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tab corner of content areaMicrobiological Analyses and Bench Biology tab corner of content areaHighlights

The Biology Laboratory routinely analyzes water samples for bacteria and biochemical oxygen demand (BOD), all factors in important health-related environmental standards.

Bacteriological Analyses

The Biology Laboratory conducts a number of bacteriological tests. These include:

  1. fecal coliform bacteria
  2. total coliform bacteria
  3. fecal streptococcus
  4. enterococci
  5. Escherichia coli
  6. Klebsiella
  7. heterotrophic plate counts

These tests are all indicative of factors important in health-related environmental standards. For particular applications, the laboratory can isolate and identify many bacteria to the species level, using either differential agar growth or biochemical tests.

Biochemical Oxygen Demand (BOD)

The Biology Laboratory regularly performs BOD analyses of water samples from around the state. BOD is often used as a permit limit or modeling parameter. BOD testing is conducted for both regular BOD tests and nitrogen-inhibited BOD (also called carbonaceous BOD or CBOD) tests. Typical testing is for either 5-day oxygen demand (BOD5) or 20-day oxygen demand (BOD20).

In addition, the Biology Laboratory conducts long-term BOD testing. This procedure involves multiple BOD measurements over a long period of time. As typically conducted, a long-term BOD involves 5 BOD measurements at intervals specified by the person requesting the test. These tests frequently run for a total of 60-120 days and are useful for modeling of discharges containing organic compounds that are slow to break down and whose oxygen demand takes place over a long period of time, for instance paper mill effluents.

Tests to help determine the health of the state's surface waters include measuring chlorophyll (which indicates the size of algae populations) and determining the grain sizes and organic content of bottom sediments.

Chlorophyll Analysis

By analyzing the chlorophyll content of the drifting and attached algae in a stream, lake, or estuary, the Biology Laboratory can estimate overall algal biomass in a water body. Used with taxonomic identification and Algal Growth Potential tests, this procedure produces a complete picture of the trophic status of a system.

Chlorophyll analyses are carried out to identify chlorophyll a and phaeophytin. Chlorophyll a is the dominant type of chlorophyll in the algae most commonly found in surface waters. Phaeophytin is a breakdown product of chlorophyll and the ratio of chlorophyll to phaeophytin provides information of the health of the algal population. During rapid growth, the proportion of phaeophytin is low. During periods of decline, such as follows prolonged cloudy weather or exposure of the algae to toxic substances, the proportion of phaeophytin is high.

Sediment Analyses

The laboratory can perform grain size analysis, using either wet or dry sieving techniques, and can determine the percent organic material in a sediment sample. Silt and clay particle sizes can also be determined, if necessary, using a Coulter Counter™ particle-counting apparatus.

Sediment grain size and organic content information is used to help understand what organisms might be expected to inhabit an area containing such sediments. Sediment characteristics are a primary factor affecting what aquatic organisms live on and within them.

Grain size information has also proven useful in storm water issues, where the period of time turbid runoff limits sunlight penetration into the body of water receiving the runoff can be important.

The Standard Operating Procedures used in preparation for and conducting all of the analyses listed above can be viewed or downloaded from the Biology Section SOPs.

Last updated: April 04, 2012

  Environmental Assessment and Restoration
Florida DEP Laboratory
2600 Blair Stone Road M.S. 6512
Tallahassee, Florida  32399-2400
850-245-8077 (phone)
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