Biological responses to fertilization of Oksrukuyik Creek, a tundra stream

Experimental additions of phosphorus or phosphorus plus nitrogen to Oksrukuyik Creek, an arctic tundra stream, stimulated production at all trophic levels relative to an unfertilized reach. Epilithic chlorophyll concentration, primary production, and respiration in the epilithic community increased in fertilized riffles, and biomass of diatoms and filamentous macroalgae increased considerably. Production and density of Baetis spp. and Orthocladius rivulorum, 2 key grazing larval insects, increased in the fertilized zone. Production and density of larval black flies, the major filter feeders in the Creek, were not affected significantly by enrichment. Fertilization increased summer growth of adult and young-of-the-year Arctic grayling Thymallus arcticus. Mean summer discharge was an important regulator of epilithic chlorophyll concentration, macroalgal biomass, Orthocladius production, and possibly fish growth. We compared our results to a similar fertilization experiment conducted in the Kuparuk River, a larger arctic tundra stream. In both systems, production increased at every trophic level, although responses of specific primary producers and insects differed, possibly because of differences in flow regimes.