Correlations between nitrate and sulfate in the soil solution of disturbed forest ecosystems

Based on data from three German forest ecosystems severely disturbed by windthrow events, correlation patterns between NO₃ ^- and SO₄ ^2- dynamics in the soil solution are described. Each of the correlation types was related to site-specific SO₄ ^2- retention processes. The relative importance of SO₄ ^2- adsorption/desorption and precipitation/dissolution was found to be different for the studied soils depending on their contents of SO₄ ^2- -adsorbing sesquioxides and of A1 hydroxy sulfate minerals. Enhanced NO₃ ^- concentrations in the soil solution resulting from excess nitrification promoted either SO₄ ^2- adsorption or the dissolution of Al hydroxy sulfates. Both processes result in different ecological consequences: Whereas the former reaction reduces anion concentration peaks in the soil solution, the latter increases them. Thus, a prediction of cation export from soil ecosystems subjected to excess nitrification has to regard site-specific interrelationships between NO₃ ^- and SO₄ ^2-. As a third type of conelation the independence of NO₃ ^- and SO₄ ^2- concentrations in the soil solution is presented. This type is suggested to be typical for soils with low SO₄ ^2-. adsorption capacity and absence of A1 hydroxy sulfates.