SAV in the Caloosahatchee Estuary;
Effects of Altered Freshwater Flow
James G. Douglass
FGCU Seagrass Scientist
Estuary
• A semi-enclosed body of water where
freshwater mixes with seawater
Salinity
SAV = Submersed Aquatic Vegetation
• True Plants that live entirely underwater
• Saltwater SAV is called seagrass
SAV has real
roots and
leaves, unlike
seaweed
• SAV
– Affected by
many aspects of
the environment
– Indicator of
Environmental
Health
Temperature
Light
Phytoplankton
Tannins
(CDOM)
Dirt & Silt
Salinity
Epiphytic Algae
Water Movement
• SAV
– Different species
need different
levels of salinity
to survive.
Salinity
Common Caloosahatchee SAV
• Turtlegrass:
– Thalassia testudinium
– Prefers full salinity of ocean
– Tolerates ~2/3 ocean salinity
• Shoalgrass:
– Halodule wrightii
– Prefers full salinity of ocean
– Tolerates ~1/2 ocean salinity
• Tapegrass:
– Vallisneria americana
– Prefers freshwater
– Tolerates ~1/4 ocean salinity
2 Types of Environmental Variation
1. Spatial variation
– Environmental conditions
vary from place to place
– Increases species diversity
2. Temporal variation
Conditions
– Environmental conditions
fluctuate over time
– Increases stress
High
Low
Past
Time
Present
Spatial Variation in an Estuary
• Salinity blends from fresh to salty along the estuary
AVERAGE Freshwater
Salinity
Species
35
Marine
Species
Live Here
Live Here
0
River
Mid Estuary
Location in Estuary
Ocean
Temporal Variation in an Estuary
• Salinity naturally fluctuates due to tides, rainfall, seasons, etc.
35
RANGE of
Salinity
Middle part of
estuary usually
varies the most
River
Mid Estuary
Location in Estuary
Ocean
0
Caloosahatchee River Estuary
Mostly Fresh
Mixed and
Variable
Mostly Salty
S-79 Dam Controls Flow to Estuary
SFWMD Scientists have determined that:
• Upper estuary gets too salty when flow is < 450 cfs
• Lower estuary gets too fresh when flow is > 2800 cfs
• Also, pollution problems during high flow
• Damming and Dumping fresh water
increase variability in estuary
35
Increased
variability due
to human
interference
RANGE of
Salinity
Increased
stress for SAV
River
Mid Estuary
Location in Estuary
Ocean
0
South FL Water Management District and the
Comprehensive Everglades Restoration Plan
CERP Projects should
decrease the temporal
variability of salinity in the
Caloosahatchee Estuary by
allowing a more steady
amount of freshwater to be
released through the S-79
lock and dam
SAV Monitoring Objectives for the
Caloosahatchee River Estuary
• Determine SAV trends and variability
from 1998 to the present
• Relate SAV status and trends to
environmental conditions
• Track SAV recovery as CERP is
implemented
Methods
• 7 sites along estuary
• Bimonthly monitoring
– 1m2 quadrats (30)
– SAV coverage, canopy
height, etc.
• Historical data from
SFWMD, back to 1998
• Including salinity data
1
2
m
Results: 1998 – 2013 Freshwater Flow
• Often, too much or too little water was released
Results: 1999 – 2013 Salinity
• Temporal variability of salinity was extreme
Analysis: Linking Salinity to S-79 Flow
• Strong Links:
– Less Flow = More Salinity
– More Flow = Less Salinity
Linking SAV to Salinity; Upper Estuary
• Vallisneria
died off
whenever
salinity got >
10 psu
• Recovery
takes years
• Down for
the count?
Linking SAV to Salinity; Middle Estuary
• Halodule
wrightii very
scarce during
low salinity
• Recovery
during higher
salinity, but
still struggling
Conclusions
• Diversity of SAV species with different salinity
tolerances should allow SAV along entire Estuary
• But temporal variability of salinity is too high
• Adhering to flow envelope (450-2800 cfs) would help
Issues for Future Research
• Interactive effects of freshwater releases, nutrients, and
grazing organisms could exacerbate salinity stresses
Invasive
freshwater
snail eats SAV,
but hates
salinity
Water releases contain nutrients
that stimulate phytoplankton in
water and epiphytes on SAV
Native
grazers
clean SAV
and love
salinity
Acknowledgements
• Elizabeth Orlando, Peter Doering and other
SFWMD Staff
• Dr. Aswani Volety, FGCU
• Lesli Haynes, Christal Niemeyer, Tim Bryant
• Sylvie Mariolan, Heather Butler, Whitney
McDowell, Spencer Talmage, Romina Robles,
Amber Chaboudy, and many other FGCU
undergraduate students