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Phycology Section, Patrick Center for Environmental Research

USGS and the Patrick Center:
Algal Biovolumes for USGS NAWQA samples

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Introduction.

The spreadsheet file (available for downloading at the Algal Autecological Data Website) contains average, standard deviation, minimum, and maximum biovolumes (µm3) of 545 algal taxa commonly occurring in samples collected by the U.S.G.S. National Water Quality Assessment Program (NAWQA). Values in the tables are based on over 40,000 measurements made by phycologists in the process of analyzing more than 2,000 quantitative (RTH and DTH) samples collected from 1993 to 2000. Only those taxa for which there were at least 10 measurements are listed. Biovolumes of algal cells ranged over 4 orders of magnitude, from 1.13 to 161643 µm3.

Biovolumes of individual taxa were measured to calculate total algal biovolume, the measure chosen by NAWQA to estimate algal biomass of whole samples. The data are presented here for use by those who may want to use them for their own biovolume calculations or to compare with their measurements. Algal analysts continue to make measurements and values are regularly added to our database. Biovolume calculations submitted to NAWQA are based on the state of the biovolume measurements at the moment the calculations are made. We intend to update annually the list of measurements on this website.

This document describes how cell dimension measurements were made and how the biovolume values in the accompanying table were calculated. More details of procedures are contained in the document describing protocols used for analysis of NAWQA algal samples: http://diatom.ansp.org/nawqa/Protocols.aspx. For more information on the NAWQA program, go to http://water.usgs.gov/nawqa/. Individual measurements used to calculate the biovolumes were made by analysts at The Academy of Natural Sciences (Frank Acker, Todd Clason, Lont Marr, Eduardo Morales, Lara Panayotoff, and Diane Winter), University of Louisville (UL) / Michigan State University (Kalina Manoylov, Eric Jordan, Tom Smith), and by private consultants (Loren Bahls, William Cody, Jackie White-Reimer).


Measurement criteria.

Criteria for determining how many measurements of each taxon to make for each NAWQA study unit changed slightly from the beginning of algal analyses. The basic rule, as originally specified by NAWQA, was to make sets of measurements for 15 cells for each taxon that occurred in abundance of 5% or more in any one sample. As the number of measurements for taxa accumulated, however, the criterion was changed. Only 5 cells were measured for taxa in new study units if the mean of those 5 cells was not significantly different from the mean of all previous measurements from other study units. If the means were significantly different, a full 15 measurements were made for the taxon. A consequence of this strategy was that common taxa accumulated a large number of measurements, and many uncommon taxa had no measurements. The rationale for not measuring dimensions of less common taxa was that those taxa would not contribute significantly to overall sample biomass. To compensate somewhat for lack of measurements for many taxa, measurements were occasionally made on less common taxa, particularly the larger taxa. During 2001, all taxa lacking measurements were assigned dimension values taken from the literature, a practice originated by analysts at the University of Louisville.


Making measurements.

In most cases, measurements were made after all counts were finished. Count data were analyzed to determine the taxa that needed to be measured. Analysts then searched for specimens on slides they had already counted and measured the required number of individuals. Measurements of length and breadth were made using an ocular micrometer. Depth measurements were made on specimens in girdle view, and occasionally by some analysts on specimens in valve view using the vernier scale on the fine-scale focus control.


Data entry and storage.

At the ANSP, most diatom cell dimension measurements were entered directly into the BIOVOL Program ( protocol P-13-39). Each individual measurement was stored in the North American Diatom Ecological Database (NADED). Measurements of soft-algae were first recorded on paper and then all were entered directly into the NADED database. At the UL, measurements of both diatoms and soft-algae were first recorded on paper, one page per taxon. In early 2001, all individual measurements were entered directly from the paper forms into the NADED database at the ANSP.


Creating combined set of cell dimension measurements.

A necessary step for calculating biovolumes is to derive an average cell volume for each taxon. Because there were only a few measurements for many taxa, we decided to combine all available measurements into one data file. This included all cell measurements by ANSP and UL for samples in study units started in both 1991 and 1994. Marina Potapova did some statistical analysis to determine, for several common taxa, if there was a significant difference between biovolumes calculated with data from individual NAWQA study units compared with biovolumes calculated using the full set of measurements. She found no significant differences. It therefore seemed reasonable to use cell biovolume averages based on the full set of measurements for calculating taxa sample biovolumes for all samples. For taxa with no, or incomplete, cell dimension measurements, we used values from the literature. For undescribed taxa with no measurements, we used average values based on measurements typical for other taxa in its genus. Using one of the aforementioned approaches, each taxon was provided a set of cell dimension measurements.


Calculation of average cell biovolume for each taxon.

We calculated average biovolumes for each taxon using the full set of measurements described above. Each individual set of measurements was used to calculate a biovolume for each taxon and then these biovolumes were averaged. Biovolumes were calculated for each taxon using the formula for the geometric shape it had been assigned by the analyst making the measurements. Standard shapes and formulas are shown in the table below. Different analysts may have chosen a different shape for the same taxon. This does not compromise accuracy of biovolume calculations because more than one geometric shape can approximate a cell shape. Nonetheless, we are planning to make assignment of shapes more consistent in the future.


Taxonomy.

The names in the list are those currently used for identification of algae in NAWQA samples collected in 1999-2001 for study units started in 1997. Some names are updated from those used in analysis of samples collected earlier.


Uncertainties.

There are a number of uncertainties in the calculation and interpretation of biovolumes that users should keep in mind. The accuracy, precision, and representativeness of cell dimensions have varying degrees of uncertainty due to measurement error, number of measurements on which averages are based, genetic variability within each taxon, phenotypic variability among geographic regions and types of habitats, and closeness of match between actual cell shape and geometric shape used for calculations. Also, a large and variable component of cell biovolume is the vacuole, so not all biovolume can be considered cytoplasm.


Formulas for Calculating Cell Biovolumes.

Shape Code # Dimensions Formula DimensionA DimensionB DimensionC
Box BOX 3 A*B*C length width depth
Cone CONE 2 A*B*B*Pi/12 height diameter at base  
Cube CUBE 1 A*A*A diameter    
Cylinder CYL 2 A*B*B*Pi/4 length diameter  
Ellipsoid ELL 2 A*B*B*Pi/6 length diameter  
Ovoid OVIOD 3 B*C*(A-B+(Pi/4*B)) length width depth
Rectangular Pyramid RCPYR 3 A*B*C/3 length width depth
Sphere SPH 1 A*A*A*Pi/6 diameter    
Triangular Pyramid TRPYR 3 A*B*C/6 pyramid height triangle base triangle height
Two Cones TWCON 2 A*B*B*Pi/12 height diameter in middle  
Two Wedges TWWEG 3 1/2*A*B*C length width depth
Wedge WEDGE 3 1/2*A*B*C length width depth