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

Abstract

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.