SEASONAL-VARIATION OF SELENIUM IN OUTDOOR EXPERIMENTAL STREAM-WETLAND SYSTEMS

Two outdoor experimental stream-wetland systems were exposed continuously to 10-mu-g/L Se(IV) over a 2-yr period. A seasonal variation in the water column Se concentration was found in wetlands; a comparable variation was not observed in the stream segments. Water column Se was never reduced by more than 20% in the streams, but was reduced by greater than 90% in midsummer in the wetlands. Accumulation of Se in plants was much higher in the wetlands than in the streams, particularly in duckweed (Lemna minor). The deposition of Se in sediments was extremely variable within the wetlands.