Characterization of dissolved organic carbon (DOC) in a dystrophic lake and an adjacent fen

Dissolved organic carbon (DOC), humicsubstances (HS), polysaccharides (PS) and lowmolecular weight acids (LMWA) werecharacterized in water from the dystrophicLake Große Fuchskuhle over a period ofseven months. In addition, porewater from anadjacent fen was investigated in order toobtain information about the DOC in thecatchment area. Size-exclusion-chromatographycombined with UV- and organic carbon(IR)-detection was used to quantify DOC andits fractions. The lake had previously beendivided into four separate sections by largesheets of plastic, and the DOC compositiondiffered markedly between the fourcompartments. Spatial variations in HS and PSconcentrations were greater than seasonalvariations. The high amounts of HS (up to58%) in the western sections of the lake,indicated influence by subsurface water fromthe fen, whereas the eastern sections weredominated by PS (up to 35%) of algal origin.These differences could be explained byhydrological conditions, indicating thatcompletely different catchment areasinfluenced the water chemistry in the separatecompartments. By characterizing the HS bytheir average molecular weight and theiraromaticity, three different groups of HScould be distinguished depending on theirorigin and fate. Microbial degradation of DOCand its fractions differed between two of thecompartments during incubation studies over aperiod of six weeks.