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1 ) The phytoplankton community competes with macrophytes, 

 especially floating macrophytes (e.g. Eichhornia), and their 

 associated epiphyton for dissolved nutrients in the water 

 column. High macrophyte standing crop could therefore depress 

 water-column nutrient concentrations; 



2) Macrophytes minimize wind mixing and resuspension of 

 nutrients from bottom sediments leading to a reduction in 

 nutrient cycling. 



Other possible explanations for the negative correlation include: 



1 ) Rooted macrophytes may proliferate in lakes that are naturally 

 low in water-column total P concentrations because they don't 

 depend on the water for their nutrient supply. Most of the P 

 they utilize is derived from the sediments (Carignan and Kalff 

 1980); 



2) When water-column nutrient concentrations are high, 

 phytoplankton and epiphyton standing crop increases and may 

 limit submerged macrophytes by shading (Sand-Jensen and 

 Sondergaard 1981). 



Response of Periphyton to Water-Column Nutrients 

 TSI variables demonstrated positive correlations with the 

 proportion of planktonic diatoms, and negative correlations with the 

 proportion of periphytic diatoms in the survey lakes. This suggests 

 that planktonic diatom populations assume greater importance 

 relative to periphyton populations in lakes that are higher in trophic 

 state. The positive correlations between water-column total P and 

 the concentrations and log-transformed accumulation rates of 

 periphytic diatoms, however, show that even if plankton assume 

 greater inportance at higher water-column nutrient concentrations, 

 periphyton production also increases with increasing trophic state. 



