Bio-Limno Methods

    Phytoplankton & Periphyton  |  Zooplankton    

Phytoplankton & Periphyton

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Analyses (identification and enumeration) of phytoplankton and periphyton samples are performed using the traditional Utermö hl settling technique and an inverted microscope equipped with phase contrast. Identifications are performed at magnifications ranging between 165X and 750X.

Michael working on the microscope

Counting units are individual cells, filaments or colonies depending on the organization of the algae. A minimum of 400 - 500 units (usually at multiple magnifications) from randomly selected transects are counted for each sample; counting at multiple magnifications allows us to correctly enumerate taxa present that may vary by several orders of magnitude in size. In cases where a sample has extremely few algal units and high particulate matter (thus yielding less than 400 units), as many transects as possible will be covered in order to have more than 70% of the chamber counted; the entire chamber is counted when possible.

Settling chambers.Identification of diatoms to species level involves boiling/digesting sub-samples in hydrogen peroxide in order to clean the frustules, followed by mounting on glass slides using Naphrax and identification at 1000X magnification under oil immersion. The diatoms identified on the mounted slides are matched with what are obtained in the fresh samples; where it is not possible to separate two or more species in the fresh samples, separation is done by proportion.

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Zooplankton is enumerated (from three 1-5 ml sub-samples) using a dissecting microscope at 41X-60X magnifications for macrozooplankton; microzooplankton (rotifers and copepod nauplii) are analysed following Utermöhl’s sedimentation technique at 165X-375X magnifications on an inverted microscope. Sub-sample volumes used depends on the density of organisms and the amount of particulate matter in the sample.


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Last modified 16 Sep 2004.