Arne Henriksen

Critical loads of acidity for surface waters

The critical load of acidity for surface waters is based on the concept that the inputs of acids to a catchment do not exceed the weathering less a given amount of ANC. The Steady State Water Chemistry (SSWC) Method is used to calculate critical loads, using present water chemistry. To ensure no damage to biological indicators such as fish species a value for ANClimit of 20 μeq/l has been used to date for calculating critical loads. The SSWC-method is sensitive to the choice of the ANClimit. In areas with little acid deposition the probability of acid episodes leading to fish kills is small even if the ANClimit is set to zero, while in areas with high acidic deposition fish kills may occur at this value. Thus, the ANClimit can be a function of the acidifying deposition to the lake, nearing zero at low deposition and increasing to higher values at higher deposition. A formulation for such an ANClimit has been worked out, and we have tested the effect of the ANClimit as a linear function of the deposition, assuming ANClimit = 0 at zero deposition with a linear increase to 50 ueq/l at a deposition of 200 meq.m−2.yr−1. For areas with high deposition the effect of a variable ANClimit is small, while in areas with low deposition the effect is significant. For Norway the exceeded area decreases from 36 to 30% using a variable ANClimit instead of a fixed value of 20 μeq/l.

Increasing contributions of nitrogen to the acidity of surface waters in Norway

The acidification of lakes in southern Norway is largely due to sulfate. Recent data from regional surveys of lakes and from monitoring stations indicates that nitrate concentrations have increased in many lakes and rivers in southernmost Norway. The ratio of NO3 to NO3 + SO4 is still low for most areas, but is 0.54 on an equivalent basis in lakes and rivers in the area of high runoff in southwestern Norway. Here, concentrations of nitrate in the runoff are lower than for sites in Central Europe, but are higher than those in North America. The sites showing increases in NO3 also increased in Al. Further increases in nitrate as a mobile anion which may be due to decreased uptake in the watershed, will contribute to acidification in the same manner as sulfate.

Steady-State Models for Calculating Critical Loads of Acidity for Surface Waters

Three models for calculating critical loads of acidity forsurface waters, which have been used in several Europeancountries to map regions sensitive to deposition of acidifyingsulfur and nitrogen, are derived and their latest modificationsare presented. Using Norwegian lake data as an example, some ofthe methods are compared and discussed. While the Steady-StateWater Chemistry (SSWC) model and the Empirical Diatom model arebased on water chemistry alone, the First-order Acidity Balance(FAB) model also includes descriptions of the most importantsinks of nitrogen (and sulfur) in the catchment soils and thelake/sediment system. This is the first time that all currentlyused models as well as some new developments for calculatingcritical loads of acidity for surface waters are presented in a single paper.

A critical limit for acid neutralizing capacity in Norwegian surface waters, based on new analyses of fish and invertebrate responses

Abstract The status of fish and invertebrate populations was analysed in the context of surface water acidification and loss of acid neutralizing capacity in Norwegian lakes and streams. The invertebrate data came from 165 sites, and the fish data included populations in 1095 lakes, plus the Atlantic salmon populations in 30 rivers. The status of both fish and invertebrates was strongly related to both acid neutralization capacity ANC (Σ base cations - Σ strong acid anions) and the concentration of labile aluminium. Ca 2+ and TOC mederated the toxicity of both low pH and high aluminium. The critical level of ANC varied among fish species, with Atlantic salmon being the most sensitive, followed by brown trout. Perch were the most tolerant of low pH/high Al n+ . Atlantic salmon status appears to be a good indicator of acidification of rivers, and trout is a useful indicator for lakes. Based on an evaluation of fish and invertebrate populations, a critical lower limit of ANC = 20 μequiv./l is suggested as the tolerance level in Norwegian surface waters.

Concentrations of heavy metals in small Norwegian lakes

Abstract As part of regional surveys of lakes in Norway the concentrations of Zn, Pb, Cu and Cd were measured in surface- and bottom-water samples collected from representative, small, pristine lakes (136 in southern Norway sampled in October 1974, 58 resampled in March 1975, and 77 in northern Norway sampled in March 1975). The lakes, a statistically representative sample of small lakes in Norway, were chosen such that their watersheds are undisturbed. Heavy-metal concentrations in these lakes thus reflect only natural inputs and anthropogenic inputs via the atmosphere. The generally low concentrations (Zn 0.5–12.0 μg l −1 ; Pb 0–2.0 μg l −1 ; Cu 0–2.0 μg l −1 ; Cd 0.1-0.5 μg l −1 ) measured in lakes in central and northern Norway provide estimates of natural “background” levels. These estimates may be too high because they include the global-scale deposition of heavy metals from the atmosphere which has increased as a result of industrial activities. Concentrations of Zn and Pb in lakes in southernmost and southeastern Norway lie above these “background” levels, apparently because of atmospheric deposition associated with the acidic precipitation that falls over southern Scandinavia. Increased heavy-metal concentrations in acid lakes may also be due to increased mobilization of metals due to acidification of soil- and surface-waters.

Impact of acid precipitation on freshwater ecosystems in Norway

Extensive studies of precipitation chemistry during the last 20 yr have clearly shown that highly polluted precipitation falls over large areas of Scandinavia, and that this pollution is increasing in severity and geographical extent. Precipitation in southern Norway, Sweden, and Finland contains large amounts of H+, SO=4, and NO−3 ions, along with heavy metals such as Cu, Zn, Cd, and Pb, that originate as air pollutants in the highly industrialized areas of Great Britain and central Europe and are transported over long distances to Scandinavia, where they are deposited in precipitation and dry-fallout.In Norway the acidification of fresh waters and accompanying decline and disappearance of fish populations were first reported in the 1920s, and since then in Sørlandet (southernmost Norway) the salmon have been eliminated from several rivers and hundreds of lakes have lost their fisheries.Justifiably, acid precipitation has become Norways number-one environmental problem, and in 1972 the government launched a major research project entitled ‘Acid precipitation — effects on forest and fish’, (the SNSF-project). Studies of freshwater ecosystems conducted by the SNSF-project include intensive research at 10 gauged watersheds and lake basins in critical acid-areas of southern Norway, extensive surveys of the geographical extent and severity of the problem over all of Norway, and field and laboratory experiments on the effect of acid waters on the growth and physiology of a variety of organisms.Large areas of western, southern, and eastern Norway have been adversely affected by acid precipitation. The pH of many lakes is below 5.0, and sulfate, rather than bicarbonate, is the major anion. Lakes in these areas are particularly vulnerable to acid precipitation because their watersheds are underlain by highly resistant bedrock with low Ca and Mg contents.Apart from the well-documented decline in fish populations, relatively little is known about the effects of acid precipitation on the biology of these aquatic ecosystems. Biological surveys indicate that low pH-values inhibit the decomposition of allochthonous organic matter, decrease the species number of phyto-and zooplankton and benthic invertebrates, and promote the growth of benthic mosses.Acid precipitation is affecting larger and larger areas of Norway. The source of the pollutants is industrial Europe, and the prognosis is a continued increase in fossil-fuel consumption. The short-term effects of the increasing acidity of freshwater ecosystems involve interference at every trophic level. The long-term impact may be quite drastic indeed.

Strong and weak acids in surface waters of southern Norway and southwestern Scotland

Abstract As part of our studies of acidification of rivers and lakes, we have measured pH, strong and weak acids as well as concentrations of major ions in lake-water samples collected regionally in southern Norway and in samples from small lakes and creeks in the New Galloway area, Scotland. Both sets of samples show a similar relationship between strong acid and H+-concentration calculated from the pH of the sample. If pH is higher than about 5.5, the strong acid concentration becomes negative, corresponding to the presence of bicarbonate or other bases. In the pH-range from 4.8 to 5.5 the strong acid concentration is usually positive, but less than the H+-concentration, indicating contributions from weak acids, which may have existed as bases before excess inputs of strong acids started. The variance in weak acid concentrations in lakes in southern Norway and in southwestern Scotland is largely explained by the concentrations of organic carbon and aluminium. Because of increased leaching of aluminium from the soil in areas where deposition of acid components from the atmosphere has increased, an increase in weak acid concentrations has probably also occurred.

Sulfate deposition to surface waters Estimating critical loads for Norway and the eastern United States.

Critical loads are the highest deposition of strong acid anions in surface waters that will not cause harmful biological effects on populations, such as declines in or extinctions of fish. Our analysis focuses on sulfate deposition because in glaciated regions sulfate is conservative in soils, whereas nitrate in biologically cycled. Sulfate also is the dominant anion in acidic deposition and in most acidic lakes. This analysis, represents the first evaluation of certain data available from Norway and the eastern United States, with an emphasis on the data from Scandinavia. The concept of dose-response is widely used in connection with water pollution. Any lake system subjected to an external dose of pollutants will have an internal resistance (or buffer capacity) to the change. The response of the lake system will depend on the relative magnitudes of the dose and the resistance parameters.

Extreme acidification in small catchments in southwestern Norway associated with a sea salt episode

During heavy storm events in January 1993 in the coastal areas of south-western Norway, a sea salt episode created extreme acidification in the afforested Svela catchment. Stream-water chloride increased sharply to eight times the normal concentration and the non-marine Na concentration was calculated to −208 μeq L−1. Negative values indicate that Na was retained in the soil profile. By ion-exchange processes this was largely compensated by an increase in stream-concentrations of Al and H+. Concentrations of inorganic monomeric Al increased from about 20 to 200 μeq L−1 and pH decreased from 4.90 to 4.45. Due to the low pH and the dramatic increase in inorganic monomeric Al the water toxicity for aquatic organisms increased. Acidification associated with the storm was also observed in a forested and a non-forested catchment, but never reached the levels of the afforested catchment. The extra vulnerability of afforested catchments may be due to their ability to intercept larger amounts of sea salts than areas less dominated by dense tree stands. Although both pH and Al went back to normal levels for the area after 3–4 months the Na/Cl-relationship in cumulated transport values indicated a longlasting effect (> 2 years) on the soil profile. Reloading the soil profile with Al and H+ back to prestorm values will affect the catchments ability to mobilize these ions during future sea salt episodes. More frequent episodes will probably result in less acid and Al-rich stream-water during the episodes than documented here due to incomplete reacidification of the soils.

Effects of Regional Reductions in Sulphur Deposition on the Chemical and Biological Recovery of Lakes within Killarney Park, Ontario, Canada

The lakes in KillarneyProvincial Park, located 40–60 km southwest ofSudbury, Ontario, were some of the first lakesin North America to be acidified by atmosphericpollutants. Acidification affected thousandsof fish and invertebrate populations in dozensof lakes. Since the 1970s, water quality hasimproved in response to atmospheric pollutionreductions and some lakes have alreadyrecovered to approximately their pre-industrialpH levels, as inferred from diatom microfossilsin lake sediments. Since the 1970s, fishspecies richness has not changed substantially,but zooplankton species richness has increasedin acidified lakes. The critical sulphur load,the amount of SO2-derived acid depositionthat can occur while still maintaining suitable water quality, was estimated to beexceeded in 38% of the park area in 1997. Depending on which of four possible NorthAmerican emission control scenarios (CLR =currently legislated reduction; CLR + 25%; CLR+ 50%; CLR + 75%) is achieved by 2010, theprojected critical loads will be exceeded inabout 0-30% of the park area in the future. There are many factors that can affectbiological recovery rates of damaged lakes, butit is expected that biological recovery willlag considerably behind observed chemicalrecovery rates.