By Charles Wolverton
Water quality sampling has been done on Bear Lake in Manistee County under the Cooperative Lakes Monitoring Program (CLMP) for many years. Secchi disk readings have been taken for over 25 years under the CLMP on Bear Lake by William Fronk and David Adams and others. Charles Wolverton has conducted the total phosphorus and chlorophyll-a water quality monitoring for about 10 years. The continuity of these water quality parameters is critically important to detecting trends in water quality in Bear Lake.
The CLMP has been conducted on many Michigan lakes for over 40 years, making it the second oldest volunteer monitoring program for lakes in the country. Since 1992 the Michigan Lakes and Streams Association has administered the CLMP jointly with the Michigan Department of Environmental Quality (DEQ) and is called Michigan Clean Water Corps (MiCorps). Visit it their website at www.micorps.org for more details about this great program.
The Secchi disk readings are taken monthly during the spring and summer and are conducted by lowering a Secchi disk attached to a measuring tape into the water and recording the depth at which the disk can no longer be seen. A Secchi disk is about 10 inches in diameter and is black and white in alternating quadrants of the disk. The Secchi disk readings indicate the relative clarity of the lake; usually the most clear in the spring and decreasing in clarity during the warm summer months as algae and other organisms are suspended in the water column. A lake with poor water clarity may have issues with excess nutrients that foster growth of algae. This test is best evaluated over a period of years as trends in water clarity are shown.
The total phosphorus sampling is done to determine the amount of this nutrient that is essential for algae and aquatic plant growth and to monitor the trophic level of the lake (i.e. productivity).
The purpose of the chlorophyll-a sampling is to measure the algae biomass in the lake; too much algae is a potential problem for the health of the lake.
Bear Lake has no inlet and only a small outlet, thus the residence time of water in Bear Lake is quite long compared to other lakes that have more “flow through.” During most of the summer there is no water running from the outlet to the lake. The longer it takes for a lake to “change its water” the more potential exists for water quality issues to arise. Bear Lake is spring-fed and is a relatively shallow basin, so nutrients and contaminants may enter the lake via the springs (i.e. groundwater), overland runoff, and stormwater drains. The lake must be monitored if we are to discern trends in water quality and possibly take corrective action before lake conditions worsen.
Water quality samples are processed at my home and frozen for delivery to the DEQ in Cadillac twice; once in mid-summer and once after sampling is completed in mid-September. The DEQ processes the water quality samples and records the findings in an annual report.
The two quantitative water quality tests that I conduct on Bear Lake each year are total phosphorus and chlorophyll-a. Samples are taken at the same location on Bear Lake as located with GPS coordinates. The DEQ determined the sampling location, which is in a basin that is about 23 feet deep.
The total phosphorus sampling is done within two weeks of ice-out in the spring (i.e. spring overturn) and in mid-September in the fall. I use my 14-foot boat to do this sample because I have to be able to extend my bare arm into the water to take the sample. This sample is done by filling two sterile sample bottles with water from one foot below the water surface. The bottles are inserted into the water upside down with the cap removed and when the bottle is about one foot below the water surface the bottle is inverted and allowed to fill with water. Some water is emptied out so the bottle doesn’t split after freezing and the cap replaced. Two samples are taken so a backup sample is available if the first sample is lost or contaminated during the analysis. The bottles are labeled and frozen until delivery to the DEQ.
The chlorophyll-a sample is conducted monthly starting in May and ending in September during a time-slot indicated by DEQ, usually between the 10th and 15th of the month. This sample is more complicated to gather and process than the phosphorus sample. Once the sampling point is reached on Bear Lake, the boat is anchored. A Secchi disk reading is taken to determine the depth of the sampling for the chlorophyll-a sample; the sampling depth is twice the Secchi disk reading (e.g. a Secchi disk reading of 10 feet means the chlorophyll-a sampling depth is 20 feet).
A plastic sample bottle with a rubber stopper is placed in a metal can weighted with a steel plate and hooked to a plastic measuring tape. The rubber stopper has two short plastic tubes through it; one lets air out of the bottle as it is lowered into the water and the other tube lets water fill the bottle as air goes out. The bottle is lowered quickly to the sample depth and then raised very slowly to allow water from all levels of the water column to enter the bottle. As long as the bubbles are rising to the surface I know that the bottle is still filling. That is important because the bottle must not be totally full when raised from the water surface. Thus, a composite sample of the entire water column is obtained.
Two smaller sample bottles are filled from the larger sample bottle; again a backup in case the first sample is lost, etc. Five drops of magnesium carbonate are put in each bottle and gently mixed. The sample bottles are placed in a small cooler for transport to shore.
Once in our kitchen, the chlorophyll-a samples are processed. Fifty milliliters of water from each bottle are placed in a syringe and the water is forced through a fine one-inch diameter filter disc placed in a plastic holder and attached to the syringe. The very small algae in the water sample are captured on the filter disc. The DEQ knows the volume of the sample (50 ml) and can determine the amount of algae on the disc and can thus determine the amount of algae in the lake water. After all 50 ml of water are forced through the filter, the filter is removed, folded and placed in a small glass sample tube and labeled. A second sample is processed in the same way. Human hands never touch the water sample or the filter. The samples are then stored in the freezer until sample turn-in day.
This sampling is important to monitor the water quality of Bear Lake. We need to watch for the early warning signs of water quality degradation and take action if needed to protect this priceless resource we all love.