One of keystone programs of MiCorps is the Cooperative Lakes Monitoring Program (CLMP). The CLMP has been around since 1974… that is an impressive length of time! Since that first year, the thousands of CLMP volunteers across Michigan have:

• Taken 92,185 secchi disk measurements,
• Grabbed 4,274 water samples for phosphorus analysis,
• Filtered 5,956 water samples for chlorophyll,
• Made 2,023 observations of the dates that ice melted off their lakes,
• Measured dissolved oxygen and temperature 52,290 times and created 3,486 dissolved oxygen and temperature lake profiles, and
• Searched 17 lakes for exotic plants and mapped out full plant communities on 12 lakes.

All of this data is entered by our volunteers and staff into a publicly accessible and searchable database!

In total, 827 inland lake basins have been monitored through one test or another through the CLMP. Michigan lake volunteers have contributed about 57,400 hours of work, not counting the time spent driving samples to State offices and going to trainings. Assuming field technicians across this time period would make an average of $9/hour, that means these volunteers have donated well over a half a million dollars in labor.

With 39 years of data comes a variety of ways to consider how Michigan lakes have changed over time. In this article, we will take a closer look at two issues that CLMP data can address: trends in trophic status, and the effects of zebra mussels on lakes.

Changes in lake trophic status

A lake’s ability to support plant and animal life defines its level of productivity, or trophic status. Lakes are commonly put into categories based on their productivity. These categories range from oligotrophic, to mesotrophic, to eutrophic. Oligotrophic lakes are generally deep and clear and have little algae growth and consequently cannot support fish populations. By contrast, highly productive eutrophic lakes are generally shallow, turbid, and support abundant aquatic plant growth and fish, provided that they don’t develop low dissolved oxygen levels. Lakes that fall between these two classifications are called mesotrophic lakes. All of these categories can be more truly understood as a continuum; for example, a mesotrophic lake may be bordering on oligotrophic while its neighbor lake may be mesotrophic but bordering on eutrophic. For more detail on trophic states, see CLMP’s annual report.

The volunteers enrolled in the CLMP take water transparency, phosphorus, and chlorophyll measurements for their lakes, which are used to place that lake into one of the trophic categories. By taking these measurements year after year, we can track how individual lakes change as well get a sense of how the overall condition of lakes in the program are changing in time.

Michigan has a mix of oligotrophic, mesotrophic, and eutrophic lakes. From 1980 through 2000, about 65% of lakes in the CLMP were classified as mesotrophic, about 20% were oligotrophic and 20% were eutrophic. Hypereutrophic lakes, which are lakes on the very high end of the eutrophic category, are rare, but there are usually 2 or 3 of these lakes enrolled in the program at any one time.

In 2010, there were significantly more oligotrophic lakes in the program (34%), while the numbers of eutrophic (11%) and mesotrophic (54%) lakes dropped. This result can indicate one of two things: 1) more oligotrophic lakes joined the program and perhaps the other types lakes dropped out, or 2) lakes that were previously categorized as mesotrophic had an improvement of water quality and were reclassified as oligotrophic.

The results indicate that the second option above is indeed what is happening here. By only looking at lakes that were enrolled in the program throughout 1980-2010, we do see that many of them change from a mesotrophic to an oligotrophic state. Therefore, we do have evidence that some lakes are becoming less productive over time, probably due to improved lake management activities, or in some cases, zebra mussels.

A valid question to ask is whether this analysis can be applied to all of the lakes in Michigan. Certainly, the Upper Peninsula is very underrepresented and thus this analysis should not be thought to reflect conditions there. In addition, lakes enrolled in the CLMP are usually monitored because there are many people that live on those lakes and care for them. With this in mind, it is reasonable to argue that these results can be representative of residential lakes in the Lower Peninsula.

Changes in lakes in relation to zebra mussels invasions

Through the help of CLMP volunteers throughout Michigan, I obtained the infestation years for 206 lakes enrolled in the CLMP. I more closely examined 30 lakes which had at least 6 years of secchi disk transparency data for both before and after the lake was infested. Where it was available, I also looked at the phosphorus and chlorophyll data for these 30 lakes. It was readily apparent that lakes respond in a huge variety of ways to the presence of zebra mussels.

Eleven of the 30 lakes showed the expected response with a noticeable increase in water transparency after the zebra mussel invasion. For example, after the zebra mussels entered Van Etten Lake in 2001, the average transparency increased from around 5 feet to around 9 feet. The total phosphorus also decreased significantly, and the average chlorophyll measurements decreased slightly.

Fourteen of the 30 lakes did not seem to change at all after the zebra mussel invasions. The exact reason for this differs from lake to lake, and would be impossible to determine without a concentrated study of each of the lakes. One possible explanation is that the zebra mussel population was never able to flourish, perhaps because of the lack of suitable hard surfaces for the mussels to latch on to. Another possible explanation for this is that nutrient inputs increased to the lake and were able to nullify the effect of the mussels. Corey Lake in St. Joseph County is one example of a lake that did not change after zebra mussel invasion.

Five of the 30 lakes changed in a manner that is contradictory to the expected results of a zebra mussel invasion; the lakes had a reduction in water transparency. This rather confounding discovery makes it clear that in dealing with biological responses, the analysis is rarely cut and dried, and there are a myriad of environmental variables that are acting upon the system which are difficult to quantify or understand. Cedar Lake in Van Buren County is an example of this intricate issue. After the zebra mussel invasion, the average secchi transparency decreased from 16 feet to 12 feet, while both the phosphorus and chlorophyll also dropped. This is the expected response from phosphorus and chlorophyll, but the opposite response from water transparency.

Conclusions

Thirty-nine years is a long time for any program to run, and this should be a cause of celebration for the MiCorps community. However, lakes change over the course of decades and centuries, so we need to stay vigilant in monitoring and measuring. Collecting and analyzing water quality will continue to be an important part of understanding how human activities affect our lakes and will continue to inform planning and management decisions.  

Author:
Paul Steen, Ph.D.
MiCorps Staff
Huron River Watershed Council