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Assessment and control of duckweed in the Maskinonge River, Keswick, Ontario

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Title: Assessment and control of duckweed in the Maskinonge River, Keswick, Ontario
Author: Warren, Jeff.; Neil, John H.
Abstract: An explosive growth of duckweed (Lemna minor, Wolffia sp.) covered 100% of the lower Maskinonge River in 1987 and created problems to commercial and public users. This condition is believed to have been the result of enriched stormwater flow from the surrounding agricultural land gaining access to the water course. During June, July and August 1987, rainfall was above the thirty year average and concentrations of ammonia, nitrate and phosphorus were the highest concentrations reported since implementation of the MOE water quality monitoring program at the Woodbine Avenue location. There has been a recent increase in the acreage of sod farms in the Maskinonge River watershed. The amount of fertilizer applied to sod is significantly greater than quantities used for other agricultural crops. For these reasons changes in land fertilizer use was probably a contributing factor to the problem in 1987 and will be in the future unless corrective action is taken. The study reported herein addresses the cause of the problem and means for future control. Two means to control the problem are discussed; improvement in water quality and the use of herbicides as a preventative measure. Water quality improvement will require the identification of specific sources of nutrients to the watercourse and action to reduce or eliminate them. An objective for water quality equivalent to the Black River is proposed. Herbicide control using Reglone A in nursery areas was found to be an effective means of preventing duckweed growth. The report recommends that a detailed evaluation of all fertilizer use and other potential sources of plant nutrients be made by an enforcement agency and that best available agricultural practice be required as the means to achieve the proposed water quality objective. A water sampling program is recommended to improve the data available on water quality and to identify specific sources of nutrient inputs. It is recommended that herbicide control be continued as a preventative measure until such time as water quality improvements ensure that the 1987 duckweed problem will not reoccur. An estimate of cost to implement the water quality monitoring and herbicide control programs are provided.
Date: 1992
Rights: Queen's Printer for Ontario, Crown Copyright, Non-Commercial Use Permitted
Rights Holder: Queen's Printer for Ontario
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