HYDROLOGICAL CHARACTERISTICS OF TAMPA BAY TRIBUTARIES 



175 



tissues of certain soft marine invertebrates are 

 about 5,000 times greater than tJie concentrations 

 observed in the sea (Bieri and Krinsley, 1958; 

 Krumholz and others, 1957). On the otlier hand, 

 this element is selectively toxic to some organ- 

 isms, including some algae, barnacles, and gastro- 

 pods. Laboratory experiments demonstrated 

 that tlie minimum dissolved copper lethal to 

 G. breve in blooming proportions is about 0.5 

 /ig.at./l. (Wilson).^ Results of this investiga- 

 tion have shown that the average concentration 

 of copper for all rivers combined is well below 

 the toxic levels for G. ireve. The frequency dis- 

 tribution of copper shows that in 75.6 percent of 

 all observations the concentrations ranged from 

 0.03 to 0.08 /ig.at./l. 



The copper concentrations (0.04 ig.at./l.) tab- 

 ulated by Chow and Thompson (1952) in the low- 

 salinity waters off the mouth of the Mississippi 

 River are comparable to the concentrations ob- 

 served in the Hillsborough River but are below 

 those observed in the other rivers. The copper 

 levels in all four rivers were higher than those 

 observed in the San Juan Channel, Washington 

 (Chow and Thompson, 1954). 



SUMMARY 



The estuarine portions of the four main Tampa 

 Bay tributaries can be characterized as subtropical 

 areas subject to considerable variations in several 

 ecologically important factors. These waters 

 seem to be strongly influenced by local precipita- 

 tion and natural phosphate deposits. 



Temperature, salinity, total and inorganic 

 phosphate-phosphorus, jiitrate-nitrite nitrogen, 

 and copper were determined monthly for the four 

 main Tampa Bay tributaries. The temperature 

 variations were characterized by rapid changes 

 during the winter and thermal homogeneity from 

 May to October. Salinity was markedly reduced 

 during months of heavy rainfall and river dis- 

 charges. High phosphate levels were observed 

 in all four rivers. Their drainage areas are rich 

 in natural phosphatic deposits. Extremely high 

 concentrations of phosphate-phosphorus obsen'ed 

 in the Alafia River exceeded those in upper 

 Tamj)a Bay. In the three remaining Tampa Bay 

 tributaries, tlie concentrations of phosphate-phos- 



> Wilson. William B. Toxicity of copper to Gymnodinium 

 ireve. (Manuscript.) 



phorus were lower than those observed in upper 

 Tampa Bay. Higher concentrations of nitrate- 

 nitrite nitrogen were noted in the Hillsborough 

 and Alafia Rivers than in the Little Manatee and 

 Manatee Rivers. The nitrate-nitrite nitrogen data 

 indicate that rivers do not enrich the waters of 

 Tampa Bay to an appreciable degree. Concentra- 

 tions of copper averaged twice those observed in 

 Tampa Bay. 



LITERATURE CITED 



Aldrich, David V., and William B. Wilson. 



1960. The effects of salinity on growth of Gunmodinium 

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 p. 57-64. 



Atkins, W. R. G. 



1953. The seasonal variation in the copper content of 

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BiERi, Robert, and E. H. Krinsley. 



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Collier, Albert, and Joel W. Hedopeth. 



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