Abstract :
Characterising the nature and origin of suspended particulate and colloidal matter in surface waters is a necessary
first step in determining the role of these materials in the transport of pollutants. With this aim in mind, samples of
suspended sediment were collected from the R. Don, Scotland, and analysed by a combination of X-ray diffraction
XRD. and vertically attenuated infrared spectroscopy VATIR.. Additionally, the carbon and nitrogen contents of
the sediment were measured. Samples were collected at eight sites along the river from the headwaters to the mouth,
twice during periods of base flow, and once during a storm. During the base flows, the amount of suspended solids
was typically no more than 1]10 mg ly1, whereas the high flow samples contained up to 150 mg ly1. XRD showed
that the crystalline component of the high flow samples consisted of the clay minerals illite, chlorite, kaolin,
hydroxy-interlayered vermiculite, and a 10r14 A° regularly interstratified micarvermiculite. Non-clay components
included quartz, feldspars, amphibole and goethite. Kaolin progressively increased in relative abundance downstream.
The clay mineralogy of base flow samples was more or less identical to high flow samples but the non-clay
components were reduced and, additionally, talc and calcite were present. The identification of many of the
crystalline components was confirmed by VATIR, and amorphous silica was identified, particularly in base flow
samples. Organic components were identified as wax, protein, and humaterfulvate. Proportionally more protein and
wax components relative to silicates occurred in base flow samples, whereas the humaterfulvate component was
most clearly identified in samples from the storm. Organic matter contents ranged from approximately 24% during
base flow to 13% during the storm, whilst the CrN ratio showed a progressive decrease downstream, irrespective of
flow conditions. Both the characteristics of the mineralogy and the organic matter suggested that topsoils were the
primary source of the suspended sediment in the R. Don. However, the presence of talc and calcite were believed to
fingerprint ground water sources, which together with the in-stream production of diatoms, may have accounted for a
significant mass fraction of the suspended particulate matter during base flows.
