Count-less chironomids?

Most papers that present microfossil assemblages report (not always accurately) the minimum number of microfossils that were counted in each sample, an important indicator of the precision of the data. Some do not. For these papers, the reader should be able to assume that the counts conform to typical practice for that microfossil. For example, I would expect a pollen or diatom stratigraphy to have counts sums of a few hundred, and a chironomid stratigraphy to have a minimum count sum of fifty (perhaps thirty). If the count sums are materially lower than this I would start to wonder if the omission was deliberate and recall Fanelli’s (2013) definition of misconduct

‘any omission or misrepresentation of the information necessary and sufficient to evaluate the validity and significance of research, at the level appropriate to the context in which the research is communicated’.

The figure below is from a paper that reconstructs July temperature for four intervals in the period ca. 570 BCE to 120 CE (Iron Age–Roman Period) using chironomids from the varved sediments of Lake Silvaplana. The paper does not report the minimum count sum; can it be estimated from the stratigraphy?

stewart_etal_4

(a) Chironomid assemblages, (b) inferred mean July air temperatures and (c) % organic matter. For part (a), percentages for each taxon are represented by black bars. Thin black lines represent the zones created using the ZONE program (Juggins, 1991).

I think the minimum count sum can be estimated. The lowest assemblage is 100% Orthocladius. This could represent one Orthocladius, a hundred, or a thousand, but I would suggest that it is unlikely to be a large count given the chironomid diversity in the lake (in contrast to polar foram assemblages which are commonly 100% Neogloboquadrina pachyderma), would make it unlikely to find just one taxon, even if that taxon is fairly dominant. The next assemblage is 100% Cricotopus, the third and fourth 100% Corynoneura, and the fifth 100 % Procladius: there are two possibilities, either the chironomid community in the lake repeatedly changed abruptly and taphonomic processes did not mix the assemblages, or the count sum for these assemblages is very low, perhaps only one. Fifty five of the 208 assemblages in the stratigraphy are monospecific.

The eight and ninth assemblages are 50% Tanytarsus and 50% another taxon. These are conceivably counts of two chironomids. The eleventh assemblage is more diverse with five taxa each with 20%, perhaps a count of five. Only a few assemblages, mainly near the top, appear to have a count sum of more than ten chironomids.

These are the lowest estimated count sums I have found, even lower than in Lake Muzzano.
Despite these extremely low count sums, a reconstruction of July temperature is made with a transfer function. Perhaps not surprisingly, the reconstruction is very noisy, with abrupt changes of over 10°C. The reconstruction is meaningless junk.

A correction is needed to report the omitted count sums, and if they are mainly in low single figures, I think the chironomid part of the paper should be retracted as no reviewer would ever have recommended publication had they known that.

About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
This entry was posted in Peer reviewed literature, transfer function and tagged , , . Bookmark the permalink.

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