Chemistry 99 



6.0 



6.4 



6.8 



7.2 



PH 



500 



FIGURE 4-11. Oxidation potential and pH prof lies in the water and sedi- 

 ments of Pond J, 11 July 1971. The profiles were taken in a stand of 

 Carex (3-cm- and 8-cm-deep water) and in an area devoid of 

 macrophytes (22 cm). 



at the shallower Carex-covered sites. Redox potentials of the pond central 

 basin sediments and of the deeper sediments (below the root zone) of the 

 plant beds ^11 within the upper part of the Eh range of lake sediments 

 reported in Hutchinson (1957). Measurements in 1973 substantiated these 

 observations, and indicated that the higher oxidation potentials in the 

 plant beds were due to the presence of Carex, rather than due to the water 

 depth. Vascular plants have passages in their stems that allow oxygen to 

 reach the roots; this facilitates the uptake and transport of phosphate and 

 other salts (Loughman 1968, Armstrong 1964). Leakage of oxygen is 

 evidently significant from the Carex in this pond, as there are relatively 

 high oxidation potentials in sediments under stands of pond vascular 

 vegetation in *■ '' Pond J (1971) and Pond C (1973). In other Carex 

 species the leakage of oxygen stops the transport of ferrous iron into roots. 

 Without this mechanism, the ferric iron would precipitate within the roots 

 and immobilize the plant's phosphorus (Jones 1975). 



Relatively high oxygen potentials have also been reported in beds of 

 Lobelia in Denmark (Wium Andersen and Andersen 1972) and in beds of 



