may be used to help policy makers derive emission abatement strategies in the context of the European Sulphur protocol renewal in 1993. In Scotland the maps may be used to aid the planning of large scale afforestation.     

The role of sea-salts in enhancing and mitigating surface water acidity

Enhancement of the acidity of fresh waters due to sea-salt “episodes” has been reported in western regions of Scotland, Ireland and Norway and eastern regions of Canada and the United States of America. In all cases these short-term pH depressions have been ascribed to cation-exchange processes in catchment soils whereby sodium ions displace acidic cations (H⁺, Al³⁺) resulting in a lowering of the Na/Cl ratio in run-off water. Studies of sea-salt episodes in different catchment types of similar sensitivity in Scotland show significant variations in chemical responses, especially in terms of acidification status. Catchments with high background salt content, in a low sulphur deposition area, show only a small increase in acidity with negligible aluminium release and most of the sodium retention matched by Ca and Mg release. Catchments in intermediate deposition areas, with low background salt levels, exhibit smaller sodium retention with increased leaching of acidity and labile aluminium. High non-marine S deposition sites, with intermediate background salt levels, reveal high levels of acidity and aluminium leaching associated with some calcium leaching and evidence of Mg retention. Mitigation of acidification occurs at sites with high background sea-salt levels (eg north west Scotland) where acidic deposition is selectively retained in catchment soils. Non-marine sulphate values in run-off are therefore much lower (often producing negative values) than those predicted from current S deposition values. Consequently such sites are presently producing false exceedances of freshwater Critical Loads when current S deposition values are used. Future reductions in S deposition will probably affect the adsorption characteristics at these sites with consequent effects on sulphate leaching.     

The role of nitrogen in acidification of Tatra Mountains lakes

An overall level as well as seasonal changes of acidification of Tatra Mountains surface waters have been studied. Measurements carried out in the Tatra Mountains National Park were concentrated on two lakes: Dlugi Staw and Zielony Staw, situated in the crystalline, granitic part of the mountains. These lakes differ from each other in altitude (1784 m and 1632 m a.s.l. respectively) as well as in quantity and variety of flora and fauna living in and around them. The wet deposition of acidifying compounds of sulphur and nitrogen, and their seasonal variability in the area of the lakes were measured and compared with the critical loads of sulphur and nitrogen for these lakes and their catchments. Results showed that the critical loads of both sulphur and nitrogen in Dlugi Staw were exceeded all over the year and in Zielony Staw the acid deposition was roughly equal to critical load. A surprisingly high concentration of nitrogen compounds in acid deposition, well above the absorption ability of both the lakes and their catchments were ascertained. Nitrogen retention coefficients calculated for the lakes were as follows: Dlugi Staw — approximately 10%, Zielony Staw — approximately 50%. Seasonal variability in nitrate ions concentration in the lakes' waters reflected their prominent acidification caused by nitrogen compounds corresponding to stages 2 and 3 in the scale proposed recently by Stoddard (Stoddard, 1994).     

Effects of acidification on the concentrations of heavy metals in running waters in Sweden

Heavy metals in running water are analysed within the Swedish Surface Water Monitoring Programme at about 80 stations. Data for selected rivers and brooks has been used to assess the effect of soil acidification on the concentrations of metals in waters. In southern Sweden, acidification shows a significant effect on Zn and Cd. In the upper parts of the drainage areas, there is an marked increased leakage of these metals from soils to waters indicated by elevated concentrations of Zn and Cd in brooks and also by high maxima during periods of low pH values. The increased leaching from forest soils also influences the concentrations in rivers in southern Sweden. During periods of high water flow, the pH values of the rivers decreases and the concentrations of Zn and Cd increases. At pH levels of 6.2–6.5 the concentrations of these metals are mostly 2–5 times higher as compared to pH levels of about 7.0. Since high concentrations of Zn and Cd coincides with high water flow, the transport of these metals has most certainly increased several times compared to the pre-industrial period. Hence, the by far most important human impact on the loading of Zn and Cd on the marine areas, surrounding southern Sweden is the increased leakage of these metals due to acidification. In northern Sweden the effects of acidification on Zn and Cd are less evident. In general, the concentrations of these metals are lower and the connection between pH and these metals are much less significant in the rivers. The links between acidification and the concentrations of Pb and Cu in the watercourses are comparatively much weaker. These two metals are more related to the content of organic matter in the waters and a possible effect of acidification is overshadowed by natural transport processes in soils and waters.     

INCREASING ROLE OF NITROGEN IN THE ACIDIFICATION OF SURFACE WATERS IN THE ADIRONDACK MOUNTAINS,NEW YORK

Assessments of the aquatic effects of acidic deposition have focused on sulfur, as have recent efforts to control the emissions of acidifying compounds. Nitrogen dynamics were excluded from most acidic deposition modeling studies because it was believed that terrestrial ecosystems strongly retain N and because modeling N is a more formidable task than modeling S due to the influence of complex biological processes on N cycling. Re-examination of available data for the Adirondack Mountains of New York suggests that N deposition may be contributing to both chronic and episodic acidification of freshwaters to a greater extent than is generally believed. Previous research concluded that N has played a limited role in acidification processes in these lakes, based on regional averages of chronic chemistry. However, it is now known that historic acidification responses have been spatially variable within the Adirondack Mountains and that the declines in lakewater pH have been less than previously believed. Lakewater NO₃ ^- concentrations are commonly in the range of 5 to 25 μeq L^-1 on a chronic basis in portions of the Adirondack region that have experienced significant chronic acidification. These NO₃ ^- concentrations correspond in magnitude to inferred historical acidification. Furthermore, the relative importance of NO₃ ^- as an agent of acidification increases dramatically during snowmelt when conditions are most toxic to fish. The consequence of not addressing N in formulating acidification recovery strategies for the Adirondacks includes the likelihood that we will overestimate the response of surface water to the mandated sulfur emissions reductions.     

Aquatic Acidification Sensitivity for Regional Environment: a Multi-Indicator Evaluation Approach

With the aggravation of acid rain pollution and the enlarging of the acid rain regions in China, the sensitivity evaluation of natural waters to acidification on a regional scale become increasingly important. Acidification models based on a single indicator cannot give much information on aquatic acidification because of their simplicity; yet acidification models based on physical, chemical, hydrological and/or biological processes are not suitable for large scale regional research because of their exceptional complexity. In this paper, a multi-indicator comprehensive model for aquatic acidification sensitivity is proposed and applied. This model comprises some of the most important factors that are considered to influence water acidification, in particular: acid neutralization capacity, acidification capacity, acidification sensitive index, cation exchange capacity of soil, pH of soil, and weathering shuck types of soil-forming. It highlights the key stages of aquatic acidification by acid neutralization capacity, acidification capacity, and acidification sensitivity index. The model thereby estimates the acidification sensitivity of natural waters by using these indicators according to a weighting system. Equal-weight and non-equal-weight approaches are separately used to combine the six indicators into an overall sensitivity index of aquatic acidification. The result derived from an application to China on a national scale indicates the practicability of this approach. In China, the sensitive natural waters emerge in Southern China, which is already a heavy acid rain region, and in Northeastern China where the rainwater is beginning to become much acidic.