Invertebrate taxa qualitative abundances in reactivated channel


As part of the Long Term Ecological Research (LTER) project in the McMurdo Dry Valleys of Antarctica, water was diverted to a relict stream channel in order to reactivate the streamflow. The purpose of this experiment was to quantify the time scales of response to the arrival of water after many years of dessication. This table contains data showing the prevalence of algal type (brown, red, orange or green) and species for the Relict Channel in the Fryxell basin.

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Within each transect, algal mats were visually identified as either orange, red, black, or green. Not all types of algal mats were found within every transect. A maximum of five algal samples of each color were collected from each transect using a #13 cork borer (diameter = 17 mm, area = 227 square mm). Algal samples were preserved in 10% formalin for laboratory identifications. Preserved algal samples were examined in the laboratory to determine species composition and relative abundance using a Nikon Diaphot phase contrast microscope. Samples were well mixed to attain an even (random) sampling of mat (some small "clumps" of algae were still present, but these did not affect the objectives of the study), and then subsamples of 2 ml were withdrawn. Each subsample was placed in a 2-ml settling chamber with a 26 mm diameter and examined at x400 magnification. To get a representative count of relative species abundance, seven random fields (a total of 0.44 square mm) needed to be examined per subsample. Within each field, algae were identified to genus and species where possible (excluding diatoms, which were counted but not identified.) Percent cover was determined in each field by measuring the length and width of all specimens using an ocular micrometer. Cell "depth" was also measured in order to estimate biovolume. All seven fields were then tallied, and the percentage of the total algal biomass was determined for each taxa. Taxonomic identifications were primarily based on the classical Antarctic literature.


Data from this table was initially included in the raw data files specified under the variable for 'file name'. These are Microsoft Excel version 6.0 files and can be found in the McMurdo LTER data manager's home directory on INSTAAR's Unix system. Once submitted to INSTAAR, the data manager combined all of the Relict Channel files that included variables for "abundance", and removed any variables that had no direct influence on the total biomass (abundance) of a given algal type. The resulting file is represented in the "relicinv.dat" file used on the web page. In October 1998, the data manager reviewed the values provided for location, and found that there was a lack of consistency among Relict Channel datasets that should contain corresponding location values. It was desirable to match locations from this dataset with those represented in the Relict Channel sample locations file, which provides more complete information about the sampling points (eg. latitude, longitude, elevation, location name). Dev Niyogi and Mike Gooseff provided assistance in translating location values, as well as in specifying coordinates for the Relict Channel sample points. As a result, the following records had the original location name replaced with a location code.


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