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The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao: [6]. Starting with the solar spectrum falling on a leaf, 47% lost due to photons outside the 400–700 nm active range (chlorophyll uses photons between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)
The concentration of chlorophyll A is used as an index of phytoplankton biomass. In the ocean, phytoplankton all contain the chlorophyll pigment, which has a greenish color. Phytoplankton are microscopic organisms that live in watery environments and changes in the amount of phytoplankton indicate the change in productivity of the ocean.
Relationships between Trophic State Index, chlorophyll, phosphorus, Secchi depth, and trophic class (after Carlson 1996) [4] Trophic State Index Chlorophyll (μg/L) Phosphorus (μg/L) Secchi depth (m) Trophic Class < 30—40 0—2.6 0—12 > 8—4 Oligotrophic or hipotrophic 40—50 2.6—7.3 12—24 4—2 Mesotrophic 50—70 7.3—56 24—96
[21] [22] [23] In this way, the concentration of chlorophyll within a leaf can be estimated. [24] Methods also exist to separate chlorophyll a and chlorophyll b. In diethyl ether, chlorophyll a has approximate absorbance maxima of 430 nm and 662 nm, while chlorophyll b has approximate maxima of 453 nm and 642 nm. [25]
Chlorophyll-a concentration is sometimes used to measure water clarity, especially when suspended sediments and colored dissolved organic matter concentrations are low. Chlorophyll-a concentration is a proxy for phytoplankton biomass, which is one way to quantify how turbid the water is due to biological primary production.
Typical examples include the Leaf Area Index, biomass, chlorophyll concentration in leaves, plant productivity, fractional vegetation cover, accumulated rainfall, etc. Such relations are often derived by correlating space-derived NDVI values with ground-measured values of these variables.
Low-nutrient, low-chlorophyll (LNLC) regions are aquatic zones that are low in nutrients (such as nitrogen, phosphorus, or iron) and consequently have low rate of primary production, as indicated by low chlorophyll concentrations. These regions can be described as oligotrophic, and about 75% of the world's oceans encompass LNLC regions.
A false color SeaWiFS image shows a high concentration of phytoplankton chlorophyll in the Brazil Current Confluence region east of Argentina. Warm colors indicate high chlorophyll levels, and cooler colors indicate lower chlorophyll. SeaWiFS data are freely accessible from a variety of websites, most of which are government run.