| Summary: | The variability of the concentration and export of the total organic carbon (TOC) was analysed in 16 rivers in Finland (northern Europe). The river basins were categorized by major landuse settings, and their geographical location ranged from the southern boreal to sub-arctic. In the long-run (1975–2000), the concentration of the TOC had a statistically significant (?p < 0.05) decreasing trend in nine rivers at least once during March, May, August and October. The estimated annual load of the TOC was statistically significantly higher (?p < 0.03) in the basins characterized by peatlands than in those dominated by fields, being on average 5.4 and 4.1 g C m–2 a–1, respectively. The winter (January–March) North Atlantic Oscillation (NAO) index predicted rather well (mean of r2 = 0.48 and p = 0.04125) the TOC load in March in the eight northernmost rivers.
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