Count sums – the preprint

I wandered lonely as a cloud
That floats on high o’er vales and hills,
When all at once I saw a crowd,
A host, of golden chironomids;
Beside the lake, beneath the trees,
Fluttering and dancing in the breeze.

Continuous as the stars that shine
And twinkle on the milky way,
They stretched in never-ending swarm
Along the margin of a bay:
Ten thousand saw I at a glance,
Tossing their heads in sprightly dance.

The waves beside them danced; but they
Out-did the sparkling waves in glee:
A poet could not but be gay,
In such a jocund company:
I gazed—and gazed—but little thought
What wealth the show to me had brought:

For oft, when on my couch I lie
In vacant or in pensive mood,
They flash upon that inward eye
Which is the bliss of solitude;
And then my heart with pleasure fills,
And dances with the chironomids.

Sincere apologies to W. Wordsworth: nothing rhymes with chironomids

But were there really ten thousand? Next time you walk by a lake, try to count the chironomids in a swarm. It is impossible, they just move about too much, and it doesn’t seem to get much easier when they are dead.

Just look at the midge stratigraphy from the eutrophic Hiidenvesi in Finland. The methods section of the paper report that “A minimum count size of 50 individuals was set” in 5 cm3 sediment samples.

11270_2017_3622_fig4_html

Midge stratigraphy from Hiidenvesi including the absolute (black bars) and relative abundances (grey bars) of chironomids and chaoborids. The chaoborid/chironomid ratio indicates the severity of anoxia and N2 diversity index represents the effective number of occurrences

Do these assemblages really look like the minimum count sum is 50?

The lowest sample has about 45% Chaoborus flavicans and just over 10% of five chironomid taxa. This looks suspiciously like a count of nine midges: four Chaoborus  (44.4%) and one each for five chironomid taxa (11.1%). This interpretation is supported by the concentration data on the left of the figure. This sample has 0.8 Chaoborus and 1 chironomid per cubic centimetre of sediment. Since 5 cm3 of sediment were sampled and 5 * (0.8 + 1) = 9, this also implies that the count sum is nine midges. Last time I checked, nine was somewhat less than fifty. The second sample from the top appears to have the largest count sum with 1.2 Chaoborus and 3 chironomids per cubic centimetre of sediment, implying a count sum of 21, less than half that reported. All the analyses based on the chironomid stratigraphy are much more uncertain than the reader would expect and may be biased.

Given the number of examples of papers that appear to have counted fewer, often far fewer, microfossils than reported, I decided to write up and submit a manuscript describing the problem and showing how the count sum can be estimated from percent data. If you don’t have at least infinite patience for the peer review process to finish, you can read a preprint on Paleorxiv. Some of the examples I report in the preprint (none of which have yet featured on this blog) appear to be due to lazy descriptions of the data, some due to assemblages being scheduled for deletion but not actually deleted, and some due to what might be described as falsification of the count sums. I also accidentally found some fabricated data – maybe more on that in another post.

About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
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