Intensive in-lake and watershed management caused Kohlman Lake, the northernmost lake in the Phalen Chain of Lakes in Minnesota, to go from a relatively turbid to a clear water state. Aquatic plants responded to the clean waters by growing up to the surface. The change in lake state and a comprehensive water quality monitoring dataset gave researchers an excellent opportunity to develop and assess a strategic aquatic plant harvesting approach to a balanced lake management plan that centers on navigation, recreation, aesthetics, water quality and ecological function.
Aquatic plants provide several ecosystem services such as habitat, food, cover and shading, temperature moderation, and nutrient uptake and sequestration. The overall approach to mechanical weed harvesting was conservative and the plant mass removed from the lake was about 14% of the peak mass that would be present without harvesting.
Harvesting removed 24% of the total phosphorus (TP) captured by aquatic plants and this accounted for 4% of the TP load derived from external sources. In addition, the cost of TP removal by aquatic plant harvesting is quite economical when compared to phosphorus management practices that take place in upland watershed areas. Data from this study suggest that harvesting certainly presents cost-effective opportunities for TP removal and has the potential to factor into dynamic and creative watershed management approaches.
Reprinted with permission from NALMS. The original article published in Lakeline, Volume 40, No. 4 Winter 2020.