172 



FISHERY BULLETIN OF THE FISH AND "WILDLIFE SERVICE 



stations 29, 31, 33, and 36 even when a red- tide 

 outbreak occurred in lower Tampa Bay and off- 

 shore areas. In view of tlie G. hreve salinity 

 tolerance findings of Aldrich and Wilson fl960), 

 it seems probable that even the maximum salinity 

 (24.83 %o) noted at these stations was too low to 

 pei'mit growth of this organism. Low concentra- 

 tions of G. hreve (up to 13 per ml.) were observed 

 in samples taken near Bradenton during the red- 

 tide outbreak in 1957. Salinity values for these 

 positive samples were somewhat higher : 25.73 Von 

 to 29.27 Von (Dragovich and othere, 1961). 



The distribution of total and inorganic phos- 

 phate-phosphorus in the rivers demonstrates the 

 influence of underlying phosphatic formations. 

 Higher concentrations of total and inorganic 

 phosphate were recorded in the Alafia, Little 

 Manatee, and Manatee Kivers which flow througli 

 a phosphatic district than in the Hillsborough 

 River which has less contact with natural phos- 

 phate deposits. 



In contrast to the scarcity of phosphorus in the 

 oceans (Harvey, 1957; Sverdrup, Jolmson, and 

 Fleming, 1946), an abundance of this important 

 nutrient element was found in all rivers flowing 

 into Tampa Bay. On the basis of in vitro work 

 (Ketchum, 1939), the concentrations observed 

 represent a more than adequate supply for phyto- 

 plankton growth. A sizable contribution of total 

 phosphorus to the waters of Tampa Bay is evident 

 from data presented in table 1. A parallel inves- 

 tigation in Tampa Bay (Dragovich and others, 

 1961) has shown that upper Tampa Bay waters 

 are richer in phosphorus than all Bay tributaries 

 with the exception of the Alafia River (table 1). 

 The Alafia River contributes the largest quantities 

 of phosphorus to Tampa Bay. Graham, Amison, 

 and Marvin (1954), in their phosphorus studies 

 of the Caloosahatchee and Peace Rivers, observed 

 a high average concentration (12.0 /tg.at./l.) of 

 total phosphorus in the Peace River. This value 

 was less than one-third that of the Alafia. Aver- 

 age concentrations of inorganic (1.21 ;u,g.at,/l.) 

 and total phosphorus (2.63 /xg.at./l.) in the Ca- 

 loosahatchee River are very low if compared with 

 the corresponding values for any of the rivers 

 flowing into Tampa Bay. 



High concentrations of total phosphorus in the 

 rivers were due largely to inorganic phosphate, 

 whicli represented 77 to 95 percent of tlie total. 



Inorganic and total phosphorus were higher at 

 the stations nearer the Bay than at the upstream 

 stations, except in the Alafia River. From figure 

 7 it is apparent that the maximum concentrations 

 of total phosphorus at station 29 were observed 

 near the bottom and at highest salinities. The 

 difference in total phosphorus values for the sur- 

 face and bottom at station 33 appears to be insig- 

 nificant. A phosphorus-salinity relation at sta- 

 tions 31 and 36 is not apparent. However, at 

 station 31 phosphorus values at the few high- 

 salinity levels noted were well below those ob- 

 served at low salinities. The maximum total phos- 

 phorus values at station 36 (fig. 7) cannot be 

 regarded as representative, for the samples were 

 extremely rich in particulate matter. 



Maximum concentrations of inorganic and total 

 phosphorus in the Alafia River were recorded 

 during the rainy season at the period of maximum 

 discharges. In the Hillsborough River, where 

 highest river discharges were recorded, a moder- 

 ate surface increase in inorganic and total phos- 

 phorus was observed from March to September at 

 both stations. This pattern was not evident in the 

 Manatee River and the Little Manatee River data. 

 High concentrations of organic phosphorus ob- 

 served in the Alafia River from May to October 

 may indicate increased biological activity. 



In contrast to the high concentrations of phos- 

 phorus, the nitrate-nitrite nitrogen observed for 

 these rivers can be considered moderate or low. 

 The distribution of nitrate-nitrite nitrogen ob- 

 servations for all stations (fig. 8) clearly shows 

 the existence of higher concentrations in the 

 Hillsborough and Alafia Rivers than in the Little 

 Manatee and Manatee Rivers. This pattern is 

 similar to that of river discharges. The concen- 

 trations of nitrate-nitrite nitrogen in the Hills- 

 borough and Alafia Rivers are comparable to the 

 surface concentrations in certain marine areas such 

 as the Gulf of Maine (Rakestraw, 1936), English 

 Channel (Cooper, 1937), or Arabian Sea off Cal- 

 cutta (Panikkar and Jayaraman, 1953), while the 

 concentrations in the Little Manatee and Manatee 

 Rivers, if compared to the same areas, are ex- 

 tremely poor. The seasonal distribution of nitrate- 

 nitrite nitrogen and its sliort-term response to 

 river discharge variation were very irregular. 



The mean concentrations of nitrate-nitrite ni- 

 trogen in the Hillsborough and Alafia Rivers are 



