Is chloride a conservative ion in forest ecosystems?

Abstract

Chloride (Cl -) has often been assumed to be relatively unreactive in forest ecosystems, and is frequently used as a conservative tracer to calculate fluxes of water and other ions. Recently, however, several studies have detailed cycling of Cl - in vegetation and soils. In this study Cl - budgets are compiled from 32 catchment studies to determine the extent to which Cl - is conserved in the passage through forest ecosystems. Chloride budgets from these sites vary from net retention (input > output) to net release (output > input). In the overall data set, including those sites with very high inputs of seasalt Cl -, there was a strong correspondence between inputs and outputs. However, sites with low Cl - deposition (<6 kg ha -1 year -1) consistently showed net release of Cl -, suggesting an internal source or a declining internal pool. The results indicate that Cl - may be a conservative ion in sites with high Cl - deposition, but in sites with low deposition Cl - may not be conservative. We discuss the possible causes of the Cl - imbalance and reasons why Cl - may not be conservative in ecosystem functions. © 2010 Springer Science+Business Media B.V.