Coloured materials in surface water in the sub Arctic Zone: An overview of its formation, properties and environmental changes

Abstract

Natural organic matter (NOM) is present in most all surface water. This material is governing all chemical and all biological processes in the aquatic environment, and play a practical role in the drinking water industry From an increasing number of international reports, it is clear that the amount of this coloured matter is increasing in areas of the northern hemisphere. We is asked why and we suggest a combination of the following four reasons: 1) Climate (temperature, humidity, nature and frequency of precipitation); 2) Quality and quantity of precipitation; 3) Nature of catchment (topography and geology), and due to changes in local climate and 4) Quality and intensity of global radiation. In the early 1960s, there were reports from Scandinavia about the decline of coloured matter in lakes. The present increase in colour in our lakes and rivers is partly due to the fact that there are less mineral acids in precipitation. However, change in climate, most probably, plays an even more important role in many regions. As a consequence of the temperature increase, there will also be a change in the amount of precipitation and change in its regional and local distribution. As NOM is “produced” in soil and as the development is based on chemical and microbiological de composition of plant residues, an increased temperature and more rain will extend the “production-area”. The “global dimming will also have a significant impact on an increased colour in surface water, as less photo-degradation and less bio-available organic matter is resulting. The positive correlation between the colour increase in surface water and the amount of precipitation, may indicate, that there might be a limited amount of water-extractable coloured material in the catchment. It is argued that that the “production” of the coloured matter will in crease and that natural losses, such as “bleach ing” etc. will be reduced down flow. Most probably a number of different environmental “ele ments” “mechanisms” are acting simultane ously and/or separately and differently.