The effects of river fertilization on mayfly (Baetis sp.) drift patterns and population density in an arctic river

The life history, drift behavior, and benthic density of Baetis (Ephemeroptera) were examined in the arctic Kuparuk River in conjunction with a whole river fertilization experiment to determine if river fertilization affected Baetis drift and life history parameters. Drift was significantly higher in the control section of the river than in the fertilized, which suggested that the control section was a less suitable habitat than the fertilized section. There was no strong linear or exponential relationship between drift and benthic density, suggesting neither of these models are adequate to describe density independence versus density dependence. However, drift patterns in the control and fertilized sections suggest that drift is more of a function of absolute food supply than space or density of individuals. Drift was also sampled along a river transect at 6-hour intervals over a diel cycle. No diel periodicity in arctic summer drift was observed. The number of adults, number of eggs/female, and egg volume were calculated for adult Baetis collected in drift samples. There was no clear linear relationship between Baetis female dry mass and the number of eggs produced per female. However, a strong linear relationship was observed between individual egg volume and Baetis female dry mass, suggesting that larger females tended to produce larger eggs rather than more eggs.