The PLHA takes Water Quality at Posey Lake seriously. Throughout its history, the number one concern of its residents has been water quality. Over the years the PLHA has developed its approach to what measures are prudent to ensure that Posey Lake water quality remains high. Currently, the PLHA has developed these actions:
- Perform testing of Water Transparency and Total Phosphorous through the Cooperative Lakes Monitoring Program (see below).
- Monitor land within the Seeley Drain Watershed for changes that might affect water quality within the watershed, such as farm fields being tiled, newpaper articles addressing the watershed or land near to Posey Lake, or other events regarding inland lake water quality issues.
Cooperative Lakes Monitoring Program
The Michigan Department of Environmental Quality (MDEQ), Michigan Lake & Stream Associations (MLSA), the Great Lakes Commission, the Huron River Watershed Council, and Michigan State University have partners to implement the Cooperative Lakes Monitoring Program (CLMP), to which Posey Lake has been a part of since 1994. Its purpose is to help citizen volunteers monitor indicators of water quality in their lake and document changes in quality. The CLMP provides sampling methods, training, workshops, technical support, quality control, and laboratory assistance to the volunteer monitors. The original program, begun in 1974, monitored water quality by measuring water clarity with a Secchi disk. In 1994, the program was expanded to monitor plant nutrient phosphorus. Currently, the CLMP supports monitoring components for Secchi disk transparency, total phosphorus, chlorophyll a, dissolved oxygen/temperature and aquatic plants. Posey Lake does not participate in the chlorophyll a, oxygen/temperature and aquatic plant monitoring programs.
Secchi Disk Transparency
Secchi disk transparency is measured from late spring to the end of the summer. Ideally, 18 weekly measurements are made from mid-May through mid-September. As a minimum, eight equally spaced measurements from the end of May to the beginning of September are accepted to provide a good summer transparency mean (average) for the lake. Frequent transparency measurements are necessary throughout the growing season since algal species composition in lakes can change significantly during the spring and summer months, which can dramatically affect overall water clarity.
Phosphorus is one of several essential nutrients that algae need to grow and reproduce. For most lakes in Michigan, phosphorus is the most important nutrient, the limiting factor, for algae growth. The total amount of phosphorus in the water is typically used to predict the level of productivity in lake. An increase in phosphorus over time is a measure of nutrient enrichment in a lake. Total phosphorus is measured during spring overturn, when the lake is generally well mixed from top to bottom, and during late summer, when the lake is at maximum temperature stratification from the surface to the bottom. Spring overturn is an opportune time of the year to sample just the surface of a lake to obtain a representative sample for estimating the total amount of phosphorus in the lake. A surface sample collected during late summer represents only the upper water layer of the lake, the epilimnion, where most algal productivity occurs. The late summer total phosphorus results along with the Secchi disk transparency and chlorophyll measurements, are used to determine the trophic status of the lake. The spring overturn total phosphorus data, collected year after year, are useful for evaluating nutrient enrichment in the lake.
Chlorophyll is the green photosynthetic pigment in the cells of plants. The amount of algae in a lake can be estimated by measuring the chlorophyll a concentration in the water. As an algal productivity indicator, chlorophyll a is often used to determine the trophic status of a lake. Chlorophyll monitoring was added to the CLMP in 1998. Volunteers were asked to collect and process five sets of chlorophyll a samples, one set per month from May through September.
Dissolved Oxygen and Temperature
Temperature and dissolved oxygen are typically measured as surface-to-bottom profiles over the deep part of the lake. Temperature is usually measured with a thermometer or an electronic meter called a thermistor. Dissolved oxygen is either measured with an electronic meter or by a chemical test. The CLMP uses an electronic meter (YSI Models 95D, 550A, or Pro20) designed to measure both temperature, with a thermistor, and dissolved oxygen. The meter is calibrated by the volunteer monitor before each sampling event.