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Browse History: Choptank River (2011) | Home (2009) | Overview (2009) | Chlorophyll a (2009)
Indicator Icon Chlorophyll a

Chlorophyll a is used as a measure of phytoplankton (microalgae) biomass. Phytoplankton biomass is controlled by factors such as water temperature and the availability of light and nutrients. Elevated phytoplankton levels can lead to reduced water clarity and decomposing phytoplankton can lead to reduced dissolved oxygen levels.

Maryland Coastal Bays - Indicator Details:





  Indicator Selection Diagram


Threshold Map


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This map shows how often chlorophyll a concentrations were within their threshold concentrations categories in 2009. Good water quality is characterized by low chlorophyll a levels that fall in the better health-threshold categories, resulting in higher scores (shown in green). In contrast, poor water quality tends to have chlorophyll a levels that fall in the worse health-threshold categories, resulting in low scores (shown in shades of orange and red). In 2009, a large proportion of the Coastal Bays had chlorophyll a levels that were in the better health-threshold categories.


Creating this map
Chlorophyll a concentrations were measured at 80 stations bi-monthly to monthly over the calendar year of 2009. The proportion of time that chlorophyll a levels were within the multiple threshold levels at each station is represented.

Data Map


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This map shows the median chlorophyll a concentration in the Coastal Bays in 2009. The lowest median chlorophyll a concentrations occurred in Sinepuxant and Chincoteague Bays, although low chlorophyll a concentrations were also observed in the northeastern bays of Assawoman and Isle of Wight. Low median chlorophyll a levels in these regions may in part be attributed to the low availability of nutrients, particularly TN. In contrast, the small western-most tributaries of Newport Bay and St. Martin River tended to have the highest median chlorophyll a concentrations, and the elevated chlorophyll a levels observed in these regions are likely due to a combination of high nutrient and light availability.

Understanding this map
Chlorophyll a concentrations were measured at 80 stations bi-monthly to monthly in 2009. The median chlorophyll a concentration is represented at each station.

Ranking


Comparison of Bay Health Index scores for 2009 () compared to
()


 Score (%)
 0               20               40               60               80              100
  
Chincoteague Bay  
Assawoman Bay  
Sinepuxent Bay  
Overall Coastal Bays  
Isle of Wight Bay  
Newport Bay  
St. Martin River  

This figure ranks each region from best to worst for chlorophyll a. Good water quality is characterized by chlorophyll a levels that are frequently within the lower concentration threshold categories, resulting in high scores (shown in green). Poor water quality tends to have chlorophyll a levels that are frequently within the higher concentration threshold categories (shown in shades of orange and red). In 2009, Sinepuxent, Chincoteague, and Assawoman Bays had the best overall chlorophyll a scores, although a good score was also observed within Isle of Wight Bay (see threshold map). Higher chlorophyll a levels in are likely due to the availability of nutrients that stimulate phytoplankton growth.


Excel Spreadsheet

Threshold Levels

ScoreThresholds (µg L-1)
100 <7.5
807.5–<15
6015–<30
4030–<50
2050–<75
0≥75