Nitrogen turnover and nitrate leaching after bark beetle attack in mountainous spruce stands of the Bavarian Forest National Park

More than 85% of the mountainous spruce forest of the Bavarian Forest National Park died after bark beetle attack during the last decade. The elemental budget of intact stands and of different stages after the dieback was investigated. N-fluxes in throughfall of intact stands were lower (12-16 kg ha^-1 a^-1) than in an earlier study in an intact mountainous spruce stand in the Bavarian Forest National Park and were reduced in the first years after the dieback (3-kg N ha^-1 a^-1). Nitrate-N fluxes by seepage water of intact stands at 40 cm depth, which is below the main rooting zone, were moderate (5-9 kg ha^-1 a^-1). After the dieback of the stands, NH₄⁺ concentrations were increased in humus efflux as were NO₃^- concentrations in mineral soil. Due to the relatively high precipitation, dilution of the elemental concentrations in seepage was considerable. Therefore, NO₃^- concentrations were usually below the level of drinking water (806 μmol NO₃^- L^-1), with lowest concentrations after the snowmelt and highest in autumn. Nitrate concentrations were elevated from the first year until the 7th year after the dieback. Total NO₃^--N losses by seepage until the 7th year after the dieback equalled 543 kg N ha^-1. Aluminium fluxes after the dieback were enhanced in the mineral soil from 55 to 503 mmol_c m^-2 a^-1 (average of 8 yr), K⁺ fluxes from 8 to 37 mmol_c m^-2 a^-1, and Mg²⁺ fluxes from 13 to 35 mmol_c m^-2 a^-1. The consequences for the nutritional status of the ecosystem, the hydrosphere, and forest management are discussed in the paper.