The aim of this research is to determine the process by
which runoff draining parts of the UK uplands becomes
discoloured. Recent increases in colour are perceived as a
problem due to the frequency with which EC surface water
directives are breached, to the increased cost of meeting
standards, to an increase in consumer complaints, and due
to the possible deleterious health effects of consuming
coloured potable water.
The work was conducted over the last four years, largely in
the Upper Burn and Nidd valleys, north Yorkshire, and at
the University of Leeds. Existing knowledge on the chemical
nature and environmental genesis of coloured water is
reviewed, and related to the chemical nature of coloured
waters examined in this study. Analysis of water quality
archives and direct monitoring of selected catchments was
conducted enabling the spatial and temporal distribution of
coloured waters to be determined. A tentative process
theory was produced, and tested by controlled laboratory
investigations.
Coloured runoff is derived from Winter Hill soil, raw acid
oligo-fibrous peat, and is most intense from areas with
slopes < 5% and high drainage densities. The seasonal
pattern of colour is highly regular, and is a product of
rainfall and soil moisture deficit.
Colour is strongly associated with discharge, and demonstrates the operation of a catchment flushing mechanism. Runoff is discoloured in a three phase process; colour production, solubilisation and removal. Colour is a product of organic decomposition, dependent upon microbiological activity, moisture deficit, temperature and peat structure. Solubilisation of colour is dependent upon solution pH, temperature, the chemical structure of organic molecules and the availability of iron. The removal of decomposition products, as colour, is strongly dependent on the moisture status of peat, and its ability to rewet after drying. The implications of these findings for future colour levels and for catchment and catchwater management are discussed.