The impact of selenium supplemented fertilization on selenium in lake ecosystems in Finland

Abstract

The impacts of Se supplemented fertilization in Finland were studied in 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 higher than that of forest lakes in late summer, but not in spring. The fraction of Se in humic substances constituted 52% of the dissolved Se in lake water, whereas selenite and selenate made up 8–9% each. Particulate Se in lake waters was about 10% of the total water Se concentration. The vertical distribution of Se in lake water was related to the growth of algae. Se accumulated in perch muscle tissue. The Se concentration of lake sediments has increased from the last century to the 1990s mainly because of agricultural activity and atmospheric fallout. The accumulation of Se in perch and the Se concentration in sediments were strongly related to the trophic state of the lakes. No clear evidence was found that Se fertilization has significantly increased Se sedimentation in lakes.