Chlorophyll a

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.

See the results for Chlorophyll a in the Northern Estuaries, Lake Okeechobee, or Southern Coastal Systems.

Photo credit: South Florida Water Management District.

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 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.

Threshold Levels

Northern Estuaries Thresholds by Station

Sub-region

StationThreshold (µg L)
St. LucieHR_19
St. LucieSE_088
St. LucieSE_036
St. LucieSE_025.3
St. LucieSE_014.3
St. LucieSE_112.96
CaloosahatcheeCES04_DBH3.4
CaloosahatcheeCES05_DBH6.78
CaloosahatcheeCES06_DBH4.85
CaloosahatcheeCES08_DBH2.3
CaloosahatcheeCES09_DBH2.095
CaloosahatcheeCES04_LEE3.45
CaloosahatcheeCES06_LEE3.85
CaloosahatcheeCES10_LEE1.51
LoxahatcheeLOX101.4
LoxahatcheeLOX201
LoxahatcheeLOX304.4
LoxahatcheeLOX402.1
LoxahatcheeLOX424
LoxahatcheeLOX513.6
LoxahatcheeLOX556.15
LoxahatcheeLOX605.8
LoxahatcheeLOX625.9
LoxahatcheeLOX654.3
LoxahatcheeLOX7210.4

 

Southern Coastal Systems Thresholds by Area

   25th percentile Median midpoint median to 75th percentile75th percentile
Sub-regionAreaZone  604020
Southwest CoastSouthwest Florida ShelfSWFS0.870021.4661111.9532.44
Southwest CoastMangrove Transition ZoneMTZ1.692.8633.8834.903
Florida BayWest Florida BayWFB0.6531.3452.0952.845
Florida BaySouth Florida BaySFB0.3270.5330.7961.059
Florida BayNorth-central Florida Bay NCFB0.5851.2162.4633.71
Florida BayNortheast Florida BayNEFB0.2540.4170.60350.79
Biscayne BayBlackwater, Manatee, Barnes Sound BMB 0.3060.5260.7180.91
Biscayne BaySouth Biscayne BaySBB0.1810.2640.3450.426
Biscayne BayCentral Biscayne Bay CBB 0.20.3130.43950.566
Biscayne BayNorth Biscayne BayNBB0.671.0481.3481.648