Bay Conditions Index
The Bay Conditions Index gives a quick assessment of the water quality in each bay during a particular year by examining three important indicators of nutrient pollution: chlorophyll a, nitrogen and phosphorus. The rating system used here was developed by a team of local water resource management professionals, incorporating the "numeric nutrient standards" proposed to the U.S. Environmental Protection Agency and based on research sponsored by the Sarasota Bay Estuary Program.
Each bay receives either a PASS or CAUTION rating, depending on whether sampling values for chlorophyll a, nitrogen, and phosphorus were below maximum thresholds established for that bay. A bay receives a PASS rating only if values for all three indicators are below their respective thresholds; otherwise, the bay receives a rating of CAUTION.
To view scores for an individual water quality parameter, choose it from the dropdown list above.
Chlorophyll a
Chlorophyll is one of the most important pigment groups. Chlorophylls give a characteristic green color to plants, algae and photosynthetic bacteria, which use the energy captured by chlorophylls (and other pigments) along with carbon dioxide and water to assemble the molecules needed for growth, cellular repair and disease prevention.
Chlorophyll a is the most common type of chlorophyll, and its concentration in bay water is used to estimate the relative abundance of phytoplankton. When water contains excess nutrients, it may cause an overgrowth of phytoplankton, reducing the clarity of the water and inhibiting the penetration of sunlight to the bay bottom, thereby adversely affecting seagrass growth. Seagrass beds provide essential habitat for macroinvertebrates, juvenile fish, manatees, and other creatures and are a hallmark of healthy coastal ecosystems.
The rating for each bay is shown at left, determined by comparing the annual mean chlorophyll level to target and threshold chlorophyll a levels defined for the individual bay:
- EXCELLENT if the annual mean value is below the target,
- GOOD if the mean value is above the target but does not exceed the threshold, and
- CAUTION if the mean value exceeds the threshold.
Total Nitrogen
Although it is an essential nutrient for plants and animals, an excess amount of nitrogen in a waterway can lead to low levels of dissolved oxygen and negatively affect various plant life and organisms. Sources of nitrogen include wastewater treatment plants, runoff from fertilized lawns and croplands, failing septic systems, runoff from animal manure and storage areas, and industrial discharges that contain corrosion inhibitors.
Nitrogen availability is most often the limiting factor in the growth of algae and other plants in estuarine and coastal systems. Higher concentrations of nitrogen are related to human population density and activity. Levels may spike temporarily after heavy rainfall due to atmospheric deposition of nitrogen and increased runoff from the watershed. Incidental releases of poorly-treated effluent or stormwater may also result in a temporary, locally restricted increase in nitrogen levels.
The rating for each bay is shown at left, determined by comparing the annual mean Total Nitrogen (TN) level to target and threshold TN levels defined for the individual bay:
- EXCELLENT if the annual mean value is below the target,
- GOOD if the mean value is above the target but does not exceed the threshold, and
- CAUTION if the mean value exceeds the threshold.
Total Phosphorous
Both nitrogen and phosphorus are necessary nutrients for plants and animals. Nitrogen is usually the most important limiting nutrient in estuaries, driving large increases of microscopic phytoplankton called "algal blooms" or increases of large aquatic bottom plants, but phosphorus can become limiting in coastal systems if nitrogen is abundant in a biologically available form. (A "limiting nutrient" is one whose lack of availability reduces the rate of growth or prevents the growth of phytoplankton or other primary producers.)
Sources of phosphorus include soil and rocks, wastewater treatment plants, runoff from fertilized lawns and cropland, runoff from animal manure storage areas, disturbed land areas, drained wetlands, water treatment, decomposition of organic matter, and commercial cleaning preparations.
The rating for each bay is shown at left, determined by comparing the annual mean Total Phosphorus (TP) level to target and threshold TP levels defined for the individual bay:
- EXCELLENT if the annual mean value is below the target,
- GOOD if the mean value is above the target but does not exceed the threshold, and
- CAUTION if the mean value exceeds the threshold.
