Aquatic plants are an important ecological component of lakes. They produce oxygen from photosynthesis, provide food and habitat for fish, and help stabilize shoreline and bottom sediments.
The distribution and abundance of aquatic plants are dependent on several variables including light penetration, bottom type, temperature, water levels, and the availability of plant nutrients. The term aquatic plants" includes both the algae and the larger aquatic plants or macrophytes. The macrophytes can be categorized into four groups: emergent, floating-leaved, submersed, and free floating. Each plant group provides unique habitat essential for a healthy fishery.
Hess Lake has the potential to naturally support abundant plant growth, both rooted plants and algae. Historical data indicated that Hess Lake once contained abundant rooted plants but, in recent years, the lake is prone to persistent algal blooms and macrophyte growth is minimal. In the absence of rooted plants, algae has become dominant in Hess Lake, and summer algae blooms are common. The lake’s reduced water clarity favors algae growth: Rooted plants don’t receive enough sunlight to stimulate their growth, while algae cells concentrate near the surface where light is plentiful. Algae growth further reduces water clarity and the cycle is perpetuated. Recent studies show blue-green algae, primarily Microcystis, is the most common type of algae in Hess Lake. Blue-green algae (also called cyanobacteria) are generally considered to be nuisance species due to their tendency to form unsightly floating scums at the lake surface. Another concern with cyanobacteria is the potential to cause harmful algal blooms (HABs) by releasing toxins into the water that, at elevated levels, cause health concerns. Recent monitoring of Hess Lake conducted by the Michigan Department of Environment, Great Lakes, and Energy indicates that while HABs have been detected in the lake, they rarely reach levels that exceed public health standards.
Secchi disk in algae
To understand the challenges of managing shallow water lakes like Hess lake, watch this video.
Purple Loosestrife is an exotic emergent plant species commonly found around lakes and in wetlands. If left unchecked, it can spread rapidly, outcompeting more beneficial native plants. Purple loosestrife may be controlled by three methods:
1. Manually remove by pulling plants out by the roots.
2. Herbicides like triclopyr are effective in killing the plant.
3. Loosestrife beetles may successfully reduce dense stands of purple loosestrife.
To measure current plant cover and bio-volume (i.e., the height of plants in the water column) hydro-acoustic surveys of Hess Lake are being conducted annually. When plants grow to the surface, they occupy 100% of the water column, and those areas are shown in red on the map. When plants are not present, 0% of the water column contains plants, and those areas are shown in blue. When plants grow half-way to the surface, they occupy 50% of the water column, and are shown in yellow. The plant bio-volume map of Hess Lake shows very little submersed plant growth currently present in the lake.
While most aquatic plants are beneficial, exotic (i.e., non-native) plant species are a problem in many lakes. In Michigan, an exotic plant of primary concern is Eurasian milfoil (Myriophyllum spicatum). Eurasian milfoil generally becomes established early in the growing season and can spread rapidly by vegetative propagation (i.e., small pieces of the plant break off, take root, and grow). The plant often forms a thick canopy at the lake surface that can degrade fish habitat and seriously hinder recreational activity. Eurasian milfoil infestations have been a problem on Hess Lake is past years.
Eurasian milfoil (Myriophyllum spicatum)
Eurasian milfoil (Myriophyllum spicatum) distribution map
Early detection and rapid response are key to effective control of invasive aquatic plant species. Each year, multiple surveys of the lake are conducted to measure plant cover and to identify exotic plant locations. If warranted, targeted treatments of exotic plants are conducted to limit their spread. The herbicide treatments require a permit from the Michigan Department of Environment, Great Lakes, and Energy. The permit dictates herbicides that are allowed, dose rates, plants targeted for treatment, and specific areas of the lake where treatments are permissible. The herbicide treatment program on Hess Lake is limited and designed to control exotic, invasive plant species while preserving beneficial native plants.