SURFACE SEDIMENTS AND THEIR RELATIONSHIP 
TO WATER QUALITY IN HILLSBOROUGH BAY, 
A HIGHLY IMPACTED SUBDIVISION OF TAMPA BAY, FLORIDA 
J.O.R. Johansson and A.P. Squires, 
City of Tampa, Bay Study Group, Dept, of Sanitary Sewers 
Tampa, Florida 
INTRODUCTION 
Hillsborough Bay is the subdivision of Tampa Bay that has received 
the heaviest industrial and municipal impacts associated with the recent 
urbanization of the Tampa Bay area. Eutrophication of bay waters caused 
by urban runoff, municipal sewage and industrial discharges, may have 
contributed to a large area of muddy high organic sediments in 
Hillsborough Bay. The upper 20cm of the sediment layer, with its 
associated biota, is an important link in the coupling between the 
benthic and pelagic communities in this shallow estuarine system. A 
eutrophic system like Hillsborough Bay supports a large crop of primary 
producers, mostly phytoplankton, which produce more organic matter than 
can be utilized by the primary consumers. Surplus organic matter and 
waste material from consumers settle to the bottom creating sediments of 
high organic content. Effluents and runoff contribute additional organic 
matter to natural background levels. Organic matter in the sediment is 
mineralized and nutrients are released to the water column where they 
become available for planktonic primary production. The metabolic 
processes associated with the benthos create an oxygen demand which may 
reduce oxygen in the overlying waters. Reduced oxygen concentrations can 
have a drastic impact on the estuarine community structure through large 
scale die-offs of the benthic and pelagic fauna. Benthic nutrient 
regeneration and the related process of dentrification are important in 
the recycling and availability of nutrients in estuaries. In Hillsborough 
Bay, however, few specifics are known of rates and pathways of these 
important links between the benthic and pelagic systems. 
This paper will summarize the composition of surface sediment and 
sediment oxygen demand rates in Hillsborough Bay. Also, a first attempt 
is made to relate the nutrients released from these sediments to the 
phytoplankton, the dominant primary producers of the bay. Much more work 
is needed to understand better how the sediments and their biota affect 
water quality in Hillsborough Bay. 
TAMPA AND HILLSBOROUGH BAY SURFACE SEDIMENT STUDIES 
In Tampa Bay, including Hillsborough Bay, several studies of 
surface sediment composition and distribution have been conducted since 
the 1950’s. 
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