New method for measuring amount of depositing materials in a lake

Abstract

1. The amount of depositing matter, or sediment, was measured by using two types of sediment-trap set up over the bottom at four stations with depths of 0.5 to 3.5m in an inshore area in the shallow southern basin of Lake Biwa in the period from May to November 1967.
2. The apparatus designed for the present experiment employs a tray (16.8cm23.0cm×2.5cm) fixed aside to a glass bottle (5.2cm in diameter at the mouth).The sediments once settled down in the tray may be assumed to be exposed nearly as freely to the action of the movement, current or turbulence, of water as the sediments on the bottom of the lake are, and may be stirred up and taken away again, whereas the bottle is presumed to retain the whole sediment deposited in it.
3. Amounts of sediments collected within 24 hours period in bottles, varying from 21.1 to 31881.8 g/m²/day, were always larger than corresponding amounts in trays, varying from 1.6 to 558.7 g/m²/day. Remarkable increase in the amount of sediment, both in bottles and in trays, is recorded with an increasing intensity of wind on the days. Sediments collected during longer periods of 15 to 39 days showed also relatively greater amounts in bottles than in trays.
4. The ignition loss of sediments collected within 24 hours period both in bottles and in trays revealed a tendency of decreasing with an increasing intensity of wind. This tendency is not clear in the sediment trapped in longer periods.
5. It is concluded that the sediment collected in the bottles contains a larger amount of matter which is stirred up from the bottom, in addition to the deposition originated from dead pelagic organisms.