Riparian Forest Harvesting Effects on Maximum Water Temperatures in Wetland-sourced Headwater Streams from the Nicola River Watershed, British Columbia, Canada

Abstract

Water temperature was continuously recorded during the ice-free season between June/July and October/November at 90 sites with lentic and lotic stream sources distributed throughout the Nicola River watershed (British Columbia, Canada) in 1999, 2000. The eight lentic-sourced stream temperature monitoring sites were located in two adjacent watersheds. The headwaters and riparian areas around the wetland outlet of the treatment watershed were harvested during the overwinter period between 1999 and 2000. Areas around and downstream of the headwater wetland outlet in the control watershed were not harvested. Reducing riparian shade by harvesting activities increased maximum stream temperatures in the treatment watershed by up to 1-2°C relative to the control watershed. Because of the general downstream cooling trends in lentic-sourced headwater streams, riparian harvesting activities in these regions have a reduced thermal impact relative to similar harvesting alongside lotic-sourced headwater streams, whose maximum stream temperatures may warm by up to 8°C following harvesting. The downstream influence of elevated maximum stream temperatures from riparian harvesting of lenticsourced headwater streams appears to be localized, but persists for at least 2 years following harvesting. Both lentic-sourced treatment and control streams in the current study relaxed Water Resour Manage (2008) 22:565-578 towards baseline equilibrium temperature estimated by the lotic-sourced watershed trend within several hundred meters of downstream travel distance, with cooling rates proportional to the distance from expected thermal equilibrium. Due to the heating in wetland-sourced stream reaches adjacent to riparian harvesting, the regions downstream of treatment areas cool more rapidly than similar regions in control watersheds as the stream attempts to achieve thermal equilibrium.

Variable-retention riparian harvesting effects on riparian air and water temperature of sub-boreal headwater streams in British Columbia

“…In contrast, Mellina et al (2002) observed moderate increases in stream temperature ranging between 0.05 and 1.1°C after riparian harvesting of lake fed small streams in the StuartTakla area in the interior of British Columbia. Wetland-headed streams in the Nicola Valley of central British Columbia were found to increase 1-2°C while groundwater streams increased up to 8°C (Rayne et al, 2008).…”

Interactions between water temperature and contaminant toxicity to freshwater fish

“…Interactions between human activities and water temperature are further compounded by factors such as clearing riparian vegetation for agriculture, forestry, or other economic development, which may reduce shading of the water surface and elevate water temperature by between 0.4 8C and 8 8C [13,14].…”

Contribution of climate change to degradation and loss of critical fish habitats in Australian marine and freshwater environments

“…Increased river temperatures are likely to affect the distribution of freshwater species, leading to increased elevation of cold-water species, accompanied by an potential upstream range extension of warm-water species (Buisson et al 2008). Negative effects of increasing temperature are also likely to be exacerbated by loss of riparian vegetation, which reduces shading and increases evaporative water loss (McKergow et al 2006;Rayne et al 2008;Davies 2010). Warmer temperatures and increased evaporation rates, combined with a drier climate across much of Australia, will result in increased drying of wetlands and waterholes in ephemeral rivers, and may result in some permanent habitats becoming intermittent (Kennard et al 2010).…”