The Mobile Anion Concept—Time for a Reappraisal?

The mobile anion concept has been used to support the argument that acid precipitation, containing elevated concentrations of nitrate and sulfate, is acidifying soils and surface waters. We believe that so much attention has been focused on the behavior of the strong acid anions that the effect of other important processes has, in some cases, been obscured. The emphasis, we believe, should be placed on processes that regulate H + in solution. Thus, we propose that the mobile anion concept (as an explanation of how acid precipitation degrades soils and surface waters) be replaced with descriptions of the mechanisms believed to control the movement of both anions and cations through ecosystems.