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Bench Biology

Bacteriological Analyses

The Bench Biology workgroup conducts bacteriological tests for enterococci, Escherichia coli, fecal coliforms and total coliforms. These bacteria are commonly found in the intestinal tract of warm-blooded animals. Their presence in water samples can indicate the potential presence of fecal pollution and enteric pathogens.

Biochemical Oxygen Demand (BOD)

The Biochemical Oxygen Demand (BOD) test is a measure of the oxygen depletion potential of ambient, surface, or effluent waters during a predetermined incubation period. It is often used as a permit limit or modeling parameter. BOD testing may be conducted for both carbonaceous and nitrogenous demand for oxygen or nitrification may be inhibited, resulting in only carbonaceous demand for oxygen. Typical testing is for 5-day oxygen demand.

Chlorophyll Analyses

By analyzing the chlorophyll content of the drifting and attached algae in a stream, lake, or estuary, the Bench Biology workgroup 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 a. 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 on 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 Bench Biology workgroup can perform grain size analysis, using a laser diffraction method, and can determine the percent organic material in a sediment sample. 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.

Toxicity Bioassays

A toxicity bioassay may be run as a screening test, where the toxicity of a sample is compared to that of a control water, or as a definitive test, where several portions of the sample are diluted with varying amounts of the control water and their results compared to the control water. A screening test may indicate if a sample has a toxic effect. A definitive test may indicate the degree of toxicity presented by the sample. Additionally, the results of a toxicity bioassay may be measured as either an acute response such as mortality or a chronic response such as growth or reproductive effects.

Samples of wastewater discharges are tested for compliance with limits established by permits. Tests for toxicity are also conducted in surface or ground waters during other investigations. 

The Bench Biology workgroup conducts acute and chronic freshwater tests using water fleas, bannerfin shiners, and fathead minnows; acute and chronic saltwater tests using mysid shrimp and inland silversides; and chronic freshwater and saltwater tests using the algae Psuedokirchneriella and Dunaliella.

Last Modified:
May 24, 2023 - 2:04pm

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