Classification of dissolved organic carbon (DOC) in river systems: Influence of catchment characteristics and autochthonous processes

Dissolved organic carbon (DOC) in surface waters is influenced by natural and anthropogenic allochthonous sources in the catchment and by autochthonous production and degradation processes. An objective differentiation procedure, a principal component analysis, has been used to answer the question: Is it possible to classify different water types using only DOC-patterns, and how do seasonal variations influence such a classification? Organic compounds from various sources and river systems were analyzed by means of automated size-exclusion chromatography. Four different DOC fractions (humic substances, polysaccharides, low molecular weight acids and low weight substances) were separated on the basis of their molecular weight characteristics and quantified on the basis of their UV absorbance. Significant differences in the quality and quantity of organic compounds were found. These were related to the character of the catchment area and to autochthonous processes. It was possible to classify peat-influenced ditch waters, peat-influenced surface waters, mineral soil-influenced and anthropogenically-influenced surface waters, and waters from small and large lake–river systems. The characterization of DOC patterns combined with principal component analysis is a powerful tool for analyzing allochthonous and autochthonous DOC sources in surface waters, especially if seasonal variations are taken into account.