THE IMPACT OF SELENIUM SUPPLEMENTED FERTILIZATION ON SELENIUM IN LAKEECOSYSTEMS IN FINLAND

The impacts of Se supplemented fertilization in Finland were studied i n relation to concentration, time variation, speciation, distribution, bioaccumulation and sedimentation of selenium (Se) in lake ecosystems . The background level of Se in lake waters (n = 41) was 58.4 ng l-1 ( 28.7-115 ng l-1) and the seasonal variation was small. The mean water Se concentration of lakes surrounded by fields was significantly highe r than that of forest lakes in late summer, but not in spring. The fra ction of Se in humic substances constituted 52% of the dissolved Se in lake water, whereas selenite and selenate made up 8-9% each. Particul ate Se in lake waters was about 10% of the total water Se concentratio n. The vertical distribution of Se in lake water was related to the gr owth of algae. Se accumulated in perch muscle tissue. The Se concentra tion of lake sediments has increased from the last century to the 1990 s mainly because of agricultural activity and atmospheric fallout. The accumulation of Se in perch and the Se concentration in sediments wer e strongly related to the trophic state of the lakes. No clear evidenc e was found that Se fertilization has significantly increased Se sedim entation in lakes.