Geochemical Fingerprinting - Application of Geochemical Tracers to Fluvial Sediment - page 14

Fig. 2.2 Relative use of tracer types identified and categorized on the basis of temporal and spa-
tial scale by D'Haen et al. ( 2012 ) for determining the provenance of fine-grained sediment in
alluvial deposits. Spatial scales defined as local (

10km 2 ), intermediate (10-10,000km 2 )and

<

10,000km 2 ); temporal scales subdivided into contemporary ( Regional ( 50ybp), and historical

(50-10,000ypb) (from D'Haen et al. 2012 ). Examples of tracers associated with each category of
tracer provided in Table 2.1

> <

subdivided into units on the basis of the underlying geology, soil type, etc., each unit
defining a distinct sediment source. Sediment sources can also be defined accord-
ing the processes of sediment generation (e.g., whether the sediment was derived
from sheet, rill, gully or bank erosion). Source areas defined according to the gen-
erating process are often referred to as source types. Particles eroded from these
defined source areas or types are transported, often intermittently, through a chan-
nel/valley network to a downstream depositional basin that serves as a long-term
sediment repository (Weltje 2012 ). In the process, particles from all of the source
areas are combined such that the sediments within the channel represent a mixture
of particles from all of the source areas in the basin. The physical and geochemical
composition of this sediment mixture (which we will refer to as river sediment) is a
function of the composition of the source area sediments and the relative amount of
sediment that each source area contributes; if both are known, then it is possible to
predict the composition of the mixture. Mathematically, this predictive calculation
is considered a linear forward problem (Weltje 2012 ). More commonly, however,
the objective is to determine the relative volume of material supplied to a particular
type of river sediment (suspended load, channel bed material, floodplain deposit,
etc.) from each sediment source. This type of calculation represents a linear inverse