Rapid decline in Eurasian watermilfoil and planktonic algae in Les Cheneaux waters over a four-year period
Authors: R. Smith
Author Affiliation: LCWC
Journal: Unpublished Report; March 2017
Abstract: Three lines of evidence suggest that characteristics of Les Cheneaux waters have changed during the past four years as reflected by a sharp decline in stemmed aquatic plants, especially Eurasian watermilfoil (EWM), and in free-floating algae (phytoplankton) densities. Eurasian watermilfoil density decreased by 80% from 2013 through 2016 in the two most infested bays, Sheppard and Cedarville, for this period. This is not to say that LCI water quality has declined. In fact, the recreational water quality of LCI waters is excellent. The shift in EWM and plankton densities appears real and, with the decline of EWM as well as the plankton community, long term shifts in the lower aquatic food web could occur. Changes in the lower food web can affect the invertebrate populations such as dragonflies, mayflies and damselflies which, in turn, can affect the fishery.
Two other lines of evidence for shifting water characteristics are the decrease in algae concentration and the simultaneous rise in Soluble Reactive Phosphorus (SRP), a primary algal nutrient during the 2013-2016 period. SRP concentration increased throughout LCI waters as the planktonic algae community density decreased. With SRP being a primary planktonic algae nutrient, it follows that SRP concentrations would increase if the algal population had less demand for using it as a nutrient.