13 



attenuation. Sand-Jenson and Sondergaard (1981) studied 

 phytoplankton and epiphyton shading effects on macrophytes in 

 Danish lakes. In oligotrophic, silicate-poor lakes, the water was 

 responsible for most of the light attenuation. Epiphyton were 

 responsible for 50% of the light attenuation to macrophytes in 

 oligotrophic, silicate-rich lakes receiving N supply. In a lake that had 

 a high nutrient supply, they determined that epiphytes were 

 responsible for 86% of the light attenuation to macrophytes. 

 Sand-Jensen and Sondergaard concluded that the shading effects that 

 epiphytes exert on macrophytes becomes a decisive factor limiting 

 depth distribution of macrophytes in lakes with high nutrient supply. 



Substrate Specificity and Growth Forms of Periphyton 



Some studies have indicated a high degree of substrate 

 specificity by epiphytic and periphytic diatoms. Round (1956) 

 characterized diatom taxa growing on plants (epiphytic) as 

 "attachment" types mostly of the genera Achnanthes, Cymbella and 

 Epithemia, whereas diatoms found on sediments (epipelic) were 

 actively motile and unattached, including the genera Navicula, 

 Amphora and Diploneis. Round noted, however, that diatom taxa 

 growing on stones (epilithic) were similar to epiphytic diatoms. Siver 

 (1978) observed that the diatom genera Achnanthes, Cocconeis and 

 Eunotia were the most abundant taxa growing on Potamogeton 

 robinsii. Blindow (1987) stated that the composition of epiphyton on 

 Potamogeton and Chara was different than the epiphytic composition 

 on Nitellopsis that was heavily marl-encrusted. Eminson and Moss 

 (1980) observed that host specificity of periphyton was greater in 



