Learn More: Chlorophyll

Chlorophyll is the green pigment found in plants and nearly all algae, in both freshwater and marine aquatic systems. Chlorophyll allows these plants and algae to use sunlight in the process of photosynthesis for growth. Chlorophyll a is one type of chlorophyll. Measurements of chlorophyll are often used to estimate algal biomass in a waterbody in order to assess a waterbody's biological productivity. Chlorophyll values vary naturally over the course of a day, in sync with light levels and photosynthetic activity (please see caveats and limitations).

Techniques to measure chlorophyll include spectrophotometry, high performance liquid chromatography (HPLC), and fluorometry. Spectrophotometry involves the collection of a water sample, filtration to concentrate chlorophyll-containing organisms, mechanical rupturing of the collected cells, and extraction of the chlorophyll from the disrupted cells into an organic solvent (acetone). Fluorometry requires the same extraction methods as spectrophotometry, but uses a fluorometer to measure discrete molecular chlorophyll fluorescence. Both spectrophotometry and fluorometry are time-consuming and require an experienced analyst to generate accurate/reproducible results; neither method can be used by continuous-monitoring water quality sensors. Water quality sondes use optical sensors to produce results. The ability of chlorophyll to fluoresce is the basis for sensors capable of measuring the analyte in situ. They induce fluorescence by shining a beam of light of the proper wavelength into the water sample, and then measuring the higher wavelength light that is emitted.

The manual methods for measuring chlorophyll a are described in the Florida Department of Environmental Protection's Standard Operating Procedures. Instrument range, resolution, and accuracy can be found in continuous measurement instrument's product documentation.

Because the real-time (continuous) water quality data presented on the Atlas goes through a series of transfers before becoming available, there can sometimes be a time delay in presenting these data. Additionally, if the water quality stations or computers transferring the data are tampered with, this may cause problems in being able to present the data in 12-hour increments. In addition, the data do not undergo the same level of quality control as other data sets prior to being presented on the Atlas. A caveat of using near-real time data is the possibility of error. Near real-time data has not undergone as many quality control procedures common to our other data sets. Therefore, occasionally due to equipment malfunction there may exist errors within the data. Every attempt is being made to mitigate these errors before they occur. Also please be aware chlorophyll values change naturally over the course of the day, with lower values early in the morning and higher values in the afternoon. Therefore, when interpreting the data it is better to examine average values or long-term trends rather than individual measurements, which may not be representative.

• Lake Ecology Primer
• Product data sheet for YSI 6600EDS Sonde
• SOP for Spectrophotometric Determination of Corrected and Uncorrected Chlorophyll a and Pheophytin