Pass

3 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:

The overall health in Sarasota Bay has remained high.  Water quality metrics remained relatively constant with a slight decrease in mean value of chlorophyll a, nitrogen, and phosphorus. Acreage of seagrass has increased.

Water Quality: All three water quality indicators (chlorophyll a, nitrogen, and phosphorus) were rated as pass (below the threshold). The mean for chlorophyll a was calculated as an arithmetic mean and the means for nitrogen and phosphorus were calculated as geometric means (Numeric Nutrient Criteria Recommendations). Both nitrogen and phosphorus indicators remained in excellent condition (nitrogen mean = 0.3679 mg/l, phosphorus mean = 0.0526 mg/l) and were below the target levels of 0.490 mg/l and 0.150 mg/l, respectively. Chlorophyll a levels decreased and improved from a rating of good in 2010 to a rating of excellent in 2011, the mean (0.004 mg/l) was below the desired target level of 0.0052 mg/l.

Biotic Indicator: Measurement of the biotic indicator, seagrass, was performed by the Southwest Florida Water Management District in 2010. The total area of seagrass in lower Sarasota Bay (that portion within Sarasota County) was estimated to be 2,995 acres. The total for the whole of Sarasota Bay was estimated to be 9,800 acres. This is well above the target threshold of 7,269 acres and reflects a 50% increase in seagrass coverage from 2004, when the acreage was estimated to be 6,515 acres.

Sarasota Bay

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
Excellent

Chlorophyll a

Score: Excellent How was this determined?
Units: mg/l Year
2011
Historical
period of record
High 0.019 0.049
Mean 0.004 0.005 0.0042586 0.0052000000
Low 0.001 0.000
No. of Samples 228 3217

Five-year Rolling Average

  • Annual Mean
Excellent

Nitrogen, Total

Score: Excellent How was this determined?
Units: mg/l Year
2011
Historical
period of record
High 0.930 1.870
Mean 0.368 0.20465446 0.5100000000
Low 0.100 0.030
No. of Samples 240 3016

Five-year Rolling Average

  • Annual Mean
Targets and thresholds shown on this graph are advisory approximations computed by Sarasota County using recent data. Regulatory thresholds have not been established. Learn more about Sarasota Bay Nitrogen targets/thresholds »
Excellent

Phosphorus, Total

Score: Excellent How was this determined?
Units: mg/l Year
2011
Historical
period of record
High 1.140 4.400
Mean 0.056 0.096 0.14325216 0.1500000000
Low 0.050 0.002
No. of Samples 296 3588

Five-year Rolling Average

  • Annual Mean

Dissolved Oxygen

Units: mg/l Year
2011
Historical
period of record
High 10.20 26.00
Mean 5.92 6.75 1.33723
Low 2.60 1.48
No. of Samples 399 6843

Five-year Rolling Average

  • Annual Mean

Apparent Color

Units: PCU Year
2011
Historical
period of record
High 75.00 95.00
Mean 14.20 13.57 9.72291
Low 3.00 0.00
No. of Samples 299 3685

Five-year Rolling Average

  • Annual Mean

BOD, Biochemical oxygen demand

Units: mg/l Year
2011
Historical
period of record
High 2.00 9.20
Mean 0.94 1.21 0.84377
Low 0.50 0.50
No. of Samples 252 2366

Five-year Rolling Average

  • Annual Mean

Dissolved oxygen saturation

Units: percent (%) Year
2011
Historical
period of record
High 151.06 214.71
Mean 81.63 97.73 19.64906
Low 31.60 21.92
No. of Samples 697 14350

Five-year Rolling Average

  • Annual Mean

Karenia brevis ("red tide")

Units: #/l Year
2011
Historical
period of record
High 4000.00 6380000.00
Mean 1031.75 78979.22 455922.90353
Low 1000.00 1000.00
No. of Samples 252 1588

Five-year Rolling Average

  • Annual Mean

Light Attenuation

Note: Light attenuation data reported for years prior to 2012 are from only the southern half of Sarasota Bay. Data for the nothern half are unavailable.
Units: K(1/m) Year
2011
Historical
period of record
High 1606.00 4350.00
Mean 578.00 492.60 473.30736
Low 0.05 0.05
No. of Samples 446 6822

Five-year Rolling Average

  • Annual Mean

Nitrogen, Ammonia + Ammonium as N

Units: ug/l Year
2011
Historical
period of record
High 49.00 159.00
Mean 12.88 11.49 11.35896
Low 5.00 5.00
No. of Samples 252 2880

Five-year Rolling Average

  • Annual Mean

Nitrogen, Kjeldahl

Units: ug/l Year
2011
Historical
period of record
High 900.00 1850.00
Mean 383.55 365.76 199.7202
Low 70.00 0.01
No. of Samples 301 3687

Five-year Rolling Average

  • Annual Mean

Nitrogen, Nitrite + Nitrate as N

Units: ug/l Year
2011
Historical
period of record
High 30.00 210.00
Mean 9.01 8.53 10.29517
Low 5.00 1.00
No. of Samples 300 4561

Five-year Rolling Average

  • Annual Mean

pH

Units: None Year
2011
Historical
period of record
High 8.50 9.62
Mean 7.56 8.07 0.34912
Low 3.90 3.90
No. of Samples 498 11995

Five-year Rolling Average

  • Annual Mean

Salinity

Units: PSS Year
2011
Historical
period of record
High 36.60 42.30
Mean 33.51 33.63 2.41955
Low 12.20 4.00
No. of Samples 396 7343

Five-year Rolling Average

  • Annual Mean

Specific conductance

Units: umho Year
2011
Historical
period of record
High 55520.00 62750.00
Mean 51803.02 51920.55 3707.7359
Low 20370.00 31.20
No. of Samples 291 3948

Five-year Rolling Average

  • Annual Mean

Temperature, water

Units: deg F Year
2011
Historical
period of record
High 91.40 100.40
Mean 77.85 77.03 9.17073
Low 44.06 35.24
No. of Samples 705 16334

Five-year Rolling Average

  • Annual Mean

Turbidity

Units: NTU Year
2011
Historical
period of record
High 24.00 39.00
Mean 2.48 2.84 2.57997
Low 0.40 0.03
No. of Samples 325 6297

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 (2011)

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 2011 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 2,022 acres

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

Impervious Features

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

19% of the land area within the 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 »

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

Acreage and Percentage within each Land Use / Land Cover Category for Sarasota Bay Watershed
Land Use Classification 1990 1995 1999 2005 2011 2014 Trend
Urban & Built-up 32,90853.3% 34,51755.9% 35,33457.3% 37,84461.3% 38,34362.1% 37,98761.6%
Agriculture 6,33810.3% 5,9459.6% 4,6467.5% 2,4974% 2,2153.6% 2,3093.7%
Rangeland 5470.9% 3370.5% 2970.5% 1990.3% 2250.4% 4300.7%
Upland Forests 3,5885.8% 2,8544.6% 2,6194.2% 2,1093.4% 1,8743% 1,9233.1%
Water 13,35021.6% 13,44521.8% 13,63322.1% 14,22723.1% 14,27823.1% 14,13122.9%
Wetlands 2,8704.7% 2,3793.9% 2,3523.8% 2,2273.6% 2,2293.6% 2,3723.8%
Barren Land 290% 1080.2% 7211.2% 90% 990.2% 1090.2%
Transportation and Utilities 1,8453% 2,1303.5% 2,1133.4% 2,6024.2% 2,4524% 2,4534%
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.