Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE-Bavaria, Germany

The decrease in anthropogenic deposition, namely SO42- and SO2, in European forest ecosystems during the last 20 years has raised questions concerning the recovery of forest ecosystems. The aim of this study was to evaluate i f the long term data of element concentrations at the Fichtelgebirge (NE-Ba varia, Germany) monitoring site indicates a relationship between the nutrie nt content of needles and the state of soil solution acidity. The soil at t he site is very acidic and has relatively small pools of exchangeable Ca an d Mg. The trees show medium to severe nutrient deficiency symptoms such as needle loss and needle yellowing. The Ca and Mg concentrations in throughfall decreased significantly during the last 12 years parallel to the significant decline in the throughfall of H+ and SO42- concentrations. Soil solution concentrations of SO42-, Ca and Mg generally decreased while the pH value remained stable. Aluminum concen trations decreased slightly, but only at a depth of 90 cm. Simultaneously a decrease in the molar Ca/Al and Mg/Al ratios in the soil solution was obse rved. Ca and Mg contents in the spruce needles decreased, emphasizing the r elevance of soil solution changes for tree nutrition. The reasons for the d elay in ecosystem recovery are due to a combination of the following two fa ctors: (1) the continued high concentrations of NO3- and SO42- in the soil solution leading to high Al concentrations and low pH values and, (2) the d ecreased rates of Ca and Mg deposition cause a correlated decrease in the c oncentration of Ca and Mg in the soil solution, since little Ca and Mg is p resent in the soil's exchangeable cation poets. It is our conclusion that d etrimental soil conditions with respect to Mg and Ca nutrition as well as t o Al stress are not easily reversed by the decreasing deposition of H+ and SO42-. Thus, forest management is still confronted with the necessity of fr equent liming to counteract the nutrient depletion in soils and subsequent nutrient deficiencies in trees.