Protecting Water Clarity in Sarasota County Bays An Implementation Strategy

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Protecting Water Clarity in Sarasota County
BaysAn Implementation Strategy
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Why Clarity?

• Community support
• Economic value
• Relates to manageable qualities
• Pollutant load
• Tributary flows
• Total Maximum Daily Loads
• Tampa Bay nitrogen management

- good partners
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Scope of Work

• Propose clarity benchmarks
• Define geographic units from data
• Restoration or no degradation
• Use objective, uniformly applied,
  scientifically defensible methods
• Community values
• Realistic and manageable
• Reporting Tool

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Spatial Unit is Water Body ID

• Reviewed spatial variation in water quality
  parameters
• Chose from various existing segmentation schemes
• WBIDs reflect variation in hydrologic inputs
• TMDL Program uses WBIDs
• Consistent with watershed planning logistical
  considerations

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Valued Community Resource
Color
Turbidity
Chlorophyll

• Seagrass used for setting water quality targets
• Tampa Bay
• Charlotte Harbor
• Indian River Lagoon

Seagrass Light Needs
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SWFWMD Aerial Seagrass Maps

• Combined all years
• Overlaid Grid
• Assigned water depth to cells
• Assigned seagrass presence or absence to cells

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Depth Distribution of Seagrass

• 90 depth criterion - like Tampa Bay
• May also depict escalating cost to implement
• Lemon Bay 90 1.42 m 4.6 ft

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Light Needed by Seagrass

• 25 light criterion
• Percent of subsurface light
• Tampa Bay (20-23)
• Sarasota Bay (20-42)
• Charlotte Harbor (15-30)
• Indian River Lagoon (24-37)

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Reference Period Light Data

• Oldest, most robust reliable data set was 1998
  to 2005
• Good distribution of variation in weather

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Calculate Light from Depth

• The amount of photosynthetically active radiation
  (PAR) penetrating the water surface is attenuated
  as a function of water depth water clarity
• Light attenuation coefficient (Kd) describes this
  exponential light loss at depth
• Lemon Bay Depth of 1.42 meters solves for a Kd of
  0.98

Kd Ln(Irradiance at surface/Irradiance at
depth) (-1) water
depth
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Compare to Data
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Evaluation of Yearly Data

• Binomial test measures the number of low clarity
  samples against the expected based on the
  reference period
• Example
• 58 Kd measurements in Lemon Bay in 2006
• 32 exceeded 0.98
• 53 exceeded during the reference period

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Score
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Sensitivity
El Nino
Hurricanes
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Evaluate Annual Data

• Evaluate 2006 Lemon Bay light attentuation data
  against reference period

• Green Report Card Not significantly different
  than expected

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Deliverables

• Protects against degradation
• Spatially specific
• Uniformly applied technique
• Realistic
• Understandable reporting tool
• Weighted on strongest facts available
• Seagrass maps water quality data
• Applies to management actions

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Watershed Planning

• Support management decisions with science
• Report Cards
• Bay Clarity
• Pollutant Load
• Seagrass
• Oysters

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The Good Life
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What its Not

• Restoration target
• Optical model
• Answer to the duration and intensity of seagrass
  light limitation questions

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Action Plan

• Implement Restoration
• Wastewater and septic systems
• Regulations or Development Standards
• County Operations
• Community Best Management Practices
• Capital Improvements