Riparian vegetation keeps water cool—a lifeline for salmon in a changing climate
River Bleng, West Cumbria
As global temperatures rise, water temperatures follow suit—presenting a huge challenge for aquatic biodiversity. Many iconic native fish species including salmonids (Atlantic salmon, brown trout), rely on cool, clean, sheltered water to survive. Thriving river buffers can help address these requirements by filtering pollutants as water travels off land, and casting vital shade over the river that helps stabilize water temperatures.
West Cumbria Rivers Trust investigated the impact of shade on water temperatures in the rivers Irt and Bleng. Summer in-water measurements were taken over a 6-month period at sites with varied tree cover to quantify the value of riparian vegetation.
River Irk site with shade and vegetation cover
River Bleng site with no river buffer and 0% shade cover
Shade-casting buffers give fish a chance to survive
Monitoring showed riparian shade massively reduces water temperatures. Without shade, temperatures reached levels that threatened fish survival.
At the 0% shade cover site on the River Bleng, maximum water temperatures exceeded 27oC on several occasions—the temperature of a swimming pool, known to threaten salmonid survival. Meanwhile, downstream at a site with 80% shade cover, the maximum temperature for the entire summer was only 20 C. On the River Irt, sites with between 50 and 70% shade cover did not exceed 22.5 C—the threshold at which salmon and trout struggle to feed.
Shady river buffers increase the ability of rivers and aquatic life to withstand climate change-related temperature increases. By reducing the impacts of high seasonal temperature spikes, buffers may help aquatic species be more resilient to other pressures.
West Cumbria Rivers Trust has since worked with a local farmer group, National Trust, Woodland Trust, Environment Agency, and volunteers, to establish additional areas of riparian tree cover by installing several tree enclosures.
“Following surveys conducted by the West Cumbria Rivers Trust, we were eager to support the commoners [who graze the surrounding land] by establishing this project. [...] this planting initiative marks an important first step in enhancing the rivers ecosystem—offering shade, contributing leaf litter, and serving as both shelter for livestock and a habitat for birds and other wildlife.”
