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Browse History: Chlorophyll a (2013)
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


This map shows how often chlorophyll a concentrations were within their threshold concentrations categories in 2013. 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 2013, 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 78 stations bi-monthly to monthly over the calendar year of 2013. The proportion of time that chlorophyll a levels were within the multiple threshold levels at each station is represented.

Data Map


This map shows the median chlorophyll a concentration in the Coastal Bays in 2013. The lowest median chlorophyll a concentrations occurred in Sinepuxent and Chincoteague Bays, and low chlorophyll a concentrations were also observed in Assawoman, Isle of Wight, and Newport Bays. Low median chlorophyll a levels in these regions may in part be attributed to the low availability of nutrients, particularly nitrogen. In contrast, St. Martin River had the highest median chlorophyll a concentrations, and the elevated chlorophyll a levels observed in these regions were likely due to a combination of high nutrient and low light availability.

Understanding this map
Chlorophyll a concentrations were measured at 78 stations bi-monthly to monthly in 2013. The median chlorophyll a concentration is represented at each station.

Ranking


Comparison of Bay Health Index scores for 2013 () compared to
()


Score Legend
 Score (%)
 0               20               40               60               80              100
  
Sinepuxent Bay  
Chincoteague Bay  
Overall Coastal Bays  
Isle of Wight Bay  
Assawoman 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 2013, Chincoteague Bay had excellent chlorophyll a, while Sinepuxent, Assawoman, Newport, and Isle of Wight Bays had very good chlorophyll a scores. St. Martin River scored as good. Higher chlorophyll a levels in St. Martin River 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