in the river show the closest response to urban runoff in either the dry 
or wet seasons. Phosphorus contributions from stormwater are 
comparatively small, averaging six to ten percent of the total load to 
the river with the remainder coming from upstream sources. Stormwater, 
however, is a significant source of suspended solids, BOD, and total 
nitrogen to the lower river, particularly during the dry season when it 
may account for 37 to 40 percent of the seasonal load (see Drew et al. in 
review). 
The lower river periodically experiences problems with low 
dissolved oxygen which result from excessive algal activity, sediment 
oxygen demand, sluggish flows and tidal salinity effects. Low dissolved 
oxygen levels are closely tied to the location of the salt wedge and 
during the dry year of 1981 were particularly low. Freshwater flow 
suppresses tidal and diurnal (algal) effects on dissolved oxygen 
fluctuations and generally increases the rivers DO concentrations, 
particularly at low to moderate flows. Low DO has been found near the 
dam during high flows, however, when oxygen poor bottom waters from the 
reservoir are released through lower control gates. 
Delaney Creek 
South of the Tampa Bypass Canal, Delaney Creek drains 
approximately 16 square miles of land which is experiencing rapid 
urbanization. A number of industrial point sources discharge into 
Delaney Creek resulting in very poor water quality. Extremely high 
concentrations of nitrogen species in the creek (Table 2) are due to 
discharges from Nitram, Inc., a nitrogen fertilizer processing plant. 
Alafia River 
Of the major rivers flowing to Tampa Bay, the Alafia River is 
notable for its poor water quality. The Alafia drains lands which 
overlie rich phosphate-bearing deposits and extensive phosphate mining 
has occurred in the watershed. Although water quality in the Alafia River 
has been affected by agricultural runoff and miscellaneous point source 
discharges, impacts associated with phosphate mining, processing, and 
enrichment have been the overwhelming perturbations. 
Although perturbations to the river still occur, impacts to water 
quality from the phosphate industry are generally not as severe today as 
in past decades. Prior to the mid-1970’s, the discharge of poorly 
treated or untreated effluents from mines and phosphate or chemical 
processing plants caused extreme loadings of phosphorus, fluoride, 
sulfate, ammonia and acids to the river. During this period the Alafia 
was particularly notorious for high concentrations of phosphorus and 
fluoride. For instance, between 1959 and 1966, total phosphorus 
concentrations commonly ranged between 10 and 30 mg/1 in the main stem of 
the river while fluoride concentrations were generally greater than 10 
mg/1 (Hand, Tauxe and Watts 1986). Water quality in the Alafia basin has 
historically been worst in the North Prong of the river due to the 
abundance of phosphate and chemical processing plant discharges. 
38 
