Dataset 793
Monthly drift samples of invertebrates from the River Pawnmpawm, Ghana
Realm: Freshwater
Climate: Tropical
Biome: Small river ecosystems Central latitude: 6.200000
Central longitude: -0.216700
Duration: 2 years, from 1970 to 1971
Climate: Tropical
Biome: Small river ecosystems Central latitude: 6.200000
Central longitude: -0.216700
Duration: 2 years, from 1970 to 1971
219 records
30 distinct species
Across the time series Elminthidae is the most frequently occurring speciesMethods
The technique used to collect drifting animals from the running water was similar to that described by Elliott (1967a). A net of nylon mesh with aperture size 0-38 to 0-42 mm, equivalent to the number 35 mesh Tyler screen and U.S. sieve 40 was used. The net was 30 cm high and 45 cm long, and carried on its downstream end a polythene, wide-mouthed jar, diameter 7 cm and length 9 cm. The net was sufficiently long to ensure that the standing wave caused by flow resistance was at least one-third of the way down the net even when it became somewhat choked with leaves at the end of a 3-h sampling period. The net was mounted on a frame made of 0-6 cm steel rod and canvas; this was supported in the water by two large polystyrene floats sandwiched between perspex sheets. The apparatus was held in position in the river by two ropes tied to branches on each bank of the river. The floats were fixed onto the net frame at one-third of the length down the sides of the frame so that the water flowing through the net was at a depth of 20 cm. The net was fixed to the inside of the canvas with snap fasteners to facilitate the collection of the samples. Samples were always collected from the same location, a section of the river with a fairly swift current and a depth always great enough for the net to float. Here there was always a current when there was any flow in the river. The site was below a 50 m riffle which was regularly sampled to investigate seasonal changes in the benthic invertebrates (Hynes, 1975). Twenty-four hour drift samples were collected at approximately monthly intervals, the net being emptied every 3 h. Night time was from 18.00 hours to 06.00 hours approximately throughout the year with half an hour variation, and the sampling periods were organized so that there were four samples from each of the day and night periods. The catch was sorted in an enamel tray, debris was removed and the animals were preserved in 5% formaldehyde solution. In addition to the monthly samples a series of samples was taken every day for 20 days over a 2-h period at sunset to investigate fluctuations in drift from day to day and the possible effect of moonlight on drift. These samples were collected half-hourly from 17.00 to 19.00 hours. Sampling was discontinued on 19 May when the net broke as a result of the much increased flow on that date. Measurements of the depth of water were made every 30 cm across the width of the river to provide a profile, both at the beginning and at the end of each set of drift samples. From the current speed and the depth profile approximate values for the total discharge of the river and the volume of water passing through the net were calculated.” [Extracted from Hynes 1975 Freshwater Biology, 5:515-532]Citation(s)
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