Walk in the Woods: We can all help prevent polluting of water that damages fish habitat
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TRURO, N.S. — Every year thousands of Nova Scotians take to the brooks, rivers and lakes to enjoy their favourite fishing spots in hopes of catching that elusive ‘big one.’ Our native speckled trout and Atlantic salmon are two of the most prized fish in the Maritimes. Along with their introduced cousins – Rainbow trout and Brown trout, and a few other new arrivals, there are tens of thousands of hours and dollars spent by fishers as they enjoy their annual outdoor recreation.
Clean, clear waters contribute to a healthy environment for Maritimers and attract tourists to our provinces. We are well known globally for our clean waters and inland fisheries.
Fish need cool, pure, fresh water flowing over a clean gravel bottom for at least part of their life cycle. These conditions are essential for successful spawning and early growth – and for the entire life of some fishes like salmon and trout.
The quality of fish habitat is a major factor that ultimately sets the limit on how many adult fish a watercourse can sustain. Introducing silt into these systems can have very bad, long-term consequences for both fish and people.
What is silt?
Silt is an inorganic material that originates from the gradual erosion of rock. Mid-way in size between sand and clay particles, it makes up a large part of our soils, and under natural conditions enters all streams in variable amounts. Although the term covers a wide range of particle sizes, most silt particles are quite small and are also described as “fines” or “sediment”.
In sufficiently high concentrations, fisheries biologists classify silt as a pollutant. That’s because its nasty impacts are just like other forms of pollution. When silt enters watercourses it is carried by the moving water until settling to the stream bottom wherever water speed slows. Because water also flows through the gravel bottoms of salmonid streams, silt can be carried into the gravel where it becomes trapped among the particles.
Effects of silt
All fish are sensitive to the effects of silt. Healthy spawning gravels that become choked with sediment may be ignored by adults. If eggs are deposited, a blanket of sediment will not only suffocate the eggs but will also smother newly hatched fish or prevent their emergence from the gravel. Juvenile fish use the spaces in the gravel as shelter or escape cover. If these spaces become filled with fine silt, these immature fish are exposed to increased predation or may be swept away by the faster-flowing currents above the gravel.
Silt, suspended in the currents, can damage sensitive gill surfaces or, in high enough concentration, clog the gills until suffocation and death occur. In muddy waters, fish cannot see their insect food supply, and may weaken or die through starvation.
These direct effects of silt on trout and salmon are aggravated by corresponding damage to a major part of their food supply – aquatic insects. Immature mayflies, stoneflies, caddisflies and blackflies have habitat requirements very similar to those of juvenile salmonids. Silt in the water can damage insect breathing organs or clog their feeding apparatus. Settled on the bottom, sediment suffocates invertebrate eggs and plugs the gravel spaces normally inhabited by these insects.
Insect populations are reduced further by silt damage to their major food supply – the algae attached to streambed rocks and gravel. Because suspended fine materials block sunlight from reaching the stream bottom, the growth of these plants is reduced or eliminated. When it settles, this sediment smothers algae already growing and prevents any further attachment to rock surfaces.
Silt can affect salmon and trout populations directly and indirectly. Even small deposits of this material are damaging. This is particularly true if silt is allowed to enter a stream over a prolonged period. There are really no safe levels of silt release.
Silt can enter watercourses due to any activity that disturbs the soil next to or from some distance away where runoff water can carry the silt into the watercourse. Common causes of siltation are road construction, road alteration, ATVs and vehicles in and around wetlands, poorly planned or implemented forest harvesting operations, and machines travelling in and around watercourses.
How can siltation be prevented?
When land use practices are properly conducted, they should have very little harmful effect on streams, and contribute very little silt. It is mostly a matter of planning, staying as far away from streams as possible, not operating in wet and soft conditions, and taking special precautions when this is impracticable.
Guidelines designed to limit sediment damage have been developed by various government departments. Information on construction of roads, ditches, culverts, bridges, sediment traps, and roadside seeding for environmentally sound road construction is available.
The Canada Fisheries Act and various provincial laws restrict activities that adversely affect water quality and fish habitat in, or adjacent to a watercourse. In fact, the Fisheries Act extends an individual’s liability beyond direct watercourse damage to include responsibility for preventing sediment damage anywhere within a watershed. Silt can originate far from the water’s edge.
Landowners, contractors and companies must receive approvals from Nova Scotia Environment and Climate Change for projects that may cause any alteration to a watercourse.
Don Cameron is a registered professional forester