Changes in molecular weight of humic substances in the Gulf of Bothnia

Humic substances were isolated in the brackish Gulf of Bothnia utilizing two techniques: ion exchange on DEAE-cellulose and hydrophobic interaction on XAD-g resin. The salinity of the water resulted in different yields for the two adsorbents. With XAD-8 resin, 30-80% of the organic carbon was isolated, whereas 5-20% was isolated on the DEAE-cellulose. The concentration of total organic carbon was rather constant but the concentration of humic substances decreased with increasing salinity. Gel filtration was used to measure the homogeneity of the humic fraction. Humic substances isolated in December were more homogeneous than those isolated in June, which indicates a degradation during the summer period which might be caused by photolysis or increased microbial degradation during the warm season.