Aluminum Chemistry in a Forested Spodosol

Abstract The Al chemistry of seeps, soil solutions and soils was evaluated at the Hubbard Brook Experimental Forest in New Hampshire. Alumino‐organic substances predominated in solutions and in the free Al fraction of soils. Concentrations of both organic and inorganic forms of Al were highest at the higher elevations. The extent of spodosol development was consistent with these observations, suggesting the rate of spodosolization is greatest at high elevations in the watershed. We also observed high levels of organic Al entering the mineral soil from the forest floor. Moreover, the historical rate of organic Al deposition within the mineral soil far exceeds the current rate of organic Al precipitation from soil solutions. Processes such as vegetation turnover and windthrow may be important to the Al cycle at Hubbard Brook. Removal of modest amounts of dissolved inorganic Al from the Bhs1 horizon, and subsequent export from the soil, occurs during winter and early spring. This process may be due to atmospheric inputs of acidic substances.