Citation:

Fuller, Matthew R., P. Leinenbach, Naomi E. Detenbeck, R. Labiosa, AND D. Isaak. Riparian vegetation shade restoration and loss effects on recent and future stream temperatures. RESTORATION ECOLOGY. Blackwell Publishing, Malden, MA, 30(7):e13626, (2022). https://doi.org/10.1111/rec.13626

Impact/Purpose:

River and stream temperatures are expected to increase as climate change proceeds this century. Consequently, species requiring cold-water habitat will be harmed by rising water temperatures unless habitat restoration or management activities are used to protect or improve available cold-water habitat.Previous research has documented the important local effect shade can have on stream cooling but extrapolating this effect to entire river networks has been difficult. Additionally, we were interested in how stream temperatures might change in the future. Our study approach used regional streamtemperature models to predict mean August stream temperatures across entire river networks flowing into the Columbia River in the northwestern U.S. We evaluated nine scenarios predicting stream temperatures for three riparian shade conditions (no riparian vegetation, current riparian vegetation, andrestored riparian vegetation) and three different climate periods (2000s, 2040s, and 2080s decades). Results suggest riparian shade restoration (for 2000s climate) could decrease mean August stream temperatures by 0.62°C across the study network. Under the same restored shade conditions andclimate, the mean August stream temperature predictions for tributaries at their confluence with the Columbia River range from 0.02-2.08°C cooler than under current shade conditions. We also looked at how state designated water quality standards for temperature would be met for different fish uses inour study system. The proportion of state-designated fish habitat for salmon and trout rearing and migration use in Oregon that meet numeric temperature water quality standards could increase by 20% under restored shade conditions. Overall, our results suggest that riparian vegetation restoration alongtributary streams could be an important strategy for partially mitigating future warming and could help maintain cold-water habitats to benefit resident aquatic species or migratory populations of salmon that increasingly need thermal refuges during the warmest months of the year.

Description:

River temperatures are expected to increase this century harming species requiring cold-water habitat unless restoration activities protect or improve habitat availability. Local shading by riparian vegetation can cool water temperatures, but uncertainty exists over the scaling of this local effect to larger spatial extents. We evaluate this issue using a regional spatial stream network temperature model with covariates representing shade effects to predict mean August stream temperatures across 78,195 km of tributaries flowing into the Columbia River in the northwestern United States. We evaluate nine scenarios predicting stream temperatures for three riparian shade conditions (current, restored, and no riparian vegetation) within three different climate periods (2000s, 2040s, and 2080s). Results suggest riparian shade restoration (2000s climate) could decrease mean August stream temperatures by 0.62°C across the study network. Under the same restored shade conditions, temperature predictions for tributaries at their confluence with the Columbia River range from 0.02 to 2.08°C cooler than under current shade conditions. The climate warming effect predicted for the 2040s and 2080s, however, is greater than the cooling effect from restoring riparian shade. Streams less than 10-m bankfull width cooled more frequently with riparian shade restoration. In Oregon, the proportion of fish habitat for salmon and trout rearing and migration that meet temperature numeric water quality criteria could be increased by 20% under restored shade conditions although net habitat declines may still occur in the future. We conclude riparian vegetation restoration could partially mitigate future warming and help maintain cold-water habitats that function as thermal refuges if implemented strategically.

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