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Long-Term Ionic Increases from a Central Appalachian Forested Watershed

USDA, Forest Service, Northeastern Forest Exp. Stn., Timber and Watershed Laboratory, P.O. Box 404, Nursery Bottom, Parsons, WV 26287.

^* Corresponding author.

ABSTRACT

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, NO^–₃ 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 NO^–₃ 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 NO^–₃ as the NO^–₃ 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 NO^–₃ probably were primary sources of the leached NO^–₃. Preferential adsorption of SO^2–₄, rather than NO^–₃, on soil colloids is given as an explanation for the lack of retention of NO^–₃ in the soil system and subsequent leaching to the stream.

The use of trade, firm, or corporation names in this article is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the USDA or the Forest Service or any product or service to the exclusion of others that may be suitable.

Received for publication August 1, 1989.