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.