Summer Phytoplankton Densities 1992-2001
Phytoplankton were collected over four austral summers (1991-92 through
1994-95) to examine seasonal and annual fluctuation in species composition and biovolume in
Lakes Fryxell, Hoare, West Lake Bonney, and East Lake Bonney. All of these lakes are
perennially ice-covered lakes located in the Dry Valleys of South Victoria Land, Antarctica.
The phytoplankton consisted primarily of cryptophyte and chlorophyte flagellates, and
filamentous cyanobacteria. Some common taxa were vertically stratified (Oscillatoria
limnetica, Phormidium angustissimum, Pyramimonas sp., Oscillatoria sp.), while others showed
no distinct vertical stratification (Chlamydomonas subcaudata, Cryptomonas sp.). The
stratification of the phytoplankton reflects the gradients of nutrients and light, and the
stability of the water column.
Discrete samples for phytoplankton enumeration were collected from the
oxygenated portion of the water column (below the bottom of the ice to a depth of 10 m) at
0.5 m intervals. Sampling was done primarily between the hours of 14:00 and 20:00 (during the
austral summer, the illuminated period is 24 h/day) by either peristaltic pump or Kemmerer
bottle. Samples were collected in 1 l bottles and preserved immediately with Lugon's solution
(American Public Health Association, 1985). Identification and counts were made with an
inverted microscope by the method of Utermohl (1958). At least 100 individuals of the most
numerous algae were counted per sample at 100x magnification. The total number of individuals
counted was dependent on the number of taxa, but ranged between 200 and 500. Counting error
ranged between 13 and 26%, depending on species. Algal species identifications were made
using Geitler (1932), Seaburg et al. (1979) and Prescott (1962). Cell volumes were estimated
for dominant taxa by measuring cell dimensions of 50-100 individuals and using closest
geometric formulas of additional dates and depths to determine changes in cell volume over
time. For rare taxa, volume estimates were made from fewer cell measurements.
Primary productivity was measured using the method of Strickland and Parsons (1972). In situ 24 h
incubations were made in triplicate 300 ml light and duplicate 300 ml dark bottles with
Na14CO3 (3 uCi per 300 ml, New England Nuclear). Following 24 h incubation, samples were well
shaken and filtered through Whatman GF/F filters in the dark. The filters were placed in
scintillation vials and acidified with 1 ml of 5% acetic acid in methanol to remove [C14]
carbonates. The [C14] fixed by biological activity was determined in Aquasol (New England
Nuclear) by liquid scintillation.
Samples for nitrate and orthophosphate were frozen within
several hours of collection, later filtered through 0.45 um Nucleopore filters and analyzed
by air-segmented continuous-flow absorption spectrophotometry (Alpkem RFA-300) (Antweiler et
al., 1993). Chlorophyll extractions were made in 95% ethanol (Jesperson and Christoffersen,
1987) and measured in a Turner Designs Model 10 Fluorometer.
| Variable | Definition |
|---|---|
| Limno Run | Code for lake's sampling location and date Code for lake's sampling location and date |
| Location Name | Name of lake where measurement was made Name of lake where measurement was made |
| Location Code | Code for site where measurement was made Code for site where measurement was made |
| DATE | Date on which sample was gathered |
| Depth (m) | Distance below ice from which sample was drawn |
| Phylum | None Phylum |
| Species | None Species |
| Density (cells/mL) | Density (cells/mL) |
| File Name | Name of file in which data was submitted Name of file in which data was submitted |
