670 Marine Microbiology 



of tlie bay and pond waters adjacent to the flats as compared with 

 the open bay and Gulf of Mexico waters shown in tlie data in 

 Figure 2, areas five to eight. It is difficult to calculate the relative 

 surface of intertidal mud flats because of the type of terrain. The 

 phosphorus values in the sediments below the salts are large 

 enough to account for the phosphates found on the surface in 

 the precipitated salt. The phosphate values for the bay waters 

 and Gulf of Mexico are within the range 0.60 to 4.02 /^'gA-total 

 P/L. Surface phosphorus values for other bays and coastal water 

 are also within this range. Strickland and Austin (15) give values 

 between approximately 1 and 3 ^gA-total P/L at 5 meters depth 

 in Departure Bay and Pacific Oceanic values from approximately 

 1 to 5 /'.gA-total P increasing with depth. Redfield (9) lists 

 average sea water as containing 2.3 /xgA-total P/L, with the 

 North Atlantic 1.25 and the North Pacific 3.0. 



The data suggest that the productivity of the bay waters is 

 probably not due to an abnormal amount of phosphorus but per- 

 haps to the rate at which the phosphorus is cycled within the 

 waters. Bruce and Hood (2) have indicated a rapid turnover rate 

 as shown by diurnal inorganic phosphate curves which vary from 

 2.4 MgA/L at 6 a.m. to 1.4 at 6 p.m. The relatively large variation 

 of inorganic phosphorus certainly suggests caution in establishing 

 routine collecting procedures for such measurements in water 

 systems. 



The release of phosphates from the sediments is apparently 

 part of the cycle of this and perhaps other nutrients. Sedimenta- 

 tion rates are relatively rapid: up to 19 cm per 100 years (11) 

 and /4 to /3 inch per year variation in the Laguna Madre (4). The 

 high rate of sedimentation and continued movement of sediments 

 from month to month during rather gusty wind conditions en- 

 traps organic and inorganic phosphorus. 



There are several mechanisms by which the entrapped phos- 

 phorus may be solublized in the sediments. Baas Becking and 

 MacKay ( 1 ) , Garrett and Goodgal ( 3 ) , and Sperber ( 12 ) discuss 

 the release of soluble phosphate from sediments which ac- 

 companies an increase in pH from 6 to 8 due to bacterial meta- 

 bolism or a decrease in Eh to the anaerobic state and accompany- 

 ing action of sulfide produced by sulfate-reducing bacteria (7). 



