sav in the caloosahatchee estuary; effects of altered freshwater flow james g. douglass fgcu...
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SAV in the Caloosahatchee Estuary;Effects of Altered Freshwater Flow
James G. DouglassFGCU 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
Salinity
Light
Dirt & Silt
Tannins (CDOM)
Water Movement
Nutrients
Epiphytic Algae
Animal
Interactions
Phytoplankton
Nutrients
Salinity
• SAV – Different species
need different levels of salinity to survive.
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 – Environmental conditions
fluctuate over time– Increases stress
Time
Cond
ition
s
Past PresentLow
High
Marine Species
Live Here
Freshwater Species
Live Here
Spatial Variation in an Estuary
Location in Estuary
AVERAGE Salinity
0
35
River OceanMid Estuary
• Salinity blends from fresh to salty along the estuary
Temporal Variation in an Estuary
Location in Estuary
RANGE of Salinity
River OceanMid Estuary0
• Salinity naturally fluctuates due to tides, rainfall, seasons, etc.35
Middle part of estuary usually varies the most
Caloosahatchee River Estuary
Mostly Salty
Mixed and Variable
Mostly Fresh
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
Location in Estuary
RANGE of Salinity
River OceanMid Estuary0
• Damming and Dumping fresh water increase variability in estuary
35
Increased variability due
to human interference
Increased stress for SAV
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 m2
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
Native grazers clean SAV and love salinity
Water releases contain nutrients that stimulate phytoplankton in water and epiphytes on SAV
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