Introduction - Application of Geochemical Tracers to Fluvial Sediment - page 7

attached to those sediments may also be of interest). Moreover, fingerprinting studies
are typically aimed at deciphering the relative contributions of sediment from a
set of sources, which may be defined spatially (e.g., by the underlying geology or
land-use/land-cover type), or according to the process that delivers sediment to the
channel (e.g., sheet, rill, gully, or bank erosion). Although a number of novel methods
have been put forth (e.g., Poulenard et al. 2009 , 2012 ), source determinations are
primarily conducted by fingerprinting sediment sources on the basis of the physical
and/or chemical characteristics of the surface sediments and then comparing selected
types of river sediment to the fingerprint. Chapter 2 begins with an overview of the
assumptions inherent in geochemical fingerprinting, before turning to amore detailed
discussion of the uncertainties involved in themethods. More specifically, it examines
the various approaches that have recently been developed to quantify and reduce
uncertainties in the utilized approach. We then leave our discussion of geochemical
tracers as defined by elemental concentrations and turn our attention in Chap. 3 to
short-lived fallout radionuclides (FRNs) (e.g., 210 Pb, 137 Cs, 7 Be). These isotopic
tracers are somewhat unique in that they cannot only be used to assess sediment
provenance (often by source type, e.g., sheet, rill, gully, and bank erosion), but can
be used to determine sediment transfer rates within and between specific landscape
units, sediment exchange and residence times within the channel bed, and the age
of alluvial deposits, among a host of other processes. FRNs, then, may be applied at
much smaller spatial scales.
In Chap. 4 , we turn our attention to radiogenic isotopes, another group of tracers
that have been extensively used to source sediment and sediment-associated con-
taminants in river systems. Some radiogenic isotopes (e.g., Sr and Nd) have been
extensively applied to source sediment, whereas others (e.g., Pb) have been used less
as a direct tracer of sediment, but rather are primarily used to track Pb contaminated
materials. The spatial scale of application varies with the specific isotopes, but as a
group ranges from an individual reach to the global tracking of contaminated dust and
aerosols. Interestingly, there is little overlap in the literature on the use of radiogenic
isotopes to trace sediments versus contaminated materials, nor are the radiogenic
isotopes extensively used as a fingerprint in the analysis of non-point source sedi-
ment provenance. While we focus on the past use of selected radiogenic isotopes as
tracers, the hope is that the text will provide insights into their wider application to
sediment-associated riverine problems.
In the final chapter (Chap. 5 ) , we examine the potential use of a set of stable
isotopes that we have only recently been able to analyze in Earth and biological
materials at the levels required for their use as environmental tracers. Study of these
'non-traditional' isotopes is therefore limited, but increasing at a nearly exponential
rate as they may be effective at determining both the provenance and biogeochemical
cycling of trace metals/metalloids. It would, in the available space, be impossible to
cover all of these “non-traditional” isotopes here. Thus, we focus on four (including
Cd, Cu, Hg, and Zn) that appear to be particularly applicable to rivers and alluvial
sediments.
An appendix containing commonly used acronyms (abbreviations), unit conver-
sions and elemental data also is included for convenience.