Potential Effects of the Diversion of Freshwater Flow from Taylor Slough to the
C-111 Canal on the Salinity, Hydrology, Prey-Base Fish Community and Roseate
Spoonbill Nesting Population of Northeastern Florida Bay.
Jerome J. Lorenz
National Audubon Society, Tavernier, FL
The preponderance of scientific evidence clearly indicates that the Northeastern
Basin of Florida Bay (defined as the basin south of Little Madeira Bay, Joe Bay
and Long Sound and east of the Black Betsy Keys) has become more saline. The
changes in freshwater flow to Florida Bay resulting from upstream water
management practices has been implicated in the increased salinity regime and in
many of the adverse ecological changes that occurred to the ecosystem in the
1980’s and 1990’s. Freshwater orignitating from either Taylor Slough or the C111 Canal enters the Northeastern Basin via a broad swath of mangrove wetlands
to the north. A currently accepted paradigm for restoring historically low salinity
regimes of the Northeastern Basin is to move more fresh water across these
wetlands, from both sources, and keep fresh water flowing from these wetlands
into Florida Bay well into the dry season. I present evidence that re-establishing
historic timing and distribution of freshwater flow may be as important, or more
important, to achieving the goal of lower salinity than an increase in overall flow
quantity.
Estimates of historic flow indicate that the vast majority of freshwater reached the
Northeastern Basin via Taylor Slough and predominantly entered the Bay through
creeks in Little Madeira Bay and western Joe Bay. Significant flow also arrived
at the Northeastern Basin via the Transverse Glades Sloughs; however, these
flows were relatively small compared to that of Taylor Slough. Today’s water
management practices have effectively reversed this situation, resulting in greatly
reduced quantities of water flowing through Taylor Slough (compared to historic
flows) and heavily augmented flows reaching the Long Sound area due to
operation of the C-111 canal. Evidence is presented that suggests this
redistribution of fresh water has resulted in increased and more variable salinity
within the Northeastern Basin and the adjacent coastal wetlands. These salinity
changes have been linked with lower secondary productivity in the prey-base fish
community of these wetlands.
Finally, the redistribution of flow from Taylor Slough to the C-111 Canal appears
to have resulted in higher and more variable water levels on the coastal wetlands
during the dry season. I will attempt to show that the increased dry season water
levels, coupled with the previously mentioned reduction in prey-base fishes, has
lowered the quality of these wetlands as foraging habitat for Roseate Spoonbills.
This reduction in foraging ground quality has manifested itself in lower nesting
success in spoonbills and may explain the observed decline in nesting effort
within the Northeastern Basin since the early 1980’s. As with the salinity regime,
a return to historic timing and distribution of freshwater flow would likely
alleviate this situation.
Lorenz, Jerome J. Tavernier Science Center, National Audubon Society, 115
Indian Mound Trail, Tavernier, FL, 33070. Phone 305-852-5092, Fax 305-8528012, jlorenz@audubon.org