Ammonium data from the Kuparuk River near Toolik Field Station, 1984-2012.

Samples from designated stations from the Kuparuk River were collected during each summer from 1984 to 2012. Phosphorus addition has occurred since 1983; station sites are relative distance from the original 1983 phosphorus dripper. Stations include sites in a reference, recovery, and fertilized reach. Reaches were defined based on the location of phosphorous addition (see methods). Phosphoric acid is added to the stream to increase the soluble reactive phosphorus by 0.32 uM. Three sampling dates occurred each summer; once in June prior to the start of fertilization and once each in July and August. Water samples were analyzed for ammonium since 1984.