Water Quality

Basic and advanced equipment for water quality testing in geoscience labs

• Secchi disk: For lakes, a matte-white (can have two opposite black quadrants) 20 cm in diameter is standard. These can be purchased or made of any material as long as at least half the disk is white. Damaged or dirty disks may not qualify as white. The attached cord used to lower it into the water can have distances (every 50 cm or so) marked with paint, tape, or knots, but should be checked periodically in case the rope or cord stretches. Remember, you'll need to bring a meter-stick too. Survey of The Green Harbor River has more information on Secchi disks and on use of transparency tubes (see below).
• Transparency tubes: to measure clarity of running water. Add water until the tube is filled and then slowly release it with the valve at the bottom of the tube until the mini-Secchi disk at the bottom of the tube is visible. (You may want to record both the water depth when the disk first becomes visible and the (lower) depth when the quadrants are perfectly clear). Record how many cm deep the water in the tube is (centimeter depths should be pre-marked on the outside of the tube using permanent marker). Like its larger relative, the mini-Secchi needs to be kept clean and bright. Transparency tube measurements are easy to make and they correlate well with such water quality parameters as suspended sediment and phosphate content (which themselves are co-related).
• Hester-Dendy invertebrate samplers: These can be purchased or easily constructed of masonite, nuts, bolts and screws. Each sampler should be tied to a brick or piece of concrete to keep it in place in the stream. Leave it in the chosen site for a fixed period of time (at least ten days to two weeks), and invertebrates will colonize the plates that make up the sampler. Have the students count the number (and types) of invertebrates on all the plates, and since you know the plate area, your students can then estimate population densities. The Project GLOBE protocol for macroinvertebrate sampling is a good starting place for information about how and where to sample. This site has information on constructing Hester-Dendy samplers, secchi disks, kick nets and other useful water quality and monitoring equipment.
• Dip nets and kick nets: Great for catching macroscopic insect larvae (and macroscopic insects). These can then be identified to families, and in some cases to species. Some species are very sensitive to certain water-quality conditions.
• Water chemistry (wet) testing: In addition to collecting samples to take back to a lab, some chemistry can be done in the field. There are a variety of kits available. Many of the protocols depend on colorimetry and don't work well if the water is already colored. It is particularly important to test multiple samples for chemical properties because these are not so easy to use. You may want to skip tests that produce hazardous waste that will have to be carried back in order to be disposed of. Two places to start are the Project GLOBE protocol for nitrate measurements and the GLOBE protocol for alkalinity tests.
• Temperature-salinity-conductivity meters: Easy to use, but not cheap (even the "budget" versions recommended for educational use). Bring extra batteries when taking these into the field. Make sure it's one of the waterproof types! Many of these have data-logging capability. See the Project GLOBE protocol on electrical conductivity for more information on these tests.
• pH meters and other ways to measure pH: Depending on what kind of water you are testing and what questions you are asking, litmus paper will probably not be precise enough. Handheld electronic sensors are more precise, but need to be calibrated for readings each day (pH buffers are readily available for this purpose). See the GLOBE protocol on pH measurements for more information.
• Other meters (dissolved oxygen, multi-meters, etc): as with temperature-salinity-conductivity meters.

Some notes on water quality studies

If you are planning to monitor a particular water body over the course of a semester or for many years, keep in mind that for some parameters, such as temperature, dissolved oxygen or pH, it's very important to test consistently at the same time of day (many long-term studies prefer samples to be taken within an hour or two of solar noon). It may also be interested to see how these parameters change in the course of a day. Field equipment may be sufficient for some tests, or it may be more appropriate to have students collect water samples in the field and bring it back to the lab for testing.

For more information on water-quality testing equipment and methods, visit the The Great North American Secchi Dip-In and the GLOBE 2003 Hydrology Chapter (more info) . The Utah Stream Team has some suggestions about making your own monitoring equipment.