Using ion-exchange resins to study soil response to experimental watershed acidification

Ion-exchange resins (IER) offer alternative approaches to measuring ionic movement in soils that may have advantages over traditional approaches in some settings, but more information is needed to understand how IER compare with traditional methods of measurement in forested ecosystems. At the Bear Brook Watershed in Maine (BBWM), one of two paired, forested watersheds is treated bi-monthly with S and N (28.8 and 25.2kg ha(-1) yr(-1) of S and N, respectively). Both IER and ceramic cup tension lysimeters were used to study soil solution responses after similar to 11 years of treatment. Results from both methods showed treatments resulted in the mobilization of base cations and Al, and higher SO4-S and inorganic N in the treated watershed. Both methods indicated similar differences in results associated with forest type (hardwoods versus softwoods), a result of differences in litter quality and atmospheric aerosol interception capacity. The correlation between lysimeter and IER data for individual analytes varied greatly. Significant correlations were evident for Na (r=0.75), Al (r=0.65), Mn (r=0.61), Fe (r=0.57), Ca (r=0.49), K (r=0.41) and NO3-N (r=0.59). No correlation was evident between IER and soil solution data for NH4-N and Pb. Both IER and soil solution techniques suggested similar interpretations of biogeochemical behavior in the watershed.