Release and Capillary Movement of Phosphorus 671 



When the Eh decreases to a -200 mv, ferric hydroxide is dis- 

 solved and any adsorbed phosphates are released. The action of 

 hydrogen sulfide also will release phosphate from iron phosphate 

 by the coupling of the iron with sulfide. In addition to the above 

 mechanisms, bacterial activity will release phosphates during 

 the decomposition of organic matter which may be entrapped 

 within the sediments. Rice (10) has shown by tracer experiments 

 that phospliorus is exchanged between the medium and the living 

 cells of phytoplankton. Garrett and Goodgal (3) discuss the 

 mechanisms by which adsorbed phosphorus may be released 

 when colloidal materials are transported from one environment 

 to another. They discuss the relative sorption of materials from 

 the dissolved state and point out that any colloidal sorption system 

 is very complex in the natural environment, and before it can be 

 understood one should know the relative sorption-desorption 

 pathways. These are complex in our turbid bays where suspended 

 matter is abundant. Hayes discusses the sorption of phosphate in 

 lake sediments in a previous chapter in this publication. 



Most of the mud flats have an annual redox potential cycle 

 whereby the oxygen transition zone may be at the surface of the 

 sediment during summer with high bacterial activity and oxygen 

 consumption, and deeper in the sediment (a few cm) during 

 winter when the bacterial activities decline. The pH, in contrast, 

 goes through a diurnal change from approximately 6.5 to 8.0 

 during respiration and photosynthesis respectively. The diurnal 

 change takes place only to the depth of light penetration, which 

 is about 0.5 cm in algal mats, clays, or silt sediments and to 1.5 

 cm in sandy sediments. 



SUMMARY 



Salts are found precipitated on exposed mud flats of the 

 bays studied. The ratio of soluble phosphorus to chloride in the 

 salts was 0.3, whereas for adjacent water it was 0.047. Up to 7.1 

 /'gA of inorganic phosphorus per 100 g of salt was found on the 

 flats. The data indicate that phosphorus was being liberated in 

 the sediments presumably through the action of bacteria and 

 chemical equilibria and concentrated in the salts evaporated from 

 sediment capillary water. Total phosphorus content of the bays. 



