Leif Lien

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.

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.

Critical loads of acidity for surface waters : Can the ANClimit be considered variable ?

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.

AL:PE PROJECTS: WATER CHEMISTRY AND CRITICAL LOADS

Water chemistry data on which all the investigations in the AL:PE 1 (Acidification of Mountain Lakes: Palaeolimnology and Ecology) and AL:PE 2 (Remote Mountain Lakes as Indicators of Air Pollution and Climate Change) projects are based, are available for 28 lakes in U.K. (Scotland), Italy, Norway and France (AL:PE 1) and in Svalbard (Norway), Ireland, Austria, Spain, Portugal, Poland, Slovakia, Slovenia and Russia (AL:PE 2). The results show high sulphate concentrations in some mountain lakes in all the countries. Nitrate and sulphate concentrations have different distribution patterns among the sites. A gradient in acidification from north (Norway) to central Europe (via U.K. to Italy) is identified for the AL:PE lakes by means of multivariate data analysis. Critical loads and their exceedance are calculated, where sufficient information is available, both according to the leaching of S, and of S plus N from the catchment. The pattern of critical load exceedance demonstrates an increasing importance of nitrate from Norway via U.K. to Italy. Leaching of N was of considerable importance to the acidification of lakes in the Italian Alps. The projects receive financial support from the European Union.

Critical loads of acidity to surface waters: Svalbard

Water samples were analysed from 162 sites in Svalbard and Bear Island. A precipitation map for Svalbard was prepared. Critical loads are described as the highest loads of pollutants that will not lead to long-term, harmful effects on biological systems. Critical loads and exceedance of critical loads for input of strong acids to surface waters at Svalbard were calculated according to equations modified to fit the deposition conditions of the islands. Maps of critical loads and exceedance of critical loads were made for inputs of strong acids. Twelve percent of the ice-free area of mainly northern Svalbard has very low critical loads of acidity ( 100 kequiv./km2/year). A minor exceedance of critical load was recorded in 5% of the ice-free area of Svalbard, and only in the northern parts.

Brown trout exposed to acid-treated and nontreated humic water from Lake Skjervatjern

Abstract Lake Skjervatjern was divided into two separate basins. One basin and its catchment were treated with sulphuric acid and ammonium nitrate. The other part was kept as a control. Brown trout was exposed to acid-treated and nontreated water from the outlets of the two basins. The results showed higher mortality in acid-treated water compared to nontreated water from Lake Skjervatjern. Chloride concentration in blood plasma was lower in fish exposed to acid-treated water, indicating a higher degree of stress. Some physical/chemical parameters showed different values for the acid-treated basin compared to water from the nontreated one, e.g., increasing concentrations of sulphur and nitrogen were seen in the acid-treated basin. However, no physical/chemical parameter or group of parameters has been identified from the two basins that can explain the difference in fish mortality and stress.