| Abstract/Description or Keywords |
This report assesses seventeen years of water quality data from the Iskut River below Johnson River, in north-western B.C. (Figure 1). This station was established in 1980 for water quality and is currently sampled on a bi-monthly (once every two months) basis by the Water Survey of Canada when they visit the co-located hydrometric site. The Iskut joins the Stikine River 8 km downstream from the sampling site, which subsequently flows into the Alaskan panhandle and into the Pacific Ocean. Mining, and forestry to a lesser extent, are the main anthropogenic influences on the Iskut River. CONCLUSIONS: _ Water quality in the Iskut River is generally very good. _ Total cadmium, chloride, colour, fluoride and total lead had statistically significant decreasing trends over the sample period. _ Extractable calcium, extractable gallium, total manganese, total molybdenum, total suspended solids (TSS) and turbidity all had statistically significant increasing trends. _ A variety of total metal concentrations exceed aquatic life guidelines seasonally (i.e. spring freshet) but these exceedences are strongly correlated with turbidity and thus, likely bound to particulate matter and not bioavailable, and include the following: o Total aluminum concentrations exceeded the guidelines at times when turbidity was high. The guidelines are expressed as dissolved concentrations of the metal. o Total arsenic, total copper and total iron concentrations exceeded the B.C. aquatic life guidelines at times when turbidity was high. o Low-level total cadmium concentrations are currently near B.C. and CCME aquatic life guidelines, but these levels are considered to be natural. o Total chromium concentrations seasonally exceed guidelines established for Cr (VI) and Cr (III). o Total zinc concentrations exceeded hardness-dependent aquatic life guidelines at times when turbidity was high. _ Both turbidity and total suspended solids had statistically significant increasing trends over the sample period. Both of these parameters are generally correlated with total metals and nutrients and may result in increasing trends and concentrations in parameters related to suspended solids (i.e. total metals). _ A number of metals need to be measured differently if comparisons are to be made to guideline values as these exist. The metals and forms required to be measured are aluminum (dissolved and inorganic monomeric, when available), chromium (trivalent and hexavalent), and iron (continue to measure total but also dissolved). _ Since total metal concentrations in the Iskut River vary greatly due to freshet, it would be beneficial to measure dissolved metals in addition to total metals for guideline comparison. A new field method for collection of low-level dissolved metals is currently being developed and should be implemented in 2009 at selected sites. RECOMMENDATIONS It is recommended that water quality and quantity monitoring continue at the Iskut River below the Johnson River to determine trans-boundary effects between British Columbia and Alaska, to determine the effect of increasing turbidity trends on related water quality parameters and to assess the impacts of upstream activities such as mining and logging. |
