Patterns of dissolved organic matter in subarctic peatlands

Abstract

AbstractSamples of water from poor to very rich fens in the Schefferville region of subarctic Quebec revealed strong spatial and temporal variations in dissolved organic carbon (DOC), ranging from 2 to 40 mg 1−1. Concentrations of DOC tend to increase during the summer and decrease in the autumn, at most sites, which probably reflects increased plant tissue decomposition and higher rates of evapotranspiration. Principal components analysis revealed that DOC is strongly associated with Fe, NO−3‐N and NO−2‐N, but essentially independent of other chemical properties of the peat water, such as pH, Ca, Mg, K, P, and NH+4‐N. Based on observed concentrations of DOC and estimates of summer runoff (June to September), export of DOC from four peatlands ranges from 1·1 to 4·9 gCm−2, with the lowest values for peatlands underlain by dolomite. Molecular weight fractionation of four samples revealed significant differences in the dissolved organic matter (DOM), with the largest fractions (GF/C to 10 000 nmw) being dominant in the more acid samples. The ratio of absorbance at 400 and 600 nm wavelengths (E4:E6) has been used as a simple indicator of differences in DOM type, ranging from 3 to 15. There is a strong seasonal pattern of increasing E4:E6 ratio during the summer at many sites, though this ratio is essentially independent of other chemical properties of peat waters.