| Abstract/Description or Keywords |
This study investigated the influence of mining on the geochemistry of fine sediments in creeks and rivers. The data for this study was collected by conducting fieldwork in the Quesnel River catchment, BC, Canada. The study area includes the drainage area of an active open pit gold- and copper mine and the drainage area of a historic hydraulic gold- and copper mine. In several creeks in the study area, five sampling sites were selected of which one drains a pristine forested area and is functioning as a control site (C1, Edney Creek). Hazeltine Creek drains an active mine and represents two sampling sites (H1 and H2). In the delta that has formed in Quesnel Lake by Hazeltine Creek, another sampling site was selected (D1, delta). In the creek draining the inactive mine, the fifth sampling site was selected (P1, Pine Creek). Data were collected by sampling bed sediment, suspended sediment and vertical profiles, and by collecting depth samples at each sampling site. Two cores were collected: one in the delta that has formed in Quesnel Lake by Hazeltine Creek and one in a pond formed upstream of a weir in Hazeltine Creek at sampling site H2. To assess the extent of the increase in heavy metal concentrations in the stream sediments and to indicate the relation to background concentrations and the adsorption properties of the sediment, the enrichment ratio was calculated. The enrichment ratio is a measure for the actual difference between background concentrations and elevated concentrations. The enrichment ratio is calculated by dividing the actual metal concentration by the regression prediction of the background concentrations. The heavy metal concentrations that were used to estimate background concentrations include the deeper samples of the core collected in the delta (n=11), the deeper samples of the vertical profiles at sampling sites H2, C1 and P1 (n=10) and the bed sediment samples taken from sampling site C1, the control site (n=6). For sampling sites H1 and H2 and the suspended sediments, heavy metal concentrations were enriched for Se, Cu, Cd, Hg, Mn and Zn. The sampling site in the delta formed in Quesnel Lake by Hazeltine Creek shows enrichment for Se, Hg and Mn. Sampling site P1 which is draining the inactive mine shows enrichment for Pb and Ni in all stream sediments. The age of the sediment in the two cores was determined in two separate ways. The first method employed the amount of 210Pb and 214Pb (Bq/Kg) in order to apply the constant rate of supply model. The second method employed the amount of 137Cs. In this method the year 1963 can be traced back. The data collected from the cores gathered in the delta formed in Quesnel Lake by Hazeltine Creek and the core gathered at sampling site H2 show different results. No sediment deposition occurred over the last 30 years in the core taken in the delta and the periods of active mining are untraceable. The core collected from sampling site H2 shows enrichment of Se during the two periods of active mining (1997-2001 and 2005-present). Further, the core shows the two active mining periods by an increase in heavy metal concentrations. This study concludes that mining activities do influence the geochemistry of fine sediments in creeks and rivers, but the influence can be minor and it does not directly indicate that the mines that have been investigated are contaminating the research areas. However, this study only concentrated on the input of heavy metal concentrations of stream sediments. In the future close monitoring of the Quesnel Lake research area is considered advisable in order to detect possible elevated heavy metal concentrations. |
