Lakes Monitoring Resources
LEARN MORE ABOUT MINNESOTA'S LAKES
What is Limnology?
Limnology is the study of freshwater and saline inland waters. It includes studying the physical, chemical and biological components of lakes, reservoirs, ponds, streams, rivers, wetlands, and estuaries. Oceanography differs because it is the study of the open ocean. Freshwater ecology differs because it is the study of just freshwater systems and does not include saline inland water.
Water Quality Parameters
Volunteers in the RMB Lakes Monitoring Program collect samples and record observations for three water quality parameters: Total Phosphorus, Chlorophyll-a, and Secchi Depth (Transparency). These three parameters are inter-related, and as a whole produce a comprehensive picture of lake water quality. As Total Phosphorus and Chlorophyll-a concentrations increase, Secchi disk depth decreases. These three parameters are also collectively used to determine Mean Trophic State Index.
Total Phosphorus
Phosphorus is a nutrient important for plant growth. In most lakes, phosphorus is the limiting nutrient that impacts plant and algal growth.
Chlorophyll-a
Chlorophyll-a is the pigment that makes plants and algae green. It is tested in lakes to determine how much algae is in the lake.
Secchi Depth (Transparency)
Transparency is how easily light can pass through a substance. In lakes, water transparency is measured using a Secchi disk.
Parameter Relationships
Total phosphorus (TP) is a “cause” parameter, while chlorophyll-a and Secchi depth are “effect” parameters. When TP increases, that means there is more food available for algae, so algal concentrations increase. When algal concentrations increase, the water becomes less transparent (cloudier), and the Secchi depth decreases. By measuring each of the three parameters, we can better pinpoint the source of water quality improvement or decline.
Trophic State Index
The results from these three parameters cover different units and ranges and cannot be directly compared to each other. In order to standardize these measurements to make them comparable, they are converted to a trophic state index (TSI).
Lake Trophic States
Scientists like to classify lakes and give names to the different lake types so they can be easily referred to. Trophic states are based on lake fertility. The root “trophy” means nutrients; therefore, lakes are classified based on the amount of available nutrients for organisms.
Lake Eutrophication
Eutrophication is a natural aging process that a lake goes through over hundreds to thousands of years, where the lake becomes shallower and more fertile. Humans can speed up the process of eutrophication by adding excess nutrients and sediment quickly.
Additional Limnology Topics
The following resources cover additional lake topics such as Minnesota's ecoregions, lake stratification and mixing, dissolved oxygen, and more!
Minnesota Ecoregions
Have you ever wondered why the lakes in southern Minnesota are generally shallower and “greener” than the lakes in northern Minnesota? This difference is mainly based on a lake’s ecoregion. An ecoregion is a geographical area where the land use (agriculture, forest, prairie, etc.), underlying geology, potential native plant community, and soils are relatively similar.
Lake Stratification & Mixing
To understand lake stratification, we first must address the relationship between water density and temperature. Water is unique in that it is denser as a liquid than a solid; therefore, ice floats. If ice sank, our lakes would behave much differently in the winter! Most lakes in Minnesota are considered dimictic, meaning they mix twice a year – spring and fall. Shallow lakes behave differently and can mix more often.
Dissolved Oxygen
Dissolved Oxygen (DO) is the amount of oxygen dissolved in lake water. Oxygen is necessary for all living organisms to survive except for some bacteria. Living organisms breathe in oxygen that is dissolved in the water. The amount of oxygen lake water can hold is directly related to temperature. The colder the water, the more dissolved oxygen it can hold.
Water Cycle
The water cycle (also called the hydrologic cycle) is the continuous movement and storage of water across the earth in all forms: liquid, solid (ice), and gas (water vapor).
Fish Distribution
Different species of fish require different habitats and food sources for survival.
External Resources
The following links will bring you to external resources to keep learning about our lakes!