Introduction - Application of Geochemical Tracers to Fluvial Sediment - page 3

Fig. 1.1 Schematic diagram of riverine sediment-dispersal system (after Schumm 1977 )
to ecosystem health. For example, the National Water Quality Inventory, a program
in the U.S. developed to assess the current condition of the nations water resources,
indicates that sediment is the second leading cause of river impairment (Fig. 1.2 )
(USEPA 2013 ). Moreover, anthropogenically derived sediment can result in rapid
episodes of reservoir sedimentation, reduce reservoir storage capacity, impact water
distribution systems, increase turbidity and reduce light penetration, degrade aquatic
habitat, and lead to a loss in aesthetic quality of the riverine environment. The annual
costs of human-induced sediment influx to rivers and streams have been estimated
to range from 20 to 50 billion dollars in North America alone (Pimentel et al. 1995 ;
Osterkamp 2004 ; Mukundan et al. 2012 ).
Froma chemical perspective, fine-grained sediments, particularly those composed
of clay minerals, Fe and Mn oxides and hydroxides, and organic matter are highly
reactive (Horowitz 1991 ). Thus, sediment suspended within the water column and
that forms the channel bed and banks, typically exhibit concentrations of hydrophobic
contaminants that are orders of magnitude higher than those associated with the
aqueous (dissolved) load. Gibbs ( 1977 ), for example, examined the concentration of
selected metals (including Cu, Co, Cr, Fe, Mn, and Ni) associated with suspended
sediment within theYukon andAmazonRiver basins, two river systems characterized
by different hydrologic regimes and geological terrains. He found that within both
basins sediment-associated trace metal levels ranged from 6,000 to more than 10,000
times greater than their dissolved concentrations. As a result, trace metal transport
was dominated by the particulate load (Fig. 1.3 ). Subsequent studies (e.g., Horowitz
and Elrick 1988 ; Meybeck and Hemler 1989 ; Horowitz 1991 ) supported Gibbs'