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

Chapter 2 - Lakes

A Typical Lake Monitoring Program

Getting Started

The first step in beginning any monitoring program is to think about your objectives or purpose for monitoring as discussed in Chapter One. Your monitoring plan may not be anything like someone else’s plan if your goals and objectives are different. Some typical objectives for citizen monitoring include characterizing the entire lake, learning about how lakes function, or assessing general lake water quality trends.

Once you have defined your purpose for sampling, you can figure out where to collect the samples, what analyses to perform, and when to do the work. The complexity of your program also will be affected by the number of volunteers and your budget.

It is often useful to begin a lake monitoring program by obtaining or drawing a rough map of the lake. Show the inflows and outflows; mark the shallow portions of lake and know deep "holes;" and show any aquatic plant beds, rocky shorelines, or other physical differences you may have noticed. Note the prevailing wind direction. You also may want to locate or record such things as the presence of stormwater runoff pipes or culverts, types of shoreline vegetation (lawns, native vegetation, or agricultural land), and adjacent land use.

Depending upon the location and development pressure around your lake, it may be interesting to revise this may periodically to provide ongoing documentation of factors that will influence lake water quality.

Selecting Sampling Locations

The selection of sampling stations is directly dependent upon your monitoring objectives. If your objective is to characterize the entire lake, and it happens to be a large lake with a number of shallow bays inflowing streams, or other distinguishing characteristics, then it is likely a number of stations will be needed to provide an adequate characterization. If your objective is to learn how lakes function, stations in physically diverse locations (bays and open water) and at different depths should be selected. Conversely, if tracking water quality trends is your objective, it could be argued that one station could be used to represent any lake.

Avoid sampling near shore, near inflows, or in the downwind direction. Prevailing winds blow algae, zooplankton, and debris down the lake and toward the shoreline; samples collected in these areas are less representative of the lake’s overall water quality. If a boat is not available, choose a location about midway down the shoreline and sample off a long pier, using a pole to collect the sample as far from the shoreline as possible.

In deep lakes, sampling two depths (near surface and near bottom) is a good idea. In a large lake, if you have sufficient volunteers and money for more than one station, choose additional stations according to your interests or physical aspects of the lake. For example, you may want to compare the mid-lake station to a shallow bay. If the lake is long, you could establish stations in a transect along the midsection. Addition of a station at the mouth of important inflowing streams will help you figure out how much they contribute to pollution in the lake.

You will always want to return as near as possible to the same location in the lake. Obviously, if you are sampling from shore this location is easy to document and remember. However, if you are sampling from a boat, it can be a little more difficult. Identify landmarks along the shore and line the boat up with them and document the location. An example field note – "Line the boat up on a visual transect between the small yellow house on the northern shore and the gray barn on the southern shore, and follow along this transect until the inflow at the eastern tip of the lake is directly across from the boat. Drop the anchor here." (By the way, it is important to use an anchor so you don’t float away from the station during the sampling.)

Selecting Parameters

Water quality parameters, too, should be selected to meet project objectives, number of volunteers, and available money. Field measurements such as pH, temperature, dissolved oxygen, and Secchi depth are inexpensive to measure once the initial equipment or chemical reagents have been purchased. This information alone is enough to do a general water quality assessment, determine trophic state, provide plenty of educational information, and even describe water quality trends if data are collected for a long enough period. Including additional parameters such as nutrient analyses and chlorophyll a just provides more in-depth information for meeting these same objectives. 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 will be money-dependent. If only a few nutrient or chlorophyll a samples can be collected, pick the stations that best meet your monitoring objectives. Information on how to collect samples for each of these measurements and different methods for analysis are described in Chapter Four.

When to Sample

Again, the monitoring objectives will be the primary factor influencing when to sample. The following assumes your monitoring objectives are fairly general.

The most critical time period in a lake is typically during the growing season. For general water quality assessment purposes, it is sufficient to monitor from April or May through September or October, either monthly or preferably, every 2 weeks. For general purposes, there is little benefit in monitoring more that every 2 weeks and, in fact, for some parameters there are statistical reasons for not doing so. If you choose to sample a lake throughout the year, even research professionals typically sample only monthly during the winter.

Samples also should be collected at about the same time of day each time you sample. This allows for some consistency in daylight hours and in all the indirect effects daylight has on the different lake processes.

Example Lake Monitoring Strategies

Educational Monitoring

In this example, the purpose of the monitoring program is not to identify or rate water quality problems, but to learn about how lakes function. The monitoring program is designed to emphasize the changes or differences between stations or through the year. DO, temperature, pH, and Secchi depth are good parameters to start with. If money were available to measure nutrients, TP and SRP would probably be the best choices. These parameters should all change noticeably with season, depth, and probably station. If the lake is deep and more than one station can be sampled, sampling at two depths likely will be more informative than sampling at two stations. Additional stations might be added to show the effect of shallow bays, inflowing streams, or other characteristics. Sampling could occur on a one-time basis or a few times through the summer and maybe once during the winter – depending of course, upon how much time you wish to spend.

General Lake Characterization

Here the objective is to collect information from all portions of the lake as a kind of baseline study to better understand the lake. Many stations would be selected to characterize each of the different parts of the lake. The inflow, outflow, small bays, weed beds, a transect of stations along the mid-section of the lake, and at two or more depths at each station are a few ideas on what stations you might select. All the parameters described would be needed for a thorough characterization. Sampling through one season would probably provide enough information to generally characterize how the different portions of the lake function. Because of the general nature of this objective, there would be little merit in continuing a sampling program such as this for very long. Perhaps after the first season a few sampling sites would be excluded and the parameters sampled would be pared down to create a less costly, more focused long-term sampling program.

Water Quality Assessment

In this case, the objective is to determine or even rate the water quality of the lake. DO, pH, temperature and Secchi depth would of course be sampled because they are easy and inexpensive. TP, SRP, and perhaps chlorophyll a would be sufficient to allow you to rate the water quality in most cases. For many scientific purposes, TN, NO , NO , and NH , data would be a great advantage. Sampling at one station and two depths would likely allow an adequate general assessment. If the ultimate objective was to use this assessment data to monitor water quality trends, the sampling program would last for a number of years and then be reinstated every few years to continue the trend monitoring.

Most monitoring programs that are not purely educational actually fall somewhere between the general characterization approach and the water quality assessment approach. Typically, at least tow stations are monitored (more in a bigger lake), and all the parameters listed are monitored, at least at the two most important stations or depths. At less important stations, just the field measurements (DO, pH, temperature, and Secchi depth) are usually taken.

The next section of Chapter Two - Lakes - provides information about how to report and analyze lake water quality data.

Return to Table of Contents | Lakes | Streams | From the Field to the Lab | Hydrology

Last updated on April 01, 2008