Studies on the biological production of three fire pools in Tokyo:VI. Seasonal variations in the amount of deposition (1)
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1) The seasonal variations in the amount and the chemical nature of the deposits were clarified by the observations which were carried out from Aug. 1951 to Dec. 1953 at three fire pools in Tokyo.<BR>2) PETRI dishes 10 cm in diameter set in the flower pots were suspended in water at the depths of 1 and 2. 5 m. respectively. At intervals of about one and two months, they were hauled up and their contents were examined.<BR>3) The amounts of deposition increase both in spring and in autumn every year, and decrease in early summer (May and June). Heavy deposition sometimes seen in autumn may indicate that substances suspended in water during the summer stagnation were precipitated at a stretch in the circulation in autumn.<BR>4) The mean values (dry weight) of deposition per day were 6-30g/m<SUP>2</SUP>, richest in Pool B, and scanty in Pool A. Loss on ignition fluctuated between 40-60 %, and organic nitrogen varied between 20-25 mg/g. The value of the former changed in direct proportion to the amount of deposition, the latter vice versa.<BR>5) The percentage of loss on ignition and the amount of organic nitrogen in the bottom muds varied from 30 % to 35 % and from 12 mg/g to 14 mg/g respectively. These values are similar to those of certain dystrophic lakes. Loss on ignition of bottom mud was 2/3 of that of deposits and 1/2of that of seston, while the amount of organic nitrogen of bottom mud was only 37 of seston and1/7 of plankton. These facts indicate that organic nitrogen in these matters must return back to the water with a high speed.<BR>6) The rate of deposition of matters in the pools varied from 2 to 6 mm thick year by year, increasing with age. The amount of accumulation was found to be 1. 26-5. 56 kg/m<SUP>2</SUP>/year, which are similar to those of certain eutrophic lakes.<BR>7) The maxima of deposit occurred either at the same time or immediately after the maxima of seston and of net production. The mean amount of organic matters in deposits is 1-3 times more than that of net production calculated on the basis of chlorophyll content, and is 3-7 times more than net production measured by using the oxygen bottle (WINKLER'S method).
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