Dissolved organic matter and its role in the soil solution chemistry in relation to organic matter accumulation on the forest floor

The aim of this study was to determine how accumulation of organic matter on the forest floor (logging residue piles) is reflected in the soil solution concentrations of dissolved organic C and N and other nutrients. The data were collected from a logging residue experiment 7 years after a clear-cut harvest of a Norway spruce stand growing on sandy soil. The solution retained in the soil matrix was extracted from soil samples by the centrifugation method. The study site was located in Paltamo, Finland. The logging residue levels were: (1) 40 kg m–2, (2) 10 kg m–2, and (3) 0 kg m–2 of fresh spruce branches. The DOC and DON concentrations were higher in the organic layer in the centrifuged soil solution due to organic matter accumulation on the forest floor as compared to the treatment where no accumulation had occurred, and these higher levels were persisting still seven years after the logging residues had been piled on the site. The NO3-N and NH4-N concentrations were generally very low. It was possible to accurately estimate the anion deficit based on the DOC concentration in the soil solution, and the increased concentration of DOC and organic anions strongly influenced the ionic balance of the centrifuged soil solution.