OULF OF MEXICO 



147 



after the blooming of Gymnodinium brevis, the 

 concentrations of inorganic phosplionis were fonnd 

 as high as 7.4 ^g-atoms/L and total phosphorus 

 (particulate organic, dissolved organic, and in- 

 organic) up to 20.4 Mg-atoms/L in the amber 

 colored water (Ketchum and Keen 1948, p. 18; 

 Gunter, Williams, Davis, and Smith, 1948, p. 

 319: Galtsoff 1948, p. 20; Smith 1949, p. 5). 



These unusually high phosphorus concentra- 

 tions suggested the need for more detailed informa- 

 tion on horizontal, vertical, and seasonal dis- 

 tribution of phosphorus compounds to clarify 

 the fundamental causes of the red tide. Ac- 

 cordingly, when the research program of the Fish 

 and Wildlife Service laboratory in Sarasota, 

 Florida, was planned studies of the distribution 

 of total, inorganic, and organic phosphorus were 

 given primary attention. Results of a detailed 

 survey at 13 stations in the rivers, along the 

 middle Florida coast, and 120 miles west to the 

 100-fathom line from May 1949 to August 1950 

 have been published (Graham, Amison, and 

 Marvin, 1954). They show a gradual decrease 

 in phosphorus content of the surface water with 

 increase in distance from shore. The phosphorus- 

 rich waters discharged from the Peace River did 

 not affect, however, the local Gulf waters to any 

 measurable degree. Beyond 14 miles from shore 

 the concentration of total phosphorus in the sur- 

 face water was usually below 0.25 fig-atoms/L 

 and inorganic phosphorus was usually below 

 0.10 Mg-atoms/L. Larger quantities of phos- 

 phorus, mostly inorganic, were found at depths 

 below 50 meters. Occasional upwelling did not 

 seem to influence the phosphorus content of the 

 eu photic zone. There was no evidence of the 

 bottom sediments contributing any appreciable 

 quantities of phosphorus to the water. Local 

 concentrations of the planktonic blue-green alga, 

 Trichodesmium, appeared to be associated with 

 high concentrations of total phosphorus. 



NITRATE-NITROGEN 



Studies of nitrate distribution in the Gulf have 

 generally paralleled those of phosphate reviewed 

 above. Vertical distribution of nitrate in the 

 middle of the Yucatin Channel in May 1933 

 (Bulletin Hydrographique, 1934, p. 103) was 

 indicated in a graph by Rakestraw (1936, p. 160, 

 fig. 11) and Rakestraw and Smith (1937, p. 9, 



259534 0—54 11 



fig. 7).' The nitrate decreased from 2.4 Mg- 



atoms/L at the surface to 1.4 ^g-atoms/L at 49 



meters, then increased regularly to a maximum 



of 37.1 Mg-atoms/L at 736 meters, then decreased 



to 24.2 Aig-atoms/L at 1,732 meters. These data 



for Yucatdn Channel water were used in the 



charts of horizontal distribution of nitrate at 



various depths (Rakestraw and Smith, 1937, 



figs. 14-16). 



Although no nitrate determinations were made 



on Gulf waters near the mouth of the Mississippi, 



Riley (1937, p. 69) reported the following data 



(supphed by A. A. Hirsch of the New Orleans 



Sewerage and Water Board Company) which are 



1935 average values for the Mississippi River 



water at New Orleans: 



Ammonia nitrogen 20 mg/m' 



Albuminoid nitrogen 350 mg/m' 



Nitrite nitrogen 5 mg/m' 



Nitrate nitrogen 200 mg/m' 



Nitrate data for two stations in the Florida 

 Straits reported by Riley (1939, p. 161) are sum- 

 marized in table 3. 



Table 3. — Vertical distribulion of nitrate-nitrogen 

 {ixg-atomsl L) in the Florida Straits 



Riley, Stommel, and Bumpus (1949, p. 16, fig. 

 6) used these surface values for southeastern Gulf 

 water in their summary chart and discussed the 

 origin of Caribbean water from the nutrient-poor 

 Equatorial and Antilles Currents. They ex- 

 plained, however, that the Caribbean "also re- 

 ceives a substantial draught of Antarctic inter- 

 mediate water, which is very rich, particularly in 

 nitrate. The maximum concentration of this 

 substance at a depth of about 800 meters in the 

 Caribbean (and possibly the Gulf of Mexico) ex- 

 ceeds the amount found anywhere else in the 

 western North Atlantic." Some of this may be 

 accumulated products of regeneration, as sug- 

 gested for phosphate (Riley 1951). 



' There appears to be a confusion of units for expre.ssine these nitrate data 

 parallel to that discussed for phosphate in footnote 5. 



