The effect of reduced atmospheric deposition on soil and soil solution chemistry at a site subjected to long-term acidification, Načetín, Czech Republic

During the 1990s the emissions of SO2 fell dramatically by about 90% in the Czech Republic; the measured throughfall deposition of sulphur to a spruce forest at Načetín in the Ore Mts. decreased from almost 50 kg ha−1 in 1994 to 15 kg ha−1 in 2005. The throughfall flux of Ca decreased from 17 kg ha−1 in 1994 to 9 kg ha−1 in 2005; no change was observed for Mg. The deposition of nitrogen ranged between 15 and 30 kg ha−1 with no statistically significant trend in the period 1994–2005. The desorption of previously stored sulphur and the decrease of Ca deposition are the main factors controlling the recovery of soil solution. The pH of the soil solution at a depth of 30 cm remains unchanged, and the Al concentration decreased from 320 μmol l−1 in 1997 to 140 μmol l−1 in 2005. The enhanced leaching of base cations relative to no acidified conditions has continued, although the Ca concentration decreased from 110 μeq l−1 in 1997 to 25 μeq l−1 in 2005 in the mineral soil solution at 30 cm depth. This dramatic change was not observed for Mg concentration in soil solution, because its deposition remained stable during the observed period. Similar patterns were observed in the deeper soil solution at 90 cm. The reduction in Ca availability resulted in lower uptake by tree assimilatory tissues, measured as concentration in needles. Since 2005, the leaching of nitrate observed in soil solution at 30 cm depth has disappeared. By 2003 a similar situation occurred at 90 cm. Higher incorporation into the trees after 1997 could be an important factor. With respect to the formerly high sulphur deposition and consequently released aluminium, which could have negatively influenced the biotic immobilization driven by microbes and fungi, the recovery may have positively impacted and therefore improved retention in the ecosystem during recent years. The delay in the successful retention of nitrogen in the ecosystem was probably caused by the high mineralization of organic matter after improvement of chemical parameters in the organic horizon (increase in pH and decrease in Al concentration). It seems that high mineralization of stored organic matter after decades of high acidic deposition could be an important factor affecting the high losses of nitrogen in spruce forest ecosystems.