USGS and the Patrick Center:
Algal Biovolumes for USGS NAWQA samples
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).
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.
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
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.
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.
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.
||diameter at base
||diameter in middle