Production of dissolved organic carbon in forested catchments

Leaf litter is an important source of natural dissolved organic carbon (DOC) in forested catchments. Rainwater percolating through fresh litter obtains higher concentrations of DOC and colour than from older forest floor material and organic soils. Chemical characterisation using DOC fractionation and tests of biodegradability show that natural litter percolates contain significant fractions of coloured and highly refractory hydrophobic acids (humic substances) and variable fractions of biodegradable compounds. Deciduous leaf litter imparts high DOC concentrations in the autumn, while coniferous litter and organic soils release DOC more evenly. Leaching from fresh deciduous litter may explain the seasonality in the concentration of DOC in discharge from forested catchments. Countrywide Norwegian data show very poor relationships between occurrences of mires in the catchment of lakes and water colour. High concentrations of DOC may occur in lakes where the catchment has a high proportion of surface runoff due to thin or impermeable soils or swamp areas. (C) 1999 Elsevier Science B.V. All rights reserved.