Of major concern in many coastal areas around the Nation is the ecological
health of bays and estuaries. A common problem in many of these areas is
increased nutrient loads as a result of agricultural, commercial,
industrial, and urban processes. Biscayne Bay is a shallow subtropical
estuary along the southern coast of Florida. The Biscayne Bay ecosystem
provides an aquatic environment that is a habitat to a diverse array of plant
and animal communities. Nutrients are essential compounds for the growth
and maintenance of all organisms and especially for the productivity of aquatic
environments. Nitrogen and phosphorus compounds are especially important
to seagrass, macroalgae, and phytoplankton. However, heavy nutrient loads to
bays and estuaries can result in conditions conducive to eutrophication and the
attendant problems of algal blooms and high phytoplankton productivity.
Additionally, reduced light penetration in the water column because of
phytoplankton blooms can adversely affect seagrasses, which many commercial
and sport fish rely on for their habitat. Providing reliable estimates of
nonpoint source nutrient loads to Biscayne Bay is important to the develop-
ment of nutrient budgets as well as input to eutrophication models. Under-
standing the effects of these nutrient loads is a necessary initial step
in planning restoration of the ecological health of Biscayne Bay.
Nutrient data have been collected from the east coast canals for many years
by various government agencies. Much of the data collected have been from grab
samples at 0.5 or 1.0 meter below the stream surface near the centroid of flow.
The degree to which these samples adequately represent nitrogen and phosphorus
concentrations within the water column of the canals of south Florida is presently
unknown and limits confidence in loading estimates. Furthermore, the relation
between discharge and nutrient concentration that occurs in natural uncontrolled
streams in other parts of the Nation may not apply to the artificially controlled
canals of south Florida. Both of these issues need to be addressed to develop
nutrient budgets and to plan effective restoration strategy now and in the
future.
Nutrient data were collected upstream of 15 coastal control structures in Dade
County. Samples were collected over a typical hydrologic period during various
flow conditions. Sampling began at 5 sites in May 1996 and at 10 sites in October
1996. Constituents collected included ammonia, nitrite, nitrate, orthophosphate,
and total phosphorus.