rough approximations and the degree of possible error varies greatly 
between streams. Acknowledging a certain level of uncertainty, nutrient 
loading estimates for eight tributaries to Tampa Bay were made by Dooris 
and Dooris (1985), and large differences in nutrient loading between 
streams were found. Using more recent water quality data, I have re- 
estimated average annual loading of selected nutrients to Tampa Bay for 
the tributaries examined by Dooris and Dooris with the exception of 
Sweetwater Creek. These nutrient loading estimates were calculated from 
the long term average streamflow averages depicted in Figure 7 and the 
mean nutrient values for 1984-85 listed in Table 2. 
These estimates generally supported the tributary ranking by 
nutrient load presented by Dooris and Dooris, but there were some notable 
differences in the results, in particular: greater organic nitrogen and 
nitrate loadings for the Hillsborough and Little Manatee Rivers and Rocky 
Creek; reduced nitrate loading for the Manatee River; and reduced 
phosphorus loading for the Alafia, Hillsborough, Manatee, and Little 
Manatee Rivers. However, in many cases these two analyses used different 
water quality stations and methods for computing total stream discharge; 
therefore, some differences in the results are expected. Due to 
differing methodologies, these two studies cannot be compared to identify 
trends over time, which would require more in-depth analysis of each 
tributary. 
It is also emphasized that these recent estimates, and many of 
those presented by Dooris and Dooris, are biased for nutrient loading 
above the brackish portion of each river and nutrient additions to the 
lower reaches of the rivers are largely ignored. For some tributaries 
(e.g., Manatee River and Rocky Creek), these downstream nutrient 
additions are particularly high, and reported nutrient loads seriously 
underestimate final nutrient loading to the bay. Since most of the 
localized nutrient loading to these lower tributary reaches is from 
stormwater runoff or point source discharges, a separate analysis of 
those factors may account for their effects. 
The seven tributaries for which nutrient loading estimates are 
made are listed in Table 3 by their average ranking based on loadings of 
total phosphorus and total nitrogen. The Alafia River has the highest 
estimated loading rates for these two parameters and nitrate. This was 
particularly pronounced for total phosphorus, as the estimated annual 
load for the Alafia was more than five times greater than the value for 
the next highest river. Similarly, the phosphorus load for the Alafia 
was 71% of the total load for the seven listed tributaries. 
The four major rivers were more closely grouped for estimated 
total nitrogen loads, with values ranging from 2.7x10^ kg/yr for the 
Little Manatee to 8.6x10^ kg/yr for the Alafia. Loading estimates for 
organic nitrogen were even more closely grouped, ranging from 1.2xl0 5 
kg/yr to 3.2x10^ kg/yr, with the Hillsborough and Manatee Rivers having 
the highest values. The results for nitrate loadings were similar to 
total phosphorus in that the Alafia had markedly higher values than the 
other tributaries due to its high nitrate concentrations. 
43 
