Effects of elevated levels of carbon dioxide and nitrogen on phytoplankton biomass and species composition.

Abstract

Due to anthropogenic sources such as fossil fuel combustion and agriculture, carbon dioxide (CO2) and nitrogen levels have increased and will continue to rise into the foreseeable future. Projected levels of CO2 and nitrogen may have similar effects on terrestrial and aquatic ecosystems, but effects on phytoplankton are unknown. Phytoplankton total biomass and/or species compostion may be affected by elevated CO2 levels, increased nitrogen levels, or elevated CO2 dependent on increased nitrogen. We simulated South Fishtail Bay of Douglas Lake in 12 tanks, using four treatments comprised of elevated CO2, increased nitrogen, combinations of elevated CO2 and increased nitrogen, and ambient levels of each. We tested phytoplankton total biomass and the ratio of diatoms to bluegreen algae from our tanks. We found no significant changes in biomass or species composition due to the different treatments. Elevated CO2 and increased nitrogen levels did not have an effect on our phytoplankton populations.