Fig. 4. Relationships between beneath-stream groundwater phosphorus concentrations vs. soil aluminum and soil iron contents at each site. Phosphorus concentration values are based on annual average (n = 12), whereas soil data are based on an average of 4 samples per site. Shown are (a) groundwater soluble reactive phosphorus (SRP) vs. Al in the B horizon, (b) groundwater total phosphorus (TP) vs. Al in the B horizon, (c) groundwater SRP vs. Fe in the A horizon, and (d) groundwater TP vs. Fe in the A horizon. Solid lines indicate significant (p < 0.05) linear regression slopes between near-stream groundwater phosphorus concentration and soil Al or soil Fe content.