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.