A COMPARATIVE ANALYSIS OF WATER QUALITY AND AQUATIC LIFE IN TWO INTERNATIONAL WATERSHEDS: A LEGACY OF MINE DRAINAGE IN THE ELK/KOOTENAI BASIN AND ANALYSIS OF RISK IN THE TRANSBOUNDARY FLATHEAD RIVER BASIN

A comparative analysis of two transboundary, international watersheds (Elk/Kootenai and Flathead) shared between British Columbia, Canada and Montana, USA, focused on observed and predicted impacts of open-pit coal mining on water quality and aquatic biota. The upper Flathead and Elk basins are underlain by the same coal formations, but with five open-pit coal mines currently operating in the Elk Valley and no coal mining in the Flathead Valley. We found nitrate and total nitrogen concentrations were significantly elevated (>1000x) at sites downstream of existing coal mining in the Elk Basin, compared to all Flathead Basin sites or reference sites above coal mines in the Elk Basin. Sulfate concentrations were also significantly elevated (>100x) in the Elk Basin sites below coal mining. Similarly, selenium concentrations were elevated (>10x) above naturally occurring levels observed among Flathead Basin streams and Elk Basin reference sites. Selenium values observed across the Flathead Basin were universally low (0.2 – 0.6ug/L), whereas, selenium in the Elk River below the mines consistently exceeded both the British Columbia aquatic life guidelines of 2ug/L and the U.S. Environmental Protection Agency (EPA) water quality standard of 5ug/L. A comprehensive survey of river deposited sediments revealed elevated concentrations of cadmium in Elk River fine sediments draining directly from the mines. Aquatic life, (algae and macroinvertebrates) showed significant effects of mining with dramatic decrease in both algal and macroinvertebrate biodiversity and increase in algal biomass and tolerant species of macroinvertebrates. Distribution and genetics of native salmonids was also assessed in the Flathead; we found aquatic habitats supporting migratory populations of endangered species of bull trout and nonhybridized westslope cutthroat trout. Selenium concentrations in westslope cutthroat trout collected from the Elk River were significantly higher than those from Flathead Lake and tributaries throughout the Elk and Flathead systems. A comprehensive, watershed-scale assessment is needed to assess the current scale of mining impacts on transboundary aquatic ecosystems and to predict threats to international boundary waters from the Elk River headwaters through Lake Koocanusa to the Kootenai River.