Gunnar Abrahamsen

Long-term experiments with acid rain in Norwegian forest ecosystems.

Acid rain is a serious international environmental problem. Scandinavian forests have suffered especially severe damage, and have been the focus of considerable research on the causes and impacts of atmospheric pollution. This book presents the results of long-term studies on acid rain in Norwegian forests. This research examined soil chemistry and biology; the impacts of acid rain on tree growth and nutrition; and its influence on ground vegetation, fungi, and seedling germination and development. Long-Term Experiments with Acid Rain in Norwegian Forest Ecosystems is a lasting contribution to the literature on acid precipitation, and will be of interest to researchers in ecology, air pollution, forestry and environmental chemistry.

Impacts of acid precipitation on coniferous forest ecosystems

This paper summarizes the results from current studies in Norway. One main approach is the application of artificial acid ‘rain’ and of lime to field plots and lysimeters.Application during two growth seasons of 50 mm mo−1 of ‘rain water’ of pH 3 to a podzol soil increased the acidity of the humus and decreased the base saturation. The reduction in base saturation was mainly due to leaching of Ca and Mg.Laboratory experiments revealed that decomposition of pine needles was not affected by any acid ‘rain’ treatment of the field plots. Liming slightly retarded the decomposition.No nitrification occurred in unlimed soils (pH 4.4-4.1). Liming increased nitrification.The soil enchytraeid (Ohgochaeta) fauna was not much affected by the acidification.Germination of spruce seeds in acidified mineral soil was negatively affected when soil pH was 4.0 or lower. Seedling establishment was even more sensitive to increasing soil acidity.Analysis of throughfall and stemflow water in southernmost Norway reveals that the total deposition of H2SO4 beneath spruce and pine is approximately two times the deposition in open terrain. A large part of this increase is probably due to dry deposition. Increased acidity of the rain seems to increase the leaching of cations from the tree crowns.Tree-ring analysis of spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.) has been based on comparisons between regions differently stressed by acid precipitation and also between sites presumed to differ in sensitivity to acidification. No effect that can be related to acid precipitation has yet been detected on diameter growth.

Effects of Artificial Acid Rain and Liming on Soil Organisms and the Decomposition of Organic Matter

Litter decomposition is an important part of nutrient cycling in natural ecosystems. A major part of the nutrients taken up by the vegetation is returned to the soil through litter fall. Decomposition begins when living tissue dies, even if it is still attached to the plant. In the boreal forest, decomposition is often slow and an accumulation of organic matter on the soil is common. This layer is inhabited by enormous numbers of soil organisms: fungi, bacteria and invertebrate animals. These organisms take part in the decomposition of organic matter; as the nutrients are moving within complicated food webs the importance of these various organisms is hard to predict.

Effects of artificial acid rain on decomposition of spruce needles and on mobilisation and leaching of elements.

SummaryDry matter and chemical changes in decomposing spruce needles were investigated after 16 and 38 weeks in laboratory lysimeters treated with distilled water or distilled water acidified to pH 3 or 2 with sulphuric acid. The water was added twice weekly in quantities equal to 100 or 200 mm month−1. The CO2 evolution and leaching of P, K, Mg, Mn, and Ca was followed together with pH measurements of the leachate.The loss of dry matter was approximately 25% during the first 16 weeks and approximately 37% after 38 weeks. At the first samling, 16 weeks, the amount of material decomposed was greater from the lysimeters given 100 mm month−1 of water. At this water quantity dilute sulphuric acid increased the decomposition. After 38 weeks sulphuric acid at pH 3 and 2 had decreased the decomposition at 200 mm month−1. However, the effects of acid application were small. The effect of treatment using acidified water on the content of monosaccharides was not consistent, whereas there was an indication of reduced decomposition of lignin when treated with 200 mm water month−1 at pH 3 and 2. Nitrogen was conserved in the lysimeters with small differences between the various treatments. The order of mobility of metal elements was K>Mg>Mn>Ca. Increasing the quantity of water increased the leaching of K especially, whereas addition of dilute sulphuric acid increased the leaching of Mg, Mn and particularly Ca. During the first 16 weeks of the experiment, sulphuric acid reduced the leaching of P while later on this treatment increased the leaching. The pH of the leachate from the lysimeters treated with distilled water was initially 4.0–4.6 increasing to approximately 6.6 after 22 weeks. The pH of the decomposed needle material was 4.6 and approximately 5.2 after 16 and 38 weeks respectively. When treated with water at pH 3 the pH of the leachate was between 4 and 5, and the pH of the needles 4.2–5.1. Treatment with water at pH 2 gave a leachate with pH just above 2 and decreased the pH of the needles that had received 200 mm ‘rain’ month−1 to 2.9.The effect of the artificial acid rain appears to be more pronounced on the leaching of metal elements than on the biological activity and the dynamics of N and P. The treatments must be considered extreme when compared with the acidity of natural rain.

Sulphur Pollution: Ca, Mg and Al in Soil and Soil Water and Possible Effects on Forest Trees

Results from field plots (with Norway spruce, Scots pine or silver birch) and lysimeters exposed to artificial rain are described. “Rain” was acidified to pH levels from 6 to 2.5 or 2 by means of H2SO4, and applied to field plots and 40 cm deep lysimeters in quantities of 50 mm month-1 in the frost-free period. Increased acidity of the “rain” increased the leaching of Ca, Mg and Al. When “rain” acidity increased from pH 3 to pH 2, Al concentration in the effluent increased from an average of 80 μmol 1-1 to an average of 1290 μmol 1-1. The Ca/Al mol ratio decreased from 7 to 0.5. Significant and corresponding changes in soil chemistry were observed. Neither the growth of trees nor the chemical properties of the foliage indicate that the trees suffered from Al-toxicity.

Mobility of heavy metals in pine forest soils as influenced by experimental acidification

The mobility of Pb, Zn, Cd and Cu was examined at two adjacent experimental plots at åmli, southern Norway, B-1 and B-2. Both experiments were established on the same glacifluvial deposits, with forest consisting of uniform stands of Pinus sylvestris L. The forest in B-1 was planted between 1968 and 1970, while B-2 consisted of naturally regenerated trees. The experiments included plots supplied with artificial rain of varying acidity over a period of seven and eight years for B-1 and B-2, respectively, in addition to control plots. In experiment B-1, experimental acidification was carried out both in unlimed plots and in plots applied with three different levels of lime. The two experiments showed distinct differences with respect to effects of the acidification on mobilization of heavy metals from the O horizon. In experiment B-1, the amount of Zn and Cd decreased with decreasing pH in artificial rain, while Pb and Cu were not appreciably affected. The reduction in Zn and Cd concentrations ceased after termination of the acidification experiment. Liming reduced the leachability of Zn, but still appreciable amounts of Zn were obviously leached from the O horizon during the experiment. In experiment B-2 a high retention even of Zn and Cd was observed in the O horizon, probably due to microbial uptake and accumulation.

Effects of long-term artificial acidification on the ground vegetation and soil in a 100 year-old stand of Scots pine (Pinus sylvestris)

A study on the effects of eight years application of artificial acid rain on the vegetation and soil in an old Scots pine forest is described. Artificial rain of pH 2.5 and 3.0 caused severe damage to mosses, especially Pleurozium schreberi and Dicranum polysetum. The presence of Melampyrum pratense decreased drastically in plots treated with ‘rain’ of pH 2.5 and 3.0. In Vaccinium myrtillus reduced leaf production was found in plots treated with ‘rain’ of pH 2.5. A considerable decrease in base saturation had taken place in plots treated with pH 2.5 and pH 3.0 ‘rain’. Exchangeable calcium and magnesium in particular had been reduced, and the content of mangnesium in tissue of Vaccinium myrtillus appeared also to be reduced in plots treated with water of pH 2.5. The study demonstrates the need for better methods in evaluating vegetation responses in field studies. The use of visual cover recording should be supplemented by frequency analysis and harvesting methods to get better estimates of changes in vegetation structure.

Effects of N and S deposition on leaching from an acid forest soil and growth of Scots pine (Pinus sylvestris L.) after 5 years of treatment

Abstract The effects of S and N deposition on leaching of ions from soil, tree growth and chemical content of needles have been studied in a lysimeter experiment. Lysimeters with Scots pine saplings were treated with artificial acid rain, in which pH was adjusted with H2SO4. Additionally, the lysimeters were treated with NH4NO3, in doses corresponding to 0, 30 and 90 kg N/ha yr. After 5 yrs of treatment, the following effects were the most pronounced: enhanced S input increased the leaching of SO42−, H+, Na+, Mg2+, Ca2+, Al, Mn2+ and NH4+ from soil. Even though a large proportion of the SO42− added was sorbed in soil, SO42− was mobile in the soil investigated. In average for all treatments, 26% of the NO3− added to the lysimeters was leached. The leaching of NH4+ was less than 5% of the amount of NH4+ applied. When treated with 90 kg N/ha yr, the leaching of both NO3− and NH4+ increased significantly, but in percent of input, the leaching of N compounds decreased. Since most of the N added was retained within the soil/plant system, the system can hardly be said to be ‘N-saturated’. Except for increased Al, H+ and NH4+ leaching, no clear relationships between the enhanced N input and leaching of other cations from soil were observed. Increased N deposition significantly increased the height of the Scots pine saplings. The height increment was accompanied by reductions in the contents of Mg, K and P in the needles. When considering the ratios Mg N , K N , Ca N , P N and Mn N in the needles, reductions were observed with increasing N input. These reductions may be caused by dilution due to the increased growth promoted by the N application, but they could also be signals of insufficient nutrient availability in the soil. In combination with N input, enhanced S input slightly increased the concentration of NH4+ in the leachate. Combined S and N input increased the content of P in the needles relative to the lysimeters receiving high doses of N, but no S. A decreased needle Mg content following the increased N input was probably strengthened by increased Mg2+ leaching due to increased S input.

Nitrogen cycling in Pinus sylvestris stands exposed to different nitrogen inputs

The objective of this study was to quantify the effects of high nitrogen (N) inputs on N cycling in a 35–45-yr-old Scots pine (Pinus sylvestris L.) forest. Nitrogen was added annually (single doses) as NH4NO3 in doses of 0 (N0), 30 (N1) and 90 (N2) kg N ha−1 yr−1. The only N input to the N0 plots was atmospheric deposition of 10 kg N ha−1 yr−1. The N cycle in these plots was tight, with almost complete retention of the incoming N. In the N1 plots the N retention was 83% after 9 yrs of N addition. The trees were the major sink, but the soil also contributed to the N retention. In the N2 plots the N retention was 63%, being mainly accounted for by accumulation in the soil. The leaching of N from the N2 stands was as high as 35 kg N ha−1 yr−1. The N2 system was N saturated.

Discussion and Synthesis

As mentioned in Chapter 1, knowledge of and concern about the effects of acidic rain in Norway go back to the late 1950s and the beginning of the 1960s. However, it was not untill the beginning of the 1970s, after the UN Conference on the Human Environment in Stockholm in 1971, that politicians and the public began showing interest in the problem. At the Stockholm Conference, Svante Oden from Sweden claimed that the soil in Scandinavia was severely acidified by acidic deposition (RMFA, RMA 1971). Norwegian botanists followed up by describing scenarios in which forest production was substantially reduced (Dahl and Skre 1971). The views of these scientists received remarkable attention and, especially in Norway, funds were given to initiate a large project on “Acid precipitation—effect on forest and fish” (The SNSF Project) (Overrein et al. 1980).