Methods Manual for Salt Lake Studies/Biological characteristics

Authors: PSJ Coleman,

Overview of biological characterisation

Salt lakes contain both macroscopic and microscopic plant and animal life. A description of the flora and fauna of a lake is an essential part of characterising the lake.

Methods for collecting, measuring the extent and identity of the biota of salt lakes will be discussed more fully in the relevant sections of this manual. This page provides an overview of the types of activities and equipment you may find useful in developing an understanding of the populations of flora and fauna in your lake.

The types of collections and measurements you may wish to obtain could include;

1. Identifying submerged aquatic macrophytes and macroalgae (SAMM), using manual collection, identification (often using a dissecting microscope) and drying & pressing voucher herbarium specimens.
2. Measuring the extent of SAMM using boat transects or aerial photography from aircraft, balloons or kites.
3. Sampling the water column for phytoplankton, using dip samples or a towed plankton net. Counting and enumeration is conducted using a compound microscope.
4. Sampling the periphyton by 'scrubbing' rocks or using artificial substrates. Once again, identification and enumeration require the use of a compound microscope.
5. Sampling benthic mats using coring devices and that trusty microscope again.
6. Sampling aquatic macroinvertebrates using dip nets and kick nets
7. Collecting terretrial invertebrates using light sheets, sweep nets, and other methods
8. Using pop nets, fish traps, kick nets and dip nets to catch fish
9. Undertaking bird point counts and recording calls
10. Recording bat calls
11. Examining the lake edges and playa surfaces for scats and tracks
12. Using hair tubes to determine whether mammals are part of the food web of your lake

Techniques and equipment are detailed in the relevant sections of this manual. Additionally, references to texts that contain detailed descriptions of some of the less common methods or equipment are also provided.

One piece of equipment that is used extensively in investigations of the biota of a salt lake is the compound microscope. The basic use and maintenance of this essential piece of equipment is described here.

The microscope and its use

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The parts of the microscope are labelled in the diagram to the right. Place slide on the stage. Rotate nosepiece so that the x10 objective is in use. Start with the objective down near the slide and coarsely focus upwards by turning the focus control towards the operator. Never focus downwards as the objective could smash into the slide.

Use the fine focus control to gain the clearest image.

Adjust the eyepieces so that the image unites. The eyepieces adjust both for distance between pupils and individual focus. Make sure that the image through the fixed eyepiece is sharp, then adjust the other eyepiece to match. It is often easier to view through a binocular microscope if you don't actually touch the eyepieces, but view from a slight distance.

Close the condenser iris just enough to give the specimen some contrast. It should be about one third closed. Too much closure results in reduction of depth of field. Remove an objective and look down the tube to check on closure.

Maintaining the microscope

Microscopes must be kept clean and dry. Refer to each microscope's manual for details of specific maintenance requirements. General advice is presented here.

Dust should be removed from the eyepieces and objectives using a blow-brush. Stubborn dirt and fingerprints may adhere to the lenses and should be removed using a softly wadded piece of laboratory lens cleaning tissue. If necessary, dampen the lens by breathing on it.

Solvents should NEVER be used to clean a microscope lens or the "blooming" will be removed, resulting in distorted images and "halos" around specimens in the field of view.

Wipe down the body of the microscope occasionally, using a damp cloth.

If an objective should come into contact with brine take immediate steps to prevent damage. Salt will corrode the objective, so unscrew the objective from the nosepiece, then unscrew the outer housing of the objective. Wipe off any brine, paying particular attention to the thread where the objective screws in to the nosepiece. Wipe over with another lens tissue, dampened with fresh water. Repeat with several changes of dampened lens tissue until all salt has been removed. Leave until completely dry before reassembling.

If dirt should enter the body of the microscope, unscrew the objectives and use a blow-brush to remove any loose debris. Regularly check that the condenser iris and lens are in working order.