Factors affecting the variation in the average molecular weight of dissolved organic carbon in freshwaters

The molecular size distribution of concentrated filtered (< 0.45 um) lakewater samples, collected from 20 lakes in Ontario, Canada, was measured using size exclusion chromatography (Sephadex G-25, fractionation range 100–5000 daltons). Average molecular weights ranged from 1225 to 2170 and a strong positive correlation was observed between average molecular weight and dissolved organic carbon concentration. Additional factors which may affect the variation in the average molecular weights among the study lakes also were examined including catchment area, lake area, pH etc. Of these, the ratio of catchment area to lake area appeared to be the most important.