2020 Volume 22 Issue 2 Pages 133-148
In the northern snowy region of Japan, chloride deicers, which are mainly composed of NaCl, are widely used to prevent road surfaces from freezing. Large amounts of the scattered chlorides accumulate at snow disposal sites and flow into streams with snowmelt runoff. Here, we studied how the snowmelt runoff affects stream water quality and organisms in Sapporo, Japan. We measured water quality at the outlet of snow disposal and adjacent stream, both at upstream （control） and downstream （impact） reaches of the outlet, for several sites. We also collected benthic algae and macroinvertebrates at both stream reaches. The results showed that the concentrations of Na＋ and Cl－ in runoff water were 2-9 times higher than those in stream water during the early snowmelt period （March）. Additionally, the concentrations of both ions in the stream water were higher in impact reaches than in control reaches, although the differences were relatively low （average ± S.D.＝1.56 ±1.27 mg L－1 for Na＋ and 3.05 ± 2.74 mg L－1 for Cl－）. For instream organisms, abundance of Trichoptera, total abundance of EPT （Ephemeroptera, Plecoptera, Trichoptera） and relative abundance of EPT to total macroinvertebrates were lower in impact reaches than in control reaches and decreased over the snowmelt period. To conserve stream ecosystems, we need to mitigate the impacts on stream water quality and organisms by preventing direct inflow of snowmelt runoff water.
