The mean concentration of NO3 (5 µM) in the precipitation was greater than the trace levels normally found in non-polluted precipitation. The NO3 is believed to originate primarily from anthropogenic sources. Anion concentrations in canopy throughfall were similar to the precipitation levels for Cl, NO3, and SO4, while PO4 concentrations showed a small increase. With the exception of Cl (a non-essential element), concentrations of all anions showed an attenuation between the A/AB and Bt horizons indicating plant uptake and/or anion sorption. There was complete retention of PO4 within the rooting zone suggesting that PO4 is a limiting nutrient in this ecosystem resulting in a very tight cycle. In contrast, NO3 concentrations leaching from the Bt1 horizon remain in the 15-50 µM range which is similar to the mean stream water concentration of 20 µM over the same time period Therefore, N appears to be present in sufficient quantities to meet the plant requirement, the excess being leached from the soil profile into the surface and ground waters.
Concentrations of NO3 and PO4 decreased by a factor of 3-4 in the A and AB horizons following oak tree removal. Concentrations in the cut plots were approximately midway between the values measured for the oak canopy and grassland plots. Sulfate similarly showed a lower, but non-significant decrease following tree removal. Chloride concentrations behaved similar to those of Na showing no statistical difference compared to the oak canopy plots.