Mesocosm studies on the influence of phosphate enrichment on ammonium and nitrate flux in an oligotrophic lake

摘要

The fate of15NHinf4sup+and15NOinf3−was followed in control and POinf4sup3−enriched 1570 l mesocosms filled with epilimnetic water from an oligotrophic Rocky Mountain lake. Volumetric incorporation of15NHinf4sup+and15NOinf3sup−into phytoplankton and bacterioplankton (particulates between 280 and 0.7 µm), and crustacean zooplankton>80 µm was enhanced by POinf4sup3−, but no increase in biomass specific rates of uptake by phytoplankton and bacteria occurred for either form of15N. Dilution of both15NHinf4sup+and15NOinf3sup−by14NHinf4sup+and14NOinf3sup−, respectively, was evident indicating regeneration of these nutrients, but regeneration rates were not effected by POinf4sup3−enrichment. The results illustrate the strong trophic coupling between N dynamics and POinf4sup3−enrichme