Annual Averages
| Indicator |
Units |
2016 |
2017 |
2018 |
2019 |
2020 |
Trend |
| Dissolved Oxygen |
mg/l |
6.16 |
6.31 |
6.16 |
5.98 |
6.61 |
|
| Dissolved oxygen saturation |
percent (%) |
89.00 |
92.61 |
89.21 |
87.60 |
95.89 |
|
| Light Attenuation |
K(1/m) |
1.57 |
1.11 |
1.51 |
1.20 |
1.04 |
|
| Salinity |
PSS |
26.18 |
29.61 |
27.76 |
29.30 |
30.18 |
|
| Turbidity |
NTU |
4.34 |
4.10 |
4.00 |
5.29 |
5.06 |
|
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 (2020)
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 »
Loading interactive contour map viewer...
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 »
Loading interactive seagrass coverage viewer...
| Year |
Acres |
| 1996 |
81.969249 |
| 1999 |
87.263219 |
| 2001 |
83.967225 |
| 2004 |
102.491433 |
| 2006 |
123.257996 |
| 2008 |
89.359946 |
| 2010 |
78.38655 |
| 2012 |
78.829976 |
| 2014 |
98.845019 |
| 2016 |
100.77192 |
| 2018 |
116.141208 |
| 2022 |
29.904177 |
Loading interactive chart...
Visit our Seagrass page to discover the beauty and importance of seagrass habitats, and sign up to help monitor their health.
Impervious Features
Dona/Roberts Bay is located within the Dona and Roberts Bay Watershed. View details about the Dona and Roberts 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.
7% of the land area within the Dona and Roberts Bay Watershed is covered by impervious surfaces
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 »
Dona/Roberts Bay is located within the Dona and Roberts Bay Watershed. The chart below shows the land use / land cover characteristics for Dona and Roberts Bay Watershed within the boundary of this Water Atlas. View details about the Dona and Roberts Bay Watershed »
Acreage and Percentage within each Land Use / Land Cover Category for Dona and Roberts Bay Watershed
| Land Use Classification |
1990 |
1995 |
1999 |
2005 |
2011 |
2014 |
2017 |
2020 |
Trend |
| Urban & Built-up |
11,51920.6% |
13,67024.4% |
15,33327.4% |
17,10130.6% |
17,69731.6% |
17,84131.9% |
18,53833.1% |
23,15637.1% |
|
| Agriculture |
14,25725.5% |
15,00626.8% |
14,65226.2% |
14,43825.8% |
13,41024% |
13,17023.5% |
12,99423.2% |
12,90920.7% |
|
| Rangeland |
3,9897.1% |
3,0395.4% |
2,6374.7% |
1,7153.1% |
2,1043.8% |
2,3094.1% |
1,7923.2% |
1,9483.1% |
|
| Upland Forests |
12,68822.7% |
10,64919% |
8,90015.9% |
7,90614.1% |
7,74213.8% |
7,70113.8% |
7,48013.4% |
7,64712.3% |
|
| Water |
1,9313.5% |
2,6164.7% |
2,7845% |
2,8655.1% |
2,8135% |
2,8665.1% |
3,0095.4% |
3,4455.5% |
|
| Wetlands |
10,34918.5% |
9,53517% |
9,68217.3% |
9,80817.5% |
9,90717.7% |
9,79517.5% |
9,83917.6% |
10,80417.3% |
|
| Barren Land |
220% |
260% |
60% |
100% |
840.2% |
510.1% |
460.1% |
180% |
|
| Transportation and Utilities |
1,2022.1% |
1,4012.5% |
1,9493.5% |
2,0993.8% |
2,1853.9% |
2,2093.9% |
2,2624% |
2,4503.9% |
|
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.
