Don’t muddy the water. Fine sediment and the potential side effects it can have on trout redds and fish populations.
Sediment is a natural component of a river system. Complex relationships between river processes and landscape interactions determine how much sediment is transported or stored within a system.
Human disturbances and increased frequency of natural disturbances from climate change can increase the amount of fine sediment entering a stream from the landscape and along with it, the potential for disturbance and/or harm to the aquatic ecosystem.
Trout can be affected in different ways by both high levels of fine sediment suspended in or deposited within their habitat. Suspended fine sediment can have direct health effects on adult trout, including increased stress levels, accelerated heart rates, clogging of gills that reduce their ability to breather, or limiting their ability to hunt. While adults may have the ability to move to cleaner water, younger trout are less able to do so. Trout embryos are particularly vulnerable as they are completely immobile while they incubate covered by gravel within the nest or ‘redd’.
During spawning, female trout create the redd for their eggs by using a sweeping motion of their tail to flush out most of the fine sediment within the gravel. This allows for the eggs to have high exposure to water and dissolved oxygen. Increased sediment infills and smothers the redd reducing available oxygen flow around the incubating eggs. The accumulation of fine sediment results in an increased buildup of metabolic wastes and prevents newly hatched trout or ‘alevins’ to escape into the water column. In both field and lab studies, increases in fine sediment have shown to cause high mortalities in embryos, and prevent alevin swim up.
Trout Unlimited Canada continues to conserve, restore and protect native trout habitat with projects such as streamside plantings and installation of instream structures that help to improve the stream’s form, function and enhance habitat. Additionally, collaboration with landowners, especially within agricultural landscapes, can also help to reduce the impacts of too much sediment and nutrients in our rivers and streams, helping to bring them back ‘into balance’.