What is it?
 Chlorophylls are complex molecules found in all photosynthetic  plants, including phytoplankton (microscopic plants dispersed in the waters). Chlorophyll, contained within the plant's cells, allows the plant to utilize sunlight as part of the their metabolism. There are several types of chlorophyll identified by slight differences in their molecular structure and constituents. These include chlorophyll a, b, c, and d. Chlorophyll a is the principal photosynthetic pigment and is common to all phytoplankton. Chlorophyll a can thus be used as a measure of phytoplankton biomass.
How is it measured?
 There are a number of different laboratory methods for the measurement of chlorophyll a, that differ according to extraction solvent used on concentrated (filtered) samples and analytical/instrumentation technique (e.g., spectrophotometer, fluorometer, high-pressure liquid chromatography). Advances in fluorescence technology have lead to the capability of semi-quantitative measurement of chlorophyll in water, without extraction or chemical treatment, thereby allowing in situ (in-lake) measurements as presented here for Cannonsville Reservoir. The in situ fluorometer measures of chlorophyll presented here have great utility, particularly within the context of this near-real-time data delivery program, to identify major features of temporal and vertical patterns of phytoplankton biomass in the reservoir. However, these in situ measurements are widely considered to be only rough approximations of chlorophyll a concentrations. The utility of these in situ measurements can be enhanced through adjustments to match the less frequent measurements of chlorophyll made through the field season by laboratory (extraction) methods
Why is it important?
The distribution and concentration of phytoplankton is of major water quality and ecologic concern. Managers are particularly concerned with the occurrences of excess concentrations of phytoplankton and associated nuisance conditions in surface waters, that occur in response to anthropogenic inputs of critical plant nutrients (particularly phosphorus). The concentration of phytoplankton is widely used as an indicator of the level of production of these microscopic plants (e.g., primary production or trophic state). Phytoplankton biomass is the primary regulator of clarity and color of water in many lakes and reservoirs.
 The most widely used measure of phytoplankton biomass is chlorophyll a. It has several advantages as a measure of phytoplankton biomass, including: (1) the measurement is relatively simple and direct, (2) it integrates cell types and ages, (2) it accounts to some extent for cell viability, and (4) it can be quantitatively coupled to important optical characteristics of water. However, the concentration of chlorophyll a is an imperfect measure of phytoplankton biomass, as the cellular content of this pigment depends on the composition of the phytoplankton community and ambient environmental conditions.
What to Look for in Our Systems?
 Concentrations of chlorophyll are usually much higher in the epilimnia of lakes and reservoirs compared to hypolimnia, because the available light limits phytoplankton production to the upper layers. The vertical pattern within the epilimnion tends to track that observed for temperature. The lower levels of the hypolimnion reflect depositing phytoplankton.
On average, higher chlorophyll a values are expected for Otisco Lake than the other two lakes because of its higher level of primary productivity (mesotropic versus oligotrophic). Further, Otisco Lake demonstrated strong metalimnetic maxima in chlorophyll a in 2002 that may be a recurring phenomenon. Limnologist have speculated for many years on the cause(s) of these distinct vertical structures.
|
