TOTAL ORGANIC-CARBON IN STREAMWATER FROM 4 LONG-TERM MONITORED CATCHMENTS IN NORWAY

By linear regression analyses, flux, concentration, and net charge (NC in mu eq/mg C) of total organic carbon (TOC) have been related to dif ferent physico-chemical parameters present in air/precipitation and st reamwater at four long-term monitored catchments in Norway, during the period 1986-1992. The catchments vary a lot with respect to annual wa ter input, acid rain, and the streamwater concentration of TOC. Thus, relationships between concentration/NC of TOC and chemical compounds i n precipitation and streamwater were often catchment-specific, However , seasonal climatic changes, like air temperature and hydrology, were found to be important for the concentration variations of TOC. The cor relation between concentration of nonmarine base cations (Sigma BC) a nd concentration of TOC at the four sites was far more significant (r= 0.86) than the corresponding correlation between nonmarine sulphate (S O4) and Sigma BC* (r=0.57). This indicates the important sole of orga nic matter in weathering reactions in the catchment. Concerning weathe ring and cation leaching of aluminum, the correlation between concentr ation of total aluminum (RAL) and SO4 was far more significant (r=0.9 3) compared with the corresponding correlation between RAL and TOC (r= 0.40). This should be expected, because a high concentration of SO4 m eans a low pH, which is needed to dissolve substantial amounts of Al f rom soils. The NC of TOC was found to be most affected by compounds in precipitation, primarily the inputs of sea salts. In the most acidifi ed areas, the influence from strong acid inputs also affects the NC of TOC, but less significantly. The concentration of Na+ in precipitatio n is much higher and the variations much larger compared with the conc entration of H+ in precipitation in the coastal areas, like Birkenes a nd especially Kaarvatn. Thus, it is reasonable that the variations in sea salt inputs (primarily NaCl) are more important for the temporary variation in NC of TOC compared with H+ ions at these sites. Only at L angtjern, the most TOC-influenced site, a significant and positive cor relation was found between H+ and the concentration of TOC in streamwa ter. This indicates that at a certain TOC level, the weak organic acid s may affect the streamwater pH. A comparison between measured and cal culated concentrations of organic Al indicated that the dissociation c onstants (pK-values) of the organic acids present at Birkenes must be higher and/or the Al-complexing constants lower compared with the cons tants given by the programme. At the three other sites, it was the oth er way around. This may explain why a negative correlation between con centrations of TOC and labile Al was present at Birkenes, while the ot her sites exhibited a corresponding positive correlation with respect to labile Al or Sigma Al-n+. The comparison also documented larger dif ferences in these constants between the sites, compared with monthly v ariations in the constants at one single site.