This is a measure of the primary productivity of a system. The level of chlorophyll a can be used to estimate the general classification of a lake or pond or identify potential problems. If possible, recreational waters should be < 0.025 mg/L or < 25 ug/L chlorophyll a, this permits some balance between recreational use and potential nuisance issues.
Chlorophyll a is the photosynthetic pigment that causes the green color in algae and plants. The concentration of chlorophyll a present in the water is directly related to the amount of algae living in the water. Excessive concentrations of algae give lakes an undesirable “pea soup” appearance. The concentration of chlorophyll a can be used to estimate the trophic status of the lake.
Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from ancient Greek: chloros = green and phyllon = leaf. Chlorophyll absorbs light most strongly in the blue and red but poorly in the green portions of the electromagnetic spectrum, hence the green color of chlorophyll-containing tissues like plant leaves. The chlorophyll pigments are named after the wavelength (in nanometers) of their red-peak absorption maximum. The identity, function, and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by the protein structure.
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 chlorophyll molecules 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.
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” (combine samples taken at different depths) because the purpose is to calculate an average chlorophyll concentration within the photic 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 photic zone can be estimated using the secchi 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 placed in a dark bottle and wrapped with aluminum foil and then 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 using a simple paper chromatography method or a spectral analysis method using a spectrophotometer.
TSIs = 60 – 14.41 [ln (Secchi Depth)]; where the Secchi Depth is reported in meters. Note that ‘ln’ is ‘natural log of.’
TSIp = 14.42 [ln (Total Phosphate)] + 4.15; where the Total Phosphate is reported as P in part per billion (ppb)
Avg TSI = (TSIs + TSIp)/2
Chlorophyll a = 2.7154^ [(Avg TSI – 30.6/)/9.8]; where chlorophyll a is reported as parts per billion (aka mg/m3); eg. If Avg TSI is 88.55, then the estimated chlorophyll a content is 367 mg/m3.
TSIc = 9.81 [ln (Chlorophyll a)] + 30.6; where the Chlorophyll a is reported in parts per billion (ppb)
This is a measure of the primary productivity of a system. The level of chlorophyll a can be used to estimate the general classification of a lake or pond or identify potential problems. If possible, recreational waters should be < 0.025 mg/L or < 25 ug/L which permits some balance between recreational use and potential nuisance issues.
Oligotrophic - "Oligotrophic lakes are characterized by a low accumulation of dissolved nutrient salts, supporting but a sparse growth of algae and other organisms, and having a high (dissolved) oxygen content owing to the low organic content. (Source)"
"Mesotrophic lakes contain a narrow range of nutrients, principally phosphate and nitrate, the concentrations of which are considered to be neither high nor low. Typically mesotrophic lakes have a nutrient concentration of 0.3 - 0.65 mg/l of nitrate and 0.01 - 0.03 mg/l of phosphate. Mesotrophic lakes potentially have the highest diversity of plants and animals of any lake type. Relative to other types of lake they contain a higher proportion of nationally scarce and rare aquatic plants. They are also important for many types of insects including dragonflies, water beetles and mayflies. (Source)"
Because of the very high levels of phosphate and nitrogen, the eutrophic system typically has a very high level of productivity. These systems are normally very high in aquatic plants and algae which are associated with nuisances. The significant algal blooms are normally followed by very low dissolved oxygen conditions and fish kills. The eutrophication process is natural, but humans can speed up the process.
"Hypereutrophic lakes are very nutrient-rich lakes characterized by frequent and severe nuisance algal blooms and low transparency. Hypereutrophic lakes have a visibility depth of less than 3 feet (90 cm), they have greater than 40 micrograms/litre total chlorophyll and greater than 100 micrograms/litre phosphorus. The excessive algal blooms can also significantly reduce oxygen levels and prevent life from functioning at lower depths creating dead zones beneath the surface. Likewise, large algal blooms can cause biodilution to occur, which is a decrease in the concentration of a pollutant with an increase in trophic level. This is opposed to biomagnification and is due to a decreased concentration from increased algal uptake" (Source).
Table 1 | Trophic Status Index (TSI) and Water Quality
* When the TSI is less than 30, the hypolimnion is likely oxygenated all year, but if it is between 30 and 40, it is likely the hypolimnion is anoxic in the summer.
Sources: Carlson, R.E. and J. Simpson. 1996. A Coordinator’s Guide to Volunteer Lake Monitoring Methods. North American Lake Management Society.
Table 2 | TSI Values, Possible Interrelationships, and Possible Interpretations.
Sources: Carlson, R.E. and J. Simpson. 1996. A Coordinator’s Guide to Volunteer Lake Monitoring Methods. North American Lake Management Society.
