WRTDS annual concentrations, loads and statistical trend likelihoods for sites in the Spokane River watershed, water years 1990-2018

A long history of mining and widespread metals contamination in the Spokane River watershed have led to the area's designation as a Superfund site and extensive, ongoing remedial actions. Long-term (water years 1990 to 2018) water-quality data from twelve sites were used to develop Weighted Regressions on Time, Discharge and Season (WRTDS) and WRTDS with Kalman filtering (WRTDS_K) models for total and dissolved cadmium, zinc and lead; total phosphorus and nitrogen; and dissolved orthophosphate. The models estimated annual mean concentrations and annual total loads, and flow-normalized annual mean concentrations and flow-normalized annual total loads. Flow-normalized annual mean concentrations and flow-normalized annual total loads were evaluated for trends, and bootstrapped model replicates were used to determine the statistical likelihood of the trends. These data were used to understand how remedial actions are affecting water quality in the Spokane River watershed and will help inform future remedial actions.