Chlorophyll is vital for photosynthesis, which allows plants to obtain energy from light. Chlorophyll molecules are specifically arranged in and around pigment protein complexes called photosystems which are embedded in the chloroplasts. In these complexes, chlorophyll serves two primary functions. The function of the vast majority of chlorophyll (up to several hundred per photosystem) is to absorb light and transfer that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. Because of chlorophyll’s selectivity regarding the wavelength of light it absorbs, areas of a leaf containing the molecule will appear green.
Spectral Analysis of Extract
To measure chlorophyll a concentration, a composite sample of the lake column within the photic zone is collected on a monthly basis during the growing season. The water sample is “composited” because the purpose is to calculate an average chlorophyll concentration within the photoic zone. The photic zone is where plants (algae and other aquatic plants) have sufficient sunlight to permit photosynthesize. Below the photic zone, there is not enough sunlight for most plants to photosynthesize. The depth of the photoic zone can be estimated using the seechi disk depth. The integrated sample allows us to examine the water column where phytoplankton live (i.e. the part of the water column with enough sunlight for photosynthesis to occur).
If the composite sample is to be filtered in the laboratory, the sample is place in a dark bottle and wrap with aluminum foil and placed in a cooler. In the laboratory, a given volume of the sample is filtered using a glass fiber filter. All of the algae and other suspended particles in the water will collect on the filter paper. The filter paper is then processed, ground, and leached to extract the chlorophyll. Once extracted from the protein structure and dissolved into a solvent (such as Acetone or Methanol), these chlorophyll pigments can be separated in a simple paper chromatography measures or a view a spectral analysis using a spectrophotometer.
Trophic State Index Equations
(Source: Carlson, R.E., 1997)
TSI = 60 - 14.41 (ln (Secchi Depth) - Seechi Depth
TSI = 14.42 (ln (Total Phosphate)+ 4.15 - TP (ppb)
TSI = 9.81 (ln Chlorophyll a) + 30.6 - Chlorophyll a (ppb)
If you would like information related to our laboratory services related to lake trophic status monitoring (Seechi, Total Phosphate, Soluble, Chlorophyll, Total Kjeldahl Nitrogen, Nitrate+Nitrite), please email lake trophic monitoring.
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