The Role of Invasive Species on Watershed Health

By Mary Jo Adams, EAC volunteer

It’s often hard to understand how the proliferation of invasive species can influence the health of a watershed.  To make it simple however, it comes down to this: water quality declines when the diversity of species which are integral to the overall ecological health of the landscape is diminished.  A watershed is made up of many, many components. The plants and animals, both large and small (even very small), that inhabit the landscape provide significant ecological services.

A plant or animal can be native or non-native (sometimes called “alien”).  The term “native” usually refers to those species that naturally occurred in any given area prior to European settlement in this country.  A non-native, alien, or introduced species is one that was brought or moved into an area where it normally would not occur.

According to the USDA, an invasive species is:

  1. non-native (or alien) to the ecosystem under consideration AND
  2. its introduction causes, or is likely to cause, economic harm, environmental harm or harm to human health.

Characteristics of invasive organisms include crowding out and out-competing other species so that they are completely eradicated or greatly reduced in numbers.

Autumn Olive. Photo by Mary Jo Adams.

The greatest impact to water quality from invasive species in the Mackinaw River Watershed is primarily from soil instability and runoff due to a loss of ground cover vegetation.  The most common invasive plants impacting the watershed in McLean County  are:

  • Multiflora Rose (Rosa multiflora)
  • Garlic Mustard (Alliaria petiolata)
  • Japanese Honeysuckle (Loncerica japonica)
  • Autumn Olive (Elaeagnus umbellate)
  • Cut-leaved Teasel (Dipsacus laciniatus)

Other invasive species of concern in the Mackinaw River Watershed are Asian Carp, which are found in the river and its tributaries, Lake Bloomington, and Evergreen Lake.

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