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Measuring Impacts of Lake Management Practices on Harmful Algal Blooms using Continuous Monitoring at the Iowa Great Lakes
YEAR: 2020
INVESTIGATORS: Corey Markfort, Gregory LeFevre, Mary Skopec

The nutrient dynamics in eutrophic shallow lakes is complicated by a number of external and in-ternal ecosystem factorsthat control the timing and rates of nutrient availability. Depending on these dynamics,abundant dense-rooted aquaticplants or algal blooms commonlyform. High-value recreational lakes, such as those that comprisethe Iowa Great Lakes, experienceadditional pres-suresdue to invasive speciesand desire to ensure clear,open water conditionsfor recreational purposes.The lakes also serve as a critical drinking water source for local communities. Manage-ment of rooted aquatic plants, includingthe amount andtiming of removal can affect internal re-cycling of nutrients, which may result inconditionsamenable for development of algal blooms.Theseblooms can consist of cyanobacteria (i.e., blue-green algae),or what have become com-monly known as harmful algal blooms (HABs).During their life cycle,HABs lead to unpleasant conditions including blue-green scums on the water surface, and under someconditions HABs release toxins into the water,which present a health risk.With this researchwe propose to addressthe following question: “To what degree doin-lake management activities,designed to improve water quality and recreation at the Iowa Great Lakes,affect the occurrence of algal blooms, particularly harm-ful algal blooms due to cyanobacteria?”Recorded trends of HABs are rising in Iowa and are a major concern due to their impacts on drink-ing water supplies and human health, on recreation, and due to the danger to livestock, pets, and wildlife. A number of Iowa lakes regularly experience HABs. Some lakes,such as Green Valley Lake,experience chronic HABs throughout the summer, while others (e.g.,Lake MacBrideand Big SpiritLake)only occasionally experience blooms.Predicting when andwhere HABs will form is still poorly understood. Nevertheless, withadvances in real-time continuous monitoring, as well as recent investments in water quality monitoring buoys by the Iowa DNR and Iowa Lakeside Laboratoryinstalled on two of the Iowa Great Lakes, there is now an opportunity to investigate how management practices intended to control water quality affect the conditionsthat result in HABs. In particular, internal recycling of nutrients may be affectedby management of invasive rooted aquatic plants, such as curly-leaf pondweed. Investigating nutrient release rates from lake sediments along with trackingthe timing and extent of management activities will provide critical data to better understand the connections between lake water quality management and HABs.Ex-treme weather resulting in sediment resuspension and release of phosphorus from lake sediments may also be a factor in the formationof HABs.

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