Chlorophyll a is the green pigment in tiny marine algae (phytoplankton) that produces food. Measuring chlorophyll is based on the amount of phytoplankton (microalgae), which uses both nitrogen and phosphorus to grow. Too much algae in the water reduces water clarity, and decomposing algae leads to reduced dissolved oxygen. In a balanced ecosystem, phytoplankton provide food for fish, crabs, oysters, and worms. When too many nutrients are available, phytoplankton may grow out of control and form algal blooms that can harm fish, shellfish, mammals, birds, and even people.
How is it measured?
Chlorophyll a is measured in the Northern Estuaries, Lake Okeechobee, and the Southern Coastal Systems.
In the Northern Estuaries, the proportion of time that chlorophyll a levels were below the threshold levels at each station were calculated and are spatially averaged into the sub-regions and then the regions. The thresholds vary between stations and regions and are based on the Boyer method and the stoplight indicator.
In Lake Okeechobee, chlorophyll a concentration, was monitored across 10 nearshore and 9 pelagic stations monthly. Algal blooms are defined by the South Florida Water Management District as equivalent to chlorophyll a concentration of ≥ 40 μg/l. The goal is to have no algal blooms, or chlorophyll a concentrations <40 μg/l.
In the Southern Coastal Systems, the multiple thresholds were used based on the median and quartiles of the data. Scores were calculated at each zone and were spatially averaged into the sub-regions and then the regions. The thresholds vary between stations and regions.
Northern Estuaries Thresholds by Station
|Station||Threshold (µg L)|
Southern Coastal Systems Thresholds by Area
|25th percentile||Median||midpoint median to 75th percentile||75th percentile|
|Southwest Coast||Southwest Florida Shelf||SWFS||0.87002||1.466111||1.953||2.44|
|Southwest Coast||Mangrove Transition Zone||MTZ||1.69||2.863||3.883||4.903|
|Florida Bay||West Florida Bay||WFB||0.653||1.345||2.095||2.845|
|Florida Bay||South Florida Bay||SFB||0.327||0.533||0.796||1.059|
|Florida Bay||North-central Florida Bay||NCFB||0.585||1.216||2.463||3.71|
|Florida Bay||Northeast Florida Bay||NEFB||0.254||0.417||0.6035||0.79|
|Biscayne Bay||Blackwater, Manatee, Barnes Sound||BMB||0.306||0.526||0.718||0.91|
|Biscayne Bay||South Biscayne Bay||SBB||0.181||0.264||0.345||0.426|
|Biscayne Bay||Central Biscayne Bay||CBB||0.2||0.313||0.4395||0.566|
|Biscayne Bay||North Biscayne Bay||NBB||0.67||1.048||1.348||1.648|