TEMPORAL AND SPATIAL VARIABILITY OF THE HYDROCHEMISTRY OF THE SPOKANE RIVER (WASHINGTON STATE, USA)

The Spokane River, which flows ~110 miles (180 km) from Lake Coeur d’Alene in northern Idaho through eastern Washington to the Columbia River, has been contaminated by historical mining practices upstream of Lake Coeur d’Alene as well as urban inputs such as stormwater and sewer overflow. As a result, people are advised to limit both their consumption of fish from some stretches of the river and their contact with shoreline sediments due to high concentrations of metals (especially lead). In addition, high concentrations of other dissolved metals (e.g., cadmium, zinc) have been documented.

The most heavily populated and industrialized area along the Spokane River is the city of Spokane and its surrounding urban area. In this study, we investigated the spatial and temporal changes in the chemical composition of the river water as it flows through Spokane’s industrial district. We collected water samples every three weeks for one year from several (five to nine) locations along a two-mile stretch of the Spokane River. To our knowledge, the river water has not been sampled this frequently. Samples were analyzed for major and minor cations (barium, calcium, iron, magnesium, potassium, sodium, strontium) and heavy metals (cadmium, lead, zinc). Water temperature and pH were measured in situ, and alkalinity was determined in the lab by titration. Stream discharge data were collected from the USGS database.

For each sampling date, the dissolved load did not change significantly along the two-mile stretch of the river which suggests that any point sources are negligible for the parameters measured. As expected, the dissolved load varied over time as a function of stream discharge. For example, concentrations of alkalinity, calcium, magnesium, and sodium were diluted during snowmelt and rain events. However, zinc concentrations were positively correlated with stream discharge.

Understanding the sources and timing of loading of heavy metals to the river, whether anthropogenic or natural, is important for watershed management.