Effects of solar ultraviolet radiation on stream ecosytems and their application to forestry practices in British Columbia.

摘要

Clear-cut logging, and removal of riparian canopy, can result in considerable increases in solar ultraviolet radiation (UVR, 280–400 nm) flux to streams, and may increase the exposure of aquatic organisms to UVR by altering the export of dissolved organic matter (DOM) from the terrestrial catchment. Riparian buffer strips have been adopted to mitigate the effects of canopy removal, however, the width and composition of prescribed buffer strips can vary, and provide variable shading to the stream. Experiments were performed along coastal streams in British Columbia to examine the effects of UVR from canopy removal on stream algal, invertebrate, and fish communities. I performed in-stream and mesocosm experiments that manipulated the exposure of stream biota to UVR by using solar exclusion filters which removed all, or portions of, incident UVR.; Increased solar UVR exposure to streams either from direct canopy removal or declines in DOM significantly decreased total invertebrate biomass and community diversity, particularly during low-flow summer months. Increased UVR exposure affected riverine food-webs in a complex manner, clearly altering community interactive processes such as herbivory. Increases in UVR exposure had even greater effects on communities when they occurred in combination with increased water temperature. The effects of UVR on benthic food-webs varied across the spectrum, with UVA (320–400 nm) predominantly inhibiting benthic algae, and UVB (280–320 nm) having the most pronounced effects on invertebrates. No significant effects of UVR on benthic communities occurred under old-growth canopies, which had significantly more diverse invertebrate assemblages. Attenuation of UVR by dissolved organic matter was important for protecting organisms from inhibitory effects of UVR, with concentrations between 2–5 mg/L DOM in a critical concentration range for biological effects. Juvenile coho salmon that live in these coastal systems avoided high intensities of solar LTVA in experimental enclosures, suggesting that UVR may influence microhabitat selection by salmonids.; These results demonstrate that increases in solar UVR exposure to streams from clear-cutting, either by directly removing riparian canopy or changing DOM, has severe effects on the productivity, diversity, and functioning of coastal stream ecosystems.