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patrickbdevaney
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mia9

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Because of this, nutrient loads for Total Phosphorous (TP), ammonium (NHx-N),
nitrate-nitrite (NOx-N), and Dissolved Inorganic Nitrogen (DIN) were independently
developed for all components of the water budget (step 2) based on various existing
sources of information, including canals, overland flow (ungauged surface water),
groundwater, and atmospheric contributions. With the exception of freshwater inflows
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and nutrient loads from canals, few direct data exist for estimating these nutrient loads.
Indirect data and regression models were used to fill the data gaps. Nutrient loads
across the boundaries of the model including the Atlantic Ocean were also estimated
from existing data.
Figure 4.1: Components of box-model used for mass-balance calculations
Calculations of nutrient concentrations in Biscayne Bay based on the estimated
loads extended an existing hydrology/salinity mass-balance model (step 3) that had
been developed previously for the South Florida Water Management District. This
model was used to investigate the linkage between freshwater inflows from the
watershed and salinity patterns in the Bay. The model domain and the
hydrology/salinity calculations were upgraded based on peer-review comments and the
model was extended to incorporate mass-balance nutrient calculations. The model was
then calibrated against measured salinity to estimate the water fluxes between each box
and validated against an independent set of salinity observations.
Evaporation
Rainfall
S, A
d
Net
discharge, QO
Evaporation Rainfall
Exchange
flux, QX
Canal Discharge
Runoff and Groundwater
SO Ocean salinity,
Net Freshwater Supply, QR
A
B
QX
QX
QX
QO
QO
QO
Net Freshwater Supply, QR
Schematic diagram showing
the components of the water
and salt mass balances for A)
a single estuarine basin in
connection with the coastal
ocean and B) additional
fluxes introduced by flow and
exchange among sub-basins
within an estuarine basin.
Conditions in any estuarine
basin or sub-basin are
characterized by its volume
(equal to the product of its
area A and average water
depth d) and average salinity
S. In case A, salinity in the
single basin is maintained
through water exchange with
the coastal ocean at salinity
SO. In case B, salinity in a subbasin is maintained by water
exchange with adjacent
basins and the ocean
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Overall the hydrology/salinity model captured well the patterns of spatial and
temporal variability in salinity in Biscayne Bay. Calibration and verification statistics
show that the box model accounts for greater that 70 percent of the variability in
measured salinity. Calculated values agree with measurements made within the same
week with an error of between 2 to 3 psu. Errors are comparable between the
calibration and verification time periods and are comparable to results achieved in the
previous box model study.
Fig 4.2: Spatial structure of the nutrient box-model.
When the model was used for nutrient mass balance calculations (step 4), the
results showed varied success at characterizing the link between nutrient loads and
concentrations in the Bay. Average values for TP concentrations assuming no loss or
SB1
SB2
2
4 6 5
7
8
SB1
SB1
SB1
S197
S26, S25, S25B
G93, S22,
S123
S21, S21A,
S20G, S20F
X18
X15
X0
X5
X17
Canal discharge
Net discharge
3
1