PROBLEMS IN FILTRATION FRACTIONATION OF C-14 PRIMARY PRODUCTIVITY SAMPLES

Sources of error in the fractionation of C-14 primary productivity samples were studied in the northern Baltic from 1984 to 1990. Acidification of the whole C-14 sample followed by 24 h in open vials to remove (CO2)-C-14 (no bubbling) proved to be a simple, accurate, and precise (C.V. 6.9%, n = 128) method for measuring apparent net primary productivity (total organic C-14). In 1985, the total recovery of organic C-14 with 0.2-mu-m cellulose acetate filters was 81% of the annual apparent net primary production. Different post-filtration treatments of the cellulose ester filters (rinsing, acidification) all gave significant unaccountable losses of up to 34% of organic C-14. No losses were recorded with glass-fiber filters. Excess release of dissolved organic C-14 due to filtration was generally unimportant, as only minor quantitative or qualitative differences were found between the < 0.2-mu-m filtrates of the whole and centrifuged samples.