mod4lab - stream ecology - measuring periphyton biomass

Module 4 Stream Ecology Laboratory

Measuring Periphyton Biomass

Presentation NameUpdated March 16, 2003 – Author

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Periphyton Biomass Measurements

Ash-Free Dry Weight

Pigment Analysis

Biovolume Measurement


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Periphyton Biomass Measurements

Many methods have been developed to collect periphyton from natural substrates. All involve quanitatively removing material from a known surface area.

Different methods may be needed to collect periphyton from rocks, woody debris, aquatic macrophytes, or other substrates.

Substrate size will also determine how samples are collected. Large boulders require the use of a device that prevents the sample from being lost downstream. If the substrate is a fist-sized cobble the rock can be paced in a pan, scraped, then washed into a bottle with stream water.


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One way to scrape a known area is to lay a plastic 35 mm slide (film removed) over the rock and scrape off the material within the slide area (scrub area = 2.3cmX3.5cm=8cm2).


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Periphyton (attached algae) sampling

Rocks don’t always look like they have much on them

Nearly all the stuff scrubbed off this one was organic matter –most of it living algaeS.Loeb and J.Reuter images


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Resulting material from a rock scrub contains macroinvertebrates, detritus, fungi, bacteria, as well as algae.


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Here’s a portion of the previous sample after being pulled on to a GF/C filter is preparation for chlorophyll extraction or AFDW determination.


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The filter is then placed in 90% acetone to extract the chlorophyll.

Pigment Analysis


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•The filter is dried to a constant weight then ashed at 555 ºC to burn off all of the organic matter.

•The difference in weight is called ‘loss upon ignition” and is a measure of the % organic content of the material

Ash-Free Dry Weight Determination

Muffle furnace


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Project NameWater Quality Samples scrub area = 2.3cmX3.5cm=8cm2

2002 8 cm2=0.0008 m2 X 3 scrubs = .0024 m2 total areaNRRI Central Analytical Labemr 12/4/02

Sample Run chlorophyll phaeophytin volume total chlorophyllPeriphyton Date Date ug/L ug/L filtered (mLs) volume (mLs) mg/m2Whatever Creek 5/6/2002 5/15/2002 130 60 45 45 2.4

Sample Run Dry Wt AFDW total volume AFDWDate Date mg/L mg/L volume (mLs) filtered (mLs) g/m2

Whatever Creek 5/6/2002 5/8/2002 156 117 319 122 6.0

chlorophyll

AFDW

Once you have a measure of chlorophyll or AFDW you’ll need to calculate per unit area.


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Periphyton Biovolume

Involves the examination of the algal cells under the microscope

Then measuring the cell dimensions with an ocular or stage micrometer and calculating cell volume.


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Periphyton Biovolume

Counting and measuring individual algae Identification to genus and species level Calculate cell volume by approximation to nearest geometrical

shape Count cells over a known area of the slide so cells per unit

volume can be determined

Rod

4/2AB

B

A

Some formulas to estimate biovolume from cell dimensions (also see Wetzel & Likens 2000)

6/3ASphere

A

Ellipsoid

6/2AB

B

A


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Taxonomic keys often include questions about size.

Determining size is basically like using a ruler. The standard ruler for a microscope is called an "ocular micrometer", which is fitted into the eyepiece of your microscope.

If you don’t have a micrometer, you can use the diameter of the field. Each of these methods requires that you first standardize your microscope against a ruler of known length; at low magnification, this standard could be a transparent office ruler, but at higher magnifications a stage micrometer is needed.

Be aware that different microscopes are not exactly the same and the size goes down with increased magnification.

mod4lab - stream ecology - measuring periphyton biomass

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