Skogsbrukets påverkan på övergödning och försurning
Sammanfattning: Acidification and eutrophication are central environmental problems in Sweden, which effects biodiversity. The Swedish forestry may contribute significantly to these environmental problems. The forestry measures that may have a major impact on nitrogen levels in groundwater and increased soil acidification are harvesting, fertilization and whole-tree harvesting. Studies have shown that even storm damage can contribute to nitrogen leaching and acidification of drainage water. The rising nitrogen levels originates in that there are no vegetation left that can pick up the nitrogen or bind it to the ground, when the trees are harvested or storm felled. Increased nitrate concentrations in the soil water may also provide an acidifying effect with reduced pH and decreased acid neutralizing ability (ANC). In this study, effects of clearcuts, thinnings, fertilization and storm damage on nitrogen levels and acidification parameters in the soil water are studied. The effects are related to the nitrogen deposition gradient, with increasing deposition from north to southwest. The results indicate that clearcutting, fertilization and storm damage in most cases, and in one case for thinning, increase the levels of nitrate in groundwater. However, the different forestry measures and the storm damage have a different magnitude of impact on nitrate content in the soil water. The acid-related parameters pH, ANC and inorganic Al were also affected by clearcutting, thinning, fertilization and storm damage. At high levels of nitrate in the groundwater, the pH, ANC decreased and the level of inorganic Al increased. To some extent, the effects were more extensive in areas with more nitrogen deposition, but a couple of sites did not follow the nitrogen deposition gradient, which suggests that there are other factors that affect the concentration of nitrate, more than gradient differences. Future studies with more sites are required to further increase the understanding of effects of forest management.
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