琵琶湖におけるクロロフィルaと溶存有機炭素の季節変化

抄録

Water samples were collected in Lake Biwa at monthly intervals from April to October in 1976 (except July) in front of Biwako-bunkakan. Each sample was passed through a Millipore filter (pore size : 0.45μm). The filtrate was concentrated by vacuum evaporation (100 : 1) at a temperature of less than 35°C. The concentrated solution was passed through a 'Sephadex G-10' column, 2.5 cm×85 cm. Ultraviolet absorbance (220 nm and 250 nm) and the concentrations of dissolved organic carbon (DOC) and carbohydrate (DCC) were determined for the eluted and concentrated solutions. The concentration of chlorophyll-a in the original water sample was determined.
(1) The concentration of chlorophyll-a ranged from 12.8 μg/l to 23.3 μg/l, that of DOC was from 1.74 mg-C/l to 3.98 mg-C/l, and that of DCC from 0.23 mg-C/l to 0.77 mg/C/l.
(2) Absorbance at 250 nm was observed to have a good relation to DOC concentration. (DOC mg-C/l =9×A₂₅₀)
(3) The chromatogram was composed of four peaks. The first peak (elution volume, 150-160 ml) mainly consisted of DCC which has molecular weights of about 700 and above. The concentration of DCC increased with that of chlorophyll-a. This fact and previous studies suggest that DCC has been produced in situ in Lake Biwa. The second peak (elution volume, 160-170 ml) and the third peak (elution volume, 210-220 ml) failed to show a correlation to the chlorophyll-a concentration. The fourth peak, which was eluted with inorganic carbon at about 300 ml, decreased with the concentration of chlorophyll-a, and its ultraviolet absorption spectrum was characteristic.