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