Increased concentrations of nitrate in forest soil water after windthrow in southern Sweden

• We assessed the effect of windthrow on nitrate concentrations in the soil water.
• 33 Plots within the Swedish Throughfall Monitoring Network (SWETHRO) were assessed.
• The maximum soil water nitrate concentrations occurred 1–4 years after the storm.
• It was not possible to demonstrate a significant correlation with nitrogen deposition.
• The potential impact on ground- and surface waters after storm events is discussed.

In January 2005, south-west Sweden was hit by a severe storm that caused large damage to the forests through massive windthrow. The aim of this study was to assess the effect of this windthrow on nitrate concentrations in the soil water below the root zone on 33 forest monitoring plots within the Swedish Throughfall Monitoring Network (SWETHRO). These sites were damaged to different extents by the storm. The analysis showed increased levels of nitrate concentrations in the soil water as a consequence of storm damaged forest. The present study concerned forest ecosystems with relatively low levels of nitrogen deposition, as compared with forests analysed in previous studies. The maximum soil water nitrate concentrations occurred 1–4 years after the storm. After 5–6 years, the concentrations were back at the same levels as before the storm event. It was not possible to demonstrate a significant correlation between increased nitrate concentrations in the soil water after the storm and the level of nitrogen deposition at the site. The potential impact on ground- and surface waters due to elevated nitrate concentrations in soil water after storm events is discussed.