Long-term ionic increases from a central Appalachian forested watershed

The electrical conductivity of stream water draining from an unmanaged and undisturbed control watershed has been increasing rather steadily, about 0.03 mS m^-1 yr^-1, since 1971. During this period, NO₃^- and Ca²⁺ concentrations increased and were shown to mathematically account for the ionic contribution to conductivity; therefore, they are believed to be primarily responsible for the increase. However, the percentage of conductivity explained by the two ions was different over time. The percentage of conductivity attributable to NO₃^- increased in a pattern very similar to concentration. In contrast, the percentage of conductivity attributable to Ca²⁺ decreased slightly over time. The Ca²⁺ is believed to be pairing with the NO₃^- as the NO₃^- ions leach through the soil. While nitrification in mature stands can be strongly inhibited, limited nitrification, especially in forest gaps, and high anthropogenic inputs of NO₃^- probably were primary sources of the leached NO₃^-. Preferential adsorption of SO₄^2-, rather than NO₃^-, on soil colloids is given as an explanation for the lack of retention of NO₃^- in the soil system and subsequent leaching to the stream.