A Citizen's Guide to Understanding and Monitoring Lakes and Streams

Chapter 3 - Streams

Selecting Station Locations

The number of sampling stations and their locations will depend on your objectives, the number of volunteers involved, your budget, and safety and access considerations. If only one station can be sampled, a logical place for it would be at or near the mouth of the stream. (If you are monitoring strictly for fun or for a class project, convenience may be the overriding factor in sampling location). If more than one station can be monitored, the headwaters of the stream or a location well above the area of human impact would be a good choice if you want "background" water quality data for comparison.

If you are interested in the effect of a tributary, locate one station above the tributary and one just below the mouth of the tributary. Pick a spot far enough below to ensure it has completely mixed with the main stream. To compare land use impacts, position stations upstream and downstream of the land use of interest, say a city or farmland. The idea is to isolate the source of interest.

NOTE: Because all stations in the watershed should be sampled on the same day, don’t establish more stations than you can comfortably sample on a short winter’s day.

Selecting Parameters

It often is possible to save money and time by not sampling for every parameter at every station. Like locations, parameters should be selected to meet project objectives, number of volunteers, and available money. Field measurements such as pH, temperature, dissolved oxygen, and stream gage height (see Chapter Five: Hydrology) are quick and inexpensive to measure once the initial equipment or chemical reagents are purchased.

TSS measurements can be made with equipment available at local high schools and so can sometimes be made with little or no lab cast. Turbidity measurements require special equipment and therefore have an associated, though low, lab cost. Usually people choose to measure either turbidity or TSS, not both since in some respects they measure the same thing. Available equipment and money may be determining factors in selecting between them). These measurements (pH, temperature, DO, and TSS or turbidity) alone can comprise an adequate monitoring program – again, depending upon your objectives. Consequently, these measurements often are made at all stations selected.

Including additional parameters such as nutrient or bacteria analyses provides more in-depth information. Since these parameters can be more expensive to analyze – depending upon the measurement method used – a decision on whether to measure them and at how many stations may be money dependent. If only a few of these samples can be collected, pick the stations that best meet your monitoring objectives. If flow measurements are being made, nutrient concentrations should be measured at the same stations to allow calculation of loadings.

Stream flow, although an important parameter, can be time consuming and difficult. Typically, flow is only measured at the most important stations, such as the mouth of the stream and just below tributaries where major changes in flow are expected. Instructions on taking stream flow measurements are included in Chapter Five.

When to Sample

A maximum sampling program would entail sampling every two weeks throughout the year. However, depending upon your objectives, a seasonal approach may be just as effective and will save time and money. This approach would entail biweekly or monthly sampling from May through September and then another spurt of sampling from December or January through March. In this way sampling will be concentrated on the most critical time periods in a stream – the low flow period when temperature and DO levels may be at their extreme, and the high flow period when pollutant loading may be at its peak. You may, of course, choose to sample during just one of these seasons; again, it will depend upon your monitoring objectives. For example, if salmon migration is a concern you might choose to sample only during late summer when high temperatures coupled with low DO could deter migration. Likewise, you might choose to sample only during storm events to estimate peak pollutant loads.

The next section discusses stream monitoring stategies.

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