Assessment of boreal forest pollution under the influence of aluminum smelter emissions in Irkutsk region of Russia

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ABSTRACT The chemical element concentrations of Scots pine needles were used in this study to evaluate the contamination of the boreal forest by emissions from three aluminum smelters (AS) with different production technologies in the Irkutsk region (Russia). The test sites were located at varying distances and directions from aluminum smelters. The total area of the surveyed forests was approximately 10,000 km2. The concentration of 26 element-pollutants in the needles (fluorine, sulfur, heavy and light metals, and metalloids) was measured to classify the tree-stands according to their level of pollution. Based on the results of cluster analysis, four levels of tree contamination have been identified: low, moderate, high, and critical. The content of fluorine in needles at the critical level of tree-stands pollution was higher than background values by 35–62 times, aluminum by 6.9–10.5 times, sulfur by 2.5–3.2 times, and heavy metals and metalloids by 4.4–15.2 times. The level of tree crown defoliation reached 70–80%, needle life expectancy decreased up to 2–3 years. All morphological parameters were below the background level, especially the weight of the shoot and needles (by 4.3–6.3 times). A map-scheme showing the distribution of polluted trees was created. Generally, the largest volume of emissions, long period of operation, and aggressive technologies of Bratsk AS have the greatest negative impact on the state of forest ecosystems compared to Irkutk AS. In the area affected by Taishet AS emissions (a new high-tech enterprise) most of the surrounding tree-stands are in satisfactory condition.