Effects of different organic carbon sources on a freshwater plankton community

We examined effects of terrestrial and aquatic detritus on optical, chemical, and biological properties of a planktonic food web in mesotrophic Calder Lake, New York. The 5400-L mesocosms received detritus from terrestrial leaves or aquatic macrophytes (added 1-2 mg dissolved organic C/L). Terrestrial detritus had significant effects on UV-B absorbance (OD₂₅₀ twofold greater), but humic substances (OD₄₄₀) remained low. Both C sources resulted in 40% declines in oxygen saturation and two- to threefold increases in dissolved inorganic and total P but no effects on NH₄⁺ or NO₃^-. Bacterial growth was stimulated by 20% in systems receiving macrophyte C but declined by 50% in systems with terrestrial C. Initially, controls had >60% greater chlorophyll a concentrations than C-amended systems, but mesocosms with macrophyte C exhibited the greatest chlorophyll a concentrations after day 10. Autotrophic nanofiagellates <20 μm (Chrysochromulina parva, Ochromonas) increased in controls but were inhibited in C-amended systems. Cyanobacteria (Coelosphaerium naeglianum, Anabaena, Dactylococcopsis acicularis) numbers increased in mesocosms with macrophyte C; densities of most algal taxa declined in terrestrial-supplemented systems, except certain flagellates (Synura, Cryptomonas, Ceratium hirundinella), which were enhanced. Abundances of heterotrophic nanoflagellates, rotifers, Daphnia pulicaria, and copepod nauplii were stimulated by macrophyte C; only the copepod Mesocyclops edax increased following addition of terrestrial C.