Arne O. Stuanes

Heavy Metal Pollution in Air-Water-Soil-Plant System of Zhuzhou City, Hunan Province, China

The sources, distribution and mobility of heavy metals in Zhuzhou City, Hunan Province, China were systematically studied based on environmental monitoring data and random sampling from fields and markets. The significant positive correlations between some pairs of heavy metals (total Cd–Hg, total Cu–Pb) within the Zhuzhou section of the Xiang River may indicate that they are coming from the same pollution sources with similar pollution channels and removal patterns in the water bodies. Heavy metals from wastewater partly settled in the sediment after entering the Xiang River, which caused an inconsistent change in heavy metal concentrations over time in the middle and lower parts of the Xiang River. There was no significant difference in total Pb and Zn in topsoil between years in the period 1990–1997, which showed the balance between input and output. Heavy metals accumulated mainly in the topsoil with little downward movement. Heavy metals in the vegetables and rice were higher than the edible standard and background value to some degree with minor exceptions. The maximum heavy metal level observed divided by the acceptable level was in the order of Cd > Pb > Cu > Zn. Significant positive correlations were only found between cabbage uptake and total soil content for Hg, Pb and Cd, with no significant correlationfor the other elements. The plant uptake of a heavy metal was somewhat influenced by the co-existence of other elements.

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.

Effects of weekly nitrogen additions on N cycling in a coniferous forest catchment, Gårdsjön, Sweden

In spite of nitrogen being a major limiting factor for forest growth in most parts of Scandinavia, increased nitrate levels in surface waters and soil water have been coupled to questions of increased inputs and decreasing immobilization of nitrogen in watersheds. To study an ecosystem response to elevated nitrogen deposition, NH4NO3 was added to a 0.52 ha forested headwater catchment in weekly portions by means of sprinklers below the canopy. Total nitrogen input as throughfall increased from the ambient 11 kg N ha−1 yr−1 to approximately 51 kg ha−1 yr−1 in the treatment years. The catchment, situated in Gardsjon, Sweden, is dominated by naturally generated Norway spruce with Scots pine in drier areas. The mean age of the forest is 104 yr. N concentrations in foliage, weight and N concentrations in litterfall, in situ net N mineralization and nitrate transformation (resin core technique), and leaching of N below the organic LFH horizon were studied on a catchment (NITREX) or plot (NITREX, CONTROL) level. This was coupled with input-output budgets to estimate fluxes and cycling of N during the pre-treatment year and the third year of treatment. There was a significant increase in net N mineralization in the NITREX plots the 3rd year of treatment, and a significant interaction between plot and year indicating a response to N addition for both net mineralization and nitrate transformation. The increased flux of nitrate from incubated soil cores, as well as the increased concentration in soil water and runoff indicated that the increased nitrification was possibly coupled with a preferential uptake of NH4N by the microflora. The spatial variability of the nitrogen transformation rates was generally large and increased with treatment. The N concentration in needle litter showed an increase the 5th year of treatment, but no effect of nitrogen addition was found on the total weight of litterfall or on the N concentration of foliage. The key processes that determine the ecosystem response to increased inputs of nitrogen seem to be net mineralization and nitrogen transformation rates, together with the mechanism and capacity of N assimilation into the soil pool. The major sink for both externally added and internally produced inorganic N was calculated to be the soil organic pool. N assimilation into the upper organic LF horizon dominated, and this assimilation is the first of three suggested ways for coniferous ecosystems to respond to increased chronic N input. Over time, the system is hypothesized to change towards a system with a reduced assimilation capacity, a possible decreased decomposition rate, and an increased export of nitrate through leaching. The time-span of these changes is still uncertain.

Soil solution chemistry during four years of NH4NO3 addition to a forested catchment at Gardsjön, Sweden

Abstract Nitrogen has been added to a forested 0.52 ha headwater catchment (G2 NITREX) at Gardsjon, Sweden, to study the ecosystem response to elevated N deposition. The catchment is dominated by naturally regenerated, mixed-age conifers, mainly Norway spruce, with Scots pine dominating in dry areas. After a pre-treatment period of about 1 yr of soil solution sampling, N was added to the whole catchment as an NH 4 NO 3 solution by means of sprinklers. Total N input as throughfall to the catchment increased from the ambient 13 kg N ha −1 yr −1 in the pre-treatment year to a total of about 50 kg N ha −1 yr −1 in the 4 treatment years. Soil solution was collected by tension lysimeters at 4 locations in G2 NITREX covering a moisture gradient from the dry upper to the lower wet parts of the catchment, at 2 locations in a nearby control catchment (F1 CONTROL), and at 2 locations in an adjacent catchment (G1 ROOF) at which ambient throughfall is excluded by a roof and replaced by unpolluted throughfall added by sprinklers. After 4 yr of N addition, the volume-weighted average NO 3 concentrations in G2 NITREX were higher than the pre-treatment values. Concentrations showed a progressive increase over time. In the 2 first treatment years this increase occurred only in the rooting zone but during the second 2 treatment years a pronounced increase also came in deeper layers. The lack of these trends in the F1 CONTROL and G1 ROOF catchments precludes natural variations in climatic conditions as the main cause for this increase. Relative to inputs, NO 3 concentrations in soil solution were low and showed large variations between the drier and wetter locations with peak concentrations in late fall and spring. Nitrate in soil solution generally constitutes less than 10% of the inorganic mobile anions and thereby contributes much less to the leaching of H + , Al, and base cations than CI and SO 4 , the dominant mobile anions. Soil solution NH 4 has not changed relative to the control and roof catchments. However, the system is changing. Increases in NO 3 leaching indicate reduced immobilization of NO 3 that can be due to episodic excess N supply of the microflora together with episodes of high waterflow.

Recovery from Acidification

Acidification and, to a lesser extent, alkalinization occur in all soils. That they do so indicates these reactions are of great importance because they affect such vital ecological processes as the solubility and exchange reactions of inorganic nutrients and toxic metals, the activities of soil animals and microorganisms, and the weathering of soil minerals.

Soil solution response to experimental addition of nitrogen to a forested catchment at Gårdsjön, Sweden

Abstract Nitrogen has been added to a forested 0.52 ha headwater catchment at Gardsjon on the southwest coast of Sweden to study the ecosystem response to elevated nitrogen deposition. The catchment is dominated by naturally generated, mixed-age conifers, mainly Norway spruce, with Scots pine in dry areas. After a pre-treatment period of about 1 year, nitrogen was added to the whole catchment as ammonium nitrate by means of sprinklers at an intensity of 3 mm h −1 (average concentration 230 mmol N1 −1 ). Total nitrogen input as throughfall to the catchment increased from the ambient 12.5 kg N ha −1 year −1 in the pre-treatment year to a total of 47.3 kg N ha −1 year −1 in the treatment years. Soil solutions were collected using tension lysimeters at four locations covering a moisture gradient from the dry upper to the wet lower parts of the watershed. Results from these locations were compared with soil solution composition at two locations in a nearby control catchment. After 2 years of nitrogen addition, the volume-weighted average nitrate concentrations in the treated catchment were higher than the pretreatment values, especially in the upper soil. Concentrations showed a progressive increase over time. The lack of the same increasing trend in the control catchment precludes natural variations in climatic conditions as the main cause for this increase. Relative to inputs, nitrate concentrations in soil solution were low and showed large variations between the drier and wetter locations. Differences in nitrate concentrations between pre-treatment and treatment periods declined with soil depth, indicating that most of the added nitrogen was consumed in the upper soil. The results from soil solution do not indicate increased nitrogen leaching below the rooting zone in the treated catchment and thus based on these results alone there is as yet no indication of nitrogen saturation.

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.

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).

Effect of Artificial Rain on Soil Chemical Properties and Forest Growth

Field plots, 150 m2 in size, were watered 27 times, 50 mm each time in the period of July 1973 to September 1978. Groundwater adjusted with sulphuric acid to pH levels of 6, 4, 3, and 2.5, was applied to treatment plots. The experiment was in a homogenous stand of Norway spruce (Picea abies) planted in 1956 on a Cambic Arenosol soil. Tree growth measurements and needle and soil samples have been taken in the period 1973 to 1986. The relatively large changes in soil chemical properties created by applying strong acid to the soil were moderated within a relatively short period after the application of acid was terminated. No effect from the acid treatments were measured on tree height and basal area growth during the watering period. However, negative effects on growth from the acid treatments gradually developed after the watering was stopped. Maximum effects occurred two to five years later. Since then, recovery has been measured. The negative effects are difficult to explain by the nutrient status of the stand as measured by standard foliar analysis. High Al concentrations in the soil solution may have been important.

Lysimeter study of effects of acid deposition on properties and leaching of gleyed dystric brunisolic soil in Norway

The effects of artificial rain of various acidities were studied in a lysimeter experiment. Lysimeters, 29 cm in diameter, and 40 cm deep contained a Gleyed Dystric Brunisol. Natural structure, stratification and original vegetation were maintained. Artificial rain was produced from groundwater with “high” concentrations of neutral salts and from rainwater with lower concentrations. pH levels of 6, 4, 3 and 2 were established by adding H2SO4. Effects of dilution with given amounts of acid were examined by comparing the effects of 50 mm “rain” month−1 of pH 3 and pH 2 with 500 mm “rain” month-1 of pH 4 and pH 3, respectively. The study continued for 5 yr. Totals of 1250 or 12500 mm “rain” were applied in addition to a natural input of 2773 mm. Increased input of SO 4 2− increased the output of SO 4 2− but, as concentration increased, sorption of SO 4 2− in the soil also increased. Concentrations of base cations in the leachate increased parallel to the output of SO 4 2− . However, significant effects on leaching of base cations and on the content of exchangeable cations in the soil, was only found in the pH 2 treatment with 1250 mm of “rain” and in the pH 4 and pH 3 treatment with 12500 mm of “rain”.