SEASONAL-VARIATION IN THE COMPOSITION OF AQUATIC ORGANIC-MATTER IN SOME NOVA-SCOTIAN BROWNWATERS - A NUCLEAR-MAGNETIC-RESONANCE APPROACH

Using a novel concentration technique (reverse osmosis and freeze-dryi ng) as well as a standard analytical technique little used with limnol ogical samples (solid state C-13 nuclear magnetic resonance), we studi ed the chemical structure of aquatic organic matter from four closely located freshwater sites in Nova Scotia. The main conclusions drawn fr om the data are that: (a) the aromatic C fraction which is assumed to be refractory remains at less than 10% of the total, with a slight inc rease in relative importance in the fall, (b) less structurally comple x aliphatic carbon decreases from winter to spring and remains at lowe r levels into later fall, (c) carbohydrates are at a maximum during th e summer, (d) the carboxylic C fraction is at a minimum in the summer and maximum in the fall and winter. Results show roughly the same annu al patterns of C composition for the two running water sites. Our data suggest that the hydrological processes which carry terrestrial and w etland DOM to streams and lakes allow a selective adsorption process o f DOM to occur in soils. We compare our data to those from other fresh water studies and suggest that the importance of aromatic carbon in fr eshwaters has probably been overestimated in the past, with a correspo nding underestimate of the more biologically labile carbohydrate and a liphatic material.