Water Clarity Report Card

Good water clarity is essential for healthy seagrasses within the Charlotte Harbor National Estuary Program (CHNEP) estuaries. Seagrasses are the most abundant and productive submerged habitat in the coastal CHNEP waters. They provide shelter, food, and nursery habitat for a great diversity of invertebrates, shellfish, fishes and marine mammals including shrimp, scallops, bait fish, sport fish, and manatees. Seagrasses provide a good indicator of overall estuarine health within CHNEP.

There are over 62,000 acres of seagrass habitat from Lemon Bay south to Estero Bay. Seagrass distribution varies by season and year, depending on rainfall, salinity, temperature, and water clarity. Seagrasses within the CHNEP are adapted to natural seasonal variability in these conditions, but are stressed by human-modified runoff that causes higher flows, turbidity and nutrients, as well as changed salinities. Seagrass location, acreage, and species diversity depend on water clarity which allows light availability for photosynthesis. Water clarity within the CHNEP is related primarily to the amount of color (tannins), algae (chlorophyll) and sediment (turbidity) in the water.

Optical Model & Water Clarity Reporting Tool

CHNEP Strata with Seagrass Restoration and Protection Targets

Within the CHNEP, seagrass protection and restoration targets have been established for each of the estuaries based on historical distribution of seagrasses as well as the deepest depth the seagrasses grow. For resource management and monitoring purposes, the CHNEP estuaries have been divided into 14 estuary "segments" that each have relatively homogeneous conditions in habitats and water quality. The seagrass protection and restoration targets for each of the 14 CHNEP estuary segments can be found below the table below.

Year CHNEP Strata with Seagrass RESTORATION Targets Strata with Seagrass PROTECTION Targets
Dona and Roberts Bay Lower Lemon Bay Tidal Peace River West Wall East Wall Matlacha Pass Tidal Caloosahatchee Estero Bay Upper Lemon Bay Tidal Myakka River Bokeelia Cape Haze Pine Island Sound San Carlos Bay
1998 -2
1999 -2
2000 -1
2001 -2 -2 -2 -2 0 -2 -2
2002 -1 -1 -1 -2 -2 0 0 -2 -2 2
2003 -2 -1 -2 -2 -2 -2 -1 -2 -2 -2 1
2004 0 0 0 0 1 1 0 -1 0 0 0 0 0 2
2005 0 0 -1 -2 -2 -2 -2 0 0 -1 -1 0 -1 -1
2006 0 0 0 0 0 0 2 1 1 1 0 0 -1 -2
2007 2 1 2 2 2 2 2 2 1 2 2 1 2 2
2008 1 -1 0 1 1 0 1 -1 0 0 2 -1 2 0
2009 0 -2 -1 -1 -1 0 0 0 1 0 1 -1 0 -1
2010 -2 -2 0 -1 0 -2 1 -1 -1 0 0 -1 0 -1
2011 -1 -1 0 -1 0 -2 1 -1 -1 -1 1 -2 0 -1
2012 0 -1 0 -2 -2 -2 2 2 -1 -1 -2 -2 2 -2
2013 -1 0 -1 -2 -2 -2 2 2 0 -1 -1 -1 2 -1
2014 0 0 0 -2 -1 1 2 2 1 -2 1 -1 2 1
2015 -2 0 -1 -2 -2 0 2 -1 -2 -2 -1 -1 2 2

Grading System for RESTORATION targets

Green = score greater than 1

Yellow = score between -1 and 1

Red = score less than -1

Improving 2
Caution 1
Caution 0
Caution -1
Declining -2

Grading System for PROTECTION targets

Green = score greater than -1

Yellow = score less than -1

Red = score less than -1 for consecutive years

Stable 2
Stable 1
Stable 0
Caution -1
Caution -2
Declining -2

Seagrass Targets

  • Dona and Roberts Bays: 112 acres to be protected and restored
  • Upper Lemon Bay: 1,009 acres to be protected
  • Lower Lemon Bay: 2,882 acres to be protected and restored
  • Tidal Myakka River: 456 acres to be protected
  • Tidal Peace River: 975 acres to be protected and restored
  • Charlotte Harbor West Wall: 2,106 acres to be protected and restored
  • Charlotte Harbor East Wall: 3,898 acres to be protected and restored
  • Charlotte Harbor Lower: 3,342 acres to be protected
  • Cape Haze: 6,998 acres to be protected
  • Pine Island Sound: 26,837 acres to be protected
  • Matlacha Pass: 9,315 acres to be protected and restored
  • San Carlos Bay: 4,372 acres to be protected
  • Tidal Caloosahatchee River*: >93 acres to be protected and restored *(to be adjusted when more detailed information becomes available)
  • Estero Bay: 3,662 acres to be protected and restored

These seagrass targets were used to develop water clarity targets for each of the CHNEP estuaries. And because water clarity in CHNEP has been shown to be primarily related to water color, chlorophyll and turbidity, it has been possible to establish water quality criteria needed to support the water clarity and seagrass targets.

Consequently, water clarity serves an important link between the biological seagrass communities and the chemical water quality conditions. Accurately measuring water clarity and calculating conditions in the past, present and future are essential to effective resource management. However, measuring water clarity in the field can be complicated by wave and cloud conditions and sensitive monitoring equipment. Water color, chlorophyll and turbidity are more reliably, precisely, and accurately measured in the field. In addition, historical records of these parameters pre-date our ability to measure water clarity. Therefore, developing the mathematical relationships between water clarity and color, chlorophyll, and turbidity for each of the CHNEP estuaries allows us to more descriptively calculate, rather than measure, water clarity conditions. Developing these mathematical relationships into an Optical Model also helps resource managers assess trends in water clarity from past conditions and under future resource management scenarios.

CHNEP contracted with Mote Marine Laboratory in 2012 to develop an Optical Model to estimate water clarity from available color, chlorophyll, and turbidity data for the CHNEP estuaries. The Optical Model was based on research in southwest Florida, the measured amount of light available at the deep edge of the seagrasses and the historical record of water quality data through 2011. The project also included development of a Water Clarity Reporting Tool by Janicki Environmental, Inc. to present trends in water clarity compared to seagrass targets in an easily understood, graphic form. The details of the Optical Model and Water Clarity Reporting Tool development and results are available in the project final report The Optical Model Spectral Validation and Annual Water Clarity Reporting Tool: Final Report (L.K. Dixon and M.R. Wessel, 2014).