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Water Wisdom: Factors contributing to last summer’s algae bloom

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By Kristin Gardner EBS CONTRIBUTOR

The Gallatin River Task Force recorded the highest average weekly water temperature in the past ten years in the West Fork during the last week of July 2018. This week aligned with the beginning of the 2018 algae bloom and suggests that water temperature, in addition to elevated nutrients, may have been an important factor that contributed to increased algae growth.

These results corroborate recent findings from a Montana Department of Environmental Quality study on the Smith River. Chace Bell, MT DEQ water quality monitoring specialist, said that a suite of factors influences river algae growth, and that their analyses points toward drivers such as long-term increases in water temperature in the spring and early summer, nitrogen and phosphorus concentrations, hardness, pH and water velocity and clarity.

This recent finding is another piece of the puzzle to explain why the Gallatin River and some tributaries experienced an unprecedented algae bloom in July and August last year. Previously, the Task Force reported that nitrogen levels in the West Fork were some of the highest ever recorded; however, other years with comparable levels did not result in such a significant algae bloom.

So, how was 2018 different from other years?

Historically, excess algae has been documented in the mainstem Gallatin, downstream of the West Fork; South Fork; and Taylor Fork. But never before were algae levels as high or as widespread as those observed in 2018.

Although streamflow was significantly above average during spring runoff, flows lessened to just slightly above normal levels during July and August. River users reported bright sunny days with little rain in July, which was verified by below average precipitation at the weather station in Meadow Village.

GRAPH COURTESY OF GALLATIN RIVER TASK FORCE

According to Pat Straub, former owner of Gallatin River Guides, “2018 was the only summer since we purchased GRG in 2012 that we did not have to cancel one fishing trip because of the Taylor Fork or West Fork blowing out from a significant rain or thunderstorm event.”

So, was 2018 the perfect storm of favorable conditions to promote algae growth? To be certain, the Task Force needs more data and has plans for an extensive study this summer, pending sufficient funding. The 2018 algae bloom shed light on just how sensitive and vulnerable the Gallatin is to changing conditions. Now more than ever, the Gallatin needs dedicated stewards to protect this invaluable community resource.

This is the first of two installments about the 2018 algae bloom and strategies to make the Gallatin more resilient. Stay tuned for the second installment, which will address steps that we, as a community, can take to make the Gallatin more resilient to future blooms.

Kristin Gardner is the executive director of the Gallatin River Task Force.

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