Caution

2 out of 3 indicators were rated as PASS.

All three indicators must pass for the bay to be rated as PASS.

Learn more about how this report is created

Summary:

While the overall health of Little Sarasota Bay is good, the concentration of chlorophyll a in the bay increased markedly during the latter half of 2015. Despite this increase, dissolved oxygen concentration improved somewhat. Light attenuation increased slightly, undoubtedly due in part to the higher chlorophyll a levels.

Water Quality: The ratings for nitrogen and phosphorus remained virtually unchanged from their 2014 values, coming in at “Good” and “Excellent, respectively. Reversing an improving trend from the previous year, chlorophyll a concentration increased by 50.7% compared to 2014, pushing its mean value to 0.0104 mg/l, equal to the threshold and demoting its rating from “Excellent” to “Caution.” The mean nitrogen concentration improved slightly, to 0.5363 mg/l. Phosphorus concentration also decreased, to (0.086 mg/l), remaining well below the target of 0.180 mg/l. The mean for chlorophyll a was calculated as an arithmetic mean and the means for nitrogen and phosphorus were calculated as geometric means (per the Numeric Nutrient Criteria outlined in the Florida Administrative Code, section 62-302.532).

Biotic Indicator: Measurement of the biotic indicator, seagrass, was performed in 2014 by the Southwest Florida Water Management District. In recent years, total seagrass acreage in Little Sarasota Bay has held steady and, at 999 acres, is well above the target level of 702 acres.

Little Sarasota Bay

Little Sarasota Bay

Water Chemistry Ratings

Total nitrogen, total phosphorus, and chlorophyll a levels are monitored carefully by water resource managers and used by regulatory authorities to determine whether a bay meets the water quality standards mandated by the Clean Water Act. The trend graphs for these indicators are shown below, along with their target and threshold values. A target value is a desirable goal to be attained, while a threshold is an undesirable level which is to be avoided. An individual indicator receives an "Excellent" rating if its mean value is below the target, a "Good" rating if its mean value is above the target but does not exceed the threshold, and a "Caution" rating if the mean value exceeds the threshold. Learn More about these ratings and how they are calculated »

The Five-year Rolling Average Graphs below illustrate the general trend of water quality parameters. They show a six-month running average, which moderates high and low values in the data.

Chart Legend
  • Trend Line
  • Annual Mean
  • Target
  • Threshold
Caution

Chlorophyll a

Score: Caution How was this determined?
Units: mg/l Year
2015
Historical
period of record
High 0.030 0.063
Mean 0.010 0.008 0.00712149 0.0082000000
Low 0.002 0.000
No. of Samples 75 1395

Five-year Rolling Average

  • Annual Mean
Good

Nitrogen, Total

Units: mg/l Year
2015
Historical
period of record
High 0.845 1.175
Mean 0.536 0.17065049 0.5200000000
Low 0.315 0.055
No. of Samples 75 1359

Five-year Rolling Average

  • Annual Mean
Excellent

Phosphorus, Total

Score: Excellent How was this determined?
Units: mg/l Year
2015
Historical
period of record
High 0.200 0.699
Mean 0.086 0.133 0.07693855 0.1800000000
Low 0.050 0.050
No. of Samples 75 1398

Five-year Rolling Average

  • Annual Mean

Dissolved Oxygen

Units: mg/l Year
2015
Historical
period of record
High 9.00 11.60
Mean 6.86 6.57 1.17293
Low 3.90 2.80
No. of Samples 72 1505

Five-year Rolling Average

  • Annual Mean

Apparent Color

Units: PCU Year
2015
Historical
period of record
High 80.00 140.00
Mean 23.73 24.87 18.76129
Low 5.00 4.00
No. of Samples 75 1398

Five-year Rolling Average

  • Annual Mean

BOD, Biochemical oxygen demand

Units: mg/l Year
2015
Historical
period of record
High 3.50 6.50
Mean 1.79 1.70 0.92238
Low 0.70 0.50
No. of Samples 74 1251

Five-year Rolling Average

  • Annual Mean

Dissolved oxygen saturation

Units: percent (%) Year
2015
Historical
period of record
High 145.00 167.00
Mean 100.46 94.95 14.84764
Low 62.00 45.00
No. of Samples 72 1506

Five-year Rolling Average

  • Annual Mean

Karenia brevis ("red tide")

Units: #/l Year
2015
Historical
period of record
High 1656000.00 2603000.00
Mean 124280.70 25660.22 165122.24573
Low 1000.00 1000.00
No. of Samples 57 724

Five-year Rolling Average

  • Annual Mean

Light Attenuation

Units: K(1/m) Year
2015
Historical
period of record
High 2.01 2.98
Mean 0.96 1.00 0.43716
Low 0.29 0.08
No. of Samples 72 1269

Five-year Rolling Average

  • Annual Mean

Nitrogen, Ammonia + Ammonium as N

Units: ug/l Year
2015
Historical
period of record
High 67.00 203.00
Mean 12.53 16.38 18.77101
Low 5.00 5.00
No. of Samples 75 1370

Five-year Rolling Average

  • Annual Mean

Nitrogen, Kjeldahl

Units: ug/l Year
2015
Historical
period of record
High 840.00 1240.00
Mean 546.27 502.75 178.40018
Low 310.00 0.05
No. of Samples 75 1398

Five-year Rolling Average

  • Annual Mean

Nitrogen, Nitrite + Nitrate as N

Units: ug/l Year
2015
Historical
period of record
High 10.00 536.00
Mean 5.15 9.14 31.16027
Low 5.00 5.00
No. of Samples 75 1955

Five-year Rolling Average

  • Annual Mean

pH

Units: None Year
2015
Historical
period of record
High 8.20 8.50
Mean 7.99 7.96 0.17732
Low 7.80 6.20
No. of Samples 72 1506

Five-year Rolling Average

  • Annual Mean

Salinity

Units: PSS Year
2015
Historical
period of record
High 35.20 39.50
Mean 29.70 30.71 4.80738
Low 19.90 7.30
No. of Samples 72 1505

Five-year Rolling Average

  • Annual Mean

Specific conductance

Units: umho Year
2015
Historical
period of record
High 53230.00 59030.00
Mean 45667.64 47087.26 6703.94615
Low 31940.00 12670.00
No. of Samples 72 1506

Five-year Rolling Average

  • Annual Mean

Temperature, water

Units: deg F Year
2015
Historical
period of record
High 88.70 92.12
Mean 79.20 77.07 8.94269
Low 61.52 47.48
No. of Samples 72 1505

Five-year Rolling Average

  • Annual Mean

Turbidity

Units: NTU Year
2015
Historical
period of record
High 18.00 18.00
Mean 3.85 3.96 2.03652
Low 1.30 0.60
No. of Samples 75 1395

Five-year Rolling Average

  • Annual Mean

Other Measures of Bay Health

In addition to nutrient levels and chlorophyll concentration, dissolved oxygen levels, and water clarity are also objective indicators of bay health. These have complex interactive cycles which are affected by rainfall, temperature, and tidal action, as well as other factors. High nutrient levels (nitrogen and phosphorus) can stimulate excessive growth of marine algae (indicated by chlorophyll a level), resulting in reduced water clarity (and increased light attenuation) and depleted oxygen levels. Both plants and animals in a bay need oxygen to survive, and the seagrasses which provide food and cover for bay creatures need light for photosynthesis.

Bay Contour Maps (2015)

Contour mapping is one of the best ways to visualize spatial differences in coastal water quality. The interactive map shown below presents monthly data for one selected water quality indicator atop an aerial view of the bay. Choose a different water quality parameter from the list at the top to change the map. Learn More about Water Quality Contour Mapping »

Showing 2015 Monthly Contour Maps for: January
Loading interactive contour map viewer...
Contour Visibility:

Visit the Water Quality Contour Mapping Tool to view and compare monthly water quality contour maps for ten different water quality indicators. In addition, you can generate your own custom maps.

Contour Legend:

  • Less than 1 mg/l
  • 1.0 - 5.9 mg/l
  • 6.0 - 10.9 mg/l
  • 11.0 - 17.9 mg/l
  • Greater than 18 mg/l

Seagrasses

Among the most important habitats in Florida's estuarine environments, seagrass beds are indispensable for the role they play in cycling nutrients, supplying food for wildlife, stabilizing sediments, and providing habitat for juvenile and adult finfish and shellfish. Use the interactive map below to observe the size, density and location of seagrass beds from year to year. The graph shows how the total amount of seagrass in the bay has changed over time. Seagrass calculations are aggregates of patchy and continuous seagrass measurements only. Recordings of attached algae are not included in these summaries.
Learn More about Seagrasses »

Showing Seagrass Coverage for :
Loading interactive seagrass coverage viewer...
Loading interactive chart...
  • Target 702 acres

Visit our Seagrass page to discover the beauty and importance of seagrass habitats, and sign up to help monitor their health.

Impervious Features

Little Sarasota Bay is located within the Little Sarasota Bay Watershed. View details about the Little Sarasota Bay Watershed »

Rain that falls on land that is in a natural state is absorbed and filtered by soils and vegetation as it makes it way into underground aquifers. However, in developed areas, "impervious surfaces" impede this process and contribute to polluted urban runoff entering surface waters. These surfaces include human infrastructure like roads, sidewalks, driveways and parking lots that are covered by impenetrable materials such as asphalt, concrete, brick and stone, as well as buildings and other permanent structures. Soils that have been disturbed and compacted by urban development are often impervious as well. Learn more about Impervious Features »

The Sarasota County Stormwater Environmental Utility (SEU) mapped impervious surfaces in the County in 2014. A map showing impervious surfaces can be viewed using the interactive Sarasota NPDES Viewer.

14% of the land area within the Little Sarasota Bay Watershed is covered by impervious surfaces

Impervious Surface Coverage by Type

Land Use / Land Cover

Land use within a bay's watershed has a major effect on its water quality. In general, less development means better water quality. Land Cover/Land Use classifications categorize land in terms of its observed physical surface characteristics (upland or wetland, e.g.), and also reflect the types of activity that are taking place on it (agriculture, urban/built-up, utilities, etc.). Florida uses as its standard a set of statewide classifications which were developed by the Florida Department of Transportation. Learn More about Land Use and Land Cover »

Little Sarasota Bay is located within the Little Sarasota Bay Watershed. The chart below shows the land use / land cover characteristics for Little Sarasota Bay Watershed within the boundary of this Water Atlas. View details about the Little Sarasota Bay Watershed »

Acreage and Percentage within each Land Use / Land Cover Category for Little Sarasota Bay Watershed
Land Use Classification 1990 1995 1999 2005 2011 2014 Trend
Urban & Built-up 8,94331.9% 10,07135.9% 10,95539% 11,83442.2% 12,10243.1% 12,16243.3%
Agriculture 3,55012.6% 3,71513.2% 3,44712.3% 3,22811.5% 3,25811.6% 4,22315%
Rangeland 8252.9% 1,5755.6% 1,8606.6% 1,8226.5% 1,4745.3% 5792.1%
Upland Forests 7,09825.3% 4,94417.6% 3,81013.6% 3,06610.9% 2,98110.6% 2,7259.7%
Water 3,42912.2% 3,75513.4% 3,78513.5% 4,12314.7% 4,14714.8% 4,17514.9%
Wetlands 3,49012.4% 3,25711.6% 3,42112.2% 3,13311.2% 3,19111.4% 3,22711.5%
Barren Land 620.2% 130% 190.1% 180.1% 190.1% 200.1%
Transportation and Utilities 6752.4% 7342.6% 7692.7% 8413% 8923.2% 9523.4%
Land Use Chart

Data Sources

The data sources listed below provided water quality data used to create the report on this page. Not all data sources provided data for every bay, and not every Bay Conditions Report used data from all listed data sources. While some data sources have no data for the scored year, they provided period-of-record (historical high, mean, low) data. Click on a data source name to review its metadata.