Did you know that, with the help of the Leelanau Conservancy, water quality samples have been taken the same way in Lake Leelanau for the past 34 years? This past spring, the Lake Leelanau Lake Association engaged Grand Valley State University to take a deep dive into these data to look for long-term trends and highlight what things we might need to keep a closer eye on. We invite you to read our summary of their analysis to learn more about the state of our lake.
In general, the results of the study were not overly surprising; the lake is getting warmer, and the phosphorus concentration is increasing. The good news is that the lake is still considered healthy, but upward trends tell us that we need to double down on our efforts to keep the lake healthy. Below, you’ll find more details on certain parameters that warrant further discussion and monitoring.
Temperature
Over the past 34 years, the water temperature during the summer months (June-September) has increased on average by 0.065°F per year in both North and South Lake Leelanau, which is not considered a significant increase. However, during the warmest months (July-August), the increase has been 0.12°F per year, which is considered significant.
The implications of warming water are noteworthy. As average surface temperatures approach or exceed 77°F (25°C), conditions become more favorable for harmful algae, like cyanobacteria, which produce a toxin that can cause serious illness or death in humans, pets, livestock, and wildlife. Additionally, warmer surface temperatures later in the year can delay the onset and duration of the ice-covered period, impacting key ecological functions of an ice-covered lake.
Lakes that support cold-water fish species are particularly vulnerable to warming. Certain species, like walleye - a common game species in North and South Lake Leelanau - prefer cooler water. As average water temperatures increase, the space that is habitable to species like this can be reduced, potentially threatening their ability to forage, reproduce, and survive through the winter.
The figure below shows the temperature profile of South Lake Leelanau (SLL) from May to October for the past three decades. The water begins to stratify in the spring once the ice is gone, continues until the air cools in the fall, and then the thermal stratification breaks down and mixing occurs. A similar pattern is seen in North Lake Leelanau.
Fish and other lake animals need oxygen to survive, which lakes primarily receive from air at the surface. Species in deeper parts of the lake depend on seasonal boosts of oxygen-rich water through lake turnover, which mixes oxygen through the water column. With warmer temperatures, turnover will begin happening earlier in the spring and later in the fall, lengthening the time before oxygen is replenished at depth. These changes can significantly affect ecosystems. Low oxygen levels can limit the growth of phytoplankton (algae) and zooplankton (microscopic animals) that form the base of the food chain, which in turn could harm species higher on the food chain, such as fish.
South Lake Leelanau Thermal Structure Phosphorus
In aquatic ecosystems, phosphorus is an essential nutrient for plant and animal life, but excess phosphorus can cause significant problems. It acts as a limiting nutrient, meaning its availability controls the growth of algae and aquatic plants. While beneficial in appropriate amounts, excessive phosphorus can lead to excessive algae growth, reduced water clarity, low dissolved oxygen, and potential harm to aquatic life. The data indicate that surface water phosphorus has increased significantly in North Lake Leelanau (NLL) in the last decade and slightly less so in SLL. The overall concentration of phosphorus is still within the healthy range but clearly increasing. Combined with rising surface water temperatures, even small increases in phosphorus can enhance the growth of algae and aquatic plants, potentially leading to nuisance and harmful algal blooms.
How can YOU help protect Lake Leelanau’s water quality?
Directly controlling the increase in water temperature is outside of our control (though we can all do our part to reduce greenhouse gas emissions!), but we can do more to reduce the amount of phosphorus entering our lake, and help improve fish habitat so the fish struggling with increasing water temperatures have a fighting chance.
Prior to the development of the lakeshore, northern Michigan lakes had approximately 100 downed trees in the water per mile of shoreline. These natural woody structures provide crucial habitat for fish. The structure of fallen trees and branches helps protect young fish and other organisms, and the shade provided by the fallen trees helps to cool the water along the shoreline (click here to read more about the importance of wood along the shoreline). YOU can do your part by allowing fallen trees to stay in the water, or you can create new habitat by putting trees in the water; however, a permit from the Michigan Department of Environment, Great Lakes, and Energy (EGLE) is required (see article linked above).
We also have some control over the amount of phosphorus that enters the lake. Even though the Michigan Fertilizer Law (1994 PA 451, Part 85) restricts the use of phosphorus fertilizers on residential and commercial lawns, there are exceptions for using them (see link above), which can result in phosphorus reaching the lake. The most important single action you can take is to naturalize your shoreline. Vegetative buffers provide habitat, and most importantly, reduce the amount of nutrients, like phosphorus, that go into the lake. It is easy to get started, and we have qualified Shoreline Ambassadors to provide you with a free shoreline consultation. Click below to schedule a consultation.
Schedule a Shoreline Consultation
Other common sources of phosphorus are from household cleaning products and septic systems. While some phosphorus is naturally removed through soil filtration and microbial action within the septic system, excessive amounts make it to the lake. Poorly maintained or failed systems can be significant contributors of phosphorus. A septic system’s lifespan typically ranges from 20 to 35 years, but this can vary significantly based on various factors. Proper maintenance (inspections every 3 years) and usage are crucial for maximizing the lifespan and functioning of your septic system. Click here to learn more about maintaining your septic system, and stay tuned for an upcoming article from us with more details on cleaning products, septic system maintenance, and lowinterest rate loans for septic system replacements.
Remember to check the ingredients on the products that go down the drain and make sure they are “phosphate-free”!
What is the Lake Leelanau Lake Association doing to protect Lake Leelanau’s water quality?
Using the information and recommendations from Grand Valley’s report, LLLA is making it a goal to more closely monitor Lake Leelanau’s water quality using State and local programs, such as the Voluntary Stream Monitoring Program and the Cooperative Lake Monitoring Program. These programs bring volunteers AND expertise from the State together to monitor our lake and tributaries. Tributaries supply 40% of the water in SLL, and this will provide an opportunity to assess their health and be proactive.
And as always, education! With a lake whose shoreline is made up primarily of private residences, it is up to you to do your part to protect Lake Leelanau, and we are here to help you become the best stewards of the lake possible.
