The Upper Kuparuk River Experiment
The Upper Kuparuk River Experiment (UKRE) began in 1983. The original goal of the UKRE was to determine the effects of adding the limiting nutrient, phosphorus, on primary productivity, insect communities, and fish growth in Arctic rivers. Phosphorus was added to the river continuously as phosphoric acid, via a peristaltic pump, from late June to mid-August, during the biologically active part of the Arctic year, and continued each year until the experimental enrichment ended in 2016. The original 1983 site of the phosphorus addition was designated as the 0 km reference point, with downstream stations assigned positive numbers and upstream stations given negative numbers based on distance from the 0 km location. The location of phosphorus addition was moved in 1985 to 0.59 km and in 1996 to 1.4 km, to create two different “Recovery” reaches. In 2011, an additional dripper was placed at 0 km to resume enrichment of the reaches between 0 km and 1.4 km. These re-fertilized areas were designated as the ”ReFert” reaches. The stream reach from 0 km to 0.59 km (formerly “Recovery A”) was designated as “ReFert-1”, and the reach from 0.6 km to 1.39 km (formerly “Recovery B”) was designated as “ReFert-2”. Sites that received continuous enrichment throughout the course of the experiment were designated as the “Fertilized” reach and sites that were never enriched were designated as the “Reference” reach. We monitored physical, chemical, and biological variables at several riffle locations in each experimental reach, and collection of data from these sites has continued beyond 2016 to track the recovery of the formerly fertilized reaches.