Eutrophication 
Eutrophication is defined as the process of increasing dissolved 
nutrient concentrations to a point where nutrient enrichment produces 
certain characteristic responses in a water body. These responses 
include algal blooms, noxious odors, declines in dissolved oxygen, and 
periodic fish kills. Such characteristic responses have been observed in 
Tampa Bay, particularly Hillsborough Bay, for 20 years prior to the FWPCA 
(1969) documentation of nutrient enrichment from partially treated sewage 
discharges as the primary cause. 
Subsequently, over $100 million was spent to upgrade the Hookers 
Point sewage treatment facility from primary to advanced or tertiary 
treatment. The upgraded plant came on line in 1979. After that, other 
studies done by the Florida Department of Environmental Regulation, the 
U.S. Geological Survey, and the City of Tampa concluded that urban runoff 
from streets and parking lots could contribute up to 25% of the 
biochemical oxygen demand, 35% of the suspended solids, and 15% of the 
nitrogen loading to Hillsborough Bay (Garrity, McCann and Murdoch 1985). 
An additional aspect of the problem was added by Fanning and Bell 
(1985) when they suggested that nutrient fluxes from the bay’s sediments 
could be important as sources of nutrients to the water column. These 
authors illustrated that ammonia (NH 3 ) in Tampa Bay reached values higher 
than those found in other studied estuaries. In addition, the ratio of 
ammonia to total inorganic nitrogen (NO 3 - + NO 2 - + NH 3 ) was quite high 
(0.84 + 0.12). Although declines in phosphorus concentrations have been 
documented for the bay, nitrogen concentrations in the water column have 
remained high (Johannson and Squires, this volume). 
Windsor (1985), examining existing water quality data for 28 
coastal areas of Florida, found only three in which nutrient enrichment 
was indicated and definite problems of oxygen depletion were observed: 
Perdido Bay, Tampa/Hillsborough Bay, and Biscayne Bay. 
Lewis et al. (1985) noted that eutrophication leading to 
microalgal and macroalgal blooms may have contributed to the decline in 
seagrasses in the bay due to reduction in downwelling light through 
competition and epiphytic algae loading on seagrass blades. Direct 
experimental evidence of this has been provided by Twilley, Kemp, Staver, 
Stevenson and Boynton (1985), where artificial nutrient loading leads to 
light attenuation by microalgae, epiphytic algae loading on leaves of 
macrophytes, and significant decreases in biomass of submerged 
macrophytes. Orth and Moore (1983) hypothesized that the significant 
loss of submerged aquatic vegetation in Cheseapeake Bay may be due, in 
part, to similar nutrient enrichment. 
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