A method to choose water depths for zooplankton samples in lakes
Date
2021-11-23
Journal Title
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Publisher
Wiley on behalf of Association for the Sciences of Limnology and Oceanography.
Abstract
As methods in the literature to sample zooplankton in lakes mostly offered general guidance on the sample
depths, a new one was developed. Using the principle of volume-weighted sampling of the lake volume and an
empirical function for the hypsometric curve, formulae for the volumes and areas of five equal sections of the
lake were derived, which were then used to calculate section mean depths. Vertical net hauls taken at the mean
depths are combined using a relation between their mean depths to produce one unbiased composite sample of
the zooplankton. While generic formulae were derived, starting values for the depths that divide the lake volume
into five equal sections are needed in order to apply the method, which then optimizes the depths; the
method is implemented in a spreadsheet. The method was applied to four hypothetical lakes of maximum
depth 12 m that cover a wide variation of lake form and how the sample depths vary with form was described;
as lake form becomes more convex, the sample depths decrease, reflecting that more of the lake volume is at
shallower depth. The method was used to estimate the whole-lake abundance of zooplankton in 51 lakes and
no practical difficulties were encountered. It can be used in lakes up to a few tens of km2 in area.
Description
Publication history: Accepted - 13 October 2021; Published online - 23 November 2021.
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Citation
Rippey, B., Macintosh, K. A., McElarney, Y. and Douglas, R. (2021) ‘A method to choose water depths for zooplankton samples in lakes’, Limnology and Oceanography: Methods. Wiley. doi: 10.1002/lom3.10464.