8 



cover a small range of difference along the pH-alkalinity- 

 conductivity complex, and they are likely to conclude that pH is the 

 important variable affecting macrophyte distribution (Jackson and 

 Charles 1988). Surveys conducted within one or a few lakes will 

 cover only a small range of water chemisty differences, and site 

 characteristics, such as waves, slope and sediment type, will prove to 

 be the most important determinants (Duarte and Kalff 1990). Within 

 a single lake, wave exposure is likely to be a leading determinant of 

 macrophyte biomass at shallow littoral depths, whereas water 

 transparency will exert more influence at greater depths (Duarte and 

 Kalff 1990). 



Effect of Macrophytes on Lake Ecosystem 



Macrophytes seem to exert considerable effects on the nutrient 

 cycling, biology, sedimentation patterns and senescence of the lakes 

 in which they occur. Rooted macrophytes obtain most of their 

 nutrients from lake sediments and thus link the sediments with 

 overlying water (Carpenter 1981). This provides a mechanism for the 

 regeneration of sedimentary nutrients into the water-column. 

 Carignan and Kalff (1982) observed that living macrophytes were 

 responsible for a 2.2% daily increase in P that represented a net 

 seasonal input to the littoral zone because the P was derived from 

 sediments. While P is not released from living macrophytes at a 

 rapid rate, substantial amounts of nutrients in the macrophyte 

 biomass are released when macrophytes die back and shoots decay. 

 Approximately 75% of the P released is in a soluble reactive form, 

 and P becomes rapidly assimilated by phytoplankton, leading to an 



