Barrie Creeks, Lovers Creek, and Hewitt's Creek Subwatershed Plan

The Barrie Creeks, Lovers Creek and Hewitt’s Creek Subwatershed Plan
5.3.7 Loss of riparian vegetation
While many policies now afford some protection to the riparian areas adjacent to the
watercourses, this has not always been the case. In many instances, vegetation in the riparian
areas of the subwatershed’s watercourses has been removed to accommodate urban
development and agricultural activities, leaving the bank vulnerable to erosion due to the
removal of the stabilizing influence of the roots of the vegetation. This can result in inputs of
sediment into the watercourse, which can settle and smother the substrate, thus eliminating
important habitat used by fish for spawning and inhabited by benthic invertebrates. Sediment in
suspension in the water can also interfere with the feeding of those fish species that are visual
feeders.
Riparian vegetation is also an important source of allochthonous material such as leaves and
branches that serve as a food source for benthic invertebrates, and can also provide cover for
fish.
In addition, riparian vegetation serves to enhance water quality – it filters the water flowing
overland, causing sediment and other contaminants to settle out or be taken up prior to reaching
the watercourses; and also helps to moderate water temperatures through the shade it
provides. Removal of this vegetation can have an influence on the type of aquatic community
able to inhabit the watercourse – a reach that may have been able to support a healthy
coldwater community may no longer be able to do so, and the community may shift to cool or
warm water community containing less sensitive species.
5.3.8 Water quality and thermal degradation
Inputs of contaminants, including high levels of chloride and suspended sediment, to
watercourses can be harmful to many species of fish and benthic invertebrates, particularly the
more sensitive species. It can force them to leave their habitats, inhibit their growth, or cause
die-offs if concentrations of a contaminant get too high.
Specific information on water quality issues pertaining to these subwatersheds can be found in
Chapter 3 - Water Quality.
Thermal degradation of a system can be caused by a number of factors. The first is the removal
of riparian vegetation and the shade that it creates. If large portions of a watercourse are
shaded, these areas may be key in maintaining cold or cool water temperatures or may be a
refuge for cool or cold water aquatic species during the hot summer temperatures. Runoff can
also cause thermal degradation in a system. As impervious surfaces (such as pavement) heat
up from the sun they easily warm any water running over them, creating a warm water source
as the water drains into a watercourse, possibly rendering the surrounding waters uninhabitable
for coldwater species. Lastly, the detention of water in a pond creates a source of warm water
into a system as it increases the surface area of the water that is exposed to sunlight, and
keeps it there for a prolonged period of time, leading to warming. Although online ponds are the
greatest concern due to their direct impact on the watercourse, offline ponds (including
stormwater ponds and detention ponds for irrigation) that discharge to watercourses are also a
concern.
Figure 5-13 illustrates the OMNR approved temperature designation of the creeks (and the
temperature at which they are managed at based on timing restrictions for in-water works) with
current temperature ratings. Where the current ratings differ from OMNR designations (i.e. cool
or warm water readings on cold water system) it indicates that the creek is experiencing thermal
degradation.
Chapter 5: Aquatic Natural Heritage 233