The size distribution and speciation of organic matter (OM) in soil solution, bog, stream, and humic and clearwater lake in the north boreal zone (Karelia region, north west Russia) during the summer base-flow period for several years were investigated. The samples were filtered in the field using cascade filtration through progressively decreasing pore size (100, 20, 10, 5, 0.8, 0.4, 0.22, 0.1, 0.046 μm, 100 kDa, 10 kDa and 1 kDa) followed by dissolved organic carbon (DOC) analysis, UV-vis and size exclusion chromatography measurements. Surrogate parameters, such as specific UV absorbance (SUVA; absorbance at 254 nm normalized for DOC concentration in l mg−1 m−1) and the absorbance ratios E254/E436, E280/E350, E254/E365, E365/E470 and E470/E655 (ratio of spectrophotometric absorbance of the sample at two wavelengths) were applied for the characterization of OM in filtered and ultrafiltered water from soil solution, bog, river and lake.