Research Context
Rivers that supply drinking water, tourism, and irrigation also carry heavy metals bound to suspended sediment. The hazard is not a single number: it depends on how sediment concentration and metal concentration move together.
Probabilistic hazard assessment of contaminated sediment in rivers
Method
A probabilistic framework rooted in multivariate and copula theory exploits the dependence structure between suspended sediment concentration (SSC) and individual heavy metals, giving the hazard probability for each metal at each SSC level. The relationships are derived separately for warm and cold seasons and for stormflow, then applied to Fountain Creek, Colorado.
Key Insights
- Warm-season and stormflow conditions carry a higher hazard likelihood than the cold season.
- Under warm or stormflow conditions at the 95th-percentile SSC, the probability that Cu, Zn, and Pb exceed the maximum allowable threshold exceeds 80 % at the study site.
- Along the creek, urban and agricultural land use considerably raise the likelihood of violating water-quality standards compared with natural land cover.
Abstract
We propose a probabilistic framework rooted in multivariate and copula theory to assess heavy metal hazard associated with contaminated sediment in freshwater rivers that provide crucial ecosystem services such as municipal water source, eco-tourism, and agricultural irrigation. Exploiting the dependence structure between suspended sediment concentration (SSC) and different heavy metals, we estimate the hazard probability associated with each heavy metal at different SSC levels. We derive these relationships for warm (spring-summer) and cold (fall-winter) seasons, as well as stormflow condition, to unpack their nonlinear associations under different environmental conditions. To demonstrate its efficacy, we apply our proposed generic framework to Fountain Creek, CO, and show heavy metal concentration in warm season and under stormflow condition bears a higher hazard likelihood compared to the cold season. Under both warm season and stormflow conditions, probability of exceeding maximum allowable threshold for all studied heavy metals (Cu, Zn, and Pb, in recoverable form) at a standard hardness of 100 mg/l CaCo3 and at a high level of SSC (95th percentile) is consistently more than 80% in our study site. Moreover, a longitudinal study along the Fountain Creek demonstrates that urban and agricultural land use considerably increase likelihoods of violating water quality standards compared to natural land cover. The novelty of this study lies in introducing a probabilistic hazard assessment framework that enables robust risk assessment with important policy implications about the likelihood of different heavy metals violating water quality standards under various SSC levels.