Mechanical Harvesting
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Lakewide / Whole Lake Management Activities
1. Mechanical Harvesting
• Principle
Mechanical harvesting is the physical removal of rooted aquatic plants (macrophytes) from the lake using a mechanical machine to cut and transport the vegetation to shore for proper disposal. This is one of the most common methods of aquatic vegetation control in New York State.
The physical removal of macrophytes serves to eliminate the symptom of excessive vegetation growth.. Immediately after harvesting, swimming and boating conditions are improved. Harvesting also serves to remove the nutrients, primarily phosphorus, stored in the plant structure thereby addressing one contributor to the cause of excessive rooted vegetation growth.
One or two harvest in a season is enough to control the growth of commonly targeted dense growing species (Kimbel and Carpenter 1981). Few cycle of removal program can effectively reduce the reoccurring growth of weeds (Louda and Stiling 2004), as seeds are regularly removed from the growing cycle, which results in removal of biomass and finally leads to long-term nutrient reduction.
Harvesting and removing cut plant material is important, because it decreases the excess nutrient loading, which may result in eutrophication (Carpenter and Adams 1978, Mahujchariyawong and Ikeda S 2001). It is predicted that half of the flux of dissolved total phosphorus (DTP) and dissolved organic material (DOM) from the littoral zone to the pelagic zone is due to the decay of aquatic plants (Carpenter 1980). The prediction, based on a eutrophic hard water lake in Wisconsin, suggests that aquatic plants can compose a substantial pool of nutrients that mechanical cutting would free up for algal growth. For instance, harvesting of macrophytes removed 37.4% of the annual phosphorous inputs and 16.4% of nitrogen inputs to a eutrophic lake in Wisconsin during a late August harvest (Carpenter and Adams 1977).
With either harvesting method, the growth rates of some species of aquatic plants may require two or more harvests during the recreational season. This increases the costs and, especially when outside contractors are involved, can create scheduling challenges.
