Priority research topics concerning water balance include the following:
Accurate quantification of surface runoff into Florida Bay clearly is a high priority. Ongoing studies (Hittle et al., 2001) have been measuring freshwater discharge into northeastern Florida Bay at five creeks in the Taylor Slough and C-111 canal basins since late 1994. Continued long-term monitoring of spatial and temporal variations in surface runoff will reduce the uncertainty of the effect of the CERP on the Florida Bay water budget, and this activity is recommended. Although sheetflow over the Buttonwood Embankment (Figure 2) between the channels that breach it was not believed to be important by Hittle et al. (2001) or Davis et al., (2002), this should be confirmed by installing instrumented sites along the embankment. Likewise, significant additional freshwater may enter the Bay by diffuse seepage through the embankment, and this process also merits evaluation. Continued research on the hydrodynamic characteristics and net outflow of water from the Shark River Slough basin (e.g., Levesque and Patino, 2001) may be useful, given that some of this water appears to reach the central Bay (Lee et al., 2002).
Aside from the shallow seepage referred to above, groundwater inputs may be important to the system in other areas. Although nearly all of this influx must be saline (Fitterman and Deszcz-Pan, 2001; Corbett et al., 1999, 2000), saline discharge that has circulated through the phosphorite-rich quartz sand deposits described in Cunningham et al. (1998) may be a significant source of phosphorus in the northwestern Bay (Brand, 2002). Furthermore, a better understanding of how the proposed hydrologic changes in the CERP may affect the position of the freshwater-saltwater contact in the subsurface should be developed. This kind of understanding may be achieved through modeling of the wetland/coastal transition zone, as described later in this chapter.
The South Florida Water Management Model (SFWMM) predicts about the same annual runoff toward Florida Bay via Craighead Basin and Taylor Slough in the year 2050 as occurs presently (Figure 3). In contrast, flows down Shark River Slough would increase from 702,000 to 1,255,000 acre-ft per year (8.66x108 to 1.55x109 cubic meters per year) (Figure 4). Hence, on average, the full CERP implementation has a minimal effect on the volume of direct fresh surface water flow into the Bay but a potentially significant effect on the discharge out of Shark River Slough and Whitewater Bay, which eventually reaches the Bay. Additional definition of these flow pathways is urgently needed for modeling of impacts in the Bay. Variability must be accounted for through analysis of the full 31-year simulation period.
After mixing with seawater, water from Shark River Slough tends to reach Florida Bay in about two to six weeks (Lee et al., 2002) and may still influence the Bay’s nutrient budget. The effects on the Bay of a Shark River Slough increase and a stable Taylor Slough/Craighead Basin freshwater flow have not been investigated, however. It is important to remember that the flows shown in Figures 3 and 4 are modeled flows, and may not accurately represent actual flows under current conditions or those after implementation of the CERP. Furthermore, the hydrologic models are subject to change (e.g., eventual conversion from the SFWMM to the South Florida Regional Simulation Model) as well as changing simulation conditions (e.g., use of a 36-year meteorological record vs. a 31-year record). Nonetheless, the implications of this potentially large shift in the magnitude of freshwater discharges down Shark River Slough as a result of the CERP need to be investigated.
Although surface and groundwater inputs are of most direct use in understanding the effects of the CERP on the Bay, an improved water budget for the Bay as a whole, including natural variability, will help put these inputs into a larger context. Nuttle et al. (2000) estimated a water budget using evaporation rates from a rough salt balance calculated for four regions of Florida Bay, with pan evaporation rates used to distribute annual evaporation seasonally. Price et al. (2001) have been using four approaches (energy flux, vapor flux, stable isotopes, and a box model of salinity) to estimate mean rates of evaporation and its spatial and temporal variation. Both the energy and vapor flux methods depend upon measurement of net radiation, water and air temperature, relative humidity, rainfall, and wind speed and direction. Price et al.’s (2001) study is only a two-year project; continuation of such work (and expansion of the monitoring