Filtration characteristics of Clarke-Bumpus samplers

Abstract

The Australian and American models of the sampler were tested at water velocities up to 3.5 kt. A calibration tank designed to simulate normal flow conditions through the flowmeter was used to calibrate flowmeter rate against flow rate measured at a 90� V-notch exit. This calibration was used to determine the discharge through samplers towed for a measured distance in a water channel. Thus the filtration characteristics of the samplers were examined. The filtration coefficient for the American sampler without a net averaged 88 %, compared with 92% for the Australian sampler. Australian nets reduced the filtration coefficient of the Australian sampler by 2-15 %. The American net had little effect on the filtration coefficient of the American sampler. The filtration coefficient varied with mesh aperture and clogging but was largely independent of towing velocity. Other experiments suggested that net length was less important, and the flow of water around the net more important, than previously thought. Above approximately 1 kt, the calibration value was nearly independent of velocity and hardly altered with net attachment no matter how fine the mesh.

A comparative analysis of zooplankton field collection and sample enumeration methods

“…Unexpectedly, the filtering efficiencies of the 112-, 135-, and 153-µm mesh nets were quite similar; we expected a more gradual increase in filtering efficiency. Our findings, however, match that of Tranter and Heron (1965), who theorized that reducing mesh size from 140-µm to 110-µm would only reduce filtration efficiency bỹ 2%. In fact, only at small mesh sizes would differences in filtration efficiency be expected to be large (Chick et al 2010).…”

“…would represent "best-case" scenarios, given that net clogging, induced by suspended particulates (e.g., phytoplankton, zooplankton, sediments), presumably affects small meshes more than larger ones (Tranter and Heron 1965;Gannon 1980).…”

“…Under ideal conditions, filtration efficiencies should not differ among nets consisting of > 330-µm mesh (these nets would be 100% efficient), whereas filtration efficiencies should be reduced by as much as 12% as mesh sizes decreased from 330-µm to 60-µm (Tranter and Heron 1965). Given that most freshwater investigations have employed mesh ≤ 153-µm in zooplankton nets, filtration efficiency effects must be considered when quantifying zooplankton demographics.…”

“…To account for filtration efficiency differences among nets in subsequent analyses of zooplankton abundance and size (not in counting method comparisons, however), we corrected water volume sampled using results from our pool experiment. In so doing, our comparisons of zooplankton abundance and size would represent "best-case" scenarios, given that net clogging, induced by suspended particulates (e.g., phytoplankton, zooplankton, sediments), presumably affects small meshes more than larger ones (Tranter and Heron 1965;Gannon 1980).…”

Identification guide to some Diaptomid species (Crustacea, Copepoda, Calanoida, Diaptomidae) of “de la Plata” River Basin (South America)

“…The samples were collected by vertical hauls with a conical plankton net with a 68 µm mesh, equipped with an anti-reflux adaptation following Tranter and Heron (1965, 1967). The samples were fixed in 4% formalin solution for qualitative analysis and with 2.5% glutaraldehyde for scanning electron microscopy (SEM).…”