Methods used were modified from Bowden et al. (1992) . Photosynthesis and respiration were estimated from linear estimates of change in oxygen within closed chambers during independent light and dark incubations (Bott et al., 1978; Pennak & LaVelle, 1979; King, 1982; Duff et al., 1984). Representative river rocks were placed in sealed Plexiglas chambers and slowly filled with river water prior to each incubation. Water was recirculated in the chamber with a stir-bar placed inside of the chamber and powered by a magnetic fans run on batteries on the outside of the chamber. A YSI® LDO probe was inserted into a port at the top of the chamber. Rocks were collected at random locations within riffles at each site. In a typical experiment, three chambers were run simultaneously, with back-to-back light-dark incubations. This was generally done twice to include 6 replicates per site on each date. Rocks were sealed in each chamber then each chamber was submerged into the river as far as possible without water coming over the top of the chamber. Black tops were placed over the chambers during dark incubations to ensure no light would reach the inside of the chamber. Dissolved oxygen and chamber temperature were measured at three minute intervals during the course of the incubation (30-90 minutes). At the end of each experiment, rocks were removed from each chamber and the aluminum foil surface area and weight/area relationships were used to determine surface area of rocks (Steinman et al. 2006). PAR was measured using a Li-Cor Quantum Sensor. Soluble reactive phosphorus was measured using colorimetric method (APHA 1998).

We used 3 experimental reaches in the Kuparuk for this analysis., -0.177k, +0.5k, and 2.0k. In 2011 a phosphorus dripper was added at 0.0k creating fertilized sections downstream from 0.0k to 3.5k. This includes both recovery sections and the fertilized section as indicated by Benstead et al. (2007). University of Alabama Box 870206   Tuscaloosa Alabama 35487 U.S.A
Funding for this project was made available from NSF-OPP#0902126.

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