Chlorophyll

**For the Mass. Department of Environmental Protection-approved SOP, get the pdf file here

Background Information

Chlorophyll indirectly measures how much algae are in a lake. The more algae, the greener the lake and the more eutrophied (over-enriched) it is. How much is too much? Here is a table to compare your total chlorophyll numbers to (you'd like your lake to be oligotrophic or mesotrophic):

Status Total Chlorophyll (µg/l)*
Oligotrophic 0-4
Mesotrophic 4-12
Eutrophic 12-50
Hyper-eutrophic 50-2000

Chlorophyll varies from day to day, so it's best to compare the mean or median for the season rather than an individual value. Another point to consider when trying to characterize your lake is that aquatic weeds compete with algae for nutrients. So a weed-choked lake will probably have very few algae in the water, which is all that the chlorophyll measure includes. If you have few aquatic weeds, the classification will work, but if weeds are a significant part of your lake's plant life, these chlorophyll criteria are meaningless.

Sampling Method

Equipment:

chlorophyll filtration apparatus

Drawing by Tom Burke

  • Filter holder, magnetic, 47 mm
  • Filtering flask, 1000 ml
  • Hand vacuum pump with gauge
  • Graduated cylinder, 500 ml
  • Glass fiber filters, 47 mm
  • Aluminum foil
  • Forceps
  • 1 or 2 1-liter sample bottles
  • Air-drying box
  • Field sheet and pencils

Rinse a 1-liter bottle (including cap) three times with surface water at the sampling site. Be sure to empty your rinse water away from your sampling location. Take a sample to elbow depth. Cap and place in cooler. If Secchi depth is greater than 3 meters, fill another 1-liter bottle.

Back on shore and in subdued light, the filter apparatus is set up with vacuum flask, filter holder, glass fiber filter, and filling funnel. Place the filter rough side (wood grain-like) up on the filter holder. Using a graduated cylinder, a precise volume is measured out; the amount is recorded. That measured sample is poured in the filling funnel and the hand-operated vacuum pump operated until the vacuum is 15" of vacuum) units. It may require some patience to filter an adequate amount of water.

Review the field data sheets to learn the Secchi disk depth at the sample site. Use the following chart to determine the appropriate volume to filter (to provide sufficient chlorophyll for analysis and minimize your time in filtering):

Secchi Depth Volume to filter
less than .2 meters 100 ml
more than .2 meters; less than 1.0 meter 300 ml
more than 1.0 meter; less than 1.6 meters 500 ml
more than 1.6 meters; less than 3.0 meters 1000 ml
more than 3.0 meters 1500 ml

Despite the seeming certainty of the above table, you should be guided by common sense. The table above is a guide to a reasonable compromise. If you can filter more water without seriously increasing the filtering time, please do so. If the filter is noticeably green and you haven't filtered the specified amount, you have still probably got enough for us to analyze. It is most important that the amount filtered be recorded to the nearest milliliter.

The above instructions describe a rule of thumb related to the Secchi disk transparency but an even better guide is a visible quantity of green or greenish brown on the filter. If you don't see more than a tinge, filter more sample. Be sure to keep track of the total amount filtered. Filtering may significantly slow in the later stages as the filter plugs up with material.

When all the measured sample has been filtered, the filling funnel is removed, the filter carefully removed from the filter holder with forceps, folded in half (green side in), and placed in the air drying box. Keep the lid on while you're filtering the next sample. Make sure to note which filters are placed where in the air drying box. When all samples have been filtered the drying box is plugged in. Air dry the sample filters for at least 45 minutes or until they are dry. Then remove them with forceps and place in aluminum foil. Label the aluminum foil with the lake name, date, site and volume of water filtered. These may be mailed, first class, to the Environmental Analysis Lab at UMass. Blaisdell House. UMass. Amherst, MA 01003.

Construction of the Air-Dryer

For detailed instructions on how to build the air dryer, see this pdf document: Instructions .