SS3.10 Ecological Implications of Terrestrial Inputs into Lakes and Ponds
Date: Tuesday, June 11, 2002
Time: 2:15:00 PM
Location: Esquimalt
 
KlugJL, Fairfield University, Fairfield, USA, jklug@mail.fairfield.edu
 
NET EFFECTS OF DOM ON PHYTOPLANKTON GROWTH DEPEND ON NUTRIENT AND LIGHT ABSORPTION CHARACTERISTICS OF DOM AND COMPETITION WITH BACTERIA FOR PHOSPHORUS.
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Terrestrially derived dissolved organic matter (DOM) has diverse effects on aquatic ecosystems. For phytoplankton, DOM alters the availability of two crucial resources, light and nutrients, through a variety of mechanisms. Experiments showed that DOM extracted from peat moss had direct positive and negative effects on phytoplankton growth. Nitrogen and phosphorus associated with DOM directly stimulated phytoplankton growth; however, indirect effects on nutrient availability mediated through bacteria were also important. Increases in DOM stimulated bacterial growth, leading to competition between phytoplankton and bacteria for phosphorus, such that algal response to DOM was reduced. The direct negative effect of DOM on phytoplankton was due to reduced light availability. Model results showed that the relative importance of the direct mechanisms changes with concentration. At low DOM concentrations, the direct effects were dominated by nutrient characteristics of DOM, whereas, at high DOM, the direct effects were dominated by light absorption. The relative importance of the indirect effects depends on the bacterial response, suggesting that the effect of DOM on bacteria must be understood in order to predict overall effects of DOM on phytoplankton.