Ecological Effects of Road Salt - The effects of road salt on the composition of macroinvertebrate fauna in three different streams receiving highway runoff.
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The present study focuses on the effects of road salt from highway runoff on macroinvertebrate communities. It was hypothesised that changes in salt concentrations will alter the composition of the macroinvertebrate fauna downstream of the reference sites. It is assumed that water quality will decrease as salt concentrations increase therefore resulting in a decrease in macroinvertebrate diversity and an absence of pollution sensitive species (EPT species). Three different streams situated in the south eastern part of Norway were investigated (Bolvikelva, Ljanselva and Gjersrudbekken). There was very little difference in the macroinvertebrate communities recorded upstream and downstream. The majority of the variation in macroinvertebrate data found using RDA (Redundancy Analysis) was between streams. This variation between streams is probably due to a number of factors such as, differences in stream size, the urbanisation of the watershed and the variation in riparian zones. There were no significant differences between the biological indices obtained at upstream and downstream sites or between seasons. This indicated no significant decrease in water quality between sites or seasons. Although the indices used in this study did demonstrate varying sensitivity. For example, ASPT often indicated a much higher water quality than the Shannon diversity index. No singular index is considered a suitable ”all round index” and a mixture of biological indices and tools would probably be a more effective monitoring technique. Based on the macroinvertebrate data sampled in this study, macroinvertebrate communities showed no acute negative responses to road salt However some species displayed a higher sensitvity to chloride than others. Community studies alone may be insensitive to any negative effects road salt may have on macroinvertebrates. Many processes often occur at the individual level before a whole community reacts to any negative impacts. Further investigation using possible biomarkers at the individual level may provide earlier warning signs to possible negative effects of road salt.