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.