Investigation of the effect of hydrological and biogeochemical linkages in the transition zone between streams and surrounding soils on invertebrate community structure as part of the McMurdo Dry Valleys Long Term Ecological Research (LTER) project. The invertebrate community structure with relation to soil moisture, salinity, and chlorophyll-a was determined. The study took place on 28 November 1997 and 31 December 1997 at the Von Guerard Stream/Harnish Creek network.
Approximately 1500g of soil or sediment were collected into Whirl-Pak(tm) bags with clean plastic scoops from 5 sections (0, 8, 16, 24, and 32 m away from the stream) along each transect. Five grams of sediment/soil were also collected from the top 1 cm for measurement of chlorophyll-a concentrations. Samples were mixed within the bags, placed into insulated coolers, and transported for analysis to the McMurdo laboratories. The soils were processed within 24 days of collection from the field. Until then, the soils were stored in a 4_C refrigerator. To extract the anhydrobiotic (coiled) nematodes, 100g of soil were placed into a beaker with 200mL 1.25M sugar solution. Then, a long spatula was used to stir the soil so that it was suspended in the sugar (30 seconds of stirring). Next, the sample was poured onto a set of No. 40 over No. 400 U.S.A. standard testing sieves that had been pre-wetted with 1.25M sugar solution. The top screen was rinsed with 1.25M sugar solution and then removed. The bottom screen was rinsed with 1.25M sugar solution that was squirted only on the front of the screen at an angle. Using this rinsing method, the soil was carefully worked to the bottom wedge of the screen, and the sugar volume was reduced by gently tapping the screen and letting more solution pass through. Next, the sample was rinsed into a 150mL beaker through a funnel, and then the funnel rinsed to catch any residue. Once the sample was collected into the 150mL beaker, the sugar and sediment was pipetted (using an automatic pipette) into a centrifuge tube containing 2M sugar solution. The pipetting was done slowly and at an angle so that the boundary between the two sugar layers was maintained. Then the beaker was rinsed with 1.25M sugar solution and the dregs were pipetted into the centrifuge tube as well. When necessary, more than one centrifuge tube was used to collect all the sample. Next, the tubes with sample were centrifuged for five minutes at 1744 RPM. Then, the liquid contents of the tube were poured through a No. 500 sieve. Finally, the contents of the sieve were rinsed into glass centrifuge tubes and stored at 4_C until counting. Samples were washed in to a counting dish and examined under a microscope at x100 or x200 magnification. Nematodes were identified as coiled or straight and counted. Total numbers in each sample were recorded on data sheets. Data were entered in to Excel files, printed, and checked for errors.