Geoscience Reference
In-Depth Information
Chapter 1
Introduction
1.1 Tracers, Fingerprints, and Riverine Sediments
Tuero Chico is a small village located along the Rio Pilcomayo of southern Bolivia.
Soils associated with its farmed floodplains possess Pb concentrations that exceed
recommended guidelines for agricultural use. The elevated levels of Pb raise a num-
ber of important questions: Is the Pb derived from upstream mining of the Potosi
precious metal-polymetallic tin deposits, or waste products disposed of in the river
from the City of Potosi? Perhaps it is natural, being derived from local mineralized
rocks that underlie the catchment? Or, could the Pb come from a combination of all
three sources? If it is frommultiple sources, howmuch comes fromeach source?And,
how far downstream does the Pb from a specific source impact sediment and water
quality? These and other complex physical and biogeochemical questions are increas-
ingly being addressed using environmental tracers. In this topic we examine the past,
current, and future use of environmental tracers to assess the provenance, movement,
and ultimate fate of sediment within river systems, particularly sediments contami-
nated by chemical substances that have the potential to degrade aquatic ecosystems
and/or human health. The term
tracer
has been defined in different ways depending
on the media (e.g., air, ice, snow, ground- or surface waters) to which it is applied.
For our purposes, a
tracer
is defined as a unique sediment-associated parameter or
set of parameters that is distinct from other sediments in the catchment, and can
therefore be used to track the movement and cycling of specific sediments from
their point of origin to their ultimate point of deposition. The term 'tracer' is often
defined and used synonymously with
fingerprint
. However, when applied to river
(fluvial) systems, a fingerprint is most commonly associated with a specific type of
analyses (fingerprinting studies) in which multiple parameters are used to distinguish
between sediments from diffuse (non-point) sources to quantify the provenance of
the sediment found in a river or riverine deposit.
The use of fingerprinting and tracing methods to assess the dynamics of sediment
generation, transport and storage has a long history in both fluvial sedimentology and
geomorphology, dating back to at least the early 20th century (e.g., Boswell
1933
).
