5.0 m-M; SRP = 0.50 ^M) compared to winter (DIN = 2.5 jiM; SRP = 0.15 pM). Direct 
measurement of subsurface ground water flow rate indicated that tides and increased 
ground water recharge enhanced flow some two-fold and six-fold, respectively. 
Accordingly, the observed seasonal coupling of OSDS-derived nutrients from ground 
waters to surface waters is maximum during summer because of seasonally maximum 
tides and increased hydraulic head during the summer wet season. The yearly average 
benthic flux of anthropogenic DIN into contiguous canal surface waters is 55 mmol rrr 2 
day 1 , a value some five-fold greater than the highest rate of benthic N-fixation 
measured in carbonate-rich tropical marine waters. 
1986 - 1987 
Montague, C. L., R. D. Bartleson, and J. A. Ley (1989) Assessment of benthic communities 
along salinity gradients in northeastern Florida Bay. Final Rep. to the National Park Service. 
Contr. CA 5280-5-8004. University of Florida and South Florida Water Management 
District from South Florida Research Center, Everglades National Park, Homestead, FL. 155 
pp. + App. 
Submerged vegetation and bottom-dwelling animals (benthic communities) were 
quantified together with aquatic system metabolism and a variety of environmental 
parameters at twelve stations along three salinity gradients in northeast Florida Bay, 
south of C-111 canal. Scheduled modifications to the canal will likely change the 
freshwater delivery to this region. Concern has been expressed about the potential 
impact this may have on a variety of fish and wildlife, especially commercially and 
recreationally valuable fishes that may use the region as habitat. Benthic communities 
are known to provide food and cover to a wide variety of juvenile and adult estuarine 
and marine fishes and shellfishes. The purpose of this assessment was to document the 
type and development of existing benthic communities and to provide information about 
how changes in salinity might affect changes in the benthic communities in this area. It 
was believed that repeatedly sampling at stations located along salinity gradients would 
meet these objectives. Following a pilot study of five field trips to 21 stations (March 
through August 1986), 12 stations were selected for final study, four in each of three 
tributary-to-bay systems in northeast Florida Bay. Within each system, stations were 
selected to be as similar as possible in all respects except salinity. The salinity change 
from upstream to outer stations was similar among the three systems. The western 
system (Taylor River, Little Madeira Bay) is considered to be little influenced by the 
C-111 canal and therefore serves as a potential control for judging future effects of 
canal modifications. The central system (Snook Creek, Joe Bay, Trout Cove) and 
eastern system (Highway Creek, Long Sound, Little Blackwater Sound) are believed to 
be directly in the pathway of any influence of canal modifications. In the main study, 
stations were sampled using identical techniques every other month for 12 months 
beginning in August 1986 (through September 1987). Benthic community development 
and metabolism were very low in general. Overall gross primary production was only 
188 g C m' 2 yr 1 . Gross primary production at outer stations, however, was three 
times higher than at upstream stations. The planktonic portion of this production was 
very low at all stations, but was twice as high at upstream stations, where it 
accounted for 44% of the gross production (as opposed to only 72 at outer stations). 
Benthic communities at outer stations, although low in production and biomass 
compared to other Florida Bay seagrass-dominated communities, had roughly 50 times 
more numbers of animals and biomass of plants than upstream stations. Plants at outer 
stations were dominated by turtlegrass ( Thalassia testudinum) and calcareous green 
macroalgae (primarily Penicillus and Udotea). The few plants at the upstream stations 
consisted mostly of shoalgrass ( Halodule wrightii), widgeongrass (Ruppia maritima), 
and the green macroalgae Chara. Roughly 95% of all animals collected at each station 
were polychaetes, peracaridean crustaceans (amphipods, isopods, and tanaids), and 
bivalve mollusks. Variation in salinity that includes frequent changes from freshwater 
305 
