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The need for research.

Physico-chemical properties and characteristics of NOM.

In spite of the fact that NOM represents a significant fraction of the solutes present in fresh water and that NOM influence all chemical and biological processes in the aquatic environment, NOM has until very recently received relatively little attention. Conventionally (in e.g. acid rain research) the NOM has simply been reported as an amount of carbon per litre (mg C L-1 TOC/DOC) and taken to account for the anion deficit in relation to the sum of cations. This has rendered little information about the role of the organic compounds in the water per se. The physico-chemical properties of NOM (e.g. hydrophobicity, acidity and complexing ability) clearly need to be better characterised. The problem has been how to parameterise the NOM.

Considerable research has been conducted on the structural characterisation of NOM by means of NMR and other spectroscopic methods (i.e. aromatic/aliphatic content). This research has documented that NOM contains a multiple of organic compounds and the composition shows great spatial and temporal variation.

The large compositional variation in time and space is also reflected in the NOM's ability to acidify and to complex metals. Attempts to determine the protolysis and complexing constants have therefore been difficult, as titration curves of this composite material exhibit large variation with no distinct endpoint. The most promising strategy to this problem has been to study the Gaussion distribution of the conditional pK' values, determining the average pK' and the standard deviations. Such constants will be of great value in simulation and prediction models.

Furthermore, there is registered a significant increase in the DOC concentration in the water sources to Norwegian waterworks during the last years. The potential problems that NOM may cause for the drinking water industry, forestry, fishing as well as global environment, justify an increased research effort.

There is therefore an urgent need for more knowledge about the physico-chemical properties and characteristics of NOM in order to:

  • Understand many of the vital processes in the environment where NOM is involved.

  • Evaluate the quantitative importance of production, mineralization, sorption and transport processes and how they may be affected by changes in environmental conditions.

  • The understanding of these processes and their quantitative importance enable us to better:

    i) Develop conceptually based prediction models for soil/soilwater interactions used in
    e.g. acid rain critical load assessments.
    ii) Treat drinking water properly.
    iii) Assess NOM's significance to forest production.
    iv) Predict NOM's mitigating effect on metal toxicity to fish and other aquatic biota.
    v) Estimate changes in carbon budget by climatic changes due to the greenhouse effect.