Streamside livestock grazing
The practice of allowing livestock to access riparian areas in and around a watercourse can result in consumption of riparian vegetation, direct input of faeces into the watercourse and trampling of the banks and bed of a watercourse.
Pathways of Effects diagrams have been developed by Fisheries and Oceans Canada as a tool to communicate potential effects of development proposals on fish and fish habitat and were developed through extensive consultation. It is expected that these diagrams will be updated to describe new activities and stressors as required.
Change in pathogens/ bacterial levels: Contamination of water with the fecal matter of livestock animals can lead to an increase in micro-organisms, such as fecal coli form bacteria. Water may also be contaminated by pathogens or disease producing bacteria or viruses which can exist in fecal material. Fecal coli form adds excess organic material to the water and the decay of this material depletes the water of oxygen, killing fish and other aquatic organisms.
Direct or indirect mortality of fish: Unpolluted and adequate stream flow is required by fish to maintain habitat accessibility, water temperature, and dissolved oxygen levels. Irresponsible water extraction can result in the dewatering of downstream areas, obstruction of fish passage, and entrainment or impingement of fish on pump screens.
Chemical barrier to fish passage: Chemicals associated with animal waste may accumulate to such high levels that render certain areas of a given watercourse inhabitable to fish and other aquatic organisms.
Change in nutrient concentrations: Some activities may cause an increase in nutrifying elements such as nitrogen and phosphorus and mineral compounds such as ammonia, nitrates, nitrites, orthophosphates. This leads to 'eutrophication', thick growths of aquatic plants (especially algae) that block light needed by aquatic vegetation, either by clouding the water column or coating the vegetation itself. When the algae die, they settle to the bottom and are consumed by bacteria during the decomposition process. This process consumes oxygen, depleting it from bottom waters. The resulting low dissolved oxygen concentrations drive fish from their preferred habitat and can cause other organisms to die.
Change in habitat structure and cover: The addition of in-stream organic structure and the deposition of eroded soil can affect the capacity of a watercourse to maintain a dispersed and diverse community of aquatic organisms by restricting habitat connectivity and the opportunities for organisms to use, colonize, and move between existing aquatic environments. The removal of in-stream and riparian vegetation can reduce channel stability, cover and protection from predators and physical disturbances, and the availability of diverse and stable habitats.
Change in water temperature: Water temperature directly affects many of the physical, biological, and chemical characteristics of a waterway. In elevated temperatures, many coldwater fish, such as trout and salmon, could experience reduced reproductive activity or direct mortality, including egg mortality. High temperatures also encourage the microbial breakdown of organic matter, leading to a depletion of dissolved oxygen in the water body.
Potential mortality of fish/ eggs/ ova from equipment: Direct injury or mortality of fish (eggs, larvae, invertebrates, etc.) from physical disruption from equipment or livestock.
Change in sediment concentrations: Increased erosion of stream bank soils and rocks result in an excess of fragmented organic and inorganic material which is transported by water, wind, ice, and gravity. These sediments, which contain nutrifying elements and can capture or absorb contaminants, are suspended or else settle and collect in waterways affecting physical processes, structural attributes, and ecological conditions such as water clarity (by reducing visibility and sunlight and damaging fish gills) and reducing the availability and quality of spawning/ rearing habitat (through infilling).
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